/*
 * Code Outline:
 *
 * calcultor()
 *
 *   Core:
 *     - init();
 *     - updateState(newState)
 *     - updateStaging(stagingValues)
 *     - operation(n1, n2, op)
 *     - numDecPress(e)
 *     - operatorPress(e)
 *
 *   Utility:
 *     - add()
 *     - subtract()
 *     - multiply()
 *     - divide()
 *     - reset()
 *     - clear()
 *     - decimalCheck();
 *     - updateDisplay();        // Updates state and Element
 *     - updateUI();             // Updates UI with state
 *     - clearStaging            // Update state and set ready:false
 *
 */

function calculator() {
  const numBtns = document.getElementsByClassName("num-btn");
  const opBtns = document.getElementsByClassName("op-btn");
  const specialBtns = document.getElementsByClassName("special-btn");
  const display = document.getElementById("display");
  const state = {
    total: 0, // number
    operand: "", // string
    currOperator: "+", // string
    display: "0", // string
  };
  const stagingValues = {
    ready: true,
    currOperator: state.currOperator,
    operand: state.operand,
  };

  // Core functions

  function init() {
    // Add Event Listeners
    Array.from(numBtns).forEach((element) =>
      element.addEventListener("click", numDecPress)
    );
    Array.from(opBtns).forEach((element) =>
      element.addEventListener("click", operatorPress)
    );
    Array.from(specialBtns).forEach((element) => {
      const value = element.textContent;
      if (value === "AC") element.addEventListener("click", reset);
      else if (value === "C") element.addEventListener("click", clear);

      //      else if(value === "C")
      //	element.addEventListener("click", clear)
    });
    updateUI();
  }

  function updateState() {
    Object.keys(stagingValues).forEach((prop) => {
      if (prop in state && stagingValues[prop] !== state[prop])
        state[prop] = stagingValues[prop];
    });
  }

  function updateStaging(newValues) {
    Object.keys(newValues).forEach((prop) => {
      if (prop in stagingValues) stagingValues[prop] = newValues[prop];
    });
  }

  function operation(n1, n2, op) {
    switch (op) {
      case "+":
        return add(n1, n2);

      case "-":
        return subtract(n1, n2);

      case "x":
        return multiply(n1, n2);

      case "/":
        if (n2 === 0) return "Goofy!";
        return divide(n1, n2);

      case "=":
        return;

      default:
        return add(n1, n2);
    }
  }

  function numDecPress(e) {
    /*
     * When a number / decimal button is pressed it will:
     * - clear the operand
     * - Move any staging values to state
     * - Update the calculator display
     *
     * */
    let startSecondOperand = false;
    const btnVal = e.target.textContent;

    // If operand is set clear it (since we are constructing a new one now)
    if (state.operand) clearOperand();

    // Push staging to state
    if (stagingValues.ready) {
      clearStaging();
      startSecondOperand = true;
    }

    // Handle decimal input
    if (btnVal === ".") {
      if (decimalCheck()) return;
      else {
        updateDisplay(state.display + ".");
        return;
      }
    }

    // Handle new operand
    if (startSecondOperand) updateDisplay(btnVal);
    else updateDisplay(state.display + btnVal);
  }

  function operatorPress(e) {
    /*
     * When an operator button is pressed it will:
     * - Check staging -> If NOT "ready" perform the operation
     * - Update state immediately with new results
     * - Send pressed OP to staging for the next operation
     * ??????
     * - Update state, the stored value for the next operation
     * */

    const pressedOp = e.target.textContent;
    const currOperand = state.operand ? state.operand : state.display;

    // Perform operation if nothing in staging
    // Perform operation if it's a repeat operation
    if (!stagingValues.ready || (stagingValues.ready && pressedOp === "=")) {
      const result = operation(
        Number(state.total),
        Number(currOperand),
        state.currOperator
      );

      const nDecimals = String(result).split(".")[1]
        ? String(result).split(".")[1].length
        : 0;
      if (/\./.test(String(result)) && nDecimals > 6) {
        // Check if value is too large for screen > 6 digits
        const val = Math.round(result * Math.pow(10, 6)) / Math.pow(10, 6);
        console.log(val);
        updateDisplay(val);
        updateTotal(val);
      } else {
        updateDisplay(result);
        updateTotal(result);
      }
      updateOperand(currOperand);
    }

    // prepare for the next operation
    if (pressedOp === "=") {
      updateStaging({
        ready: true,
      });
    } else {
      updateStaging({
        currOperator: pressedOp,
        ready: true,
      });
    }
  }

  // Utility functions
  function add(n1, n2) {
    return n1 + n2;
  }
  function subtract(n1, n2) {
    return n1 - n2;
  }
  function multiply(n1, n2) {
    return n1 * n2;
  }
  function divide(n1, n2) {
    return n1 / n2;
  }
  function reset() {
    updateStaging({
      ready: true,
      currOperator: "+", // string
      operand: "", // string
    });
    updateState();

    updateDisplay("0");
    state.total = 0;
  }
  function decimalCheck() {
    const regx = new RegExp(state.display);
    return regx.test(".");
  }

  function updateDisplay(value) {
    /*
     * Update ONLY the State's display for UI Updates
     * - Send new value to staging and immediately update state
     * - Refresh the UI with the new values
     * */
    state.display = value;
    updateUI();
  }

  function updateTotal(value) {
    state.total = value;
  }

  function updateOperand(value) {
    state.operand = value;
  }

  function updateUI() {
    display.textContent = state.display;
  }

  function clearStaging() {
    updateState();
    updateStaging({ ready: false });
  }

  function clearOperand() {
    state.operand = "";
  }

  init(); // Initialize calculator
}

calculator();