// Include the libraries:
#include <Keypad.h>
#include <LiquidCrystal_I2C.h>
#include <Wire.h>

const byte ROWS = 4; // define number of rows
const byte COLS = 4; // define number of columns
byte rowPins[] = {9, 8, 7, 6}; // connect first four pins to 9, 8, 7, 6
byte colPins[] = {5, 4, 3, 2}; // connect last four pins to 5, 4, 3, 2

// define the key labels
char hexaKeys[ROWS][COLS] = {
  {'1','2','3','a'},
  {'4','5','6','b'},
  {'7','8','9','c'},
  {'*','0','#','d'}
};

LiquidCrystal_I2C lcd(0x27, 20, 4);
Keypad kp = Keypad(makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS);

void setup() {
  lcd.init(); // initialize the LCD
  lcd.backlight(); // turn on the backlight
  Serial.begin(9600); // Start serial monitor

  delay(100);

  lcd.home(); // set cursor at top left
  lcdLineXY(1, 1, "Cybalent's Calc :)", true); // print starting text
  lcdLineXY(3, 2, "Code by kos256", false); // you gotta include me too :P
  delay(2000); // wait 2 seconds

  lcdLineXY(1, 0, "Tap * key for help", true); delay(1000);
  lcd.clear();
}

bool containsChar(char* items, char target, int itemLen) {
  bool result = false;

  for (int i = 0; i < itemLen; i++) {
    if (items[i] == target) {
      result = true;
      break;
    }
  }

  return result;
}

String backspace(String str) {
  String result = str;
  if(str.length() > 0) {
    result.remove(result.length() - 1);
  }

  return result;
}

void lcdLine(String text, int line, bool clr) {
  if(clr) lcd.clear();

  lcd.setCursor(0, line-1);
  lcd.print(text);
}

void lcdLineXY(int x, int y, String text, bool clr) {
  if(clr) lcd.clear();

  lcd.setCursor(x, y);
  lcd.print(text);
}

String expression = "";
bool exitMenu = false;
bool redrawHelpMenu = false;

void loop() {
  
  while(1) {
    lcd.blink();
    lcdLine(expression, 1, true);
    char key;

    while(1) {
      key = kp.getKey(); // get the pressed key on the keypad
      if(key) break;
    }
    lcd.noBlink();

    if(containsChar("1234567890", key, 10)) {
      expression += String(key);
    }
    if(containsChar("abcd", key, 4)) {
      if(key=='a') {
        expression += "+";
      }
      if(key=='b') {
        expression += "-";
      }
      if(key=='c') {
        expression += "*";
      }
      if(key=='d') {
        expression += "/";
      }
    }
    
    if(containsChar("*#", key, 2)) { // If * or # is pressed then run this statement
      if(key == '#') { // If # is pressed, evaluate the expression and calculate.
        char esbuf[2]; String cResult;
        bool SYNTAX_signsTogether, SYNTAX_noNumbers, SYNTAX_empty, SYNTAX_strayOperator;
        // temporary expression buffers (sebuf = expression syntax buffer)
        // calc result

        /* Error codes (cuz ain't no way im putting the whole reason up on screen)
        01 - Empty expression.
        02 - Repeated operator. {e.g. 4++7*96/+2}
        03 - Only operator(s), no numbers. {e.g. The whole expression is literally just "+".}
        04 - Stray operator. {e.g. "*37-4" or "13+7-" or both.}
        */

        // Check for syntax errors:
        lcdLine("Calculating...", 3, false);
        cResult = "<no calc method>";

        SYNTAX_empty = expression.length() == 0; // expression is empty
        
        //if(containsChar("+-/*", expression[0], 4)) SYNTAX_strayOperator = true; // if there's a operator at the start of the expression
        
        if(!SYNTAX_empty) {
          for (int i = 0; i < expression.length()-1; i++) {
            esbuf[0] = expression[i];
            esbuf[1] = expression[i+1];

            bool SYNTAX_signsTogether = containsChar("+-*/", esbuf[0], 4) && containsChar("+-*/", esbuf[1], 4);

            if(SYNTAX_signsTogether) {
              cResult = "Syntax error! 02"; // repeated operator
              break;
            }
            Serial.println(String(i) + " " + String(esbuf[0]) + String(esbuf[1]));
            delay(10);
          }
          SYNTAX_strayOperator = 
            containsChar("+-*/", esbuf[1], 4) || // if there's a operator at the start of the expression or
            containsChar("+-*/", expression[0], 4); // if there's a operator at the end of the expression
          SYNTAX_noNumbers = true; // only operators, no numbers
          for (int i = 0; i < expression.length(); i++) {
            if(containsChar("1234567890", expression[i], 10)) {
              SYNTAX_noNumbers = false;
              break;
            }
          }
        }

        // todo edit mode
        
        if (SYNTAX_strayOperator) cResult = "Syntax error! 04";
        if (SYNTAX_empty) cResult = "Syntax error! 01";
        if (SYNTAX_noNumbers) cResult = "Syntax error! 03";
        

        // Do the actual calculation:

        

        lcdLine("                    ", 3, false);
        lcdLine("= " + String(cResult), 3, false);
        lcd.noBlink();
        while(1) {
          key = kp.getKey();
          if(key) break;
        }
        if(key == '#') {
          expression = "";
        }
      }
      if(key == '*') { // If * is pressed, do the help stuff...
        while(1) {
          lcdLineXY(6, 0, "* Help *", true); // Display title
          lcdLineXY(1, 1, "Controls", false); // Display first option (Controls)
          lcdLineXY(1, 2, "More options...", false); // Display second option (More...)
          lcdLineXY(1, 3, "Back", false); // Display third option (Exit help menu)
          lcdLineXY(10, 3, "A - Select", false);
          exitMenu = false;
          redrawHelpMenu = false;

          int menui = 0; // Menu index stores what option is currently selected.

          lcdLine(">", menui+2, false);

          while(1) {
            while(1) {
              key = kp.getKey();
              if(key) {
                break;
              }
            }
            
            if(key == 'a') { // If A (select) is pressed, select the current option.
              if (menui == 2) { // If back is selected, exit the menu loop.
                exitMenu = true;
                break;
              }
              if (menui == 1) { // If more is selected, show a new menu.
                menui = 0;
                lcdLineXY(1, 0, "Backspace", true);
                lcdLineXY(1, 1, "Clear [AC]", false);
                lcdLineXY(1, 2, "Symbols", false);
                lcdLineXY(1, 3, "Edit mode", false);
                lcdLine(">", menui+1, false);

                /* to do:
                  Add a symbol submenu.
                  Include:
                    - Brackets
                    - Sqrt
                    - Cbrt
                    - Exponent
                */

                while(1) {
                  while(1) {
                    key = kp.getKey();
                    if(key) {
                      break;
                    }
                  }

                  if(key=='8') { // If 8 (down) is pressed, increase menu index.
                    lcdLine(" ", menui+1, false);
                    if(menui != 3) menui++;
                  }
                  if(key=='2') { // If 2 (up) is pressed, decrease menu index.
                    lcdLine(" ", menui+1, false);
                    if(menui != 0) menui--;
                  }

                  if(key=='a') { // Current option selected.
                    if(menui == 0) { // If selected Backspace then delete last char of expression and exit menu loop.
                      exitMenu = true;
                      expression = backspace(expression);
                      break;
                    }
                    if(menui == 1) { // If selected Clear then clear whole expression and exit menu loop.
                      exitMenu = true;
                      expression = "";
                      break;
                    }
                  }

                  lcdLine(">", menui+1, false);
                }
              }
              if(exitMenu) break;

              if (menui == 0) { // If Controls is selected, show the controls sequence.
                while(1) {
                  // limit.       "xxxxxxxxxxxxxxxxxxxx"
                  lcdLineXY(6, 0, "Welcome!", true);
                  lcdLineXY(0, 1, "If you're a new user", false);
                  lcdLineXY(0, 2, "this guide is yours.", false);
                  lcdLineXY(0, 3, "Press any button...", false);
                  while(1) {key=kp.getKey(); if(key){break;}}

                  lcdLineXY(0, 0, "If you want to exit", true);
                  lcdLineXY(0, 1, "this guide anytime,", false);
                  lcdLineXY(0, 2, "simply press B.", false);
                  lcdLineXY(0, 3, "Otherwise press any!", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  lcdLineXY(0, 0, "First things first..", true);
                  lcdLineXY(0, 1, "How do you type?", false);
                  lcdLineXY(0, 2, "Just press numbers,", false);
                  lcdLineXY(0, 3, "watch them appear!", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  lcdLineXY(0, 0, "During calc mode:", true);
                  lcdLineXY(0, 1, "A: Add     B: Minus", false);
                  lcdLineXY(0, 2, "C: Times   D: Divide", false);
                  lcdLineXY(0, 3, "#: Calculate", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  lcdLineXY(0, 0, "If you press any", true);
                  lcdLineXY(0, 1, "button after calcul-", false);
                  lcdLineXY(0, 2, "ating the expression", false);
                  //lcdLineXY(0, 3, "", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  lcdLineXY(0, 0, "You can edit the", true);
                  lcdLineXY(0, 1, "expression. But if", false);
                  lcdLineXY(0, 2, "you press # again,", false);
                  lcdLineXY(0, 3, "it'll clear it all.", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  lcdLineXY(0, 0, "During menus:", true);
                  lcdLineXY(0, 1, "2: Up     8: Down", false);
                  lcdLineXY(0, 2, "4: Left   6: Right", false);
                  lcdLineXY(0, 3, "A: Select B: Back", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  lcdLineXY(0, 0, "Having trouble with", true);
                  lcdLineXY(0, 1, "Up Down Left Right?", false);
                  lcdLineXY(0, 2, "Think of it like a", false);
                  lcdLineXY(0, 3, "WASD keypad!", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;
                  
                  lcdLineXY(0, 0, "Edit mode allows you", true);
                  lcdLineXY(0, 1, "to edit your current", false);
                  lcdLineXY(0, 2, "expression in case", false);
                  lcdLineXY(0, 3, "you made a mistake.", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;
                  // limit.       "xxxxxxxxxxxxxxxxxxxx"
                  lcdLineXY(0, 0, "A & B to move cursor", true);
                  lcdLineXY(0, 1, "C to backspace", false);
                  lcdLineXY(0, 2, "D to clear all", false);
                  lcdLineXY(0, 3, "# to quit edit mode.", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  lcdLineXY(0, 0, "You can always press", true);
                  lcdLineXY(0, 1, "the * key at almost", false);
                  lcdLineXY(0, 2, "any time to view", false);
                  lcdLineXY(0, 3, "corresponding guides", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  //lcdLineXY(0, 0, "", true);
                  lcdLineXY(1, 1, "Calc mode keypad", true);
                  lcdLineXY(0, 2, "Press any button....", false);
                  //lcdLineXY(0, 3, "corresponding guides", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  lcdLineXY(3, 0, "1|2|3|+", true);
                  lcdLineXY(3, 1, "4|5|6|-", true);
                  lcdLineXY(3, 2, "7|8|9|*", false);
                  lcdLineXY(3, 3, "H|0|=|/", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  //lcdLineXY(0, 0, "", true);
                  lcdLineXY(5, 1, "Menu keypad", true);
                  lcdLineXY(0, 2, "Press any button....", false);
                  //lcdLineXY(0, 3, "corresponding guides", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  lcdLineXY(3, 0, " |U| |OK", true);
                  lcdLineXY(3, 1, "L| |R|BACK", true);
                  lcdLineXY(3, 2, " |D| | ", false);
                  lcdLineXY(3, 3, " | | | ", false);
                  // lcd custom char function
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  //lcdLineXY(0, 0, "", true);
                  lcdLineXY(2, 1, "Edit mode keypad", true);
                  lcdLineXY(0, 2, "Press any button....", false);
                  //lcdLineXY(0, 3, "corresponding guides", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  lcdLineXY(3, 0, " |U| | ", true);
                  lcdLineXY(3, 1, "L| |R| ", true);
                  lcdLineXY(3, 2, " |D| | ", false);
                  lcdLineXY(2, 3, "OK| | | ", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  //lcdLineXY(0, 0, "", true);
                  lcdLineXY(0, 1, "That's basically it!", true);
                  lcdLineXY(5, 2, "have fun :)", false);
                  //lcdLineXY(0, 3, "", false);
                  while(1) {key=kp.getKey(); if(key){break;}}
                  if(key == 'b') break;

                  // limit.       "xxxxxxxxxxxxxxxxxxxx"
                  break;
                }
                redrawHelpMenu = true;
              }
            }

            if(key == '8') { // If 8 (down) is pressed, increase menu index.
              lcdLine(" ", menui+2, false);
              if(menui != 2) menui++;
            }
            if(key == '2') { // If 2 (up) is pressed, decrease menu index.
              lcdLine(" ", menui+2, false);
              if(menui != 0) menui--;
            }
            
            lcdLine(">", menui+2, false);
            if(exitMenu || redrawHelpMenu) break;
          }
          if(exitMenu) break;
        }
      }
    }
  }
}