import type { Theme } from "@earendil-works/pi-coding-agent";

interface ResolvedColor {
	css: string;
	rgb?: readonly [number, number, number];
}

export interface LanVoiceWebTheme {
	colorScheme: "dark" | "light" | "light dark";
	pageColor: string;
	variables: string;
}

export function resolveLanVoiceWebTheme(theme: Theme): LanVoiceWebTheme {
	const colors = {
		accent: resolveAnsiColor(theme.getFgAnsi("accent"), "CanvasText"),
		border: resolveAnsiColor(theme.getFgAnsi("border"), "CanvasText"),
		borderMuted: resolveAnsiColor(theme.getFgAnsi("borderMuted"), "GrayText"),
		dim: resolveAnsiColor(theme.getFgAnsi("dim"), "GrayText"),
		error: resolveAnsiColor(theme.getFgAnsi("error"), "CanvasText"),
		muted: resolveAnsiColor(theme.getFgAnsi("muted"), "GrayText"),
		success: resolveAnsiColor(theme.getFgAnsi("success"), "CanvasText"),
		text: resolveAnsiColor(theme.getFgAnsi("text"), "CanvasText"),
		warning: resolveAnsiColor(theme.getFgAnsi("warning"), "CanvasText"),
		customMessageBg: resolveAnsiColor(theme.getBgAnsi("customMessageBg"), "Canvas"),
		selectedBg: resolveAnsiColor(theme.getBgAnsi("selectedBg"), "Canvas"),
		toolErrorBg: resolveAnsiColor(theme.getBgAnsi("toolErrorBg"), "Canvas"),
		toolPendingBg: resolveAnsiColor(theme.getBgAnsi("toolPendingBg"), "Canvas"),
		toolSuccessBg: resolveAnsiColor(theme.getBgAnsi("toolSuccessBg"), "Canvas"),
		userMessageBg: resolveAnsiColor(theme.getBgAnsi("userMessageBg"), "Canvas"),
	};
	const page = colors.userMessageBg;
	return {
		colorScheme: page.rgb ? (relativeLuminance(page.rgb) > 0.5 ? "light" : "dark") : "light dark",
		pageColor: page.css,
		variables: Object.entries(colors)
			.map(([name, color]) => `--pi-${toKebabCase(name)}:${color.css}`)
			.join(";"),
	};
}

function resolveAnsiColor(ansi: string, resetColor: string): ResolvedColor {
	if (/\x1b\[(?:39|49)m/u.test(ansi)) return { css: resetColor };
	const trueColor = /\x1b\[(?:38|48);2;(\d+);(\d+);(\d+)m/u.exec(ansi);
	if (trueColor) return rgbColor(Number(trueColor[1]), Number(trueColor[2]), Number(trueColor[3]));
	const indexed = /\x1b\[(?:38|48);5;(\d+)m/u.exec(ansi);
	if (indexed) return rgbColor(...ansi256ToRgb(Number(indexed[1])));
	throw new Error("Pi theme returned an unsupported color sequence");
}

function ansi256ToRgb(index: number): [number, number, number] {
	if (!Number.isInteger(index) || index < 0 || index > 255) throw new Error("Pi theme returned an invalid indexed color");
	if (index < 16) {
		return [
			[0, 0, 0], [128, 0, 0], [0, 128, 0], [128, 128, 0],
			[0, 0, 128], [128, 0, 128], [0, 128, 128], [192, 192, 192],
			[128, 128, 128], [255, 0, 0], [0, 255, 0], [255, 255, 0],
			[0, 0, 255], [255, 0, 255], [0, 255, 255], [255, 255, 255],
		][index] as [number, number, number];
	}
	if (index < 232) {
		const value = index - 16;
		const channel = (part: number) => part === 0 ? 0 : 55 + part * 40;
		return [channel(Math.floor(value / 36)), channel(Math.floor((value % 36) / 6)), channel(value % 6)];
	}
	const gray = 8 + (index - 232) * 10;
	return [gray, gray, gray];
}

function rgbColor(red: number, green: number, blue: number): ResolvedColor {
	if (![red, green, blue].every((channel) => Number.isInteger(channel) && channel >= 0 && channel <= 255)) {
		throw new Error("Pi theme returned an invalid RGB color");
	}
	return { css: `rgb(${red} ${green} ${blue})`, rgb: [red, green, blue] };
}

function relativeLuminance([red, green, blue]: readonly [number, number, number]): number {
	const linear = (channel: number) => {
		const value = channel / 255;
		return value <= 0.04045 ? value / 12.92 : ((value + 0.055) / 1.055) ** 2.4;
	};
	return 0.2126 * linear(red) + 0.7152 * linear(green) + 0.0722 * linear(blue);
}

function toKebabCase(value: string): string {
	return value.replace(/[A-Z]/gu, (character) => `-${character.toLowerCase()}`);
}