package daemon

import (
	"context"
	"crypto/tls"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net"
	"net/http"
	"sort"
	"strconv"
	"strings"
	"time"

	"banger/internal/api"
	"banger/internal/model"
	"banger/internal/store"
	"banger/internal/system"
	"banger/internal/vmdns"
	"banger/internal/vsockagent"
)

// StatsService owns the "observe a VM" surface: stats collection
// (CPU / memory / disk), listening-port enumeration, vsock-agent
// health probes, the background poller that refreshes stats for every
// live VM, and the auto-stop-when-idle sweep.
//
// Split out from VMService (commit 3 of the god-service decomposition):
// nothing here orchestrates lifecycle. The three VMService touch
// points stats genuinely needs — vmAlive, vmHandles, the per-VM lock
// helpers, plus cleanupRuntime for the stale-VM sweep — come in as
// function-typed closures so StatsService has no back-reference to
// its sibling. Same pattern WorkspaceService already uses.
type StatsService struct {
	runner         system.CommandRunner
	logger         *slog.Logger
	config         model.DaemonConfig
	store          *store.Store
	net            *HostNetwork
	beginOperation func(ctx context.Context, name string, attrs ...any) *operationLog

	// vmAlive / vmHandles are the minimum pair needed to answer "is
	// this VM actually running right now?" + "what PID is it?".
	// Closures over VMService so we re-read d.vm at call time — wire
	// order in wireServices puts d.vm before d.stats, so these are
	// safe by the time anything on StatsService fires.
	vmAlive   func(vm model.VMRecord) bool
	vmHandles func(vmID string) model.VMHandles

	// Lock helpers: stats collection and the stale-sweep both mutate
	// VM records (persist new stats, flip State to Stopped on auto-
	// stop) and so need the same per-VM mutex lifecycle ops hold.
	withVMLockByRef   func(ctx context.Context, idOrName string, fn func(model.VMRecord) (model.VMRecord, error)) (model.VMRecord, error)
	withVMLockByIDErr func(ctx context.Context, id string, fn func(model.VMRecord) error) error

	// cleanupRuntime is the auto-stop-sweep's only call into the
	// lifecycle side — forcibly tears down a VM that's been idle past
	// AutoStopStaleAfter. Keeping it as a closure means StatsService
	// never directly dereferences VMService.
	cleanupRuntime func(ctx context.Context, vm model.VMRecord, preserveDisks bool) error
}

type statsServiceDeps struct {
	runner            system.CommandRunner
	logger            *slog.Logger
	config            model.DaemonConfig
	store             *store.Store
	net               *HostNetwork
	beginOperation    func(ctx context.Context, name string, attrs ...any) *operationLog
	vmAlive           func(vm model.VMRecord) bool
	vmHandles         func(vmID string) model.VMHandles
	withVMLockByRef   func(ctx context.Context, idOrName string, fn func(model.VMRecord) (model.VMRecord, error)) (model.VMRecord, error)
	withVMLockByIDErr func(ctx context.Context, id string, fn func(model.VMRecord) error) error
	cleanupRuntime    func(ctx context.Context, vm model.VMRecord, preserveDisks bool) error
}

func newStatsService(deps statsServiceDeps) *StatsService {
	return &StatsService{
		runner:            deps.runner,
		logger:            deps.logger,
		config:            deps.config,
		store:             deps.store,
		net:               deps.net,
		beginOperation:    deps.beginOperation,
		vmAlive:           deps.vmAlive,
		vmHandles:         deps.vmHandles,
		withVMLockByRef:   deps.withVMLockByRef,
		withVMLockByIDErr: deps.withVMLockByIDErr,
		cleanupRuntime:    deps.cleanupRuntime,
	}
}

// ---- stats ----

func (s *StatsService) GetVMStats(ctx context.Context, idOrName string) (model.VMRecord, model.VMStats, error) {
	vm, err := s.withVMLockByRef(ctx, idOrName, func(vm model.VMRecord) (model.VMRecord, error) {
		return s.getVMStatsLocked(ctx, vm)
	})
	if err != nil {
		return model.VMRecord{}, model.VMStats{}, err
	}
	return vm, vm.Stats, nil
}

func (s *StatsService) HealthVM(ctx context.Context, idOrName string) (result api.VMHealthResult, err error) {
	_, err = s.withVMLockByRef(ctx, idOrName, func(vm model.VMRecord) (model.VMRecord, error) {
		result.Name = vm.Name
		if !s.vmAlive(vm) {
			result.Healthy = false
			return vm, nil
		}
		if strings.TrimSpace(vm.Runtime.VSockPath) == "" {
			return model.VMRecord{}, errors.New("vm has no vsock path")
		}
		if vm.Runtime.VSockCID == 0 {
			return model.VMRecord{}, errors.New("vm has no vsock cid")
		}
		if err := s.net.ensureSocketAccess(ctx, vm.Runtime.VSockPath, "firecracker vsock socket"); err != nil {
			return model.VMRecord{}, err
		}
		pingCtx, cancel := context.WithTimeout(ctx, 3*time.Second)
		defer cancel()
		if err := vsockagent.Health(pingCtx, s.logger, vm.Runtime.VSockPath); err != nil {
			return model.VMRecord{}, err
		}
		result.Healthy = true
		return vm, nil
	})
	return result, err
}

func (s *StatsService) PingVM(ctx context.Context, idOrName string) (result api.VMPingResult, err error) {
	health, err := s.HealthVM(ctx, idOrName)
	if err != nil {
		return api.VMPingResult{}, err
	}
	return api.VMPingResult{Name: health.Name, Alive: health.Healthy}, nil
}

func (s *StatsService) getVMStatsLocked(ctx context.Context, vm model.VMRecord) (model.VMRecord, error) {
	stats, err := s.collectStats(ctx, vm)
	if err == nil {
		vm.Stats = stats
		vm.UpdatedAt = model.Now()
		_ = s.store.UpsertVM(ctx, vm)
		if s.logger != nil {
			s.logger.Debug("vm stats collected", append(vmLogAttrs(vm), "rss_bytes", stats.RSSBytes, "vsz_bytes", stats.VSZBytes, "cpu_percent", stats.CPUPercent)...)
		}
	}
	return vm, nil
}

// pollStats runs on the daemon's background ticker; refreshes stats
// for every VM the store knows about, skipping ones that aren't alive.
func (s *StatsService) pollStats(ctx context.Context) error {
	vms, err := s.store.ListVMs(ctx)
	if err != nil {
		return err
	}
	for _, vm := range vms {
		if err := s.withVMLockByIDErr(ctx, vm.ID, func(vm model.VMRecord) error {
			if !s.vmAlive(vm) {
				return nil
			}
			stats, err := s.collectStats(ctx, vm)
			if err != nil {
				if s.logger != nil {
					s.logger.Debug("vm stats collection failed", append(vmLogAttrs(vm), "error", err.Error())...)
				}
				return nil
			}
			vm.Stats = stats
			vm.UpdatedAt = model.Now()
			return s.store.UpsertVM(ctx, vm)
		}); err != nil {
			return err
		}
	}
	return nil
}

// stopStaleVMs auto-stops any running VM whose LastTouchedAt is older
// than config.AutoStopStaleAfter. This is the only path through
// StatsService that actually mutates VM lifecycle state — it needs
// cleanupRuntime to tear down the kernel + process side.
func (s *StatsService) stopStaleVMs(ctx context.Context) (err error) {
	if s.config.AutoStopStaleAfter <= 0 {
		return nil
	}
	op := s.beginOperation(ctx, "vm.stop_stale")
	defer func() {
		if err != nil {
			op.fail(err)
			return
		}
		op.done()
	}()
	vms, err := s.store.ListVMs(ctx)
	if err != nil {
		return err
	}
	now := model.Now()
	for _, vm := range vms {
		if err := s.withVMLockByIDErr(ctx, vm.ID, func(vm model.VMRecord) error {
			if !s.vmAlive(vm) {
				return nil
			}
			if now.Sub(vm.LastTouchedAt) < s.config.AutoStopStaleAfter {
				return nil
			}
			op.stage("stopping_vm", vmLogAttrs(vm)...)
			_ = s.net.sendCtrlAltDel(ctx, vm.Runtime.APISockPath)
			_ = s.net.waitForExit(ctx, s.vmHandles(vm.ID).PID, vm.Runtime.APISockPath, 10*time.Second)
			_ = s.cleanupRuntime(ctx, vm, true)
			vm.State = model.VMStateStopped
			vm.Runtime.State = model.VMStateStopped
			clearRuntimeTeardownState(&vm)
			vm.UpdatedAt = model.Now()
			return s.store.UpsertVM(ctx, vm)
		}); err != nil {
			return err
		}
	}
	return nil
}

func (s *StatsService) collectStats(ctx context.Context, vm model.VMRecord) (model.VMStats, error) {
	stats := model.VMStats{
		CollectedAt:        model.Now(),
		SystemOverlayBytes: system.AllocatedBytes(vm.Runtime.SystemOverlay),
		WorkDiskBytes:      system.AllocatedBytes(vm.Runtime.WorkDiskPath),
		MetricsRaw:         system.ParseMetricsFile(vm.Runtime.MetricsPath),
	}
	if s.vmAlive(vm) {
		if ps, err := system.ReadProcessStats(ctx, s.vmHandles(vm.ID).PID); err == nil {
			stats.CPUPercent = ps.CPUPercent
			stats.RSSBytes = ps.RSSBytes
			stats.VSZBytes = ps.VSZBytes
		}
	}
	return stats, nil
}

// ---- ports ----

const httpProbeTimeout = 750 * time.Millisecond

func (s *StatsService) PortsVM(ctx context.Context, idOrName string) (result api.VMPortsResult, err error) {
	_, err = s.withVMLockByRef(ctx, idOrName, func(vm model.VMRecord) (model.VMRecord, error) {
		result.Name = vm.Name
		result.DNSName = strings.TrimSpace(vm.Runtime.DNSName)
		if result.DNSName == "" && strings.TrimSpace(vm.Name) != "" {
			result.DNSName = vmdns.RecordName(vm.Name)
		}
		if !s.vmAlive(vm) {
			return model.VMRecord{}, fmt.Errorf("vm %s is not running", vm.Name)
		}
		if strings.TrimSpace(vm.Runtime.GuestIP) == "" {
			return model.VMRecord{}, errors.New("vm has no guest IP")
		}
		if strings.TrimSpace(vm.Runtime.VSockPath) == "" {
			return model.VMRecord{}, errors.New("vm has no vsock path")
		}
		if vm.Runtime.VSockCID == 0 {
			return model.VMRecord{}, errors.New("vm has no vsock cid")
		}
		if err := s.net.ensureSocketAccess(ctx, vm.Runtime.VSockPath, "firecracker vsock socket"); err != nil {
			return model.VMRecord{}, err
		}
		portsCtx, cancel := context.WithTimeout(ctx, 3*time.Second)
		defer cancel()
		listeners, err := vsockagent.Ports(portsCtx, s.logger, vm.Runtime.VSockPath)
		if err != nil {
			return model.VMRecord{}, err
		}
		result.Ports = buildVMPorts(vm, listeners)
		return vm, nil
	})
	return result, err
}

func buildVMPorts(vm model.VMRecord, listeners []vsockagent.PortListener) []api.VMPort {
	endpointHost := strings.TrimSpace(vm.Runtime.DNSName)
	if endpointHost == "" {
		endpointHost = strings.TrimSpace(vm.Runtime.GuestIP)
	}
	probeHost := strings.TrimSpace(vm.Runtime.GuestIP)
	ports := make([]api.VMPort, 0, len(listeners))
	for _, listener := range listeners {
		if listener.Port <= 0 {
			continue
		}
		port := api.VMPort{
			Proto:       strings.ToLower(strings.TrimSpace(listener.Proto)),
			BindAddress: strings.TrimSpace(listener.BindAddress),
			Port:        listener.Port,
			PID:         listener.PID,
			Process:     strings.TrimSpace(listener.Process),
			Command:     strings.TrimSpace(listener.Command),
			Endpoint:    net.JoinHostPort(endpointHost, strconv.Itoa(listener.Port)),
		}
		if port.Command == "" {
			port.Command = port.Process
		}
		if port.Proto == "tcp" && probeHost != "" && endpointHost != "" {
			if scheme, ok := probeWebListener(probeHost, listener.Port); ok {
				port.Proto = scheme
				port.Endpoint = scheme + "://" + net.JoinHostPort(endpointHost, strconv.Itoa(listener.Port)) + "/"
			}
		}
		ports = append(ports, port)
	}
	sort.Slice(ports, func(i, j int) bool {
		if ports[i].Proto != ports[j].Proto {
			return ports[i].Proto < ports[j].Proto
		}
		if ports[i].Port != ports[j].Port {
			return ports[i].Port < ports[j].Port
		}
		if ports[i].PID != ports[j].PID {
			return ports[i].PID < ports[j].PID
		}
		if ports[i].Process != ports[j].Process {
			return ports[i].Process < ports[j].Process
		}
		return ports[i].BindAddress < ports[j].BindAddress
	})
	return dedupeVMPorts(ports)
}

func probeWebListener(guestIP string, port int) (string, bool) {
	if probeHTTPScheme("https", guestIP, port) {
		return "https", true
	}
	if probeHTTPScheme("http", guestIP, port) {
		return "http", true
	}
	return "", false
}

func probeHTTPScheme(scheme, guestIP string, port int) bool {
	if strings.TrimSpace(guestIP) == "" || port <= 0 {
		return false
	}
	url := scheme + "://" + net.JoinHostPort(strings.TrimSpace(guestIP), strconv.Itoa(port)) + "/"
	req, err := http.NewRequest(http.MethodGet, url, nil)
	if err != nil {
		return false
	}
	transport := &http.Transport{Proxy: nil}
	if scheme == "https" {
		transport.TLSClientConfig = &tls.Config{InsecureSkipVerify: true}
	}
	client := &http.Client{
		Timeout: httpProbeTimeout,
		CheckRedirect: func(req *http.Request, via []*http.Request) error {
			return http.ErrUseLastResponse
		},
		Transport: transport,
	}
	resp, err := client.Do(req)
	if err != nil {
		return false
	}
	defer resp.Body.Close()
	_, _ = io.Copy(io.Discard, io.LimitReader(resp.Body, 1))
	return resp.ProtoMajor >= 1
}

func dedupeVMPorts(ports []api.VMPort) []api.VMPort {
	if len(ports) < 2 {
		return ports
	}
	deduped := make([]api.VMPort, 0, len(ports))
	seen := make(map[string]struct{}, len(ports))
	for _, port := range ports {
		key := port.Proto + "\x00" + port.Endpoint
		if _, ok := seen[key]; ok {
			continue
		}
		seen[key] = struct{}{}
		deduped = append(deduped, port)
	}
	return deduped
}