/**
 * The desktop the worker drives: windows, screen capture, OCR and input.
 * On Windows this is a long-running PowerShell helper (desktop.ps1) in the
 * signed-in session; tests use a fake with the same interface.
 */
import { existsSync } from 'node:fs';
import { mkdir, readFile, writeFile } from 'node:fs/promises';
import { dirname } from 'node:path';
import type { Subprocess } from 'bun';
import helperScript from './desktop.ps1' with { type: 'text' };

export interface WindowInfo {
	hwnd: number;
	pid: number;
	title: string;
	className: string;
	exe: string | null;
	visible: boolean;
	minimized: boolean;
	x: number;
	y: number;
	width: number;
	height: number;
	/** The client area (no title bar or borders) in screen coordinates. */
	clientX: number;
	clientY: number;
	clientWidth: number;
	clientHeight: number;
}

export interface SessionInfo {
	sessionId: number;
	consoleSessionId: number;
	/** "Default" when unlocked; "Winlogon" or null when locked or on a secure screen. */
	inputDesktop: string | null;
	screenWidth: number;
	screenHeight: number;
	idleMs: number;
}

export interface OcrLine {
	text: string;
	x: number;
	y: number;
	width: number;
	height: number;
}

export interface CaptureOptions {
	x: number;
	y: number;
	width: number;
	height: number;
	path: string;
	format?: 'png' | 'jpeg';
	maxWidth?: number;
	scale?: number;
	invert?: boolean;
	quality?: number;
}

export interface Desktop {
	session(): Promise<SessionInfo>;
	/** Top-level windows of processes whose executable is under a folder. */
	windows(under: string): Promise<WindowInfo[]>;
	window(hwnd: number): Promise<WindowInfo | null>;
	processes(under: string): Promise<{ pid: number; path: string }[]>;
	kill(pids: number[]): Promise<number>;
	/** Posts WM_CLOSE to a process's windows. */
	close(pid: number): Promise<number>;
	focus(hwnd: number): Promise<boolean>;
	move(hwnd: number, x: number, y: number): Promise<boolean>;
	setTitle(hwnd: number, title: string): Promise<boolean>;
	capture(options: CaptureOptions): Promise<{ width: number; height: number }>;
	ocr(path: string): Promise<OcrLine[]>;
	ocrReady(): Promise<{ language: string; maxDimension: number }>;
	click(x: number, y: number, right?: boolean): Promise<boolean>;
	type(text: string): Promise<number>;
	key(vk: number): Promise<void>;
	/** Keeps the PC from sleeping and the display on while the helper runs. */
	stayAwake(on: boolean): Promise<boolean>;
	stop(): void;
}

interface Pending {
	resolve(value: unknown): void;
	reject(err: Error): void;
	timer: ReturnType<typeof setTimeout>;
}

export class WindowsDesktop implements Desktop {
	private process: Subprocess<'pipe', 'pipe', 'pipe'> | null = null;
	private pending = new Map<number, Pending>();
	private nextId = 1;
	private ready: Promise<void> | null = null;
	private lastError = '';

	constructor(
		private scriptPath: string,
		private log: (...parts: unknown[]) => void = () => {}
	) {}

	/**
	 * Writes the helper next to the program when it differs from this build's copy,
	 * with a byte order mark: Windows PowerShell reads a script without one as ANSI.
	 */
	static async writeScript(path: string) {
		const content = `\uFEFF${helperScript.replace(/^\uFEFF/, '')}`;
		const current = existsSync(path) ? await readFile(path, 'utf8') : null;
		if (current === content) return;
		await mkdir(dirname(path), { recursive: true });
		await writeFile(path, content);
	}

	private start(): Promise<void> {
		if (this.ready) return this.ready;
		this.ready = (async () => {
			await WindowsDesktop.writeScript(this.scriptPath);
			const process = Bun.spawn(
				[
					'powershell.exe',
					'-NoProfile',
					'-NonInteractive',
					'-ExecutionPolicy',
					'Bypass',
					'-File',
					this.scriptPath
				],
				{ stdin: 'pipe', stdout: 'pipe', stderr: 'pipe', windowsHide: true }
			);
			this.process = process;
			let resolveReady!: () => void;
			let rejectReady!: (err: Error) => void;
			const ready = new Promise<void>((resolve, reject) => {
				resolveReady = resolve;
				rejectReady = reject;
			});
			this.pending.set(0, {
				resolve: () => resolveReady(),
				reject: rejectReady,
				timer: setTimeout(() => rejectReady(new Error('The desktop helper did not start')), 60_000)
			});
			void this.readLines(process);
			void (async () => {
				for await (const chunk of process.stderr)
					this.lastError = new TextDecoder().decode(chunk).trim().slice(-500) || this.lastError;
			})();
			void process.exited.then((code) => {
				if (this.process !== process) return;
				this.process = null;
				this.ready = null;
				const error = new Error(
					`The desktop helper exited (${code})${this.lastError ? `: ${this.lastError}` : ''}`
				);
				for (const waiter of this.pending.values()) {
					clearTimeout(waiter.timer);
					waiter.reject(error);
				}
				this.pending.clear();
			});
			await ready;
		})();
		this.ready.catch(() => {
			this.ready = null;
			this.process?.kill();
			this.process = null;
		});
		return this.ready;
	}

	private async readLines(process: Subprocess<'pipe', 'pipe', 'pipe'>) {
		let buffer = '';
		const decoder = new TextDecoder();
		for await (const chunk of process.stdout) {
			buffer += decoder.decode(chunk, { stream: true });
			let newline: number;
			while ((newline = buffer.indexOf('\n')) >= 0) {
				const line = buffer.slice(0, newline).trim();
				buffer = buffer.slice(newline + 1);
				if (!line) continue;
				let message: { id: number; ok: boolean; result?: unknown; error?: string };
				try {
					message = JSON.parse(line.replace(/^\uFEFF/, ''));
				} catch {
					this.log('desktop helper:', line.slice(0, 200));
					continue;
				}
				const waiter = this.pending.get(message.id);
				if (!waiter) continue;
				this.pending.delete(message.id);
				clearTimeout(waiter.timer);
				if (message.ok) waiter.resolve(message.result ?? null);
				else waiter.reject(new Error(message.error ?? 'desktop helper error'));
			}
		}
	}

	async call<T>(cmd: string, args: Record<string, unknown> = {}, timeoutMs = 20_000): Promise<T> {
		await this.start();
		const process = this.process;
		if (!process) throw new Error('The desktop helper is not running');
		const id = this.nextId++;
		return new Promise<T>((resolve, reject) => {
			const timer = setTimeout(() => {
				this.pending.delete(id);
				// A stuck helper is restarted on the next call.
				this.process = null;
				this.ready = null;
				process.kill();
				reject(new Error(`The desktop helper did not answer ${cmd} in time`));
			}, timeoutMs);
			this.pending.set(id, { resolve: resolve as (value: unknown) => void, reject, timer });
			process.stdin.write(`${JSON.stringify({ id, cmd, ...args })}\n`);
			void process.stdin.flush();
		});
	}

	session() {
		return this.call<SessionInfo>('session');
	}
	windows(under: string) {
		return this.call<WindowInfo[]>('windows', { under });
	}
	window(hwnd: number) {
		return this.call<WindowInfo | null>('window', { hwnd });
	}
	processes(under: string) {
		return this.call<{ pid: number; path: string }[]>('processes', { under });
	}
	kill(pids: number[]) {
		return pids.length ? this.call<number>('kill', { pids }) : Promise.resolve(0);
	}
	close(pid: number) {
		return this.call<number>('close', { pid });
	}
	focus(hwnd: number) {
		return this.call<boolean>('focus', { hwnd });
	}
	move(hwnd: number, x: number, y: number) {
		return this.call<boolean>('move', { hwnd, x, y });
	}
	setTitle(hwnd: number, title: string) {
		return this.call<boolean>('title', { hwnd, title });
	}
	capture(options: CaptureOptions) {
		return this.call<{ width: number; height: number }>('capture', { ...options });
	}
	ocr(path: string) {
		return this.call<OcrLine[]>('ocr', { path }, 40_000);
	}
	ocrReady() {
		return this.call<{ language: string; maxDimension: number }>('ocrReady', {}, 40_000);
	}
	click(x: number, y: number, right = false) {
		return this.call<boolean>('click', { x, y, right });
	}
	type(text: string) {
		return this.call<number>('type', { text });
	}
	async key(vk: number) {
		await this.call('key', { vk });
	}
	stayAwake(on: boolean) {
		return this.call<boolean>('awake', { on });
	}

	stop() {
		const process = this.process;
		this.process = null;
		this.ready = null;
		try {
			process?.stdin.end();
		} catch {
			/* already gone */
		}
		setTimeout(() => process?.kill(), 1000);
	}
}