package main

import (
	"strconv"
	"strings"
)

type Day3Mul struct {
	size int
	number1 int
	number2 int
}

func Day3ParseMulInstruction(text string) *Day3Mul {
	max_length := 0
	max_length += 4 // mul(
	max_length += 3 // 999
	max_length += 1 // ,
	max_length += 3 // 999
	max_length += 1 // )

	if len(text) < 4 {
		return nil
	}

	if len(text) > max_length {
		text = text[:max_length]
	}

	if text[0:4] != "mul(" {
		return nil
	}

	comma_index := strings.IndexRune(text, ',')
	if (comma_index == -1) {
		return nil
	}

	closing_index := strings.IndexRune(text, ')')
	if (closing_index == -1) {
		return nil
	}

	number1_text := text[4:comma_index]
	number2_text := text[(comma_index+1):closing_index]

	number1, err := strconv.ParseUint(number1_text, 10, 0)
	if err != nil {
		return nil
	}
	if number1 > 999 {
		return nil
	}

	number2, err := strconv.ParseUint(number2_text, 10, 0)
	if err != nil {
		return nil
	}
	if number2 > 999 {
		return nil
	}

	inst := Day3Mul{
		size: closing_index + 1,
		number1: int(number1),
		number2: int(number2),
	}

	return &inst
}

func Day3Part1(lines []string) error {
	answer := 0

	for _, line := range lines {
		cursor := 0
		for cursor < len(line) {
			inst := Day3ParseMulInstruction(line[cursor:])
			if inst != nil {
				cursor += inst.size
				answer += inst.number1 * inst.number2
			} else {
				cursor += 1
			}
		}
	}


	println(answer)

	return nil
}

func Day3StartsWith(haystack string, needle string) bool {
	if len(haystack) < len(needle) {
		return false
	}

	return haystack[:len(needle)] == needle
}

func Day3Part2(lines []string) error {
	answer := 0

	do_inst := "do()"
	dont_inst := "don't()"

	enabled := true
	for _, line := range lines {
		cursor := 0
		for cursor < len(line) {
			rest := line[cursor:]
			if Day3StartsWith(rest, do_inst) {
				enabled = true
				cursor += len(do_inst)
				continue
			}

			if Day3StartsWith(rest, dont_inst) {
				enabled = false
				cursor += len(dont_inst)
				continue
			}

			if enabled {
				inst := Day3ParseMulInstruction(rest)
				if inst != nil {
					cursor += inst.size
					answer += inst.number1 * inst.number2
					continue
				}
			}

			cursor += 1
		}
	}


	println(answer)

	return nil
}