/**
 * PluginDevWatcher — watches local-path plugin directories for file changes
 * and triggers worker restarts so plugin authors get a fast rebuild-and-reload
 * cycle without manually restarting the server.
 *
 * Only plugins installed from a local path (i.e. those with a non-null
 * `packagePath` in the DB) are watched. File changes in the plugin's package
 * directory trigger a debounced worker restart via the lifecycle manager.
 *
 * @see PLUGIN_SPEC.md §27.2 — Local Development Workflow
 */
import { watch, type FSWatcher } from "node:fs";
import { existsSync, readFileSync, statSync } from "node:fs";
import path from "node:path";
import { logger } from "../middleware/logger.js";
import type { PluginLifecycleManager } from "./plugin-lifecycle.js";

const log = logger.child({ service: "plugin-dev-watcher" });

/** Debounce interval for file changes (ms). */
const DEBOUNCE_MS = 500;

export interface PluginDevWatcher {
  /** Start watching a local-path plugin directory. */
  watch(pluginId: string, packagePath: string): void;
  /** Stop watching a specific plugin. */
  unwatch(pluginId: string): void;
  /** Stop all watchers and clean up. */
  close(): void;
}

export type ResolvePluginPackagePath = (
  pluginId: string,
) => Promise<string | null | undefined>;

export interface PluginDevWatcherFsDeps {
  existsSync?: typeof existsSync;
  watch?: typeof watch;
  readFileSync?: typeof readFileSync;
  statSync?: typeof statSync;
}

type PluginWatchTarget = {
  path: string;
  recursive: boolean;
};

type PluginPackageJson = {
  paperclipPlugin?: {
    manifest?: string;
    worker?: string;
    ui?: string;
  };
};

function shouldIgnorePath(filename: string | null | undefined): boolean {
  if (!filename) return false;
  const normalized = filename.replace(/\\/g, "/");
  const segments = normalized.split("/").filter(Boolean);
  return segments.some(
    (segment) =>
      segment === "node_modules" ||
      segment === ".git" ||
      segment === ".vite" ||
      segment === ".paperclip-sdk" ||
      segment.startsWith("."),
  );
}

export function resolvePluginWatchTargets(
  packagePath: string,
  fsDeps?: Pick<PluginDevWatcherFsDeps, "existsSync" | "readFileSync" | "statSync">,
): PluginWatchTarget[] {
  const fileExists = fsDeps?.existsSync ?? existsSync;
  const readFile = fsDeps?.readFileSync ?? readFileSync;
  const statFile = fsDeps?.statSync ?? statSync;
  const absPath = path.resolve(packagePath);
  const targets = new Map<string, PluginWatchTarget>();

  function addWatchTarget(targetPath: string, recursive: boolean): void {
    const resolved = path.resolve(targetPath);
    if (!fileExists(resolved)) return;

    const existing = targets.get(resolved);
    if (existing) {
      existing.recursive = existing.recursive || recursive;
      return;
    }

    targets.set(resolved, { path: resolved, recursive });
  }

  // Watch the package root non-recursively so top-level files like package.json
  // can trigger reloads without traversing node_modules or other deep trees.
  addWatchTarget(absPath, false);

  const packageJsonPath = path.join(absPath, "package.json");
  if (!fileExists(packageJsonPath)) {
    return [...targets.values()];
  }

  let packageJson: PluginPackageJson | null = null;
  try {
    packageJson = JSON.parse(readFile(packageJsonPath, "utf8")) as PluginPackageJson;
  } catch {
    packageJson = null;
  }

  const entrypointPaths = [
    packageJson?.paperclipPlugin?.manifest,
    packageJson?.paperclipPlugin?.worker,
    packageJson?.paperclipPlugin?.ui,
  ].filter((value): value is string => typeof value === "string" && value.length > 0);

  if (entrypointPaths.length === 0) {
    addWatchTarget(path.join(absPath, "dist"), true);
    return [...targets.values()];
  }

  for (const relativeEntrypoint of entrypointPaths) {
    const resolvedEntrypoint = path.resolve(absPath, relativeEntrypoint);
    if (!fileExists(resolvedEntrypoint)) continue;

    const stat = statFile(resolvedEntrypoint);
    if (stat.isDirectory()) {
      addWatchTarget(resolvedEntrypoint, true);
    } else {
      addWatchTarget(path.dirname(resolvedEntrypoint), true);
    }
  }

  return [...targets.values()];
}

/**
 * Create a PluginDevWatcher that monitors local plugin directories and
 * restarts workers on file changes.
 */
export function createPluginDevWatcher(
  lifecycle: PluginLifecycleManager,
  resolvePluginPackagePath?: ResolvePluginPackagePath,
  fsDeps?: PluginDevWatcherFsDeps,
): PluginDevWatcher {
  const watchers = new Map<string, FSWatcher[]>();
  const debounceTimers = new Map<string, ReturnType<typeof setTimeout>>();
  const fileExists = fsDeps?.existsSync ?? existsSync;
  const watchFs = fsDeps?.watch ?? watch;

  function watchPlugin(pluginId: string, packagePath: string): void {
    // Don't double-watch
    if (watchers.has(pluginId)) return;

    const absPath = path.resolve(packagePath);
    if (!fileExists(absPath)) {
      log.warn(
        { pluginId, packagePath: absPath },
        "plugin-dev-watcher: package path does not exist, skipping watch",
      );
      return;
    }

    try {
      const watcherTargets = resolvePluginWatchTargets(absPath, fsDeps);
      if (watcherTargets.length === 0) {
        log.warn(
          { pluginId, packagePath: absPath },
          "plugin-dev-watcher: no valid watch targets found, skipping watch",
        );
        return;
      }

      const activeWatchers = watcherTargets.map((target) => {
        const watcher = watchFs(target.path, { recursive: target.recursive }, (_event, filename) => {
          if (shouldIgnorePath(filename)) return;

          // Debounce: multiple rapid file changes collapse into one restart
          const existing = debounceTimers.get(pluginId);
          if (existing) clearTimeout(existing);

          debounceTimers.set(
            pluginId,
            setTimeout(() => {
              debounceTimers.delete(pluginId);
              log.info(
                { pluginId, changedFile: filename, watchTarget: target.path },
                "plugin-dev-watcher: file change detected, restarting worker",
              );

              lifecycle.restartWorker(pluginId).catch((err) => {
                log.warn(
                  {
                    pluginId,
                    err: err instanceof Error ? err.message : String(err),
                  },
                  "plugin-dev-watcher: failed to restart worker after file change",
                );
              });
            }, DEBOUNCE_MS),
          );
        });

        watcher.on("error", (err) => {
          log.warn(
            {
              pluginId,
              packagePath: absPath,
              watchTarget: target.path,
              err: err instanceof Error ? err.message : String(err),
            },
            "plugin-dev-watcher: watcher error, stopping watch for this plugin",
          );
          unwatchPlugin(pluginId);
        });

        return watcher;
      });

      watchers.set(pluginId, activeWatchers);
      log.info(
        {
          pluginId,
          packagePath: absPath,
          watchTargets: watcherTargets.map((target) => ({
            path: target.path,
            recursive: target.recursive,
          })),
        },
        "plugin-dev-watcher: watching local plugin for changes",
      );
    } catch (err) {
      log.warn(
        {
          pluginId,
          packagePath: absPath,
          err: err instanceof Error ? err.message : String(err),
        },
        "plugin-dev-watcher: failed to start file watcher",
      );
    }
  }

  function unwatchPlugin(pluginId: string): void {
    const pluginWatchers = watchers.get(pluginId);
    if (pluginWatchers) {
      for (const watcher of pluginWatchers) {
        watcher.close();
      }
      watchers.delete(pluginId);
    }
    const timer = debounceTimers.get(pluginId);
    if (timer) {
      clearTimeout(timer);
      debounceTimers.delete(pluginId);
    }
  }

  function close(): void {
    lifecycle.off("plugin.loaded", handlePluginLoaded);
    lifecycle.off("plugin.enabled", handlePluginEnabled);
    lifecycle.off("plugin.disabled", handlePluginDisabled);
    lifecycle.off("plugin.unloaded", handlePluginUnloaded);

    for (const [pluginId] of watchers) {
      unwatchPlugin(pluginId);
    }
  }

  async function watchLocalPluginById(pluginId: string): Promise<void> {
    if (!resolvePluginPackagePath) return;

    try {
      const packagePath = await resolvePluginPackagePath(pluginId);
      if (!packagePath) return;
      watchPlugin(pluginId, packagePath);
    } catch (err) {
      log.warn(
        {
          pluginId,
          err: err instanceof Error ? err.message : String(err),
        },
        "plugin-dev-watcher: failed to resolve plugin package path",
      );
    }
  }

  function handlePluginLoaded(payload: { pluginId: string }): void {
    void watchLocalPluginById(payload.pluginId);
  }

  function handlePluginEnabled(payload: { pluginId: string }): void {
    void watchLocalPluginById(payload.pluginId);
  }

  function handlePluginDisabled(payload: { pluginId: string }): void {
    unwatchPlugin(payload.pluginId);
  }

  function handlePluginUnloaded(payload: { pluginId: string }): void {
    unwatchPlugin(payload.pluginId);
  }

  lifecycle.on("plugin.loaded", handlePluginLoaded);
  lifecycle.on("plugin.enabled", handlePluginEnabled);
  lifecycle.on("plugin.disabled", handlePluginDisabled);
  lifecycle.on("plugin.unloaded", handlePluginUnloaded);

  return {
    watch: watchPlugin,
    unwatch: unwatchPlugin,
    close,
  };
}