#include <stdint.h>
#include <stdio.h>
#include <rom/ets_sys.h>

/* =========================================================
   ESP32 GPIO Register Addresses
   These addresses come from the ESP32 memory map.
   We use them to control GPIO pins directly.
   ========================================================= */
#define GPIO_ENABLE_REG  0x3FF44020
#define GPIO_OUT_REG     0x3FF44004
#define GPIO_IN_REG      0x3FF4403C

/* =========================================================
   Pin Connections
   ========================================================= */
#define RED_LED_PIN      2
#define YELLOW_LED_PIN   4
#define GREEN_LED_PIN    5
#define SWITCH_PIN       12

/* =========================================================
   Timing Configuration
   ========================================================= */
#define SHORT_DELAY_US   300000
#define LONG_DELAY_US    700000
#define BLINK_TIMES      3

/* =========================================================
   Application Constants and State
   ========================================================= */
const uint8_t SWITCH_ACTIVE = 1;

uint8_t system_mode = 0;

/* =========================================================
   GPIO Output Enable
   This function configures a GPIO pin as output.
   It sets the selected bit in GPIO_ENABLE_REG.
   ========================================================= */
void gpio_enable_output(uint8_t pin)
{
    volatile uint32_t *gpio_enable;

    gpio_enable = (volatile uint32_t *)GPIO_ENABLE_REG;

    *gpio_enable |= (1UL << pin);
}

/* =========================================================
   GPIO Set HIGH
   This function makes one GPIO output HIGH.
   It does not affect the other GPIO pins.
   ========================================================= */
void gpio_set_high(uint8_t pin)
{
    volatile uint32_t *gpio_out;

    gpio_out = (volatile uint32_t *)GPIO_OUT_REG;

    *gpio_out |= (1UL << pin);
}

/* =========================================================
   GPIO Set LOW
   This function makes one GPIO output LOW.
   It does not affect the other GPIO pins.
   ========================================================= */
void gpio_set_low(uint8_t pin)
{
    volatile uint32_t *gpio_out;

    gpio_out = (volatile uint32_t *)GPIO_OUT_REG;

    *gpio_out &= ~(1UL << pin);
}

/* =========================================================
   GPIO Read Input
   This function reads one selected GPIO pin.
   It returns 1 if the pin is HIGH.
   It returns 0 if the pin is LOW.
   ========================================================= */
uint8_t gpio_read_pin(uint8_t pin)
{
    volatile uint32_t *gpio_in;

    gpio_in = (volatile uint32_t *)GPIO_IN_REG;

    uint32_t input_value = *gpio_in;
    uint32_t pin_mask = (1UL << pin);

    if ((input_value & pin_mask) != 0)
    {
        return 1;
    }

    return 0;
}

/* =========================================================
   Turn All LEDs OFF
   ========================================================= */
void turn_all_leds_off(void)
{
    gpio_set_low(RED_LED_PIN);
    gpio_set_low(YELLOW_LED_PIN);
    gpio_set_low(GREEN_LED_PIN);
}

/* =========================================================
   Normal Mode
   Green LED ON only.
   ========================================================= */
void show_normal_mode(void)
{
    turn_all_leds_off();

    gpio_set_high(GREEN_LED_PIN);
}

/* =========================================================
   Warning Mode
   Yellow LED blinks three times.
   Then Red LED turns ON.
   ========================================================= */
void show_warning_mode(void)
{
    turn_all_leds_off();

    for (uint8_t blink_counter = 0; blink_counter < BLINK_TIMES; blink_counter++)
    {
        gpio_set_high(YELLOW_LED_PIN);
        ets_delay_us(SHORT_DELAY_US);

        gpio_set_low(YELLOW_LED_PIN);
        ets_delay_us(SHORT_DELAY_US);
    }

    gpio_set_high(RED_LED_PIN);
    ets_delay_us(LONG_DELAY_US);
}

/* =========================================================
   Update System Mode
   If switch is ON, system enters warning mode.
   If switch is OFF, system returns to normal mode.
   ========================================================= */
void update_system_mode(void)
{
    uint8_t switch_state = gpio_read_pin(SWITCH_PIN);

    if (switch_state == SWITCH_ACTIVE)
    {
        system_mode = 1;
    }
    else
    {
        system_mode = 0;
    }
}

/* =========================================================
   Display Current Mode
   ========================================================= */
void display_current_mode(void)
{
    if (system_mode == 0)
    {
        show_normal_mode();
    }
    else
    {
        show_warning_mode();
    }
}

/* =========================================================
   Print Debug Information
   ========================================================= */
void print_debug_info(void)
{
    uint8_t switch_state = gpio_read_pin(SWITCH_PIN);

    printf("Switch = %u | System Mode = %u\n",
           switch_state,
           system_mode);
}

/* =========================================================
   Main Application
   ========================================================= */
void app_main(void)
{
    gpio_enable_output(RED_LED_PIN);
    gpio_enable_output(YELLOW_LED_PIN);
    gpio_enable_output(GREEN_LED_PIN);

    turn_all_leds_off();

    while (1)
    {
        update_system_mode();

        display_current_mode();

        print_debug_info();

        ets_delay_us(SHORT_DELAY_US);
    }
}