import {query, QueryResult} from "./MysqlConnectionManager";
import {Connection} from "mysql";
import Model from "./Model";
import Pagination from "../Pagination";
import ModelRelation from "./ModelRelation";
import ModelFactory from "./ModelFactory";

export default class ModelQuery<M extends Model> {
    public static select<M extends Model>(factory: ModelFactory<M>, ...fields: string[]): ModelQuery<M> {
        return new ModelQuery(QueryType.SELECT, factory, fields.length > 0 ? fields : ['*']);
    }

    public static update<M extends Model>(factory: ModelFactory<M>, data: {
        [key: string]: any
    }): ModelQuery<M> {
        const fields = [];
        for (let key in data) {
            if (data.hasOwnProperty(key)) {
                fields.push(new UpdateFieldValue(key, data[key], false));
            }
        }
        return new ModelQuery(QueryType.UPDATE, factory, fields);
    }

    public static delete<M extends Model>(factory: ModelFactory<M>): ModelQuery<M> {
        return new ModelQuery(QueryType.DELETE, factory);
    }

    private readonly type: QueryType;
    private readonly factory: ModelFactory<M>;
    private readonly table: string;
    private readonly fields: (string | SelectFieldValue | UpdateFieldValue)[];
    private _leftJoin?: string;
    private _leftJoinOn: WhereFieldValue[] = [];
    private _where: WhereFieldValue[] = [];
    private _limit?: number;
    private _offset?: number;
    private _sortBy?: string;
    private _sortDirection?: 'ASC' | 'DESC';
    private readonly relations: string[] = [];
    private _pivot?: string[];

    private constructor(type: QueryType, factory: ModelFactory<M>, fields?: (string | SelectFieldValue | UpdateFieldValue)[]) {
        this.type = type;
        this.factory = factory;
        this.table = factory.table;
        this.fields = fields || [];
    }

    public leftJoin(table: string): this {
        this._leftJoin = table;
        return this;
    }

    public on(field1: string, field2: string, test: WhereTest = WhereTest.EQ, operator: WhereOperator = WhereOperator.AND): this {
        this._leftJoinOn.push(new WhereFieldValue(field1, field2, true, test, operator));
        return this;
    }

    public where(field: string, value: string | Date | ModelQuery<any> | any, test: WhereTest = WhereTest.EQ, operator: WhereOperator = WhereOperator.AND): this {
        this._where.push(new WhereFieldValue(field, value, false, test, operator));
        return this;
    }

    public limit(limit: number, offset: number = 0): this {
        this._limit = limit;
        this._offset = offset;
        return this;
    }

    public sortBy(field: string, direction: 'ASC' | 'DESC' = 'ASC'): this {
        this._sortBy = field;
        this._sortDirection = direction;
        return this;
    }

    /**
     * @param relation The relation field name to eagerload
     */
    public with(relation: string): this {
        this.relations.push(relation);
        return this;
    }

    public pivot(...fields: string[]): this {
        this._pivot = fields;
        return this;
    }

    public toString(final: boolean = false): string {
        let query = '';

        if (this._pivot) this.fields.push(...this._pivot);

        let fields = this.fields.join(',');

        let join = '';
        if (this._leftJoin) {
            join = `LEFT JOIN ${this._leftJoin} ON ${this._leftJoinOn[0]}`;
            for (let i = 1; i < this._leftJoinOn.length; i++) {
                join += this._leftJoinOn[i].toString(false);
            }
        }

        let where = '';
        if (this._where.length > 0) {
            where = `WHERE ${this._where[0]}`;
            for (let i = 1; i < this._where.length; i++) {
                where += this._where[i].toString(false);
            }
        }

        let limit = '';
        if (typeof this._limit === 'number') {
            limit = `LIMIT ${this._limit}`;
            if (typeof this._offset === 'number' && this._offset !== 0) {
                limit += ` OFFSET ${this._offset}`;
            }
        }

        let orderBy = '';
        if (typeof this._sortBy === 'string') {
            orderBy = `ORDER BY ${this._sortBy} ${this._sortDirection}`;
        }

        switch (this.type) {
            case QueryType.SELECT:
                query = `SELECT ${fields} FROM ${this.table} ${join} ${where} ${orderBy} ${limit}`;
                break;
            case QueryType.UPDATE:
                query = `UPDATE ${this.table} SET ${fields} ${where} ${orderBy} ${limit}`;
                break;
            case QueryType.DELETE:
                query = `DELETE FROM ${this.table} ${where} ${orderBy} ${limit}`;
                break;

        }

        return final ? query : `(${query})`;
    }

    public build(): string {
        return this.toString(true);
    }

    public get variables(): any[] {
        const variables: any[] = [];
        this.fields?.filter(v => v instanceof FieldValue)
            .flatMap(v => (<FieldValue>v).variables)
            .forEach(v => variables.push(v));
        this._where.flatMap(v => v.variables)
            .forEach(v => variables.push(v));
        return variables;
    }

    public async execute(connection?: Connection): Promise<QueryResult> {
        return await query(this.build(), this.variables, connection);
    }

    public async get(connection?: Connection): Promise<ModelQueryResult<M>> {
        const queryResult = await this.execute();
        const models: ModelQueryResult<M> = [];

        if (this._pivot) models.pivot = [];

        // Eager loading init
        const relationMap: { [p: string]: ModelRelation<any, any, any>[] } = {};
        for (const relation of this.relations) {
            relationMap[relation] = [];
        }

        for (const result of queryResult.results) {
            const model = this.factory.create(result);
            models.push(model);

            if (this._pivot) {
                const obj: any = {};
                for (const field of this._pivot) {
                    obj[field] = result[field.split('.')[1]];
                }
                models.pivot!.push(obj);
            }

            // Eager loading init map
            for (const relation of this.relations) {
                if (model[relation] === undefined) throw new Error(`Relation ${relation} doesn't exist on ${model.constructor.name}.`);
                relationMap[relation].push(model[relation]);
            }
        }

        // Eager loading execute
        for (const relationName of this.relations) {
            const relations = relationMap[relationName];
            if (relations.length > 0) {
                const allModels = await relations[0].eagerLoad(relations);
                await Promise.all(relations.map(r => r.populate(allModels)));
            }
        }

        return models;
    }

    public async paginate(page: number, perPage: number, connection?: Connection): Promise<ModelQueryResult<M>> {
        this.limit(perPage, (page - 1) * perPage);
        const result = await this.get(connection);
        result.pagination = new Pagination<M>(result, page, perPage, await this.count(true, connection));
        return result;
    }

    public async first(): Promise<M | null> {
        const models = await this.limit(1).get();
        return models.length > 0 ? models[0] : null;
    }

    public async count(removeLimit: boolean = false, connection?: Connection): Promise<number> {
        if (removeLimit) {
            this._limit = undefined;
            this._offset = undefined;
        }
        this._sortBy = undefined;
        this._sortDirection = undefined;

        this.fields.splice(0, this.fields.length);
        this.fields.push('COUNT(*)');
        let queryResult = await this.execute(connection);
        return queryResult.results[0]['COUNT(*)'];
    }
}

export interface ModelQueryResult<M extends Model> extends Array<M> {
    pagination?: Pagination<M>;
    pivot?: { [p: string]: any }[];
}

export enum QueryType {
    SELECT,
    UPDATE,
    DELETE,
}

export enum WhereOperator {
    AND = 'AND',
    OR = 'OR',
}

export enum WhereTest {
    EQ = '=',
    NE = '!=',
    GT = '>',
    GE = '>=',
    LT = '<',
    LE = '<=',
    IN = ' IN ',
}

class FieldValue {
    protected readonly field: string;
    protected value: any;
    protected raw: boolean;

    constructor(field: string, value: any, raw: boolean) {
        this.field = field;
        this.value = value;
        this.raw = raw;
    }

    public toString(first: boolean = true): string {
        const valueStr = this.raw || this.value === null || this.value instanceof ModelQuery ? this.value :
            (Array.isArray(this.value) ? `(${'?'.repeat(this.value.length).split('').join(',')})` : '?');
        return `${!first ? ',' : ''}${this.field}${this.test}${valueStr}`;
    }

    protected get test(): string {
        return '=';
    }

    public get variables(): any[] {
        if (this.value instanceof ModelQuery) return this.value.variables;
        if (this.raw || this.value === null) return [];
        if (Array.isArray(this.value)) return this.value;
        return [this.value];
    }
}

class SelectFieldValue extends FieldValue {
    public toString(first: boolean = true): string {
        return `(${this.value instanceof ModelQuery ? this.value : '?'}) AS ${this.field}`;
    }
}

class UpdateFieldValue extends FieldValue {
}

class WhereFieldValue extends FieldValue {
    private readonly _test: WhereTest;
    private readonly operator: WhereOperator;

    constructor(field: string, value: any, raw: boolean, test: WhereTest, operator: WhereOperator) {
        super(field, value, raw);
        this._test = test;
        this.operator = operator;
    }

    public toString(first: boolean = true): string {
        return (!first ? ` ${this.operator} ` : '') + super.toString(true);
    }

    protected get test(): string {
        if (this.value === null) {
            if (this._test === WhereTest.EQ) {
                return ' IS ';
            } else if (this._test === WhereTest.NE) {
                return ' IS NOT ';
            }
        }
        return this._test;
    }
}