import {Constraint, QuerySource} from '../types'
import {AbstractBuilder} from '../builder/AbstractBuilder'
import {AppClass} from '../../lifecycle/AppClass'
import {ColumnBuilder, IndexBuilder, TableBuilder} from '../schema/TableBuilder'
import {Collectable, Collection, Maybe} from '../../util'

/** A scalar value which can be interpolated safely into an SQL query. */
export type ScalarEscapeValue = null | undefined | string | number | boolean | Date | QuerySafeValue;

/** A list of scalar escape values. */
export type VectorEscapeValue<T extends ScalarEscapeValue> = T[] | Collection<T>

/** All possible escaped query values. */
export type EscapeValue<T extends ScalarEscapeValue = ScalarEscapeValue> = T | VectorEscapeValue<T> // FIXME | Select<any>

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

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

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

    /** Cast the value to a query-safe string. */
    toString(): string {
        return String(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: unknown): QuerySafeValue {
    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 a query source object as a qualified table name string ("tablename" as "alias").
     * @param source
     */
    public abstract renderQuerySource(source: QuerySource): string;

    /**
     * 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 an "UPDATE ..." query string, setting column values
     * for multiple distinct records based on their primary key.
     * @param builder
     * @param primaryKey
     * @param dataRows
     */
    public abstract renderBatchUpdate(builder: AbstractBuilder<any>, primaryKey: string, dataRows: Collectable<{[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
     * ```ts
     * dialect.renderUpdateSet({field1: 'value', field2: 45})
     * // => "SET field1 = 'value', field2 = 45"
     * ```
     *
     * @param data
     */
    public abstract renderUpdateSet(data: {[key: string]: EscapeValue}): string;

    /**
     * Given a table schema-builder, render a `CREATE TABLE...` query.
     * @param builder
     */
    public abstract renderCreateTable(builder: TableBuilder): string;

    /**
     * Given a table schema-builder, render an `ALTER TABLE...` query.
     * @param builder
     */
    public abstract renderAlterTable(builder: TableBuilder): Maybe<string>;

    /**
     * Given a table schema-builder, render a `DROP TABLE...` query.
     * @param builder
     */
    public abstract renderDropTable(builder: TableBuilder): string;

    /**
     * Render the table-column definitions for the table defined by
     * the given schema-builder.
     *
     * @example
     * ```ts
     * dialect.renderTableColumns(builder)
     * // => ['col1 varchar(100) NULL', 'col2 serial NOT NULL']
     * ```
     *
     * @param builder
     */
    public abstract renderTableColumns(builder: TableBuilder): string[];

    /**
     * Given an index schema-builder, render a `CREATE INDEX...` query.
     * @param builder
     */
    public abstract renderCreateIndex(builder: IndexBuilder): string;

    /**
     * Given a column schema-builder, render an `ALTER TABLE... DROP COLUMN...` query.
     * @param builder
     */
    public abstract renderDropColumn(builder: ColumnBuilder): string;

    /**
     * Given an index schema-builder, render a `DROP INDEX...` query.
     * @param builder
     */
    public abstract renderDropIndex(builder: IndexBuilder): string;

    /**
     * Given an index schema-builder, render an `ALTER INDEX... RENAME...` query.
     * @param builder
     */
    public abstract renderRenameIndex(builder: IndexBuilder): string;

    /**
     * Given an index schema-builder, render either an `ALTER INDEX...` query,
     * or a `DROP INDEX...; CREATE INDEX...` query.
     * @param builder
     */
    public abstract renderRecreateIndex(builder: IndexBuilder): string;

    /**
     * Given a series of fully-formed queries, render them as a single transaction.
     * @example
     * ```ts
     * const queries = [
     *  'SELECT * FROM a',
     *  'UPDATE b SET col = 123',
     * ]
     *
     * dialect.renderTransaction(queries)
     * // => 'BEGIN; SELECT * FROM a; UPDATE b SET col = 123; COMMIT;'
     * ```
     * @param queries
     */
    public abstract renderTransaction(queries: string[]): string;

    /**
     * Get the expression for the current timestamp as an escaped value.
     * @example `raw('NOW()')`
     */
    public abstract currentTimestamp(): QuerySafeValue;

    /**
     * Given a table schema-builder, render a series of queries as a transaction
     * that apply the given schema to database.
     * @todo handle constraints better - ConstraintBuilder
     * @param builder
     */
    public renderCommitSchemaTransaction(builder: TableBuilder): string {
        if ( builder.isDropping() || builder.isDroppingIfExists() ) {
            // If we're dropping the table, just return the DROP TABLE query
            return this.renderTransaction([
                this.renderDropTable(builder),
            ])
        }

        // Render the queries to create/update/drop indexes
        const indexes = Object.values(builder.getIndexes())
            .filter(index => !index.isExisting() || index.isDirty())
            .map(index => {
                if ( index.isDropping() || index.isDroppingIfExists() ) {
                    return this.renderDropIndex(index)
                }

                if ( index.isExisting() ) {
                    // The index was changed in the schema, but exists in the DB
                    return this.renderRecreateIndex(index)
                }

                return this.renderCreateIndex(index)
            })

        // Render the queries to rename indexes AFTER the above operations
        const renamedIndexes = Object.values(builder.getIndexes())
            .filter(idx => idx.getRename())
            .map(x => this.renderRenameIndex(x))

        let parts: string[] = []

        // Render the CREATE/ALTER TABLE query
        if ( !builder.isExisting() && builder.isDirty() ) {
            parts.push(this.renderCreateTable(builder))
        } else if ( builder.isExisting() && builder.isDirty() ) {
            const alterTable = this.renderAlterTable(builder)
            if ( alterTable ) {
                parts.push(alterTable)
            }
        }

        // Render the various schema queries as a single transaction
        parts = parts.concat(...indexes)
        parts = parts.concat(...renamedIndexes)
        return this.renderTransaction(parts)
    }
}