/**
 * Unicode half-block color thumbnails for terminals without Kitty/iTerm/Sixel.
 * Works on Windows Terminal + WSL (truecolor ANSI).
 */
import { PNG } from "pngjs";
import jpeg from "jpeg-js";

export interface RgbaImage {
	width: number;
	height: number;
	data: Uint8Array; // RGBA
}

function clamp(n: number, lo: number, hi: number): number {
	return Math.max(lo, Math.min(hi, n));
}

export function decodeBase64Image(
	base64: string,
	mimeType: string,
): RgbaImage | null {
	try {
		const buf = Buffer.from(base64, "base64");
		if (mimeType === "image/png" || (buf[0] === 0x89 && buf[1] === 0x50)) {
			const png = PNG.sync.read(buf);
			return { width: png.width, height: png.height, data: png.data };
		}
		if (mimeType === "image/jpeg" || (buf[0] === 0xff && buf[1] === 0xd8)) {
			const jpg = jpeg.decode(buf, { useTArray: true, formatAsRGBA: true });
			return {
				width: jpg.width,
				height: jpg.height,
				data: jpg.data as Uint8Array,
			};
		}
		// gif/webp: no pure-js lightweight decoder here
		return null;
	} catch {
		return null;
	}
}

function sample(
	img: RgbaImage,
	x: number,
	y: number,
): [number, number, number, number] {
	const sx = clamp(Math.floor(x), 0, img.width - 1);
	const sy = clamp(Math.floor(y), 0, img.height - 1);
	const i = (sy * img.width + sx) * 4;
	return [img.data[i]!, img.data[i + 1]!, img.data[i + 2]!, img.data[i + 3]!];
}

function avg2(
	a: [number, number, number, number],
	b: [number, number, number, number],
): [number, number, number] {
	// alpha-aware against dark background
	const aa = a[3] / 255;
	const ba = b[3] / 255;
	const ar = a[0] * aa;
	const ag = a[1] * aa;
	const ab = a[2] * aa;
	const br = b[0] * ba;
	const bg = b[1] * ba;
	const bb = b[2] * ba;
	return [
		Math.round((ar + br) / 2),
		Math.round((ag + bg) / 2),
		Math.round((ab + bb) / 2),
	];
}

function fg(r: number, g: number, b: number, ch: string): string {
	return `\x1b[38;2;${r};${g};${b}m${ch}\x1b[39m`;
}

function bg(r: number, g: number, b: number, ch: string): string {
	return `\x1b[48;2;${r};${g};${b}m${ch}\x1b[49m`;
}

function cell(
	top: [number, number, number],
	bottom: [number, number, number],
): string {
	// Use half block: upper color = fg, lower color = bg, char = ▀
	return `\x1b[38;2;${top[0]};${top[1]};${top[2]}m\x1b[48;2;${bottom[0]};${bottom[1]};${bottom[2]}m▀\x1b[0m`;
}

/**
 * Render image to half-block ANSI lines.
 * Each terminal row covers 2 image rows.
 */
export function renderHalfBlock(
	img: RgbaImage,
	maxCols: number,
	maxRows: number,
): string[] {
	const maxWidth = Math.max(4, Math.floor(maxCols));
	const maxHeightCells = Math.max(2, Math.floor(maxRows));
	// Each cell is 1 col wide and 2 image-pixels tall.
	const scale = Math.min(
		maxWidth / img.width,
		(maxHeightCells * 2) / img.height,
		1,
	);
	const outW = Math.max(1, Math.floor(img.width * scale));
	const outHPx = Math.max(2, Math.floor(img.height * scale));
	// even height
	const hPx = outHPx % 2 === 0 ? outHPx : outHPx + 1;
	const rows = hPx / 2;

	const lines: string[] = [];
	for (let row = 0; row < rows; row++) {
		let line = "";
		const y0 = (row * 2 * img.height) / hPx;
		const y1 = ((row * 2 + 1) * img.height) / hPx;
		for (let col = 0; col < outW; col++) {
			const x = ((col + 0.5) * img.width) / outW;
			const topPx = sample(img, x, y0 + 0.25);
			const botPx = sample(img, x, y1 + 0.25);
			// composite alpha on black
			const top: [number, number, number] = [
				Math.round((topPx[0] * topPx[3]) / 255),
				Math.round((topPx[1] * topPx[3]) / 255),
				Math.round((topPx[2] * topPx[3]) / 255),
			];
			const bot: [number, number, number] = [
				Math.round((botPx[0] * botPx[3]) / 255),
				Math.round((botPx[1] * botPx[3]) / 255),
				Math.round((botPx[2] * botPx[3]) / 255),
			];
			line += cell(top, bot);
		}
		lines.push(line);
	}
	return lines;
}

export function thumbnailLinesFromBase64(
	base64: string,
	mimeType: string,
	maxCols: number,
	maxRows: number,
): string[] | null {
	const img = decodeBase64Image(base64, mimeType);
	if (!img) return null;
	return renderHalfBlock(img, maxCols, maxRows);
}

// silence unused import helpers if tree-shaken
void fg;
void bg;
void avg2;