const fs = require("fs");

function readByBuffer(buffer) {
	if (!Buffer.isBuffer(buffer) || buffer.length < 4) {
		return { contentType: "application/octet-stream", extension: "" };
	}
	buffer = buffer.slice(0, 16);

	// ---------- IMAGES ----------

	// PNG
	if (
		buffer.length >= 8 &&
		buffer[0] === 0x89 &&
		buffer[1] === 0x50 &&
		buffer[2] === 0x4e &&
		buffer[3] === 0x47
	) {
		return { contentType: "image/png", extension: "png" };
	}

	// JPEG
	if (buffer[0] === 0xff && buffer[1] === 0xd8) {
		return { contentType: "image/jpeg", extension: "jpg" };
	}

	// GIF
	if (buffer[0] === 0x47 && buffer[1] === 0x49 && buffer[2] === 0x46) {
		return { contentType: "image/gif", extension: "gif" };
	}

	// WEBP
	if (
		buffer.length >= 12 &&
		buffer[0] === 0x52 && // R
		buffer[1] === 0x49 && // I
		buffer[2] === 0x46 && // F
		buffer[3] === 0x46 && // F
		buffer[8] === 0x57 && // W
		buffer[9] === 0x45 && // E
		buffer[10] === 0x42 && // B
		buffer[11] === 0x50 // P
	) {
		return { contentType: "image/webp", extension: "webp" };
	}

	// ---------- VIDEO / AUDIO ----------

	// MP4 / M4V / MOV (ISO BMFF)
	if (buffer.length >= 12 && buffer.slice(4, 8).toString() === "ftyp") {
		const brand = buffer.slice(8, 12).toString();

		if (["isom", "mp41", "mp42"].includes(brand)) {
			return { contentType: "video/mp4", extension: "mp4" };
		}

		if (["M4V ", "M4VH"].includes(brand)) {
			return { contentType: "video/x-m4v", extension: "m4v" };
		}

		if (brand === "qt  ") {
			return { contentType: "video/quicktime", extension: "mov" };
		}
	}

	// MP3
	if (
		buffer.slice(0, 3).toString() === "ID3" ||
		(buffer[0] === 0xff && (buffer[1] & 0xe0) === 0xe0)
	) {
		return { contentType: "audio/mpeg", extension: "mp3" };
	}

	// WAV
	if (
		buffer.slice(0, 4).toString() === "RIFF" &&
		buffer.slice(8, 12).toString() === "WAVE"
	) {
		return { contentType: "audio/wav", extension: "wav" };
	}

	// OGG
	if (buffer.slice(0, 4).toString() === "OggS") {
		return { contentType: "audio/ogg", extension: "ogg" };
	}

	// ---------- DOCUMENTS ----------

	// PDF
	if (buffer.slice(0, 4).toString() === "%PDF") {
		return { contentType: "application/pdf", extension: "pdf" };
	}

	// ZIP (docx, xlsx, apk, etc.)
	if (buffer[0] === 0x50 && buffer[1] === 0x4b) {
		return { contentType: "application/zip", extension: "zip" };
	}

	// ---------- TEXT ----------

	// UTF-8 text (heuristic)
	const text = buffer.toString("utf8");
	if (/^[\x09\x0A\x0D\x20-\x7E]*$/.test(text)) {
		return { contentType: "text/plain", extension: "txt" };
	}

	// ---------- FALLBACK ----------
	return {
		contentType: "application/octet-stream",
		extension: "",
	};
}

function readByPath(pathToFile) {
	const size = 16;
	const fd = fs.openSync(pathToFile, "r");
	try {
		const buffer = Buffer.alloc(size);
		fs.readSync(fd, buffer, 0, size, 0);
		return readByBuffer(buffer);
	} catch (err) {
		console.error(err);
	} finally {
		fs.closeSync(fd);
	}
}

module.exports = { byPath: readByPath, byBuffer: readByBuffer };