/**
 * Intrinsic image dimensions from file headers.
 *
 * pi-tui already exports getImageDimensions(), but it is imported here through
 * a narrow wrapper so a missing/renamed export degrades to a sane default
 * instead of throwing at extension load.
 */

export interface Dimensions {
	widthPx: number;
	heightPx: number;
}

/** Used when a header cannot be parsed. 4:3 keeps the grid from going silly. */
export const DEFAULT_DIMENSIONS: Dimensions = { widthPx: 800, heightPx: 600 };

function png(buf: Buffer): Dimensions | null {
	if (buf.length < 24) return null;
	if (buf.readUInt32BE(0) !== 0x89504e47) return null;
	// IHDR is always the first chunk: width/height at fixed offsets.
	return { widthPx: buf.readUInt32BE(16), heightPx: buf.readUInt32BE(20) };
}

function gif(buf: Buffer): Dimensions | null {
	if (buf.length < 10) return null;
	if (buf.toString("ascii", 0, 3) !== "GIF") return null;
	return { widthPx: buf.readUInt16LE(6), heightPx: buf.readUInt16LE(8) };
}

function jpeg(buf: Buffer): Dimensions | null {
	if (buf.length < 4 || buf[0] !== 0xff || buf[1] !== 0xd8) return null;
	let offset = 2;
	while (offset + 9 < buf.length) {
		if (buf[offset] !== 0xff) {
			offset++; // Resync over padding bytes.
			continue;
		}
		const marker = buf[offset + 1]!;
		const length = buf.readUInt16BE(offset + 2);
		// SOF0-SOF15, excluding DHT(c4), JPG(c8) and DAC(cc) which are not frames.
		if (marker >= 0xc0 && marker <= 0xcf && marker !== 0xc4 && marker !== 0xc8 && marker !== 0xcc) {
			return { heightPx: buf.readUInt16BE(offset + 5), widthPx: buf.readUInt16BE(offset + 7) };
		}
		if (length < 2) return null; // Malformed: would loop forever.
		offset += 2 + length;
	}
	return null;
}

function webp(buf: Buffer): Dimensions | null {
	if (buf.length < 30) return null;
	if (buf.toString("ascii", 0, 4) !== "RIFF" || buf.toString("ascii", 8, 12) !== "WEBP") return null;
	const format = buf.toString("ascii", 12, 16);
	if (format === "VP8 ") {
		return { widthPx: buf.readUInt16LE(26) & 0x3fff, heightPx: buf.readUInt16LE(28) & 0x3fff };
	}
	if (format === "VP8L") {
		const bits = buf.readUInt32LE(21);
		return { widthPx: (bits & 0x3fff) + 1, heightPx: ((bits >> 14) & 0x3fff) + 1 };
	}
	if (format === "VP8X") {
		const w = buf[24]! | (buf[25]! << 8) | (buf[26]! << 16);
		const h = buf[27]! | (buf[28]! << 8) | (buf[29]! << 16);
		return { widthPx: w + 1, heightPx: h + 1 };
	}
	return null;
}

/** Best-effort intrinsic size. Never throws. */
export function imageDimensions(bytes: Buffer): Dimensions {
	const parsed = png(bytes) ?? gif(bytes) ?? jpeg(bytes) ?? webp(bytes);
	if (!parsed || parsed.widthPx <= 0 || parsed.heightPx <= 0) return DEFAULT_DIMENSIONS;
	return parsed;
}