MuDBase/server/test/reference_model/DBReferenceModel.ts

import { AlbumWithRefsWithId, ArtistWithRefsWithId, DBDataFormat, PostTrackRequest, TrackWithDetails, TrackWithRefsWithId } from "../../../client/src/api/api";
import { makeNotFoundError } from "../../db/common";
import filterInPlace from "../../lib/filterInPlace";

// The mock reference database is in the same format as
// the JSON import/export format, for multiple users.
export type ReferenceDatabase = Record<number, DBDataFormat>

type ObjectsType = "tracks" | "artists" | "tags" | "albums";

// Get a fresh ID for a new object.
function getNewId(db: ReferenceDatabase, objectsType: ObjectsType): number {
    let highest: number = 1;
    for (const data of Object.values(db)) {
        data[objectsType].forEach((obj: any) => highest = Math.max(highest, obj.id));
    }
    return highest + 1;
}

// Check a (set of) IDs for presence in the objects array.
// All have to exist for it to return true.
function checkExists(objects: any[], ids: number[]) {
    return ids.reduce((prev: boolean, id: number) => {
        return prev && objects.find((object: any) => object.id === id);
    }, true);
}

// If not in the array, put the number in the array.
function ensureInSet(n: number, s: number[]) {
    if (!(n in s)) { s.push(n); }
}

// For a set of objects, ensure they point to another object.
function ensureLinked(fromObjects: number[], fromObjectsType: ObjectsType,
    toId: number, toObjectsType: ObjectsType, data: DBDataFormat) {
    if (toObjectsType === 'tracks') {
        fromObjects.forEach((fromId: number) => ensureInSet(toId, 
            (data[fromObjectsType][fromId] as AlbumWithRefsWithId | ArtistWithRefsWithId).trackIds))
    }
}

// Create a new object.
export interface LinkField { field: string, otherObjectType: ObjectsType };
export function createObject(
    userId: number,
    object: any,
    objectType: ObjectsType,
    singularLinkFields: LinkField[],
    pluralLinkFields: LinkField[],
    db: ReferenceDatabase
): { id: number } {
    // Existence checks
    if (!(userId in db)) { throw makeNotFoundError() }
    singularLinkFields.forEach((f: LinkField) => {
        if (!checkExists(db[userId][f.otherObjectType], object[f.field] ? [object[f.field]] : [])) {
            throw makeNotFoundError();
        }
    });
    pluralLinkFields.forEach((f: LinkField) => {
        if (!checkExists(db[userId][f.otherObjectType], object[f.field] || [])) {
            throw makeNotFoundError();
        }
    });

    // Create an ID and the object
    let id = getNewId(db, objectType);
    db[userId][objectType].push({
        ...object,
        id: id,
    })

    // reverse links
    singularLinkFields.forEach((f: LinkField) => {
        ensureLinked(object[f.field] ? [object[f.field]] : [], f.otherObjectType, id, objectType, db[userId]);
    });
    pluralLinkFields.forEach((f: LinkField) => {
        ensureLinked(object[f.field] || [], f.otherObjectType, id, objectType, db[userId]);
    });

    return { id: id };
}

// Create a new track.
export function createTrack(userId: number, track: PostTrackRequest, db: ReferenceDatabase): { id: number } {
    return createObject(
        userId,
        track,
        'tracks',
        [{ field: 'albumId', otherObjectType: 'albums' }],
        [
            { field: 'artistIds', otherObjectType: 'artists' },
            { field: 'tagIds', otherObjectType: 'tags' },
        ],
        db
    );
}

// Delete a track.
export function deleteTrack(userId: number, id: number, db: ReferenceDatabase): void {
    // Existence checks
    if (!(userId in db)) { throw makeNotFoundError() }

    // Find the object to delete.
    let idx = db[userId].tracks.findIndex((track: TrackWithRefsWithId) => track.id === id);
    if (idx < 0) {
        // Not found
        throw makeNotFoundError();
    }

    // Remove references
    db[userId].albums.forEach((x: AlbumWithRefsWithId) => { filterInPlace(x.trackIds, (tid: number) => tid !== id); })
    db[userId].artists.forEach((x: ArtistWithRefsWithId) => { filterInPlace(x.trackIds, (tid: number) => tid !== id); })

    // Delete the object
    db[userId].tracks.splice(idx, 1);
}