import {Connection} from './connection/Connection'
import {Inject, Singleton} from '../di'
import {ErrorWithContext, uuid4} from '../util'
import {AppClass} from '../lifecycle/AppClass'
import {Logging} from '../service/Logging'

/**
 * A singleton, non-unit service that stores and retrieves database connections by name.
 */
@Singleton()
export class DatabaseService extends AppClass {
    @Inject()
    protected logging!: Logging

    /** Mapping of connection name -> connection instance for connections registered with this service. */
    protected readonly connections: { [key: string]: Connection } = {}

    /**
     * Register a new connection instance by name.
     * @param name
     * @param connection
     */
    register(name: string, connection: Connection): this {
        if ( this.connections[name] ) {
            this.logging.warn(`Overriding duplicate connection: ${name}`)
        }

        this.connections[name] = connection
        return this
    }

    /**
     * Returns true if a connection is registered with the given name.
     * @param name
     */
    has(name: string): boolean {
        return Boolean(this.connections[name])
    }

    /**
     * Get a connection instance by its name. Throws if none exists.
     * @param name
     */
    get(name = 'default'): Connection {
        if ( !this.has(name) ) {
            throw new ErrorWithContext(`No such connection is registered: ${name}`)
        }

        return this.connections[name]
    }

    /**
     * Return an array of the names of all registered connections.
     */
    names(): string[] {
        return Object.keys(this.connections)
    }

    /** Get a guaranteed-unique connection name. */
    uniqueName(): string {
        let name: string

        do {
            name = uuid4()
        } while (this.has(name))

        return name
    }
}