import fsp from 'node:fs/promises';

import { sessionsDb } from '@/modules/database/index.js';
import { providerRegistry } from '@/modules/providers/provider.registry.js';
import type {
  FetchHistoryOptions,
  FetchHistoryResult,
  LLMProvider,
  NormalizedMessage,
} from '@/shared/types.js';
import { AppError } from '@/shared/utils.js';

/**
 * Removes one file if it exists.
 */
async function removeFileIfExists(filePath: string): Promise<boolean> {
  try {
    await fsp.unlink(filePath);
    return true;
  } catch (error) {
    const code = (error as NodeJS.ErrnoException).code;
    if (code === 'ENOENT') {
      return false;
    }
    throw error;
  }
}

/**
 * Application service for provider-backed session message operations.
 *
 * Callers pass a provider id and this service resolves the concrete provider
 * class, keeping normalization/history call sites decoupled from implementation
 * file layout.
 */
export const sessionsService = {
  /**
   * Lists provider ids that can load session history and normalize live messages.
   */
  listProviderIds(): LLMProvider[] {
    return providerRegistry.listProviders().map((provider) => provider.id);
  },

  /**
   * Normalizes one provider-native event into frontend session message events.
   */
  normalizeMessage(
    providerName: string,
    raw: unknown,
    sessionId: string | null,
  ): NormalizedMessage[] {
    return providerRegistry.resolveProvider(providerName).sessions.normalizeMessage(raw, sessionId);
  },

  /**
   * Fetches persisted history by session id.
   *
   * Provider and provider-specific lookup hints are resolved from the indexed
   * session metadata in the database.
   */
  fetchHistory(
    sessionId: string,
    options: Pick<FetchHistoryOptions, 'limit' | 'offset'> = {},
  ): Promise<FetchHistoryResult> {
    const session = sessionsDb.getSessionById(sessionId);
    if (!session) {
      throw new AppError(`Session "${sessionId}" was not found.`, {
        code: 'SESSION_NOT_FOUND',
        statusCode: 404,
      });
    }

    const provider = session.provider as LLMProvider;
    return providerRegistry.resolveProvider(provider).sessions.fetchHistory(sessionId, {
      limit: options.limit ?? null,
      offset: options.offset ?? 0,
      projectPath: session.project_path ?? '',
    });
  },

  /**
   * Deletes one persisted session row by id.
   *
   * When `deletedFromDisk` is true and a session `jsonl_path` exists, the path
   * is deleted from disk before the DB row is removed.
   */
  async deleteSessionById(
    sessionId: string,
    deletedFromDisk = false,
  ): Promise<{ sessionId: string; deletedFromDisk: boolean }> {
    const session = sessionsDb.getSessionById(sessionId);
    if (!session) {
      throw new AppError(`Session "${sessionId}" was not found.`, {
        code: 'SESSION_NOT_FOUND',
        statusCode: 404,
      });
    }

    let removedFromDisk = false;
    if (deletedFromDisk && session.jsonl_path) {
      removedFromDisk = await removeFileIfExists(session.jsonl_path);
    }

    const deleted = sessionsDb.deleteSessionById(sessionId);
    if (!deleted) {
      throw new AppError(`Session "${sessionId}" was not found.`, {
        code: 'SESSION_NOT_FOUND',
        statusCode: 404,
      });
    }

    return { sessionId, deletedFromDisk: removedFromDisk };
  },

  /**
   * Renames one session by id without requiring the caller to pass provider.
   */
  renameSessionById(sessionId: string, summary: string): { sessionId: string; summary: string } {
    const session = sessionsDb.getSessionById(sessionId);
    if (!session) {
      throw new AppError(`Session "${sessionId}" was not found.`, {
        code: 'SESSION_NOT_FOUND',
        statusCode: 404,
      });
    }

    sessionsDb.updateSessionCustomName(sessionId, summary);
    return { sessionId, summary };
  },
};