import { timingSafeEqual } from 'node:crypto';

/**
 * Timing-safe string comparison that prevents timing attacks.
 *
 * Uses `crypto.timingSafeEqual` which runs in constant time regardless of
 * where the strings differ. Returns false for mismatched-length inputs
 * to avoid leaking length information via early return.
 *
 * @param left - The first string to compare.
 * @param right - The second string to compare.
 * @returns True if both strings are equal.
 */
const timingSafeCompare = (left: string, right: string): boolean => {
  const leftBuffer = Buffer.from(left);
  const rightBuffer = Buffer.from(right);

  if (leftBuffer.length !== rightBuffer.length) {
    return false;
  }

  return timingSafeEqual(leftBuffer, rightBuffer);
};

export interface SigV4Result {
  isValid: boolean;
  credential: {
    accessKey: string;
    date: string;
    region: string;
    service: string;
  } | null;
  errorCode?: string;
}

export interface VerifyPresignedUrlInput {
  url: string;
  method: string;
  headers: Record<string, string>;
  s3AccessKey: string;
  s3SecretKey: string;
  region: string;
  now?: Date;
}

const SERVICE = 's3';
const TERMINATION = 'aws4_request';

/**
 * Maximum acceptable clock skew between client and server for header-based
 * SigV4 authentication. AWS allows 15 minutes.
 */
const MAX_CLOCK_SKEW_MS = 15 * 60 * 1000;

// eslint-disable-next-line @typescript-eslint/no-explicit-any
const buf = (data: string | ArrayBuffer | Uint8Array): Uint8Array => {
  if (data instanceof Uint8Array) return data;
  if (data instanceof ArrayBuffer) return new Uint8Array(data);
  return new TextEncoder().encode(data);
};

const sha256Hex = async (data: string | Uint8Array | ArrayBuffer): Promise<string> => {
  const hashBuffer = await crypto.subtle.digest('SHA-256', buf(data) as never);
  const hashArray = Array.from(new Uint8Array(hashBuffer));
  return hashArray.map((b) => b.toString(16).padStart(2, '0')).join('');
};

const hmacSha256 = async (key: Uint8Array, message: string): Promise<Uint8Array> => {
  const cryptoKey = await crypto.subtle.importKey(
    'raw',
    key as never,
    { name: 'HMAC', hash: 'SHA-256' },
    false,
    ['sign'],
  );
  const result = await crypto.subtle.sign('HMAC', cryptoKey, buf(message) as never);
  return new Uint8Array(result);
};

const getSigningKey = async (
  secretKey: string,
  dateStamp: string,
  region: string,
): Promise<Uint8Array> => {
  let key = await hmacSha256(buf(`AWS4${secretKey}`), dateStamp);
  key = await hmacSha256(key, region);
  key = await hmacSha256(key, SERVICE);
  return await hmacSha256(key, TERMINATION);
};

const hmacHex = async (key: Uint8Array, message: string): Promise<string> => {
  const result = await hmacSha256(key, message);
  return Array.from(result)
    .map((b) => b.toString(16).padStart(2, '0'))
    .join('');
};

const parseAuthorizationHeader = (authHeader: string) => {
  const credentialMatch = authHeader.match(/Credential=([^,]+)/);
  const signedHeadersMatch = authHeader.match(/SignedHeaders=([^,]+)/);
  const signatureMatch = authHeader.match(/Signature=([^,]+)/);

  if (!credentialMatch || !signedHeadersMatch || !signatureMatch) return null;

  const credentialParts = credentialMatch[1].split('/');
  if (credentialParts.length !== 5) return null;

  return {
    accessKey: credentialParts[0],
    date: credentialParts[1],
    region: credentialParts[2],
    service: credentialParts[3],
    termination: credentialParts[4],
    signedHeaders: signedHeadersMatch[1],
    signature: signatureMatch[1],
  };
};

const buildCanonicalRequest = (
  method: string,
  canonicalUri: string,
  canonicalQueryString: string,
  signedHeaders: string,
  headers: Record<string, string>,
  hashedPayload: string,
): string => {
  const canonicalHeaders = signedHeaders
    .split(';')
    .map((h) => {
      const value = headers[h.toLowerCase()] || '';
      return `${h.toLowerCase()}:${value.trim()}\n`;
    })
    .join('');

  return `${method}\n${canonicalUri}\n${canonicalQueryString}\n${canonicalHeaders}\n${signedHeaders}\n${hashedPayload}`;
};

/**
 * Normalizes a URI per AWS SigV4 requirements plus RFC 3986:
 *
 * 1. Decode percent-encoded characters
 * 2. Remove dot-segments (`.` and `..`) per RFC 3986 section 5.2.4
 *
 * @param uri - The raw URI path to normalize.
 * @returns The normalized URI path.
 */
const normalizeUri = (uri: string): string => {
  if (!uri || uri === '') return '/';

  // AWS SigV4 requires URI-decoded paths in the canonical request
  // Only `.` and `..` segments are removed per RFC 3986 section 5.2.4
  // Empty segments (from `//` or trailing `/`) are preserved — they are
  // part of the URI and the SDK signs them.
  const decoded = decodeURIComponent(uri);
  const segments = decoded.split('/');
  const result: string[] = [];

  for (const segment of segments) {
    if (segment === '.') continue;
    if (segment === '..') {
      result.pop();
      continue;
    }
    result.push(segment);
  }

  // Join preserves empty first segment (from leading /) automatically
  return result.join('/') || '/';
};

const awsEncode = (value: string): string =>
  encodeURIComponent(value).replace(
    /[!'()*]/g,
    (ch) => `%${ch.charCodeAt(0).toString(16).toUpperCase()}`,
  );

export const buildCanonicalQueryString = (
  searchParams: URLSearchParams,
  excludeKeys: Set<string> = new Set(),
): string => {
  const pairs: Array<[string, string]> = [];
  for (const [key, value] of searchParams.entries()) {
    if (!excludeKeys.has(key)) pairs.push([key, value]);
  }
  // AWS SigV4 requires UTF-8 byte-order (code point) comparison, NOT localeCompare
  pairs.sort(([ak, av], [bk, bv]) => {
    const a = `${awsEncode(ak)}=${awsEncode(av)}`;
    const b = `${awsEncode(bk)}=${awsEncode(bv)}`;
    if (a < b) return -1;
    if (a > b) return 1;
    return 0;
  });
  return pairs.map(([key, value]) => `${awsEncode(key)}=${awsEncode(value)}`).join('&');
};

const getHashedPayload = async (body: string | null): Promise<string> => {
  if (!body || body.length === 0) return await sha256Hex('');
  return await sha256Hex(body);
};

/**
 * Parses an AWS SigV4 `x-amz-date` value (e.g. `20260707T120000Z`) into a Date.
 *
 * @param amzDate - The date string in `YYYYMMDDTHHmmssZ` format.
 * @returns The parsed Date, or null if the format is invalid.
 */
const parseAmzDateUtc = (amzDate: string): Date | null => {
  const match = amzDate.match(/^(\d{4})(\d{2})(\d{2})T(\d{2})(\d{2})(\d{2})Z$/);
  if (!match) return null;
  const [, year, month, day, hour, minute, second] = match;
  return new Date(
    Date.UTC(
      Number.parseInt(year, 10),
      Number.parseInt(month, 10) - 1,
      Number.parseInt(day, 10),
      Number.parseInt(hour, 10),
      Number.parseInt(minute, 10),
      Number.parseInt(second, 10),
    ),
  );
};

/**
 * Validates that `host` is included in the signed headers list.
 *
 * AWS SigV4 mandates that `host` is always signed. Reject requests that
 * omit it to prevent header injection / replay variants.
 *
 * @param signedHeaders - The semicolon-separated signed headers string.
 * @returns True if `host` is present.
 */
const validateSignedHeaders = (signedHeaders: string): boolean => {
  return signedHeaders.split(';').some((h) => h.toLowerCase() === 'host');
};

export const verifySignature = async (
  method: string,
  url: string,
  headers: Record<string, string>,
  body: string | null,
  s3AccessKey: string,
  s3SecretKey: string,
  region: string,
): Promise<SigV4Result> => {
  const authHeader = headers.authorization;
  if (!authHeader?.startsWith('AWS4-HMAC-SHA256')) {
    return { isValid: false, credential: null, errorCode: 'AccessDenied' };
  }

  const parsed = parseAuthorizationHeader(authHeader);
  if (!parsed) {
    return { isValid: false, credential: null, errorCode: 'AccessDenied' };
  }

  if (!timingSafeCompare(parsed.accessKey, s3AccessKey)) {
    return { isValid: false, credential: null, errorCode: 'SignatureDoesNotMatch' };
  }

  if (!timingSafeCompare(parsed.region, region)) {
    return { isValid: false, credential: null, errorCode: 'SignatureDoesNotMatch' };
  }

  // Validate service and termination in credential scope (M2)
  if (parsed.service !== SERVICE || parsed.termination !== TERMINATION) {
    return { isValid: false, credential: null, errorCode: 'SignatureDoesNotMatch' };
  }

  // Validate host is in signed headers (LOW/host)
  if (!validateSignedHeaders(parsed.signedHeaders)) {
    return { isValid: false, credential: null, errorCode: 'AccessDenied' };
  }

  const parsedUrl = new URL(url, 'http://localhost');
  const canonicalUri = normalizeUri(parsedUrl.pathname);
  const canonicalQueryString = buildCanonicalQueryString(parsedUrl.searchParams);

  const contentSha256 = headers['x-amz-content-sha256'] || null;
  if (contentSha256?.startsWith('STREAMING-')) {
    return { isValid: false, credential: null, errorCode: 'NotImplemented' };
  }

  // CRITICAL: Use the x-amz-content-sha256 header value in the canonical
  // request because that's what the client signed. The actual body hash is
  // verified by verifyBodyHash() after streaming, ensuring integrity without
  // breaking SigV4.
  const hashedPayload = contentSha256 || (await getHashedPayload(body));

  const canonicalRequest = buildCanonicalRequest(
    method,
    canonicalUri,
    canonicalQueryString,
    parsed.signedHeaders,
    headers,
    hashedPayload,
  );

  const hashedCanonicalRequest = await sha256Hex(canonicalRequest);

  // M1: Fall back to Date header if x-amz-date is missing
  const amzDate = headers['x-amz-date'] || headers.date || '';

  // H5: Validate request freshness (clock skew / replay protection)
  if (amzDate) {
    const requestDate = parseAmzDateUtc(amzDate);
    if (requestDate) {
      const now = Date.now();
      const skew = Math.abs(now - requestDate.getTime());
      if (skew > MAX_CLOCK_SKEW_MS) {
        return { isValid: false, credential: null, errorCode: 'RequestExpired' };
      }
    }
  }

  const dateStamp = parsed.date;

  // M3: Ensure date in credential scope matches x-amz-date
  if (amzDate) {
    const amzDateStamp = amzDate.slice(0, 8); // "YYYYMMDD"
    if (amzDateStamp !== dateStamp) {
      return { isValid: false, credential: null, errorCode: 'SignatureDoesNotMatch' };
    }
  }

  const credentialScope = `${dateStamp}/${region}/${parsed.service}/${parsed.termination}`;

  const stringToSign = `AWS4-HMAC-SHA256\n${amzDate}\n${credentialScope}\n${hashedCanonicalRequest}`;

  const signingKey = await getSigningKey(s3SecretKey, dateStamp, region);
  const expectedSignature = await hmacHex(signingKey, stringToSign);

  if (!timingSafeCompare(expectedSignature, parsed.signature)) {
    return { isValid: false, credential: null, errorCode: 'SignatureDoesNotMatch' };
  }

  return {
    isValid: true,
    credential: {
      accessKey: parsed.accessKey,
      date: parsed.date,
      region: parsed.region,
      service: parsed.service,
    },
  };
};

export const verifyPresignedUrl = async ({
  url,
  method,
  headers,
  s3AccessKey,
  s3SecretKey,
  region,
  now = new Date(),
}: VerifyPresignedUrlInput): Promise<SigV4Result> => {
  const parsedUrl = new URL(url);
  const searchParams = parsedUrl.searchParams;

  const algorithm = searchParams.get('X-Amz-Algorithm');
  const credential = searchParams.get('X-Amz-Credential');
  const signedHeaders = searchParams.get('X-Amz-SignedHeaders');
  const signature = searchParams.get('X-Amz-Signature');
  const expiresText = searchParams.get('X-Amz-Expires');
  const amzDate = searchParams.get('X-Amz-Date');

  if (
    algorithm !== 'AWS4-HMAC-SHA256' ||
    !credential ||
    !signedHeaders ||
    !signature ||
    !expiresText ||
    !amzDate
  ) {
    return { isValid: false, credential: null, errorCode: 'AccessDenied' };
  }

  const expires = Number.parseInt(expiresText, 10);
  const signedAt = parseAmzDateUtc(amzDate);
  if (!Number.isFinite(expires) || expires <= 0 || !signedAt) {
    return { isValid: false, credential: null, errorCode: 'AccessDenied' };
  }
  // AWS S3 spec limits presigned URLs to 7 days (604800 seconds)
  const MAX_PRESIGNED_EXPIRY_SECONDS = 604800;
  if (
    now.getTime() > signedAt.getTime() + expires * 1000 ||
    expires > MAX_PRESIGNED_EXPIRY_SECONDS
  ) {
    return { isValid: false, credential: null, errorCode: 'AccessDenied' };
  }

  const credParts = credential.split('/');
  if (credParts.length !== 5) {
    return { isValid: false, credential: null, errorCode: 'AccessDenied' };
  }
  const [accessKey, dateStamp, credentialRegion, service, termination] = credParts;
  if (
    !timingSafeCompare(accessKey, s3AccessKey) ||
    !timingSafeCompare(credentialRegion, region) ||
    service !== SERVICE ||
    termination !== TERMINATION
  ) {
    return { isValid: false, credential: null, errorCode: 'SignatureDoesNotMatch' };
  }

  // Validate host is in signed headers for presigned URLs too
  if (!validateSignedHeaders(signedHeaders)) {
    return { isValid: false, credential: null, errorCode: 'AccessDenied' };
  }

  const signedHeaderList = signedHeaders.split(';').filter(Boolean);
  const canonicalHeaders = signedHeaderList
    .map((headerName) => {
      const lower = headerName.toLowerCase();
      const value = lower === 'host' ? headers.host || parsedUrl.host : headers[lower] || '';
      return `${lower}:${value.trim()}\n`;
    })
    .join('');

  const canonicalRequest = `${method}\n${normalizeUri(parsedUrl.pathname)}\n${buildCanonicalQueryString(searchParams, new Set(['X-Amz-Signature']))}\n${canonicalHeaders}\n${signedHeaders}\nUNSIGNED-PAYLOAD`;
  const hashedCanonicalRequest = await sha256Hex(canonicalRequest);
  const credentialScope = `${dateStamp}/${region}/${SERVICE}/${TERMINATION}`;
  const stringToSign = `AWS4-HMAC-SHA256\n${amzDate}\n${credentialScope}\n${hashedCanonicalRequest}`;
  const expectedSignature = await hmacHex(
    await getSigningKey(s3SecretKey, dateStamp, region),
    stringToSign,
  );

  if (!timingSafeCompare(expectedSignature, signature)) {
    return { isValid: false, credential: null, errorCode: 'SignatureDoesNotMatch' };
  }
  return { isValid: true, credential: { accessKey, date: dateStamp, region, service } };
};

export const isS3Request = (headers: Record<string, string>): boolean => {
  const auth = headers.authorization || '';
  return auth.startsWith('AWS4-HMAC-SHA256');
};

/**
 * Verifies that the actual body SHA-256 matches the `x-amz-content-sha256`
 * header from the original request.
 *
 * This MUST be called AFTER the body has been fully streamed and hashed,
 * as a second pass after `verifySignature` (which cannot hash a streaming
 * body without consuming it).
 *
 * @param bodySha256 - The SHA-256 hex digest of the actual body content.
 * @param headers - The original request headers.
 * @returns An error result on mismatch, or null if the check passes.
 */
export const verifyBodyHash = (
  bodySha256: string,
  headers: Record<string, string>,
): SigV4Result | null => {
  const claimedHash = headers['x-amz-content-sha256'];
  // If the client sent UNSIGNED-PAYLOAD, skip verification
  if (!claimedHash || claimedHash === 'UNSIGNED-PAYLOAD' || claimedHash.startsWith('STREAMING-')) {
    return null;
  }
  if (claimedHash !== bodySha256) {
    return { isValid: false, credential: null, errorCode: 'BadDigest' };
  }
  return null;
};