package com.stedi.test

import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.text.TextUtils
import android.view.View
import android.widget.TextView

class MainActivity : AppCompatActivity() {
    private val KEY_LEFT = "KEY_LEFT"
    private val KEY_OPERATION = "KEY_OPERATION"
    private val KEY_RIGHT = "KEY_RIGHT"
    private val KEY_CALCULATED = "KEY_CALCULATED"

    private lateinit var tvOut: TextView

    private var left: String? = null
    private var operation: Operation? = null
    private var right: String? = null
    private var calculated: Boolean = false

    private val numbers = intArrayOf(R.id.btn0, R.id.btn1, R.id.btn2, R.id.btn3, R.id.btn4, R.id.btn5, R.id.btn6, R.id.btn7, R.id.btn8, R.id.btn9)

    private enum class Operation(val id: Int, val symbol: String, val calculate: (left: Double, right: Double) -> Double) {
        Dot(R.id.btnDot, ".", calculate = { _, _ -> 0.0 }),
        Plus(R.id.btnPlus, "+", calculate = { left, right -> left + right }),
        Minus(R.id.btnMinus, "-", calculate = { left, right -> left - right }),
        Multi(R.id.btnMulti, "*", calculate = { left, right -> left * right }),
        Divide(R.id.btnDivide, "/", calculate = { left, right -> left / right }),
        Result(R.id.btnResult, "=", calculate = { _, _ -> 0.0 })
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.main_activity)
        tvOut = findViewById(R.id.tvOut)

        if (savedInstanceState != null) {
            left = savedInstanceState.getString(KEY_LEFT, null)
            operation = savedInstanceState.getSerializable(KEY_OPERATION) as Operation?
            right = savedInstanceState.getString(KEY_RIGHT, null)
            calculated = savedInstanceState.getBoolean(KEY_CALCULATED, false)
        }

        reCalculate()
    }

    override fun onBackPressed() {
        cancelLastInput()
    }

    override fun onSaveInstanceState(outState: Bundle?) {
        super.onSaveInstanceState(outState)
        if (outState != null) {
            outState.putString(KEY_LEFT, left)
            outState.putSerializable(KEY_OPERATION, operation)
            outState.putString(KEY_RIGHT, right)
            outState.putBoolean(KEY_CALCULATED, calculated)
        }
    }

    fun number(view: View) {
        if (calculated) {
            return
        }

        val number = numbers.indexOf(view.id)
        addSymbol(number.toString())
        reCalculate()
    }

    fun operation(view: View) {
        if (calculated) {
            return
        }

        val operation = Operation.values().single { it.id == view.id }
        addOperation(operation)
        reCalculate()
    }

    private fun addOperation(newOperation: Operation) {
        if (newOperation == Operation.Dot) {
            addSymbol(newOperation.symbol)
            return
        }

        if (newOperation == Operation.Result) {
            val right = right
            if (left != null && operation != null && right != null) {
                this.right = removeLastDot(right)
                calculated = true
            }
            return
        }

        if (operation != null) {
            return
        }

        val left = left
        if (left == null) {
            return
        } else {
            this.left = removeLastDot(left)
        }

        operation = newOperation
    }

    private fun addSymbol(symbol: String) {
        if (operation == null) {
            left = addSymbolToPart(left, symbol)
        } else {
            right = addSymbolToPart(right, symbol)
        }
    }

    private fun addSymbolToPart(to: String?, symbol: String): String? {
        if (symbol == Operation.Dot.symbol && !isDotCanBeAdded(to)) {
            return to
        }
        return if (to == null) symbol else to + symbol
    }

    private fun reCalculate() {
        val left = left
        val operation = operation
        val right = right

        if (calculated && left != null && operation != null && right != null) {
            try {
                val result = operation.calculate.invoke(left.toDouble(), right.toDouble())
                tvOut.text = getFilledOutput(result.toString())
            } catch (e: Exception) {
                e.printStackTrace()
                cancelLastInput()
            }
        } else {
            tvOut.text = getFilledOutput()
        }
    }

    private fun cancelLastInput() {
        when {
            calculated -> calculated = false
            right != null -> right = null
            operation != null -> operation = null
            left != null -> left = null
        }
        reCalculate()
    }

    private fun getFilledOutput(result: String? = null): String {
        val resultS = if (result == null) "" else "= $result"
        return "${left ?: ""} ${operation?.symbol ?: ""} ${right ?: ""} $resultS"
    }

    private fun isDotCanBeAdded(to: String?): Boolean {
        return !TextUtils.isEmpty(to) && to?.contains(Operation.Dot.symbol) == false
    }

    private fun removeLastDot(to: String): String {
        if (to.endsWith(Operation.Dot.symbol)) {
            return to.replace(Operation.Dot.symbol, "")
        }
        return to
    }
}