import http, { type IncomingMessage, type ServerResponse } from "node:http";
import { generateCuratorPage } from "./curator-page.js";
import type { SummaryMeta } from "./summary-review.js";

const STALE_THRESHOLD_MS = 30000;
const WATCHDOG_INTERVAL_MS = 5000;
const MAX_BODY_SIZE = 64 * 1024;

type ServerState = "SEARCHING" | "RESULT_SELECTION" | "COMPLETED";

export interface CuratorServerOptions {
	queries: string[];
	sessionToken: string;
	timeout: number;
	availableProviders: { perplexity: boolean; exa: boolean; gemini: boolean };
	defaultProvider: string;
	summaryModels: Array<{ value: string; label: string }>;
	defaultSummaryModel: string | null;
}

export interface CuratorServerCallbacks {
	onSubmit: (payload: { selectedQueryIndices: number[]; summary?: string; summaryMeta?: SummaryMeta; rawResults?: boolean }) => void;
	onCancel: (reason: "user" | "timeout" | "stale") => void;
	onProviderChange: (provider: string) => void;
	onAddSearch: (query: string, queryIndex: number, provider?: string) => Promise<{
		answer: string;
		results: Array<{ title: string; url: string; domain: string }>;
		provider: string;
	}>;
	onSummarize: (
		selectedQueryIndices: number[],
		signal: AbortSignal,
		model?: string,
		feedback?: string,
	) => Promise<{ summary: string; meta: SummaryMeta }>;
	onRewriteQuery: (query: string, signal: AbortSignal) => Promise<string>;
}

export interface CuratorServerHandle {
	server: http.Server;
	url: string;
	close: () => void;
	pushResult: (queryIndex: number, data: { answer: string; results: Array<{ title: string; url: string; domain: string }>; provider: string }) => void;
	pushError: (queryIndex: number, error: string, provider?: string) => void;
	searchesDone: () => void;
}

function sendJson(res: ServerResponse, status: number, payload: unknown): void {
	res.writeHead(status, {
		"Content-Type": "application/json",
		"Cache-Control": "no-store",
	});
	res.end(JSON.stringify(payload));
}

function parseJSONBody(req: IncomingMessage): Promise<unknown> {
	return new Promise((resolve, reject) => {
		let body = "";
		let size = 0;
		req.on("data", (chunk: Buffer) => {
			size += chunk.length;
			if (size > MAX_BODY_SIZE) {
				req.destroy();
				reject(new Error("Request body too large"));
				return;
			}
			body += chunk.toString();
		});
		req.on("end", () => {
			try {
				resolve(JSON.parse(body));
			} catch (err) {
				const message = err instanceof Error ? err.message : String(err);
				reject(new Error(`Invalid JSON: ${message}`));
			}
		});
		req.on("error", reject);
	});
}

async function parseBodyOrSend(req: IncomingMessage, res: ServerResponse): Promise<unknown | null> {
	try {
		return await parseJSONBody(req);
	} catch (err) {
		const message = err instanceof Error ? err.message : "Invalid body";
		const status = message === "Request body too large" ? 413 : 400;
		sendJson(res, status, { ok: false, error: message });
		return null;
	}
}

function normalizeSelectedIndices(
	value: unknown,
	options: { allowEmpty: boolean; maxExclusive: number },
): { ok: true; indices: number[] } | { ok: false; error: string } {
	if (!Array.isArray(value)) {
		return { ok: false, error: "Invalid selection" };
	}

	if (!options.allowEmpty && value.length === 0) {
		return { ok: false, error: "Invalid selection" };
	}

	const normalized: number[] = [];
	const seen = new Set<number>();
	for (const item of value) {
		if (typeof item !== "number" || !Number.isInteger(item) || item < 0) {
			return { ok: false, error: "Invalid selection" };
		}
		if (item >= options.maxExclusive) {
			return { ok: false, error: "Invalid selection" };
		}
		if (seen.has(item)) {
			continue;
		}
		seen.add(item);
		normalized.push(item);
	}

	if (!options.allowEmpty && normalized.length === 0) {
		return { ok: false, error: "Invalid selection" };
	}

	return { ok: true, indices: normalized };
}

function normalizeSummaryMeta(value: unknown): SummaryMeta | null {
	if (!value || typeof value !== "object") return null;
	const meta = value as Record<string, unknown>;

	const model = meta.model;
	if (model !== null && typeof model !== "string") return null;

	const durationMs = meta.durationMs;
	if (typeof durationMs !== "number" || !Number.isFinite(durationMs) || durationMs < 0) return null;

	const tokenEstimate = meta.tokenEstimate;
	if (typeof tokenEstimate !== "number" || !Number.isFinite(tokenEstimate) || tokenEstimate < 0) return null;

	const fallbackUsed = meta.fallbackUsed;
	if (typeof fallbackUsed !== "boolean") return null;

	const fallbackReason = meta.fallbackReason;
	if (fallbackReason !== undefined && typeof fallbackReason !== "string") return null;

	const edited = meta.edited;
	if (edited !== undefined && typeof edited !== "boolean") return null;

	return {
		model,
		durationMs,
		tokenEstimate,
		fallbackUsed,
		fallbackReason,
		edited,
	};
}

export function startCuratorServer(
	options: CuratorServerOptions,
	callbacks: CuratorServerCallbacks,
): Promise<CuratorServerHandle> {
	const {
		queries,
		sessionToken,
		timeout,
		availableProviders,
		defaultProvider,
		summaryModels,
		defaultSummaryModel,
	} = options;
	let browserConnected = false;
	let lastHeartbeatAt = Date.now();
	let completed = false;
	let watchdog: NodeJS.Timeout | null = null;
	let state: ServerState = "SEARCHING";
	let sseResponse: ServerResponse | null = null;
	const sseBuffer: string[] = [];
	let nextQueryIndex = queries.length;
	let summarizeAbortController: AbortController | null = null;
	let summarizeRequestSeq = 0;

	let sseKeepalive: NodeJS.Timeout | null = null;

	const abortInFlightSummarize = (): void => {
		if (!summarizeAbortController) return;
		summarizeAbortController.abort();
		summarizeAbortController = null;
	};

	const markCompleted = (): boolean => {
		if (completed) return false;
		completed = true;
		state = "COMPLETED";
		if (watchdog) {
			clearInterval(watchdog);
			watchdog = null;
		}
		if (sseKeepalive) {
			clearInterval(sseKeepalive);
			sseKeepalive = null;
		}
		abortInFlightSummarize();
		if (sseResponse) {
			try { sseResponse.end(); } catch {}
			sseResponse = null;
		}
		return true;
	};

	const touchHeartbeat = (): void => {
		lastHeartbeatAt = Date.now();
		browserConnected = true;
	};

	function validateToken(body: unknown, res: ServerResponse): boolean {
		if (!body || typeof body !== "object") {
			sendJson(res, 400, { ok: false, error: "Invalid body" });
			return false;
		}
		if ((body as { token?: string }).token !== sessionToken) {
			sendJson(res, 403, { ok: false, error: "Invalid session" });
			return false;
		}
		return true;
	}

	function isAvailableProvider(provider: string): boolean {
		if (provider === "perplexity") return availableProviders.perplexity;
		if (provider === "exa") return availableProviders.exa;
		if (provider === "gemini") return availableProviders.gemini;
		return false;
	}

	function sendSSE(event: string, data: unknown): void {
		const payload = `event: ${event}\ndata: ${JSON.stringify(data)}\n\n`;
		const res = sseResponse;
		if (res && !res.writableEnded && res.socket && !res.socket.destroyed) {
			try { res.write(payload); return; } catch {}
		}
		sseBuffer.push(payload);
	}

	const pageHtml = generateCuratorPage(
		queries,
		sessionToken,
		timeout,
		availableProviders,
		defaultProvider,
		summaryModels,
		defaultSummaryModel,
	);

	const server = http.createServer(async (req, res) => {
		try {
			const method = req.method || "GET";
			const url = new URL(req.url || "/", `http://${req.headers.host || "127.0.0.1"}`);

			if (method === "GET" && url.pathname === "/") {
				const token = url.searchParams.get("session");
				if (token !== sessionToken) {
					res.writeHead(403, { "Content-Type": "text/plain" });
					res.end("Invalid session");
					return;
				}
				touchHeartbeat();
				res.writeHead(200, {
					"Content-Type": "text/html; charset=utf-8",
					"Cache-Control": "no-store",
				});
				res.end(pageHtml);
				return;
			}

			if (method === "GET" && url.pathname === "/events") {
				const token = url.searchParams.get("session");
				if (token !== sessionToken) {
					res.writeHead(403, { "Content-Type": "text/plain" });
					res.end("Invalid session");
					return;
				}
				if (state === "COMPLETED") {
					sendJson(res, 409, { ok: false, error: "No events available" });
					return;
				}
				if (sseResponse) {
					try { sseResponse.end(); } catch {}
				}
				res.writeHead(200, {
					"Content-Type": "text/event-stream",
					"Cache-Control": "no-cache",
					Connection: "keep-alive",
					"X-Accel-Buffering": "no",
				});
				res.flushHeaders();
				if (res.socket) res.socket.setNoDelay(true);
				sseResponse = res;
				if (sseBuffer.length > 0) {
					const pending = sseBuffer.splice(0, sseBuffer.length);
					for (let i = 0; i < pending.length; i++) {
						const msg = pending[i];
						try {
							res.write(msg);
						} catch {
							sseBuffer.unshift(...pending.slice(i));
							break;
						}
					}
				}
				if (sseKeepalive) clearInterval(sseKeepalive);
				sseKeepalive = setInterval(() => {
					if (sseResponse) {
						try { sseResponse.write(":keepalive\n\n"); } catch {}
					}
				}, 15000);
				req.on("close", () => {
					if (sseResponse === res) sseResponse = null;
				});
				return;
			}

			if (method === "POST" && url.pathname === "/heartbeat") {
				const body = await parseBodyOrSend(req, res);
				if (!body) return;
				if (!validateToken(body, res)) return;
				touchHeartbeat();
				sendJson(res, 200, { ok: true });
				return;
			}

			if (method === "POST" && url.pathname === "/provider") {
				const body = await parseBodyOrSend(req, res);
				if (!body) return;
				if (!validateToken(body, res)) return;
				const { provider } = body as { provider?: string };
				if (typeof provider !== "string" || provider.length === 0) {
					sendJson(res, 400, { ok: false, error: "Invalid provider" });
					return;
				}
				if (!isAvailableProvider(provider)) {
					sendJson(res, 400, { ok: false, error: `Provider unavailable: ${provider}` });
					return;
				}
				setImmediate(() => callbacks.onProviderChange(provider));
				sendJson(res, 200, { ok: true });
				return;
			}

			if (method === "POST" && url.pathname === "/search") {
				const body = await parseBodyOrSend(req, res);
				if (!body) return;
				if (!validateToken(body, res)) return;
				if (state === "COMPLETED") {
					sendJson(res, 409, { ok: false, error: "Session closed" });
					return;
				}
				const { query, provider } = body as { query?: string; provider?: string };
				if (typeof query !== "string" || query.trim().length === 0) {
					sendJson(res, 400, { ok: false, error: "Invalid query" });
					return;
				}
				if (provider !== undefined) {
					if (typeof provider !== "string" || provider.length === 0) {
						sendJson(res, 400, { ok: false, error: "Invalid provider" });
						return;
					}
					if (!isAvailableProvider(provider)) {
						sendJson(res, 400, { ok: false, error: `Provider unavailable: ${provider}` });
						return;
					}
				}
				const qi = nextQueryIndex++;
				touchHeartbeat();
				try {
					const result = await callbacks.onAddSearch(query.trim(), qi, provider);
					sendJson(res, 200, {
						ok: true,
						queryIndex: qi,
						answer: result.answer,
						results: result.results,
						provider: result.provider,
					});
				} catch (err) {
					const message = err instanceof Error ? err.message : "Search failed";
					sendJson(res, 200, {
						ok: true,
						queryIndex: qi,
						error: message,
						provider: typeof provider === "string" && provider.length > 0 ? provider : undefined,
					});
				}
				return;
			}

			if (method === "POST" && url.pathname === "/summarize") {
				const body = await parseBodyOrSend(req, res);
				if (!body) return;
				if (!validateToken(body, res)) return;
				if (state === "COMPLETED") {
					sendJson(res, 409, { ok: false, error: "Session closed" });
					return;
				}

				const parsed = normalizeSelectedIndices((body as { selected?: unknown }).selected, {
					allowEmpty: false,
					maxExclusive: nextQueryIndex,
				});
				if (!parsed.ok) {
					sendJson(res, 400, { ok: false, error: parsed.error });
					return;
				}

				let model: string | undefined;
				const bodyModel = (body as { model?: unknown }).model;
				if (bodyModel !== undefined) {
					if (typeof bodyModel !== "string") {
						sendJson(res, 400, { ok: false, error: "Invalid model" });
						return;
					}
					const trimmedModel = bodyModel.trim();
					model = trimmedModel.length > 0 ? trimmedModel : undefined;
				}

				const bodyFeedback = (body as { feedback?: unknown }).feedback;
				const feedback = typeof bodyFeedback === "string" && bodyFeedback.trim().length > 0
					? bodyFeedback.trim()
					: undefined;

				abortInFlightSummarize();
				const controller = new AbortController();
				summarizeAbortController = controller;
				const requestId = ++summarizeRequestSeq;

				try {
					const result = await callbacks.onSummarize(parsed.indices, controller.signal, model, feedback);
					if (requestId !== summarizeRequestSeq || state === "COMPLETED") {
						sendJson(res, 409, { ok: false, error: "Summarize request superseded" });
						return;
					}
					sendJson(res, 200, {
						ok: true,
						summary: result.summary,
						meta: result.meta,
					});
				} catch (err) {
					const message = err instanceof Error ? err.message : "Summary generation failed";
					const status = controller.signal.aborted ? 409 : 500;
					sendJson(res, status, { ok: false, error: message });
				} finally {
					if (summarizeAbortController === controller) {
						summarizeAbortController = null;
					}
				}
				return;
			}

			if (method === "POST" && url.pathname === "/rewrite") {
				const body = await parseBodyOrSend(req, res);
				if (!body) return;
				if (!validateToken(body, res)) return;
				if (state === "COMPLETED") {
					sendJson(res, 409, { ok: false, error: "Session closed" });
					return;
				}
				const { query } = body as { query?: unknown };
				if (typeof query !== "string" || query.trim().length === 0) {
					sendJson(res, 400, { ok: false, error: "Invalid query" });
					return;
				}
				const controller = new AbortController();
				req.on("close", () => controller.abort());
				touchHeartbeat();
				try {
					const rewritten = await callbacks.onRewriteQuery(query.trim(), controller.signal);
					sendJson(res, 200, { ok: true, query: rewritten });
				} catch (err) {
					const message = err instanceof Error ? err.message : "Rewrite failed";
					const status = controller.signal.aborted ? 409 : 500;
					sendJson(res, status, { ok: false, error: message });
				}
				return;
			}

			if (method === "POST" && url.pathname === "/submit") {
				const body = await parseBodyOrSend(req, res);
				if (!body) return;
				if (!validateToken(body, res)) return;

				const parsed = normalizeSelectedIndices((body as { selected?: unknown }).selected, {
					allowEmpty: true,
					maxExclusive: nextQueryIndex,
				});
				if (!parsed.ok) {
					sendJson(res, 400, { ok: false, error: parsed.error });
					return;
				}

				let summary: string | undefined;
				const bodySummary = (body as { summary?: unknown }).summary;
				if (bodySummary !== undefined) {
					if (typeof bodySummary !== "string") {
						sendJson(res, 400, { ok: false, error: "Invalid summary" });
						return;
					}
					const trimmedSummary = bodySummary.trim();
					summary = trimmedSummary.length > 0 ? trimmedSummary : undefined;
				}

				let summaryMeta: SummaryMeta | undefined;
				const bodySummaryMeta = (body as { summaryMeta?: unknown }).summaryMeta;
				if (bodySummaryMeta !== undefined) {
					const parsedSummaryMeta = normalizeSummaryMeta(bodySummaryMeta);
					if (!parsedSummaryMeta) {
						sendJson(res, 400, { ok: false, error: "Invalid summaryMeta" });
						return;
					}
					summaryMeta = parsedSummaryMeta;
				}

				if (state !== "SEARCHING" && state !== "RESULT_SELECTION") {
					sendJson(res, 409, { ok: false, error: "Cannot submit in current state" });
					return;
				}
				if (!markCompleted()) {
					sendJson(res, 409, { ok: false, error: "Session closed" });
					return;
				}
				const rawResults = (body as { rawResults?: unknown }).rawResults === true;
				sendJson(res, 200, { ok: true });
				setImmediate(() => callbacks.onSubmit({ selectedQueryIndices: parsed.indices, summary, summaryMeta, rawResults }));
				return;
			}

			if (method === "POST" && url.pathname === "/cancel") {
				const body = await parseBodyOrSend(req, res);
				if (!body) return;
				if (!validateToken(body, res)) return;
				if (!markCompleted()) {
					sendJson(res, 200, { ok: true });
					return;
				}
				const { reason } = body as { reason?: string };
				sendJson(res, 200, { ok: true });
				const cancelReason = reason === "timeout" ? "timeout" : "user";
				setImmediate(() => callbacks.onCancel(cancelReason));
				return;
			}

			res.writeHead(404, { "Content-Type": "text/plain" });
			res.end("Not found");
		} catch (err) {
			const message = err instanceof Error ? err.message : "Server error";
			sendJson(res, 500, { ok: false, error: message });
		}
	});

	return new Promise((resolve, reject) => {
		const onError = (err: Error) => {
			reject(new Error(`Curator server failed to start: ${err.message}`));
		};

		server.once("error", onError);
		server.listen(0, "127.0.0.1", () => {
			server.off("error", onError);
			const addr = server.address();
			if (!addr || typeof addr === "string") {
				reject(new Error("Curator server: invalid address"));
				return;
			}
			const url = `http://localhost:${addr.port}/?session=${sessionToken}`;

			watchdog = setInterval(() => {
				if (completed || !browserConnected) return;
				if (Date.now() - lastHeartbeatAt <= STALE_THRESHOLD_MS) return;
				if (!markCompleted()) return;
				setImmediate(() => callbacks.onCancel("stale"));
			}, WATCHDOG_INTERVAL_MS);

			resolve({
				server,
				url,
				close: () => {
					const wasOpen = markCompleted();
					try { server.close(); } catch {}
					if (wasOpen) {
						setImmediate(() => callbacks.onCancel("stale"));
					}
				},
				pushResult: (queryIndex, data) => {
					if (completed) return;
					sendSSE("result", { queryIndex, query: queries[queryIndex] ?? "", ...data });
				},
				pushError: (queryIndex, error, provider) => {
					if (completed) return;
					sendSSE("search-error", { queryIndex, query: queries[queryIndex] ?? "", error, provider });
				},
				searchesDone: () => {
					if (completed) return;
					sendSSE("done", {});
					state = "RESULT_SELECTION";
				},
			});
		});
	});
}