collection_diff.ts

type CollectionDiff<TModified, TNew = TModified, TDeleted = TModified> = {
    new: TNew[];
    modified: TModified[];
    deleted: TDeleted[];
};

export const calcCollectionDiff = <L, R = L>(
    left: Iterable<L> | Array<L>,
    right: Iterable<R> | Array<R>,
    getLeftKey: (item: L) => string,
    getRightKey: (item: R) => string,
    areEqual: (leftItem: L, rightItem: R) => boolean,
) => {
    const result: CollectionDiff<R, R, L> = {
        new: [],
        deleted: [],
        modified: [],
    };

    const leftItemKeys: string[] = [];

    for (const leftItem of left) {
        const leftItemKey = getLeftKey(leftItem);
        leftItemKeys.push(leftItemKey);
        let found = false;
        for (const righItem of right) {
            const rightItemKey = getRightKey(righItem);
            if (rightItemKey === leftItemKey) {
                found = true;
                if (!areEqual(leftItem, righItem)) {
                    result.modified.push(righItem);
                }
                break;
            }
        }
        if (!found) {
            result.deleted.push(leftItem);
        }
    }

    for (const rightItem of right) {
        const rightItemKey = getRightKey(rightItem);
        if (leftItemKeys.indexOf(rightItemKey) === -1) {
            result.new.push(rightItem);
        }
    }

    return result;
};