import { open } from "node:fs/promises";
const IMAGE_TYPE_SNIFF_BYTES = 4100;
const PNG_SIGNATURE = [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a];
export function detectSupportedImageMimeType(buffer) {
    if (startsWith(buffer, [0xff, 0xd8, 0xff])) {
        return buffer[3] === 0xf7 ? null : "image/jpeg";
    }
    if (startsWith(buffer, PNG_SIGNATURE)) {
        return isPng(buffer) && !isAnimatedPng(buffer) ? "image/png" : null;
    }
    if (startsWithAscii(buffer, 0, "GIF")) {
        return "image/gif";
    }
    if (startsWithAscii(buffer, 0, "RIFF") && startsWithAscii(buffer, 8, "WEBP")) {
        return "image/webp";
    }
    return null;
}
export async function detectSupportedImageMimeTypeFromFile(filePath) {
    const fileHandle = await open(filePath, "r");
    try {
        const buffer = Buffer.alloc(IMAGE_TYPE_SNIFF_BYTES);
        const { bytesRead } = await fileHandle.read(buffer, 0, IMAGE_TYPE_SNIFF_BYTES, 0);
        return detectSupportedImageMimeType(buffer.subarray(0, bytesRead));
    }
    finally {
        await fileHandle.close();
    }
}
function isPng(buffer) {
    return (buffer.length >= 16 && readUint32BE(buffer, PNG_SIGNATURE.length) === 13 && startsWithAscii(buffer, 12, "IHDR"));
}
function isAnimatedPng(buffer) {
    let offset = PNG_SIGNATURE.length;
    while (offset + 8 <= buffer.length) {
        const chunkLength = readUint32BE(buffer, offset);
        const chunkTypeOffset = offset + 4;
        if (startsWithAscii(buffer, chunkTypeOffset, "acTL"))
            return true;
        if (startsWithAscii(buffer, chunkTypeOffset, "IDAT"))
            return false;
        const nextOffset = offset + 8 + chunkLength + 4;
        if (nextOffset <= offset || nextOffset > buffer.length)
            return false;
        offset = nextOffset;
    }
    return false;
}
function readUint32BE(buffer, offset) {
    return ((buffer[offset] ?? 0) * 0x1000000 +
        ((buffer[offset + 1] ?? 0) << 16) +
        ((buffer[offset + 2] ?? 0) << 8) +
        (buffer[offset + 3] ?? 0));
}
function startsWith(buffer, bytes) {
    if (buffer.length < bytes.length)
        return false;
    return bytes.every((byte, index) => buffer[index] === byte);
}
function startsWithAscii(buffer, offset, text) {
    if (buffer.length < offset + text.length)
        return false;
    for (let index = 0; index < text.length; index++) {
        if (buffer[offset + index] !== text.charCodeAt(index))
            return false;
    }
    return true;
}
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