import {Constraint} from "../types";
import {AbstractBuilder} from "../builder/AbstractBuilder";
import {AppClass} from "../../lifecycle/AppClass";

/**
 * A value which can be escaped to be interpolated into an SQL query.
 */
export type EscapeValue = null | undefined | string | number | boolean | Date | QuerySafeValue | EscapeValue[] // FIXME | Select<any>

/**
 * Object mapping string field names to EscapeValue items.
 */
export type EscapeValueObject = { [field: string]: EscapeValue }

/**
 * A wrapper class whose value is save to inject directly into a query.
 */
export class QuerySafeValue {
    constructor(
        /** The unescaped value. */
        public readonly originalValue: any,

        /** The query-safe sanitized value. */
        public readonly value: any,
    ) { }

    /** Cast the value to a query-safe string. */
    toString() {
        return this.value
    }
}

/**
 * Treat the value as raw SQL that can be injected directly into a query.
 * This is dangerous and should NEVER be used to wrap user input.
 * @param value
 */
export function raw(value: any) {
    return new QuerySafeValue(value, value)
}

/**
 * Abstract class defining a particular dialect of SQL that is used to render
 * query builders to strings of SQL of that dialect for execution by Connection
 * instances.
 */
export abstract class SQLDialect extends AppClass {
    /**
     * Escape the given value and return the query-safe equivalent.
     * @param value
     */
    public abstract escape(value: EscapeValue): QuerySafeValue

    /**
     * Render the given query builder as a "SELECT ..." query string.
     *
     * This function should escape the values before they are included in the query string.
     * @param builder
     */
    public abstract renderSelect(builder: AbstractBuilder<any>): string;

    /**
     * Render the given query builder as an "UPDATE ..." query string, setting the
     * column values from the given data object.
     *
     * This function should escape the values before they are included in the query string.
     * @param builder
     * @param data
     */
    public abstract renderUpdate(builder: AbstractBuilder<any>, data: {[key: string]: EscapeValue}): string;

    /**
     * Render the given query builder as a "DELETE ..." query string.
     *
     * This function should escape the values before they are included in the query string.
     * @param builder
     */
    public abstract renderDelete(builder: AbstractBuilder<any>): string;

    /**
     * Render the given query builder as a query that can be used to test if at
     * least 1 row exists for the given builder.
     *
     * The resultant query should return at least 1 row if that condition is met,
     * and should return NO rows otherwise.
     *
     * This function should escape the values before they are included in the query string.
     *
     * @example
     * The PostgreSQL dialect achieves this by removing the user-specified fields,
     * select-ing `TRUE`, and applying `LIMIT 1` to the query. This returns a single
     * row if the constraints have results, and nothing otherwise.
     *
     * @param builder
     */
    public abstract renderExistential(builder: AbstractBuilder<any>): string;

    /**
     * Render the given query as an "INSERT ..." query string, inserting rows for
     * the given data object(s).
     *
     * This function should escape the values before they are included in the query string.
     *
     * @param builder
     * @param data
     */
    public abstract renderInsert(builder: AbstractBuilder<any>, data: {[key: string]: EscapeValue}|{[key: string]: EscapeValue}[]): string;

    /**
     * Wrap the given query string as a "SELECT ..." query that returns the number of
     * rows matched by the original query string.
     *
     * The resultant query should return the `extollo_render_count` field with the
     * number of rows that the original `query` would return.
     *
     * @param query
     */
    public abstract renderCount(query: string): string;

    /**
     * Given a rendered "SELECT ..." query string, wrap it such that the query will
     * only return the rows ranging from the `start` to `end` indices.
     *
     * @param query
     * @param start
     * @param end
     */
    public abstract renderRangedSelect(query: string, start: number, end: number): string;

    /**
     * Given an array of Constraint objects, render them as WHERE-clause SQL in this dialect.
     *
     * This function should escape the values before they are included in the query string.
     *
     * @example
     * ```ts
     * dialect.renderConstraints([
     *  {
     *      field: 'id',
     *      operator: '<',
     *      operand: 44,
     *      preop: 'AND',
     *  },
     *  {
     *      field: 'id',
     *      operator: '>',
     *      operand: 30,
     *      preop: 'AND',
     *  },
     * ])  // => 'id < 44 AND id > 30'
     * ```
     *
     * @param constraints
     */
    public abstract renderConstraints(constraints: Constraint[]): string;

    /**
     * Render the "SET ... [field = value ...]" portion of the update query.
     *
     * This function should escape the values before they are included in the query string.
     *
     * @example
     * dialect.renderUpdateSet({field1: 'value', field2: 45})
     * // => "SET field1 = 'value', field2 = 45"
     *
     * @param data
     */
    public abstract renderUpdateSet(data: {[key: string]: EscapeValue}): string;
}