import type { AuthDiagnostic, GroupCatalog } from "./group-catalog.js";
import { isUsableAuthenticationSecret } from "./secret-policy.js";
import { parseConfiguredTransportUrl } from "./url-policy.js";

const MAX_RESPONSE_BYTES = 1024 * 1024;
const REQUEST_TIMEOUT_MS = 5_000;

export interface AuthentikGroupCatalogOptions {
  baseUrl: string;
  apiToken: string;
  fetch?: typeof globalThis.fetch;
}

function diagnostic(
  code: AuthDiagnostic["code"],
  message: string,
  field?: string,
): AuthDiagnostic {
  return { level: "error", code, message, ...(field === undefined ? {} : { field }) };
}

function catalogUnreachable(): AuthDiagnostic {
  return diagnostic("oidc_group_catalog_unreachable", "The configured group catalog is unavailable.");
}

function catalogUnauthorized(): AuthDiagnostic {
  return diagnostic("oidc_group_catalog_unauthorized", "The configured group catalog credentials were rejected.");
}

function missing(name: string): AuthDiagnostic {
  return diagnostic("oidc_mapped_group_missing", "A configured authorization group does not exist.", name);
}

function ambiguous(name: string): AuthDiagnostic {
  return diagnostic("oidc_mapped_group_ambiguous", "A configured authorization group is ambiguous.", name);
}

function stableCompare(left: string, right: string): number {
  return left < right ? -1 : left > right ? 1 : 0;
}

function abortReason(signal: AbortSignal): unknown {
  return signal.reason ?? new DOMException("The operation was aborted", "AbortError");
}

function cancelResponse(response: Response): void {
  try {
    const cancelled = response.body?.cancel();
    if (cancelled) void cancelled.catch(() => undefined);
  } catch { /* cancellation is advisory and never changes the diagnostic */ }
}

function cancelReader(reader: ReadableStreamDefaultReader<Uint8Array>): void {
  try {
    const cancelled = reader.cancel();
    void cancelled.catch(() => undefined);
  } catch { /* cancellation is advisory and never changes the diagnostic */ }
}

function awaitWithAbort<T>(
  operation: Promise<T>,
  signal: AbortSignal,
  onLateResolution?: (value: T) => void,
): Promise<T> {
  return new Promise<T>((resolve, reject) => {
    let settled = false;
    const abort = () => {
      if (settled) return;
      settled = true;
      signal.removeEventListener("abort", abort);
      reject(abortReason(signal));
    };
    if (signal.aborted) {
      abort();
      return;
    }
    signal.addEventListener("abort", abort, { once: true });
    operation.then(
      (value) => {
        if (settled) {
          try { onLateResolution?.(value); } catch { /* best-effort cleanup only */ }
          return;
        }
        settled = true;
        signal.removeEventListener("abort", abort);
        resolve(value);
      },
      (error: unknown) => {
        if (settled) return;
        settled = true;
        signal.removeEventListener("abort", abort);
        reject(error);
      },
    );
  });
}

function validContentLength(response: Response): boolean {
  const value = response.headers.get("content-length");
  if (value === null) return true;
  if (!/^\d+$/.test(value)) return false;
  const length = Number(value);
  return Number.isSafeInteger(length) && length <= MAX_RESPONSE_BYTES;
}

async function readBounded(response: Response, signal: AbortSignal): Promise<Uint8Array | undefined> {
  if (!validContentLength(response)) {
    cancelResponse(response);
    return undefined;
  }
  const reader = response.body?.getReader();
  if (!reader) return new Uint8Array();
  const chunks: Uint8Array[] = [];
  let size = 0;
  let complete = false;
  try {
    while (true) {
      const { done, value } = await awaitWithAbort(reader.read(), signal);
      if (done) break;
      if (value.byteLength > MAX_RESPONSE_BYTES - size) return undefined;
      chunks.push(value);
      size += value.byteLength;
    }
    complete = true;
    const body = new Uint8Array(size);
    let offset = 0;
    for (const chunk of chunks) {
      body.set(chunk, offset);
      offset += chunk.byteLength;
    }
    return body;
  } finally {
    if (!complete) cancelReader(reader);
    try { reader.releaseLock(); } catch { /* reader may already be unusable */ }
  }
}

type GroupResult = "present" | "missing" | "ambiguous" | "unauthorized" | "unreachable";

function exactResult(name: string, parsed: unknown): GroupResult {
  if (!parsed || typeof parsed !== "object" || Array.isArray(parsed)) return "unreachable";
  const record = parsed as { results?: unknown; pagination?: unknown };
  if (!Array.isArray(record.results) || record.results.length > 2
    || !record.pagination || typeof record.pagination !== "object"
    || Array.isArray(record.pagination)) return "unreachable";
  if (!Object.prototype.hasOwnProperty.call(record.pagination, "next")) return "unreachable";
  const next = (record.pagination as { next: unknown }).next;
  if (next !== null) {
    if (typeof next !== "string" || next.length === 0 || next.length > 2048 || /\p{Cc}/u.test(next)) return "unreachable";
    try {
      const continuation = new URL(next);
      if (continuation.protocol !== "https:" || continuation.username || continuation.password || continuation.hash) return "unreachable";
    } catch {
      return "unreachable";
    }
    return "ambiguous";
  }
  const resultNames: string[] = [];
  for (const result of record.results) {
    if (!result || typeof result !== "object" || Array.isArray(result)
      || typeof (result as { name?: unknown }).name !== "string") return "unreachable";
    resultNames.push((result as { name: string }).name);
  }
  const exactMatches = resultNames.filter((candidate) => candidate === name).length;
  if (exactMatches === 0) return "missing";
  return exactMatches === 1 ? "present" : "ambiguous";
}

export function createAuthentikGroupCatalog(options: AuthentikGroupCatalogOptions): GroupCatalog {
  const origin = parseConfiguredTransportUrl(options.baseUrl, { allowLoopbackHttp: false, originOnly: true });
  const fetchImplementation = options.fetch ?? globalThis.fetch;
  const valid = origin !== undefined
    && isUsableAuthenticationSecret("THT_AUTHENTIK_API_TOKEN", options.apiToken)
    && typeof fetchImplementation === "function";

  async function verify(name: string, signal: AbortSignal): Promise<GroupResult> {
    if (!origin || !valid || signal.aborted) return "unreachable";
    const target = new URL("/api/v3/core/groups/", origin);
    target.searchParams.set("name", name);
    target.searchParams.set("include_users", "false");
    target.searchParams.set("page_size", "2");
    const timeout = new AbortController();
    const timer = setTimeout(() => timeout.abort(), REQUEST_TIMEOUT_MS);
    timer.unref();
    const requestSignal = AbortSignal.any([signal, timeout.signal]);
    try {
      const response = await awaitWithAbort(
        Promise.resolve().then(() => fetchImplementation(target, {
          headers: { accept: "application/json", authorization: `Bearer ${options.apiToken}` },
          redirect: "error",
          signal: requestSignal,
        })),
        requestSignal,
        cancelResponse,
      );
      if (response.redirected || response.type === "opaqueredirect" || response.status >= 300 && response.status < 400) {
        cancelResponse(response);
        return "unreachable";
      }
      if (response.status === 401 || response.status === 403) {
        cancelResponse(response);
        return "unauthorized";
      }
      if (!response.ok) {
        cancelResponse(response);
        return "unreachable";
      }
      const body = await readBounded(response, requestSignal);
      if (body === undefined) return "unreachable";
      try {
        return exactResult(name, JSON.parse(new TextDecoder("utf-8", { fatal: true }).decode(body)));
      } catch {
        return "unreachable";
      }
    } catch {
      return "unreachable";
    } finally {
      clearTimeout(timer);
    }
  }

  return {
    async verifyConfiguredGroups(names, signal) {
      const diagnostics: AuthDiagnostic[] = [];
      for (const name of [...new Set(names)].sort(stableCompare)) {
        const outcome = await verify(name, signal);
        if (outcome === "present") continue;
        if (outcome === "missing") diagnostics.push(missing(name));
        else if (outcome === "ambiguous") diagnostics.push(ambiguous(name));
        else if (outcome === "unauthorized") return [catalogUnauthorized()];
        else return [catalogUnreachable()];
      }
      return diagnostics;
    },
  };
}