'use strict';

var Enc = require('./encoding.js');
var SSH = module.exports;

SSH.pack = function (opts) {
  var jwk = opts.jwk;
  var els = [];
  var ssh = {
    type: ''
  , _elements: els
  , comment: opts.comment || ''
  };
  var len;

  if ("RSA" === jwk.kty) {
    ssh.type = 'ssh-rsa';
    els.push(Enc.binToHex(ssh.type));
    els.push(SSH._padRsa(Enc.base64ToHex(jwk.e)));
    els.push(SSH._padRsa(Enc.base64ToHex(jwk.n)));
    return SSH._packElements(ssh);
  }

  if ("P-256" === jwk.crv) {
    ssh.type = 'ecdsa-sha2-nistp256';
    els.push(Enc.binToHex(ssh.type));
    els.push(Enc.binToHex('nistp256'));
    len = 32;
  } else if ("P-384" === jwk.crv) {
    ssh.type = 'ecdsa-sha2-nistp384';
    els.push(Enc.binToHex(ssh.type));
    els.push(Enc.binToHex('nistp384'));
    len = 48;
  } else {
    throw new Error("unknown key type " + (jwk.crv || jwk.kty));
  }

  els.push('04'
    + SSH._padEc(Enc.base64ToHex(jwk.x), len)
    + SSH._padEc(Enc.base64ToHex(jwk.y), len)
  );
  return SSH._packElements(ssh);
};

SSH._packElements = function (ssh) {
  var hex = ssh._elements.map(function (hex) {
    return SSH._numToUint32Hex(hex.length/2) + hex;
  }).join('');
  return [ ssh.type, Enc.hexToBase64(hex), ssh.comment ].join(' ');
};

SSH._numToUint32Hex = function (num) {
  var hex = num.toString(16);
  while (hex.length < 8) {
    hex = '0' + hex;
  }
  return hex;
};

SSH._padRsa = function (hex) {
  // BigInt is negative if the high order bit 0x80 is set,
  // so ASN1, SSH, and many other formats pad with '0x00'
  // to signifiy a positive number.
  var i = parseInt(hex.slice(0, 2), 16);
  if (0x80 & i) {
    return '00' + hex;
  }
  return hex;
};

SSH._padEc = function (hex, len) {
  while (hex.length < len * 2) {
    hex = '00' + hex;
  }
  return hex;
};