// Copyright (C) 2026 Whiterun LLC,
// This software is licensed under the GNU Lesser General Public License (LGPL), version 3.0 or later.
// A copy of the license can be found in the LICENSE file or at https://www.gnu.org/licenses/lgpl-3.0.html

import { debug, Scope, LogScope } from "./log.js";
import { EventEmitter } from "eventemitter3";

async function sleep(ms: number): Promise<void> {
  return new Promise((resolve) => setTimeout(resolve, ms));
}

export interface VisibilityChangeContext<TClient> {
  client: TClient;
  state: "hidden" | "visible";
  setPaused: (_value: boolean) => void;
  isPaused: () => boolean;
  startConnectionLoop: () => void;
}

export interface ConnectionManagerOptions<
  TClient extends ConnectionClient = ConnectionClient,
> {
  reconnectInterval?: number;
  maxReconnectAttempts?: number;
  enableVisibilityHandling?: boolean;
  scope?: LogScope;
  onVisibilityChange?: (
    _context: VisibilityChangeContext<TClient>,
  ) => void | Promise<void>;
}

export interface ConnectionClient extends EventEmitter {
  connect(): Promise<void>;
  disconnect(..._args: any[]): Promise<void | boolean>;
}

export interface ConnectionManagerResult {
  cleanup: () => Promise<void>;
  startConnectionLoop: () => void;
}

export const createConnectionManager = <TClient extends ConnectionClient>(
  client: TClient,
  callbacks: {
    onConnected: (_client: TClient) => void;
    onReconnecting: (_client: TClient, _reason: string | null) => void;
    onDisconnected: (_client: TClient) => void;
    onError?: (_client: TClient, _error: any) => void;
  },
  events: {
    connected: string;
    disconnected: string;
    error?: string;
  },
  options: ConnectionManagerOptions<TClient> = {},
): ConnectionManagerResult => {
  const {
    reconnectInterval = 5000,
    maxReconnectAttempts = Infinity,
    enableVisibilityHandling = true,
    scope = Scope.Network,
    onVisibilityChange,
  } = options;

  let isPaused = false;
  let reconnectLoop: Promise<void> | null = null;
  let visibilityChangeHandler: (() => void) | null = null;

  const triggerReconnect = (reason: string | null) => {
    if (!isPaused) {
      callbacks.onReconnecting(client, reason);
      reconnectLoop = null;
      startConnectionLoop();
    }
  };

  const onConnected = () => callbacks.onConnected(client);
  client.on(events.connected, onConnected);

  const onDisconnected = (...args: any[]) => {
    const err = args[0] instanceof Error ? args[0].message : null;
    debug(scope, "Disconnected event received", err);
    triggerReconnect(err);
  };

  const onError = (err: any) => {
    const errorMsg = err?.message || String(err);
    debug(scope, "Error event received", errorMsg);
    triggerReconnect(errorMsg);
    if (callbacks.onError) {
      callbacks.onError(client, err);
    }
  };

  client.on(events.disconnected, onDisconnected);
  if (events.error) {
    client.on(events.error, onError);
  }

  const setupVisibilityHandling = () => {
    if (typeof document === "undefined") {
      return;
    }

    visibilityChangeHandler = () => {
      const state = document.visibilityState as "hidden" | "visible";

      if (onVisibilityChange) {
        const context: VisibilityChangeContext<TClient> = {
          client,
          state,
          setPaused: (value: boolean) => {
            isPaused = value;
          },
          isPaused: () => isPaused,
          startConnectionLoop,
        };
        (async () => {
          try {
            await onVisibilityChange(context);
          } catch (err) {
            debug(scope, "Error in custom visibility change handler:", err);
          }
        })();
        return;
      }

      if (state === "hidden") {
        isPaused = true;
        (async () => {
          try {
            await client.disconnect();
            callbacks.onDisconnected(client);
          } catch (err) {
            debug(scope, "Error disconnecting on visibility change:", err);
          }
        })();
      } else if (state === "visible") {
        if (isPaused) {
          isPaused = false;
          startConnectionLoop();
        }
      }
    };

    document.addEventListener("visibilitychange", visibilityChangeHandler);
  };

  const startConnectionLoop = () => {
    if (reconnectLoop) {
      return;
    }

    reconnectLoop = (async () => {
      let reconnectAttempts = 0;
      let wasConnected = false;

      while (true) {
        if (isPaused) {
          await sleep(1000);
          continue;
        }

        try {
          await client.connect();
          // onConnected is fired via the "connection" event emitted inside client.connect()
          // — do NOT call callbacks.onConnected here too, that would double-fire it.
          reconnectAttempts = 0;
          wasConnected = true;
          reconnectLoop = null;
          return;
        } catch (e) {
          reconnectAttempts++;

          if (wasConnected || reconnectAttempts === 1) {
            callbacks.onReconnecting(client, `${e}`);
            wasConnected = false;
          }

          if (reconnectAttempts > maxReconnectAttempts) {
            callbacks.onDisconnected(client);
            reconnectLoop = null;
            return;
          }

          try {
            await client.disconnect();
          } catch (disconnectError) {
            debug(scope, "Failed to disconnect client", disconnectError);
          }

          await sleep(reconnectInterval);
        }
      }
    })();
  };

  if (enableVisibilityHandling) {
    setupVisibilityHandling();
  }

  const cleanup = async () => {
    isPaused = true;

    if (typeof document !== "undefined" && visibilityChangeHandler !== null) {
      document.removeEventListener("visibilitychange", visibilityChangeHandler);
    }

    client.off(events.connected, onConnected);
    client.off(events.disconnected, onDisconnected);
    if (events.error) {
      client.off(events.error, onError);
    }

    callbacks.onDisconnected(client);

    try {
      await client.disconnect();
    } catch (e) {
      debug(scope, "Failed to disconnect client during cleanup", e);
    }
  };

  return {
    cleanup,
    startConnectionLoop,
  };
};