// Ensure that the DiffFormatterPlugin is only installed once.
if(!version.extensions.DiffFormatterPlugin) {
version.extensions.DiffFormatterPlugin = {installed:true};

if(version.major < 2 || (version.major == 2 && version.minor < 1)) {
    alertAndThrow('DiffFormatterPlugin requires TiddlyWiki 2.1 or later.');
}

diffFormatter = {}; // 'namespace' for local functions

diffFormatter.init = function() {
    var stylesheet = store.getTiddlerText(tiddler.title + "##StyleSheet");
    if(stylesheet) { // check necessary because it happens more than once for some reason
        config.shadowTiddlers["StyleSheetDiffFormatter"] = stylesheet;
        store.addNotification("StyleSheetDiffFormatter", refreshStyles);
    }
};

diffFormatter.added = {
    name: 'diffAdded',
    match: '^\\+',
    termRegExp: /(\n)/mg,
    handler: function(w)
    {
        var e = createTiddlyElement(w.output,'span',null,'added');
        w.subWikifyTerm(e,this.termRegExp);
        createTiddlyElement(w.output,'br');
    }
};

diffFormatter.removed = {
    name: 'diffRemoved',
    match: '^-',
    termRegExp: /(\n)/mg,
    handler: function(w)
    {
        var e = createTiddlyElement(w.output,'span',null,'removed');
        w.subWikifyTerm(e,this.termRegExp);
        createTiddlyElement(w.output,'br');
    }
};

diffFormatter.charDiff = {
    name: 'diffChars',
    match: '^(?:@@|[+-]{3}) ',
    lookaheadRegExp: /^(?:@@|[+-]{3}) .*\n/mg,
    handler: function(w)
    {
        this.lookaheadRegExp.lastIndex = w.matchStart;
        var lookaheadMatch = this.lookaheadRegExp.exec(w.source);
        if(lookaheadMatch && lookaheadMatch.index == w.matchStart) {
            w.nextMatch = this.lookaheadRegExp.lastIndex;
        }
    }
};

// add new formatters
diffFormatter.init();
config.formatters.push(diffFormatter.added);
config.formatters.push(diffFormatter.removed);

diffFormatter.replaceFormatter = function()
{
    for(var i=0; i<config.formatters.length; i++) {
        if(config.formatters[i].name == 'characterFormat') {
            config.formatters.splice(i,0,diffFormatter.charDiff);
            break;
        }
    }
};
diffFormatter.replaceFormatter();

}// end of 'install only once'