element-web/src/ComposerHistoryManager.js

//@flow
/*
Copyright 2017 Aviral Dasgupta

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

import { Value } from 'slate';
import Html from 'slate-html-serializer';
import { Markdown as Md } from 'slate-md-serializer';
import Plain from 'slate-plain-serializer';
import * as RichText from './RichText';
import Markdown from './Markdown';

import _clamp from 'lodash/clamp';

type MessageFormat = 'rich' | 'markdown';

class HistoryItem {

    // Keeping message for backwards-compatibility
    message: string;
    value: Value;
    format: MessageFormat = 'rich';

    constructor(value: ?Value, format: ?MessageFormat) {
        this.value = value;
        this.format = format;
    }

    static fromJSON(obj): HistoryItem {
        return new HistoryItem(
            Value.fromJSON(obj.value),
            obj.format
        );
    }

    toJSON(): Object {
        return {
            value: this.value.toJSON(),
            format: this.format
        };
    }

    // FIXME: rather than supporting storing history in either format, why don't we pick
    // one canonical form?
    toValue(outputFormat: MessageFormat): Value {
        if (outputFormat === 'markdown') {
            if (this.format === 'rich') {
                // convert a rich formatted history entry to its MD equivalent
                return Plain.deserialize(Md.serialize(this.value));
                // return ContentState.createFromText(RichText.stateToMarkdown(contentState));
            }
            else if (this.format === 'markdown') {
                return this.value;
            }
        } else if (outputFormat === 'rich') {
            if (this.format === 'markdown') {
                // convert MD formatted string to its rich equivalent.
                return Md.deserialize(Plain.serialize(this.value));
                // return RichText.htmlToContentState(new Markdown(contentState.getPlainText()).toHTML());
            }
            else if (this.format === 'rich') {
                return this.value;
            }
        }
        console.error("unknown format -> outputFormat conversion");
        return this.value;
    }
}

export default class ComposerHistoryManager {
    history: Array<HistoryItem> = [];
    prefix: string;
    lastIndex: number = 0;
    currentIndex: number = 0;

    constructor(roomId: string, prefix: string = 'mx_composer_history_') {
        this.prefix = prefix + roomId;

        // TODO: Performance issues?
        let item;
        for (; item = sessionStorage.getItem(`${this.prefix}[${this.currentIndex}]`); this.currentIndex++) {
            try {
                this.history.push(
                    HistoryItem.fromJSON(JSON.parse(item))
                );
            }
            catch (e) {
                console.warn("Throwing away unserialisable history", e);
            }
        }
        this.lastIndex = this.currentIndex;
    }

    save(value: Value, format: MessageFormat) {
        const item = new HistoryItem(value, format);
        this.history.push(item);
        this.currentIndex = this.lastIndex + 1;
        sessionStorage.setItem(`${this.prefix}[${this.lastIndex++}]`, JSON.stringify(item.toJSON()));
    }

    getItem(offset: number, format: MessageFormat): ?Value {
        this.currentIndex = _clamp(this.currentIndex + offset, 0, this.lastIndex - 1);
        const item = this.history[this.currentIndex];
        return item ? item.toValue(format) : null;
    }
}