[NEW] Add ON_PRE_SETTING_UPDATE hook to apps

[shiqimei]

What? ⛵

This PR introduces a new onPreSettingUpdate hook into apps. In this way, app developers can validate new setting update before it takes effects.

Why? 🤔

RFC 37

Links 🌎

PS 👀

[shiqimei]

import {
    IAppAccessors, IConfigurationExtend, IConfigurationModify, IEnvironmentRead, IHttp, ILogger, IRead,
} from '@rocket.chat/apps-engine/definition/accessors';
import { App } from '@rocket.chat/apps-engine/definition/App';
import { InvalidSettingException } from '@rocket.chat/apps-engine/definition/exceptions';
import { IAppInfo } from '@rocket.chat/apps-engine/definition/metadata';
import { ISetting, SettingType } from '@rocket.chat/apps-engine/definition/settings';
import { ISettingUpdateContext } from '../../apps-engine/definition/settings/ISettingUpdateContext';

export class AppsSettings extends App {
    constructor(info: IAppInfo, logger: ILogger, accessors: IAppAccessors) {
        super(info, logger, accessors);
    }

    public async initialize(configurationExtend: IConfigurationExtend, environmentRead: IEnvironmentRead): Promise<void> {
        configurationExtend.settings.provideSetting({
            id: 'Telegram',
            public: true,
            type: SettingType.SELECT,
            packageValue: 'none',
            value: 'none',
            values: [
                {
                    key: 'none',
                    i18nLabel: 'none',
                },
                {
                    key: 'name',
                    i18nLabel: 'name',
                },
                {
                    key: 'username',
                    i18nLabel: 'username',
                },
                {
                    key: 'nickname',
                    i18nLabel: 'nickname',
                },
            ],
            i18nLabel: 'telegram_agents_display_name',
            i18nDescription: 'telegram_agents_display_name_description',
            required: true,
        });
    }

    public async onPreSettingUpdate(context: ISettingUpdateContext, configurationModify: IConfigurationModify, read: IRead, http: IHttp): Promise<ISetting> {
        const { oldSetting, newSetting: setting } = context;
        console.log({ oldSetting: oldSetting.value, newSetting: setting.value });

        switch (setting.id) {
            case 'Telegram': {
                switch (setting.value) {
                    case 'none':
                        throw new InvalidSettingException('The value of the setting Telegram cannot be `none`');
                }
                break;
            }
        }
        return setting;
    }
}

The app for testing:
apps-settings_0.0.1.zip

screeshots:

[codecov]

Codecov Report

Merging #417 (4a521e0) into alpha (a507056) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            alpha     #417      +/-   ##
==========================================
+ Coverage   48.67%   48.72%   +0.04%     
==========================================
  Files         103      103              
  Lines        3244     3247       +3     
  Branches      476      478       +2     
==========================================
+ Hits         1579     1582       +3     
  Misses       1665     1665              

Impacted Files	Coverage Δ
src/server/managers/AppSettingsManager.ts	100.00% <100.00%> (ø)

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