// Pace already received text while preserving network completion and cancellation.
var ChatReply = (function(){
    function create(options){
        const now = options.now || Date.now;
        const readyAt = now() + 300;
        const segmenter = typeof Intl !== 'undefined' && Intl.Segmenter
            ? new Intl.Segmenter(undefined, {granularity:'grapheme'}) : null;
        let text = '', characters = [], visible = 0;
        let startedAt = null, timer = null, card = null;
        let complete = false, closed = false;

        function clearTimer(){
            if(timer !== null) clearTimeout(timer);
            timer = null;
        }
        function schedule(delay){
            if(timer === null && !closed) timer = setTimeout(function(){
                try{ draw(false); }
                catch(error){ closed = true; clearTimer(); options.onError(error); }
            }, delay);
        }
        function draw(force){
            clearTimer();
            if(closed) return;
            const animate = !force && options.shouldAnimate();
            if(animate && now() < readyAt){ schedule(readyAt - now()); return; }
            if(card){
                const show = card;
                card = null;
                show();
            }
            if(visible < characters.length){
                if(startedAt === null) startedAt = now();
                const elapsed = Math.max(0, now() - startedAt);
                const rate = Math.max(45, characters.length / 4);
                visible = animate ? Math.min(characters.length, Math.max(visible + 1, Math.floor(elapsed * rate / 1000))) : characters.length;
                options.onText(characters.slice(0, visible).join(''));
            }
            if(visible < characters.length){ schedule(16); return; }
            if(complete){
                closed = true;
                options.onComplete();
            }
        }
        function update(){
            if(closed) return;
            if(!options.shouldAnimate()) draw(true);
            else schedule(Math.max(0, readyAt - now()));
        }
        function setText(value){
            text = value;
            characters = segmenter ? Array.from(segmenter.segment(text), item => item.segment) : Array.from(text);
        }
        return {
            append:function(value){
                if(closed) return;
                card = null;
                setText(text + value);
                update();
            },
            replace:function(value){
                if(closed) return;
                card = null;
                setText(value);
                visible = 0;
                update();
            },
            card:function(show){
                if(closed) return;
                setText('');
                visible = 0;
                card = show;
                update();
            },
            complete:function(){ complete = true; update(); },
            flush:function(){ draw(true); },
            cancel:function(){ closed = true; clearTimer(); },
        };
    }
    return {create:create};
})();