import { randomUUID } from 'node:crypto';
import fs from 'node:fs';
import { mkdir, readFile, readdir, stat, writeFile } from 'node:fs/promises';
import path from 'node:path';
import readline from 'node:readline';

import type { NextFunction, Request, RequestHandler, Response } from 'express';

import type {
  AnyRecord,
  ApiSuccessShape,
  AppErrorOptions,
  NormalizedMessage,
} from '@/shared/types.js';

//----------------- NORMALIZED MESSAGE HELPER INPUT TYPES ------------
/**
 * Input payload accepted by `createNormalizedMessage`.
 *
 * Callers provide provider-specific fields plus the required `kind/provider`
 * pair; this helper fills missing envelope fields (`id`, `sessionId`,
 * `timestamp`) in a consistent way.
 */
type NormalizedMessageInput =
  {
    kind: NormalizedMessage['kind'];
    provider: NormalizedMessage['provider'];
    id?: string | null;
    sessionId?: string | null;
    timestamp?: string | null;
  } & Record<string, unknown>;

// ---------------------------
//----------------- HTTP HANDLER UTILITIES ------------
/**
 * Wraps arbitrary data in the standard API success envelope.
 *
 * Use this helper in route handlers to keep successful JSON responses consistent
 * across endpoints.
 */
export function createApiSuccessResponse<TData>(
  data: TData,
): ApiSuccessShape<TData> {
  return {
    success: true,
    data,
  };
}

/**
 * Converts an async Express handler into a standard `RequestHandler` and routes
 * rejected promises to Express error middleware.
 *
 * Use this to avoid repeating `try/catch(next)` in every async route.
 */
export function asyncHandler(
  handler: (req: Request, res: Response, next: NextFunction) => Promise<unknown>
): RequestHandler {
  return (req, res, next) => {
    void Promise.resolve(handler(req, res, next)).catch(next);
  };
}

// ---------------------------
//----------------- SHARED ERROR UTILITIES ------------
/**
 * Shared application error with HTTP status and machine-readable code metadata.
 *
 * Throw this from service/route layers when the caller should receive a
 * controlled error response rather than a generic 500.
 */
export class AppError extends Error {
  readonly code: string;
  readonly statusCode: number;
  readonly details?: unknown;

  constructor(message: string, options: AppErrorOptions = {}) {
    super(message);
    this.name = 'AppError';
    this.code = options.code ?? 'INTERNAL_ERROR';
    this.statusCode = options.statusCode ?? 500;
    this.details = options.details;
  }
}

// ---------------------------
//----------------- NORMALIZED PROVIDER MESSAGE UTILITIES ------------
/**
 * Generates a stable unique id for normalized provider messages.
 */
export function generateMessageId(prefix = 'msg'): string {
  return `${prefix}_${randomUUID()}`;
}

/**
 * Creates a normalized provider message and fills the shared envelope fields.
 *
 * Provider adapters and live SDK handlers pass through provider-specific fields,
 * while this helper guarantees every emitted event has an id, session id,
 * timestamp, and provider marker.
 */
export function createNormalizedMessage(fields: NormalizedMessageInput): NormalizedMessage {
  return {
    ...fields,
    id: fields.id || generateMessageId(fields.kind),
    sessionId: fields.sessionId || '',
    timestamp: fields.timestamp || new Date().toISOString(),
    provider: fields.provider,
  };
}

// ---------------------------
//----------------- MCP CONFIG PARSING UTILITIES ------------
/**
 * Safely narrows an unknown value to a plain object record.
 *
 * This deliberately rejects arrays, `null`, and primitive values so callers can
 * treat the returned value as a JSON-style object map without repeating the same
 * defensive shape checks at every config read site.
 */
export const readObjectRecord = (value: any): AnyRecord | null => {
  if (!value || typeof value !== 'object' || Array.isArray(value)) {
    return null;
  }

  return value as AnyRecord;
};

/**
 * Reads an optional string from unknown input and normalizes empty or whitespace-only
 * values to `undefined`.
 *
 * This is useful when parsing config files where a field may be missing, present
 * with the wrong type, or present as an empty string that should be treated as
 * "not configured".
 */
export const readOptionalString = (value: unknown): string | undefined => {
  if (typeof value !== 'string') {
    return undefined;
  }

  const normalized = value.trim();
  return normalized.length > 0 ? normalized : undefined;
};

/**
 * Reads an optional string array from unknown input.
 *
 * Non-array values are ignored, and any array entries that are not strings are
 * filtered out. This lets provider config readers consume loosely shaped JSON/TOML
 * data without failing on incidental invalid members.
 */
export const readStringArray = (value: unknown): string[] | undefined => {
  if (!Array.isArray(value)) {
    return undefined;
  }

  return value.filter((entry): entry is string => typeof entry === 'string');
};

/**
 * Reads an optional string-to-string map from unknown input.
 *
 * The function first ensures the source value is a plain object, then keeps only
 * keys whose values are strings. If no valid entries remain, it returns `undefined`
 * so callers can distinguish "no usable map" from an empty object that was
 * intentionally authored downstream.
 */
export const readStringRecord = (value: unknown): Record<string, string> | undefined => {
  const record = readObjectRecord(value);
  if (!record) {
    return undefined;
  }

  const normalized: Record<string, string> = {};
  for (const [key, entry] of Object.entries(record)) {
    if (typeof entry === 'string') {
      normalized[key] = entry;
    }
  }

  return Object.keys(normalized).length > 0 ? normalized : undefined;
};

/**
 * Reads a JSON config file and guarantees a plain object result.
 *
 * Missing files are treated as an empty config object so provider-specific MCP
 * readers can operate against first-run environments without special-case file
 * existence checks. If the file exists but contains invalid JSON, the parse error
 * is preserved and rethrown.
 */
export const readJsonConfig = async (filePath: string): Promise<Record<string, unknown>> => {
  try {
    const content = await readFile(filePath, 'utf8');
    const parsed = JSON.parse(content) as Record<string, unknown>;
    return readObjectRecord(parsed) ?? {};
  } catch (error) {
    const code = (error as NodeJS.ErrnoException).code;
    if (code === 'ENOENT') {
      return {};
    }

    throw error;
  }
};

/**
 * Writes a JSON config file with stable, human-readable formatting.
 *
 * The parent directory is created automatically so callers can persist config into
 * provider-specific folders without pre-creating the directory tree. Output always
 * ends with a trailing newline to keep the file diff-friendly.
 */
export const writeJsonConfig = async (filePath: string, data: Record<string, unknown>): Promise<void> => {
  await mkdir(path.dirname(filePath), { recursive: true });
  await writeFile(filePath, `${JSON.stringify(data, null, 2)}\n`, 'utf8');
};

// ---------------------------
//----------------- SESSION SYNCHRONIZER TITLE HELPERS ------------
/**
 * Produces a compact session title suitable for UI rendering and DB storage.
 *
 * Use this when converting provider-native names into a consistent title value.
 * The helper collapses repeated whitespace, trims the result, and truncates it
 * to 120 characters so every provider writes stable and bounded metadata.
 * If the normalized input is empty, it returns the supplied fallback title.
 */
export function normalizeSessionName(rawValue: string | undefined, fallback: string): string {
  const normalized = (rawValue ?? '').replace(/\s+/g, ' ').trim();
  if (!normalized) {
    return fallback;
  }

  return normalized.slice(0, 120);
}

// ---------------------------
//----------------- SESSION SYNCHRONIZER FILESYSTEM HELPERS ------------
/**
 * Recursively discovers files that match one extension, with optional incremental filtering.
 *
 * Provider synchronizers call this to find transcript artifacts under provider
 * home directories. Pass `lastScanAt` to include only files created after the
 * previous scan, or pass `null` to perform a full rescan. Missing directories
 * are treated as empty because not every provider exists on every machine.
 */
export async function findFilesRecursivelyCreatedAfter(
  rootDir: string,
  extension: string,
  lastScanAt: Date | null,
  fileList: string[] = []
): Promise<string[]> {
  try {
    const entries = await readdir(rootDir, { withFileTypes: true });
    for (const entry of entries) {
      const fullPath = path.join(rootDir, entry.name);

      if (entry.isDirectory()) {
        await findFilesRecursivelyCreatedAfter(fullPath, extension, lastScanAt, fileList);
        continue;
      }

      if (!entry.isFile() || !entry.name.endsWith(extension)) {
        continue;
      }

      if (!lastScanAt) {
        fileList.push(fullPath);
        continue;
      }

      const fileStat = await stat(fullPath);
      if (fileStat.birthtime > lastScanAt) {
        fileList.push(fullPath);
      }
    }
  } catch {
    // Missing provider folders are expected in first-run or partial setups.
  }

  return fileList;
}

/**
 * Reads file creation/update timestamps and maps them to DB-friendly ISO strings.
 *
 * Session indexers use this to persist `created_at` and `updated_at` metadata
 * when upserting sessions. If the file cannot be read, an empty object is
 * returned so indexing can continue for other files.
 */
export async function readFileTimestamps(
  filePath: string
): Promise<{ createdAt?: string; updatedAt?: string }> {
  try {
    const fileStat = await stat(filePath);
    return {
      createdAt: fileStat.birthtime.toISOString(),
      updatedAt: fileStat.mtime.toISOString(),
    };
  } catch {
    return {};
  }
}

// ---------------------------
//----------------- SESSION SYNCHRONIZER JSONL PARSING HELPERS ------------
/**
 * Builds a first-seen key/value lookup map from a JSONL file.
 *
 * Use this for provider index files where session id -> display name metadata
 * is stored line-by-line. The first value for each key wins, preserving the
 * earliest known label while avoiding repeated map overwrites.
 */
export async function buildLookupMap(
  filePath: string,
  keyField: string,
  valueField: string
): Promise<Map<string, string>> {
  const lookup = new Map<string, string>();

  try {
    const fileStream = fs.createReadStream(filePath);
    const lineReader = readline.createInterface({ input: fileStream, crlfDelay: Infinity });

    for await (const line of lineReader) {
      const trimmed = line.trim();
      if (!trimmed) {
        continue;
      }

      const parsed = JSON.parse(trimmed) as Record<string, unknown>;
      const key = parsed[keyField];
      const value = parsed[valueField];

      if (typeof key === 'string' && typeof value === 'string' && !lookup.has(key)) {
        lookup.set(key, value);
      }
    }
  } catch {
    // Missing or unreadable lookup files should not block session sync.
  }

  return lookup;
}

/**
 * Reads a JSONL file and returns the first extracted payload that matches caller criteria.
 *
 * The caller supplies an `extractor` that validates provider-specific row
 * shapes. This helper centralizes line-by-line parsing and lets indexers stop
 * scanning as soon as one valid row is found.
 */
export async function extractFirstValidJsonlData<T>(
  filePath: string,
  extractor: (parsedJson: unknown) => T | null | undefined
): Promise<T | null> {
  try {
    const fileStream = fs.createReadStream(filePath);
    const lineReader = readline.createInterface({ input: fileStream, crlfDelay: Infinity });

    for await (const line of lineReader) {
      const trimmed = line.trim();
      if (!trimmed) {
        continue;
      }

      const parsed = JSON.parse(trimmed);
      const extracted = extractor(parsed);
      if (extracted) {
        lineReader.close();
        fileStream.close();
        return extracted;
      }
    }
  } catch {
    // Ignore malformed or missing artifacts so full scans keep progressing.
  }

  return null;
}