// Daemon Server - Owns long-lived LspClient instances keyed by
// (server.id, rootDir). Accepts NDJSON requests over a Unix socket and
// dispatches them to the appropriate client, lazily spawning servers and
// reaping idle ones via ServerConfig.idleTtlMs.
import * as fs from "node:fs";
import * as net from "node:net";
import * as path from "node:path";
import { LspClient } from "./client.ts";
import { findRoot, pickServer, pathToUri } from "./root.ts";
import type { ServerConfig } from "./types.ts";
import {
  logPath,
  socketPath,
  tryConnect,
  type DaemonRequest,
  type DaemonResponse,
} from "./daemonProtocol.ts";

// Default Idle TTL - 5 minutes. Per-server overrides via ServerConfig.idleTtlMs.
const DEFAULT_IDLE_TTL_MS = 5 * 60 * 1000;

// Client Entry - One LspClient per (server.id, rootDir), plus the bookkeeping
// needed to keep files in sync and evict on idleness.
interface ClientEntry {
  key: string;
  server: ServerConfig;
  rootDir: string;
  client: LspClient;
  // ready: gates concurrent requests during startup so we only initialize once.
  ready: Promise<void>;
  // opened: URI -> last-synced mtimeMs. Used to decide didOpen vs didChange vs nothing.
  opened: Map<string, number>;
  // serializer: per-entry mutex so file-sync (didOpen/didChange) can't race
  // with itself when two requests for the same file land concurrently.
  serializer: Promise<unknown>;
  idleTimer: NodeJS.Timeout | null;
  ttlMs: number;
  lastUsed: number;
}

const entries = new Map<string, ClientEntry>();

// Log - Single helper so we can prefix and easily silence in tests.
function log(...args: unknown[]) {
  process.stdout.write(
    `[${new Date().toISOString()}] ` +
      args.map((a) => (typeof a === "string" ? a : JSON.stringify(a))).join(" ") +
      "\n",
  );
}

// Get Or Create Entry - Looks up the cached client for a file, spawning a
// fresh LspClient if needed. The returned entry is guaranteed to have its
// `ready` promise resolved before the caller uses it.
async function getOrCreateEntry(filePath: string): Promise<ClientEntry> {
  const server = pickServer(filePath);
  const rootDir = findRoot(filePath, server.rootMarkers);
  const key = `${server.id}::${rootDir}`;
  const existing = entries.get(key);
  if (existing) {
    await existing.ready;
    return existing;
  }
  // Cold Start - Build the entry synchronously so concurrent callers all
  // await the same `ready` promise instead of racing to spawn duplicates.
  const client = new LspClient(server);
  const ttlMs = server.idleTtlMs ?? DEFAULT_IDLE_TTL_MS;
  const entry: ClientEntry = {
    key,
    server,
    rootDir,
    client,
    ready: (async () => {
      log(`spawn`, server.id, rootDir);
      await client.start(rootDir);
      await client.waitForReady();
      log(`ready`, server.id);
    })(),
    opened: new Map(),
    serializer: Promise.resolve(),
    idleTimer: null,
    ttlMs,
    lastUsed: Date.now(),
  };
  entries.set(key, entry);
  try {
    await entry.ready;
  } catch (err) {
    entries.delete(key);
    throw err;
  }
  bumpIdle(entry);
  return entry;
}

// Bump Idle - Resets the idle eviction timer. Called on every request that
// touches the entry. We log evictions so the daemon's behavior is visible.
function bumpIdle(entry: ClientEntry) {
  entry.lastUsed = Date.now();
  if (entry.idleTimer) clearTimeout(entry.idleTimer);
  entry.idleTimer = setTimeout(() => evict(entry, "idle"), entry.ttlMs);
}

function evict(entry: ClientEntry, reason: string) {
  if (!entries.has(entry.key)) return;
  log(`evict`, entry.key, reason);
  entries.delete(entry.key);
  if (entry.idleTimer) clearTimeout(entry.idleTimer);
  void entry.client.dispose();
  // Auto Shutdown - If this was the last entry, there's nothing left to
  // manage. Tear down the daemon so it doesn't sit idle forever.
  if (entries.size === 0) {
    shutdownDaemon("all entries evicted");
  }
}

// Sync File - Ensures the language server has the current contents of the
// file. Sends didOpen on first access, didChange on subsequent calls when
// the on-disk mtime has advanced. Serialized per-entry to avoid races.
async function syncFile(
  entry: ClientEntry,
  filePath: string,
): Promise<{ uri: string; changed: boolean }> {
  const uri = pathToUri(filePath);
  const run = async () => {
    const stat = fs.statSync(filePath);
    const prev = entry.opened.get(uri);
    if (prev === undefined) {
      entry.client.openDocument(filePath);
      entry.opened.set(uri, stat.mtimeMs);
      return { uri, changed: true };
    } else if (prev !== stat.mtimeMs) {
      entry.client.notifyChange(filePath);
      entry.opened.set(uri, stat.mtimeMs);
      return { uri, changed: true };
    }
    return { uri, changed: false };
  };
  // Chain onto the per-entry serializer so concurrent syncs queue up.
  const next = entry.serializer.then(run, run);
  entry.serializer = next.catch(() => undefined);
  return next;
}

// Inject textDocument.uri - Mirrors the helper in commands.ts; we don't
// reuse it because the daemon path operates on raw method strings rather
// than the LspCommand union.
function withDoc(uri: string, params: Record<string, unknown>): Record<string, unknown> {
  const existing = (params.textDocument as Record<string, unknown>) ?? {};
  return { ...params, textDocument: { uri, ...existing } };
}

// Handle Request - Dispatches a single parsed DaemonRequest. Returns a
// DaemonResponse; never throws (errors are returned as { ok: false }).
async function handle(req: DaemonRequest): Promise<DaemonResponse> {
  try {
    switch (req.op) {
      case "request": {
        const filePath = path.resolve(req.file);
        const entry = await getOrCreateEntry(filePath);
        const { uri } = await syncFile(entry, filePath);
        bumpIdle(entry);
        const result = await entry.client.sendRequest(
          req.method,
          withDoc(uri, req.params),
        );
        return { id: req.id, ok: true, result };
      }
      case "diagnostics": {
        const filePath = path.resolve(req.file);
        const entry = await getOrCreateEntry(filePath);
        const { uri, changed } = await syncFile(entry, filePath);
        bumpIdle(entry);
        if (changed) entry.client.clearDiagnostics(uri);
        const result = await entry.client.waitForDiagnostics(
          uri,
          req.timeoutMs ?? 1500,
        );
        return { id: req.id, ok: true, result };
      }
      case "status": {
        const result = {
          socket: socketPath(),
          servers: Array.from(entries.values()).map((e) => ({
            id: e.server.id,
            rootDir: e.rootDir,
            openedFiles: Array.from(e.opened.keys()),
            idleMs: Date.now() - e.lastUsed,
            ttlMs: e.ttlMs,
          })),
        };
        return { id: req.id, ok: true, result };
      }
      case "destroy_server": {
        // Manual Kill - Evict entries matching the server ID (or all if
        // unspecified). This is explicitly destructive; the caller knows
        // what it's doing.
        const toDestroy = req.serverId
          ? Array.from(entries.values()).filter(
              (e) => e.server.id === req.serverId,
            )
          : Array.from(entries.values());
        for (const entry of toDestroy) {
          evict(entry, "manual destroy");
        }
        return {
          id: req.id,
          ok: true,
          result: { destroyed: toDestroy.map((e) => e.key) },
        };
      }
      case "shutdown": {
        // Acknowledge first, then tear down on next tick so the response
        // has a chance to flush before we close listeners.
        setImmediate(() => shutdownDaemon("shutdown request"));
        return { id: req.id, ok: true, result: { stopping: true } };
      }
    }
  } catch (err) {
    return {
      id: req.id,
      ok: false,
      error: (err as Error)?.message ?? String(err),
    };
  }
  // Exhaustiveness - Should be unreachable given the union above.
  throw new Error("unreachable");
}

// Handle Connection - Reads NDJSON from a client socket; each line is one
// independent request. Multiple requests may share a connection.
function handleConnection(sock: net.Socket) {
  let buf = "";
  sock.on("data", async (chunk) => {
    buf += chunk.toString("utf8");
    let nl: number;
    // Process All Complete Lines - Leftover stays in buf for the next chunk.
    while ((nl = buf.indexOf("\n")) !== -1) {
      const line = buf.slice(0, nl);
      buf = buf.slice(nl + 1);
      if (!line.trim()) continue;
      let req: DaemonRequest;
      try {
        req = JSON.parse(line);
      } catch (err) {
        sock.write(
          JSON.stringify({
            id: 0,
            ok: false,
            error: `bad json: ${(err as Error).message}`,
          }) + "\n",
        );
        continue;
      }
      const resp = await handle(req);
      sock.write(JSON.stringify(resp) + "\n");
    }
  });
  sock.on("error", (err) => log("conn error", err.message));
}

let server: net.Server | null = null;

// Shutdown Daemon - Stops accepting connections, disposes all LspClients,
// removes the socket file, and exits. Called on SIGTERM/SIGINT and via
// the explicit `shutdown` op.
function shutdownDaemon(reason: string) {
  log(`shutdown`, reason);
  if (server) server.close();
  for (const entry of entries.values()) {
    if (entry.idleTimer) clearTimeout(entry.idleTimer);
    void entry.client.dispose();
  }
  entries.clear();
  try {
    fs.unlinkSync(socketPath());
  } catch {
    // Ignore - already gone.
  }
  // Give pending writes a moment, then exit.
  setTimeout(() => process.exit(0), 100);
}

// Start Daemon - Binds the Unix socket, handling stale-socket cleanup.
// If another daemon is already listening, we exit cleanly so racing
// `ensureDaemon` callers converge on a single instance.
export async function startDaemon(): Promise<void> {
  const sock = socketPath();
  // Stale Socket Detection - If something exists at the path, try to
  // connect. A successful connect means another daemon owns it (we exit);
  // a failed connect means the socket file is stale (we unlink it).
  if (fs.existsSync(sock)) {
    try {
      const probe = await tryConnect(sock, 200);
      probe.destroy();
      log(`another daemon already listening on ${sock}, exiting`);
      process.exit(0);
    } catch {
      try {
        fs.unlinkSync(sock);
      } catch {
        // Ignore - listen() will surface a clearer error if this matters.
      }
    }
  }
  server = net.createServer(handleConnection);
  await new Promise<void>((resolve, reject) => {
    server!.once("error", reject);
    server!.listen(sock, () => {
      // Restrict Permissions - Socket is per-user; nobody else should poke at it.
      try {
        fs.chmodSync(sock, 0o600);
      } catch {
        // Ignore - best effort.
      }
      resolve();
    });
  });
  log(`listening on ${sock} (logs: ${logPath()})`);
  process.on("SIGTERM", () => shutdownDaemon("SIGTERM"));
  process.on("SIGINT", () => shutdownDaemon("SIGINT"));
}