#include "Arduino.h"

// ============================================================================
// STUDENT CONFIGURATION
// Replace 0 with your student number (numeric digits only)
// Example: For UP1234567, enter 1234567
// ============================================================================
#define STUDENT_NUMBER 2290659

// ============================================================================
// SYSTEM PARAMETERS - AUTO-GENERATED FROM STUDENT_NUMBER
// DO NOT MODIFY MANUALLY - Computed by generateParameters()
// ============================================================================
struct SystemParams {
  float v1, v2, v3;                  // Conveyor speeds (cm/s)
  float d0, d1, d2, d3, d4;          // Conv1 distances from obstruction sensor (cm)
  float d5, d6;                      // Conv2/Conv3 total lengths (cm)
  float L_min, L_max, L_threshold;   // Length criteria (cm)
  float W_min, W_max, W_threshold;   // Weight criteria (g)
  float T_gate;                      // Gate mechanical response time (ms)
  int C1, C2, C3;                    // Area capacities (products)
  int productInterval;               // Product loading interval (ms)
};

SystemParams sp;

#define DIST_LEAD   10.0f   // Fixed: entry point to obstruction sensor (cm)
#define DEBUG_PIN   12

// ============================================================================
// TYPE DEFINITIONS
// ============================================================================
enum class ProductEventType {
  OBSTRUCTION_SENSOR_RISE,
  OBSTRUCTION_SENSOR_FALL,
  G2_CHECK,                       // Size gate check
  WEIGHT_SENSOR_ENTER_WINDOW,
  WEIGHT_SENSOR_EXIT_WINDOW,
  G3_CHECK,                       // Weight gate check
  BARCODE_SENSOR_ENTER_WINDOW,
  BARCODE_SENSOR_EXIT_WINDOW,
  G4_CHECK,                       // Routing gate check
  ARRIVE_DESTINATION,             // Product reaches final area
  FINISH
};

struct Product {
  float length;       // Product length (cm)
  float weight;       // Product weight (g)
  int   barcodeID;    // Barcode tracking number
};

struct ProductEvent {
  uint64_t         triggerTimeMicros;
  ProductEventType eventType;
  int              gateExpected;       // For gate checks: expected gate state (0 or 1)
  int              destArea;           // For ARRIVE: destination area (0=A1, 1=A2, 2=A3)
};

struct ProductScheduler {
  Product product;
  ProductEvent events[16];
  int totalEvents;
  int currentEventIndex;
  int debugPin;
  hw_timer_t* timerHandle;
};

// Gate error counters: [0]=G2, [1]=G3, [2]=G4
// Check these to verify your gate control is correct (should all be 0)
volatile int errorGateCNT[3] = {0};

// Ground truth area counts (maintained by simulator)
volatile int simAreaCount[3] = {0, 0, 0};  // Area1, Area2, Area3

extern void startSimulator(void);

// ============================================================================
// PARAMETER GENERATION (deterministic from student number)
// ============================================================================
static uint32_t paramHash(uint32_t seed, uint32_t idx) {
  uint32_t v = seed * 2654435761u + idx * 2246822519u;
  v ^= v >> 16;
  v *= 0x45d9f3bu;
  v ^= v >> 16;
  return v;
}

static float paramRangeF(uint32_t seed, uint32_t idx, float lo, float hi) {
  return lo + (float)(paramHash(seed, idx) % 10001u) / 10000.0f * (hi - lo);
}

static int paramRangeI(uint32_t seed, uint32_t idx, int lo, int hi) {
  return lo + (int)(paramHash(seed, idx) % (uint32_t)(hi - lo + 1));
}

void generateParameters(uint32_t sn) {
  if (sn == 0) {
    // Default parameters (no student number set)
    sp.v1 = 100.0f;  sp.v2 = 120.0f;  sp.v3 = 80.0f;
    sp.d0 = 15.0f;   sp.d1 = 25.0f;   sp.d2 = 35.0f;
    sp.d3 = 45.0f;   sp.d4 = 55.0f;
    sp.d5 = 40.0f;   sp.d6 = 40.0f;
    sp.L_min = 4.5f;  sp.L_max = 5.5f;  sp.L_threshold = 5.0f;
    sp.W_min = 90.0f;  sp.W_max = 110.0f;  sp.W_threshold = 100.0f;
    sp.T_gate = 3.0f;
    sp.C1 = 5;  sp.C2 = 10;  sp.C3 = 10;
    sp.productInterval = 500;
    return;
  }

  sp.v1 = paramRangeF(sn, 1, 80.0f, 120.0f);
  sp.v2 = paramRangeF(sn, 2, 100.0f, 150.0f);
  sp.v3 = paramRangeF(sn, 3, 60.0f, 100.0f);

  sp.d0 = paramRangeF(sn, 4, 12.0f, 20.0f);
  sp.d1 = sp.d0 + paramRangeF(sn, 5, 8.0f, 15.0f);
  sp.d2 = sp.d1 + paramRangeF(sn, 6, 8.0f, 15.0f);
  sp.d3 = sp.d2 + paramRangeF(sn, 7, 8.0f, 15.0f);
  sp.d4 = sp.d3 + paramRangeF(sn, 8, 8.0f, 15.0f);
  sp.d5 = paramRangeF(sn, 9, 30.0f, 50.0f);
  sp.d6 = paramRangeF(sn, 10, 30.0f, 50.0f);

  sp.L_min = paramRangeF(sn, 11, 4.0f, 5.0f);
  sp.L_max = sp.L_min + paramRangeF(sn, 12, 0.8f, 1.5f);
  sp.L_threshold = (sp.L_min + sp.L_max) / 2.0f;

  sp.W_min = paramRangeF(sn, 13, 80.0f, 100.0f);
  sp.W_max = sp.W_min + paramRangeF(sn, 14, 15.0f, 30.0f);
  sp.W_threshold = (sp.W_min + sp.W_max) / 2.0f;

  sp.T_gate = paramRangeF(sn, 15, 2.0f, 5.0f);

  sp.C1 = paramRangeI(sn, 16, 3, 8);
  sp.C2 = paramRangeI(sn, 17, 8, 15);
  sp.C3 = paramRangeI(sn, 18, 8, 15);

  sp.productInterval = paramRangeI(sn, 19, 400, 600);
}

void printParameters() {
  Serial.println("========== SmartSort System Parameters ==========");
  Serial.printf("Student Number: %u\n", (unsigned)STUDENT_NUMBER);
  Serial.println("----- Conveyor Speeds -----");
  Serial.printf("  v1 (Conv1): %.1f cm/s\n", sp.v1);
  Serial.printf("  v2 (Conv2): %.1f cm/s\n", sp.v2);
  Serial.printf("  v3 (Conv3): %.1f cm/s\n", sp.v3);
  Serial.println("----- Distances (from obstruction sensor, cm) -----");
  Serial.printf("  d0 (to G2):      %.1f\n", sp.d0);
  Serial.printf("  d1 (to Weight):  %.1f\n", sp.d1);
  Serial.printf("  d2 (to G3):      %.1f\n", sp.d2);
  Serial.printf("  d3 (to Barcode): %.1f\n", sp.d3);
  Serial.printf("  d4 (to G4):      %.1f\n", sp.d4);
  Serial.printf("  d5 (Conv2 len):  %.1f\n", sp.d5);
  Serial.printf("  d6 (Conv3 len):  %.1f\n", sp.d6);
  Serial.println("----- Length Criteria (cm) -----");
  Serial.printf("  L_min=%.2f  L_max=%.2f  L_threshold=%.2f\n", sp.L_min, sp.L_max, sp.L_threshold);
  Serial.println("----- Weight Criteria (g) -----");
  Serial.printf("  W_min=%.2f  W_max=%.2f  W_threshold=%.2f\n", sp.W_min, sp.W_max, sp.W_threshold);
  Serial.println("----- Timing & Capacity -----");
  Serial.printf("  T_gate=%.1f ms  Interval=%d ms\n", sp.T_gate, sp.productInterval);
  Serial.printf("  C1=%d  C2=%d  C3=%d\n", sp.C1, sp.C2, sp.C3);
  Serial.println("=================================================");
}

// ============================================================================
// PRODUCT ARRAY - Generated based on parameters to cover all sorting paths
// Students may modify this array for additional testing
// ============================================================================
#define MAX_TEST_PRODUCTS 20
Product productArray[MAX_TEST_PRODUCTS];
int numProducts = 0;

void generateProductArray() {
  int idx = 0;
  float Lmid = (sp.L_min + sp.L_max) / 2.0f;
  float Wmid = (sp.W_min + sp.W_max) / 2.0f;

  // Category 1: Size abnormal (too short) -> Area 1 via G2
  productArray[idx++] = {sp.L_min - 0.5f, Wmid, 1001};
  productArray[idx++] = {sp.L_min - 1.0f, Wmid + 3.0f, 1002};

  // Category 2: Size abnormal (too long) -> Area 1 via G2
  productArray[idx++] = {sp.L_max + 0.5f, Wmid, 1003};
  productArray[idx++] = {sp.L_max + 0.8f, Wmid - 2.0f, 1004};

  // Category 3: Normal size, weight too light -> Area 1 via G3
  productArray[idx++] = {Lmid, sp.W_min - 5.0f, 1005};
  productArray[idx++] = {sp.L_min + 0.1f, sp.W_min - 3.0f, 1006};

  // Category 4: Normal size, weight too heavy -> Area 1 via G3
  productArray[idx++] = {Lmid, sp.W_max + 5.0f, 1007};
  productArray[idx++] = {sp.L_max - 0.1f, sp.W_max + 3.0f, 1008};

  // Category 5: Normal, small & light -> Area 2 (L<=Lthresh AND W<=Wthresh)
  productArray[idx++] = {sp.L_min + 0.1f, sp.W_min + 1.0f, 1009};
  productArray[idx++] = {sp.L_threshold, sp.W_threshold, 1010};       // Edge case: exactly at threshold
  productArray[idx++] = {sp.L_threshold - 0.1f, sp.W_threshold - 1.0f, 1011};

  // Category 6: Normal, large or heavy -> Area 3
  productArray[idx++] = {sp.L_threshold + 0.1f, sp.W_threshold - 1.0f, 1012};
  productArray[idx++] = {sp.L_min + 0.2f, sp.W_threshold + 1.0f, 1013};
  productArray[idx++] = {sp.L_max - 0.1f, sp.W_max - 1.0f, 1014};
  productArray[idx++] = {sp.L_threshold + 0.2f, sp.W_threshold + 2.0f, 1015};

  // Edge cases
  productArray[idx++] = {sp.L_min, sp.W_min, 1016};    // Exactly at min boundaries -> Area 2
  productArray[idx++] = {sp.L_max, sp.W_max, 1017};    // Exactly at max -> Area 3
  productArray[idx++] = {Lmid, Wmid, 1018};             // Center values -> Area 2

  numProducts = idx;
}

/*!!!!!!!!!!!!!!!!!!ANY CODE ABOVE THIS LINE SHOULD NOT BE MODIFIED BY STUDENTS!!!!!!!!!!!!!!!!!!!*/
/*=========================== INTERFACE BETWEEN SIMULATOR AND STUDENT CODE ============================*/

/*
   g_obstructionSensorPin outputs the physical signal of the obstruction sensor (for oscilloscope).
*/
#define g_obstructionSensorPin    32

/*
   Debug output pins for gate signals (for oscilloscope verification).
   The simulator does NOT read these - they are for your debugging only.
*/
#define gate2DebugPin             33
#define gate3DebugPin             27
#define gate4DebugPin             14

/*
   SHARED VARIABLES - DO NOT RENAME
   The simulator uses these to provide sensor data and check your gate controls.
*/
// ========== Simulator writes, students read ==========
volatile bool   g_obstructionSensor = false;  // Obstruction sensor state
volatile int    g_barcodeReader     = 0;       // Barcode reading (0=invalid/not in window)
volatile float  g_weightSensor      = 0.0f;    // Weight reading (0=invalid/not in window)

// ========== Students write, simulator reads ==========
// G1 (Intake): true=allow products in, false=block entry
volatile bool   g_gate1Ctrl = true;
// G2 (Size divert): false=let pass, true=activate pusher (divert to Area 1)
volatile bool   g_gate2Ctrl = false;
// G3 (Weight divert): false=let pass, true=activate pusher (divert to Area 1)
volatile bool   g_gate3Ctrl = false;
// G4 (Routing): false=route to Conv2/Area2, true=route to Conv3/Area3
volatile bool   g_gate4Ctrl = false;

/*================================= IMPLEMENT YOUR RTOS CODE BELOW ===================================*/

#define LENGTH_TOL_CM          0.005f
#define WEIGHT_TOL_G           0.005f

#define RECENT_HISTORY_SIZE    6
#define GATE_QUEUE_LENGTH      32
#define ARRIVAL_QUEUE_LENGTH   24


// ============================================================================
// DATA TYPES
// ============================================================================

// Obstruction sensor timestamp pair.
typedef struct {
  int64_t riseUs;
  int64_t fallUs;
} sensor_edge_pair_t;


// Product information used internally.
typedef struct {
  uint32_t sequenceNo;       // Internal sequence number before barcode is known
  float lengthCm;
  float weightG;
  int barcode;
  int destination;           // 1=A1, 2=A2, 3=A3
} product_track_t;


// Argument passed to one product-control task.
typedef struct {
  sensor_edge_pair_t edges;
  uint32_t sequenceNo;
  uint32_t epoch;
} product_task_arg_t;


// Record stored for sortRT recent product output.
typedef struct {
  uint32_t sequenceNo;
  int barcode;
  float lengthCm;
  float weightG;
  int destination;
} recent_product_record_t;


// Controller state, statistics, and capacity tracking.
typedef struct {
  int areaOccupancy[3];      // Current area occupancy: [0]=A1, [1]=A2, [2]=A3
  int inTransit[3];          // Products predicted to arrive but not arrived yet

  float totalLength;
  float totalWeight;
  int totalProducts;

  float area2Length;
  float area2Weight;
  int area2Products;

  float area3Length;
  float area3Weight;
  int area3Products;
} controller_state_t;


// Gate ID for dedicated gate-control system.
typedef enum {
  SORT_GATE_G2 = 2,
  SORT_GATE_G3 = 3,
  SORT_GATE_G4 = 4
} sort_gate_id_t;


// Gate command sent to gate-control queue.
typedef struct {
  sort_gate_id_t gateId;
  bool requiredState;
  int64_t commandTimeUs;
  int64_t releaseTimeUs;
  uint32_t epoch;
} gate_command_t;


// Gate pulse task argument.
typedef struct {
  gate_command_t command;
} gate_task_arg_t;


// Arrival event sent to Core 1 arrival tracking task.
typedef struct {
  uint32_t sequenceNo;
  int barcode;
  float lengthCm;
  float weightG;
  int destination;
  int64_t arrivalTimeUs;
  uint32_t epoch;
} arrival_event_t;


// ============================================================================
// GLOBAL VARIABLES
// ============================================================================

// Queue from obstruction ISR to product dispatcher.
static QueueHandle_t edgeQueue = NULL;

// Queue from product tasks to gate-control task.
static QueueHandle_t gateQueue = NULL;

// Queue from product tasks to Core 1 arrival tracker.
static QueueHandle_t arrivalQueue = NULL;

// Mutex for state/statistics/recent-history protection.
static SemaphoreHandle_t stateMutex = NULL;

// Timestamp pair built by ISR.
static volatile sensor_edge_pair_t activeEdges = {0, 0};

// Main controller state.
static controller_state_t systemState = {0};

// Recent products for sortRT output.
static recent_product_record_t recentHistory[RECENT_HISTORY_SIZE];
static int recentWritePos = 0;
static int recentCount = 0;

// Product sequence number.
// Incremented whenever a complete obstruction timestamp pair is received.
static volatile uint32_t nextSequenceNumber = 1;

// Epoch invalidates old pending tasks after reset.
static volatile uint32_t controllerEpoch = 1;

// System mode flags.
static volatile bool emergencyActive = false;
static volatile bool capacityBlocked = false;
static volatile bool capacityMessageShown = false;
static volatile int blockedArea = 0;


// ============================================================================
// FORWARD DECLARATIONS
// ============================================================================

static int64_t travelTimeUs(float distanceCm, float speedCmPerSec);
static void waitUntilUs(int64_t targetUs);
static void waitUntilUsWithEpoch(int64_t targetUs, uint32_t epoch);

static bool epochExpired(uint32_t epoch);

static bool lengthAccepted(float lengthCm);
static bool weightAccepted(float weightG);
static bool shouldRouteArea2(float lengthCm, float weightG);

static void updateGate1FromCapacity();
static void reserveDestination(int destination);
static void addRecentProduct(uint32_t sequenceNo,
                             int barcode,
                             float lengthCm,
                             float weightG,
                             int destination);
static void completeArrival(uint32_t sequenceNo,
                            int barcode,
                            float lengthCm,
                            float weightG,
                            int destination);

static float readWeightAtWindow(int64_t centerTimeUs, float lengthCm, uint32_t epoch);
static int readBarcodeAtWindow(int64_t centerTimeUs, float lengthCm, uint32_t epoch);

static volatile bool* gatePointer(sort_gate_id_t gateId);
static void queueGateAction(sort_gate_id_t gateId,
                            bool requiredState,
                            int64_t gateCheckTimeUs,
                            float productLengthCm,
                            uint32_t epoch);

static void queueArrivalEvent(uint32_t sequenceNo,
                              int barcode,
                              float lengthCm,
                              float weightG,
                              int destination,
                              int64_t arrivalTimeUs,
                              uint32_t epoch);

static void resetControllerState();
static void clearAreasByOperator();

void productControlTask(void *pvParameters);
void gateDispatcherTask(void *pvParameters);
void gatePulseTask(void *pvParameters);
void arrivalTrackerTask(void *pvParameters);


// ============================================================================
// TIME HELPERS
// ============================================================================

static int64_t travelTimeUs(float distanceCm, float speedCmPerSec) {
  if (speedCmPerSec <= 0.0f) {
    return 0;
  }

  return (int64_t)((distanceCm / speedCmPerSec) * 1000000.0f);
}


static void waitUntilUs(int64_t targetUs) {
  while (!emergencyActive) {
    int64_t nowUs = esp_timer_get_time();
    int64_t remainingUs = targetUs - nowUs;

    if (remainingUs <= 0) {
      return;
    }

    if (remainingUs > 4000) {
      int delayMs = (int)((remainingUs - 2000) / 1000);

      if (delayMs < 1) {
        delayMs = 1;
      }

      vTaskDelay(pdMS_TO_TICKS(delayMs));
    }
    else {
      delayMicroseconds((uint32_t)remainingUs);
      return;
    }
  }
}


static void waitUntilUsWithEpoch(int64_t targetUs, uint32_t epoch) {
  while (!emergencyActive && !epochExpired(epoch)) {
    int64_t nowUs = esp_timer_get_time();
    int64_t remainingUs = targetUs - nowUs;

    if (remainingUs <= 0) {
      return;
    }

    if (remainingUs > 4000) {
      int delayMs = (int)((remainingUs - 2000) / 1000);

      if (delayMs < 1) {
        delayMs = 1;
      }

      vTaskDelay(pdMS_TO_TICKS(delayMs));
    }
    else {
      delayMicroseconds((uint32_t)remainingUs);
      return;
    }
  }
}


static bool epochExpired(uint32_t epoch) {
  return epoch != controllerEpoch;
}


// ============================================================================
// CLASSIFICATION HELPERS
// ============================================================================

static bool lengthAccepted(float lengthCm) {
  return (lengthCm >= (sp.L_min - LENGTH_TOL_CM) &&
          lengthCm <= (sp.L_max + LENGTH_TOL_CM));
}


static bool weightAccepted(float weightG) {
  return (weightG >= (sp.W_min - WEIGHT_TOL_G) &&
          weightG <= (sp.W_max + WEIGHT_TOL_G));
}


static bool shouldRouteArea2(float lengthCm, float weightG) {
  return (lengthCm <= (sp.L_threshold + LENGTH_TOL_CM) &&
          weightG <= (sp.W_threshold + WEIGHT_TOL_G));
}


// ============================================================================
// CAPACITY, STATISTICS, AND REPORTING HELPERS
// ============================================================================

static void updateGate1FromCapacity() {
  if (stateMutex == NULL) {
    return;
  }

  // Startup guard:
  // Before startSimulator() generates parameters, capacities are 0.
  if (sp.C1 <= 0 || sp.C2 <= 0 || sp.C3 <= 0) {
    g_gate1Ctrl = true;
    capacityBlocked = false;
    capacityMessageShown = false;
    blockedArea = 0;
    return;
  }

  xSemaphoreTake(stateMutex, portMAX_DELAY);

  int areaFull = 0;

  if ((systemState.areaOccupancy[0] + systemState.inTransit[0]) >= sp.C1) {
    areaFull = 1;
  }
  else if ((systemState.areaOccupancy[1] + systemState.inTransit[1]) >= sp.C2) {
    areaFull = 2;
  }
  else if ((systemState.areaOccupancy[2] + systemState.inTransit[2]) >= sp.C3) {
    areaFull = 3;
  }

  if (emergencyActive) {
    g_gate1Ctrl = false;
  }
  else if (areaFull != 0) {
    g_gate1Ctrl = false;
    capacityBlocked = true;
    blockedArea = areaFull;
  }
  else {
    g_gate1Ctrl = true;
    capacityBlocked = false;
    capacityMessageShown = false;
    blockedArea = 0;
  }

  xSemaphoreGive(stateMutex);
}


static void reserveDestination(int destination) {
  int index = destination - 1;

  if (index < 0 || index > 2 || stateMutex == NULL) {
    return;
  }

  xSemaphoreTake(stateMutex, portMAX_DELAY);
  systemState.inTransit[index]++;
  xSemaphoreGive(stateMutex);

  updateGate1FromCapacity();
}


static void addRecentProduct(uint32_t sequenceNo,
                             int barcode,
                             float lengthCm,
                             float weightG,
                             int destination) {
  if (stateMutex == NULL) {
    return;
  }

  xSemaphoreTake(stateMutex, portMAX_DELAY);

  recentHistory[recentWritePos].sequenceNo = sequenceNo;
  recentHistory[recentWritePos].barcode = barcode;
  recentHistory[recentWritePos].lengthCm = lengthCm;
  recentHistory[recentWritePos].weightG = weightG;
  recentHistory[recentWritePos].destination = destination;

  recentWritePos = (recentWritePos + 1) % RECENT_HISTORY_SIZE;

  if (recentCount < RECENT_HISTORY_SIZE) {
    recentCount++;
  }

  xSemaphoreGive(stateMutex);
}


static void completeArrival(uint32_t sequenceNo,
                            int barcode,
                            float lengthCm,
                            float weightG,
                            int destination) {
  int index = destination - 1;

  if (index < 0 || index > 2 || stateMutex == NULL) {
    return;
  }

  xSemaphoreTake(stateMutex, portMAX_DELAY);

  if (systemState.inTransit[index] > 0) {
    systemState.inTransit[index]--;
  }

  systemState.areaOccupancy[index]++;

  systemState.totalLength += lengthCm;
  systemState.totalWeight += weightG;
  systemState.totalProducts++;

  if (destination == 2) {
    systemState.area2Length += lengthCm;
    systemState.area2Weight += weightG;
    systemState.area2Products++;
  }
  else if (destination == 3) {
    systemState.area3Length += lengthCm;
    systemState.area3Weight += weightG;
    systemState.area3Products++;
  }

  xSemaphoreGive(stateMutex);

  addRecentProduct(sequenceNo, barcode, lengthCm, weightG, destination);

  updateGate1FromCapacity();
}


// ============================================================================
// SENSOR READING HELPERS
// ============================================================================

static float readWeightAtWindow(int64_t centerTimeUs, float lengthCm, uint32_t epoch) {
  float weight = 0.0f;

  int64_t halfWindowUs = travelTimeUs(lengthCm * 0.10f, sp.v1);
  int64_t startUs = centerTimeUs - halfWindowUs + 300;
  int64_t endUs   = centerTimeUs + halfWindowUs - 300;

  waitUntilUsWithEpoch(startUs, epoch);

  while (!emergencyActive && !epochExpired(epoch) && esp_timer_get_time() <= endUs) {
    if (g_weightSensor > 0.0f) {
      weight = g_weightSensor;
      break;
    }

    delayMicroseconds(300);
  }

  return weight;
}


static int readBarcodeAtWindow(int64_t centerTimeUs, float lengthCm, uint32_t epoch) {
  int barcode = 0;

  int64_t halfWindowUs = travelTimeUs(lengthCm * 0.10f, sp.v1);
  int64_t startUs = centerTimeUs - halfWindowUs + 300;
  int64_t endUs   = centerTimeUs + halfWindowUs - 300;

  waitUntilUsWithEpoch(startUs, epoch);

  while (!emergencyActive && !epochExpired(epoch) && esp_timer_get_time() <= endUs) {
    if (g_barcodeReader != 0) {
      barcode = g_barcodeReader;
      break;
    }

    delayMicroseconds(300);
  }

  return barcode;
}


// ============================================================================
// DEDICATED GATE-CONTROL SYSTEM
// ============================================================================

static volatile bool* gatePointer(sort_gate_id_t gateId) {
  if (gateId == SORT_GATE_G2) {
    return &g_gate2Ctrl;
  }

  if (gateId == SORT_GATE_G3) {
    return &g_gate3Ctrl;
  }

  if (gateId == SORT_GATE_G4) {
    return &g_gate4Ctrl;
  }

  return NULL;
}


static void queueGateAction(sort_gate_id_t gateId,
                            bool requiredState,
                            int64_t gateCheckTimeUs,
                            float productLengthCm,
                            uint32_t epoch) {
  if (gateQueue == NULL || epochExpired(epoch)) {
    return;
  }

  gate_command_t command;

  int64_t leadUs = (int64_t)(sp.T_gate * 1000.0f);

  command.gateId = gateId;
  command.requiredState = requiredState;

  // Command before product front edge reaches the gate.
  command.commandTimeUs = gateCheckTimeUs - leadUs;

  // Release after product back edge clears the gate.
  command.releaseTimeUs =
    gateCheckTimeUs + travelTimeUs(productLengthCm, sp.v1) + 2000;

  command.epoch = epoch;

  xQueueSend(gateQueue, &command, pdMS_TO_TICKS(10));
}


void gateDispatcherTask(void *pvParameters) {
  gate_command_t command;

  while (true) {
    if (xQueueReceive(gateQueue, &command, portMAX_DELAY) == pdTRUE) {
      if (epochExpired(command.epoch)) {
        continue;
      }

      gate_task_arg_t *arg =
        (gate_task_arg_t *)pvPortMalloc(sizeof(gate_task_arg_t));

      if (arg == NULL) {
        continue;
      }

      arg->command = command;

      BaseType_t created = xTaskCreatePinnedToCore(
                             gatePulseTask,
                             "GatePulse",
                             2048,
                             arg,
                             9,
                             NULL,
                             0
                           );

      if (created != pdPASS) {
        vPortFree(arg);
      }
    }
  }
}


void gatePulseTask(void *pvParameters) {
  gate_task_arg_t *arg = (gate_task_arg_t *)pvParameters;

  if (arg == NULL) {
    vTaskDelete(NULL);
    return;
  }

  gate_command_t command = arg->command;
  vPortFree(arg);

  volatile bool *gateSignal = gatePointer(command.gateId);

  if (gateSignal == NULL || epochExpired(command.epoch)) {
    vTaskDelete(NULL);
    return;
  }

  waitUntilUsWithEpoch(command.commandTimeUs, command.epoch);

  if (emergencyActive || epochExpired(command.epoch)) {
    vTaskDelete(NULL);
    return;
  }

  *gateSignal = command.requiredState;

  waitUntilUsWithEpoch(command.releaseTimeUs, command.epoch);

  if (emergencyActive || epochExpired(command.epoch)) {
    vTaskDelete(NULL);
    return;
  }


  vTaskDelete(NULL);
}


// ============================================================================
// ARRIVAL TRACKING TASK ON CORE 1
// ============================================================================

static void queueArrivalEvent(uint32_t sequenceNo,
                              int barcode,
                              float lengthCm,
                              float weightG,
                              int destination,
                              int64_t arrivalTimeUs,
                              uint32_t epoch) {
  if (arrivalQueue == NULL || epochExpired(epoch)) {
    return;
  }

  arrival_event_t event;

  event.sequenceNo = sequenceNo;
  event.barcode = barcode;
  event.lengthCm = lengthCm;
  event.weightG = weightG;
  event.destination = destination;
  event.arrivalTimeUs = arrivalTimeUs;
  event.epoch = epoch;

  xQueueSend(arrivalQueue, &event, pdMS_TO_TICKS(10));
}


void arrivalTrackerTask(void *pvParameters) {
  arrival_event_t event;

  while (true) {
    if (xQueueReceive(arrivalQueue, &event, portMAX_DELAY) == pdTRUE) {
      if (emergencyActive || epochExpired(event.epoch)) {
        continue;
      }

      waitUntilUsWithEpoch(event.arrivalTimeUs, event.epoch);

      if (!emergencyActive && !epochExpired(event.epoch)) {
        completeArrival(event.sequenceNo,
                        event.barcode,
                        event.lengthCm,
                        event.weightG,
                        event.destination);
      }
    }
  }
}


// ============================================================================
// RESET AND CLEAR
// ============================================================================

static void resetControllerState() {
  controllerEpoch++;

  if (controllerEpoch == 0) {
    controllerEpoch = 1;
  }

  if (stateMutex != NULL) {
    xSemaphoreTake(stateMutex, portMAX_DELAY);

    memset(&systemState, 0, sizeof(systemState));
    memset(recentHistory, 0, sizeof(recentHistory));

    recentWritePos = 0;
    recentCount = 0;
    nextSequenceNumber = 1;

    xSemaphoreGive(stateMutex);
  }

  if (edgeQueue != NULL) {
    xQueueReset(edgeQueue);
  }

  if (gateQueue != NULL) {
    xQueueReset(gateQueue);
  }

  if (arrivalQueue != NULL) {
    xQueueReset(arrivalQueue);
  }

  emergencyActive = false;
  capacityBlocked = false;
  capacityMessageShown = false;
  blockedArea = 0;

  g_gate1Ctrl = true;
  g_gate2Ctrl = false;
  g_gate3Ctrl = false;
  g_gate4Ctrl = false;
}


// Simulates an operator emptying the physical destination areas.
// Historical statistics remain unchanged.
static void clearAreasByOperator() {
  if (stateMutex != NULL) {
    xSemaphoreTake(stateMutex, portMAX_DELAY);

    systemState.areaOccupancy[0] = 0;
    systemState.areaOccupancy[1] = 0;
    systemState.areaOccupancy[2] = 0;

    xSemaphoreGive(stateMutex);
  }

  capacityBlocked = false;
  capacityMessageShown = false;
  blockedArea = 0;

  updateGate1FromCapacity();
}


// ============================================================================
// OBSTRUCTION SENSOR ISR
// ============================================================================

void IRAM_ATTR obstructionSensorInterrupt() {
  BaseType_t higherPriorityTaskWoken = pdFALSE;

  if (g_obstructionSensor == true) {
    activeEdges.riseUs = esp_timer_get_time();
  }
  else {
    activeEdges.fallUs = esp_timer_get_time();

    if (edgeQueue != NULL) {
      xQueueSendFromISR(edgeQueue,
                        (void*)&activeEdges,
                        &higherPriorityTaskWoken);
    }

    if (higherPriorityTaskWoken) {
      portYIELD_FROM_ISR();
    }
  }
}


// ============================================================================
// PRODUCT DISPATCH TASK - CORE 0
// ============================================================================

void productProcessingTask(void *pvParameters) {
  sensor_edge_pair_t edges;

  while (true) {
    if (xQueueReceive(edgeQueue, &edges, portMAX_DELAY) == pdTRUE) {
      if (emergencyActive) {
        continue;
      }

      product_task_arg_t *arg =
        (product_task_arg_t *)pvPortMalloc(sizeof(product_task_arg_t));

      if (arg == NULL) {
        continue;
      }

      arg->edges = edges;
      arg->epoch = controllerEpoch;

      // Internal tracking before barcode is known.
      arg->sequenceNo = nextSequenceNumber++;

      BaseType_t created = xTaskCreatePinnedToCore(
                             productControlTask,
                             "ProductControl",
                             4096,
                             arg,
                             8,
                             NULL,
                             0
                           );

      if (created != pdPASS) {
        vPortFree(arg);
      }
    }
  }
}


// ============================================================================
// SINGLE PRODUCT CONTROL TASK - CORE 0
// ============================================================================

void productControlTask(void *pvParameters) {
  product_task_arg_t *arg = (product_task_arg_t *)pvParameters;

  if (arg == NULL) {
    vTaskDelete(NULL);
    return;
  }

  sensor_edge_pair_t edges = arg->edges;
  uint32_t sequenceNo = arg->sequenceNo;
  uint32_t myEpoch = arg->epoch;

  vPortFree(arg);

  if (emergencyActive || epochExpired(myEpoch)) {
    vTaskDelete(NULL);
    return;
  }

  product_track_t product;

  product.sequenceNo = sequenceNo;
  product.lengthCm = 0.0f;
  product.weightG = 0.0f;
  product.barcode = 0;
  product.destination = 0;

  // ------------------------------------------------------------------------
  // 1. Length calculation
  // ------------------------------------------------------------------------
  int64_t blockedUs = edges.fallUs - edges.riseUs;

  if (blockedUs <= 0) {
    vTaskDelete(NULL);
    return;
  }

  product.lengthCm = (float)blockedUs * sp.v1 / 1000000.0f;

  // Gate front-edge check times.
  int64_t g2CheckUs = edges.riseUs + travelTimeUs(sp.d0, sp.v1);
  int64_t g3CheckUs = edges.riseUs + travelTimeUs(sp.d2, sp.v1);
  int64_t g4CheckUs = edges.riseUs + travelTimeUs(sp.d4, sp.v1);

  // ------------------------------------------------------------------------
  // 2. G2 size classification
  // ------------------------------------------------------------------------
  if (!lengthAccepted(product.lengthCm)) {
    product.destination = 1;
    product.weightG = 0.0f;
    product.barcode = 0;

    reserveDestination(1);

    queueGateAction(SORT_GATE_G2,
                    true,
                    g2CheckUs,
                    product.lengthCm,
                    myEpoch);

    queueArrivalEvent(product.sequenceNo,
                      product.barcode,
                      product.lengthCm,
                      product.weightG,
                      product.destination,
                      g2CheckUs + 5000,
                      myEpoch);

    vTaskDelete(NULL);
    return;
  }

  queueGateAction(SORT_GATE_G2,
                  false,
                  g2CheckUs,
                  product.lengthCm,
                  myEpoch);

  if (emergencyActive || epochExpired(myEpoch)) {
    vTaskDelete(NULL);
    return;
  }

  // ------------------------------------------------------------------------
  // 3. Weight measurement
  // From falling edge, product centre is length/2 ahead of obstruction sensor.
  // ------------------------------------------------------------------------
  float weightCentreDistance = sp.d1 - (product.lengthCm / 2.0f);

  if (weightCentreDistance < 0.0f) {
    weightCentreDistance = 0.0f;
  }

  int64_t weightCentreUs =
    edges.fallUs + travelTimeUs(weightCentreDistance, sp.v1);

  product.weightG = readWeightAtWindow(weightCentreUs,
                                       product.lengthCm,
                                       myEpoch);

  if (emergencyActive || epochExpired(myEpoch)) {
    vTaskDelete(NULL);
    return;
  }

  // ------------------------------------------------------------------------
  // 4. G3 weight classification
  // ------------------------------------------------------------------------
  if (!weightAccepted(product.weightG)) {
    product.destination = 1;
    product.barcode = 0;

    reserveDestination(1);

    queueGateAction(SORT_GATE_G3,
                    true,
                    g3CheckUs,
                    product.lengthCm,
                    myEpoch);

    queueArrivalEvent(product.sequenceNo,
                      product.barcode,
                      product.lengthCm,
                      product.weightG,
                      product.destination,
                      g3CheckUs + 5000,
                      myEpoch);

    vTaskDelete(NULL);
    return;
  }

  queueGateAction(SORT_GATE_G3,
                  false,
                  g3CheckUs,
                  product.lengthCm,
                  myEpoch);

  if (emergencyActive || epochExpired(myEpoch)) {
    vTaskDelete(NULL);
    return;
  }

  // ------------------------------------------------------------------------
  // 5. Barcode reading
  // ------------------------------------------------------------------------
  float barcodeCentreDistance = sp.d3 - (product.lengthCm / 2.0f);

  if (barcodeCentreDistance < 0.0f) {
    barcodeCentreDistance = 0.0f;
  }

  int64_t barcodeCentreUs =
    edges.fallUs + travelTimeUs(barcodeCentreDistance, sp.v1);

  product.barcode = readBarcodeAtWindow(barcodeCentreUs,
                                        product.lengthCm,
                                        myEpoch);

  if (emergencyActive || epochExpired(myEpoch)) {
    vTaskDelete(NULL);
    return;
  }

  // ------------------------------------------------------------------------
  // 6. G4 final routing
  // ------------------------------------------------------------------------
  if (shouldRouteArea2(product.lengthCm, product.weightG)) {
    product.destination = 2;

    reserveDestination(2);

    queueGateAction(SORT_GATE_G4,
                    false,
                    g4CheckUs,
                    product.lengthCm,
                    myEpoch);

    int64_t arrivalUs = g4CheckUs + travelTimeUs(sp.d5, sp.v2);

    queueArrivalEvent(product.sequenceNo,
                      product.barcode,
                      product.lengthCm,
                      product.weightG,
                      product.destination,
                      arrivalUs,
                      myEpoch);
  }
  else {
    product.destination = 3;

    reserveDestination(3);

    queueGateAction(SORT_GATE_G4,
                    true,
                    g4CheckUs,
                    product.lengthCm,
                    myEpoch);

    int64_t arrivalUs = g4CheckUs + travelTimeUs(sp.d6, sp.v3);

    queueArrivalEvent(product.sequenceNo,
                      product.barcode,
                      product.lengthCm,
                      product.weightG,
                      product.destination,
                      arrivalUs,
                      myEpoch);
  }

  vTaskDelete(NULL);
}


// ============================================================================
// BACKGROUND TASK - CORE 1
// ============================================================================

void backgroundTask(void *pvParameters) {
  TickType_t lastWake = xTaskGetTickCount();

  while (true) {
    // --------------------------------------------------------------------
    // Serial command handling
    // --------------------------------------------------------------------
    while (Serial.available() > 0) {
      String command = Serial.readStringUntil('\n');
      command.trim();

      if (command == "reset") {
        resetControllerState();
      }
      else if (command == "clear") {
        clearAreasByOperator();
      }
      else if (command == "emergency") {
        emergencyActive = true;

        g_gate1Ctrl = false;
        g_gate2Ctrl = false;
        g_gate3Ctrl = false;
        g_gate4Ctrl = false;

        Serial.println("EMERGENCY: System halted");
      }
      else if (command == "stat") {
        float Lavg = 0.0f;
        float Wavg = 0.0f;
        float L2avg = 0.0f;
        float W2avg = 0.0f;
        float L3avg = 0.0f;
        float W3avg = 0.0f;

        if (stateMutex != NULL) {
          xSemaphoreTake(stateMutex, portMAX_DELAY);

          if (systemState.totalProducts > 0) {
            Lavg = systemState.totalLength / systemState.totalProducts;
            Wavg = systemState.totalWeight / systemState.totalProducts;
          }

          if (systemState.area2Products > 0) {
            L2avg = systemState.area2Length / systemState.area2Products;
            W2avg = systemState.area2Weight / systemState.area2Products;
          }

          if (systemState.area3Products > 0) {
            L3avg = systemState.area3Length / systemState.area3Products;
            W3avg = systemState.area3Weight / systemState.area3Products;
          }

          xSemaphoreGive(stateMutex);
        }

        Serial.printf("sortSTAT: %.2f,%.2f,%.2f,%.2f,%.2f,%.2f\n",
                      Lavg, L2avg, L3avg, Wavg, W2avg, W3avg);
      }
      else {
      }
    }

    // --------------------------------------------------------------------
    // G1 capacity control
    // --------------------------------------------------------------------
    updateGate1FromCapacity();

    if (capacityBlocked && !capacityMessageShown) {
      Serial.printf("Area %d has reached full capacity. G1 is closed. Type clear after the operator empties the area.\n",
                    blockedArea);
      capacityMessageShown = true;
    }

    if (stateMutex != NULL) {
      xSemaphoreTake(stateMutex, portMAX_DELAY);
      if (emergencyActive || capacityBlocked) {}
      else {
        Serial.printf("sortRT: %03d,%03d,%03d",
                      systemState.areaOccupancy[0],
                      systemState.areaOccupancy[1],
                      systemState.areaOccupancy[2]);

        for (int i = 0; i < recentCount; i++) {
          int index =
            (recentWritePos - recentCount + i + RECENT_HISTORY_SIZE)
            % RECENT_HISTORY_SIZE;

          recent_product_record_t r = recentHistory[index];

          int trackingNumber = r.barcode;

          // If barcode failed or is not available, output 0 as required.
          if (trackingNumber == 0) {
            trackingNumber = 0;
          }

          Serial.printf(",%d,%.1f,%.1f,A%d",
                        trackingNumber,
                        r.lengthCm,
                        r.weightG,
                        r.destination);
        }

        Serial.println();
      }

      xSemaphoreGive(stateMutex);
    }

    vTaskDelayUntil(&lastWake, pdMS_TO_TICKS(1000));
  }
}


// ============================================================================
// SETUP
// ============================================================================

void setup() {
  Serial.begin(115200);

  edgeQueue = xQueueCreate(10, sizeof(sensor_edge_pair_t));

  if (edgeQueue == NULL) {
    Serial.println("ERROR: edgeQueue creation failed");
  }

  gateQueue = xQueueCreate(GATE_QUEUE_LENGTH, sizeof(gate_command_t));

  if (gateQueue == NULL) {
    Serial.println("ERROR: gateQueue creation failed");
  }

  arrivalQueue = xQueueCreate(ARRIVAL_QUEUE_LENGTH, sizeof(arrival_event_t));

  if (arrivalQueue == NULL) {
    Serial.println("ERROR: arrivalQueue creation failed");
  }

  stateMutex = xSemaphoreCreateMutex();

  if (stateMutex == NULL) {
    Serial.println("ERROR: stateMutex creation failed");
  }

  // Initial gate states.
  g_gate1Ctrl = true;
  g_gate2Ctrl = false;
  g_gate3Ctrl = false;
  g_gate4Ctrl = false;

  // Dedicated gate-control system on Core 0.
  xTaskCreatePinnedToCore(
    gateDispatcherTask,
    "GateDispatcher",
    4096,
    NULL,
    9,
    NULL,
    0
  );

  // Core 0: Conveyor 1 inspection, measurements, and route decisions.
  xTaskCreatePinnedToCore(
    productProcessingTask,
    "ProductDispatcher",
    4096,
    NULL,
    10,
    NULL,
    0
  );

  // Core 1: Arrival tracking for Conveyor 2/3 and destination updates.
  xTaskCreatePinnedToCore(
    arrivalTrackerTask,
    "ArrivalTracker",
    4096,
    NULL,
    4,
    NULL,
    1
  );

  // Core 1: Serial status, commands, and G1 capacity monitoring.
  xTaskCreatePinnedToCore(
    backgroundTask,
    "StatusCommandTask",
    4096,
    NULL,
    2,
    NULL,
    1
  );

  // Start simulator after all student RTOS objects/tasks are ready.
  startSimulator();
}


// ============================================================================
// LOOP
// ============================================================================

void loop() {
  vTaskDelay(portMAX_DELAY);
}

/******************************************** END OF STUDENT CODE *****************************************/
/*!!!!!!!!!!!!!!!!!!!!!!!!!!! ANY CODE BELOW THIS LINE SHOULD NOT BE MODIFIED !!!!!!!!!!!!!!!!!!!!!!!!!!!*/
/*================================ START OF SIMULATOR ENGINE ============================================*/

volatile int currentProductIndex = 0;
const int MAX_SCHEDULERS = 4;
ProductScheduler g_schedulers[MAX_SCHEDULERS];

static inline uint64_t distanceToMicros(float distance_cm, float speed_cm_s) {
  double tSec = (double)distance_cm / (double)speed_cm_s;
  return (uint64_t)(tSec * 1e6);
}

void fillProductEvents(ProductScheduler &sch) {
  const Product &p = sch.product;
  sch.totalEvents = 0;
  sch.currentEventIndex = 0;

  auto &events = sch.events;
  int idx = 0;

  uint64_t leadTime = distanceToMicros(DIST_LEAD, sp.v1);

  // Determine product's ground-truth path
  bool sizeOk   = (p.length >= sp.L_min && p.length <= sp.L_max);
  bool weightOk = (p.weight >= sp.W_min && p.weight <= sp.W_max);
  bool isSmallLight = sizeOk && weightOk &&
                      (p.length <= sp.L_threshold) && (p.weight <= sp.W_threshold);

  // Pre-compute destination area index (0=A1, 1=A2, 2=A3)
  int destArea;
  if (!sizeOk) destArea = 0;
  else if (!weightOk) destArea = 0;
  else if (isSmallLight) destArea = 1;
  else destArea = 2;

  // 1. Obstruction sensor: front edge arrives
  events[idx].triggerTimeMicros = leadTime;
  events[idx].eventType = ProductEventType::OBSTRUCTION_SENSOR_RISE;
  events[idx].gateExpected = 0;
  events[idx].destArea = 0;
  idx++;

  // 2. Obstruction sensor: back edge leaves
  uint64_t fallTime = distanceToMicros(p.length, sp.v1);
  events[idx].triggerTimeMicros = leadTime + fallTime;
  events[idx].eventType = ProductEventType::OBSTRUCTION_SENSOR_FALL;
  events[idx].gateExpected = 0;
  events[idx].destArea = 0;
  idx++;

  // 3. G2 check (size gate) - front edge at d0
  // G2: true=divert (size abnormal), expected true if !sizeOk
  uint64_t g2Time = distanceToMicros(sp.d0, sp.v1) + leadTime;
  events[idx].triggerTimeMicros = g2Time;
  events[idx].eventType = ProductEventType::G2_CHECK;
  events[idx].gateExpected = sizeOk ? 0 : 1;
  events[idx].destArea = 0;
  idx++;

  if (!sizeOk) {
    // Product diverted at G2 -> Area 1
    events[idx].triggerTimeMicros = g2Time + 5000;
    events[idx].eventType = ProductEventType::ARRIVE_DESTINATION;
    events[idx].gateExpected = 0;
    events[idx].destArea = 0;
    idx++;

    events[idx].triggerTimeMicros = g2Time + 10000;
    events[idx].eventType = ProductEventType::FINISH;
    events[idx].gateExpected = 0;
    events[idx].destArea = 0;
    idx++;
  } else {
    // 4. Weight sensor window
    uint64_t centerAtWeight = distanceToMicros(sp.d1 + p.length / 2.0f, sp.v1) + leadTime;
    uint64_t halfWindowW = distanceToMicros(p.length * 0.1f, sp.v1);
    events[idx].triggerTimeMicros = centerAtWeight - halfWindowW;
    events[idx].eventType = ProductEventType::WEIGHT_SENSOR_ENTER_WINDOW;
    events[idx].gateExpected = 0;
    events[idx].destArea = 0;
    idx++;

    events[idx].triggerTimeMicros = centerAtWeight + halfWindowW;
    events[idx].eventType = ProductEventType::WEIGHT_SENSOR_EXIT_WINDOW;
    events[idx].gateExpected = 0;
    events[idx].destArea = 0;
    idx++;

    // 5. G3 check (weight gate) - front edge at d2
    // G3: true=divert (weight abnormal), expected true if !weightOk
    uint64_t g3Time = distanceToMicros(sp.d2, sp.v1) + leadTime;
    events[idx].triggerTimeMicros = g3Time;
    events[idx].eventType = ProductEventType::G3_CHECK;
    events[idx].gateExpected = weightOk ? 0 : 1;
    events[idx].destArea = 0;
    idx++;

    if (!weightOk) {
      // Product diverted at G3 -> Area 1
      events[idx].triggerTimeMicros = g3Time + 5000;
      events[idx].eventType = ProductEventType::ARRIVE_DESTINATION;
      events[idx].gateExpected = 0;
      events[idx].destArea = 0;
      idx++;

      events[idx].triggerTimeMicros = g3Time + 10000;
      events[idx].eventType = ProductEventType::FINISH;
      events[idx].gateExpected = 0;
      events[idx].destArea = 0;
      idx++;
    } else {
      // 6. Barcode sensor window
      uint64_t centerAtBarcode = distanceToMicros(sp.d3 + p.length / 2.0f, sp.v1) + leadTime;
      uint64_t halfWindowB = distanceToMicros(p.length * 0.1f, sp.v1);
      events[idx].triggerTimeMicros = centerAtBarcode - halfWindowB;
      events[idx].eventType = ProductEventType::BARCODE_SENSOR_ENTER_WINDOW;
      events[idx].gateExpected = 0;
      events[idx].destArea = 0;
      idx++;

      events[idx].triggerTimeMicros = centerAtBarcode + halfWindowB;
      events[idx].eventType = ProductEventType::BARCODE_SENSOR_EXIT_WINDOW;
      events[idx].gateExpected = 0;
      events[idx].destArea = 0;
      idx++;

      // 7. G4 check (routing gate) - front edge at d4
      // G4: false=Conv2/Area2, true=Conv3/Area3
      uint64_t g4Time = distanceToMicros(sp.d4, sp.v1) + leadTime;
      events[idx].triggerTimeMicros = g4Time;
      events[idx].eventType = ProductEventType::G4_CHECK;
      events[idx].gateExpected = isSmallLight ? 0 : 1;
      events[idx].destArea = 0;
      idx++;

      // 8. Arrive at destination area
      uint64_t arriveTime;
      if (isSmallLight) {
        arriveTime = g4Time + distanceToMicros(sp.d5, sp.v2);
      } else {
        arriveTime = g4Time + distanceToMicros(sp.d6, sp.v3);
      }
      events[idx].triggerTimeMicros = arriveTime;
      events[idx].eventType = ProductEventType::ARRIVE_DESTINATION;
      events[idx].gateExpected = 0;
      events[idx].destArea = destArea;
      idx++;

      events[idx].triggerTimeMicros = arriveTime + 5000;
      events[idx].eventType = ProductEventType::FINISH;
      events[idx].gateExpected = 0;
      events[idx].destArea = 0;
      idx++;
    }
  }

  sch.totalEvents = idx;

  // Sort events by time
  for (int i = 0; i < sch.totalEvents - 1; i++) {
    for (int j = i + 1; j < sch.totalEvents; j++) {
      if (events[i].triggerTimeMicros > events[j].triggerTimeMicros) {
        ProductEvent tmp = events[i];
        events[i] = events[j];
        events[j] = tmp;
      }
    }
  }
}

void printProductEvents(const ProductScheduler &sch) {
  Serial.println("===== Product Event Timeline =====");
  Serial.printf("Length: %.2f cm  Weight: %.2f g  Barcode: %d\n",
                sch.product.length, sch.product.weight, sch.product.barcodeID);

  bool sizeOk = (sch.product.length >= sp.L_min && sch.product.length <= sp.L_max);
  bool weightOk = (sch.product.weight >= sp.W_min && sch.product.weight <= sp.W_max);
  const char* dest = "???";
  if (!sizeOk) dest = "Area1(size)";
  else if (!weightOk) dest = "Area1(weight)";
  else if (sch.product.length <= sp.L_threshold && sch.product.weight <= sp.W_threshold) dest = "Area2";
  else dest = "Area3";
  Serial.printf("Expected destination: %s\n", dest);

  for (int i = 0; i < sch.totalEvents; i++) {
    const ProductEvent &evt = sch.events[i];
    float timeMs = evt.triggerTimeMicros / 1000.0f;
    Serial.printf("  %d: %.3f ms - ", i, timeMs);
    switch (evt.eventType) {
      case ProductEventType::OBSTRUCTION_SENSOR_RISE:   Serial.println("OBSTRUCTION_RISE"); break;
      case ProductEventType::OBSTRUCTION_SENSOR_FALL:   Serial.println("OBSTRUCTION_FALL"); break;
      case ProductEventType::G2_CHECK:                  Serial.println("G2_CHECK (size)"); break;
      case ProductEventType::WEIGHT_SENSOR_ENTER_WINDOW: Serial.println("WEIGHT_ENTER"); break;
      case ProductEventType::WEIGHT_SENSOR_EXIT_WINDOW: Serial.println("WEIGHT_EXIT"); break;
      case ProductEventType::G3_CHECK:                  Serial.println("G3_CHECK (weight)"); break;
      case ProductEventType::BARCODE_SENSOR_ENTER_WINDOW: Serial.println("BARCODE_ENTER"); break;
      case ProductEventType::BARCODE_SENSOR_EXIT_WINDOW: Serial.println("BARCODE_EXIT"); break;
      case ProductEventType::G4_CHECK:                  Serial.println("G4_CHECK (route)"); break;
      case ProductEventType::ARRIVE_DESTINATION:        Serial.println("ARRIVE_DESTINATION"); break;
      case ProductEventType::FINISH:                    Serial.println("FINISH"); break;
      default: Serial.println("UNKNOWN"); break;
    }
  }
  Serial.println("==================================");
}

// Hardware timer ISR - executes product events
void ARDUINO_ISR_ATTR onTimerInterrupt(void* arg) {
  ProductScheduler* sch = (ProductScheduler*)arg;
  hw_timer_t* timer = sch->timerHandle;

  if (!timer) return;

  if (sch->currentEventIndex >= sch->totalEvents) {
    timerEnd(timer);
    sch->timerHandle = nullptr;
    return;
  }

  // Get current event
  ProductEvent evt = sch->events[sch->currentEventIndex];
  sch->currentEventIndex++;

  // Execute event logic (no floating-point comparisons - all pre-computed)
  int evtType = (int)evt.eventType;

  if (evtType == (int)ProductEventType::OBSTRUCTION_SENSOR_RISE) {
    g_obstructionSensor = true;
    digitalWrite(g_obstructionSensorPin, HIGH);
    obstructionSensorInterrupt();
  }
  else if (evtType == (int)ProductEventType::OBSTRUCTION_SENSOR_FALL) {
    g_obstructionSensor = false;
    digitalWrite(g_obstructionSensorPin, LOW);
    obstructionSensorInterrupt();
  }
  else if (evtType == (int)ProductEventType::WEIGHT_SENSOR_ENTER_WINDOW) {
    g_weightSensor = sch->product.weight;
  }
  else if (evtType == (int)ProductEventType::WEIGHT_SENSOR_EXIT_WINDOW) {
    g_weightSensor = 0.0f;
  }
  else if (evtType == (int)ProductEventType::BARCODE_SENSOR_ENTER_WINDOW) {
    g_barcodeReader = sch->product.barcodeID;
  }
  else if (evtType == (int)ProductEventType::BARCODE_SENSOR_EXIT_WINDOW) {
    g_barcodeReader = 0;
  }
  else if (evtType == (int)ProductEventType::G2_CHECK) {
    // G2: true=divert. Pre-computed expected value in gateExpected
    if ((int)g_gate2Ctrl != evt.gateExpected) {
      errorGateCNT[0]++;
    }
  }
  else if (evtType == (int)ProductEventType::G3_CHECK) {
    // G3: true=divert. Pre-computed expected value in gateExpected
    if ((int)g_gate3Ctrl != evt.gateExpected) {
      errorGateCNT[1]++;
    }
  }
  else if (evtType == (int)ProductEventType::G4_CHECK) {
    // G4: false=Conv2, true=Conv3. Pre-computed expected value
    if ((int)g_gate4Ctrl != evt.gateExpected) {
      errorGateCNT[2]++;
    }
  }
  else if (evtType == (int)ProductEventType::ARRIVE_DESTINATION) {
    simAreaCount[evt.destArea]++;
  }
  else if (evtType == (int)ProductEventType::FINISH) {
    digitalWrite(sch->debugPin, LOW);
  }

  // Set up next event or end timer
  if (sch->currentEventIndex < sch->totalEvents) {
    timerAlarm(timer, sch->events[sch->currentEventIndex].triggerTimeMicros, false, 0);
  } else {
    timerEnd(timer);
    sch->timerHandle = nullptr;
  }
}

hw_timer_t* allocateTimerForProduct(ProductScheduler &sch) {
  digitalWrite(sch.debugPin, HIGH);
  fillProductEvents(sch);

  hw_timer_t* timer = timerBegin(1000000);  // 1MHz = 1us resolution
  if (!timer) return nullptr;

  sch.timerHandle = timer;
  timerAttachInterruptArg(timer, &onTimerInterrupt, (void*)&sch);

  if (sch.totalEvents > 0) {
    digitalWrite(sch.debugPin, LOW);
    timerWrite(timer, 0);
    timerAlarm(timer, sch.events[0].triggerTimeMicros, false, 0);
  }
  return timer;
}

// Status reporting task - prints simulator state periodically
void statusReportTask(void *pvParameters) {
  vTaskDelay(2000 / portTICK_PERIOD_MS);  // Initial delay
  while (true) {
    Serial.printf("[SIM] Products loaded: %d/%d | Area counts: A1=%d A2=%d A3=%d | Gate errors: G2=%d G3=%d G4=%d\n",
                  currentProductIndex, numProducts,
                  simAreaCount[0], simAreaCount[1], simAreaCount[2],
                  errorGateCNT[0], errorGateCNT[1], errorGateCNT[2]);

    // Check if all products finished
    if (currentProductIndex >= numProducts) {
      bool allDone = true;
      for (int i = 0; i < MAX_SCHEDULERS; i++) {
        if (g_schedulers[i].timerHandle != nullptr) {
          allDone = false;
          break;
        }
      }
      if (allDone) {
        int totalArrived = simAreaCount[0] + simAreaCount[1] + simAreaCount[2];
        Serial.println("\n=== SIMULATION COMPLETE ===");
        Serial.printf("Total products processed: %d/%d\n", totalArrived, numProducts);
        Serial.printf("Area 1: %d  Area 2: %d  Area 3: %d\n",
                      simAreaCount[0], simAreaCount[1], simAreaCount[2]);
        Serial.printf("Gate errors: G2=%d  G3=%d  G4=%d\n",
                      errorGateCNT[0], errorGateCNT[1], errorGateCNT[2]);
        if (errorGateCNT[0] == 0 && errorGateCNT[1] == 0 && errorGateCNT[2] == 0) {
          Serial.println("Result: ALL GATES CORRECT!");
        } else {
          Serial.println("Result: GATE ERRORS DETECTED - check your control logic");
        }
        Serial.println("===========================\n");
        vTaskDelete(NULL);
        return;
      }
    }
    vTaskDelay(2000 / portTICK_PERIOD_MS);
  }
}

// Product loading task - loads products at fixed intervals, checks G1 gate
void productLoadingTask(void *pvParameters) {
  TickType_t xLastWakeTime = xTaskGetTickCount();

  while (true) {
    if (currentProductIndex < numProducts) {
      // Check G1 intake gate
      if (g_gate1Ctrl) {
        bool schedulerFound = false;
        for (int i = 0; i < MAX_SCHEDULERS; i++) {
          if (g_schedulers[i].timerHandle == nullptr) {
            g_schedulers[i].product = productArray[currentProductIndex];
            g_schedulers[i].debugPin = DEBUG_PIN + currentProductIndex % 3;

            hw_timer_t* t = allocateTimerForProduct(g_schedulers[i]);
            if (!t) {
              Serial.println("ERROR: No hardware timer available!");
            } else {
              currentProductIndex++;
              schedulerFound = true;
            }
            break;
          }
        }
        if (!schedulerFound) {
          // No scheduler available this cycle, will retry next interval
        }
      } else {
        // G1 is closed - product blocked at intake
        // The product remains in the queue, will be loaded when G1 opens
      }
    }
    vTaskDelayUntil(&xLastWakeTime, sp.productInterval / portTICK_PERIOD_MS);
  }
}

void startSimulator(void) {
  // Generate parameters from student number
  generateParameters(STUDENT_NUMBER);
  printParameters();

  // Generate test product array
  generateProductArray();

  Serial.printf("\nGenerated %d test products:\n", numProducts);
  for (int i = 0; i < numProducts; i++) {
    bool sizeOk = (productArray[i].length >= sp.L_min && productArray[i].length <= sp.L_max);
    bool weightOk = (productArray[i].weight >= sp.W_min && productArray[i].weight <= sp.W_max);
    const char* dest;
    if (!sizeOk) dest = "A1(size)";
    else if (!weightOk) dest = "A1(weight)";
    else if (productArray[i].length <= sp.L_threshold && productArray[i].weight <= sp.W_threshold) dest = "A2";
    else dest = "A3";
    Serial.printf("  [%d] L=%.2f W=%.2f BC=%d -> %s\n",
                  i, productArray[i].length, productArray[i].weight, productArray[i].barcodeID, dest);
  }
  Serial.println();

  // Setup GPIO pins
  pinMode(g_obstructionSensorPin, OUTPUT);
  pinMode(DEBUG_PIN, OUTPUT);
  pinMode(DEBUG_PIN + 1, OUTPUT);
  pinMode(DEBUG_PIN + 2, OUTPUT);
  digitalWrite(DEBUG_PIN, LOW);
  digitalWrite(DEBUG_PIN + 1, LOW);
  digitalWrite(DEBUG_PIN + 2, LOW);

  // Initialize sensor outputs
  g_obstructionSensor = false;
  g_barcodeReader = 0;
  g_weightSensor = 0.0f;

  // Initialize gate controls to default
  g_gate1Ctrl = true;
  g_gate2Ctrl = false;
  g_gate3Ctrl = false;
  g_gate4Ctrl = false;

  // Reset counters
  currentProductIndex = 0;
  for (int i = 0; i < MAX_SCHEDULERS; i++) {
    g_schedulers[i].timerHandle = nullptr;
  }
  for (int i = 0; i < 3; i++) {
    errorGateCNT[i] = 0;
    simAreaCount[i] = 0;
  }

  // Create product loading task (highest priority)
  xTaskCreate(
    productLoadingTask,
    "ProductLoader",
    2048,
    NULL,
    configMAX_PRIORITIES - 1,
    NULL
  );

  // Create status reporting task
  xTaskCreate(
    statusReportTask,
    "StatusReport",
    2048,
    NULL,
    1,
    NULL
  );

  Serial.println("=== SmartSort Simulator Started ===\n");
}