servitor/engine/src/main/kotlin/wf/servitor/engine/Engine.kt

package wf.servitor.engine

import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.channels.Channel
import kotlinx.coroutines.channels.sendBlocking
import kotlinx.coroutines.selects.whileSelect
import org.apache.activemq.artemis.api.core.client.ClientMessage
import org.apache.commons.jexl3.JexlEngine
import org.apache.commons.jexl3.JexlException
import org.koin.core.KoinComponent
import org.koin.core.inject
import org.koin.core.qualifier.named
import wf.servitor.common.Event.*
import wf.servitor.common.event.Session
import wf.servitor.common.workflow.Step
import wf.servitor.common.workflow.StepContinuation
import wf.servitor.engine.dispatcher.NamespaceAwareMapContext
import wf.servitor.engine.exception.UnresolvedRemoteCallException

class Engine : KoinComponent {
    private val jexl by inject<JexlEngine>()
    private val session by inject<Session>(named("queue.task"))
    private val channel = Channel<ClientMessage>(2)
    private var cancel = Channel<Unit>()

    suspend fun run() {
        session.onMessage {
            channel.sendBlocking(it)
        }

        whileSelect {
            channel.onReceive {
                val task: Task = session.extract(it)

                println("Got task!")
                println(task)

                // TODO check tombstone store

                executeTask(task)

                true
            }

            cancel.onReceive {
                false
            }
        }


        session.close()
    }

    suspend fun stop() {
        this.cancel.send(Unit)
    }

    private fun executeTask(task: Task) {
        session.sendUpdate(TaskUpdate(task, "running"))

        val workflow = task.workflow
        val step = workflow.getStep(task.flow, task.path)

        if (step === null) {
            endTask(task)
            return
        }

        val script = step.getScript()

        if (script === null) {
            session.sendUpdate(TaskUpdate(task, "done"))
            nextTask(step, task)
            return
        }

        try {
            val (res, context) = this.execute(script, task)
            session.sendUpdate(TaskUpdate(task.copy(context = context), "done"))
            nextTask(step, task, context, res)
        } catch (e: UnresolvedRemoteCallException) {
            session.queueRelay(Relay(e.service, e.method, e.arguments, task))
            return
        } catch (e: Throwable) {
            session.sendUpdate(TaskUpdate(task, "error"))
            return
        }
    }

    private fun nextTask(
        step: Step,
        task: Task,
        context: Map<String, Any?> = task.context,
        result: Any? = null
    ) {
        when (val continuation = step.next(result)) {
            StepContinuation.End -> {
                val endedTask = task.copy(context = context, dispatchedValues = listOf())
                endTask(endedTask)
            }

            StepContinuation.Continue -> {
                val next: List<Int>? = run select@{
                    val newList = task.path.toMutableList()
                    if (newList.count() > 1) {
                        val tree = newList.indices.drop(1).map {
                            newList.subList(0, it) to task.workflow.getStep(task.flow, newList.subList(0, it - 1))
                        }.reversed()

                        for ((path, parent) in tree) {
                            if (parent == null) {
                                continue
                            }

                            path[path.lastIndex]++
                            if (parent.children() < path[path.lastIndex] && null != parent.getChild(path[path.lastIndex])) {
                                return@select path
                            }
                        }
                    }

                    val lastNext = listOf(newList.first() + 1)

                    if (task.workflow.getStep(task.flow, lastNext) !== null) {
                        lastNext
                    } else {
                        null
                    }
                }

                if (next === null) {
                    endTask(task, context)
                } else {
                    session.queueTask(task.copy(context = context, path = next, dispatchedValues = listOf()))
                }
            }

            is StepContinuation.Flow -> {
                session.queueTask(Task(task.workflow, task.context, continuation.name))
            }

            is StepContinuation.Step -> {
                val stepList: List<Step> = task.workflow.flows[task.flow]?.steps ?: listOf()
                var found = false
                for (item in 0..stepList.count()) {
                    if (stepList[item].name == continuation.name) {
                        session.queueTask(
                            task.copy(
                                context = context,
                                path = listOf(item),
                                dispatchedValues = listOf()
                            )
                        )
                        found = true
                        break
                    }
                }

                if (!found) {
                    session.sendUpdate(TaskUpdate(task, "error"))
                    TODO("Do correct error handling")
                }
            }
        }
    }

    private fun endTask(
        task: Task,
        context: Map<String, Any?> = task.context
    ) {
        session.sendUpdate(TaskUpdate(task.copy(dispatchedValues = listOf(), context = context), "ended"))
    }

    private fun execute(input: String, task: Task): Pair<Any?, Map<String, Any?>> {
        try {
            val mutableContext = task.context.toMutableMap()
            val jc = NamespaceAwareMapContext(task.workflow, mutableContext, task.dispatchedValues.toMutableList())
            val script = jexl.createScript(input)
            return script.execute(jc) to mutableContext
        } catch (j: JexlException) {
            val cause = j.cause
            if (cause is UnresolvedRemoteCallException) {
                throw cause
            }

            throw j
        }
    }
}