/**
 * Vite configuration for the DMS frontend application.
 */
import { defineConfig, loadEnv } from 'vite';

/**
 * Parses a comma-separated environment value into normalized entries.
 *
 * @param rawValue Raw comma-separated value.
 * @returns List of non-empty normalized entries.
 */
function parseCsvList(rawValue: string | undefined): string[] {
  if (!rawValue) {
    return [];
  }

  return rawValue
    .split(',')
    .map((entry) => entry.trim())
    .filter((entry) => entry.length > 0);
}

/**
 * Extracts hostnames from CORS origin values.
 *
 * @param rawValue JSON array string or comma-separated origin list.
 * @returns Hostnames parsed from valid origins.
 */
function parseCorsOriginHosts(rawValue: string | undefined): string[] {
  if (!rawValue) {
    return [];
  }

  let origins: string[] = [];

  try {
    const parsedOrigins = JSON.parse(rawValue);
    if (Array.isArray(parsedOrigins)) {
      origins = parsedOrigins.filter((entry): entry is string => typeof entry === 'string');
    } else if (typeof parsedOrigins === 'string') {
      origins = [parsedOrigins];
    }
  } catch {
    origins = parseCsvList(rawValue);
  }

  return origins.flatMap((origin) => {
    try {
      const parsedUrl = new URL(origin);
      return parsedUrl.hostname ? [parsedUrl.hostname] : [];
    } catch {
      return [];
    }
  });
}

/**
 * Builds the Vite allowed host list from environment-driven inputs.
 *
 * @param env Environment variable key-value map.
 * @returns De-duplicated hostnames, or undefined to keep Vite defaults.
 */
function buildAllowedHosts(env: Record<string, string>): string[] | undefined {
  const explicitHosts = parseCsvList(env.VITE_ALLOWED_HOSTS);
  const corsOriginHosts = parseCorsOriginHosts(env.CORS_ORIGINS);
  const mergedHosts = Array.from(new Set([...explicitHosts, ...corsOriginHosts]));

  return mergedHosts.length > 0 ? mergedHosts : undefined;
}

/**
 * Exports frontend build and dev-server settings.
 */
export default defineConfig(({ mode }) => {
  const env = loadEnv(mode, process.cwd(), '');
  const allowedHosts = buildAllowedHosts(env);

  return {
    server: {
      host: '0.0.0.0',
      port: 5173,
      ...(allowedHosts ? { allowedHosts } : {}),
    },
  };
});