/**
 * Proactive Token Refresh Queue
 * 
 * Ported from LLM-API-Key-Proxy's BackgroundRefresher.
 * 
 * This module provides background token refresh to ensure OAuth tokens
 * remain valid without blocking user requests. It periodically checks
 * all accounts and refreshes tokens that are approaching expiry.
 * 
 * Features:
 * - Non-blocking background refresh (doesn't block requests)
 * - Configurable refresh buffer (default: 30 minutes before expiry)
 * - Configurable check interval (default: 5 minutes)
 * - Serialized refresh to prevent concurrent refresh storms
 * - Integrates with existing AccountManager and token refresh logic
 * - Silent operation: no console output, uses structured logger
 */

import type { AccountManager, ManagedAccount } from "./accounts";
import type { PluginClient, OAuthAuthDetails } from "./types";
import { refreshAccessToken } from "./token";
import { createLogger } from "./logger";

const log = createLogger("refresh-queue");

/** Configuration for the proactive refresh queue */
export interface ProactiveRefreshConfig {
  /** Enable proactive token refresh (default: true) */
  enabled: boolean;
  /** Seconds before expiry to trigger proactive refresh (default: 1800 = 30 minutes) */
  bufferSeconds: number;
  /** Interval between refresh checks in seconds (default: 300 = 5 minutes) */
  checkIntervalSeconds: number;
}

export const DEFAULT_PROACTIVE_REFRESH_CONFIG: ProactiveRefreshConfig = {
  enabled: true,
  bufferSeconds: 1800, // 30 minutes
  checkIntervalSeconds: 300, // 5 minutes
};

/** State for tracking refresh operations */
interface RefreshQueueState {
  isRunning: boolean;
  intervalHandle: ReturnType<typeof setInterval> | null;
  isRefreshing: boolean;
  lastCheckTime: number;
  lastRefreshTime: number;
  refreshCount: number;
  errorCount: number;
}

/**
 * Proactive Token Refresh Queue
 * 
 * Runs in the background and proactively refreshes tokens before they expire.
 * This ensures that user requests never block on token refresh.
 * 
 * All logging is silent by default - uses structured logger with TUI integration.
 */
export class ProactiveRefreshQueue {
  private readonly config: ProactiveRefreshConfig;
  private readonly client: PluginClient;
  private readonly providerId: string;
  private accountManager: AccountManager | null = null;
  
  private state: RefreshQueueState = {
    isRunning: false,
    intervalHandle: null,
    isRefreshing: false,
    lastCheckTime: 0,
    lastRefreshTime: 0,
    refreshCount: 0,
    errorCount: 0,
  };

  constructor(
    client: PluginClient,
    providerId: string,
    config?: Partial<ProactiveRefreshConfig>,
  ) {
    this.client = client;
    this.providerId = providerId;
    this.config = {
      ...DEFAULT_PROACTIVE_REFRESH_CONFIG,
      ...config,
    };
  }

  /**
   * Set the account manager to use for refresh operations.
   * Must be called before start().
   */
  setAccountManager(manager: AccountManager): void {
    this.accountManager = manager;
  }

  /**
   * Check if a token needs proactive refresh.
   * Returns true if the token expires within the buffer period.
   */
  needsRefresh(account: ManagedAccount): boolean {
    if (!account.expires) {
      // No expiry set - assume it's fine
      return false;
    }

    const now = Date.now();
    const bufferMs = this.config.bufferSeconds * 1000;
    const refreshThreshold = now + bufferMs;

    return account.expires <= refreshThreshold;
  }

  /**
   * Check if a token is already expired.
   */
  isExpired(account: ManagedAccount): boolean {
    if (!account.expires) {
      return false;
    }
    return account.expires <= Date.now();
  }

  /**
   * Get all accounts that need proactive refresh.
   */
  getAccountsNeedingRefresh(): ManagedAccount[] {
    if (!this.accountManager) {
      return [];
    }

    return this.accountManager.getAccounts().filter((account) => {
      // Skip disabled accounts - they shouldn't receive proactive refresh
      if (account.enabled === false) {
        return false;
      }
      // Only refresh if not already expired (let the main flow handle expired tokens)
      if (this.isExpired(account)) {
        return false;
      }
      return this.needsRefresh(account);
    });
  }

  /**
   * Perform a single refresh check iteration.
   * This is called periodically by the background interval.
   */
  private async runRefreshCheck(): Promise<void> {
    if (this.state.isRefreshing) {
      // Already refreshing - skip this iteration
      return;
    }

    if (!this.accountManager) {
      return;
    }

    this.state.isRefreshing = true;
    this.state.lastCheckTime = Date.now();

    try {
      const accountsToRefresh = this.getAccountsNeedingRefresh();

      if (accountsToRefresh.length === 0) {
        return;
      }

      log.debug("Found accounts needing refresh", { count: accountsToRefresh.length });

      // Refresh accounts serially to avoid concurrent refresh storms
      for (const account of accountsToRefresh) {
        if (!this.state.isRunning) {
          // Queue was stopped - abort
          break;
        }

        try {
          const auth = this.accountManager.toAuthDetails(account);
          const refreshed = await this.refreshToken(auth, account);

          if (refreshed) {
            this.accountManager.updateFromAuth(account, refreshed);
            this.state.refreshCount++;
            this.state.lastRefreshTime = Date.now();

            // Persist the refreshed token
            try {
              await this.accountManager.saveToDisk();
            } catch {
              // Non-fatal - token is refreshed in memory
            }
          }
        } catch (error) {
          this.state.errorCount++;
          // Log but don't throw - continue with other accounts
          log.warn("Failed to refresh account", {
            accountIndex: account.index,
            error: error instanceof Error ? error.message : String(error),
          });
        }
      }
    } finally {
      this.state.isRefreshing = false;
    }
  }

  /**
   * Refresh a single token.
   */
  private async refreshToken(
    auth: OAuthAuthDetails,
    account: ManagedAccount,
  ): Promise<OAuthAuthDetails | undefined> {
    const minutesUntilExpiry = account.expires
      ? Math.round((account.expires - Date.now()) / 60000)
      : "unknown";

    log.debug("Proactively refreshing token", {
      accountIndex: account.index,
      email: account.email ?? "unknown",
      minutesUntilExpiry,
    });

    return refreshAccessToken(auth, this.client, this.providerId);
  }

  /**
   * Start the background refresh queue.
   */
  start(): void {
    if (this.state.isRunning) {
      return;
    }

    if (!this.config.enabled) {
      log.debug("Proactive refresh disabled by config");
      return;
    }

    this.state.isRunning = true;
    const intervalMs = this.config.checkIntervalSeconds * 1000;

    log.debug("Started proactive refresh queue", {
      checkIntervalSeconds: this.config.checkIntervalSeconds,
      bufferSeconds: this.config.bufferSeconds,
    });

    // Run initial check after a short delay (let things settle)
    setTimeout(() => {
      if (this.state.isRunning) {
        this.runRefreshCheck().catch((error) => {
          log.error("Initial check failed", {
            error: error instanceof Error ? error.message : String(error),
          });
        });
      }
    }, 5000);

    // Set up periodic checks
    this.state.intervalHandle = setInterval(() => {
      this.runRefreshCheck().catch((error) => {
        log.error("Check failed", {
          error: error instanceof Error ? error.message : String(error),
        });
      });
    }, intervalMs);
  }

  /**
   * Stop the background refresh queue.
   */
  stop(): void {
    if (!this.state.isRunning) {
      return;
    }

    this.state.isRunning = false;

    if (this.state.intervalHandle) {
      clearInterval(this.state.intervalHandle);
      this.state.intervalHandle = null;
    }

    log.debug("Stopped proactive refresh queue", {
      refreshCount: this.state.refreshCount,
      errorCount: this.state.errorCount,
    });
  }

  /**
   * Get current queue statistics.
   */
  getStats(): {
    isRunning: boolean;
    isRefreshing: boolean;
    lastCheckTime: number;
    lastRefreshTime: number;
    refreshCount: number;
    errorCount: number;
  } {
    return { ...this.state };
  }

  /**
   * Check if the queue is currently running.
   */
  isRunning(): boolean {
    return this.state.isRunning;
  }
}

/**
 * Create a proactive refresh queue instance.
 */
export function createProactiveRefreshQueue(
  client: PluginClient,
  providerId: string,
  config?: Partial<ProactiveRefreshConfig>,
): ProactiveRefreshQueue {
  return new ProactiveRefreshQueue(client, providerId, config);
}