package day14

import (
	"bufio"
	"errors"
	"fmt"
	"os"
	"strconv"
	"strings"
)

type Point struct {
	x int
	y int
}

func parsePoint(v string) (result Point, err error) {
	var parts []string = strings.Split(v, ",")
	if len(parts) != 2 {
		err = errors.New("Weird number of parts in point")
		return
	}

	x, xerr := strconv.Atoi(parts[0])
	if xerr != nil {
		err = xerr
		return
	}

	y, yerr := strconv.Atoi(parts[1])
	if yerr != nil {
		err = yerr
		return
	}

	result = Point{x, y}
	return
}

type Segment struct {
	start Point
	end   Point
}

func parseSegments(line string) (result []Segment, err error) {
	parts := strings.Split(line, " -> ")
	result = []Segment{}
	var left *Point = nil

	for _, rightString := range parts {
		right, rerr := parsePoint(rightString)
		if rerr != nil {
			err = rerr
			return
		}
		if left != nil {
			result = append(result, Segment{*left, right})
		}
		left = &right
	}

	return
}

func segmentPoints(segments []Segment) []Point {
	retval := []Point{}

	for _, segment := range segments {
		retval = append(retval, segment.start, segment.end)
	}

	return retval
}

func findExtents(segments []Segment) (leftmost int, rightmost int, bottom int) {
	leftmost = int(^uint(0) >> 1)
	rightmost = 0
	bottom = 0

	for _, point := range segmentPoints(segments) {
		if point.x < leftmost {
			leftmost = point.x
		}
		if point.x > rightmost {
			rightmost = point.x
		}
		if point.y > bottom {
			bottom = point.y
		}
	}

	return
}

type Cell int

const (
	Air Cell = iota
	Stone
	Sand
	Start
)

func drawGraph(graph [][]Cell) {
	for _, line := range graph {
		for _, v := range line {
			switch v {
			case Air:
				fmt.Printf(".")
			case Stone:
				fmt.Printf("#")
			case Sand:
				fmt.Printf("O")
			case Start:
				fmt.Printf("+")
			default:
				fmt.Printf("?")
			}
		}
		fmt.Println()
	}
	fmt.Println()
}

type State int

const (
	Good State = iota
	Stop
	Done
)

func nextStep(curX int, curY int, graph [][]Cell) (nextX int, nextY int, state State) {
	if curY+1 >= len(graph) {
		state = Done
		return
	}

	if graph[curY+1][curX] == Air {
		nextX = curX
		nextY = curY + 1
		state = Good
		return
	}

	if curX == 0 {
		state = Done
		return
	}

	if graph[curY+1][curX-1] == Air {
		nextX = curX - 1
		nextY = curY + 1
		state = Good
		return
	}

	if curX+1 >= len(graph[0]) {
		state = Done
		return
	}

	if graph[curY+1][curX+1] == Air {
		nextX = curX + 1
		nextY = curY + 1
		state = Good
		return
	}

	state = Stop
	return
}

func dropGrain(startX int, graph [][]Cell) bool {
	curX := startX
	curY := 0

	for true {
		nextX, nextY, result := nextStep(curX, curY, graph)
		switch result {
		case Done:
			return true
		case Stop:
			result := graph[curY][curX] == Start
			graph[curY][curX] = Sand
			return result
		case Good:
			curX = nextX
			curY = nextY
		}
	}

	return true
}

func Run(filename string) {
	file, err := os.Open(filename)

	if err != nil {
		fmt.Println("Error opening file:", err)
		return
	}

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanLines)
	segments := []Segment{}

	for scanner.Scan() {
		line := scanner.Text()
		newSegments, err := parseSegments(line)

		if err != nil {
			fmt.Println("PANIC", err)
			return
		}

		for _, segment := range newSegments {
			segments = append(segments, segment)
		}
	}

	file.Close()

	fmt.Println(segments)
	leftmostX, rightmostX, bottomY := findExtents(segments)
	fmt.Println("Leftmost X value is", leftmostX)
	fmt.Println("Rightmost X value is", rightmostX)
	fmt.Println("Bottom Y value is", bottomY)
	leftmostX = 0
	rightmostX += 500
	width := rightmostX - leftmostX
	graph := [][]Cell{}
	for y := 0; y <= bottomY+2; y++ {
		line := []Cell{}

		for x := 0; x <= width; x++ {
			line = append(line, Air)
		}
		graph = append(graph, line)
	}
	segments = append(segments, Segment{Point{leftmostX, bottomY + 2}, Point{rightmostX, bottomY + 2}})
	for _, segment := range segments {
		if segment.start.x == segment.end.x {
			var top int
			var bottom int

			if segment.start.y < segment.end.y {
				top = segment.start.y
				bottom = segment.end.y
			} else {
				top = segment.end.y
				bottom = segment.start.y
			}

			for current := top; current <= bottom; current++ {
				graph[current][segment.start.x-leftmostX] = Stone
			}

			continue
		}

		if segment.start.y == segment.end.y {
			var left int
			var right int

			if segment.start.x < segment.end.x {
				left = segment.start.x
				right = segment.end.x
			} else {
				left = segment.end.x
				right = segment.start.x
			}

			for current := left; current <= right; current++ {
				graph[segment.start.y][current-leftmostX] = Stone
			}

			continue
		}

		fmt.Println("PANIC: Diagonal line!?")
		return
	}
	graph[0][500-leftmostX] = Start
	drawGraph(graph)
	count := 0
	for !dropGrain(500-leftmostX, graph) {
		count += 1
	}
	drawGraph(graph)
	fmt.Println("Dropped", count, "grains of sand")
	if graph[0][500-leftmostX] != Sand {
		fmt.Println("PANIC: NOT WIDE ENOUGH")
	}
}