import { watch, type FSWatcher } from "node:fs";
import fs from "node:fs/promises";
import path from "node:path";
import { pipeline } from "node:stream/promises";
import type { FileSystemProvider } from "./fs/provider";
import type { SessionRegistry } from "./fs/registry";
import type { SettingsStore } from "./store/settings";
import { appDataDir } from "./store/paths";
import type { TransferEngine } from "./transfers/engine";

// Built-in editor guard: bigger than this is not a config file.
const MAX_EDIT_BYTES = 2 * 1024 * 1024;
const SAVE_DEBOUNCE_MS = 400;

/** Read a whole file as UTF-8 through any provider (local or sftp). */
export async function readFileText(
	provider: FileSystemProvider,
	filePath: string,
): Promise<string> {
	const stat = await provider.stat(filePath);
	if (stat.size > MAX_EDIT_BYTES) {
		throw new Error(
			`File is ${Math.round(stat.size / 1024 / 1024)}MB — too large for the built-in editor. Use a custom editor instead.`,
		);
	}
	const chunks: Buffer[] = [];
	const stream = provider.createReadStream(filePath);
	for await (const chunk of stream) {
		chunks.push(typeof chunk === "string" ? Buffer.from(chunk) : chunk);
	}
	return Buffer.concat(chunks).toString("utf8");
}

/** Write UTF-8 content through any provider. */
export function writeFileText(
	provider: FileSystemProvider,
	filePath: string,
	content: string,
): Promise<void> {
	return new Promise((resolve, reject) => {
		const stream = provider.createWriteStream(filePath);
		stream.on("error", reject);
		stream.end(Buffer.from(content, "utf8"), () => resolve());
	});
}

/**
 * Launch a file in an external editor.
 *
 * PORTABILITY: this is the only platform-specific piece of the edit feature.
 * macOS delivers the file to any GUI app via `open [-a app]`; Windows via
 * `cmd /c start` (empty "" arg = window title slot); Linux via the app
 * directly or `xdg-open`. Everything else (temp download, directory watch,
 * auto-upload) is platform-neutral. Windows path pending first smoke test.
 */
function launchEditor(filePath: string, editorApp: string): void {
	let args: string[];
	switch (process.platform) {
		case "darwin":
			args = editorApp ? ["open", "-a", editorApp, filePath] : ["open", filePath];
			break;
		case "win32":
			args = editorApp
				? ["cmd", "/c", "start", "", editorApp, filePath]
				: ["cmd", "/c", "start", "", filePath];
			break;
		default:
			args = editorApp ? [editorApp, filePath] : ["xdg-open", filePath];
	}
	Bun.spawn(args, { stdout: "ignore", stderr: "ignore" });
}

interface WatchedEdit {
	sessionId: string;
	remotePath: string;
	tempDir: string;
	tempFile: string;
	watcher: FSWatcher;
	debounce: ReturnType<typeof setTimeout> | null;
}

/**
 * External-editor flow for remote files: download to a temp dir, open the
 * editor, watch the directory (survives atomic rename-saves), and enqueue an
 * upload job on every save. Watchers die with their session; temp dirs left
 * behind by a crash are offered for cleanup at next boot.
 */
export class EditManager {
	private readonly editsDir = path.join(appDataDir(), "edits");
	private watched: WatchedEdit[] = [];

	constructor(
		private registry: SessionRegistry,
		private engine: TransferEngine,
		private settings: SettingsStore,
	) {}

	async editExternal(sessionId: string, filePath: string): Promise<{ watching: boolean }> {
		const { editorApp } = await this.settings.load();

		if (sessionId === "local") {
			launchEditor(filePath, editorApp);
			return { watching: false };
		}

		const provider = this.registry.get(sessionId);
		const tempDir = path.join(this.editsDir, crypto.randomUUID().slice(0, 8));
		const name = provider.basename(filePath);
		const tempFile = path.join(tempDir, name);

		await fs.mkdir(tempDir, { recursive: true });
		await fs.writeFile(
			path.join(tempDir, "meta.json"),
			JSON.stringify({ remotePath: filePath, sessionId, downloadedAt: new Date().toISOString() }),
		);
		const { createWriteStream } = await import("node:fs");
		await pipeline(provider.createReadStream(filePath), createWriteStream(tempFile));

		launchEditor(tempFile, editorApp);

		const edit: WatchedEdit = {
			sessionId,
			remotePath: filePath,
			tempDir,
			tempFile,
			watcher: watch(tempDir, (_event, changed) => {
				if (changed !== name) return;
				if (edit.debounce) clearTimeout(edit.debounce);
				edit.debounce = setTimeout(() => this.uploadEdit(edit), SAVE_DEBOUNCE_MS);
			}),
			debounce: null,
		};
		this.watched.push(edit);
		console.log(`[edit] watching ${tempFile} -> ${sessionId}:${filePath}`);
		return { watching: true };
	}

	private uploadEdit(edit: WatchedEdit): void {
		const provider = this.registry.get(edit.sessionId);
		this.engine.enqueue({
			srcSessionId: "local",
			items: [{ path: edit.tempFile, type: "file" }],
			dstSessionId: edit.sessionId,
			dstDir: provider.dirname(edit.remotePath),
		});
	}

	/**
	 * Park unsaveable editor content (window closed, session dead) in the
	 * leftovers dir so the next-boot prompt offers it back to the user.
	 */
	async rescueDraft(name: string, content: string): Promise<void> {
		const dir = path.join(this.editsDir, crypto.randomUUID().slice(0, 8));
		await fs.mkdir(dir, { recursive: true });
		await fs.writeFile(
			path.join(dir, "meta.json"),
			JSON.stringify({ name, rescuedAt: new Date().toISOString() }),
		);
		await fs.writeFile(path.join(dir, name), content, "utf8");
		console.log(`[edit] rescued unsaved draft of ${name} -> ${dir}`);
	}

	/** Session gone (disconnect, tab close, death): stop its watchers, drop temps. */
	stopForSession(sessionId: string): void {
		const [mine, rest] = [
			this.watched.filter((w) => w.sessionId === sessionId),
			this.watched.filter((w) => w.sessionId !== sessionId),
		];
		this.watched = rest;
		for (const edit of mine) {
			edit.watcher.close();
			if (edit.debounce) clearTimeout(edit.debounce);
			void fs.rm(edit.tempDir, { recursive: true, force: true });
		}
	}

	/** Temp files from previous runs (crash / quit mid-edit). */
	async listLeftovers(): Promise<string[]> {
		const names: string[] = [];
		let entries: string[];
		try {
			entries = await fs.readdir(this.editsDir);
		} catch {
			return names;
		}
		const active = new Set(this.watched.map((w) => path.basename(w.tempDir)));
		for (const entry of entries) {
			if (active.has(entry)) continue;
			try {
				const files = await fs.readdir(path.join(this.editsDir, entry));
				const file = files.find((f) => f !== "meta.json");
				names.push(file ?? entry);
			} catch {
				names.push(entry);
			}
		}
		return names;
	}

	async clearLeftovers(): Promise<void> {
		const active = new Set(this.watched.map((w) => path.basename(w.tempDir)));
		let entries: string[] = [];
		try {
			entries = await fs.readdir(this.editsDir);
		} catch {
			return;
		}
		for (const entry of entries) {
			if (active.has(entry)) continue;
			await fs.rm(path.join(this.editsDir, entry), { recursive: true, force: true });
		}
	}
}