import {
  ChannelType,
  Client,
  Events,
  GatewayIntentBits,
  type Message,
} from "discord.js";

import { closeDb } from "@/db/client";
import { processCatalogSync } from "@/lib/catalog/sync";
import {
  compareLunarisVersions,
  parseLunarisVersionChange,
} from "@/lib/catalog/version";
import { closeRedisClient } from "@/lib/redis/client";

const RETRY_DELAYS_MS = [0, 30_000, 120_000, 600_000, 1_800_000] as const;

function required(name: string): string {
  const value = process.env[name]?.trim();
  if (!value) throw new Error(`${name} is required for the Discord catalog worker.`);
  return value;
}

function log(event: string, details: Record<string, unknown> = {}): void {
  console.log(JSON.stringify({ component: "discord-catalog-worker", event, ...details }));
}

function messageText(message: Message): string {
  return [
    message.content,
    ...message.embeds.flatMap((embed) => [
      embed.title ?? "",
      embed.description ?? "",
      ...embed.fields.flatMap((field) => [field.name, field.value]),
    ]),
  ].join("\n");
}

function wait(milliseconds: number, signal: AbortSignal): Promise<boolean> {
  if (signal.aborted) return Promise.resolve(false);
  return new Promise((resolve) => {
    const timer = setTimeout(() => {
      signal.removeEventListener("abort", aborted);
      resolve(true);
    }, milliseconds);
    const aborted = () => {
      clearTimeout(timer);
      resolve(false);
    };
    signal.addEventListener("abort", aborted, { once: true });
  });
}

const token = required("DISCORD_BOT_TOKEN");
const channelId = required("DISCORD_CHANNEL_ID");
const shutdown = new AbortController();
const client = new Client({
  intents: [
    GatewayIntentBits.Guilds,
    GatewayIntentBits.GuildMessages,
    GatewayIntentBits.MessageContent,
  ],
});

let pendingVersion: string | null = null;
let runner: Promise<void> | null = null;

async function syncWithRetry(version: string): Promise<void> {
  for (let attempt = 0; attempt < RETRY_DELAYS_MS.length; attempt += 1) {
    if (shutdown.signal.aborted) return;
    if (
      pendingVersion &&
      compareLunarisVersions(pendingVersion, version) > 0
    ) {
      log("sync_superseded", { version, pendingVersion });
      return;
    }
    if (!(await wait(RETRY_DELAYS_MS[attempt], shutdown.signal))) return;
    if (
      pendingVersion &&
      compareLunarisVersions(pendingVersion, version) > 0
    ) {
      log("sync_superseded", { version, pendingVersion });
      return;
    }

    try {
      log("sync_started", { version, attempt: attempt + 1 });
      const result = await processCatalogSync(version);
      log(result === "synced" ? "sync_completed" : "sync_ignored", {
        version,
        reason: result === "unchanged" ? "current-or-older" : undefined,
      });
      return;
    } catch (cause) {
      const message = cause instanceof Error ? cause.message : String(cause);
      if (attempt === RETRY_DELAYS_MS.length - 1) {
        log("sync_failed", { version, attempts: attempt + 1, error: message });
        return;
      }
      log("sync_retrying", { version, attempt: attempt + 1, error: message });
    }
  }
}

async function drain(): Promise<void> {
  while (pendingVersion && !shutdown.signal.aborted) {
    const version = pendingVersion;
    pendingVersion = null;
    await syncWithRetry(version);
  }
}

function enqueue(version: string, source: "history" | "message"): void {
  if (!pendingVersion || compareLunarisVersions(version, pendingVersion) > 0) {
    pendingVersion = version;
    log("version_queued", { version, source });
  }
  if (!runner) {
    runner = drain().finally(() => {
      runner = null;
    });
  }
}

function handleMessage(message: Message, source: "history" | "message"): void {
  if (message.channelId !== channelId || message.author.id === client.user?.id) return;
  const change = parseLunarisVersionChange(messageText(message));
  if (change) enqueue(change.targetVersion, source);
}

client.on(Events.MessageCreate, (message) => handleMessage(message, "message"));
client.on(Events.Error, (cause) => log("discord_error", { error: cause.message }));
client.on(Events.Warn, (message) => log("discord_warning", { message }));

let stopWorker: (() => void) | undefined;
const stopped = new Promise<void>((resolve) => {
  stopWorker = resolve;
});
const stop = () => {
  shutdown.abort();
  stopWorker?.();
};
process.once("SIGINT", stop);
process.once("SIGTERM", stop);

try {
  const ready = new Promise<void>((resolve) => {
    client.once(Events.ClientReady, () => resolve());
  });
  await client.login(token);
  await Promise.race([ready, stopped]);
  if (!shutdown.signal.aborted) {
    log("discord_ready", { userId: client.user?.id, channelId });

    const channel = await client.channels.fetch(channelId);
    if (
      !channel ||
      (channel.type !== ChannelType.GuildText &&
        channel.type !== ChannelType.GuildAnnouncement)
    ) {
      throw new Error("DISCORD_CHANNEL_ID must identify a guild text channel.");
    }
    const messages = await channel.messages.fetch({ limit: 25 });
    for (const message of messages.values()) handleMessage(message, "history");

    await stopped;
  }
} finally {
  shutdown.abort();
  client.destroy();
  await Promise.resolve(runner).catch(() => undefined);
  await Promise.all([closeDb(), closeRedisClient()]);
  log("stopped");
}