/**
 * Speech Services Configuration
 *
 * Issue #401: Environment variables and validation for STT (speech-to-text),
 * TTS (text-to-speech), and speech service limits.
 *
 * Validates conditional requirements at startup:
 * - STT_BASE_URL is required when STT_ENABLED=true
 * - TTS_DEFAULT_URL is required when TTS_ENABLED=true
 * - TTS_PREMIUM_URL is required when TTS_PREMIUM_ENABLED=true
 * - TTS_FALLBACK_URL is required when TTS_FALLBACK_ENABLED=true
 */

import { registerAs } from "@nestjs/config";

// ==========================================
// Default values
// ==========================================

const STT_DEFAULTS = {
  baseUrl: "http://speaches:8000/v1",
  model: "Systran/faster-whisper-large-v3-turbo",
  language: "en",
} as const;

const TTS_DEFAULT_DEFAULTS = {
  url: "http://kokoro-tts:8880/v1",
  voice: "af_heart",
  format: "mp3",
} as const;

const TTS_PREMIUM_DEFAULTS = {
  url: "http://chatterbox-tts:8881/v1",
} as const;

const TTS_FALLBACK_DEFAULTS = {
  url: "http://openedai-speech:8000/v1",
} as const;

const LIMITS_DEFAULTS = {
  maxUploadSize: 25_000_000,
  maxDurationSeconds: 600,
  maxTextLength: 4096,
} as const;

// ==========================================
// Types
// ==========================================

export interface SttConfig {
  enabled: boolean;
  baseUrl: string;
  model: string;
  language: string;
}

export interface TtsDefaultConfig {
  enabled: boolean;
  url: string;
  voice: string;
  format: string;
}

export interface TtsPremiumConfig {
  enabled: boolean;
  url: string;
}

export interface TtsFallbackConfig {
  enabled: boolean;
  url: string;
}

export interface TtsConfig {
  default: TtsDefaultConfig;
  premium: TtsPremiumConfig;
  fallback: TtsFallbackConfig;
}

export interface SpeechLimitsConfig {
  maxUploadSize: number;
  maxDurationSeconds: number;
  maxTextLength: number;
}

export interface SpeechConfig {
  stt: SttConfig;
  tts: TtsConfig;
  limits: SpeechLimitsConfig;
}

// ==========================================
// Helper: parse boolean env var
// ==========================================

function parseBooleanEnv(value: string | undefined): boolean {
  return value === "true" || value === "1";
}

// ==========================================
// Enabled checks
// ==========================================

/**
 * Check if speech-to-text (STT) is enabled via environment variable.
 */
export function isSttEnabled(): boolean {
  return parseBooleanEnv(process.env.STT_ENABLED);
}

/**
 * Check if text-to-speech (TTS) default engine is enabled via environment variable.
 */
export function isTtsEnabled(): boolean {
  return parseBooleanEnv(process.env.TTS_ENABLED);
}

/**
 * Check if TTS premium engine (Chatterbox) is enabled via environment variable.
 */
export function isTtsPremiumEnabled(): boolean {
  return parseBooleanEnv(process.env.TTS_PREMIUM_ENABLED);
}

/**
 * Check if TTS fallback engine (Piper/OpenedAI) is enabled via environment variable.
 */
export function isTtsFallbackEnabled(): boolean {
  return parseBooleanEnv(process.env.TTS_FALLBACK_ENABLED);
}

// ==========================================
// Validation helpers
// ==========================================

/**
 * Check if an environment variable has a non-empty value.
 */
function isEnvVarSet(envVar: string): boolean {
  const value = process.env[envVar];
  return value !== undefined && value.trim() !== "";
}

/**
 * Validate that required env vars are set when a service is enabled.
 * Throws with a helpful error message listing missing vars and how to disable.
 */
function validateRequiredVars(
  serviceName: string,
  enabledFlag: string,
  requiredVars: string[]
): void {
  const missingVars: string[] = [];

  for (const envVar of requiredVars) {
    if (!isEnvVarSet(envVar)) {
      missingVars.push(envVar);
    }
  }

  if (missingVars.length > 0) {
    throw new Error(
      `${serviceName} is enabled (${enabledFlag}=true) but required environment variables are missing or empty: ${missingVars.join(", ")}. ` +
        `Either set these variables or disable by setting ${enabledFlag}=false.`
    );
  }
}

/**
 * Validate that a numeric env var, if set, is a positive integer.
 */
function validatePositiveInteger(envVar: string): void {
  const value = process.env[envVar];
  if (value === undefined || value.trim() === "") {
    return; // Not set, will use default
  }

  const parsed = parseInt(value, 10);
  if (isNaN(parsed) || parsed <= 0 || String(parsed) !== value.trim()) {
    throw new Error(`${envVar} must be a positive integer. Current value: "${value}".`);
  }
}

// ==========================================
// Main validation
// ==========================================

/**
 * Validates speech configuration at startup.
 * Call this during module initialization to fail fast if misconfigured.
 *
 * Validates:
 * - STT_BASE_URL is set when STT_ENABLED=true
 * - TTS_DEFAULT_URL is set when TTS_ENABLED=true
 * - TTS_PREMIUM_URL is set when TTS_PREMIUM_ENABLED=true
 * - TTS_FALLBACK_URL is set when TTS_FALLBACK_ENABLED=true
 * - Numeric limits are positive integers (when set)
 *
 * @throws Error if any required configuration is missing or invalid
 */
export function validateSpeechConfig(): void {
  // STT validation
  if (isSttEnabled()) {
    validateRequiredVars("STT", "STT_ENABLED", ["STT_BASE_URL"]);
  }

  // TTS default validation
  if (isTtsEnabled()) {
    validateRequiredVars("TTS", "TTS_ENABLED", ["TTS_DEFAULT_URL"]);
  }

  // TTS premium validation
  if (isTtsPremiumEnabled()) {
    validateRequiredVars("TTS premium", "TTS_PREMIUM_ENABLED", ["TTS_PREMIUM_URL"]);
  }

  // TTS fallback validation
  if (isTtsFallbackEnabled()) {
    validateRequiredVars("TTS fallback", "TTS_FALLBACK_ENABLED", ["TTS_FALLBACK_URL"]);
  }

  // Limits validation (only if set, otherwise defaults are used)
  validatePositiveInteger("SPEECH_MAX_UPLOAD_SIZE");
  validatePositiveInteger("SPEECH_MAX_DURATION_SECONDS");
  validatePositiveInteger("SPEECH_MAX_TEXT_LENGTH");
}

// ==========================================
// Config getter
// ==========================================

/**
 * Get the full speech configuration object with typed values and defaults.
 *
 * @returns SpeechConfig with all STT, TTS, and limits configuration
 */
export function getSpeechConfig(): SpeechConfig {
  return {
    stt: {
      enabled: isSttEnabled(),
      baseUrl: process.env.STT_BASE_URL ?? STT_DEFAULTS.baseUrl,
      model: process.env.STT_MODEL ?? STT_DEFAULTS.model,
      language: process.env.STT_LANGUAGE ?? STT_DEFAULTS.language,
    },
    tts: {
      default: {
        enabled: isTtsEnabled(),
        url: process.env.TTS_DEFAULT_URL ?? TTS_DEFAULT_DEFAULTS.url,
        voice: process.env.TTS_DEFAULT_VOICE ?? TTS_DEFAULT_DEFAULTS.voice,
        format: process.env.TTS_DEFAULT_FORMAT ?? TTS_DEFAULT_DEFAULTS.format,
      },
      premium: {
        enabled: isTtsPremiumEnabled(),
        url: process.env.TTS_PREMIUM_URL ?? TTS_PREMIUM_DEFAULTS.url,
      },
      fallback: {
        enabled: isTtsFallbackEnabled(),
        url: process.env.TTS_FALLBACK_URL ?? TTS_FALLBACK_DEFAULTS.url,
      },
    },
    limits: {
      maxUploadSize: parseInt(
        process.env.SPEECH_MAX_UPLOAD_SIZE ?? String(LIMITS_DEFAULTS.maxUploadSize),
        10
      ),
      maxDurationSeconds: parseInt(
        process.env.SPEECH_MAX_DURATION_SECONDS ?? String(LIMITS_DEFAULTS.maxDurationSeconds),
        10
      ),
      maxTextLength: parseInt(
        process.env.SPEECH_MAX_TEXT_LENGTH ?? String(LIMITS_DEFAULTS.maxTextLength),
        10
      ),
    },
  };
}

// ==========================================
// NestJS ConfigModule registerAs factory
// ==========================================

/**
 * NestJS ConfigModule namespace factory for speech configuration.
 *
 * Usage in a module:
 * ```typescript
 * import { speechConfig } from './speech.config';
 *
 * @Module({
 *   imports: [ConfigModule.forFeature(speechConfig)],
 * })
 * export class SpeechModule {}
 * ```
 *
 * Then inject via ConfigService:
 * ```typescript
 * constructor(private config: ConfigService) {
 *   const sttUrl = this.config.get<string>('speech.stt.baseUrl');
 * }
 * ```
 */
export const speechConfig = registerAs("speech", (): SpeechConfig => {
  return getSpeechConfig();
});