import { blobToArrayBuffer } from "./blobToArrayBuffer"
import { findBlockOfData } from "./findBlockOfData"
import { hexToData } from "./hexToData"
import fs from "fs"

/** 从一个 ArrayBuffer 中提取其中的 Png 数据，通常是文件缩略图 */
export function extractPng(data: ArrayBuffer | Uint8Array) {
    const PNG_START = hexToData("89504e470d0a1a0a")
    const PNG_END = hexToData("0049454e44ae426082")

    let cur = 0
    let isDone = false
    let blocks: Uint8Array[] = []
    do {
        let re = findBlockOfData(data, PNG_START, PNG_END, cur)
        if (re) {
            blocks.push(re.block)
            cur = re.offsetEnd
        } else {
            isDone = true
        }
    } while (!isDone && cur < data.byteLength)

    return blocks
}