import ModelQuery, {ModelQueryResult, WhereTest} from "./ModelQuery";
import Model from "./Model";
import ModelFactory from "./ModelFactory";

export default abstract class ModelRelation<S extends Model, O extends Model, R extends O | O[] | null> {
    protected readonly model: S;
    protected readonly foreignFactory: ModelFactory<O>;
    private readonly query: ModelQuery<O>;
    protected readonly queryModifiers: QueryModifier<O>[] = [];
    protected readonly filters: ModelFilter<O>[] = [];
    protected cachedModels?: R;

    protected constructor(model: S, foreignFactory: ModelFactory<O>) {
        this.model = model;
        this.foreignFactory = foreignFactory;
        this.query = this.foreignFactory.select();
    }

    public abstract clone(): ModelRelation<S, O, R>;

    public constraint(queryModifier: QueryModifier<O>): this {
        this.queryModifiers.push(queryModifier);
        return this;
    }

    public filter(modelFilter: ModelFilter<O>): this {
        this.filters.push(modelFilter);
        return this;
    }

    protected getFinalQuery(): ModelQuery<O> {
        for (const modifier of this.queryModifiers) modifier(this.query);
        this.queryModifiers.splice(0, this.queryModifiers.length); // Empty modifier now that they were applied
        return this.query;
    }

    public abstract getModelID(): any;

    protected abstract async compute(query: ModelQuery<O>): Promise<R>;

    public async get(): Promise<R> {
        if (this.cachedModels === undefined) {
            this.cachedModels = await this.compute(this.getFinalQuery());
        }
        return this.cachedModels;
    }

    public getOrFail(): R {
        if (this.cachedModels === undefined) throw new Error('Models were not fetched');
        return this.cachedModels;
    }

    public abstract async eagerLoad(relations: ModelRelation<S, O, R>[]): Promise<ModelQueryResult<O>>;

    public abstract async populate(models: ModelQueryResult<O>): Promise<void>;
}

export class OneModelRelation<S extends Model, O extends Model> extends ModelRelation<S, O, O | null> {
    protected readonly dbProperties: RelationDatabaseProperties;

    constructor(model: S, foreignFactory: ModelFactory<O>, dbProperties: RelationDatabaseProperties) {
        super(model, foreignFactory);
        this.dbProperties = dbProperties;
    }

    public clone(): OneModelRelation<S, O> {
        return new OneModelRelation(this.model, this.foreignFactory, this.dbProperties);
    }

    public getModelID() {
        return this.model[this.dbProperties.localKey];
    }

    protected async compute(query: ModelQuery<O>): Promise<O | null> {
        this.getFinalQuery().where(this.dbProperties.foreignKey, this.getModelID());
        return await query.first();
    }

    public async get(): Promise<O | null> {
        const model = await super.get();
        if (model) {
            for (const filter of this.filters) {
                if (!(await filter(model))) {
                    return null;
                }
            }
        }
        return model;
    }

    public async eagerLoad(relations: ModelRelation<S, O, O | null>[]): Promise<ModelQueryResult<O>> {
        const ids = relations.map(r => r.getModelID()).filter(id => id !== null && id !== undefined);
        if (ids.length === 0) return [];

        const query = this.getFinalQuery();
        query.where(this.dbProperties.foreignKey, ids, WhereTest.IN);
        return await query.get();
    }

    public async populate(models: ModelQueryResult<O>): Promise<void> {
        this.cachedModels = models.filter(m => m[this.dbProperties.foreignKey] === this.getModelID())[0] || null;
    }

}

export class ManyModelRelation<S extends Model, O extends Model> extends ModelRelation<S, O, O[]> {
    protected readonly dbProperties: RelationDatabaseProperties;

    constructor(model: S, foreignFactory: ModelFactory<O>, dbProperties: RelationDatabaseProperties) {
        super(model, foreignFactory);
        this.dbProperties = dbProperties;
    }

    public clone(): ManyModelRelation<S, O> {
        return new ManyModelRelation<S, O>(this.model, this.foreignFactory, this.dbProperties);
    }

    public cloneReduceToOne(): OneModelRelation<S, O> {
        return new OneModelRelation<S, O>(this.model, this.foreignFactory, this.dbProperties);
    }

    public getModelID(): any {
        return this.model[this.dbProperties.localKey];
    }

    protected async compute(query: ModelQuery<O>): Promise<O[]> {
        this.getFinalQuery().where(this.dbProperties.foreignKey, this.getModelID());
        return await query.get();
    }

    public async get(): Promise<O[]> {
        let models = await super.get();
        for (const filter of this.filters) {
            const newModels = [];
            for (const model of models) {
                if (await filter(model)) {
                    newModels.push(model);
                }
            }
            models = newModels;
        }
        return models;
    }

    public async eagerLoad(relations: ModelRelation<S, O, O[]>[]): Promise<ModelQueryResult<O>> {
        const ids = relations.map(r => r.getModelID()).filter(id => id !== null && id !== undefined);
        if (ids.length === 0) return [];

        const query = this.getFinalQuery();
        query.where(this.dbProperties.foreignKey, ids, WhereTest.IN);
        return await query.get();
    }

    public async populate(models: ModelQueryResult<O>): Promise<void> {
        this.cachedModels = models.filter(m => m[this.dbProperties.foreignKey] === this.getModelID());
    }

}

export class ManyThroughModelRelation<S extends Model, O extends Model> extends ModelRelation<S, O, O[]> {
    protected readonly dbProperties: PivotRelationDatabaseProperties;

    constructor(model: S, foreignFactory: ModelFactory<O>, dbProperties: PivotRelationDatabaseProperties) {
        super(model, foreignFactory);
        this.dbProperties = dbProperties;
        this.constraint(query => query
            .leftJoin(`${this.dbProperties.pivotTable} as pivot`)
            .on(`pivot.${this.dbProperties.foreignPivotKey}`, `${this.foreignFactory.table}.${this.dbProperties.foreignKey}`)
        );
    }

    public clone(): ManyThroughModelRelation<S, O> {
        return new ManyThroughModelRelation<S, O>(this.model, this.foreignFactory, this.dbProperties);
    }

    public getModelID(): any {
        return this.model[this.dbProperties.localKey];
    }

    protected async compute(query: ModelQuery<O>): Promise<O[]> {
        this.getFinalQuery().where(`pivot.${this.dbProperties.localPivotKey}`, this.getModelID());
        return await query.get();
    }

    public async get(): Promise<O[]> {
        let models = await super.get();
        for (const filter of this.filters) {
            const newModels = [];
            for (const model of models) {
                if (await filter(model)) {
                    newModels.push(model);
                }
            }
            models = newModels;
        }
        return models;
    }

    public async eagerLoad(relations: ModelRelation<S, O, O[]>[]): Promise<ModelQueryResult<O>> {
        const ids = relations.map(r => r.getModelID());
        if (ids.length === 0) return [];

        const query = this.getFinalQuery();
        query.where(`pivot.${this.dbProperties.localPivotKey}`, ids, WhereTest.IN);
        query.pivot(`pivot.${this.dbProperties.localPivotKey}`, `pivot.${this.dbProperties.foreignPivotKey}`);
        return await query.get();
    }

    public async populate(models: ModelQueryResult<O>): Promise<void> {
        const ids = models.pivot!
            .filter(p => p[this.dbProperties.localPivotKey] === this.getModelID())
            .map(p => p[this.dbProperties.foreignPivotKey]);
        this.cachedModels = models.filter(m => ids.indexOf(m[this.dbProperties.foreignKey]) >= 0);
    }

}


export type QueryModifier<M extends Model> = (query: ModelQuery<M>) => ModelQuery<M>;

export type ModelFilter<O extends Model> = (model: O) => boolean | Promise<boolean>;

export type RelationDatabaseProperties = {
    localKey: string;
    foreignKey: string;
};

export type PivotRelationDatabaseProperties = RelationDatabaseProperties & {
    pivotTable: string;
    localPivotKey: string;
    foreignPivotKey: string;
};