package runner

import (
	"errors"
	"fmt"
	"log"
	workflow "runner/internal/workflow"
	"sync"
)

type Runner struct {
	Labels map[string]string
	Driver ContainerDriver
	Tasks  map[string]*Task
	Runs   int
	// Deferred tasks, in order their were scheduled.
	deferred []func()
}

func NewRunner(driver ContainerDriver, labels map[string]string) Runner {
	return Runner{
		Driver: driver,
		Labels: labels,
		Tasks:  map[string]*Task{},
	}
}

// Adds a task to deferral queue.
func (r *Runner) DeferTask(task func()) {
	r.deferred = append(r.deferred, task)
}

// Consumes deferred tasks, if any.
//
// Each task is executed within a go routine and the call will
// wait until all the tasks are completed before returning.
func (r *Runner) RunDeferredTasks() {
	log.Printf("Running %d deferred tasks.", len(r.deferred))

	var tracker sync.WaitGroup

	for _, deferred := range r.deferred {
		tracker.Add(1)
		go func() {
			defer tracker.Done()
			deferred()
		}()
		r.deferred = nil
	}

	tracker.Wait()
}

func (r *Runner) GetImageUriByLabel(label string) string {
	uri, exists := r.Labels[label]

	if exists {
		return uri
	}

	return "debian:latest"
}

func (r *Runner) GetContainerName(jobId string) string {
	return fmt.Sprintf("runner-%s", jobId)
}

func (r *Runner) AddTask() string {
	task := NewTask()
	r.Tasks[task.Id] = &task

	return task.Id
}

func (r *Runner) GetTask(taskId string) *Task {
	task, _ := r.Tasks[taskId]

	return task
}

// Executes a workflow using the runner.
//
// This is the high-level call that will set up the container
// that the jobs will be executed in, run the jobs's steps and
// tear down the container once no longer useful.
func (r *Runner) Execute(workflow workflow.Workflow) Task {
	log.Printf("Executing workflow: %s", workflow.SourcePath)
	task := r.GetTask(r.AddTask())

	for _, job := range workflow.Jobs {
		jobContext := task.GetJobContext(task.AddJob())
		jobContext.SetStatus("started")

		runnerImage := r.GetImageUriByLabel(job.RunsOn)
		containerName := r.GetContainerName(jobContext.Id)

		log.Printf("Using image %s (label: %s)", runnerImage, job.RunsOn)

		if pullError := r.PullContainer(runnerImage); pullError != nil {
			jobContext.SetStatus("failed").SetError(pullError)
			continue
		}

		if runError := r.RunJobInContainer(runnerImage, containerName, job); runError != nil {
			jobContext.SetStatus("failed").SetError(runError)
			continue
		}

		jobContext.SetStatus("success")
	}

	r.RunDeferredTasks()

	return *task
}

// Executes a job within a container.
//
// The container is started before the job steps are run and cleaned up after.
func (r *Runner) RunJobInContainer(imageUri string, containerId string, job workflow.Job) error {
	r.Driver.Start(imageUri, containerId)

	r.DeferTask(func() {
		log.Printf("Started cleaning up %s", containerId)
		r.Driver.Stop(containerId)
	})

	log.Printf("Started %s", containerId)
	for _, step := range job.Steps {
		log.Printf("Run: %s", step.Run)

		if err := r.RunCommandInContainer(containerId, step.Run); err != nil {
			return err
		}
	}

	return nil
}

// Pulls the container from the registry provided its image uri.
func (r *Runner) PullContainer(uri string) error {
	return r.Driver.Pull(uri)
}

// Executes a command within the given container.
//
// If the command raises an error while in the container or fails to run
// the command at all, an error is returned, otherwise nil.
func (r *Runner) RunCommandInContainer(containerId string, command string) error {
	result := r.Driver.Exec(containerId, command)

	if result.Error != nil {
		return result.Error
	}

	if result.ExitCode != 0 {
		return errors.New(fmt.Sprintf("Command returned a non-zero exit code (%d).", result.ExitCode))
	}

	return nil
}