package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

func main() {
	fmt.Println("ALU")
	if len(os.Args) < 2 {
		fmt.Println("Must pass filename as argument")
		os.Exit(1)
	}
	test(os.Args[1])
	//part1(os.Args[1])
}

func test(fn string) {
	fmt.Println("# Test")
	num := "15"
	alu := NewALU()
	alu.ReadProgram(fn)
	var done bool
	for !done {
		fmt.Println("Converting", num)
		alu.BufferInput(strings.Split(num, ""))
		alu.run()
		if num == "0" {
			done = true
		}
		num = decNum(num, len(num)-1)
	}
}

func decNum(num string, idx int) string {
	if idx < 0 {
		return num
	}
	if len(num) < idx {
		return num
	}
	if num[idx] == '0' && idx > 0 {
		num = num[:idx] + "9" + num[idx+1:]
		return decNum(num, idx-1)
	}
	num = num[:idx] + string(num[idx]-1) + num[idx+1:]
	return num
}

func part1(fn string) {
	fmt.Println("# Part 1")
	var done bool
	num := "99999999999999"
	alu := NewALU()
	alu.ReadProgram(fn)
	for !done {
		fmt.Println("Checking Model No.", num)
		alu.BufferInput(strings.Split(num, ""))
		alu.run()
		if alu.registers["z"] == 0 {
			fmt.Println("-> It's good.")
			done = true
		}
		num = decModelNum(num, len(num)-1)
	}
}

func decModelNum(num string, idx int) string {
	if len(num) < idx {
		return num
	}
	if num[idx] == '1' {
		num = num[:idx] + "9" + num[idx+1:]
		return decModelNum(num, idx-1)
	}
	num = num[:idx] + string(num[idx]-1) + num[idx+1:]
	return num
}

const (
	INPUT_MODE_USER = iota
	INPUT_MODE_CHAN
)

type ALU struct {
	program   []string
	registers map[string]int
	ptr       int
	inputMode int
	inputChan chan string
}

func NewALU() *ALU {
	return &ALU{
		registers: map[string]int{"w": 0, "x": 0, "y": 0, "z": 0},
		ptr:       0,
		inputChan: make(chan string, 14),
	}
}

func (alu *ALU) BufferInput(inp []string) {
	alu.inputMode = INPUT_MODE_CHAN
	for i := range inp {
		alu.inputChan <- inp[i]
	}
}

func (alu *ALU) ReadProgram(fn string) error {
	file, err := os.Open(fn)
	if err != nil {
		return err
	}
	defer file.Close()

	var lines []string
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		lines = append(lines, scanner.Text())
	}
	alu.program = lines
	return scanner.Err()
}

func (alu *ALU) printRegisters() {
	fmt.Printf("Registers:\nw: %d\nx: %d\ny: %d\nz: %d\n", alu.registers["w"], alu.registers["x"], alu.registers["y"], alu.registers["z"])
}

func (alu *ALU) run() {
	for alu.ptr = 0; alu.ptr < len(alu.program); alu.ptr++ {
		pts := strings.Split(alu.program[alu.ptr], " ")
		switch pts[0] {
		case "inp":
			alu.registers[pts[1]] = alu.inp()
		case "add":
			alu.registers[pts[1]] = alu.add(alu.value(pts[1]), alu.value(pts[2]))
		case "mul":
			alu.registers[pts[1]] = alu.mul(alu.value(pts[1]), alu.value(pts[2]))
		case "div":
			alu.registers[pts[1]] = alu.div(alu.value(pts[1]), alu.value(pts[2]))
		case "mod":
			alu.registers[pts[1]] = alu.mod(alu.value(pts[1]), alu.value(pts[2]))
		case "eql":
			alu.registers[pts[1]] = alu.eql(alu.value(pts[1]), alu.value(pts[2]))
		}
	}
}

func (alu *ALU) inp() int {
	if alu.inputMode == INPUT_MODE_USER {
		var inp string
		var err error
		var v int
		for inp == "" || err != nil {
			fmt.Println("Input value:")
			reader := bufio.NewReader(os.Stdin)
			inp, _ = reader.ReadString('\n')
			inp = strings.TrimSpace(inp)
			v, err = strconv.Atoi(inp)
			if err != nil {
				fmt.Println("Must be an integer.")
			}
		}
		return v
	} else if alu.inputMode == INPUT_MODE_CHAN {
		v, err := strconv.Atoi(<-alu.inputChan)
		if err == nil {
			return v
		}
	}
	return 0
}

func (alu *ALU) value(a string) int {
	switch a {
	case "w", "x", "y", "z":
		return alu.registers[a]
	default:
		return h.Atoi(a)
	}
}

func (alu *ALU) add(a, b int) int {
	return a + b
}

func (alu *ALU) mul(a, b int) int {
	return a * b
}

func (alu *ALU) div(a, b int) int {
	if b == 0 {
		return 0
	}
	aD, bD := float64(a), float64(b)
	d := aD / bD
	if d > 0 {
		return int(math.Floor(d))
	}
	return int(math.Ceil(d))
}

func (alu *ALU) mod(a, b int) int {
	if a < 0 || b <= 0 {
		return 0
	}
	return a % b
}

func (alu *ALU) eql(a, b int) int {
	if a == b {
		return 1
	}
	return 0
}