/* vim: ts=4:sw=4:expandtab
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

;(function() {
    'use strict';

    // Insert some bytes into the emscripten memory and return a pointer
    function _allocate(bytes) {
        var address = Module._malloc(bytes.length);
        Module.HEAPU8.set(bytes, address);

        return address;
    }

    function _readBytes(address, length, array) {
        array.set(Module.HEAPU8.subarray(address, address + length));
    }

    var basepoint = new Uint8Array(32);
    basepoint[0] = 9;

    window.curve25519 = {
        keyPair: function(privKey) {
            var priv = new Uint8Array(privKey);
            priv[0]  &= 248;
            priv[31] &= 127;
            priv[31] |= 64

            // Where to store the result
            var publicKey_ptr = Module._malloc(32);

            // Get a pointer to the private key
            var privateKey_ptr = _allocate(priv);

            // The basepoint for generating public keys
            var basepoint_ptr = _allocate(basepoint);

            // The return value is just 0, the operation is done in place
            var err = Module._curve25519_donna(publicKey_ptr,
                                               privateKey_ptr,
                                               basepoint_ptr);

            var res = new Uint8Array(32);
            _readBytes(publicKey_ptr, 32, res);

            Module._free(publicKey_ptr);
            Module._free(privateKey_ptr);
            Module._free(basepoint_ptr);

            return Promise.resolve({ pubKey: res.buffer, privKey: privKey });
        },
        sharedSecret: function(pubKey, privKey) {
            // Where to store the result
            var sharedKey_ptr = Module._malloc(32);

            // Get a pointer to our private key
            var privateKey_ptr = _allocate(new Uint8Array(privKey));

            // Get a pointer to their public key, the basepoint when you're
            // generating a shared secret
            var basepoint_ptr = _allocate(new Uint8Array(pubKey));

            // Return value is 0 here too of course
            var err = Module._curve25519_donna(sharedKey_ptr,
                                               privateKey_ptr,
                                               basepoint_ptr);

            var res = new Uint8Array(32);
            _readBytes(sharedKey_ptr, 32, res);

            Module._free(sharedKey_ptr);
            Module._free(privateKey_ptr);
            Module._free(basepoint_ptr);

            return Promise.resolve(res.buffer);
        },
        sign: function(privKey, message) {
            // Where to store the result
            var signature_ptr = Module._malloc(64);

            // Get a pointer to our private key
            var privateKey_ptr = _allocate(new Uint8Array(privKey));

            // Get a pointer to the message
            var message_ptr = _allocate(new Uint8Array(message));

            var err = Module._curve25519_sign(signature_ptr,
                                              privateKey_ptr,
                                              message_ptr,
                                              message.byteLength);

            var res = new Uint8Array(64);
            _readBytes(signature_ptr, 64, res);

            Module._free(signature_ptr);
            Module._free(privateKey_ptr);
            Module._free(message_ptr);

            return Promise.resolve(res.buffer);
        },
        verify: function(pubKey, message, sig) {
            // Get a pointer to their public key
            var publicKey_ptr = _allocate(new Uint8Array(pubKey));

            // Get a pointer to the signature
            var signature_ptr = _allocate(new Uint8Array(sig));

            // Get a pointer to the message
            var message_ptr = _allocate(new Uint8Array(message));

            var res = Module._curve25519_verify(signature_ptr,
                                                publicKey_ptr,
                                                message_ptr,
                                                message.byteLength);

            Module._free(publicKey_ptr);
            Module._free(signature_ptr);
            Module._free(message_ptr);

            return new Promise(function(resolve, reject) {
                if (res !== 0) {
                    reject(new Error("Invalid signature"));
                } else {
                    resolve();
                }
            });
        }
    };
})();