import { readFileSync } from 'fs'

let input = `.|...\\....
|.-.\\.....
.....|-...
........|.
..........
.........\\
..../.\\\\..
.-.-/..|..
.|....-|.\\
..//.|....`

function parse(input: string): string[][] {
    const lines = input.trim().split('\n')
    return Array.from({ length: lines.length }, (_, y) =>
        Array.from({ length: lines[0].length }, (_, x) => lines[y][x]),
    )
}

function isOutOfBounds({ x, y }: State, grid: string[][]): boolean {
    return x < 0 || y < 0 || y >= grid.length || x >= grid[0].length
}

type Direction = 'up' | 'down' | 'left' | 'right'

type State = {
    x: number
    y: number
    direction: Direction
    seen: Set<string>
}

function move(state: State): State {
    const { x, y, direction } = state
    switch (direction) {
        case 'up':
            return { ...state, y: y - 1 }
        case 'down':
            return { ...state, y: y + 1 }
        case 'left':
            return { ...state, x: x - 1 }
        case 'right':
            return { ...state, x: x + 1 }
    }
}

function solve(input: string) {
    const grid = parse(input)
    const state: State = {
        x: 0,
        y: 0,
        direction: 'right',
        // A path history of (x,y,direction) so we can detect when beam is stuck in cycle
        seen: new Set(),
    }
    const energized = new Set<string>()

    function step(state: State) {
        if (isOutOfBounds(state, grid)) return

        const { x, y, direction, seen } = state

        //Check for path cycle
        const key = `${x},${y},${direction}`
        if (seen.has(key)) return
        seen.add(key)

        energized.add(`${x},${y}`)

        // render(grid, energized)
        switch (grid[y][x]) {
            case '.':
                step(move(state))
                break
            case '|':
                switch (direction) {
                    case 'up':
                    case 'down':
                        step(move(state))
                        break
                    case 'left':
                    case 'right':
                        step(move({ ...state, direction: 'up' }))
                        step(move({ ...state, direction: 'down' }))
                        break
                }
                break
            case '-':
                switch (direction) {
                    case 'left':
                    case 'right':
                        step(move(state))
                        break
                    case 'up':
                    case 'down':
                        step(move({ ...state, direction: 'left' }))
                        step(move({ ...state, direction: 'right' }))
                        break
                }
                break
            case '/':
                switch (direction) {
                    case 'up':
                        step(move({ ...state, direction: 'right' }))
                        break
                    case 'down':
                        step(move({ ...state, direction: 'left' }))
                        break
                    case 'left':
                        step(move({ ...state, direction: 'down' }))
                        break
                    case 'right':
                        step(move({ ...state, direction: 'up' }))
                        break
                }
                break
            case '\\':
                switch (direction) {
                    case 'up':
                        step(move({ ...state, direction: 'left' }))
                        break
                    case 'down':
                        step(move({ ...state, direction: 'right' }))
                        break
                    case 'left':
                        step(move({ ...state, direction: 'up' }))
                        break
                    case 'right':
                        step(move({ ...state, direction: 'down' }))
                        break
                }
                break
        }
    }

    step(state)
    render(grid, energized)
    console.log(energized.size)
}

function render(grid: string[][], energized: Set<string>) {
    for (let y = 0; y < grid.length; y++) {
        let row = ''
        for (let x = 0; x < grid[0].length; x++) {
            row += energized.has(`${x},${y}`) ? '#' : grid[y][x]
        }
        console.log(row)
    }
}

input = readFileSync('day16.txt', { encoding: 'utf8' })
solve(input)