import { randomUUID } from 'node:crypto';
import type { DomainNodeType } from './domain-access.js';
import {
  assertRegisteredNodeRegistrationEndpoint,
  type NodeRegistrationEndpoint,
} from './node-registration.js';

const REQUEST_SCHEMA = 'gh-aios.node-registration-claim-request/v1' as const;
const RESPONSE_SCHEMA = 'gh-aios.node-registration-claim-response/v1' as const;
const MAX_RESPONSE_BYTES = 64 * 1024;
const REQUEST_TIMEOUT_MS = 5_000;
const MAX_CLOCK_SKEW_MS = 5 * 60 * 1000;
const IDENTIFIER_PATTERN = /^[A-Z0-9][A-Z0-9._:-]{1,159}$/;
const ACCOUNT_ID_PATTERN = /^[A-Za-z0-9][A-Za-z0-9._-]{0,79}$/;

export interface NodeRegistrationClaimLookup {
  accountId: string;
  domainId: string;
  endpoint: NodeRegistrationEndpoint;
  nodeId: string;
  nodeType: DomainNodeType;
}

export interface NodeRegistrationClaimRequestBody {
  accountId: string;
  domainId: string;
  endpointId: string;
  issuedAt: number;
  nodeId: string;
  nodeType: DomainNodeType;
  requestId: string;
  schema: typeof REQUEST_SCHEMA;
}

export interface NodeRegistrationClaimSource {
  read(lookup: Readonly<NodeRegistrationClaimLookup>): Promise<unknown | null>;
}

type FetchImplementation = (input: string, init: RequestInit) => Promise<Response>;

function invalidTransport(): never {
  throw new Error('node_registration_claim_transport_invalid');
}

function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === 'object' && value !== null && !Array.isArray(value);
}

function hasExactKeys(record: Record<string, unknown>, keys: string[]): boolean {
  const expected = [...keys].sort();
  const actual = Object.keys(record).sort();
  return actual.length === expected.length && actual.every((key, index) => key === expected[index]);
}

function buildRequest(
  lookup: Readonly<NodeRegistrationClaimLookup>,
  now: number,
  requestId: string,
): Readonly<NodeRegistrationClaimRequestBody> {
  let endpoint: NodeRegistrationEndpoint;
  try {
    endpoint = assertRegisteredNodeRegistrationEndpoint(lookup.endpoint);
  } catch {
    invalidTransport();
  }
  if (endpoint.status !== 'ACTIVE'
    || !endpoint.domainIds.includes(lookup.domainId)
    || !endpoint.nodeTypes.includes(lookup.nodeType)
    || !ACCOUNT_ID_PATTERN.test(lookup.accountId)
    || !IDENTIFIER_PATTERN.test(lookup.domainId)
    || !IDENTIFIER_PATTERN.test(lookup.nodeId)
    || !IDENTIFIER_PATTERN.test(requestId)
    || !Number.isSafeInteger(now)) invalidTransport();
  return Object.freeze({
    accountId: lookup.accountId,
    domainId: lookup.domainId,
    endpointId: endpoint.endpointId,
    issuedAt: now,
    nodeId: lookup.nodeId,
    nodeType: lookup.nodeType,
    requestId,
    schema: REQUEST_SCHEMA,
  });
}

async function readLimitedBody(response: Response): Promise<Uint8Array> {
  if (!response.body) invalidTransport();
  const reader = response.body.getReader();
  const chunks: Uint8Array[] = [];
  let total = 0;
  try {
    while (true) {
      const { done, value } = await reader.read();
      if (done) break;
      total += value.byteLength;
      if (total > MAX_RESPONSE_BYTES) invalidTransport();
      chunks.push(value);
    }
  } finally {
    reader.releaseLock();
  }
  const body = new Uint8Array(total);
  let offset = 0;
  for (const chunk of chunks) {
    body.set(chunk, offset);
    offset += chunk.byteLength;
  }
  return body;
}

function parseResponse(input: unknown, request: NodeRegistrationClaimRequestBody): unknown | null {
  if (!isRecord(input)
    || !hasExactKeys(input, ['claim', 'requestId', 'schema', 'status'])
    || input.schema !== RESPONSE_SCHEMA
    || input.requestId !== request.requestId
    || (input.status !== 'ISSUED' && input.status !== 'NOT_FOUND')) invalidTransport();
  if (input.status === 'NOT_FOUND') {
    if (input.claim !== null) invalidTransport();
    return null;
  }
  if (!isRecord(input.claim)) invalidTransport();
  return input.claim;
}

export class HttpNodeRegistrationClaimSource implements NodeRegistrationClaimSource {
  constructor(
    private readonly fetchImpl: FetchImplementation = fetch,
    private readonly now: () => number = Date.now,
    private readonly requestId: () => string = () => `NODE-REQ-${randomUUID().toUpperCase()}`,
  ) {}

  async read(lookup: Readonly<NodeRegistrationClaimLookup>): Promise<unknown | null> {
    const issuedAt = this.now();
    const request = buildRequest(lookup, issuedAt, this.requestId());
    let response: Response;
    try {
      response = await this.fetchImpl(lookup.endpoint.url, {
        body: JSON.stringify(request),
        cache: 'no-store',
        credentials: 'omit',
        headers: {
          Accept: 'application/json',
          'Content-Type': 'application/json',
        },
        method: 'POST',
        redirect: 'manual',
        referrerPolicy: 'no-referrer',
        signal: AbortSignal.timeout(REQUEST_TIMEOUT_MS),
      });
    } catch {
      invalidTransport();
    }
    if (response.status !== 200
      || response.redirected
      || !response.headers.get('content-type')?.toLowerCase().startsWith('application/json')) {
      invalidTransport();
    }
    const contentLength = response.headers.get('content-length');
    if (contentLength && (!/^\d+$/.test(contentLength) || Number(contentLength) > MAX_RESPONSE_BYTES)) {
      invalidTransport();
    }
    let decoded: string;
    try {
      decoded = new TextDecoder('utf-8', { fatal: true }).decode(await readLimitedBody(response));
    } catch {
      invalidTransport();
    }
    let parsed: unknown;
    try {
      parsed = JSON.parse(decoded);
    } catch {
      invalidTransport();
    }
    if (Math.abs(this.now() - issuedAt) > MAX_CLOCK_SKEW_MS) invalidTransport();
    return parseResponse(parsed, request);
  }
}