// Text drafts stay in this visitor's browser, independently for each conversation.
var ChatDrafts = {
    create(options){
        const scope = /^[0-9a-f]{64}$/.test(options.scope || '') ? options.scope : null;
        const prefix = scope ? 'baiyue-draft-v1:' + scope + ':' : null;
        const activeKey = scope ? 'baiyue-active-chat-v1:' + scope : null;
        const memory = new Map();
        const dirty = new Set();
        let current = 'new';
        function id(value){
            if(value === null || value === 'new') return 'new';
            const key = String(value);
            return /^[1-9][0-9]{0,18}$/.test(key) ? key : null;
        }
        function storage(name){
            try{ return options[name](); }catch(error){ return null; }
        }
        function read(value){
            const key = id(value);
            if(!key) return '';
            if(dirty.has(key)) return memory.get(key) || '';
            if(prefix){
                try{
                    const saved = storage('storage').getItem(prefix + key);
                    if(saved !== null){
                        const data = JSON.parse(saved);
                        if(data && data.version === 1 && typeof data.text === 'string'){
                            memory.set(key, data.text);
                            return data.text;
                        }
                    }
                    memory.delete(key);
                    return '';
                }catch(error){}
            }
            return memory.get(key) || '';
        }
        function write(value, text){
            const key = id(value);
            if(!key || typeof text !== 'string') return false;
            if(text) memory.set(key, text); else memory.delete(key);
            dirty.add(key);
            if(!prefix) return false;
            try{
                const target = storage('storage');
                if(text) target.setItem(prefix + key, JSON.stringify({version:1,text:text}));
                else target.removeItem(prefix + key);
                dirty.delete(key);
                return true;
            }catch(error){ return false; }
        }
        function active(value){
            if(arguments.length){
                current = id(value) || 'new';
                if(activeKey) try{ storage('tabStorage').setItem(activeKey, current); }catch(error){}
            }else if(activeKey){
                try{ const saved=storage('tabStorage').getItem(activeKey); if(saved !== null) current = id(saved) || current; }catch(error){}
            }
            return current;
        }
        function clear(){
            memory.clear();
            dirty.clear();
            if(prefix){
                try{
                    const target = storage('storage');
                    for(let index = target.length - 1; index >= 0; index--){
                        const key = target.key(index);
                        if(key && key.startsWith(prefix)) target.removeItem(key);
                    }
                }catch(error){}
            }
            active('new');
        }
        return {read:read,write:write,active:active,remove:value=>write(value,''),clear:clear};
    }
};