//@ts-check
const fs = require('fs')
const jimp = require('jimp')

const screen = getScreenDimensions()
const buffer = Buffer.alloc(screen.width * screen.height * screen.byteDepth)
//TODO: implement automatic cache cleanup
/**
 * @type {{ [key: string]: import('@jimp/core').Bitmap }}
 */
const imageCache = {}

function getScreenDimensions() {
    const vsize = fs.readFileSync('/sys/class/graphics/fb0/virtual_size', { encoding: 'utf-8' }).split(',')
    const byteDepth = parseInt(fs.readFileSync('/sys/class/graphics/fb0/bits_per_pixel').toString()) / 8

    return {
        width: parseInt(vsize[0]),
        height: parseInt(vsize[1]),
        byteDepth
    }
}

/**
 * @param { Buffer } data
 */
function flip(data = buffer) {
    try {
        fs.writeFileSync('/dev/fb0', data, { encoding: 'binary' })
    } catch(e) {
        console.log("could not write to /dev/fb0")
        console.log(e)
    }
}

function clear() {
    buffer.fill(0)
}

/**
 * @param {string} filepath
 */
function removeFromCache(filepath) {
    delete imageCache[filepath]
}

/**
 * @param {string} filepath
 * @returns { Promise<import('@jimp/core').Bitmap> } BGRA buffer
 */
async function readImgFile(filepath) {
    const img = await jimp.read(filepath)
    const bitmap = img.bitmap
    bitmap.data = rgbaTObgra(bitmap.data)
    return bitmap
}

/**
 * @param { number } x
 * @param { number } y
 * @param { import('@jimp/core').Bitmap | Pencil } bitmap
 */
function drawBitmap(x, y, bitmap, handleTransparency = true) {
    for(let dy = 0; dy < bitmap.height; dy++) {
        let bitmapLineEnd = bitmap.width * screen.byteDepth * (dy + 1)
        let bitmapLineStart = bitmap.width * screen.byteDepth * dy
        let dx = x

        const offscreenRight = dx + bitmap.width - screen.width
        if(offscreenRight > 0) {
            bitmapLineEnd -= offscreenRight*4
        }

        const offscreenLeft = -dx
        if(offscreenLeft > 0) {
            bitmapLineStart += offscreenLeft*4
            dx = 0
        }

        const offscreenTop = -y
        if(offscreenTop >= dy) {
            dy = offscreenTop
            continue
        }

        const offscreenBottom = bitmap.height + y - screen.height
        if(offscreenBottom > 0 && bitmap.height - offscreenBottom <= dy) {
            break
        }

        if(bitmapLineEnd < bitmapLineStart) {
            continue
        }


        const line = bitmap.data.subarray(bitmapLineStart, bitmapLineEnd)

        const bufferPlacement =  dx * screen.byteDepth + screen.width * (dy + y) * screen.byteDepth

        if(handleTransparency) {
            const currentLine = buffer.subarray(bufferPlacement, bufferPlacement + line.length)
            for(let i=0; i < line.length; i += 4) {
                const transparency = line.readUInt8(i+3) / 255
                if(transparency < 1) {
                    /** @type { Uint8Array } */
                    const newLine = new Uint8Array(3)
                    for(let j=0; j < 3; j++) {
                        newLine[j] = (currentLine.readUInt8(j+i)*1-transparency + line.readUInt8(j+i)*transparency)
                    }
                    line.set(newLine, i)
                }
            }
        }

        buffer.set(Array.from(line), bufferPlacement)
    }
}

/**
 * @param { number } x
 * @param { number } y
 * @param { string } filepath
 * @description this function work fine but will use caching. to clear the cache you can use removeFromCache(filepath) or you can keep the cache on the
 * client side and use readImgFile and drawBitmap methods instead
 */
async function drawImgFile(x, y, filepath) {
    //not caching would imply reading the image each time we want to write it to the screen even for small movement
    let bitmap;
    if(!imageCache[filepath]) {
        bitmap = await readImgFile(filepath)
        imageCache[filepath] = bitmap
    } else {
        bitmap = imageCache[filepath]
    }
    drawBitmap(x, y, bitmap)
}

/**
 *  @param { Buffer } buff
 */
function rgbaTObgra(buff) {
    for(let i=0; i < buff.length; i += 4) {
        const r = buff.readUInt8(i)
        const b = buff.readUInt8(i+2)

        buff.set([b], i)
        buff.set([r], i+2)
    }
    return buff
}

/**
 * @param { string } color
 * @returns { number[] }
 */
function parseHexColor(color) {
    if(!color.startsWith('#') || color.length !== 7) {
        throw new Error('invalid hex color code')
    }
    const r = parseInt(color.substring(1,2), 16)
    const v = parseInt(color.substring(3,4), 16)
    const b = parseInt(color.substring(5,6), 16)
    return [b, v, r, 0]
}

/**
 *
 * @param { number } x
 * @param { number } y
 * @param { string | number[] } colorCode
 */
function setPixel(x, y, colorCode) {
    if (screen.byteDepth !== 4) {
        throw new Error('Depth not supported yet')
    }

    if(typeof colorCode === 'string') {
        colorCode = parseHexColor(colorCode)
    }
    buffer.set(colorCode, (x + y * screen.width) * screen.byteDepth)
}

module.exports = { flip, clear, getScreenDimensions, drawImgFile, readImgFile, drawBitmap, parseHexColor, setPixel, removeFromCache }