import { toCanvas } from "./toCanvas"

let canvasSource!: HTMLCanvasElement

export async function checkImgDark(img: HTMLImageElement, each?: (img: HTMLImageElement) => void) {
    if (!canvasSource) canvasSource = document.createElement("canvas")
    let ctx = canvasSource.getContext("2d")
    if (!ctx) throw new Error("[checkImgDark] canvas.getContext;")

    const R = 2
    canvasSource.width = R
    canvasSource.height = R

    await toCanvas(img, canvasSource, { useCanvasSize: true, clear: true })
    let imageData = ctx.getImageData(0, 0, R, R)
    imageData.data

    let gVals = []
    for (let i = 0; i < 4; i++) {
        let start = i * 4
        let r = imageData.data[start]
        let g = imageData.data[start + 1]
        let b = imageData.data[start + 2]
        let a = imageData.data[start + 3]
        let gVal = r * 0.299 + g * 0.587 + b * 0.114
        // console.log("checkImgDark", { r, g, b, a, gVal })
        if (a > 0) {
            gVals.push(gVal)
        }
    }
    let agVal = gVals.reduce((a, b) => a + b, 0) / gVals.length
    let isDark = agVal < 200

    // console.log("checkImgDark", { isDark, agVal, gVals }, imageData.data)

    if (each) each(img)
    return isDark
}