import Knex from "knex";
import { isConstructorDeclaration } from "typescript";
import * as api from '../../client/src/api/api';
import { TagBaseWithRefs, TagWithDetails, TagWithId, TagWithRefs, TagWithRefsWithId } from "../../client/src/api/api";
import { DBError, DBErrorKind } from "../endpoints/types";

export async function getTagChildrenRecursive(id: number, userId: number, trx: any): Promise<number[]> {
    const directChildren = (await trx.select('id')
        .from('tags')
        .where({ 'user': userId })
        .where({ 'parentId': id })).map((r: any) => r.id);

    const indirectChildrenPromises = directChildren.map(
        (child: number) => getTagChildrenRecursive(child, userId, trx)
    );
    const indirectChildrenNested = await Promise.all(indirectChildrenPromises);
    const indirectChildren = indirectChildrenNested.flat();

    return [
        ...directChildren,
        ...indirectChildren,
    ]
}

// Returns the id of the created tag.
export async function createTag(userId: number, tag: TagWithRefs, knex: Knex): Promise<number> {
    return await knex.transaction(async (trx) => {
        // If applicable, retrieve the parent tag.
        const maybeParent: number | null =
            tag.parentId ?
                (await trx.select('id')
                    .from('tags')
                    .where({ 'user': userId })
                    .where({ 'id': tag.parentId }))[0]['id'] :
                null;

        // Check if the parent was found, if applicable.
        if (tag.parentId && maybeParent !== tag.parentId) {
            const e: DBError = {
                name: "DBError",
                kind: DBErrorKind.ResourceNotFound,
                message: 'Not all to-be-linked resources were found.',
            };
            throw e;
        }

        // Create the new tag.
        var newTag: any = {
            name: tag.name,
            user: userId,
        };
        if (maybeParent) {
            newTag['parentId'] = maybeParent;
        }
        const tagId = (await trx('tags')
            .insert(newTag)
            .returning('id') // Needed for Postgres
        )[0];

        return tagId;
    })
}

export async function deleteTag(userId: number, tagId: number, knex: Knex) {

    await knex.transaction(async (trx) => {
        // Start retrieving any child tags.
        const childTagsPromise =
            getTagChildrenRecursive(tagId, userId, trx);

        // Start retrieving the tag itself.
        const tagPromise = trx.select('id')
            .from('tags')
            .where({ 'user': userId })
            .where({ id: tagId })
            .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined)

        // Wait for the requests to finish.
        var [tag, children] = await Promise.all([tagPromise, childTagsPromise]);

        // Merge all IDs.
        const toDelete = [tag, ...children];

        // Check that we found all objects we need.
        if (!tag) {
            const e: DBError = {
                name: "DBError",
                kind: DBErrorKind.ResourceNotFound,
                message: 'Not all to-be-linked resources were found.',
            };
            throw e;
        }

        // Start deleting artist associations with the tag.
        const deleteArtistsPromise: Promise<any> =
            trx.delete()
                .from('artists_tags')
                .whereIn('tagId', toDelete);

        // Start deleting album associations with the tag.
        const deleteAlbumsPromise: Promise<any> =
            trx.delete()
                .from('albums_tags')
                .whereIn('tagId', toDelete);

        // Start deleting track associations with the tag.
        const deleteTracksPromise: Promise<any> =
            trx.delete()
                .from('tracks_tags')
                .whereIn('tagId', toDelete);


        // Start deleting the tag and its children.
        const deleteTags: Promise<any> = trx('tags')
            .where({ 'user': userId })
            .whereIn('id', toDelete)
            .del();

        await Promise.all([deleteArtistsPromise, deleteAlbumsPromise, deleteTracksPromise, deleteTags])
    })
}

export async function getTag(userId: number, tagId: number, knex: Knex): Promise<TagWithDetails> {
    const tagPromise: Promise<TagWithRefsWithId | undefined> =
        knex.select(['id', 'name', 'parentId'])
            .from('tags')
            .where({ 'user': userId })
            .where({ 'id': tagId })
            .then((r: TagWithRefsWithId[] | undefined) => r ? r[0] : undefined);

    const parentPromise: Promise<TagWithId | null> =
        tagPromise
            .then((r: TagWithRefsWithId | undefined) =>
                (r && r.parentId) ? (
                    getTag(userId, r.parentId, knex)
                        .then((rr: TagWithDetails | null) => rr ? { ...rr, id: r.parentId || 0 } : null)
                ) : null
            )

    const [maybeTag, maybeParent] = await Promise.all([tagPromise, parentPromise]);

    if (maybeTag) {
        let result: TagWithDetails = {
            mbApi_typename: "tag",
            name: maybeTag.name,
            parent: maybeParent,
        }
        return result;
    } else {
        const e: DBError = {
            name: "DBError",
            kind: DBErrorKind.ResourceNotFound,
            message: 'Not all resources were found.',
        };
        throw e;
    }
}

export async function modifyTag(userId: number, tagId: number, tag: TagBaseWithRefs, knex: Knex): Promise<void> {
    await knex.transaction(async (trx) => {
        // Start retrieving the parent tag.
        const parentTagIdPromise: Promise<number | undefined | null> = tag.parentId ?
            trx.select('id')
                .from('tags')
                .where({ 'user': userId })
                .where({ 'id': tag.parentId })
                .then((ts: any) => ts.map((t: any) => t['tagId'])) :
            (async () => { return null })();

        // Start retrieving the tag itself.
        const tagPromise = trx.select('id')
            .from('tags')
            .where({ 'user': userId })
            .where({ id: tagId })
            .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined)

        // Wait for the requests to finish.
        var [dbTag, parent] = await Promise.all([tagPromise, parentTagIdPromise]);

        // Check that we found all objects we need.
        if ((tag.parentId && !parent) ||
            !dbTag) {
            const e: DBError = {
                name: "DBError",
                kind: DBErrorKind.ResourceNotFound,
                message: 'Not all resources were found.',
            };
            throw e;
        }

        // Modify the tag.
        await trx('tags')
            .where({ 'user': userId })
            .where({ 'id': tagId })
            .update({
                name: tag.name,
                parentId: tag.parentId || null,
            })
    })
}

export async function mergeTag(userId: number, fromId: number, toId: number, knex: Knex): Promise<void> {
    await knex.transaction(async (trx) => {
        // Start retrieving the "from" tag.
        const fromTagIdPromise = trx.select('id')
            .from('tags')
            .where({ 'user': userId })
            .where({ id: fromId })
            .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined)

        // Start retrieving the "to" tag.
        const toTagIdPromise = trx.select('id')
            .from('tags')
            .where({ 'user': userId })
            .where({ id: toId })
            .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined)

        // Wait for the requests to finish.
        var [fromTagId, toTagId] = await Promise.all([fromTagIdPromise, toTagIdPromise]);

        // Check that we found all objects we need.
        if (!fromTagId || !toTagId) {
            const e: DBError = {
                name: "DBError",
                kind: DBErrorKind.ResourceNotFound,
                message: 'Not all resources were found.',
            };
            throw e;
        }

        // Assign new tag ID to any objects referencing the to-be-merged tag.
        const cPromise = trx('tags')
            .where({ 'user': userId })
            .where({ 'parentId': fromId })
            .update({ 'parentId': toId });
        const sPromise = trx('songs_tags')
            .where({ 'tagId': fromId })
            .update({ 'tagId': toId });
        const arPromise = trx('artists_tags')
            .where({ 'tagId': fromId })
            .update({ 'tagId': toId });
        const alPromise = trx('albums_tags')
            .where({ 'tagId': fromId })
            .update({ 'tagId': toId });
        await Promise.all([sPromise, arPromise, alPromise, cPromise]);

        // Delete the original tag.
        await trx('tags')
            .where({ 'user': userId })
            .where({ 'id': fromId })
            .del();
    })
}