package jobs

import (
	"context"
	"errors"
	"strings"
	"sync"
	"time"

	"go.opentelemetry.io/otel/attribute"
	apierrors "k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apiserver/pkg/endpoints/request"

	"github.com/grafana/grafana-app-sdk/logging"
	"github.com/grafana/grafana/apps/provisioning/pkg/apifmt"
	provisioning "github.com/grafana/grafana/apps/provisioning/pkg/apis/provisioning/v0alpha1"
	"github.com/grafana/grafana/pkg/apimachinery/identity"
	"github.com/grafana/grafana/pkg/infra/tracing"
)

// Store is an abstraction for the storage API.
// This exists to allow for unit testing.
//
//go:generate mockery --name Store --structname MockStore --inpackage --filename store_mock.go --with-expecter
type Store interface {
	// Claim takes a job from storage, marks it as ours, and returns it.
	//
	// Any job which has not been claimed by another worker is fair game.
	//
	// If err is not nil, the job and rollback values are always nil.
	// The err may be ErrNoJobs if there are no jobs to claim.
	Claim(ctx context.Context) (job *provisioning.Job, rollback func(), err error)

	// Complete marks a job as completed and removes it from the active job store.
	// Callers are responsible for writing the job to history after calling this.
	Complete(ctx context.Context, job *provisioning.Job) error

	// Update saves the job back to the store.
	Update(ctx context.Context, job *provisioning.Job) (*provisioning.Job, error)

	// RenewLease renews the lease for a claimed job, extending its expiry time.
	// Returns an error if the lease cannot be renewed (e.g., job was completed or lease expired).
	RenewLease(ctx context.Context, job *provisioning.Job) error

	// Get retrieves a job by name for conflict resolution.
	Get(ctx context.Context, namespace, name string) (*provisioning.Job, error)

	// ListExpiredJobs lists jobs with expired leases (claim timestamp older than the given time).
	// Returns jobs in batches up to the specified limit.
	ListExpiredJobs(ctx context.Context, expiredBefore time.Time, limit int) ([]*provisioning.Job, error)
}

// jobDriver drives jobs to completion and manages the job queue.
// There may be multiple jobDrivers running in parallel.
// The jobDriver processes jobs but does not handle cleanup - that's handled by ConcurrentJobDriver.
type jobDriver struct {
	// Timeout for processing a job. This must be less than a claim expiry.
	jobTimeout time.Duration

	// JobInterval is the time between job ticks. This should be relatively low.
	jobInterval time.Duration

	// LeaseRenewalInterval is how often to renew job leases.
	leaseRenewalInterval time.Duration

	// Store is the job storage backend.
	store Store
	// RepoGetter lets us access repositories to pass to the worker.
	repoGetter RepoGetter

	// save info about finished jobs
	historicJobs HistoryWriter

	// Workers process the job.
	// Only the first worker who supports the job will process it; the rest are ignored.
	workers []Worker

	// notifications channel for job create events
	notifications chan struct{}

	// Mutex to protect concurrent access to job processing
	mu sync.Mutex
	// currentJob is the job currently being processed
	currentJob *provisioning.Job
}

func NewJobDriver(
	jobTimeout, jobInterval, leaseRenewalInterval time.Duration,
	store Store,
	repoGetter RepoGetter,
	historicJobs HistoryWriter,
	notifications chan struct{},
	workers ...Worker,
) (*jobDriver, error) {
	return &jobDriver{
		jobTimeout:           jobTimeout,
		jobInterval:          jobInterval,
		leaseRenewalInterval: leaseRenewalInterval,
		store:                store,
		repoGetter:           repoGetter,
		historicJobs:         historicJobs,
		workers:              workers,
		notifications:        notifications,
	}, nil
}

// Run drives jobs to completion. This is a blocking function.
// It will run until the context is canceled or an error occurs.
// This is a thread-safe function; it may be called from multiple goroutines.
//
// Note: This function intentionally does NOT create a tracing span because it runs indefinitely
// until shutdown. Individual job processing operations already have their own spans.
func (d *jobDriver) Run(ctx context.Context) error {
	jobTicker := time.NewTicker(d.jobInterval)
	defer jobTicker.Stop()

	logger := logging.FromContext(ctx).With("logger", "job-driver")
	ctx = logging.Context(ctx, logger)
	ctx, _, err := identity.WithProvisioningIdentity(ctx, "*") // "*" grants us access to all namespaces.
	if err != nil {
		return apifmt.Errorf("failed to grant provisioning identity: %w", err)
	}

	// Drive without waiting on startup.
	d.processJobsUntilDoneOrError(ctx)

	for {
		select {
		case <-ctx.Done():
			logger.Info("job driver stopped")
			return nil // Context cancellation is expected during shutdown
		case <-jobTicker.C:
			d.processJobsUntilDoneOrError(ctx)
		case <-d.notifications:
			d.processJobsUntilDoneOrError(ctx)
		}
	}
}

// This will keep processing jobs until there are none left (or we hit an error)
func (d *jobDriver) processJobsUntilDoneOrError(ctx context.Context) {
	for {
		// Check if context is cancelled before attempting to claim jobs
		if ctx.Err() != nil {
			return
		}

		err := d.claimAndProcessOneJob(ctx)
		if err != nil {
			if !errors.Is(err, ErrNoJobs) {
				logging.FromContext(ctx).Error("failed to drive jobs", "error", err)
			}
			return
		}
	}
}

func (d *jobDriver) claimAndProcessOneJob(ctx context.Context) error {
	ctx, span := tracing.Start(ctx, "provisioning.jobs.claim_and_process_one_job")
	defer span.End()

	logger := logging.FromContext(ctx)

	// Claim a job to work on.
	claimedJob, rollback, err := d.store.Claim(ctx)
	if err != nil {
		if !errors.Is(err, ErrNoJobs) {
			span.RecordError(err)
		}
		return apifmt.Errorf("failed to claim job: %w", err)
	}
	// Ensure that the job is cleaned up if we fail to complete it.
	// The rollback function does not care about cancellations.
	defer rollback()

	namespace := claimedJob.GetNamespace()
	logger = logger.With("job", claimedJob.GetName(), "namespace", namespace)
	ctx = logging.Context(ctx, logger)
	d.currentJob = claimedJob

	span.SetAttributes(
		attribute.String("job.name", claimedJob.GetName()),
		attribute.String("job.namespace", namespace),
		attribute.String("job.repository", claimedJob.Spec.Repository),
		attribute.String("job.action", string(claimedJob.Spec.Action)),
	)

	// Now that we have a job, we need to augment our namespace to grant ourselves permission to work on it.
	// Incidentally, this also limits our permissions to only the namespace of the job.
	ctx = request.WithNamespace(ctx, namespace)
	ctx, _, err = identity.WithProvisioningIdentity(ctx, namespace)
	if err != nil {
		return apifmt.Errorf("failed to grant provisioning identity: %w", err)
	}

	jobctx, cancel := context.WithTimeout(ctx, d.jobTimeout)
	defer cancel() // Ensure resources are released when the function returns

	// Set up lease renewal goroutine
	leaseRenewalCtx, cancelLeaseRenewal := context.WithCancel(jobctx)
	leaseExpired := make(chan struct{})

	go d.leaseRenewalLoop(leaseRenewalCtx, logger, leaseExpired)
	defer cancelLeaseRenewal()

	recorder := newJobProgressRecorder(d.onProgress())
	recorder.SetMessage(ctx, "start job")

	// Process the job with lease loss detection
	err = d.processJobWithLeaseCheck(jobctx, recorder, leaseExpired)
	end := time.Now()
	logger.Debug("job processed", "duration", end.Sub(recorder.Started()), "error", err)

	// Check if parent context was cancelled (graceful shutdown)
	if ctx.Err() != nil {
		logger.Debug("context cancel - job will retry")
		// Don't complete the job - let it be retried by another worker
		d.mu.Lock()
		d.currentJob = nil
		d.mu.Unlock()
		return nil
	}

	// Capture job timeout (but not parent context cancellation)
	if jobctx.Err() != nil && err == nil && ctx.Err() == nil {
		err = jobctx.Err()
	}

	// Record job processing error on span
	if err != nil {
		span.RecordError(err)
	}

	// Complete the job
	d.mu.Lock()
	d.currentJob.Status = recorder.Complete(ctx, err)
	defer func() {
		d.currentJob = nil
		d.mu.Unlock()
	}()

	// Save the finished job
	err = d.historicJobs.WriteJob(ctx, d.currentJob.DeepCopy())
	if err != nil {
		// We're not going to return this as it is not critical. Not ideal, but not critical.
		logger.Warn("failed to write historic job", "error", err)
	}

	// Mark the job as completed.
	if err := d.store.Complete(ctx, d.currentJob); err != nil {
		span.RecordError(err)
		return apifmt.Errorf("failed to complete job '%s' in '%s': %w", d.currentJob.GetName(), d.currentJob.GetNamespace(), err)
	}
	logger.Info("job complete")

	return nil
}

// leaseRenewalLoop continuously renews the lease for a job until the context is cancelled.
// If lease renewal fails persistently, it signals via the leaseExpired channel.
//
// Note: This function intentionally does NOT create a tracing span because it runs indefinitely
// for the lifetime of a job. Individual RenewLease calls already have their own spans.
func (d *jobDriver) leaseRenewalLoop(ctx context.Context, logger logging.Logger, leaseExpired chan struct{}) {
	ticker := time.NewTicker(d.leaseRenewalInterval)
	defer ticker.Stop()

	logger.Debug("start lease renewal loop", "renewal_interval", d.leaseRenewalInterval)

	consecutiveFailures := 0
	maxFailures := 3 // Allow a few failures before giving up

	for {
		select {
		case <-ctx.Done():
			logger.Debug("lease renewal loop stopped")
			return
		case <-ticker.C:
			d.mu.Lock()
			if d.currentJob == nil {
				d.mu.Unlock()
				return
			}

			err := d.store.RenewLease(ctx, d.currentJob)
			d.mu.Unlock()

			if err != nil {
				consecutiveFailures++
				if apierrors.IsNotFound(err) ||
					strings.Contains(err.Error(), "job no longer exists") {
					logger.Error("job no longer exists - lease expired", "error", err)
					close(leaseExpired)
					return
				}

				logger.Warn("failed to renew lease", "error", err, "consecutive_failures", consecutiveFailures)

				if consecutiveFailures >= maxFailures {
					logger.Error("too many consecutive lease renewal failures - job will be aborted",
						"consecutive_failures", consecutiveFailures, "max_failures", maxFailures)
					close(leaseExpired)
					return
				}
			} else {
				if consecutiveFailures > 0 {
					logger.Debug("lease renewal recovered", "previous_failures", consecutiveFailures)
				}
				consecutiveFailures = 0
			}
		}
	}
}

// processJobWithLeaseCheck processes a job but aborts if the lease expires or context is cancelled.
func (d *jobDriver) processJobWithLeaseCheck(ctx context.Context, recorder JobProgressRecorder, leaseExpired <-chan struct{}) error {
	// Run the job processing in a goroutine so we can monitor lease expiry
	resultChan := make(chan error, 1)
	go func() {
		resultChan <- d.processJob(ctx, recorder)
	}()

	select {
	case err := <-resultChan:
		return err
	case <-leaseExpired:
		return apifmt.Errorf("job aborted due to lease expiry")
	case <-ctx.Done():
		// Return context error directly - caller will determine if this is due to graceful shutdown
		// or job timeout based on which context was cancelled
		return ctx.Err()
	}
}

func (d *jobDriver) processJob(ctx context.Context, recorder JobProgressRecorder) error {
	ctx, span := tracing.Start(ctx, "provisioning.jobs.process_job")
	defer span.End()

	logger := logging.FromContext(ctx)
	d.mu.Lock()
	if d.currentJob == nil {
		d.mu.Unlock()
		return nil
	}

	// Here it's safe to copy as only job spec is used for processing
	job := d.currentJob.DeepCopy()
	repoName := d.currentJob.Spec.Repository
	namespace := d.currentJob.Namespace
	d.mu.Unlock()

	span.SetAttributes(
		attribute.String("job.repository", repoName),
		attribute.String("job.action", string(job.Spec.Action)),
	)

	for _, worker := range d.workers {
		if !worker.IsSupported(ctx, *job) {
			continue
		}

		repo, err := d.repoGetter.GetRepository(ctx, namespace, repoName)
		if err != nil {
			span.RecordError(err)
			return apifmt.Errorf("failed to get repository '%s': %w", repoName, err)
		}

		r := repo.Config()
		if r.DeletionTimestamp != nil && !r.DeletionTimestamp.IsZero() {
			logger.Info("repository marked for deletion - skip job",
				"name", r.Name,
				"namespace", r.Namespace,
				"deletionTimestamp", r.DeletionTimestamp,
			)
			return nil
		}

		err = worker.Process(ctx, repo, *job, recorder)
		if err != nil {
			span.RecordError(err)
		}
		return err
	}

	err := apifmt.Errorf("no workers were registered to handle the job")
	span.RecordError(err)
	return err
}

func (d *jobDriver) onProgress() ProgressFn {
	return func(ctx context.Context, status provisioning.JobStatus) error {
		ctx, span := tracing.Start(ctx, "provisioning.jobs.update_progress")
		defer span.End()

		logging.FromContext(ctx).Debug("job progress", "status", status)

		const maxRetries = 3
		for attempt := 0; attempt < maxRetries; attempt++ {
			d.mu.Lock()
			if d.currentJob == nil {
				d.mu.Unlock()
				return nil
			}

			// Use the current job for the first attempt; on retry attempts, fetch fresh data from the store to resolve conflicts
			if attempt > 0 {
				// Fetch the latest version to resolve conflicts
				latest, err := d.store.Get(ctx, d.currentJob.GetNamespace(), d.currentJob.GetName())
				if err != nil {
					d.mu.Unlock()
					if apierrors.IsNotFound(err) {
						// Job was completed/deleted, nothing to update
						return nil
					}
					return apifmt.Errorf("failed to fetch job for progress update: %w", err)
				}

				*d.currentJob = *latest
			}

			job := d.currentJob
			// Update status on the current job
			job.Status = status
			updated, err := d.store.Update(ctx, job)
			if err != nil {
				if apierrors.IsConflict(err) && attempt < maxRetries-1 {
					// Conflict detected, retry with fresh data
					logging.FromContext(ctx).Debug("progress update conflict, retrying", "attempt", attempt+1)
					continue
				}
				d.mu.Unlock()
				return apifmt.Errorf("failed to update job progress: %w", err)
			}

			// Update succeeded, update our local copy
			*d.currentJob = *updated
			d.mu.Unlock()

			span.SetAttributes(
				attribute.String("job.state", string(status.State)),
				attribute.Int("attempt", attempt+1),
			)
			return nil
		}

		err := apifmt.Errorf("failed to update job progress after %d attempts", maxRetries)
		span.RecordError(err)
		return err
	}
}