package datasets

import (
	"context"
	"errors"
	"fmt"
	"sync"
	"sync/atomic"
	"time"

	"github.com/google/uuid"
	"go.uber.org/zap"

	"predictor-refactored/internal/weather"
)

// JobStatus is the lifecycle state of a download job.
type JobStatus string

const (
	JobPending   JobStatus = "pending"
	JobRunning   JobStatus = "running"
	JobComplete  JobStatus = "complete"
	JobFailed    JobStatus = "failed"
	JobCancelled JobStatus = "cancelled"
)

// JobInfo is the externally-visible snapshot of a download job.
type JobInfo struct {
	ID         string
	Source     string
	Dataset    DatasetID
	Status     JobStatus
	StartedAt  time.Time
	EndedAt    *time.Time
	Err        string
	Total      int
	Done       int
	Bytes      int64
}

type jobEntry struct {
	id        string
	source    string
	dataset   DatasetID
	startedAt time.Time
	cancel    context.CancelFunc

	mu      sync.Mutex
	status  JobStatus
	endedAt time.Time
	errStr  string

	total atomic.Int64
	done  atomic.Int64
	bytes atomic.Int64
}

func (e *jobEntry) snapshot() JobInfo {
	e.mu.Lock()
	info := JobInfo{
		ID: e.id, Source: e.source, Dataset: e.dataset,
		StartedAt: e.startedAt, Status: e.status, Err: e.errStr,
	}
	if !e.endedAt.IsZero() {
		ts := e.endedAt
		info.EndedAt = &ts
	}
	e.mu.Unlock()
	info.Total = int(e.total.Load())
	info.Done = int(e.done.Load())
	info.Bytes = e.bytes.Load()
	return info
}

type jobProgress struct{ e *jobEntry }

func (p jobProgress) SetTotal(n int)  { p.e.total.Store(int64(n)) }
func (p jobProgress) StepComplete()   { p.e.done.Add(1) }
func (p jobProgress) Bytes(n int64)   { p.e.bytes.Add(n) }

// loadedDataset bundles a loaded WindField with its identity and coverage.
type loadedDataset struct {
	ID       DatasetID
	Field    weather.WindField
	Coverage Coverage
}

// Manager coordinates dataset downloads and exposes the active WindFields.
type Manager struct {
	src      Source
	store    Storage
	throttle Throttle
	log      *zap.Logger

	activeMu sync.RWMutex
	active   []loadedDataset

	jobsMu sync.RWMutex
	jobs   map[string]*jobEntry

	inFlight sync.Map // key: dataset filename, value: jobID
}

// New wires a Manager.
func New(src Source, store Storage, throttle Throttle, log *zap.Logger) *Manager {
	if log == nil {
		log = zap.NewNop()
	}
	if src.ID() != store.SourceID() {
		log.Warn("source/store ID mismatch",
			zap.String("src", src.ID()),
			zap.String("store", store.SourceID()))
	}
	return &Manager{
		src: src, store: store, throttle: throttle, log: log,
		jobs: make(map[string]*jobEntry),
	}
}

// Source returns the underlying source ID.
func (m *Manager) Source() string { return m.src.ID() }

// Active returns the currently-loaded global WindField (the dataset with
// IsGlobal subset, most recently loaded). Returns nil if no global
// dataset is loaded; in cluster setups with only regional subsets, callers
// should use SelectFor.
func (m *Manager) Active() weather.WindField {
	m.activeMu.RLock()
	defer m.activeMu.RUnlock()
	for _, d := range m.active {
		if d.ID.Subset.IsGlobal() {
			return d.Field
		}
	}
	if len(m.active) > 0 {
		return m.active[0].Field
	}
	return nil
}

// Ready reports whether at least one dataset is loaded.
func (m *Manager) Ready() bool { return m.Active() != nil }

// SelectFor returns a loaded WindField whose coverage contains (t, lat, lng).
// Returns nil when no loaded dataset covers the query.
func (m *Manager) SelectFor(t time.Time, lat, lng float64) weather.WindField {
	m.activeMu.RLock()
	defer m.activeMu.RUnlock()
	for _, d := range m.active {
		if d.Coverage.Covers(t, lat, lng) {
			return d.Field
		}
	}
	// Fallback: any global dataset is permissive about region.
	for _, d := range m.active {
		if d.ID.Subset.IsGlobal() {
			return d.Field
		}
	}
	return nil
}

// LoadedDatasets returns snapshots of every currently-loaded dataset.
func (m *Manager) LoadedDatasets() []LoadedDatasetInfo {
	m.activeMu.RLock()
	defer m.activeMu.RUnlock()
	out := make([]LoadedDatasetInfo, 0, len(m.active))
	for _, d := range m.active {
		out = append(out, LoadedDatasetInfo{ID: d.ID, Coverage: d.Coverage})
	}
	return out
}

// LoadedDatasetInfo is a serializable snapshot of one active dataset.
type LoadedDatasetInfo struct {
	ID       DatasetID
	Coverage Coverage
}

// ListEpochs returns all stored datasets, newest first.
func (m *Manager) ListEpochs() ([]DatasetID, error) { return m.store.List() }

// ListJobs returns snapshots of every job recorded since startup.
func (m *Manager) ListJobs() []JobInfo {
	m.jobsMu.RLock()
	defer m.jobsMu.RUnlock()
	out := make([]JobInfo, 0, len(m.jobs))
	for _, e := range m.jobs {
		out = append(out, e.snapshot())
	}
	return out
}

// GetJob returns the snapshot for a job.
func (m *Manager) GetJob(id string) (JobInfo, bool) {
	m.jobsMu.RLock()
	e, ok := m.jobs[id]
	m.jobsMu.RUnlock()
	if !ok {
		return JobInfo{}, false
	}
	return e.snapshot(), true
}

// CancelJob cancels a running job.
func (m *Manager) CancelJob(id string) bool {
	m.jobsMu.RLock()
	e, ok := m.jobs[id]
	m.jobsMu.RUnlock()
	if !ok {
		return false
	}
	e.mu.Lock()
	terminal := e.status == JobComplete || e.status == JobFailed || e.status == JobCancelled
	e.mu.Unlock()
	if terminal {
		return false
	}
	e.cancel()
	return true
}

// Remove deletes a stored dataset. If the dataset is currently loaded,
// it is unloaded first.
func (m *Manager) Remove(id DatasetID) error {
	m.activeMu.Lock()
	out := m.active[:0]
	var removed *loadedDataset
	for i := range m.active {
		d := m.active[i]
		if d.ID.Equals(id) {
			removed = &d
			continue
		}
		out = append(out, d)
	}
	m.active = out
	m.activeMu.Unlock()
	if removed != nil {
		closeField(removed.Field, m.log)
	}
	return m.store.Remove(id)
}

// Download starts (or resumes) a download job for id in the background.
func (m *Manager) Download(id DatasetID) string {
	key := id.Filename()
	if existing, ok := m.inFlight.Load(key); ok {
		return existing.(string)
	}

	jobID := uuid.New().String()
	if other, loaded := m.inFlight.LoadOrStore(key, jobID); loaded {
		return other.(string)
	}

	ctx, cancel := context.WithCancel(context.Background())
	now := time.Now().UTC()
	e := &jobEntry{
		id:        jobID,
		source:    m.src.ID(),
		dataset:   id,
		startedAt: now,
		status:    JobPending,
		cancel:    cancel,
	}
	m.jobsMu.Lock()
	m.jobs[jobID] = e
	m.jobsMu.Unlock()

	if m.store.Exists(id) {
		go m.completeShortCircuit(ctx, e)
		return jobID
	}
	go m.runDownload(ctx, e)
	return jobID
}

// Load swaps in id's stored dataset, making it available to predictions.
func (m *Manager) Load(ctx context.Context, id DatasetID) error {
	if !m.store.Exists(id) {
		return fmt.Errorf("dataset %s not present on disk", id.Filename())
	}
	field, err := m.src.Open(ctx, id, m.store)
	if err != nil {
		return fmt.Errorf("open dataset: %w", err)
	}
	cov := m.src.Coverage(id)
	m.activeMu.Lock()
	// Replace any previously-loaded dataset with the same ID.
	for i := range m.active {
		if m.active[i].ID.Equals(id) {
			closeField(m.active[i].Field, m.log)
			m.active[i] = loadedDataset{ID: id, Field: field, Coverage: cov}
			m.activeMu.Unlock()
			return nil
		}
	}
	m.active = append(m.active, loadedDataset{ID: id, Field: field, Coverage: cov})
	m.activeMu.Unlock()
	m.log.Info("loaded dataset",
		zap.String("filename", id.Filename()),
		zap.String("source", m.src.ID()))
	return nil
}

// Refresh ensures the freshest global dataset is downloaded and active.
//
// Returns the JobID started, or empty string when nothing was scheduled.
func (m *Manager) Refresh(ctx context.Context, freshnessTTL time.Duration) (string, error) {
	if a := m.activeGlobal(); a != nil && time.Since(a.ID.Epoch) < freshnessTTL {
		return "", nil
	}

	if datasets, err := m.store.List(); err == nil {
		for _, id := range datasets {
			if !id.Subset.IsGlobal() {
				continue
			}
			if time.Since(id.Epoch) > freshnessTTL {
				continue
			}
			if a := m.activeGlobal(); a != nil && a.ID.Equals(id) {
				return "", nil
			}
			if err := m.Load(ctx, id); err == nil {
				return "", nil
			}
		}
	}

	latest, err := m.src.LatestEpoch(ctx)
	if err != nil {
		return "", fmt.Errorf("latest epoch: %w", err)
	}
	id := DatasetID{Epoch: latest}
	if a := m.activeGlobal(); a != nil && !latest.After(a.ID.Epoch) {
		return "", nil
	}

	jobID := m.Download(id)
	go m.loadAfterCompletion(jobID, id)
	return jobID, nil
}

// activeGlobal returns the currently-loaded global dataset, if any.
func (m *Manager) activeGlobal() *loadedDataset {
	m.activeMu.RLock()
	defer m.activeMu.RUnlock()
	for i := range m.active {
		if m.active[i].ID.Subset.IsGlobal() {
			d := m.active[i]
			return &d
		}
	}
	return nil
}

func (m *Manager) loadAfterCompletion(jobID string, id DatasetID) {
	for {
		info, ok := m.GetJob(jobID)
		if !ok {
			return
		}
		switch info.Status {
		case JobComplete:
			if err := m.Load(context.Background(), id); err != nil {
				m.log.Error("load after download", zap.Error(err))
			}
			return
		case JobFailed, JobCancelled:
			return
		}
		time.Sleep(2 * time.Second)
	}
}

func (m *Manager) runDownload(ctx context.Context, e *jobEntry) {
	defer m.inFlight.Delete(e.dataset.Filename())

	e.mu.Lock()
	e.status = JobRunning
	e.mu.Unlock()

	m.log.Info("download started",
		zap.String("job", e.id),
		zap.String("dataset", e.dataset.Filename()))

	err := m.src.Download(ctx, e.dataset, m.store, jobProgress{e: e}, m.throttle)
	now := time.Now().UTC()

	e.mu.Lock()
	e.endedAt = now
	switch {
	case errors.Is(err, context.Canceled):
		e.status = JobCancelled
	case err != nil:
		e.status = JobFailed
		e.errStr = err.Error()
	default:
		e.status = JobComplete
	}
	finalStatus := e.status
	e.mu.Unlock()

	m.log.Info("download finished",
		zap.String("job", e.id),
		zap.String("status", string(finalStatus)),
		zap.NamedError("err", err))
}

func (m *Manager) completeShortCircuit(ctx context.Context, e *jobEntry) {
	_ = ctx
	defer m.inFlight.Delete(e.dataset.Filename())
	now := time.Now().UTC()
	e.mu.Lock()
	e.status = JobComplete
	e.endedAt = now
	e.mu.Unlock()
}

// Close releases all resources, cancelling any in-flight jobs.
func (m *Manager) Close() error {
	m.jobsMu.Lock()
	for _, e := range m.jobs {
		e.cancel()
	}
	m.jobsMu.Unlock()

	m.activeMu.Lock()
	for _, d := range m.active {
		closeField(d.Field, m.log)
	}
	m.active = nil
	m.activeMu.Unlock()
	return nil
}

func closeField(f weather.WindField, log *zap.Logger) {
	if c, ok := f.(interface{ Close() error }); ok && c != nil {
		if err := c.Close(); err != nil && log != nil {
			log.Warn("close dataset", zap.Error(err))
		}
	}
}