package service

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"

	"metis/pkg/facts"
	"metis/pkg/inventory"
	"metis/pkg/sentinel"
)

type JobStatus string

const (
	JobQueued  JobStatus = "queued"
	JobRunning JobStatus = "running"
	JobDone    JobStatus = "done"
	JobError   JobStatus = "error"
)

// Device describes a flashable block device.
type Device struct {
	Name      string `json:"name"`
	Path      string `json:"path"`
	Model     string `json:"model,omitempty"`
	Transport string `json:"transport,omitempty"`
	Type      string `json:"type,omitempty"`
	Note      string `json:"note,omitempty"`
	Removable bool   `json:"removable"`
	Hotplug   bool   `json:"hotplug"`
	SizeBytes int64  `json:"size_bytes"`
}

// Job is a long-running Metis action visible in the UI.
type Job struct {
	ID             string    `json:"id"`
	Kind           string    `json:"kind"`
	Node           string    `json:"node,omitempty"`
	Host           string    `json:"host,omitempty"`
	Builder        string    `json:"builder,omitempty"`
	Device         string    `json:"device,omitempty"`
	Status         JobStatus `json:"status"`
	Stage          string    `json:"stage,omitempty"`
	StageStartedAt time.Time `json:"stage_started_at,omitempty"`
	Message        string    `json:"message,omitempty"`
	Artifact       string    `json:"artifact,omitempty"`
	ProgressPct    float64   `json:"progress_pct"`
	Written        int64     `json:"written_bytes,omitempty"`
	Total          int64     `json:"total_bytes,omitempty"`
	Error          string    `json:"error,omitempty"`
	StartedAt      time.Time `json:"started_at"`
	UpdatedAt      time.Time `json:"updated_at,omitempty"`
	FinishedAt     time.Time `json:"finished_at,omitempty"`
}

// Event is a user-facing activity item for recent changes and runs.
type Event struct {
	Time    time.Time      `json:"time"`
	Kind    string         `json:"kind"`
	Summary string         `json:"summary"`
	Details map[string]any `json:"details,omitempty"`
}

// SnapshotRecord stores the last fact snapshot pushed by a node sentinel.
type SnapshotRecord struct {
	Node        string            `json:"node"`
	CollectedAt time.Time         `json:"collected_at"`
	Snapshot    sentinel.Snapshot `json:"snapshot"`
}

// PageState is the UI/API view model.
type PageState struct {
	LocalHost        string                     `json:"local_host"`
	DefaultFlashHost string                     `json:"default_flash_host"`
	SelectedHost     string                     `json:"selected_host"`
	FlashHosts       []string                   `json:"flash_hosts"`
	Nodes            []inventory.NodeSpec       `json:"nodes"`
	Jobs             []*Job                     `json:"jobs"`
	Devices          []Device                   `json:"devices"`
	PreferredDevice  string                     `json:"preferred_device,omitempty"`
	DeviceError      string                     `json:"device_error,omitempty"`
	Events           []Event                    `json:"events"`
	Snapshots        []SnapshotRecord           `json:"snapshots"`
	Targets          map[string]facts.Targets   `json:"targets"`
	Artifacts        map[string]ArtifactSummary `json:"artifacts"`
}

// ArtifactSummary describes the latest built image for a node.
type ArtifactSummary struct {
	Node        string    `json:"node,omitempty"`
	Ref         string    `json:"ref,omitempty"`
	BuildTag    string    `json:"build_tag,omitempty"`
	LocalPath   string    `json:"local_path,omitempty"`
	HostPath    string    `json:"host_path,omitempty"`
	BuilderHost string    `json:"builder_host,omitempty"`
	Compressed  bool      `json:"compressed,omitempty"`
	UpdatedAt   time.Time `json:"updated_at"`
	SizeBytes   int64     `json:"size_bytes"`
}

// App coordinates builds, flashes, sentinel snapshots, and the web UI state.
type App struct {
	settings  Settings
	inventory *inventory.Inventory
	metrics   *Metrics

	mu            sync.RWMutex
	jobs          map[string]*Job
	snapshots     map[string]SnapshotRecord
	targets       map[string]facts.Targets
	artifactStore map[string]ArtifactSummary
}

// NewApp creates a Metis service app instance.
func NewApp(settings Settings) (*App, error) {
	if err := os.MkdirAll(settings.CacheDir, 0o755); err != nil {
		return nil, err
	}
	if err := os.MkdirAll(settings.ArtifactDir, 0o755); err != nil {
		return nil, err
	}
	if err := os.MkdirAll(filepath.Dir(settings.HistoryPath), 0o755); err != nil {
		return nil, err
	}
	inv, err := inventory.Load(settings.InventoryPath)
	if err != nil {
		return nil, err
	}
	app := &App{
		settings:      settings,
		inventory:     inv,
		metrics:       NewMetrics(),
		jobs:          map[string]*Job{},
		snapshots:     map[string]SnapshotRecord{},
		targets:       map[string]facts.Targets{},
		artifactStore: map[string]ArtifactSummary{},
	}
	_ = app.loadSnapshots()
	_ = app.loadTargets()
	_ = app.loadArtifacts()
	return app, nil
}

// State returns the current UI/API snapshot.
func (a *App) State(deviceHost string) PageState {
	if strings.TrimSpace(deviceHost) == "" {
		deviceHost = a.settings.DefaultFlashHost
	}
	a.mu.RLock()
	jobs := make([]*Job, 0, len(a.jobs))
	for _, job := range a.jobs {
		copyJob := *job
		jobs = append(jobs, &copyJob)
	}
	sort.Slice(jobs, func(i, j int) bool {
		return jobs[i].StartedAt.After(jobs[j].StartedAt)
	})

	snaps := make([]SnapshotRecord, 0, len(a.snapshots))
	for _, snap := range a.snapshots {
		snaps = append(snaps, snap)
	}
	aTargets := map[string]facts.Targets{}
	for key, value := range a.targets {
		aTargets[key] = value
	}
	a.mu.RUnlock()

	sort.Slice(snaps, func(i, j int) bool {
		return snaps[i].Node < snaps[j].Node
	})

	flashHosts := a.flashHosts()
	devices, deviceErr := a.ListDevices(deviceHost)
	preferredDevice := preferredDevice(devices)
	return PageState{
		LocalHost:        a.settings.LocalHost,
		DefaultFlashHost: a.settings.DefaultFlashHost,
		SelectedHost:     deviceHost,
		FlashHosts:       flashHosts,
		Nodes:            append([]inventory.NodeSpec{}, a.inventory.Nodes...),
		Jobs:             jobs,
		Devices:          devices,
		PreferredDevice:  preferredDevice,
		DeviceError:      errorString(deviceErr),
		Events:           a.recentEvents(40),
		Snapshots:        snaps,
		Targets:          aTargets,
		Artifacts:        a.artifacts(),
	}
}

// Build starts a background image build for a node.
func (a *App) Build(node string) (*Job, error) {
	if _, _, err := a.inventory.FindNode(node); err != nil {
		return nil, err
	}
	job := a.newJob("build", node, "", "")
	go a.runBuild(job, false)
	return job, nil
}

// Replace starts a background build+flash workflow for a node.
func (a *App) Replace(node, host, device string) (*Job, error) {
	if host == "" {
		host = a.settings.DefaultFlashHost
	}
	if _, _, err := a.inventory.FindNode(node); err != nil {
		return nil, err
	}
	if _, err := a.ensureDevice(host, device); err != nil {
		return nil, err
	}
	job := a.newJob("replace", node, host, device)
	go a.runBuild(job, true)
	return job, nil
}

// StoreSnapshot records a pushed sentinel snapshot.
func (a *App) StoreSnapshot(record SnapshotRecord) error {
	if record.Node == "" {
		record.Node = record.Snapshot.Hostname
	}
	if record.CollectedAt.IsZero() {
		record.CollectedAt = time.Now().UTC()
	}
	if strings.TrimSpace(record.Node) == "" {
		return fmt.Errorf("snapshot node required")
	}
	a.mu.Lock()
	a.snapshots[record.Node] = record
	a.mu.Unlock()
	if err := a.persistSnapshots(); err != nil {
		return err
	}
	a.metrics.RecordSnapshot(record.Node, "ok", record.CollectedAt)
	a.appendEvent(Event{
		Time:    record.CollectedAt,
		Kind:    "sentinel.snapshot",
		Summary: fmt.Sprintf("Captured sentinel snapshot for %s", record.Node),
		Details: map[string]any{
			"node":        record.Node,
			"kernel":      record.Snapshot.Kernel,
			"k3s_version": record.Snapshot.K3sVersion,
		},
	})
	return nil
}

// WatchSentinel recomputes class targets and logs meaningful drift.
func (a *App) WatchSentinel() (*Event, error) {
	a.mu.RLock()
	snaps := make([]facts.Snapshot, 0, len(a.snapshots))
	for _, snap := range a.snapshots {
		snaps = append(snaps, facts.Snapshot{
			Hostname:      snap.Node,
			Kernel:        snap.Snapshot.Kernel,
			OSImage:       snap.Snapshot.OSImage,
			K3sVersion:    firstLine(snap.Snapshot.K3sVersion),
			Containerd:    firstLine(snap.Snapshot.Containerd),
			PackageSample: snap.Snapshot.PackageSample,
			DropInsSample: snap.Snapshot.DropInsSample,
		})
	}
	prevTargets := map[string]facts.Targets{}
	for key, value := range a.targets {
		prevTargets[key] = value
	}
	a.mu.RUnlock()

	nextTargets := facts.RecommendTargets(a.inventory, snaps)
	changes := diffTargets(prevTargets, nextTargets)

	a.mu.Lock()
	a.targets = nextTargets
	a.mu.Unlock()
	if err := a.persistTargets(); err != nil {
		return nil, err
	}

	event := &Event{
		Time:    time.Now().UTC(),
		Kind:    "sentinel.watch",
		Summary: "Metis sentinel watch completed with no template changes",
		Details: map[string]any{
			"classes": len(nextTargets),
			"changes": 0,
		},
	}
	if len(changes) > 0 {
		event.Summary = fmt.Sprintf("Metis sentinel watch detected %d template change(s)", len(changes))
		event.Details["changes"] = changes
	}
	a.appendEvent(*event)
	a.metrics.RecordWatch("ok")
	a.metrics.SetDriftTargets(nextTargets, len(changes))
	return event, nil
}

func (a *App) newJob(kind, node, host, device string) *Job {
	job := &Job{
		ID:          fmt.Sprintf("%d", time.Now().UTC().UnixNano()),
		Kind:        kind,
		Node:        node,
		Host:        host,
		Device:      device,
		Status:      JobQueued,
		ProgressPct: 0,
		StartedAt:   time.Now().UTC(),
		UpdatedAt:   time.Now().UTC(),
	}
	a.mu.Lock()
	a.jobs[job.ID] = job
	a.mu.Unlock()
	return job
}

func (a *App) job(id string) *Job {
	a.mu.RLock()
	defer a.mu.RUnlock()
	return a.jobs[id]
}

func (a *App) setJob(id string, update func(*Job)) {
	a.mu.Lock()
	defer a.mu.Unlock()
	job := a.jobs[id]
	if job == nil {
		return
	}
	update(job)
	job.UpdatedAt = time.Now().UTC()
}

func (a *App) failJob(id string, err error) {
	a.completeJob(id, func(j *Job) {
		j.Status = JobError
		j.Error = err.Error()
		j.Message = err.Error()
	})
}

func (a *App) completeJob(id string, update func(*Job)) {
	a.mu.Lock()
	defer a.mu.Unlock()
	job := a.jobs[id]
	if job == nil {
		return
	}
	update(job)
	if job.Status != JobError {
		job.Status = JobDone
	}
	job.UpdatedAt = time.Now().UTC()
	job.FinishedAt = time.Now().UTC()
}

func (a *App) appendEvent(event Event) {
	line, err := json.Marshal(event)
	if err != nil {
		return
	}
	f, err := os.OpenFile(a.settings.HistoryPath, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o644)
	if err != nil {
		return
	}
	defer f.Close()
	_, _ = f.Write(append(line, '\n'))
}

func (a *App) recentEvents(limit int) []Event {
	f, err := os.Open(a.settings.HistoryPath)
	if err != nil {
		return nil
	}
	defer f.Close()
	events := make([]Event, 0, limit)
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		var event Event
		if err := json.Unmarshal(scanner.Bytes(), &event); err != nil {
			continue
		}
		events = append(events, event)
	}
	if len(events) > limit {
		events = events[len(events)-limit:]
	}
	for i, j := 0, len(events)-1; i < j; i, j = i+1, j-1 {
		events[i], events[j] = events[j], events[i]
	}
	return events
}

func cachedImageName(source string) string {
	return strings.TrimSuffix(filepath.Base(source), ".xz")
}

func (a *App) flashHosts() []string {
	hosts := map[string]struct{}{}
	for _, host := range a.settings.FlashHosts {
		if value := strings.TrimSpace(host); value != "" {
			hosts[value] = struct{}{}
		}
	}
	for _, host := range []string{a.settings.DefaultFlashHost, a.settings.LocalHost} {
		if value := strings.TrimSpace(host); value != "" {
			hosts[value] = struct{}{}
		}
	}
	for _, node := range clusterNodes() {
		if value := strings.TrimSpace(node.Name); value != "" {
			hosts[value] = struct{}{}
		}
	}
	out := make([]string, 0, len(hosts))
	for host := range hosts {
		out = append(out, host)
	}
	sort.Strings(out)
	if a.settings.DefaultFlashHost == "" {
		return out
	}
	return moveToFront(out, a.settings.DefaultFlashHost)
}

func (a *App) loadSnapshots() error {
	data, err := os.ReadFile(a.settings.SnapshotsPath)
	if err != nil {
		return err
	}
	var snapshots map[string]SnapshotRecord
	if err := json.Unmarshal(data, &snapshots); err != nil {
		return err
	}
	a.mu.Lock()
	a.snapshots = snapshots
	a.mu.Unlock()
	for _, snap := range snapshots {
		a.metrics.RecordSnapshot(snap.Node, "ok", snap.CollectedAt)
	}
	return nil
}

func (a *App) persistSnapshots() error {
	a.mu.RLock()
	data, err := json.MarshalIndent(a.snapshots, "", "  ")
	a.mu.RUnlock()
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(a.settings.SnapshotsPath), 0o755); err != nil {
		return err
	}
	return os.WriteFile(a.settings.SnapshotsPath, data, 0o644)
}

func (a *App) loadTargets() error {
	data, err := os.ReadFile(a.settings.TargetsPath)
	if err != nil {
		return err
	}
	var targets map[string]facts.Targets
	if err := json.Unmarshal(data, &targets); err != nil {
		return err
	}
	a.mu.Lock()
	a.targets = targets
	a.mu.Unlock()
	a.metrics.SetDriftTargets(targets, 0)
	return nil
}

func (a *App) persistTargets() error {
	a.mu.RLock()
	data, err := json.MarshalIndent(a.targets, "", "  ")
	a.mu.RUnlock()
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(a.settings.TargetsPath), 0o755); err != nil {
		return err
	}
	return os.WriteFile(a.settings.TargetsPath, data, 0o644)
}

func diffTargets(prev, next map[string]facts.Targets) []string {
	classes := map[string]struct{}{}
	for class := range prev {
		classes[class] = struct{}{}
	}
	for class := range next {
		classes[class] = struct{}{}
	}
	out := make([]string, 0)
	for class := range classes {
		if !targetsEqual(prev[class], next[class]) {
			out = append(out, class)
		}
	}
	sort.Strings(out)
	return out
}

func targetsEqual(a, b facts.Targets) bool {
	if a.Kernel != b.Kernel || a.OSImage != b.OSImage || a.Containerd != b.Containerd || a.K3sVersion != b.K3sVersion {
		return false
	}
	if len(a.Packages) != len(b.Packages) {
		return false
	}
	for key, value := range a.Packages {
		if b.Packages[key] != value {
			return false
		}
	}
	return true
}

func humanBytes(value int64) string {
	const unit = 1024
	if value < unit {
		return fmt.Sprintf("%d B", value)
	}
	div, exp := int64(unit), 0
	for n := value / unit; n >= unit; n /= unit {
		div *= unit
		exp++
	}
	return fmt.Sprintf("%.1f %ciB", float64(value)/float64(div), "KMGTPE"[exp])
}

func firstLine(value string) string {
	value = strings.TrimSpace(value)
	if idx := strings.IndexByte(value, '\n'); idx >= 0 {
		return strings.TrimSpace(value[:idx])
	}
	return value
}

func preferredDevice(devices []Device) string {
	if len(devices) == 0 {
		return ""
	}
	return devices[0].Path
}

func errorString(err error) string {
	if err == nil {
		return ""
	}
	return err.Error()
}

func deviceScore(device Device) int {
	score := 0
	model := strings.ToLower(strings.TrimSpace(device.Model))
	switch {
	case strings.Contains(model, "microsd"), strings.Contains(model, "micro sd"):
		score += 60
	case strings.Contains(model, "sdxc"), strings.Contains(model, "sdhc"), strings.Contains(model, "sd "):
		score += 50
	case strings.Contains(model, "card"), strings.Contains(model, "reader"):
		score += 40
	}
	if device.Removable {
		score += 20
	}
	if device.Hotplug {
		score += 10
	}
	if device.Transport == "usb" {
		score += 5
	}
	if strings.HasPrefix(device.Name, "mmcblk") {
		score += 25
	}
	return score
}

func moveToFront(values []string, preferred string) []string {
	if preferred == "" || len(values) < 2 {
		return values
	}
	out := append([]string{}, values...)
	for idx, value := range out {
		if value != preferred {
			continue
		}
		copy(out[1:idx+1], out[:idx])
		out[0] = preferred
		return out
	}
	return out
}

func deleteNodeObject(node string) error {
	if err := deleteNodeObjectInCluster(node); err == nil {
		return nil
	}
	cmd := exec.Command("kubectl", "delete", "node", node, "--ignore-not-found")
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("delete node: %w: %s", err, strings.TrimSpace(string(out)))
	}
	return nil
}

func deleteNodeObjectInCluster(node string) error {
	kube, err := inClusterKubeClient()
	if err != nil {
		return errors.New("not running in cluster")
	}
	return kube.deleteRequest(fmt.Sprintf("/api/v1/nodes/%s", node))
}