/**
 * Lightweight fetch wrapper that:
 * - Adds an X-Correlation-ID header to every request
 * - Exposes helpers to parse the standard error envelope
 * - Provides helpers to build user-facing error messages with correlation ID
 */
(function () {
  // Ensure global app object exists
  window.app = window.app || {};

  const CORRELATION_HEADER = 'X-Correlation-ID';

  function generateCorrelationId() {
    try {
      if (window.crypto && typeof window.crypto.randomUUID === 'function') {
        return window.crypto.randomUUID();
      }
    } catch (_) {}
    // Fallback RFC4122-ish UUID
    const s4 = () => Math.floor((1 + Math.random()) * 0x10000).toString(16).slice(1);
    return (
      s4() + s4() + '-' + s4() + '-' + s4() + '-' +
      s4() + '-' + s4() + s4() + s4()
    );
  }

  function normalizeHeaders(input) {
    if (!input) return new Headers();
    return input instanceof Headers ? input : new Headers(input);
  }

  const originalFetch = window.fetch.bind(window);

  async function wrappedFetch(resource, options = {}) {
    const url = typeof resource === 'string' ? resource : (resource && resource.url) || '';
    const headers = normalizeHeaders(options.headers);

    // Inject correlation id if not present
    let outgoingCid = headers.get(CORRELATION_HEADER);
    if (!outgoingCid) {
      outgoingCid = generateCorrelationId();
      headers.set(CORRELATION_HEADER, outgoingCid);
    }

    // Inject Authorization header if JWT token is available and not already provided
    try {
      const storedToken = (window.app && window.app.token) || (typeof localStorage !== 'undefined' && localStorage.getItem('auth_token'));
      if (storedToken && !headers.has('Authorization')) {
        headers.set('Authorization', `Bearer ${storedToken}`);
      }
    } catch (_) {
      // Ignore storage access errors (e.g., privacy mode)
    }

    const requestInit = { ...options, headers };

    const response = await originalFetch(resource, requestInit);

    try {
      const incomingCid = (response && response.headers && response.headers.get(CORRELATION_HEADER)) || null;
      // Track last seen correlation id for diagnostics/UI messaging
      window.app.lastCorrelationId = incomingCid || outgoingCid || null;
    } catch (_) {}

    return response;
  }

  /**
   * Parse the standardized error envelope from a failed response.
   * Returns a normalized object with message, correlationId, code, details.
   */
  async function parseErrorEnvelope(response) {
    let body = null;
    try {
      body = await response.clone().json();
    } catch (_) {
      // not JSON; try text as last resort
      try {
        const txt = await response.clone().text();
        body = { detail: txt };
      } catch (_) {
        body = null;
      }
    }

    const headerCid = response && response.headers ? response.headers.get(CORRELATION_HEADER) : null;
    const envelopeCid = body && (body.correlation_id || (body.error && body.error.correlation_id));
    const correlationId = headerCid || envelopeCid || window.app.lastCorrelationId || null;

    const message = body && body.error && body.error.message
      ? String(body.error.message)
      : body && typeof body.detail === 'string' && body.detail.trim()
        ? String(body.detail)
        : `HTTP ${response.status}`;

    const code = body && body.error ? (body.error.code || null) : null;
    const details = body && body.error ? (body.error.details || null) : null;

    return { message, correlationId, code, details, raw: body };
  }

  /**
   * Create an Error populated from a failed Response and optional fallback message.
   */
  async function toError(response, fallbackMessage = null) {
    const parsed = await parseErrorEnvelope(response);
    const msg = parsed && parsed.message ? parsed.message : (fallbackMessage || `HTTP ${response.status}`);
    const err = new Error(msg);
    err.status = response.status;
    err.correlationId = parsed.correlationId || null;
    if (parsed && parsed.code) err.code = parsed.code;
    if (parsed && parsed.details) err.details = parsed.details;
    return err;
  }

  /**
   * Format a message suitable for UI alerts with correlation id reference.
   * Example: formatAlert(err, 'Error saving customer')
   */
  function formatAlert(errorOrMessage, prefix = null) {
    const isError = errorOrMessage instanceof Error;
    const message = isError ? errorOrMessage.message : String(errorOrMessage || '');
    const correlationId = isError && errorOrMessage.correlationId
      ? errorOrMessage.correlationId
      : (window.app && window.app.lastCorrelationId) || null;
    const base = prefix ? `${prefix}: ${message}` : message;
    return correlationId ? `${base} (Ref: ${correlationId})` : base;
  }

  // Expose helpers
  window.http = {
    parseErrorEnvelope,
    toError,
    formatAlert,
  };

  // Install wrapper
  window.fetch = wrappedFetch;
})();