import {QueryResult} from '../../db/types.ts'
import {make} from '../../../../di/src/global.ts'
import Database from '../../service/Database.ts'
import {logger} from '../../../../lib/src/service/logging/global.ts'
import {Connection} from '../../db/Connection.ts'
import {ResultCollection} from './result/ResultCollection.ts'
import {ResultIterable} from './result/ResultIterable.ts'
import ResultOperator from './result/ResultOperator.ts'
import {collect, Collection} from '../../../../lib/src/collection/Collection.ts'
import NoTargetOperatorError from '../../error/NoTargetOperatorError.ts'

/**
 * Base class for a query that can be executed in a database connection.
 * @abstract
 */
export default abstract class ConnectionExecutable<T> {
    /**
     * Render the query to raw SQL, starting with the base indentation level.
     * @param {number} level
     * @return string
     */
    abstract sql(level: number): string

    /**
     * Cast the query to an SQL statement which counts the incoming rows.
     * @return string
     */
    to_count(): string {
        return `SELECT COUNT(*) AS to_count FROM (${this.sql(0)}) AS target_query`
    }

    /**
     * Get the result row for this query at index i.
     * @param {number} i
     * @return Promise<any>
     */
    async get_row(i: number): Promise<T | undefined> {
        if ( !(this.__target_connection instanceof Connection) ) {
            throw new Error('Unable to execute database item: no target connection.')
        }

        const query = `SELECT * FROM (${this.sql(0)}) AS target_query OFFSET ${i} LIMIT 1`
        const result = await this.__target_connection.query(query)
        const row = result.rows.first()
        if ( row ) {
            if ( !this.__target_operator ) throw new NoTargetOperatorError()

            const inflated = this.__target_operator.inflate_row(row)
            await this.__target_operator.process_eager_loads(this, collect([inflated]))

            return inflated
        }
    }

    /**
     * Get a range of resultant rows for this query between the start and end indices.
     * @param {string} start
     * @param {string} end
     * @return Promise<Collection>
     */
    async get_range(start: number, end: number): Promise<Collection<T>> {
        if ( !(this.__target_connection instanceof Connection) ) {
            throw new Error('Unable to execute database item: no target connection.')
        }

        const query = `SELECT * FROM (${this.sql(0)}) AS target_query OFFSET ${start} LIMIT ${(end - start) + 1}`
        const result = await this.__target_connection.query(query)
        const inflated = result.rows.map(row => {
            if ( !this.__target_operator ) throw new NoTargetOperatorError()
            return this.__target_operator.inflate_row(row)
        })

        if ( !this.__target_operator ) throw new NoTargetOperatorError()
        await this.__target_operator.process_eager_loads(this, inflated)

        return inflated
    }

    /**
     * Get an iterator for this result set.
     * @return ResultIterable
     */
    iterator(): ResultIterable<T> {
        return new ResultIterable<T>(this)
    }

    /**
     * Get the results as an async collection, with the processing chunk size.
     * @param {number} chunk_size
     * @return ResultCollection
     */
    results(chunk_size = 1000) {
        return new ResultCollection<T>(this.iterator(), chunk_size)
    }

    /**
     * The database connection to execute the statement in.
     * @type Connection
     */
    __target_connection?: Connection

    /**
     * The result operator to use to process the incoming rows.
     * @type ResultOperator
     */
    __target_operator?: ResultOperator<T>

    /**
     * Set the target connection.
     * @param {string|Connection} connection - the connection or connection name
     * @return ConnectionExecutable
     */
    target_connection(connection: string | Connection) {
        this.__target_connection = typeof connection === 'string' ? make(Database).connection(connection) : connection
        return this
    }

    /**
     * Set the target operator.
     * @param {ResultOperator} operator
     * @return ConnectionExecutable
     */
    target_operator(operator: ResultOperator<T>) {
        this.__target_operator = operator
        return this
    }

    /**
     * Execute the query and get back the raw result.
     * @return Promise<QueryResult>
     */
    async execute(): Promise<QueryResult> {
        if ( !(this.__target_connection instanceof Connection) ) {
            throw new Error('Unable to execute database item: no target connection.')
        }

        return this.execute_in_connection(this.__target_connection)
    }

    /**
     * Count the number of returned rows.
     * @return Promise<number>
     */
    async count(): Promise<number> {
        if ( !(this.__target_connection instanceof Connection) ) {
            throw new Error('Unable to execute database item: no target connection.')
        }

        const result = await this.__target_connection.query(this.to_count())
        const row = result.rows.first()
        if ( row ) return Number(row.to_count)
        return 0
    }

    /**
     * True if the number of rows returned is greater than 0.
     * @return Promise<boolean>
     */
    async exists(): Promise<boolean> {
        return (await this.count()) > 0
    }

    /**
     * Execute the query in the given connection and return the raw result.
     * @param {string|Connection} connection - the connection or connection name
     * @return Promise<QueryResult>
     */
    async execute_in_connection(connection: string | Connection): Promise<QueryResult> {
        const conn = typeof connection === 'string' ? make(Database).connection(connection) : connection

        logger.debug(`Executing statement in connection: ${conn.name}`)

        const sql = this.sql(0)
        logger.verbose(sql)

        return conn.query(sql)
    }
}