package task_state_machine

// SPDX-License-Identifier: GPL-3.0-or-later

import (
	"context"
	"fmt"

	"github.com/rs/zerolog"
	"github.com/rs/zerolog/log"

	"projects.blender.org/studio/flamenco/internal/manager/eventbus"
	"projects.blender.org/studio/flamenco/internal/manager/persistence"
	"projects.blender.org/studio/flamenco/pkg/api"
)

// taskFailJobPercentage is the percentage of a job's tasks that need to fail to
// trigger failure of the entire job.
const taskFailJobPercentage = 10 // Integer from 0 to 100.

// StateMachine handles task and job status changes.
type StateMachine struct {
	persist     PersistenceService
	broadcaster ChangeBroadcaster
	logStorage  LogStorage
}

func NewStateMachine(persist PersistenceService, broadcaster ChangeBroadcaster, logStorage LogStorage) *StateMachine {
	return &StateMachine{
		persist:     persist,
		broadcaster: broadcaster,
		logStorage:  logStorage,
	}
}

// TaskStatusChange updates the task's status to the new one.
// `task` is expected to still have its original status, and have a filled `Job` pointer.
func (sm *StateMachine) TaskStatusChange(
	ctx context.Context,
	task *persistence.Task,
	newTaskStatus api.TaskStatus,
) error {
	oldTaskStatus := task.Status

	if err := sm.taskStatusChangeOnly(ctx, task, newTaskStatus); err != nil {
		return err
	}

	if err := sm.updateJobAfterTaskStatusChange(ctx, task, oldTaskStatus); err != nil {
		return fmt.Errorf("updating job after task status change: %w", err)
	}
	return nil
}

// taskStatusChangeOnly updates the task's status to the new one, but does not "ripple" the change to the job.
// `task` is expected to still have its original status, and have a filled `Job` pointer.
func (sm *StateMachine) taskStatusChangeOnly(
	ctx context.Context,
	task *persistence.Task,
	newTaskStatus api.TaskStatus,
) error {
	if task.JobUUID == "" {
		log.Panic().Str("task", task.UUID).Msg("task without job UUID, cannot handle this")
		return nil // Will not run because of the panic.
	}

	oldTaskStatus := task.Status
	task.Status = newTaskStatus

	logger := log.With().
		Str("task", task.UUID).
		Str("job", task.JobUUID).
		Str("taskStatusOld", string(oldTaskStatus)).
		Str("taskStatusNew", string(newTaskStatus)).
		Logger()
	logger.Debug().Msg("task state changed")

	if err := sm.persist.SaveTaskStatus(ctx, task); err != nil {
		return fmt.Errorf("saving task to database: %w", err)
	}

	if oldTaskStatus != newTaskStatus {
		// logStorage already logs any error, and an error here shouldn't block the
		// rest of the function.
		_ = sm.logStorage.WriteTimestamped(logger, task.JobUUID, task.UUID,
			fmt.Sprintf("task changed status %s -> %s", oldTaskStatus, newTaskStatus))
	}

	// Broadcast this change to the SocketIO clients.
	taskUpdate := eventbus.NewTaskUpdate(task)
	taskUpdate.PreviousStatus = &oldTaskStatus
	sm.broadcaster.BroadcastTaskUpdate(taskUpdate)

	return nil
}

// updateJobAfterTaskStatusChange updates the job status based on the status of
// this task and other tasks in the job.
func (sm *StateMachine) updateJobAfterTaskStatusChange(
	ctx context.Context, task *persistence.Task, oldTaskStatus api.TaskStatus,
) error {
	job := task.Job
	if job == nil {
		log.Panic().Str("task", task.UUID).Msg("task without job, cannot handle this")
		return nil // Will not run because of the panic.
	}

	logger := log.With().
		Str("job", task.JobUUID).
		Str("task", task.UUID).
		Str("taskStatusOld", string(oldTaskStatus)).
		Str("taskStatusNew", string(task.Status)).
		Logger()

	// Every 'case' in this switch MUST return. Just for sanity's sake.
	switch task.Status {
	case api.TaskStatusQueued:
		// Re-queueing a task on a completed job should re-queue the job too.
		return sm.jobStatusIfAThenB(ctx, logger, job, api.JobStatusCompleted, api.JobStatusRequeueing, "task was queued")

	case api.TaskStatusPaused:
		// Pausing a task has no impact on the job.
		return nil

	case api.TaskStatusCanceled:
		return sm.updateJobOnTaskStatusCanceled(ctx, logger, job)

	case api.TaskStatusFailed:
		return sm.updateJobOnTaskStatusFailed(ctx, logger, job)

	case api.TaskStatusActive, api.TaskStatusSoftFailed:
		switch job.Status {
		case api.JobStatusActive, api.JobStatusCancelRequested:
			// Do nothing, job is already in the desired status.
			return nil
		default:
			logger.Info().Msg("job became active because one of its task changed status")
			reason := fmt.Sprintf("task became %s", task.Status)
			return sm.JobStatusChange(ctx, job, api.JobStatusActive, reason)
		}

	case api.TaskStatusCompleted:
		return sm.updateJobOnTaskStatusCompleted(ctx, logger, job)

	default:
		logger.Warn().Msg("task obtained status that Flamenco did not expect")
		return nil
	}
}

// If the job has status 'ifStatus', move it to status 'thenStatus'.
func (sm *StateMachine) jobStatusIfAThenB(
	ctx context.Context,
	logger zerolog.Logger,
	job *persistence.Job,
	ifStatus, thenStatus api.JobStatus,
	reason string,
) error {
	if job.Status != ifStatus {
		return nil
	}
	logger.Info().
		Str("jobStatusOld", string(ifStatus)).
		Str("jobStatusNew", string(thenStatus)).
		Msg("Job will change status because one of its task changed status")
	return sm.JobStatusChange(ctx, job, thenStatus, reason)
}

// isJobPausingComplete returns true when the job status is pause-requested and there are no more active tasks.
func (sm *StateMachine) isJobPausingComplete(ctx context.Context, job *persistence.Job) (bool, error) {
	if job.Status != api.JobStatusPauseRequested {
		return false, nil
	}
	numActive, _, err := sm.persist.CountTasksOfJobInStatus(ctx, job, api.TaskStatusActive)
	if err != nil {
		return false, err
	}
	return numActive == 0, nil
}

// updateJobOnTaskStatusCanceled conditionally escalates the cancellation of a task to cancel the job.
func (sm *StateMachine) updateJobOnTaskStatusCanceled(ctx context.Context, logger zerolog.Logger, job *persistence.Job) error {
	// If no more tasks can run, cancel the job.
	numRunnable, _, err := sm.persist.CountTasksOfJobInStatus(ctx, job,
		api.TaskStatusActive, api.TaskStatusQueued, api.TaskStatusSoftFailed)
	if err != nil {
		return err
	}
	if numRunnable == 0 {
		// NOTE: this does NOT cancel any non-runnable (paused/failed) tasks. If that's desired, just cancel the job as a whole.
		logger.Info().Msg("canceled task was last runnable task of job, canceling job")
		return sm.JobStatusChange(ctx, job, api.JobStatusCanceled, "canceled task was last runnable task of job, canceling job")
	}

	// Deal with the special case when the job is in pause-requested status.
	toBePaused, err := sm.isJobPausingComplete(ctx, job)
	if err != nil {
		return err
	}
	if toBePaused {
		return sm.JobStatusChange(ctx, job, api.JobStatusPaused, "no more active tasks after task cancellation")
	}

	return nil
}

// updateJobOnTaskStatusFailed conditionally escalates the failure of a task to fail the entire job.
func (sm *StateMachine) updateJobOnTaskStatusFailed(ctx context.Context, logger zerolog.Logger, job *persistence.Job) error {
	// Count the number of failed tasks. If it is over the threshold, fail the job.
	numFailed, numTotal, err := sm.persist.CountTasksOfJobInStatus(ctx, job, api.TaskStatusFailed)
	if err != nil {
		return err
	}
	failedPercentage := int(float64(numFailed) / float64(numTotal) * 100)
	failLogger := logger.With().
		Int("taskNumTotal", numTotal).
		Int("taskNumFailed", numFailed).
		Int("failedPercentage", failedPercentage).
		Int("threshold", taskFailJobPercentage).
		Logger()

	if failedPercentage >= taskFailJobPercentage {
		failLogger.Info().Msg("failing job because too many of its tasks failed")
		return sm.JobStatusChange(ctx, job, api.JobStatusFailed, "too many tasks failed")
	}
	// If the job didn't fail, this failure indicates that at least the job is active.
	failLogger.Info().Msg("task failed, but not enough to fail the job")

	// Deal with the special case when the job is in pause-requested status.
	toBePaused, err := sm.isJobPausingComplete(ctx, job)
	if err != nil {
		return err
	}
	if toBePaused {
		return sm.JobStatusChange(ctx, job, api.JobStatusPaused, "no more active tasks after task failure")
	}

	return sm.jobStatusIfAThenB(ctx, logger, job, api.JobStatusQueued, api.JobStatusActive,
		"task failed, but not enough to fail the job")
}

// updateJobOnTaskStatusCompleted conditionally escalates the completion of a task to complete the entire job.
func (sm *StateMachine) updateJobOnTaskStatusCompleted(ctx context.Context, logger zerolog.Logger, job *persistence.Job) error {
	numComplete, numTotal, err := sm.persist.CountTasksOfJobInStatus(ctx, job, api.TaskStatusCompleted)
	if err != nil {
		return err
	}
	if numComplete == numTotal {
		logger.Info().Msg("all tasks of job are completed, job is completed")
		return sm.JobStatusChange(ctx, job, api.JobStatusCompleted, "all tasks completed")
	}

	// Deal with the special case when the job is in pause-requested status.
	toBePaused, err := sm.isJobPausingComplete(ctx, job)
	if err != nil {
		return err
	}
	if toBePaused {
		return sm.JobStatusChange(ctx, job, api.JobStatusPaused, "no more active tasks after task completion")
	}

	logger.Info().
		Int("taskNumTotal", numTotal).
		Int("taskNumComplete", numComplete).
		Msg("task completed; there are more tasks to do")
	return sm.jobStatusIfAThenB(ctx, logger, job, api.JobStatusQueued, api.JobStatusActive, "no more tasks to do")
}

// JobStatusChange gives a Job a new status, and handles the resulting status changes on its tasks.
func (sm *StateMachine) JobStatusChange(
	ctx context.Context,
	job *persistence.Job,
	newJobStatus api.JobStatus,
	reason string,
) error {
	// Job status changes can trigger task status changes, which can trigger the
	// next job status change. Keep looping over these job status changes until
	// there is no more change left to do.
	var err error
	for newJobStatus != "" && newJobStatus != job.Status {
		oldJobStatus := job.Status
		job.Activity = fmt.Sprintf("Changed to status %q: %s", newJobStatus, reason)

		logger := log.With().
			Str("job", job.UUID).
			Str("jobStatusOld", string(oldJobStatus)).
			Str("jobStatusNew", string(newJobStatus)).
			Str("reason", reason).
			Logger()
		logger.Info().Msg("job status changed")

		newJobStatus, err = sm.jobStatusSet(ctx, job, newJobStatus, reason, logger)
		if err != nil {
			return err
		}
	}

	return nil
}

// jobStatusReenforce acts as if the job just transitioned to its current
// status, and performs another round of task status updates. This is normally
// not necessary, but can be used when normal job/task status updates got
// interrupted somehow.
func (sm *StateMachine) jobStatusReenforce(
	ctx context.Context,
	job *persistence.Job,
	reason string,
) error {
	// Job status changes can trigger task status changes, which can trigger the
	// next job status change. Keep looping over these job status changes until
	// there is no more change left to do.
	var err error
	newJobStatus := job.Status

	for {
		oldJobStatus := job.Status
		job.Activity = fmt.Sprintf("Reenforcing status %q: %s", newJobStatus, reason)

		logger := log.With().
			Str("job", job.UUID).
			Str("reason", reason).
			Logger()
		if newJobStatus == job.Status {
			logger := logger.With().
				Str("jobStatus", string(job.Status)).
				Logger()
			logger.Info().Msg("job status reenforced")
		} else {
			logger := logger.With().
				Str("jobStatusOld", string(oldJobStatus)).
				Str("jobStatusNew", string(newJobStatus)).
				Logger()
			logger.Info().Msg("job status changed")
		}

		newJobStatus, err = sm.jobStatusSet(ctx, job, newJobStatus, reason, logger)
		if err != nil {
			return err
		}

		if newJobStatus == "" || newJobStatus == oldJobStatus {
			// Do this check at the end of the loop, and not the start, so that at
			// least one iteration is run.
			break
		}
	}

	return nil
}

// jobStatusSet saves the job with the new status and handles updates to tasks
// as well. If the task status change should trigger another job status change,
// the new job status is returned.
func (sm *StateMachine) jobStatusSet(ctx context.Context,
	job *persistence.Job,
	newJobStatus api.JobStatus,
	reason string,
	logger zerolog.Logger,
) (api.JobStatus, error) {
	oldJobStatus := job.Status
	job.Status = newJobStatus

	// Persist the new job status.
	err := sm.persist.SaveJobStatus(ctx, job)
	if err != nil {
		return "", fmt.Errorf("saving job status change %q to %q to database: %w",
			oldJobStatus, newJobStatus, err)
	}

	// Handle the status change.
	result, err := sm.updateTasksAfterJobStatusChange(ctx, logger, job, oldJobStatus)
	if err != nil {
		return "", fmt.Errorf("updating job's tasks after job status change: %w", err)
	}

	// Broadcast this change to the SocketIO clients.
	jobUpdate := eventbus.NewJobUpdate(job)
	jobUpdate.PreviousStatus = &oldJobStatus
	jobUpdate.RefreshTasks = result.massTaskUpdate
	sm.broadcaster.BroadcastJobUpdate(jobUpdate)

	return result.followingJobStatus, nil
}

// tasksUpdateResult is returned by `updateTasksAfterJobStatusChange`.
type tasksUpdateResult struct {
	// FollowingJobStatus is set when the task updates should trigger another job status update.
	followingJobStatus api.JobStatus
	// massTaskUpdate is true when multiple/all tasks were updated simultaneously.
	// This hasn't triggered individual task updates to SocketIO clients, and thus
	// the resulting SocketIO job update should indicate all tasks must be
	// reloaded.
	massTaskUpdate bool
}

// updateTasksAfterJobStatusChange updates the status of its tasks based on the
// new status of this job.
//
// NOTE: this function assumes that the job already has its new status.
//
// Returns the new state the job should go into after this change, or an empty
// string if there is no subsequent change necessary.
func (sm *StateMachine) updateTasksAfterJobStatusChange(
	ctx context.Context,
	logger zerolog.Logger,
	job *persistence.Job,
	oldJobStatus api.JobStatus,
) (tasksUpdateResult, error) {

	// Every case in this switch MUST return, for sanity sake.
	switch job.Status {
	case api.JobStatusCompleted, api.JobStatusCanceled, api.JobStatusPaused:
		// Nothing to do; this will happen as a response to all tasks receiving this status.
		return tasksUpdateResult{}, nil

	case api.JobStatusActive:
		// Nothing to do; this happens when a task gets started, which has nothing to
		// do with other tasks in the job.
		return tasksUpdateResult{}, nil

	case api.JobStatusCancelRequested, api.JobStatusFailed:
		jobStatus, err := sm.cancelTasks(ctx, logger, job)
		return tasksUpdateResult{
			followingJobStatus: jobStatus,
			massTaskUpdate:     true,
		}, err

	case api.JobStatusPauseRequested:
		jobStatus, err := sm.pauseTasks(ctx, logger, job)
		return tasksUpdateResult{
			followingJobStatus: jobStatus,
			massTaskUpdate:     true,
		}, err

	case api.JobStatusRequeueing:
		jobStatus, err := sm.requeueTasks(ctx, logger, job, oldJobStatus)
		return tasksUpdateResult{
			followingJobStatus: jobStatus,
			massTaskUpdate:     true,
		}, err

	case api.JobStatusQueued:
		jobStatus, err := sm.checkTaskCompletion(ctx, logger, job)
		return tasksUpdateResult{
			followingJobStatus: jobStatus,
			massTaskUpdate:     true,
		}, err

	default:
		logger.Warn().Msg("unknown job status change, ignoring")
		return tasksUpdateResult{}, nil
	}
}

// Directly cancel any task that might run in the future.
//
// Returns the next job status, if a status change is required.
func (sm *StateMachine) cancelTasks(
	ctx context.Context, logger zerolog.Logger, job *persistence.Job,
) (api.JobStatus, error) {
	logger.Info().Msg("cancelling tasks of job")

	// Any task that is running or might run in the future should get cancelled.
	taskStatusesToCancel := []api.TaskStatus{
		api.TaskStatusActive,
		api.TaskStatusQueued,
		api.TaskStatusSoftFailed,
	}
	err := sm.persist.UpdateJobsTaskStatusesConditional(
		ctx, job, taskStatusesToCancel, api.TaskStatusCanceled,
		fmt.Sprintf("Manager cancelled this task because the job got status %q.", job.Status),
	)
	if err != nil {
		return "", fmt.Errorf("cancelling tasks of job %s: %w", job.UUID, err)
	}

	// If cancellation was requested, it has now happened, so the job can transition.
	if job.Status == api.JobStatusCancelRequested {
		logger.Info().Msg("all tasks of job cancelled, job can go to 'cancelled' status")
		return api.JobStatusCanceled, nil
	}

	// This could mean cancellation was triggered by failure of the job, in which
	// case the job is already in the correct status.
	return "", nil
}

func (sm *StateMachine) pauseTasks(
	ctx context.Context, logger zerolog.Logger, job *persistence.Job,
) (api.JobStatus, error) {
	logger.Info().Msg("pausing tasks of job")

	// Any task that might run in the future should get paused.
	// Active tasks should remain active until finished.
	taskStatusesToPause := []api.TaskStatus{
		api.TaskStatusQueued,
		api.TaskStatusSoftFailed,
	}
	err := sm.persist.UpdateJobsTaskStatusesConditional(
		ctx, job, taskStatusesToPause, api.TaskStatusPaused,
		fmt.Sprintf("Manager paused this task because the job got status %q.", job.Status),
	)
	if err != nil {
		return "", fmt.Errorf("pausing tasks of job %s: %w", job.UUID, err)
	}

	// If pausing was requested, it has now happened, so the job can transition.
	toBePaused, err := sm.isJobPausingComplete(ctx, job)
	if err != nil {
		return "", err
	}
	if toBePaused {
		logger.Info().Msg("all tasks of job paused, job can go to 'paused' status")
		return api.JobStatusPaused, nil
	}

	return api.JobStatusPauseRequested, nil
}

// requeueTasks re-queues all tasks of the job.
//
// This function assumes that the current job status is "requeueing".
//
// Returns the new job status, if this status transition should be followed by
// another one.
func (sm *StateMachine) requeueTasks(
	ctx context.Context, logger zerolog.Logger, job *persistence.Job, oldJobStatus api.JobStatus,
) (api.JobStatus, error) {
	if job.Status != api.JobStatusRequeueing {
		logger.Warn().Msg("unexpected job status in StateMachine::requeueTasks()")
	}

	var err error

	switch oldJobStatus {
	case api.JobStatusUnderConstruction:
		// Nothing to do, the job compiler has just finished its work; the tasks have
		// already been set to 'queued' status.
		logger.Debug().Msg("ignoring job status change")
		return "", nil
	case api.JobStatusCompleted:
		// Re-queue all tasks.
		err = sm.persist.UpdateJobsTaskStatuses(ctx, job, api.TaskStatusQueued,
			fmt.Sprintf("Queued because job transitioned status from %q to %q", oldJobStatus, job.Status))
	default:
		statusesToUpdate := []api.TaskStatus{
			api.TaskStatusCanceled,
			api.TaskStatusFailed,
			api.TaskStatusPaused,
			api.TaskStatusSoftFailed,
		}
		// Re-queue only the non-completed tasks.
		err = sm.persist.UpdateJobsTaskStatusesConditional(ctx, job,
			statusesToUpdate, api.TaskStatusQueued,
			fmt.Sprintf("Queued because job transitioned status from %q to %q", oldJobStatus, job.Status))
	}
	if err != nil {
		return "", fmt.Errorf("queueing tasks of job %s: %w", job.UUID, err)
	}

	// TODO: also reset the 'failed by workers' blocklist.

	// The appropriate tasks have been requeued, so now the job can go from "requeueing" to "queued".
	return api.JobStatusQueued, nil
}

// checkTaskCompletion returns "completed" as next job status when all tasks of
// the job are completed.
//
// Returns the new job status, if this status transition should be followed by
// another one.
func (sm *StateMachine) checkTaskCompletion(
	ctx context.Context, logger zerolog.Logger, job *persistence.Job,
) (api.JobStatus, error) {

	numCompleted, numTotal, err := sm.persist.CountTasksOfJobInStatus(ctx, job, api.TaskStatusCompleted)
	if err != nil {
		return "", fmt.Errorf("checking task completion of job %s: %w", job.UUID, err)
	}

	if numCompleted < numTotal {
		logger.Debug().
			Int("numTasksCompleted", numCompleted).
			Int("numTasksTotal", numTotal).
			Msg("not all tasks of job are completed")
		return "", nil
	}

	logger.Info().Msg("job has all tasks completed, transition job to 'completed'")
	return api.JobStatusCompleted, nil
}

// CheckStuck finds jobs that are 'stuck' in their current status. This is meant
// to run at startup of Flamenco Manager, and checks to see if there are any
// jobs in a status that a human will not be able to fix otherwise.
func (sm *StateMachine) CheckStuck(ctx context.Context) {
	stuckJobs, err := sm.persist.FetchJobsInStatus(ctx, api.JobStatusCancelRequested, api.JobStatusRequeueing)
	if err != nil {
		log.Error().Err(err).Msg("unable to fetch stuck jobs")
		return
	}

	for _, job := range stuckJobs {
		err := sm.jobStatusReenforce(ctx, job, "checking stuck jobs")
		if err != nil {
			log.Error().Str("job", job.UUID).Err(err).Msg("error getting job un-stuck")
		}
	}
}