import { existsSync, readFileSync } from "node:fs";
import path from "node:path";
import dotenv from "dotenv";
import chokidar, { type FSWatcher } from "chokidar";
import { parse as parseYaml } from "yaml";
import { configSchema, type Config } from "./schema";
import { interpolateEnv } from "./interpolate";
import { createLogger } from "@/lib/logger";

const log = createLogger("config");

const CONFIG_DIR = path.join(process.cwd(), "config");
const CONFIG_PATH = path.join(CONFIG_DIR, "config.yml");
const ENV_PATH = path.join(CONFIG_DIR, ".env");

function widgetCount(config: Config): number {
  return config.groups.reduce((sum, group) => sum + group.widgets.length, 0);
}

export class ConfigError extends Error {}

function loadEnv(): Record<string, string | undefined> {
  if (!existsSync(ENV_PATH)) return { ...process.env };
  const parsed = dotenv.parse(readFileSync(ENV_PATH));
  return { ...process.env, ...parsed };
}

export function readConfig(): Config {
  if (!existsSync(CONFIG_PATH)) {
    throw new ConfigError(`Config file not found at ${CONFIG_PATH}`);
  }

  const raw = readFileSync(CONFIG_PATH, "utf-8");
  const env = loadEnv();

  let interpolated: string;
  try {
    interpolated = interpolateEnv(raw, env);
  } catch (err) {
    throw new ConfigError((err as Error).message);
  }

  let parsedYaml: unknown;
  try {
    parsedYaml = parseYaml(interpolated);
  } catch (err) {
    throw new ConfigError(`Failed to parse config.yml: ${(err as Error).message}`);
  }

  const result = configSchema.safeParse(parsedYaml);
  if (!result.success) {
    const issues = result.error.issues
      .map((issue) => `  - ${issue.path.join(".") || "(root)"}: ${issue.message}`)
      .join("\n");
    throw new ConfigError(`config.yml failed validation:\n${issues}`);
  }

  return result.data;
}

type ConfigListener = (config: Config) => void;
type ConfigErrorListener = (error: ConfigError) => void;

class ConfigStore {
  private current: Config | null = null;
  private watcher: FSWatcher | null = null;
  private readonly listeners = new Set<ConfigListener>();
  private readonly errorListeners = new Set<ConfigErrorListener>();

  load(): Config {
    this.current = readConfig();
    log.info("config loaded", { groups: this.current.groups.length, widgets: widgetCount(this.current) });
    return this.current;
  }

  get(): Config {
    return this.current ?? this.load();
  }

  onUpdate(listener: ConfigListener): () => void {
    this.listeners.add(listener);
    return () => this.listeners.delete(listener);
  }

  onError(listener: ConfigErrorListener): () => void {
    this.errorListeners.add(listener);
    return () => this.errorListeners.delete(listener);
  }

  watch(): void {
    if (this.watcher) return;
    this.watcher = chokidar.watch([CONFIG_PATH, ENV_PATH], {
      awaitWriteFinish: { stabilityThreshold: 200, pollInterval: 50 },
      ignoreInitial: true,
    });
    this.watcher.on("all", (event) => {
      log.debug("watched file changed", { event });
      this.reload();
    });
    log.info("watching config files", { paths: [CONFIG_PATH, ENV_PATH] });
  }

  stop(): void {
    this.watcher?.close();
    this.watcher = null;
  }

  private reload(): void {
    try {
      const next = readConfig();
      this.current = next;
      log.info("config reloaded", { groups: next.groups.length, widgets: widgetCount(next) });
      for (const listener of this.listeners) listener(next);
    } catch (err) {
      const configError = err instanceof ConfigError ? err : new ConfigError((err as Error).message);
      log.error("config reload failed", { error: configError.message });
      for (const listener of this.errorListeners) listener(configError);
    }
  }
}

// Next.js bundles app/** through its own compiler pass, giving it a module
// registry separate from server.ts (loaded directly via tsx). A plain module
// singleton would end up duplicated - one instance watched by server.ts,
// another frozen instance used by SSR. Both still share the same Node
// process/heap, so keying off globalThis gives every module graph the same
// instance.
declare global {
  var __pulsenodeConfigStore: ConfigStore | undefined;
}

export const configStore = globalThis.__pulsenodeConfigStore ?? new ConfigStore();
globalThis.__pulsenodeConfigStore = configStore;