cryptpad/www/common/chainpad.js

(function(){
var r=function(){var e="function"==typeof require&&require,r=function(i,o,u){o||(o=0);var n=r.resolve(i,o),t=r.m[o][n];if(!t&&e){if(t=e(n))return t}else if(t&&t.c&&(o=t.c,n=t.m,t=r.m[o][t.m],!t))throw new Error('failed to require "'+n+'" from '+o);if(!t)throw new Error('failed to require "'+i+'" from '+u);return t.exports||(t.exports={},t.call(t.exports,t,t.exports,r.relative(n,o))),t.exports};return r.resolve=function(e,n){var i=e,t=e+".js",o=e+"/index.js";return r.m[n][t]&&t?t:r.m[n][o]&&o?o:i},r.relative=function(e,t){return function(n){if("."!=n.charAt(0))return r(n,t,e);var o=e.split("/"),f=n.split("/");o.pop();for(var i=0;i<f.length;i++){var u=f[i];".."==u?o.pop():"."!=u&&o.push(u)}return r(o.join("/"),t,e)}},r}();r.m = [];
r.m[0] = {
"Patch.js": function(module, exports, require){
/*
 * Copyright 2014 XWiki SAS
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
var Common = require('./Common');
var Operation = require('./Operation');
var Sha = require('./SHA256');

var Patch = module.exports;

var create = Patch.create = function (parentHash) {
    return {
        type: 'Patch',
        operations: [],
        parentHash: parentHash,
        isCheckpoint: false
    };
};

var check = Patch.check = function (patch, docLength_opt) {
    Common.assert(patch.type === 'Patch');
    Common.assert(Array.isArray(patch.operations));
    Common.assert(/^[0-9a-f]{64}$/.test(patch.parentHash));
    for (var i = patch.operations.length - 1; i >= 0; i--) {
        Operation.check(patch.operations[i], docLength_opt);
        if (i > 0) {
            Common.assert(!Operation.shouldMerge(patch.operations[i], patch.operations[i-1]));
        }
        if (typeof(docLength_opt) === 'number') {
            docLength_opt += Operation.lengthChange(patch.operations[i]);
        }
    }
    if (patch.isCheckpoint) {
        Common.assert(patch.operations.length === 1);
        Common.assert(patch.operations[0].offset === 0);
        if (typeof(docLength_opt) === 'number') {
            Common.assert(!docLength_opt || patch.operations[0].toRemove === docLength_opt);
        }
    }
};

var toObj = Patch.toObj = function (patch) {
    if (Common.PARANOIA) { check(patch); }
    var out = new Array(patch.operations.length+1);
    var i;
    for (i = 0; i < patch.operations.length; i++) {
        out[i] = Operation.toObj(patch.operations[i]);
    }
    out[i] = patch.parentHash;
    return out;
};

var fromObj = Patch.fromObj = function (obj) {
    Common.assert(Array.isArray(obj) && obj.length > 0);
    var patch = create();
    var i;
    for (i = 0; i < obj.length-1; i++) {
        patch.operations[i] = Operation.fromObj(obj[i]);
    }
    patch.parentHash = obj[i];
    if (Common.PARANOIA) { check(patch); }
    return patch;
};

var hash = function (text) {
    return Sha.hex_sha256(text);
};

var addOperation = Patch.addOperation = function (patch, op) {
    if (Common.PARANOIA) {
        check(patch);
        Operation.check(op);
    }
    for (var i = 0; i < patch.operations.length; i++) {
        if (Operation.shouldMerge(patch.operations[i], op)) {
            op = Operation.merge(patch.operations[i], op);
            patch.operations.splice(i,1);
            if (op === null) {
                //console.log("operations cancelled eachother");
                return;
            }
            i--;
        } else {
            var out = Operation.rebase(patch.operations[i], op);
            if (out === op) {
                // op could not be rebased further, insert it here to keep the list ordered.
                patch.operations.splice(i,0,op);
                return;
            } else {
                op = out;
                // op was rebased, try rebasing it against the next operation.
            }
        }
    }
    patch.operations.push(op);
    if (Common.PARANOIA) { check(patch); }
};

var createCheckpoint = Patch.createCheckpoint =
    function (parentContent, checkpointContent, parentContentHash_opt)
{
    var op = Operation.create(0, parentContent.length, checkpointContent);
    if (Common.PARANOIA && parentContentHash_opt) {
        Common.assert(parentContentHash_opt === hash(parentContent));
    }
    parentContentHash_opt = parentContentHash_opt || hash(parentContent);
    var out = create(parentContentHash_opt);
    addOperation(out, op);
    out.isCheckpoint = true;
    return out;
};

var clone = Patch.clone = function (patch) {
    if (Common.PARANOIA) { check(patch); }
    var out = create();
    out.parentHash = patch.parentHash;
    for (var i = 0; i < patch.operations.length; i++) {
        out.operations[i] = Operation.clone(patch.operations[i]);
    }
    return out;
};

var merge = Patch.merge = function (oldPatch, newPatch) {
    if (Common.PARANOIA) {
        check(oldPatch);
        check(newPatch);
    }
    oldPatch = clone(oldPatch);
    for (var i = newPatch.operations.length-1; i >= 0; i--) {
        addOperation(oldPatch, newPatch.operations[i]);
    }
    return oldPatch;
};

var apply = Patch.apply = function (patch, doc)
{
    if (Common.PARANOIA) {
        check(patch);
        Common.assert(typeof(doc) === 'string');
        Common.assert(Sha.hex_sha256(doc) === patch.parentHash);
    }
    var newDoc = doc;
    for (var i = patch.operations.length-1; i >= 0; i--) {
        newDoc = Operation.apply(patch.operations[i], newDoc);
    }
    return newDoc;
};

var lengthChange = Patch.lengthChange = function (patch)
{
    if (Common.PARANOIA) { check(patch); }
    var out = 0;
    for (var i = 0; i < patch.operations.length; i++) {
        out += Operation.lengthChange(patch.operations[i]);
    }
    return out;
};

var invert = Patch.invert = function (patch, doc)
{
    if (Common.PARANOIA) {
        check(patch);
        Common.assert(typeof(doc) === 'string');
        Common.assert(Sha.hex_sha256(doc) === patch.parentHash);
    }
    var rpatch = create();
    var newDoc = doc;
    for (var i = patch.operations.length-1; i >= 0; i--) {
        rpatch.operations[i] = Operation.invert(patch.operations[i], newDoc);
        newDoc = Operation.apply(patch.operations[i], newDoc);
    }
    for (var i = rpatch.operations.length-1; i >= 0; i--) {
        for (var j = i - 1; j >= 0; j--) {
            rpatch.operations[i].offset += rpatch.operations[j].toRemove;
            rpatch.operations[i].offset -= rpatch.operations[j].toInsert.length;
        }
    }
    rpatch.parentHash = Sha.hex_sha256(newDoc);
    if (Common.PARANOIA) { check(rpatch); }
    return rpatch;
};

var simplify = Patch.simplify = function (patch, doc, operationSimplify)
{
    if (Common.PARANOIA) {
        check(patch);
        Common.assert(typeof(doc) === 'string');
        Common.assert(Sha.hex_sha256(doc) === patch.parentHash);
    }
    operationSimplify = operationSimplify || Operation.simplify;
    var spatch = create(patch.parentHash);
    var newDoc = doc;
    var outOps = [];
    var j = 0;
    for (var i = patch.operations.length-1; i >= 0; i--) {
        outOps[j] = operationSimplify(patch.operations[i], newDoc, Operation.simplify);
        if (outOps[j]) {
            newDoc = Operation.apply(outOps[j], newDoc);
            j++;
        }
    }
    spatch.operations = outOps.reverse();
    if (!spatch.operations[0]) {
        spatch.operations.shift();
    }
    if (Common.PARANOIA) {
        check(spatch);
    }
    return spatch;
};

var equals = Patch.equals = function (patchA, patchB) {
    if (patchA.operations.length !== patchB.operations.length) { return false; }
    for (var i = 0; i < patchA.operations.length; i++) {
        if (!Operation.equals(patchA.operations[i], patchB.operations[i])) { return false; }
    }
    return true;
};

var transform = Patch.transform = function (origToTransform, transformBy, doc, transformFunction) {
    if (Common.PARANOIA) {
        check(origToTransform, doc.length);
        check(transformBy, doc.length);
        Common.assert(Sha.hex_sha256(doc) === origToTransform.parentHash);
    }
    Common.assert(origToTransform.parentHash === transformBy.parentHash);
    var resultOfTransformBy = apply(transformBy, doc);

    var toTransform = clone(origToTransform);
    var text = doc;
    for (var i = toTransform.operations.length-1; i >= 0; i--) {
        for (var j = transformBy.operations.length-1; j >= 0; j--) {
            try {
                toTransform.operations[i] = Operation.transform(text,
                                                                toTransform.operations[i],
                                                                transformBy.operations[j],
                                                                transformFunction);
            } catch (e) {
                console.error("The pluggable transform function threw an error, " +
                    "failing operational transformation");
                return create(Sha.hex_sha256(resultOfTransformBy));
            }
            if (!toTransform.operations[i]) {
                break;
            }
        }
        if (Common.PARANOIA && toTransform.operations[i]) {
            Operation.check(toTransform.operations[i], resultOfTransformBy.length);
        }
    }
    var out = create(transformBy.parentHash);
    for (var i = toTransform.operations.length-1; i >= 0; i--) {
        if (toTransform.operations[i]) {
            addOperation(out, toTransform.operations[i]);
        }
    }

    out.parentHash = Sha.hex_sha256(resultOfTransformBy);

    if (Common.PARANOIA) {
        check(out, resultOfTransformBy.length);
    }
    return out;
};

var random = Patch.random = function (doc, opCount) {
    Common.assert(typeof(doc) === 'string');
    opCount = opCount || (Math.floor(Math.random() * 30) + 1);
    var patch = create(Sha.hex_sha256(doc));
    var docLength = doc.length;
    while (opCount-- > 0) {
        var op = Operation.random(docLength);
        docLength += Operation.lengthChange(op);
        addOperation(patch, op);
    }
    check(patch);
    return patch;
};

},
"SHA256.js": function(module, exports, require){
/* A JavaScript implementation of the Secure Hash Algorithm, SHA-256
 * Version 0.3 Copyright Angel Marin 2003-2004 - http://anmar.eu.org/
 * Distributed under the BSD License
 * Some bits taken from Paul Johnston's SHA-1 implementation
 */
(function () {
    var chrsz = 8;  /* bits per input character. 8 - ASCII; 16 - Unicode  */
    function safe_add (x, y) {
        var lsw = (x & 0xFFFF) + (y & 0xFFFF);
        var msw = (x >> 16) + (y >> 16) + (lsw >> 16);
        return (msw << 16) | (lsw & 0xFFFF);
    }
    function S (X, n) {return ( X >>> n ) | (X << (32 - n));}
    function R (X, n) {return ( X >>> n );}
    function Ch(x, y, z) {return ((x & y) ^ ((~x) & z));}
    function Maj(x, y, z) {return ((x & y) ^ (x & z) ^ (y & z));}
    function Sigma0256(x) {return (S(x, 2) ^ S(x, 13) ^ S(x, 22));}
    function Sigma1256(x) {return (S(x, 6) ^ S(x, 11) ^ S(x, 25));}
    function Gamma0256(x) {return (S(x, 7) ^ S(x, 18) ^ R(x, 3));}
    function Gamma1256(x) {return (S(x, 17) ^ S(x, 19) ^ R(x, 10));}
    function newArray (n) {
        var a = [];
        for (;n>0;n--) {
            a.push(undefined);
        }
        return a;
    }
    function core_sha256 (m, l) {
        var K = [0x428A2F98,0x71374491,0xB5C0FBCF,0xE9B5DBA5,0x3956C25B,0x59F111F1,0x923F82A4,0xAB1C5ED5,0xD807AA98,0x12835B01,0x243185BE,0x550C7DC3,0x72BE5D74,0x80DEB1FE,0x9BDC06A7,0xC19BF174,0xE49B69C1,0xEFBE4786,0xFC19DC6,0x240CA1CC,0x2DE92C6F,0x4A7484AA,0x5CB0A9DC,0x76F988DA,0x983E5152,0xA831C66D,0xB00327C8,0xBF597FC7,0xC6E00BF3,0xD5A79147,0x6CA6351,0x14292967,0x27B70A85,0x2E1B2138,0x4D2C6DFC,0x53380D13,0x650A7354,0x766A0ABB,0x81C2C92E,0x92722C85,0xA2BFE8A1,0xA81A664B,0xC24B8B70,0xC76C51A3,0xD192E819,0xD6990624,0xF40E3585,0x106AA070,0x19A4C116,0x1E376C08,0x2748774C,0x34B0BCB5,0x391C0CB3,0x4ED8AA4A,0x5B9CCA4F,0x682E6FF3,0x748F82EE,0x78A5636F,0x84C87814,0x8CC70208,0x90BEFFFA,0xA4506CEB,0xBEF9A3F7,0xC67178F2];
        var HASH = [0x6A09E667, 0xBB67AE85, 0x3C6EF372, 0xA54FF53A, 0x510E527F, 0x9B05688C, 0x1F83D9AB, 0x5BE0CD19];
        var W = newArray(64);
        var a, b, c, d, e, f, g, h, i, j;
        var T1, T2;
        /* append padding */
        m[l >> 5] |= 0x80 << (24 - l % 32);
        m[((l + 64 >> 9) << 4) + 15] = l;
        for ( var i = 0; i<m.length; i+=16 ) {
            a = HASH[0]; b = HASH[1]; c = HASH[2]; d = HASH[3];
            e = HASH[4]; f = HASH[5]; g = HASH[6]; h = HASH[7];
            for ( var j = 0; j<64; j++) {
                if (j < 16) {
                    W[j] = m[j + i];
                } else {
                    W[j] = safe_add(safe_add(safe_add(Gamma1256(
                        W[j - 2]), W[j - 7]), Gamma0256(W[j - 15])), W[j - 16]);
                }
                T1 = safe_add(safe_add(safe_add(
                    safe_add(h, Sigma1256(e)), Ch(e, f, g)), K[j]), W[j]);
                T2 = safe_add(Sigma0256(a), Maj(a, b, c));
                h = g; g = f; f = e; e = safe_add(d, T1);
                d = c; c = b; b = a; a = safe_add(T1, T2);
            }
            HASH[0] = safe_add(a, HASH[0]); HASH[1] = safe_add(b, HASH[1]);
            HASH[2] = safe_add(c, HASH[2]); HASH[3] = safe_add(d, HASH[3]);
            HASH[4] = safe_add(e, HASH[4]); HASH[5] = safe_add(f, HASH[5]);
            HASH[6] = safe_add(g, HASH[6]); HASH[7] = safe_add(h, HASH[7]);
        }
        return HASH;
    }
    function str2binb (str) {
        var bin = Array();
        var mask = (1 << chrsz) - 1;
        for(var i = 0; i < str.length * chrsz; i += chrsz)
            bin[i>>5] |= (str.charCodeAt(i / chrsz) & mask) << (24 - i%32);
        return bin;
    }
    function binb2hex (binarray) {
        var hexcase = 0; /* hex output format. 0 - lowercase; 1 - uppercase */
        var hex_tab = hexcase ? "0123456789ABCDEF" : "0123456789abcdef";
        var str = "";
        for (var i = 0; i < binarray.length * 4; i++) {
            str += hex_tab.charAt((binarray[i>>2] >> ((3 - i%4)*8+4)) & 0xF) +
                hex_tab.charAt((binarray[i>>2] >> ((3 - i%4)*8  )) & 0xF);
        }
        return str;
    }
    function hex_sha256(s){
        return binb2hex(core_sha256(str2binb(s),s.length * chrsz));
    }
    module.exports.hex_sha256 = hex_sha256;
}());

},
"Common.js": function(module, exports, require){
/*
 * Copyright 2014 XWiki SAS
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

var PARANOIA = module.exports.PARANOIA = true;

/* Good testing but slooooooooooow */
var VALIDATE_ENTIRE_CHAIN_EACH_MSG = module.exports.VALIDATE_ENTIRE_CHAIN_EACH_MSG = false;

/* throw errors over non-compliant messages which would otherwise be treated as invalid */
var TESTING = module.exports.TESTING = false;

var assert = module.exports.assert = function (expr) {
    if (!expr) { throw new Error("Failed assertion"); }
};

var isUint = module.exports.isUint = function (integer) {
    return (typeof(integer) === 'number') &&
        (Math.floor(integer) === integer) &&
        (integer >= 0);
};

var randomASCII = module.exports.randomASCII = function (length) {
    var content = [];
    for (var i = 0; i < length; i++) {
        content[i] = String.fromCharCode( Math.floor(Math.random()*256) % 57 + 65 );
    }
    return content.join('');
};

var strcmp = module.exports.strcmp = function (a, b) {
    if (PARANOIA && typeof(a) !== 'string') { throw new Error(); }
    if (PARANOIA && typeof(b) !== 'string') { throw new Error(); }
    return ( (a === b) ? 0 : ( (a > b) ? 1 : -1 ) );
}

},
"Message.js": function(module, exports, require){
/*
 * Copyright 2014 XWiki SAS
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
var Common = require('./Common');
var Operation = require('./Operation');
var Patch = require('./Patch');
var Sha = require('./SHA256');

var Message = module.exports;

var REGISTER     = Message.REGISTER     = 0;
var REGISTER_ACK = Message.REGISTER_ACK = 1;
var PATCH        = Message.PATCH        = 2;
var DISCONNECT   = Message.DISCONNECT   = 3;
var CHECKPOINT   = Message.CHECKPOINT   = 4;

var check = Message.check = function(msg) {
    Common.assert(msg.type === 'Message');
    if (msg.messageType === PATCH || msg.messageType === CHECKPOINT) {
        Patch.check(msg.content);
        Common.assert(typeof(msg.lastMsgHash) === 'string');
    } else {
        throw new Error("invalid message type [" + msg.messageType + "]");
    }
};

var create = Message.create = function (type, content, lastMsgHash) {
    var msg = {
        type: 'Message',
        messageType: type,
        content: content,
        lastMsgHash: lastMsgHash
    };
    if (Common.PARANOIA) { check(msg); }
    return msg;
};

var toString = Message.toString = function (msg) {
    if (Common.PARANOIA) { check(msg); }
    if (msg.messageType === PATCH || msg.messageType === CHECKPOINT) {
        return JSON.stringify([msg.messageType, Patch.toObj(msg.content), msg.lastMsgHash]);
    } else {
        throw new Error();
    }
};

var discardBencode = function (msg, arr) {
    var len = msg.substring(0,msg.indexOf(':'));
    msg = msg.substring(len.length+1);
    var value = msg.substring(0,Number(len));
    msg = msg.substring(value.length);

    if (arr) { arr.push(value); }
    return msg;
};

var fromString = Message.fromString = function (str) {
    var m = JSON.parse(str);
    if (m[0] !== CHECKPOINT && m[0] !== PATCH) { throw new Error("invalid message type " + m[0]); }
    var msg = create(m[0], Patch.fromObj(m[1]), m[2]);
    if (m[0] === CHECKPOINT) { msg.content.isCheckpoint = true; }
    return msg;
};

var hashOf = Message.hashOf = function (msg) {
    if (Common.PARANOIA) { check(msg); }
    var hash = Sha.hex_sha256(toString(msg));
    return hash;
};

},
"ChainPad.js": function(module, exports, require){
/*
 * Copyright 2014 XWiki SAS
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
var Common = module.exports.Common = require('./Common');
var Operation = module.exports.Operation = require('./Operation');
var Patch = module.exports.Patch = require('./Patch');
var Message = module.exports.Message = require('./Message');
var Sha = module.exports.Sha = require('./SHA256');

var ChainPad = {};

// hex_sha256('')
var EMPTY_STR_HASH = module.exports.EMPTY_STR_HASH =
    'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855';
var ZERO = '0000000000000000000000000000000000000000000000000000000000000000';

// Default number of patches between checkpoints (patches older than this will be pruned)
// default for realtime.config.checkpointInterval
var DEFAULT_CHECKPOINT_INTERVAL = 200;

// Default number of milliseconds to wait before syncing to the server
var DEFAULT_AVERAGE_SYNC_MILLISECONDS = 300;

var enterChainPad = function (realtime, func) {
    return function () {
        if (realtime.failed) { return; }
        func.apply(null, arguments);
    };
};

var debug = function (realtime, msg) {
    if (realtime.logLevel > 0) {
        console.log("[" + realtime.userName + "]  " + msg);
    }
};

var schedule = function (realtime, func, timeout) {
    if (realtime.aborted) { return; }
    if (!timeout) {
        timeout = Math.floor(Math.random() * 2 * realtime.config.avgSyncMilliseconds);
    }
    var to = setTimeout(enterChainPad(realtime, function () {
        realtime.schedules.splice(realtime.schedules.indexOf(to), 1);
        func();
    }), timeout);
    realtime.schedules.push(to);
    return to;
};

var unschedule = function (realtime, schedule) {
    var index = realtime.schedules.indexOf(schedule);
    if (index > -1) {
        realtime.schedules.splice(index, 1);
    }
    clearTimeout(schedule);
};

var onMessage = function (realtime, message, callback) {
    if (!realtime.messageHandlers.length) {
        callback("no onMessage() handler registered");
    }
    for (var i = 0; i < realtime.messageHandlers.length; i++) {
        realtime.messageHandlers[i](message, function () {
            callback.apply(null, arguments);
            callback = function () { };
        });
    }
};

var sendMessage = function (realtime, msg, callback) {
    var strMsg = Message.toString(msg);

    onMessage(realtime, strMsg, function (err) {
        if (err) {
            debug(realtime, "Posting to server failed [" + err + "]");
            realtime.pending = null;
        } else {
            var pending = realtime.pending;
            realtime.pending = null;
            Common.assert(pending.hash === msg.hashOf);
            handleMessage(realtime, strMsg, true);
            pending.callback();
        }
    });

    msg.hashOf = msg.hashOf || Message.hashOf(msg);

    var timeout = schedule(realtime, function () {
        debug(realtime, "Failed to send message [" + msg.hashOf + "] to server");
        sync(realtime);
    }, 10000 + (Math.random() * 5000));

    if (realtime.pending) { throw new Error("there is already a pending message"); }
    realtime.pending = {
        hash: msg.hashOf,
        callback: function () {
            if (realtime.initialMessage && realtime.initialMessage.hashOf === msg.hashOf) {
                debug(realtime, "initial Ack received [" + msg.hashOf + "]");
                realtime.initialMessage = null;
            }
            unschedule(realtime, timeout);
            realtime.syncSchedule = schedule(realtime, function () { sync(realtime); }, 0);
            callback();
        }
    };
    if (Common.PARANOIA) { check(realtime); }
};

var sync = function (realtime) {
    if (Common.PARANOIA) { check(realtime); }
    if (realtime.syncSchedule && !realtime.pending) {
        unschedule(realtime, realtime.syncSchedule);
        realtime.syncSchedule = null;
    } else {
        //debug(realtime, "already syncing...");
        // we're currently waiting on something from the server.
        return;
    }

    realtime.uncommitted = Patch.simplify(
        realtime.uncommitted, realtime.authDoc, realtime.config.operationSimplify);

    if (realtime.uncommitted.operations.length === 0) {
        //debug(realtime, "No data to sync to the server, sleeping");
        realtime.syncSchedule = schedule(realtime, function () { sync(realtime); });
        return;
    }

    if (((parentCount(realtime, realtime.best) + 1) % realtime.config.checkpointInterval) === 0) {
        var best = realtime.best;
        debug(realtime, "Sending checkpoint");
        var cpp = Patch.createCheckpoint(realtime.authDoc,
                                         realtime.authDoc,
                                         realtime.best.content.inverseOf.parentHash);
        var cp = Message.create(Message.CHECKPOINT, cpp, realtime.best.hashOf);
        sendMessage(realtime, cp, function () {
            debug(realtime, "Checkpoint sent and accepted");
        });
        return;
    }

    var msg;
    if (realtime.best === realtime.initialMessage) {
        msg = realtime.initialMessage;
    } else {
        msg = Message.create(Message.PATCH, realtime.uncommitted, realtime.best.hashOf);
    }

    sendMessage(realtime, msg, function () {
        //debug(realtime, "patch sent");
    });
};

var create = ChainPad.create = function (config) {
    config = config || {};
    var initialState = config.initialState || '';
    config.checkpointInterval = config.checkpointInterval || DEFAULT_CHECKPOINT_INTERVAL;
    config.avgSyncMilliseconds = config.avgSyncMilliseconds || DEFAULT_AVERAGE_SYNC_MILLISECONDS;

    var realtime = {
        type: 'ChainPad',

        authDoc: '',

        config: config,

        logLevel: (typeof(config.logLevel) === 'number') ? config.logLevel : 1,

        /** A patch representing all uncommitted work. */
        uncommitted: null,

        uncommittedDocLength: initialState.length,

        patchHandlers: [],
        changeHandlers: [],

        messageHandlers: [],

        schedules: [],
        aborted: false,

        syncSchedule: null,

        registered: false,

        // this is only used if PARANOIA is enabled.
        userInterfaceContent: undefined,

        failed: false,

        // hash and callback for previously send patch, currently in flight.
        pending: null,

        messages: {},
        messagesByParent: {},

        rootMessage: null,

        userName: config.userName || 'anonymous',
    };

    if (Common.PARANOIA) {
        realtime.userInterfaceContent = initialState;
    }

    var zeroPatch = Patch.create(EMPTY_STR_HASH);
    if (initialState !== '') {
        var initialOp = Operation.create(0, 0, initialState);
        Patch.addOperation(zeroPatch, initialOp);
    }
    zeroPatch.inverseOf = Patch.invert(zeroPatch, '');
    zeroPatch.inverseOf.inverseOf = zeroPatch;
    var zeroMsg = Message.create(Message.PATCH, zeroPatch, ZERO);
    zeroMsg.hashOf = Message.hashOf(zeroMsg);
    zeroMsg.parentCount = 0;
    realtime.messages[zeroMsg.hashOf] = zeroMsg;
    (realtime.messagesByParent[zeroMsg.lastMessageHash] || []).push(zeroMsg);
    realtime.rootMessage = zeroMsg;
    realtime.best = zeroMsg;
    realtime.authDoc = initialState;
    realtime.uncommitted = Patch.create(zeroPatch.inverseOf.parentHash);

    if (Common.PARANOIA) {
        realtime.userInterfaceContent = initialState;
    }
    return realtime;
};

var getParent = function (realtime, message) {
    return message.parent = message.parent || realtime.messages[message.lastMsgHash];
};

var check = ChainPad.check = function(realtime) {
    Common.assert(realtime.type === 'ChainPad');
    Common.assert(typeof(realtime.authDoc) === 'string');

    Patch.check(realtime.uncommitted, realtime.authDoc.length);

    var uiDoc = Patch.apply(realtime.uncommitted, realtime.authDoc);
    if (uiDoc.length !== realtime.uncommittedDocLength) {
        Common.assert(0);
    }
    if (realtime.userInterfaceContent !== '') {
        Common.assert(uiDoc === realtime.userInterfaceContent);
    }

    if (!Common.VALIDATE_ENTIRE_CHAIN_EACH_MSG) { return; }

    var doc = realtime.authDoc;
    var patchMsg = realtime.best;
    Common.assert(patchMsg.content.inverseOf.parentHash === realtime.uncommitted.parentHash);
    var patches = [];
    do {
        patches.push(patchMsg);
        doc = Patch.apply(patchMsg.content.inverseOf, doc);
    } while ((patchMsg = getParent(realtime, patchMsg)));
    Common.assert(doc === '');
    while ((patchMsg = patches.pop())) {
        doc = Patch.apply(patchMsg.content, doc);
    }
    Common.assert(doc === realtime.authDoc);
};

var doOperation = ChainPad.doOperation = function (realtime, op) {
    if (Common.PARANOIA) {
        check(realtime);
        realtime.userInterfaceContent = Operation.apply(op, realtime.userInterfaceContent);
    }
    Operation.check(op, realtime.uncommittedDocLength);
    Patch.addOperation(realtime.uncommitted, op);
    realtime.uncommittedDocLength += Operation.lengthChange(op);
};

var doPatch = ChainPad.doPatch = function (realtime, patch) {
    if (Common.PARANOIA) {
        check(realtime);
        Common.assert(Patch.invert(realtime.uncommitted).parentHash === patch.parentHash);
        realtime.userInterfaceContent = Patch.apply(patch, realtime.userInterfaceContent);
    }
    Patch.check(patch, realtime.uncommittedDocLength);
    realtime.uncommitted = Patch.merge(realtime.uncommitted, patch);
    realtime.uncommittedDocLength += Patch.lengthChange(patch);
};

var isAncestorOf = function (realtime, ancestor, decendent) {
    if (!decendent || !ancestor) { return false; }
    if (ancestor === decendent) { return true; }
    return isAncestorOf(realtime, ancestor, getParent(realtime, decendent));
};

var parentCount = function (realtime, message) {
    if (typeof(message.parentCount) !== 'number') {
        message.parentCount = parentCount(realtime, getParent(realtime, message)) + 1;
    }
    return message.parentCount;
};

var applyPatch = function (realtime, isFromMe, patch) {
    Common.assert(patch);
    Common.assert(patch.inverseOf);
    if (isFromMe && !patch.isInitialStatePatch) {
        var inverseOldUncommitted = Patch.invert(realtime.uncommitted, realtime.authDoc);
        var userInterfaceContent = Patch.apply(realtime.uncommitted, realtime.authDoc);
        if (Common.PARANOIA) {
            Common.assert(userInterfaceContent === realtime.userInterfaceContent);
        }
        realtime.uncommitted = Patch.merge(inverseOldUncommitted, patch);
        realtime.uncommitted = Patch.invert(realtime.uncommitted, userInterfaceContent);

    } else {
        realtime.uncommitted =
            Patch.transform(
                realtime.uncommitted, patch, realtime.authDoc, realtime.config.transformFunction);
    }
    realtime.uncommitted.parentHash = patch.inverseOf.parentHash;

    realtime.authDoc = Patch.apply(patch, realtime.authDoc);

    if (Common.PARANOIA) {
        Common.assert(realtime.uncommitted.parentHash === patch.inverseOf.parentHash);
        Common.assert(Sha.hex_sha256(realtime.authDoc) === realtime.uncommitted.parentHash);
        realtime.userInterfaceContent = Patch.apply(realtime.uncommitted, realtime.authDoc);
    }
};

var revertPatch = function (realtime, isFromMe, patch) {
    applyPatch(realtime, isFromMe, patch.inverseOf);
};

var getBestChild = function (realtime, msg) {
    var best = msg;
    (realtime.messagesByParent[msg.hashOf] || []).forEach(function (child) {
        Common.assert(child.lastMsgHash === msg.hashOf);
        child = getBestChild(realtime, child);
        if (parentCount(realtime, child) > parentCount(realtime, best)) { best = child; }
    });
    return best;
};

var pushUIPatch = function (realtime, patch) {
    if (patch.operations.length) {
        // push the uncommittedPatch out to the user interface.
        for (var i = 0; i < realtime.patchHandlers.length; i++) {
            realtime.patchHandlers[i](patch);
        }
        for (var i = 0; i < realtime.changeHandlers.length; i++) {
            for (var j = patch.operations.length; j >= 0; j--) {
                var op = patch.operations[j];
                realtime.changeHandlers[i](op.offset, op.toRemove, op.toInsert);
            }
        }
    }
};

var handleMessage = ChainPad.handleMessage = function (realtime, msgStr, isFromMe) {

    if (Common.PARANOIA) { check(realtime); }
    var msg = Message.fromString(msgStr);

    // otherwise it's a disconnect.
    if (msg.messageType !== Message.PATCH && msg.messageType !== Message.CHECKPOINT) {
        debug(realtime, "unrecognized message type " + msg.messageType);
        return;
    }

    msg.hashOf = Message.hashOf(msg);

    if (realtime.messages[msg.hashOf]) {
        debug(realtime, "Patch [" + msg.hashOf + "] is already known");
        if (Common.PARANOIA) { check(realtime); }
        return;
    }

    realtime.messages[msg.hashOf] = msg;
    (realtime.messagesByParent[msg.lastMsgHash] =
        realtime.messagesByParent[msg.lastMsgHash] || []).push(msg);

    if (!isAncestorOf(realtime, realtime.rootMessage, msg)) {
        if (realtime.rootMessage === realtime.best && msg.content.isCheckpoint) {
            // We're starting with a trucated chain from a checkpoint, we will adopt this
            // as the root message and go with it...
            var userDoc = Patch.apply(realtime.uncommitted, realtime.authDoc);
            Common.assert(!Common.PARANOIA || realtime.userInterfaceContent === userDoc);
            var fixUserDocPatch = Patch.invert(realtime.uncommitted, realtime.authDoc);
            Patch.addOperation(fixUserDocPatch,
                Operation.create(0, realtime.authDoc.length, msg.content.operations[0].toInsert));
            fixUserDocPatch =
                Patch.simplify(fixUserDocPatch, userDoc, realtime.config.operationSimplify);

            msg.parentCount = 0;
            realtime.rootMessage = realtime.best = msg;

            realtime.authDoc = msg.content.operations[0].toInsert;
            realtime.uncommitted = Patch.create(Sha.hex_sha256(realtime.authDoc));
            realtime.uncommittedDocLength = realtime.authDoc.length;
            pushUIPatch(realtime, fixUserDocPatch);

            if (Common.PARANOIA) { realtime.userInterfaceContent = realtime.authDoc; }
            return;
        } else {
            // we'll probably find the missing parent later.
            debug(realtime, "Patch [" + msg.hashOf + "] not connected to root");
            if (Common.PARANOIA) { check(realtime); }
            return;
        }
    }

    // of this message fills in a hole in the chain which makes another patch better, swap to the
    // best child of this patch since longest chain always wins.
    msg = getBestChild(realtime, msg);
    msg.isFromMe = isFromMe;
    var patch = msg.content;

    // Find the ancestor of this patch which is in the main chain, reverting as necessary
    var toRevert = [];
    var commonAncestor = realtime.best;
    if (!isAncestorOf(realtime, realtime.best, msg)) {
        var pcBest = parentCount(realtime, realtime.best);
        var pcMsg = parentCount(realtime, msg);
        if (pcBest < pcMsg
          || (pcBest === pcMsg
            && Common.strcmp(realtime.best.hashOf, msg.hashOf) > 0))
        {
            // switch chains
            while (commonAncestor && !isAncestorOf(realtime, commonAncestor, msg)) {
                toRevert.push(commonAncestor);
                commonAncestor = getParent(realtime, commonAncestor);
            }
            Common.assert(commonAncestor);
        } else {
            debug(realtime, "Patch [" + msg.hashOf + "] chain is ["+pcMsg+"] best chain is ["+pcBest+"]");
            if (Common.PARANOIA) { check(realtime); }
            return;
        }
    }

    // Find the parents of this patch which are not in the main chain.
    var toApply = [];
    var current = msg;
    do {
        toApply.unshift(current);
        current = getParent(realtime, current);
        Common.assert(current);
    } while (current !== commonAncestor);


    var authDocAtTimeOfPatch = realtime.authDoc;

    for (var i = 0; i < toRevert.length; i++) {
        Common.assert(typeof(toRevert[i].content.inverseOf) !== 'undefined');
        authDocAtTimeOfPatch = Patch.apply(toRevert[i].content.inverseOf, authDocAtTimeOfPatch);
    }

    // toApply.length-1 because we do not want to apply the new patch.
    for (var i = 0; i < toApply.length-1; i++) {
        if (typeof(toApply[i].content.inverseOf) === 'undefined') {
            toApply[i].content.inverseOf = Patch.invert(toApply[i].content, authDocAtTimeOfPatch);
            toApply[i].content.inverseOf.inverseOf = toApply[i].content;
        }
        authDocAtTimeOfPatch = Patch.apply(toApply[i].content, authDocAtTimeOfPatch);
    }

    if (Sha.hex_sha256(authDocAtTimeOfPatch) !== patch.parentHash) {
        debug(realtime, "patch [" + msg.hashOf + "] parentHash is not valid");
        if (Common.PARANOIA) { check(realtime); }
        if (Common.TESTING) { throw new Error(); }
        delete realtime.messages[msg.hashOf];
        return;
    }

    if (patch.isCheckpoint) {
        // Ok, we have a checkpoint patch.
        // If the chain length is not equal to checkpointInterval then this patch is invalid.
        var i = 0;
        var checkpointP;
        for (var m = getParent(realtime, msg); m; m = getParent(realtime, m)) {
            if (m.content.isCheckpoint) {
                if (checkpointP) {
                    checkpointP = m;
                    break;
                }
                checkpointP = m;
            }
        }
        if (checkpointP && checkpointP !== realtime.rootMessage) {
            var point = parentCount(realtime, checkpointP);
            if ((point % realtime.config.checkpointInterval) !== 0) {
                debug(realtime, "checkpoint [" + msg.hashOf + "] at invalid point [" + point + "]");
                if (Common.PARANOIA) { check(realtime); }
                if (Common.TESTING) { throw new Error(); }
                delete realtime.messages[msg.hashOf];
                return;
            }

            // Time to prune some old messages from the chain
            debug(realtime, "checkpoint [" + msg.hashOf + "]");
            for (var m = getParent(realtime, checkpointP); m; m = getParent(realtime, m)) {
                debug(realtime, "pruning [" + m.hashOf + "]");
                delete realtime.messages[m.hashOf];
                delete realtime.messagesByParent[m.hashOf];
            }
            realtime.rootMessage = checkpointP;
        }
    } else {
        var simplePatch =
            Patch.simplify(patch, authDocAtTimeOfPatch, realtime.config.operationSimplify);
        if (!Patch.equals(simplePatch, patch)) {
            debug(realtime, "patch [" + msg.hashOf + "] can be simplified");
            if (Common.PARANOIA) { check(realtime); }
            if (Common.TESTING) { throw new Error(); }
            delete realtime.messages[msg.hashOf];
            return;
        }
    }

    patch.inverseOf = Patch.invert(patch, authDocAtTimeOfPatch);
    patch.inverseOf.inverseOf = patch;

    realtime.uncommitted = Patch.simplify(
        realtime.uncommitted, realtime.authDoc, realtime.config.operationSimplify);
    var oldUserInterfaceContent = Patch.apply(realtime.uncommitted, realtime.authDoc);
    if (Common.PARANOIA) {
        Common.assert(oldUserInterfaceContent === realtime.userInterfaceContent);
    }

    // Derive the patch for the user's uncommitted work
    var uncommittedPatch = Patch.invert(realtime.uncommitted, realtime.authDoc);

    for (var i = 0; i < toRevert.length; i++) {
        debug(realtime, "reverting [" + toRevert[i].hashOf + "]");
        uncommittedPatch = Patch.merge(uncommittedPatch, toRevert[i].content.inverseOf);
        revertPatch(realtime, toRevert[i].isFromMe, toRevert[i].content);
    }

    for (var i = 0; i < toApply.length; i++) {
        debug(realtime, "applying [" + toApply[i].hashOf + "]");
        uncommittedPatch = Patch.merge(uncommittedPatch, toApply[i].content);
        applyPatch(realtime, toApply[i].isFromMe, toApply[i].content);
    }

    uncommittedPatch = Patch.merge(uncommittedPatch, realtime.uncommitted);
    uncommittedPatch = Patch.simplify(
        uncommittedPatch, oldUserInterfaceContent, realtime.config.operationSimplify);

    realtime.uncommittedDocLength += Patch.lengthChange(uncommittedPatch);
    realtime.best = msg;

    if (Common.PARANOIA) {
        // apply the uncommittedPatch to the userInterface content.
        var newUserInterfaceContent = Patch.apply(uncommittedPatch, oldUserInterfaceContent);
        Common.assert(realtime.userInterfaceContent.length === realtime.uncommittedDocLength);
        Common.assert(newUserInterfaceContent === realtime.userInterfaceContent);
    }

    pushUIPatch(realtime, uncommittedPatch);

    if (Common.PARANOIA) { check(realtime); }
};

var getDepthOfState = function (content, minDepth, realtime) {
    Common.assert(typeof(content) === 'string');

    // minimum depth is an optional argument which defaults to zero
    var minDepth = minDepth || 0;

    if (minDepth === 0 && realtime.authDoc === content) {
        return 0;
    }

    var hash = Sha.hex_sha256(content);

    var patchMsg = realtime.best;
    var depth = 0;

    do {
        if (depth < minDepth) {
            // you haven't exceeded the minimum depth
        } else {
            //console.log("Exceeded minimum depth");
            // you *have* exceeded the minimum depth
            if (patchMsg.content.parentHash === hash) {
                // you found it!
                return depth + 1;
            }
        }
        depth++;
    } while ((patchMsg = getParent(realtime, patchMsg)));
    return -1;
};

module.exports.create = function (conf) {
    var realtime = ChainPad.create(conf);
    var out = {
        onPatch: enterChainPad(realtime, function (handler) {
            Common.assert(typeof(handler) === 'function');
            realtime.patchHandlers.push(handler);
        }),
        patch: enterChainPad(realtime, function (patch, x, y) {
            if (typeof(patch) === 'number') {
                // Actually they meant to call realtime.change()
                out.change(patch, x, y);
                return;
            }
            doPatch(realtime, patch);
        }),

        onChange: enterChainPad(realtime, function (handler) {
            Common.assert(typeof(handler) === 'function');
            realtime.changeHandlers.push(handler);
        }),
        change: enterChainPad(realtime, function (offset, count, chars) {
            if (count === 0 && chars === '') { return; }
            doOperation(realtime, Operation.create(offset, count, chars));
        }),

        onMessage: enterChainPad(realtime, function (handler) {
            Common.assert(typeof(handler) === 'function');
            realtime.messageHandlers.push(handler);
        }),

        message: enterChainPad(realtime, function (message) {
            handleMessage(realtime, message, false);
        }),

        start: enterChainPad(realtime, function () {
            if (realtime.syncSchedule) { unschedule(realtime, realtime.syncSchedule); }
            realtime.syncSchedule = schedule(realtime, function () { sync(realtime); });
        }),

        abort: enterChainPad(realtime, function () {
            realtime.aborted = true;
            realtime.schedules.forEach(function (s) { clearTimeout(s) });
        }),

        sync: enterChainPad(realtime, function () { sync(realtime); }),

        getAuthDoc: function () { return realtime.authDoc; },

        getUserDoc: function () { return Patch.apply(realtime.uncommitted, realtime.authDoc); },

        getDepthOfState: function (content, minDepth) {
            return getDepthOfState(content, minDepth, realtime);
        }
    };
    return out;
};

},
"Operation.js": function(module, exports, require){
/*
 * Copyright 2014 XWiki SAS
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
var Common = require('./Common');

var Operation = module.exports;

var check = Operation.check = function (op, docLength_opt) {
    Common.assert(op.type === 'Operation');
    Common.assert(Common.isUint(op.offset));
    Common.assert(Common.isUint(op.toRemove));
    Common.assert(typeof(op.toInsert) === 'string');
    Common.assert(op.toRemove > 0 || op.toInsert.length > 0);
    Common.assert(typeof(docLength_opt) !== 'number' || op.offset + op.toRemove <= docLength_opt);
};

var create = Operation.create = function (offset, toRemove, toInsert) {
    var out = {
        type: 'Operation',
        offset: offset || 0,
        toRemove: toRemove || 0,
        toInsert: toInsert || '',
    };
    if (Common.PARANOIA) { check(out); }
    return out;
};

var toObj = Operation.toObj = function (op) {
    if (Common.PARANOIA) { check(op); }
    return [op.offset,op.toRemove,op.toInsert];
};

var fromObj = Operation.fromObj = function (obj) {
    Common.assert(Array.isArray(obj) && obj.length === 3);
    return create(obj[0], obj[1], obj[2]);
};

var clone = Operation.clone = function (op) {
    return create(op.offset, op.toRemove, op.toInsert);
};

/**
 * @param op the operation to apply.
 * @param doc the content to apply the operation on
 */
var apply = Operation.apply = function (op, doc)
{
    if (Common.PARANOIA) {
        check(op);
        Common.assert(typeof(doc) === 'string');
        Common.assert(op.offset + op.toRemove <= doc.length);
    }
    return doc.substring(0,op.offset) + op.toInsert + doc.substring(op.offset + op.toRemove);
};

var invert = Operation.invert = function (op, doc) {
    if (Common.PARANOIA) {
        check(op);
        Common.assert(typeof(doc) === 'string');
        Common.assert(op.offset + op.toRemove <= doc.length);
    }
    var rop = clone(op);
    rop.toInsert = doc.substring(op.offset, op.offset + op.toRemove);
    rop.toRemove = op.toInsert.length;
    return rop;
};

var simplify = Operation.simplify = function (op, doc) {
    if (Common.PARANOIA) {
        check(op);
        Common.assert(typeof(doc) === 'string');
        Common.assert(op.offset + op.toRemove <= doc.length);
    }
    var rop = invert(op, doc);
    op = clone(op);

    var minLen = Math.min(op.toInsert.length, rop.toInsert.length);
    var i;
    for (i = 0; i < minLen && rop.toInsert[i] === op.toInsert[i]; i++) ;
    op.offset += i;
    op.toRemove -= i;
    op.toInsert = op.toInsert.substring(i);
    rop.toInsert = rop.toInsert.substring(i);

    if (rop.toInsert.length === op.toInsert.length) {
        for (i = rop.toInsert.length-1; i >= 0 && rop.toInsert[i] === op.toInsert[i]; i--) ;
        op.toInsert = op.toInsert.substring(0, i+1);
        op.toRemove = i+1;
    }

    if (op.toRemove === 0 && op.toInsert.length === 0) { return null; }
    return op;
};

var equals = Operation.equals = function (opA, opB) {
    return (opA.toRemove === opB.toRemove
        && opA.toInsert === opB.toInsert
        && opA.offset === opB.offset);
};

var lengthChange = Operation.lengthChange = function (op)
{
    if (Common.PARANOIA) { check(op); }
    return op.toInsert.length - op.toRemove;
};

/*
 * @return the merged operation OR null if the result of the merger is a noop.
 */
var merge = Operation.merge = function (oldOpOrig, newOpOrig) {
    if (Common.PARANOIA) {
        check(newOpOrig);
        check(oldOpOrig);
    }

    var newOp = clone(newOpOrig);
    var oldOp = clone(oldOpOrig);
    var offsetDiff = newOp.offset - oldOp.offset;

    if (newOp.toRemove > 0) {
        var origOldInsert = oldOp.toInsert;
        oldOp.toInsert = (
             oldOp.toInsert.substring(0,offsetDiff)
           + oldOp.toInsert.substring(offsetDiff + newOp.toRemove)
        );
        newOp.toRemove -= (origOldInsert.length - oldOp.toInsert.length);
        if (newOp.toRemove < 0) { newOp.toRemove = 0; }

        oldOp.toRemove += newOp.toRemove;
        newOp.toRemove = 0;
    }

    if (offsetDiff < 0) {
        oldOp.offset += offsetDiff;
        oldOp.toInsert = newOp.toInsert + oldOp.toInsert;

    } else if (oldOp.toInsert.length === offsetDiff) {
        oldOp.toInsert = oldOp.toInsert + newOp.toInsert;

    } else if (oldOp.toInsert.length > offsetDiff) {
        oldOp.toInsert = (
            oldOp.toInsert.substring(0,offsetDiff)
          + newOp.toInsert
          + oldOp.toInsert.substring(offsetDiff)
        );
    } else {
        throw new Error("should never happen\n" +
                        JSON.stringify([oldOpOrig,newOpOrig], null, '  '));
    }

    if (oldOp.toInsert === '' && oldOp.toRemove === 0) {
        return null;
    }
    if (Common.PARANOIA) { check(oldOp); }

    return oldOp;
};

/**
 * If the new operation deletes what the old op inserted or inserts content in the middle of
 * the old op's content or if they abbut one another, they should be merged.
 */
var shouldMerge = Operation.shouldMerge = function (oldOp, newOp) {
    if (Common.PARANOIA) {
        check(oldOp);
        check(newOp);
    }
    if (newOp.offset < oldOp.offset) {
        return (oldOp.offset <= (newOp.offset + newOp.toRemove));
    } else {
        return (newOp.offset <= (oldOp.offset + oldOp.toInsert.length));
    }
};

/**
 * Rebase newOp against oldOp.
 *
 * @param oldOp the eariler operation to have happened.
 * @param newOp the later operation to have happened (in time).
 * @return either the untouched newOp if it need not be rebased,
 *                the rebased clone of newOp if it needs rebasing, or
 *                null if newOp and oldOp must be merged.
 */
var rebase = Operation.rebase = function (oldOp, newOp) {
    if (Common.PARANOIA) {
        check(oldOp);
        check(newOp);
    }
    if (newOp.offset < oldOp.offset) { return newOp; }
    newOp = clone(newOp);
    newOp.offset += oldOp.toRemove;
    newOp.offset -= oldOp.toInsert.length;
    return newOp;
};

/**
 * this is a lossy and dirty algorithm, everything else is nice but transformation
 * has to be lossy because both operations have the same base and they diverge.
 * This could be made nicer and/or tailored to a specific data type.
 *
 * @param toTransform the operation which is converted *MUTATED*.
 * @param transformBy an existing operation which also has the same base.
 * @return toTransform *or* null if the result is a no-op.
 */

var transform0 = Operation.transform0 = function (text, toTransformOrig, transformByOrig) {
    // Cloning the original transformations makes this algorithm such that it
    // **DOES NOT MUTATE ANYMORE**
    var toTransform = Operation.clone(toTransformOrig);
    var transformBy = Operation.clone(transformByOrig);

    if (toTransform.offset > transformBy.offset) {
        if (toTransform.offset > transformBy.offset + transformBy.toRemove) {
            // simple rebase
            toTransform.offset -= transformBy.toRemove;
            toTransform.offset += transformBy.toInsert.length;
            return toTransform;
        }
        // goto the end, anything you deleted that they also deleted should be skipped.
        var newOffset = transformBy.offset + transformBy.toInsert.length;
        toTransform.toRemove = 0; //-= (newOffset - toTransform.offset);
        if (toTransform.toRemove < 0) { toTransform.toRemove = 0; }
        toTransform.offset = newOffset;
        if (toTransform.toInsert.length === 0 && toTransform.toRemove === 0) {
            return null;
        }
        return toTransform;
    }
    if (toTransform.offset + toTransform.toRemove < transformBy.offset) {
        return toTransform;
    }
    toTransform.toRemove = transformBy.offset - toTransform.offset;
    if (toTransform.toInsert.length === 0 && toTransform.toRemove === 0) {
        return null;
    }
    return toTransform;
};

/**
 * @param toTransform the operation which is converted
 * @param transformBy an existing operation which also has the same base.
 * @return a modified clone of toTransform *or* toTransform itself if no change was made.
 */
var transform = Operation.transform = function (text, toTransform, transformBy, transformFunction) {
    if (Common.PARANOIA) {
        check(toTransform);
        check(transformBy);
    }
    transformFunction = transformFunction || transform0;
    toTransform = clone(toTransform);
    var result = transformFunction(text, toTransform, transformBy);
    if (Common.PARANOIA && result) { check(result); }
    return result;
};

/** Used for testing. */
var random = Operation.random = function (docLength) {
    Common.assert(Common.isUint(docLength));
    var offset = Math.floor(Math.random() * 100000000 % docLength) || 0;
    var toRemove = Math.floor(Math.random() * 100000000 % (docLength - offset)) || 0;
    var toInsert = '';
    do {
        var toInsert = Common.randomASCII(Math.floor(Math.random() * 20));
    } while (toRemove === 0 && toInsert === '');
    return create(offset, toRemove, toInsert);
};

}
};
ChainPad = r("ChainPad.js");}());