import ConnectionExecutable from './ConnectionExecutable.ts'
import {QueryResult, QueryRow} from '../../db/types.ts'
import {Connection} from '../../db/Connection.ts'
import {Collection} from '../../../../lib/src/collection/Collection.ts'
import NoTargetOperatorError from '../../error/NoTargetOperatorError.ts'

/**
 * Variant of the ConnectionExecutable used to build queries that mutate data. This
 * structure overrides methods to ensure that the query is run only once.
 * @extends ConnectionExecutable
 * @abstract
 */
export default abstract class ConnectionMutable<T> extends ConnectionExecutable<T> {
    /**
     * The cached execution result.
     * @type QueryResult
     */
    __execution_result?: QueryResult

    async get_row(i: number): Promise<T | undefined> {
        const result = await this.get_execution_result()
        const row = result.rows.at(i)
        if ( !this.__target_operator ) throw new NoTargetOperatorError()
        if ( row ) return this.__target_operator.inflate_row(row)
    }

    async get_range(start: number, end: number): Promise<Collection<T>> {
        const result = await this.get_execution_result()
        const rows: Collection<QueryRow> = result.rows.slice(start, end + 1) as Collection<QueryRow>
        return rows.map(row => {
            if ( !this.__target_operator ) throw new NoTargetOperatorError()
            return this.__target_operator.inflate_row(row)
        })
    }

    async count() {
        const result = await this.get_execution_result()
        return result.row_count
    }

    /**
     * Get the query result. Executes the query if it hasn't already. If it has,
     * return the cached query result.
     * @return Promise<QueryResult>
     */
    async get_execution_result(): Promise<QueryResult> {
        if ( this.__execution_result ) return this.__execution_result
        else return this.execute()
    }

    async execute_in_connection(connection: string | Connection): Promise<QueryResult> {
        const result = await super.execute_in_connection(connection)
        this.__execution_result = result
        return result
    }

}