package year25

import (
	"bufio"
	"fmt"
	"io"
	"iter"
	"log"
	"strconv"
)

func Day1Part1(r io.Reader, l *log.Logger) (any, error) {
	dial := 50
	solution := 0
	for pair := range day1GetPairs(r) {
		dial += pair.MustValue()
		dial %= 100
		if dial < 0 {
			dial = 100 + dial
		}
		if dial == 0 {
			solution += 1
		}
		l.Printf("The dial is rotated %s(%d) to point at 0 `once` \n", pair, pair.MustValue())
	}

	return solution, nil
}

func Day1Part2Slow(r io.Reader, l *log.Logger) (any, error) {
	dial := 50
	solution := 0
	for pair := range day1GetPairs(r) {
		nextDial, count := day1AdvanceSimulation(dial, pair.MustValue())
		dial = nextDial
		solution += count

		if count > 0 {
			l.Printf("The dial is rotated %s(%d) to point at %d, during this points to 0 (%d)\n", pair, pair.MustValue(), dial, count)
		} else {
			l.Printf("The dial is rotated %s(%d) to point at %d\n", pair, pair.MustValue(), dial)
		}
	}

	return solution, nil
}

func Day1Part2Fast(r io.Reader, l *log.Logger) (any, error) {
	dial := 50
	solution := 0
	for pair := range day1GetPairs(r) {
		value := pair.MustValue()

		nextDial, count := day1Advance(dial, value)

		dial = nextDial
		solution += count

		if count > 0 {
			l.Printf("The dial is rotated %s(%d) to point at %d, during this points to 0 (%d)\n", pair, pair.MustValue(), dial, count)
		} else {
			l.Printf("The dial is rotated %s(%d) to point at %d\n", pair, pair.MustValue(), dial)
		}
	}

	return solution, nil
}

func day1GetPairs(r io.Reader) iter.Seq[Day1Pair] {
	return func(yield func(Day1Pair) bool) {
		scanner := bufio.NewScanner(r)
		scanner.Split(bufio.ScanLines)
		for scanner.Scan() {
			pair := Day1Pair(scanner.Text())
			if !yield(pair) {
				return
			}
		}
		if err := scanner.Err(); err != nil {
			panic(err)
		}
	}
}

type Day1Pair string

func (p Day1Pair) Value() (int, error) {
	valueStr := string(p[1:])
	v, err := strconv.Atoi(valueStr)
	if err != nil {
		return 0, fmt.Errorf("failed to convert action value to int")
	}
	switch p[0] {
	case 'L':
		return -v, nil
	case 'R':
		return v, nil
	default:
		return 0, fmt.Errorf("unknown action value %q", p[0])
	}
}
func (p Day1Pair) MustValue() int {
	v, err := p.Value()
	if err != nil {
		panic(err)
	}
	return v
}

func day1AdvanceSimulation(dial int, value int) (int, int) {
	solution := 0
	for value < 0 {
		value += 1
		dial -= 1
		if dial == 0 {
			solution += 1
		}
		if dial == -1 {
			dial = 99
		}
	}
	for value > 0 {
		value -= 1
		dial += 1
		if dial == 100 {
			dial = 0
			solution += 1
		}
	}

	return dial, solution
}

func day1Advance(dial, step int) (next int, count int) {
	next = dial + step
	count += next / 100
	if count < 0 {
		count = -count
	}

	next = next % 100
	if dial != 0 && step < 0 && next <= 0 {
		count += 1
	}

	if next < 0 {
		next += 100
	}
	return
}