'use strict';

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

SSH.parse = function (ssh) {
  ssh = ssh.split(/\s+/g);

  var result = { type: ssh[0], jwk: null, comment: ssh[2] || '' };
  var buf = Enc.base64ToBuf(ssh[1]);
  var els = SSH.parseElements(buf);
  var typ = Enc.bufToBin(els[0]);
  var len;

  // RSA keys are all the same
  if (SSH.types.rsa === typ) {
    result.jwk = {
      kty: 'RSA'
    , n: Enc.bufToUrlBase64(els[2])
    , e: Enc.bufToUrlBase64(els[1])
    };
    return result;
  }

  // EC keys are each different
  if (SSH.types.p256 === typ) {
    len = 32;
    result.jwk = { kty: 'EC', crv: 'P-256' };
  } else if (SSH.types.p384 === typ) {
    len = 48;
    result.jwk = { kty: 'EC', crv: 'P-384' };
  } else {
    throw new Error("Unsupported ssh public key type: "
      + Enc.bufToBin(els[0]));
  }

  // els[1] is just a repeat of a subset of els[0]
  var x = els[2].slice(1, 1 + len);
  var y = els[2].slice(1 + len, 1 + len + len);

  // I don't think EC keys use 0x00 padding, but just in case
  if (0x00 === x[0]) { x = x.slice(1); }
  if (0x00 === y[0]) { y = y.slice(1); }

  result.jwk.x = Enc.bufToUrlBase64(x);
  result.jwk.y = Enc.bufToUrlBase64(y);

  return result;
};

SSH.parseElements = function (buf) {
  var fulllen = buf.byteLength || buf.length;
  var offset = (buf.byteOffset || 0);
  var i = 0;
  var index = 0;
  // using dataview to be browser-compatible (I do want _some_ code reuse)
  var dv = new DataView(buf.buffer.slice(offset, offset + fulllen));
  var els = [];
  var el;
  var len;

  while (index < fulllen) {
    i += 1;
    if (i > 15) { throw new Error("15+ elements, probably not a public ssh key"); }
    len = dv.getUint32(index, false);
    index += 4;
    el = buf.slice(index, index + len);
    // remove BigUInt '00' prefix
    if (0x00 === el[0]) {
      el = el.slice(1);
    }
    els.push(el);
    index += len;
  }
  if (fulllen !== index) {
    throw new Error(els.map(function (b) {
      return Enc.bufToHex(b);
    }).join('\n') + "invalid ssh public key length");
  }

  return els;
};

SSH.types = {
  // 19 '00000013'
  // e c d s a - s h a 2 - n i s t p 2 5 6
  // 65636473612d736861322d6e69737470323536
  // 6e69737470323536
  p256: 'ecdsa-sha2-nistp256'

  // 19 '00000013'
  // e c d s a - s h a 2 - n i s t p 3 8 4
  // 65636473612d736861322d6e69737470333834
  // 6e69737470323536
, p384: 'ecdsa-sha2-nistp384'

  // 7 '00000007'
  // s s h - r s a
  // 7373682d727361
, rsa: 'ssh-rsa'
};