/*
 Copyright 2017 Michael Telatynski <7t3chguy@gmail.com>

 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 { MatrixEvent, EventType, RelationType } from "matrix-js-sdk/src/matrix";

import SettingsStore from "./settings/SettingsStore";
import { IRoomState } from "./components/structures/RoomView";

interface IDiff {
    isMemberEvent: boolean;
    isJoin?: boolean;
    isPart?: boolean;
    isDisplaynameChange?: boolean;
    isAvatarChange?: boolean;
}

function memberEventDiff(ev: MatrixEvent): IDiff {
    const diff: IDiff = {
        isMemberEvent: ev.getType() === EventType.RoomMember,
    };

    // If is not a Member Event then the other checks do not apply, so bail early.
    if (!diff.isMemberEvent) return diff;

    const content = ev.getContent();
    const prevContent = ev.getPrevContent();

    const isMembershipChanged = content.membership !== prevContent.membership;
    diff.isJoin = isMembershipChanged && content.membership === "join";
    diff.isPart = isMembershipChanged && content.membership === "leave" && ev.getStateKey() === ev.getSender();

    const isJoinToJoin = !isMembershipChanged && content.membership === "join";
    diff.isDisplaynameChange = isJoinToJoin && content.displayname !== prevContent.displayname;
    diff.isAvatarChange = isJoinToJoin && content.avatar_url !== prevContent.avatar_url;
    return diff;
}

/**
 * Determines whether the given event should be hidden from timelines.
 * @param ev The event
 * @param ctx An optional RoomContext to pull cached settings values from to avoid
 *     hitting the settings store
 */
export default function shouldHideEvent(ev: MatrixEvent, ctx?: IRoomState): boolean {
    // Accessing the settings store directly can be expensive if done frequently,
    // so we should prefer using cached values if a RoomContext is available
    const isEnabled = ctx
        ? (name: keyof IRoomState) => ctx[name]
        : (name: string) => SettingsStore.getValue(name, ev.getRoomId());

    // Hide redacted events
    // Deleted events with a thread are always shown regardless of user preference
    // to make sure that a thread can be accessible even if the root message is deleted
    if (ev.isRedacted() && !isEnabled("showRedactions") && !ev.getThread()) return true;

    // Hide replacement events since they update the original tile (if enabled)
    if (ev.isRelation(RelationType.Replace)) return true;

    const eventDiff = memberEventDiff(ev);

    if (eventDiff.isMemberEvent) {
        if ((eventDiff.isJoin || eventDiff.isPart) && !isEnabled("showJoinLeaves")) return true;
        if (eventDiff.isAvatarChange && !isEnabled("showAvatarChanges")) return true;
        if (eventDiff.isDisplaynameChange && !isEnabled("showDisplaynameChanges")) return true;
    }

    return false;
}