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GraphQL API for Alchemist
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/*
 * Copyright (C) 2010-2024, Danilo Pianini and contributors
 * listed, for each module, in the respective subproject's build.gradle.kts file.
 *
 * This file is part of Alchemist, and is distributed under the terms of the
 * GNU General Public License, with a linking exception,
 * as described in the file LICENSE in the Alchemist distribution's top directory.
 */

package it.unibo.alchemist.boundary.monitors

import io.ktor.server.engine.ApplicationEngine
import io.ktor.server.engine.embeddedServer
import io.ktor.server.netty.Netty
import it.unibo.alchemist.boundary.OutputMonitor
import it.unibo.alchemist.boundary.graphql.monitor.EnvironmentSubscriptionMonitor
import it.unibo.alchemist.boundary.graphql.server.modules.graphQLModule
import it.unibo.alchemist.boundary.graphql.server.modules.graphQLRoutingModule
import it.unibo.alchemist.boundary.graphql.utils.DefaultGraphQLSettings
import it.unibo.alchemist.model.Environment
import it.unibo.alchemist.model.Position
import it.unibo.alchemist.model.Time
import kotlinx.coroutines.CoroutineDispatcher
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking
import org.slf4j.LoggerFactory

private val logger = LoggerFactory.getLogger(GraphQLMonitor::class.java)

/**
 * An [OutputMonitor] observing the [environment] through a GraphQL server listening on [host]:[port].
 * The server is started in a new coroutine on the [serverDispatcher] dispatcher.
 * By default, the server is stopped after the simulation terminates.
 * This behavior can be changed by setting [teardownOnSimulationTermination] to false.
 */
class GraphQLMonitor> @JvmOverloads constructor(
    val environment: Environment,
    val host: String = DefaultGraphQLSettings.DEFAULT_HOST,
    val port: Int = DefaultGraphQLSettings.DEFAULT_PORT,
    val teardownOnSimulationTermination: Boolean = true,
    private val serverDispatcher: CoroutineDispatcher = Dispatchers.Default,
) : OutputMonitor {

    private val subscriptionMonitor = EnvironmentSubscriptionMonitor()
    private lateinit var server: ApplicationEngine

    override fun initialized(environment: Environment) {
        environment.simulation.addOutputMonitor(subscriptionMonitor)
        server = makeServer()
        val mutex = java.util.concurrent.Semaphore(0)
        Thread(
            {
                runBlocking {
                    launch(serverDispatcher) {
                        mutex.release()
                        server.start(wait = true)
                    }
                }
            },
            "alchemist-graphql-server@$host:$port",
        ).start()
        runBlocking {
            logger.info("Starting GraphQL server at $host:${server.resolvedConnectors().first().port}")
        }
        mutex.acquireUninterruptibly()
    }

    override fun finished(environment: Environment, time: Time, step: Long) {
        if (teardownOnSimulationTermination) {
            server.stop()
        }
    }

    private fun makeServer(): ApplicationEngine =
        embeddedServer(
            Netty,
            port = port,
            host = host,
            module = {
                graphQLModule([email protected])
                graphQLRoutingModule()
            },
        )
}