import * as fb from "firebase";
import { computed, observable, runInAction } from "mobx";

type Query = fb.firestore.Query;
type DocumentReference = fb.firestore.DocumentReference;
type DocumentSnapshot = fb.firestore.DocumentSnapshot;
type LoadingDocumentSnapshot = DocumentSnapshot | undefined;
type Dictionary<T> = { [key: string]: T };
// type QuerySnapshot = fb.firestore.QuerySnapshot;
// type LoadingCollectionSnapshot = QuerySnapshot | undefined;

export interface FireResource<T> {
    exists(): boolean;
    loading(): boolean;
    get(): T;
}

export class FireDocument<T> implements FireResource<T> {

    private name: string;

    @observable private _snapshot: LoadingDocumentSnapshot = undefined;
    @computed get snapshot() { return this._snapshot; }
    set snapshot(snapshot: LoadingDocumentSnapshot) { this._snapshot = snapshot; }

    constructor(doc: DocumentReference) {
        this.load(doc);
    }

    exists() {
        return this.snapshot !== undefined && this.snapshot.exists;
    }

    loading() {
        return this.snapshot === undefined;
    }

    get(): T {
        if (this.snapshot !== undefined && this.snapshot.exists) {
            return this.snapshot.data() as T;
        } else {
            throw new Error(`Snapshot for ${this.name} doesn't exist`);
        }
    }

    private async load(doc: DocumentReference) {
        this.snapshot = await doc.get();
    }
}

export class FireCollection<T, U = Dictionary<T>> implements FireResource<U> {

    private name: string;
    private filter: (doc: DocumentSnapshot) => boolean;
    private transform: (docs: DocumentSnapshot[]) => U;

    @observable private _snapshot: U | undefined = undefined;
    @observable private _exists: boolean = false;

    @computed get snapshot() { return this._snapshot; }
    set snapshot(snapshot: U | undefined) { this._snapshot = snapshot; }

    constructor(col: Query) {
        this.load(col);
        this.transform =
            (docs: DocumentSnapshot[]) =>
                Object.assign({}, ...docs.map(doc => ({ [doc.id]: doc.data() as T })));
    }

    loading() {
        return this.snapshot === undefined;
    }

    exists() {
        return this._exists;
    }

    setFilter(filter: (doc: DocumentSnapshot) => boolean) {
        this.filter = filter;
    }

    setTransform(transform: (docs: DocumentSnapshot[]) => U) {
        this.transform = transform;
    }

    get(): U {
        if (this.snapshot !== undefined && this.exists()) {
            return this.snapshot;
        } else {
            throw new Error(`Snapshot for ${this.name} doesn't exist`);
        }
    }

    private async load(col: Query) {
        const snapshot = await col.get();
        const filtered = snapshot.docs.filter(doc => this.filter ? this.filter(doc) : true);
        runInAction(() => this._exists = filtered.length > 0);
        this.snapshot = this.transform(filtered);
    }
}