const DEFAULT_ALLOWED_METHODS = [
  "GET",
  "POST",
  "PUT",
  "PATCH",
  "DELETE",
  "OPTIONS",
];
const DEFAULT_ALLOWED_HEADERS = [
  "Content-Type",
  "Authorization",
  "X-Requested-With",
];
const DEFAULT_EXPOSED_HEADERS = ["Content-Length", "Content-Type"];
const IS_DEVELOPMENT = Deno.env.get("DEVELOPMENT") === "true";

export interface CorsOptions {
  allowedOrigins: Set<string>;
  allowCredentials?: boolean;
  allowedMethods?: string[];
  allowedHeaders?: string[];
  exposeHeaders?: string[];
  requestHeaders?: string | null;
  maxAgeSeconds?: number;
}

function normalizeOrigin(raw: string | null | undefined): string | null {
  if (!raw) return null;
  try {
    const trimmed = raw.trim();
    const hasScheme = /^https?:\/\//i.test(trimmed);
    const needsHttp = /^(localhost|127\.0\.0\.1)/i.test(trimmed);
    const candidate = hasScheme
      ? trimmed
      : `${needsHttp ? "http" : "https"}://${trimmed}`;
    const url = new URL(candidate);
    if (url.protocol !== "http:" && url.protocol !== "https:") {
      return null;
    }
    return `${url.protocol}//${url.host}`;
  } catch {
    return null;
  }
}

function parseOriginList(raw: string | null | undefined): Set<string> {
  const allowed = new Set<string>();
  if (!raw) return allowed;
  for (const entry of raw.split(",")) {
    const normalized = normalizeOrigin(entry.trim());
    if (normalized) {
      allowed.add(normalized);
    }
  }
  return allowed;
}

function deriveDefaultEdgeOrigins(): Set<string> {
  const allowed = new Set<string>();
  const redirectHome = normalizeOrigin(Deno.env.get("REDIRECT_HOME"));
  if (redirectHome) {
    allowed.add(redirectHome);
  }

  const hostname = Deno.env.get("HOSTNAME_DENO");
  const port = Deno.env.get("PORT");
  if (hostname && port) {
    const devOrigin = normalizeOrigin(`http://${hostname}:${port}`);
    if (devOrigin) {
      allowed.add(devOrigin);
    }
  }

  return allowed;
}

const EDGE_ALLOWED_ORIGINS = (() => {
  const fromEnv = parseOriginList(Deno.env.get("EDGE_ALLOWED_ORIGINS"));
  if (fromEnv.size > 0) {
    return fromEnv;
  }
  return deriveDefaultEdgeOrigins();
})();

const ISLAND_ALLOWED_ORIGINS = new Set([
  "https://cyberhybridhub.com",
  "http://cyberhybridhub.com",
  "http://localhost:8080",
  "http://96.3.218.128",
  "https://96.3.218.126",
]);

function mergeVary(current: string | null, incoming: string): string {
  const parts = new Set<string>();
  for (const entry of (current ?? "").split(",")) {
    const trimmed = entry.trim();
    if (trimmed) {
      parts.add(trimmed);
    }
  }
  for (const entry of incoming.split(",")) {
    const trimmed = entry.trim();
    if (trimmed) {
      parts.add(trimmed);
    }
  }
  return Array.from(parts).join(", ");
}

function buildAllowedHeaders(
  baseHeaders: string[],
  requestHeaders?: string | null,
): string[] {
  const allowed = new Set(baseHeaders.map((header) => header.toLowerCase()));
  if (requestHeaders) {
    for (const header of requestHeaders.split(",")) {
      const trimmed = header.trim();
      if (trimmed) {
        allowed.add(trimmed.toLowerCase());
      }
    }
  }
  return Array.from(allowed).map((header) =>
    header
      .split("-")
      .map((part) => part.charAt(0).toUpperCase() + part.slice(1))
      .join("-")
  );
}

export function isIslandFetchRequestAllowed(
  url: URL,
  originHeader?: string | null,
): boolean {
  if (IS_DEVELOPMENT) return true;

  // Check if the request origin is allowed
  if (originHeader) {
    const normalizedOrigin = normalizeOrigin(originHeader);
    if (normalizedOrigin && ISLAND_ALLOWED_ORIGINS.has(normalizedOrigin)) {
      return true;
    }
  }

  // Fallback to checking the URL origin
  return ISLAND_ALLOWED_ORIGINS.has(url.origin);
}

export function getCorsHeaders(
  origin: string | null,
  options: CorsOptions,
): Headers {
  const headers = new Headers();
  const normalizedOrigin = normalizeOrigin(origin);
  if (!normalizedOrigin || !options.allowedOrigins.has(normalizedOrigin)) {
    return headers;
  }

  headers.set("Access-Control-Allow-Origin", normalizedOrigin);
  headers.set(
    "Access-Control-Allow-Methods",
    (options.allowedMethods ?? DEFAULT_ALLOWED_METHODS).join(", "),
  );
  headers.set(
    "Access-Control-Allow-Headers",
    buildAllowedHeaders(
      options.allowedHeaders ?? DEFAULT_ALLOWED_HEADERS,
      options.requestHeaders,
    ).join(", "),
  );
  headers.set(
    "Access-Control-Expose-Headers",
    (options.exposeHeaders ?? DEFAULT_EXPOSED_HEADERS).join(", "),
  );
  if (options.allowCredentials ?? true) {
    headers.set("Access-Control-Allow-Credentials", "true");
  }
  if (options.maxAgeSeconds) {
    headers.set("Access-Control-Max-Age", `${options.maxAgeSeconds}`);
  }
  headers.set(
    "Vary",
    "Origin, Access-Control-Request-Method, Access-Control-Request-Headers",
  );
  return headers;
}

export function getEdgeCorsHeaders(
  origin: string | null,
  requestHeaders?: string | null,
): Headers {
  return getCorsHeaders(origin, {
    allowedOrigins: EDGE_ALLOWED_ORIGINS,
    requestHeaders,
  });
}

export function getIslandCorsHeaders(
  origin: string | null,
  requestHeaders?: string | null,
): Headers {
  return getCorsHeaders(origin, {
    allowedOrigins: ISLAND_ALLOWED_ORIGINS,
    requestHeaders,
  });
}

export function withCors(response: Response, corsHeaders: Headers): Response {
  if (!corsHeaders || corsHeaders.values().toArray().length === 0) {
    return response;
  }
  const headers = new Headers(response.headers);
  for (const [key, value] of corsHeaders.entries()) {
    if (key.toLowerCase() === "vary") {
      headers.set("Vary", mergeVary(headers.get("Vary"), value));
    } else {
      headers.set(key, value);
    }
  }
  return new Response(response.body, {
    status: response.status,
    statusText: response.statusText,
    headers,
  });
}

export function createCorsPreflightResponse(
  _request: Request,
  corsHeaders: Headers,
): Response {
  if (!corsHeaders || !corsHeaders.get("Access-Control-Allow-Origin")) {
    return new Response("Forbidden", { status: 403 });
  }
  return new Response(null, { status: 204, headers: corsHeaders });
}

export function getEdgeAllowedOrigins(): string[] {
  return Array.from(EDGE_ALLOWED_ORIGINS);
}