hydrogen-web/src/domain/session/room/timeline/TilesCollection.js

/*
Copyright 2020 Bruno Windels <bruno@windels.cloud>

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 {BaseObservableList} from "../../../../observable/list/BaseObservableList.js";
import {sortedIndex} from "../../../../utils/sortedIndex.js";

// maps 1..n entries to 0..1 tile. Entries are what is stored in the timeline, either an event or fragmentboundary
// for now, tileCreator should be stable in whether it returns a tile or not.
// e.g. the decision to create a tile or not should be based on properties
// not updated later on (e.g. event type)
// also see big comment in onUpdate
export class TilesCollection extends BaseObservableList {
    constructor(entries, tileCreator) {
        super();
        this._entries = entries;
        this._tiles = null;
        this._entrySubscription = null;
        this._tileCreator = tileCreator;
        this._emitSpontanousUpdate = this._emitSpontanousUpdate.bind(this);
    }

    _emitSpontanousUpdate(tile, params) {
        const entry = tile.lowerEntry;
        const tileIdx = this._findTileIdx(entry);
        this.emitUpdate(tileIdx, tile, params);
    }

    onSubscribeFirst() {
        this._entrySubscription = this._entries.subscribe(this);
        this._populateTiles();
    }

    _populateTiles() {
        this._tiles = [];
        let currentTile = null;
        for (let entry of this._entries) {
            if (!currentTile || !currentTile.tryIncludeEntry(entry)) {
                currentTile = this._tileCreator(entry);
                if (currentTile) {
                    this._tiles.push(currentTile);
                }
            }
        }
        let prevTile = null;
        for (let tile of this._tiles) {
            if (prevTile) {
                prevTile.updateNextSibling(tile);
            }
            tile.updatePreviousSibling(prevTile);
            prevTile = tile;
        }
        if (prevTile) {
            prevTile.updateNextSibling(null);
        }
        // now everything is wired up,
        // allow tiles to emit updates
        for (const tile of this._tiles) {
            tile.setUpdateEmit(this._emitSpontanousUpdate);
        }
    }

    _findTileIdx(entry) {
        return sortedIndex(this._tiles, entry, (entry, tile) => {
            // negate result because we're switching the order of the params
            return -tile.compareEntry(entry);
        });
    }

    _findTileAtIdx(entry, idx) {
        const tile = this._getTileAtIdx(idx);
        if (tile && tile.compareEntry(entry) === 0) {
            return tile;
        }
    }

    _getTileAtIdx(tileIdx) {
        if (tileIdx >= 0 && tileIdx < this._tiles.length) {
            return this._tiles[tileIdx];
        }
        return null;
    }

    onUnsubscribeLast() {
        this._entrySubscription = this._entrySubscription();
        this._tiles = null;
    }

    onReset() {
        // if TileViewModel were disposable, dispose here, or is that for views to do? views I suppose ...
        this._buildInitialTiles();
        this.emitReset();
    }

    onAdd(index, entry) {
        const tileIdx = this._findTileIdx(entry);
        const prevTile = this._getTileAtIdx(tileIdx - 1);
        if (prevTile && prevTile.tryIncludeEntry(entry)) {
            this.emitUpdate(tileIdx - 1, prevTile);
            return;
        }
        // not + 1 because this entry hasn't been added yet
        const nextTile = this._getTileAtIdx(tileIdx);
        if (nextTile && nextTile.tryIncludeEntry(entry)) {
            this.emitUpdate(tileIdx, nextTile);
            return;
        }

        const newTile = this._tileCreator(entry);
        if (newTile) {
            if (prevTile) {
                prevTile.updateNextSibling(newTile);
                // this emits an update while the add hasn't been emitted yet
                newTile.updatePreviousSibling(prevTile);
            }
            if (nextTile) {
                newTile.updateNextSibling(nextTile);
                nextTile.updatePreviousSibling(newTile);
            }
            this._tiles.splice(tileIdx, 0, newTile);
            this.emitAdd(tileIdx, newTile);
            // add event is emitted, now the tile
            // can emit updates
            newTile.setUpdateEmit(this._emitSpontanousUpdate);
        }
        // find position by sort key
        // ask siblings to be included? both? yes, twice: a (insert c here) b, ask a(c), if yes ask b(a), else ask b(c)? if yes then b(a)?
    }

    onUpdate(index, entry, params) {
        const tileIdx = this._findTileIdx(entry);
        const tile = this._findTileAtIdx(entry, tileIdx);
        if (tile) {
            const action = tile.updateEntry(entry, params);
            if (action.shouldRemove) {
                this._removeTile(tileIdx, tile);
            }
            if (action.shouldUpdate) {
                this.emitUpdate(tileIdx, tile, action.updateParams);
            }
        }
        // technically we should handle adding a tile here as well
        // in case before we didn't have a tile for it but now we do
        // but in reality we don't have this use case as the type and msgtype
        // doesn't change. Decryption maybe is the exception?


        // outcomes here can be
        //   tiles should be removed (got redacted and we don't want it in the timeline)
        //   tile should be added where there was none before ... ?
        //   entry should get it's own tile now
        //   merge with neighbours? ... hard to imagine use case for this  ...
    }

    _removeTile(tileIdx, tile) {
        const prevTile = this._getTileAtIdx(tileIdx - 1);
        const nextTile = this._getTileAtIdx(tileIdx + 1);
        this._tiles.splice(tileIdx, 1);
        prevTile && prevTile.updateNextSibling(nextTile);
        nextTile && nextTile.updatePreviousSibling(prevTile);
        tile.setUpdateEmit(null);
        this.emitRemove(tileIdx, tile);
    }

    // would also be called when unloading a part of the timeline
    onRemove(index, entry) {
        const tileIdx = this._findTileIdx(entry);
        const tile = this._findTileAtIdx(entry, tileIdx);
        if (tile) {
            const removeTile = tile.removeEntry(entry);
            if (removeTile) {
                this._removeTile(tileIdx, tile);
            } else {
                this.emitUpdate(tileIdx, tile);
            }
        }
    }

    onMove(fromIdx, toIdx, value) {
        // this ... cannot happen in the timeline?
        // perhaps we can use this event to support a local echo (in a different fragment)
        // to be moved to the key of the remote echo, so we don't loose state ... ?
    }

    [Symbol.iterator]() {
        return this._tiles.values();
    }

    get length() {
        return this._tiles.length;
    }

    getFirst() {
        return this._tiles[0];
    }
}

import {ObservableArray} from "../../../../observable/list/ObservableArray.js";
import {UpdateAction} from "./UpdateAction.js";

export function tests() {
    class TestTile {
        constructor(entry) {
            this.entry = entry;
            this.update = null;
        }
        setUpdateEmit(update) {
            this.update = update;
        }
        tryIncludeEntry() {
            return false;
        }
        compareEntry(b) {
            return this.entry.n - b.n;
        }
        removeEntry() {
            return true;
        }
        get upperEntry() {
            return this.entry;
        }

        get lowerEntry() {
            return this.entry;
        }
        updateNextSibling() {}
        updatePreviousSibling() {}
        updateEntry() {
            return UpdateAction.Nothing;
        }
    }

    return {
        "don't emit update before add": assert => {
            class UpdateOnSiblingTile extends TestTile {
                updateNextSibling() {
                    // this happens with isContinuation
                    this.update && this.update(this, "next");
                }
                updatePreviousSibling() {
                    // this happens with isContinuation
                    this.update && this.update(this, "previous");
                }
            }
            const entries = new ObservableArray([{n: 5}, {n: 10}]);
            const tiles = new TilesCollection(entries, entry => new UpdateOnSiblingTile(entry));
            let receivedAdd = false;
            tiles.subscribe({
                onAdd(idx, tile) {
                    assert(tile.entry.n, 7);
                    receivedAdd = true;
                },
                onUpdate(idx, tile) {
                    if (tile.entry.n === 7) {
                        assert(!receivedAdd, "receiving update before add");
                    }
                }
            });
            entries.insert(1, {n: 7});
            assert(receivedAdd);
        },
    }
}