'use strict';

var crypto = require('crypto');

// 1.2.840.10045.3.1.7
// prime256v1 (ANSI X9.62 named elliptic curve)
var OBJ_ID_EC  = '06 08 2A8648CE3D030107'.replace(/\s+/g, '').toLowerCase();

function fromBase64(b64) {
  var buf;
  var ab;
  if ('undefined' === typeof atob) {
    buf = Buffer.from(b64, 'base64');
    return buf.buffer.slice(buf.byteOffset, buf.byteOffset + buf.byteLength);
  }
  buf = atob(b64);
  ab = new ArrayBuffer(buf.length);
  ab = new Uint8Array(ab);
  buf.split('').forEach(function (ch, i) {
    ab[i] = ch.charCodeAt(0);
  });
  return ab.buffer;
}

function parsePem(pem) {
  var typ;
  var pub;
  var crv;
  var der = fromBase64(pem.split(/\n/).filter(function (line, i) {
    if (0 === i) {
      if (/ PUBLIC /.test(line)) {
        pub = true;
      } else if (/ PRIVATE /.test(line)) {
        pub = false;
      }
      if (/ EC/.test(line)) {
        typ = 'EC';
      }
    }
    return !/---/.test(line);
  }).join(''));

  if (!typ || 'EC' === typ) {
    var hex = toHex(der).toLowerCase();
    if (-1 !== hex.indexOf(OBJ_ID_EC)) {
      typ = 'EC';
      crv = 'P-256';
    } else {
      // TODO more than just P-256
      console.warn("unsupported ec curve");
    }
  }

  return { typ: typ, pub: pub, der: der, crv: crv };
}

function toHex(ab) {
  var hex = [];
  var u8 = new Uint8Array(ab);
  var size = u8.byteLength;
  var i;
  var h;
  for (i = 0; i < size; i += 1) {
    h = u8[i].toString(16);
    if (2 === h.length) {
      hex.push(h);
    } else {
      hex.push('0' + h);
    }
  }
  return hex.join('');
}

function fromHex(hex) {
  if ('undefined' !== typeof Buffer) {
    return Buffer.from(hex, 'hex');
  }
  var ab = new ArrayBuffer(hex.length/2);
  var i;
  var j;
  ab = new Uint8Array(ab);
  for (i = 0, j = 0; i < (hex.length/2); i += 1) {
    ab[i] = parseInt(hex.slice(j, j+1), 16);
    j += 2;
  }
  return ab.buffer;
}

function readEcPubkey(der) {
  // the key is the last 520 bits of both the private key and the public key
  // he 3 bits prior identify the key as
  var x, y;
  var compressed;
  var keylen = 32;
  var offset = 64;
  var headerSize = 4;
  var header = toHex(der.slice(der.byteLength - (offset + headerSize), der.byteLength - offset));

  if ('03420004' !== header) {
    offset = 32;
    header = toHex(der.slice(der.byteLength - (offset + headerSize), der.byteLength - offset));
    if ('03420002' !== header) {
      throw new Error("not a valid EC P-256 key (expected 0x0342004 or 0x0342002 as pub key preamble, but found " + header + ")");
    }
  }

  // The one good thing that came from the b***kchain hysteria: good EC documentation
  // https://davidederosa.com/basic-blockchain-programming/elliptic-curve-keys/
  compressed = ('2' === header[header.byteLength -1]);
  x = der.slice(der.byteLength - offset, (der.byteLength - offset) + keylen);
  if (!compressed) {
    y = der.slice(der.byteLength - keylen, der.byteLength);
  }

  return {
    x: x
  , y: y || null
  };
}

function formatAsPem(str) {
  var finalString = '';

  while (str.length > 0) {
      finalString += str.substring(0, 64) + '\n';
      str = str.substring(64);
  }
  return finalString;
}

function toBase64(der) {
  if ('undefined' === typeof btoa) {
    return Buffer.from(der).toString('base64');
  }
	var chs = [];
	der.forEach(function (b) {
		chs.push(String.fromCharCode(b));
	});
  return btoa(chs.join(''));
}

// these are static ASN.1 segments
// The head specifies that there will be 3 segments and a content length
// (those segments will be content, signature header, and signature)
var csrHead = '30 82 {0seq0len}'.replace(/\s+/g, '');
// The tail specifies the ES256 signature header (and is followed by the signature
var csrEcFoot =
  ( '30 0A'
      // 1.2.840.10045.4.3.2 ecdsaWithSHA256
      // (ANSI X9.62 ECDSA algorithm with SHA256)
    + '06 08 2A 86 48 CE 3D 04 03 02'
  + '03 {len} 00' // bit stream (why??)
    + '30 {rslen}'  // sequence
      + '02 {rlen} {r}' // integer r
      + '02 {slen} {s}' // integer s
  ).replace(/\s+/g, '');
var csrDomains = '82 {dlen} {domain.tld}';  // 2+n bytes (type 82?)

function strToHex(str) {
  return str.split('').map(function (ch) {
    var h = ch.charCodeAt(0).toString(16);
    if (2 === h.length) {
      return h;
    }
    return '0' + h;
  }).join('');
}

function numToHex(d) {
  d = d.toString(16);
  if (d.length % 2) {
    return '0' + d;
  }
  return d;
}

function fromHex(hex) {
  if ('undefined' !== typeof Buffer) {
    return Buffer.from(hex, 'hex');
  }
  var ab = new ArrayBuffer(hex.length/2);
  var i;
  var j;
  ab = new Uint8Array(ab);
  for (i = 0, j = 0; i < (hex.length/2); i += 1) {
    ab[i] = parseInt(hex.slice(j, j+1), 16);
    j += 2;
  }
  return ab.buffer;
}

function createCsrBodyEc(domains, xy) {
  var altnames = domains.map(function (d) {
    return csrDomains.replace(/{dlen}/, numToHex(d.length)).replace(/{domain\.tld}/, strToHex(d));
  }).join('').replace(/\s+/g, '');
  var sublen = domains[0].length;
  var sanlen = (altnames.length/2);
  var publen = xy.x.byteLength;
  var compression = '04';
  var hxy = '';
  // 04 == x+y, 02 == x-only
  if (xy.y) {
    publen += xy.y.byteLength;
  } else {
    // Note: I don't intend to support compression - it isn't used by most
    // libraries and it requir more dependencies for bigint ops to deflate.
    // This is more just a placeholder. It won't work right now anyway
    // because compression requires an exta bit stored (odd vs even), which
    // I haven't learned yet, and I'm not sure if it's allowed at all
    compression = '02';
  }
  hxy += toHex(xy.x);
  if (xy.y) {
    hxy += toHex(xy.y);
  }

  var body = [ '30 81 {+85+n}'                                        // 4 bytes, sequence
    .replace(/{[^}]+}/, numToHex(
        3
      + 13 + sublen
      + 27 + publen // Length for EC-related P-256 stuff
      + 30 + sanlen
    ))

      // #0 Total 3
    , '02 01 00'                                                      // 3 bytes, int 0

      // Subject
      // #1 Total 2+11+n
    , '30 {3.2.0seqlen}'                                              // 2 bytes, sequence
      .replace(/{[^}]+}/, numToHex(2+2+5+2+sublen))
      , '31 {4.3.0setlen}'                                            // 2 bytes, set
        .replace(/{[^}]+}/, numToHex(2+5+2+sublen))
        , '30 {5.4.0seqlen}'                                          // 2 bytes, sequence
          .replace(/{[^}]+}/, numToHex(5+2+sublen))
        , '06 03 55 04 03'                                            // 5 bytes, object id (commonName)
        , '0C {dlen} {domain.tld}'                                    // 2+n bytes, utf8string
          .replace(/{dlen}/, numToHex(sublen))
          .replace(/{domain\.tld}/, strToHex(domains[0]))

      // P-256 Public Key
      // #2 Total 2+25+xy
    , '30 {+25+xy}'                                                   // 2 bytes, sequence
      .replace(/{[^}]+}/, numToHex(2+9+10+3+1+publen))
      , '30 13'                                                       // 2 bytes, sequence
          // 1.2.840.10045.2.1 ecPublicKey
          // (ANSI X9.62 public key type)
        , '06 07 2A 86 48 CE 3D 02 01'                                // 9 bytes, object id
          // 1.2.840.10045.3.1.7 prime256v1
          // (ANSI X9.62 named elliptic curve)
        , '06 08 2A 86 48 CE 3D 03 01 07'                             // 10 bytes, object id
      , '03 {xylen} 00 {xy}'                                          // 3+1+n bytes
        .replace(/{xylen}/, numToHex(publen+2))
        .replace(/{xy}/, compression + hxy)

      // Altnames
      // #3 Total 2+28+n
    , 'A0 {+28}'                                                      // 2 bytes, ?? [4B]
      .replace(/{[^}]+}/, numToHex(2+11+2+2+2+5+2+2+sanlen))
      , '30 {+26}'                                                    // 2 bytes, sequence
        .replace(/{[^}]+}/, numToHex(11+2+2+2+5+2+2+sanlen))
          // (extensionRequest (PKCS #9 via CRMF))
        , '06 09 2A 86 48 86 F7 0D 01 09 0E'                          // 11 bytes, object id
          , '31 {+13}'                                                // 2 bytes, set
            .replace(/{[^}]+}/, numToHex(2+2+5+2+2+sanlen))
            , '30 {+11}'                                              // 2 bytes, sequence
              .replace(/{[^}]+}/, numToHex(2+5+2+2+sanlen))
              , '30 {+9}'                                             // 2 bytes, sequence
                .replace(/{[^}]+}/, numToHex(5+2+2+sanlen))
                  // (subjectAltName (X.509 extension))
                , '06 03 55 1D 11'                                    // 5 bytes, object id
                , '04 {+2}'                                           // 2 bytes, octet string
                  .replace(/{[^}]+}/, numToHex(2+sanlen))
                  , '30 {+n}'                                         // 2 bytes, sequence
                    .replace(/{[^}]+}/, numToHex(sanlen))
                    , '{altnames}'                                    // n (elements of sequence)
                      .replace(/{altnames}/, altnames)
  ];
  body = body.join('').replace(/\s+/g, '');
  return fromHex(body);
}

// https://gist.github.com/codermapuche/da4f96cdb6d5ff53b7ebc156ec46a10a
function signEc(keypem, ab) {
  // Signer is a stream
  var sign = crypto.createSign('SHA256');
  sign.write(new Uint8Array(ab));
  sign.end();

  // The signature is ASN1 encoded
  var sig = sign.sign(keypem);

  // Convert to a JavaScript ArrayBuffer just because
  sig = new Uint8Array(sig.buffer.slice(sig.byteOffset, sig.byteOffset + sig.byteLength));

  // The first two bytes '30 xx' signify SEQUENCE and LENGTH
  // The sequence length byte will be a single byte because the signature is less that 128 bytes (0x80, 1024-bit)
  // (this would not be true for P-521, but I'm not supporting that yet)
  // The 3rd byte will be '02', signifying INTEGER
  // The 4th byte will tell us the length of 'r' (which, on occassion, will be less than the full 255 bytes)
  var rIndex = 3;
  var rLen = sig[rIndex];
  var rEnd = rIndex + 1 + rLen;
  var sIndex = rEnd + 1;
  var sLen = sig[sIndex];
  var sEnd = sIndex + 1 + sLen;
  var r = sig.slice(rIndex + 1, rEnd);
  var s = sig.slice(sIndex + 1, sEnd); // this should be end-of-file

  // ASN1 INTEGER types use the high-order bit to signify a negative number,
  // hence a leading '00' is used for numbers that begin with '80' or greater
  // which is why r length is sometimes a byte longer than its bit length
  if (0 === s[0]) { s = s.slice(1); }
  if (0 === r[0]) { r = r.slice(1); }

  return { raw: sig.buffer, r: r.buffer, s: s.buffer };
}

function createEcCsr(domains, keypem, ecpub) {
  // TODO get pub from priv

  var csrBody = createCsrBodyEc(domains, ecpub);
  var sig = signEc(keypem, csrBody);
  var rLen = sig.r.byteLength;
  var rc = '';
  var sLen = sig.s.byteLength;
  var sc = '';

  if (0x80 & new Uint8Array(sig.r)[0]) { rc = '00'; rLen += 1; }
  if (0x80 & new Uint8Array(sig.s)[0]) { sc = '00'; sLen += 1; }

  var csrSig = csrEcFoot
    .replace(/{len}/, numToHex(1 + 2 + 2 + 2 + rLen + sLen))
    .replace(/{rslen}/, numToHex(2 + 2 + rLen + sLen))
    .replace(/{rlen}/, numToHex(rLen))
    .replace(/{r}/, rc + toHex(sig.r))
    .replace(/{slen}/, numToHex(sLen))
    .replace(/{s}/, sc + toHex(sig.s))
  ;

  // Note: If we supported P-521 a number of the lengths would change
  // by one byte and that would be... annoying to update
  var len = csrBody.byteLength + (csrSig.length/2);
  /*
  console.log('sig:', sig.raw.byteLength, toHex(sig.raw));
  console.log('r:', sig.r.byteLength, toHex(sig.r));
  console.log('s:', sig.s.byteLength, toHex(sig.s));
  console.log('csr sig:', csrSig.length / 2, csrSig);
  console.log('csrBodyLen + csrSigLen', numToHex(len));
  */
  var head = csrHead.replace(/{[^}]+}/, numToHex(len));
  var ab = new Uint8Array(new ArrayBuffer((head.length/2) + len));
  var i = 0;
  fromHex(head).forEach(function (b) {
    ab[i] = b;
    i += 1;
  });
  csrBody.forEach(function (b) {
    ab[i] = b;
    i += 1;
  });
  fromHex(csrSig).forEach(function (b) {
    ab[i] = b;
    i += 1;
  });

  return ab;
}

function createEcCsrPem(domains, keypem) {
  var pemblock = parsePem(keypem);
  var ecpub = readEcPubkey(pemblock.der);
  var ab = createEcCsr(domains, keypem, ecpub);
  var pem = formatAsPem(toBase64(ab));
  return '-----BEGIN CERTIFICATE REQUEST-----\n' + pem + '-----END CERTIFICATE REQUEST-----';
}

// Taken from Unibabel
// https://git.coolaj86.com/coolaj86/unibabel.js#readme
// https://coolaj86.com/articles/base64-unicode-utf-8-javascript-and-you/
function utf8ToUint8Array(str) {
  var escstr = encodeURIComponent(str);
  // replaces any uri escape sequence, such as %0A,
  // with binary escape, such as 0x0A
  var binstr = escstr.replace(/%([0-9A-F]{2})/g, function(match, p1) {
    return String.fromCharCode('0x' + p1);
  });
  var buf = new Uint8Array(binstr.length);
  binstr.split('').forEach(function (ch, i) {
    buf[i] = ch.charCodeAt(0);
  });

  return buf;
}

function ensurePem(key) {
  if (!key) { throw new Error("no private key given"); }
  // whether PEM or DER, convert to Uint8Array
  if ('string' === typeof key) { key = utf8ToUint8Array(key); }

  // for consistency
  if (key instanceof Buffer) { key = new Uint8Array(key.buffer.slice(key.byteOffset, key.byteOffset + key.byteLength)); }

  // just as a sanity check
  if (key instanceof Array) {
    key = Uint8Array.from(key);
    if (!key.every(function (el) {
      return ('number' === typeof el) && (el >= 0) && (el <= 255);
    })) {
      throw new Error("key was an array, but not an array of ints between 0 and 255");
    }
  }

  // no matter which path we take, we should arrive at a Uint8Array
  if (!(key instanceof Uint8Array)) {
    throw new Error("typeof key is '" + typeof key + "', not any of the supported types: utf8 string,"
      + " binary string, node Buffer, Uint8Array, or Array of ints between 0 and 255");
  }

  // if DER, convert to PEM
  if ((0x30 === key[0]) && (0x80 & key[1])) {
    key = toBase64(key);
  }
  key = [].map.call(key, function (i) {
    return String.fromCharCode(i);
  }).join('');
  if ('M' === key[0]) {
    key = '-----BEGIN EC PRIVATE KEY-----\n' + key + '-----END EC PRIVATE KEY-----';
  }
  if ('-' === key[0]) {
    return key;
  } else {
    throw new Error("key does not appear to be in PEM formt (does not begin with either '-' or 'M'),"
      + " nor DER format (does not begin with 0x308X)");
  }
}

/*global Promise*/
module.exports = function (opts) {
  // We're using a Promise here to be compatible with the browser version
  // which uses the webcrypto API for some of the conversions
  return Promise.resolve().then(function () {

    // We do a bit of extra error checking for user convenience
    if (!opts) { throw new Error("You must pass options with key and domains to ecdsacsr"); }
    if (!Array.isArray(opts.domains) || 0 === opts.domains.length) {
      new Error("You must pass options.domains as a non-empty array");
    }

    // I need to check that 例.中国 is a valid domain name
    if (!opts.domains.every(function (d) {
      // allow punycode? xn--
      if ('string' === typeof d /*&& /\./.test(d) && !/--/.test(d)*/) {
        return true;
      }
    })) {
      throw new Error("You must pass options.domains as utf8 strings (not punycode)");
    }
    var key = ensurePem(opts.key);

    return createEcCsrPem(opts.domains, key);
  });
};