/**
 * Runtime configuration for the realtime gateway.
 *
 * All values come from environment variables (see ../.env.example).
 * This module is pure: it parses and validates only — no I/O, no side
 * effects — so it can be unit-tested by passing an explicit env object.
 */

export interface RealtimeConfig {
  /** WebSocket gateway port (ws). */
  port: number
  /** HTTP health/metrics port. */
  healthPort: number
  /** Shared JWT secret (HS256) used to verify client tokens. Required. */
  jwtSecret: string
  /** Redis connection URL (cross-node fan-out, presence). */
  redisUrl: string
  /** API base URL (token/session verification fallback). */
  apiUrl: string
  /** Pino log level: fatal | error | warn | info | debug | trace. */
  logLevel: string
  /** Rate-limit window in milliseconds per client. */
  rateLimitWindowMs: number
  /** Max messages per client per window. */
  rateLimitMax: number
  /** Maximum sockets per document room. */
  maxRoomSize: number
  /** Use the Redis update log + presence (REALTIME_REDIS=0 → in-memory, dev). */
  useRedis: boolean
  /** Use the Prisma doc store + resolvers (REALTIME_DB=0 → in-memory/fail-closed, dev). */
  useDatabase: boolean
  /**
   * The shared service token for the API's internal endpoints
   * (`INTERNAL_SERVICE_TOKEN`, TASK-0092 slice 2). Non-empty → the doc
   * store talks to the API over HTTP (`HttpDocStore`); empty → the
   * in-process Prisma store (single-node dev) — the fail-closed contract
   * (an empty token never opens the internal surface).
   */
  internalServiceToken: string
  /** Trust the X-Forwarded-For client IP (server behind a proxy). */
  trustProxy: boolean
}

/** Parse an integer env var; throws a descriptive error on bad values. */
function parseIntEnv(name: string, value: string | undefined, fallback: number): number {
  if (value === undefined || value === '') return fallback
  const parsed = Number.parseInt(value, 10)
  if (!Number.isInteger(parsed) || parsed <= 0) {
    throw new Error(`Invalid value for ${name}: "${value}" (expected a positive integer)`)
  }
  return parsed
}

/** Parse a boolean env var; treats "0"/"false" (case-insensitive) as false. */
function parseBoolEnv(name: string, value: string | undefined, fallback: boolean): boolean {
  if (value === undefined || value === '') return fallback
  return !/^(0|false|no|off)$/i.test(value.trim())
}

/**
 * Load and validate the realtime configuration.
 *
 * Reads `env` (defaults to `process.env`). Throws when `JWT_SECRET` is
 * missing or empty — the gateway cannot securely accept connections
 * without a signing secret.
 */
export function loadConfig(env: NodeJS.ProcessEnv = process.env): RealtimeConfig {
  const jwtSecret = env.JWT_SECRET?.trim() ?? ''
  if (jwtSecret.length === 0) {
    throw new Error('Missing required environment variable: JWT_SECRET')
  }

  return {
    // `REALTIME_PORT` is the documented gateway port (docs/development/
    // development-guide.md); it must NOT fall back to the shared `PORT` env,
    // which in the dev stack is the API's 4000 (that collision was a latent
    // bug: the gateway tried to bind :4000 and died with EADDRINUSE).
    // `PORT` is kept as an explicit fallback for standalone runs.
    port: parseIntEnv('REALTIME_PORT', env.REALTIME_PORT ?? env.PORT, 4001),
    healthPort: parseIntEnv('REALTIME_HEALTH_PORT', env.REALTIME_HEALTH_PORT ?? env.HEALTH_PORT, 4002),
    jwtSecret,
    redisUrl: env.REDIS_URL ?? 'redis://localhost:6379',
    apiUrl: env.API_URL ?? 'http://localhost:4000',
    logLevel: env.LOG_LEVEL ?? 'info',
    rateLimitWindowMs: parseIntEnv('RATE_LIMIT_WINDOW_MS', env.RATE_LIMIT_WINDOW_MS, 60000),
    rateLimitMax: parseIntEnv('RATE_LIMIT_MAX', env.RATE_LIMIT_MAX, 300),
    maxRoomSize: parseIntEnv('MAX_ROOM_SIZE', env.MAX_ROOM_SIZE, 200),
    useRedis: parseBoolEnv('REALTIME_REDIS', env.REALTIME_REDIS, true),
    useDatabase: parseBoolEnv('REALTIME_DB', env.REALTIME_DB, true),
    internalServiceToken: env.INTERNAL_SERVICE_TOKEN?.trim() ?? '',
    trustProxy: parseBoolEnv('REALTIME_TRUST_PROXY', env.REALTIME_TRUST_PROXY, false),
  }
}