package daemon

import (
	"bufio"
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"net"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"banger/internal/api"
	"banger/internal/config"
	"banger/internal/model"
	"banger/internal/paths"
	"banger/internal/rpc"
	"banger/internal/store"
	"banger/internal/system"
	"banger/internal/vmdns"
)

type Daemon struct {
	layout         paths.Layout
	config         model.DaemonConfig
	store          *store.Store
	runner         system.CommandRunner
	logger         *slog.Logger
	mu             sync.Mutex
	closing        chan struct{}
	once           sync.Once
	pid            int
	listener       net.Listener
	vmDNS          *vmdns.Server
	imageBuild     func(context.Context, imageBuildSpec) error
	requestHandler func(context.Context, rpc.Request) rpc.Response
}

func Open(ctx context.Context) (d *Daemon, err error) {
	layout, err := paths.Resolve()
	if err != nil {
		return nil, err
	}
	if err := paths.Ensure(layout); err != nil {
		return nil, err
	}
	cfg, err := config.Load(layout)
	if err != nil {
		return nil, err
	}
	logger, normalizedLevel, err := newDaemonLogger(os.Stderr, cfg.LogLevel)
	if err != nil {
		return nil, err
	}
	cfg.LogLevel = normalizedLevel
	db, err := store.Open(layout.DBPath)
	if err != nil {
		return nil, err
	}
	d = &Daemon{
		layout:  layout,
		config:  cfg,
		store:   db,
		runner:  system.NewRunner(),
		logger:  logger,
		closing: make(chan struct{}),
		pid:     os.Getpid(),
	}
	d.logger.Info("daemon opened", "socket", layout.SocketPath, "state_dir", layout.StateDir, "runtime_dir", cfg.RuntimeDir, "log_level", cfg.LogLevel)
	if err = d.startVMDNS(vmdns.DefaultListenAddr); err != nil {
		d.logger.Error("daemon open failed", "stage", "start_vm_dns", "error", err.Error())
		return nil, err
	}
	defer func() {
		if err != nil {
			_ = d.stopVMDNS()
		}
	}()
	if err = d.ensureDefaultImage(ctx); err != nil {
		d.logger.Error("daemon open failed", "stage", "ensure_default_image", "error", err.Error())
		return nil, err
	}
	if err = d.reconcile(ctx); err != nil {
		d.logger.Error("daemon open failed", "stage", "reconcile", "error", err.Error())
		return nil, err
	}
	return d, nil
}

func (d *Daemon) Close() error {
	var err error
	d.once.Do(func() {
		if d.logger != nil {
			d.logger.Info("daemon closing")
		}
		close(d.closing)
		if d.listener != nil {
			_ = d.listener.Close()
		}
		err = errors.Join(d.stopVMDNS(), d.store.Close())
	})
	return err
}

func (d *Daemon) Serve(ctx context.Context) error {
	_ = os.Remove(d.layout.SocketPath)
	listener, err := net.Listen("unix", d.layout.SocketPath)
	if err != nil {
		if d.logger != nil {
			d.logger.Error("daemon listen failed", "socket", d.layout.SocketPath, "error", err.Error())
		}
		return err
	}
	d.listener = listener
	defer listener.Close()
	defer os.Remove(d.layout.SocketPath)
	if err := os.Chmod(d.layout.SocketPath, 0o600); err != nil {
		return err
	}
	if d.logger != nil {
		d.logger.Info("daemon serving", "socket", d.layout.SocketPath, "pid", d.pid)
	}

	go d.backgroundLoop()

	for {
		conn, err := listener.Accept()
		if err != nil {
			select {
			case <-ctx.Done():
				return nil
			case <-d.closing:
				return nil
			default:
			}
			if ne, ok := err.(net.Error); ok && ne.Temporary() {
				if d.logger != nil {
					d.logger.Warn("daemon accept temporary failure", "error", err.Error())
				}
				time.Sleep(100 * time.Millisecond)
				continue
			}
			if d.logger != nil {
				d.logger.Error("daemon accept failed", "error", err.Error())
			}
			return err
		}
		go d.handleConn(conn)
	}
}

func (d *Daemon) handleConn(conn net.Conn) {
	defer conn.Close()
	reader := bufio.NewReader(conn)
	var req rpc.Request
	if err := json.NewDecoder(reader).Decode(&req); err != nil {
		if d.logger != nil {
			d.logger.Warn("daemon request decode failed", "remote", conn.RemoteAddr().String(), "error", err.Error())
		}
		_ = json.NewEncoder(conn).Encode(rpc.NewError("bad_request", err.Error()))
		return
	}
	reqCtx, cancel := context.WithCancel(context.Background())
	defer cancel()
	stopWatch := d.watchRequestDisconnect(conn, reader, req.Method, cancel)
	defer stopWatch()
	resp := d.dispatch(reqCtx, req)
	if reqCtx.Err() != nil {
		return
	}
	if err := json.NewEncoder(conn).Encode(resp); err != nil && d.logger != nil {
		d.logger.Warn("daemon response encode failed", "method", req.Method, "remote", conn.RemoteAddr().String(), "error", err.Error())
	}
}

func (d *Daemon) watchRequestDisconnect(conn net.Conn, reader *bufio.Reader, method string, cancel context.CancelFunc) func() {
	if conn == nil || reader == nil {
		return func() {}
	}
	done := make(chan struct{})
	var once sync.Once
	go func() {
		go func() {
			<-done
			if deadlineSetter, ok := conn.(interface{ SetReadDeadline(time.Time) error }); ok {
				_ = deadlineSetter.SetReadDeadline(time.Now())
			}
		}()
		var buf [1]byte
		for {
			_, err := reader.Read(buf[:])
			if err == nil {
				continue
			}
			select {
			case <-done:
				return
			default:
			}
			if d.logger != nil {
				d.logger.Info("daemon request canceled", "method", method, "remote", conn.RemoteAddr().String(), "error", err.Error())
			}
			cancel()
			return
		}
	}()
	return func() {
		once.Do(func() {
			close(done)
		})
	}
}

func (d *Daemon) dispatch(ctx context.Context, req rpc.Request) rpc.Response {
	if req.Version != rpc.Version {
		return rpc.NewError("bad_version", fmt.Sprintf("unsupported version %d", req.Version))
	}
	if d.requestHandler != nil {
		return d.requestHandler(ctx, req)
	}
	switch req.Method {
	case "ping":
		result, _ := rpc.NewResult(api.PingResult{Status: "ok", PID: d.pid})
		return result
	case "shutdown":
		go d.Close()
		result, _ := rpc.NewResult(api.ShutdownResult{Status: "stopping"})
		return result
	case "vm.create":
		params, err := rpc.DecodeParams[api.VMCreateParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, err := d.CreateVM(ctx, params)
		return marshalResultOrError(api.VMShowResult{VM: vm}, err)
	case "vm.list":
		vms, err := d.store.ListVMs(ctx)
		return marshalResultOrError(api.VMListResult{VMs: vms}, err)
	case "vm.show":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, err := d.FindVM(ctx, params.IDOrName)
		return marshalResultOrError(api.VMShowResult{VM: vm}, err)
	case "vm.start":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, err := d.StartVM(ctx, params.IDOrName)
		return marshalResultOrError(api.VMShowResult{VM: vm}, err)
	case "vm.stop":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, err := d.StopVM(ctx, params.IDOrName)
		return marshalResultOrError(api.VMShowResult{VM: vm}, err)
	case "vm.kill":
		params, err := rpc.DecodeParams[api.VMKillParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, err := d.KillVM(ctx, params)
		return marshalResultOrError(api.VMShowResult{VM: vm}, err)
	case "vm.restart":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, err := d.RestartVM(ctx, params.IDOrName)
		return marshalResultOrError(api.VMShowResult{VM: vm}, err)
	case "vm.delete":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, err := d.DeleteVM(ctx, params.IDOrName)
		return marshalResultOrError(api.VMShowResult{VM: vm}, err)
	case "vm.set":
		params, err := rpc.DecodeParams[api.VMSetParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, err := d.SetVM(ctx, params)
		return marshalResultOrError(api.VMShowResult{VM: vm}, err)
	case "vm.stats":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, stats, err := d.GetVMStats(ctx, params.IDOrName)
		return marshalResultOrError(api.VMStatsResult{VM: vm, Stats: stats}, err)
	case "vm.logs":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, err := d.FindVM(ctx, params.IDOrName)
		if err != nil {
			return rpc.NewError("not_found", err.Error())
		}
		return marshalResultOrError(api.VMLogsResult{LogPath: vm.Runtime.LogPath}, nil)
	case "vm.ssh":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		vm, err := d.TouchVM(ctx, params.IDOrName)
		if err != nil {
			return rpc.NewError("not_found", err.Error())
		}
		if vm.State != model.VMStateRunning || !system.ProcessRunning(vm.Runtime.PID, vm.Runtime.APISockPath) {
			return rpc.NewError("not_running", fmt.Sprintf("vm %s is not running", vm.Name))
		}
		return marshalResultOrError(api.VMSSHResult{Name: vm.Name, GuestIP: vm.Runtime.GuestIP}, nil)
	case "image.list":
		images, err := d.store.ListImages(ctx)
		return marshalResultOrError(api.ImageListResult{Images: images}, err)
	case "image.show":
		params, err := rpc.DecodeParams[api.ImageRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		image, err := d.FindImage(ctx, params.IDOrName)
		return marshalResultOrError(api.ImageShowResult{Image: image}, err)
	case "image.build":
		params, err := rpc.DecodeParams[api.ImageBuildParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		image, err := d.BuildImage(ctx, params)
		return marshalResultOrError(api.ImageShowResult{Image: image}, err)
	case "image.delete":
		params, err := rpc.DecodeParams[api.ImageRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		image, err := d.DeleteImage(ctx, params.IDOrName)
		return marshalResultOrError(api.ImageShowResult{Image: image}, err)
	default:
		return rpc.NewError("unknown_method", req.Method)
	}
}

func (d *Daemon) backgroundLoop() {
	statsTicker := time.NewTicker(d.config.StatsPollInterval)
	staleTicker := time.NewTicker(model.DefaultStaleSweepInterval)
	defer statsTicker.Stop()
	defer staleTicker.Stop()
	for {
		select {
		case <-d.closing:
			return
		case <-statsTicker.C:
			if err := d.pollStats(context.Background()); err != nil && d.logger != nil {
				d.logger.Error("background stats poll failed", "error", err.Error())
			}
		case <-staleTicker.C:
			if err := d.stopStaleVMs(context.Background()); err != nil && d.logger != nil {
				d.logger.Error("background stale sweep failed", "error", err.Error())
			}
		}
	}
}

func (d *Daemon) startVMDNS(addr string) error {
	server, err := vmdns.New(addr, d.logger)
	if err != nil {
		return err
	}
	d.vmDNS = server
	if d.logger != nil {
		d.logger.Info("vm dns serving", "dns_addr", server.Addr())
	}
	return nil
}

func (d *Daemon) stopVMDNS() error {
	if d.vmDNS == nil {
		return nil
	}
	err := d.vmDNS.Close()
	d.vmDNS = nil
	return err
}

func (d *Daemon) ensureDefaultImage(ctx context.Context) error {
	if d.config.DefaultImageName == "" {
		return nil
	}
	desired, ok := d.desiredDefaultImage()
	if !ok {
		if d.logger != nil {
			d.logger.Debug("default image skipped", "image_name", d.config.DefaultImageName, "rootfs_path", d.config.DefaultRootfs, "kernel_path", d.config.DefaultKernel)
		}
		return nil
	}

	image, err := d.store.GetImageByName(ctx, d.config.DefaultImageName)
	switch {
	case err == nil:
		if image.Managed {
			if d.logger != nil {
				d.logger.Debug("managed default image left untouched", append(imageLogAttrs(image), "managed", image.Managed)...)
			}
			return nil
		}
		if defaultImageMatches(image, desired) {
			if d.logger != nil {
				d.logger.Debug("default image already current", imageLogAttrs(image)...)
			}
			return nil
		}
		updated := desired
		updated.ID = image.ID
		updated.CreatedAt = image.CreatedAt
		updated.UpdatedAt = model.Now()
		if err := d.store.UpsertImage(ctx, updated); err != nil {
			return err
		}
		if d.logger != nil {
			d.logger.Info("default image reconciled", append(imageLogAttrs(updated), "previous_rootfs_path", image.RootfsPath, "previous_kernel_path", image.KernelPath)...)
		}
		return nil
	case errors.Is(err, sql.ErrNoRows):
		id, err := model.NewID()
		if err != nil {
			return err
		}
		now := model.Now()
		desired.ID = id
		desired.CreatedAt = now
		desired.UpdatedAt = now
		if err := d.store.UpsertImage(ctx, desired); err != nil {
			return err
		}
		if d.logger != nil {
			d.logger.Info("default image registered", append(imageLogAttrs(desired), "managed", desired.Managed)...)
		}
		return nil
	default:
		return err
	}
}

func (d *Daemon) desiredDefaultImage() (model.Image, bool) {
	rootfs := d.config.DefaultRootfs
	kernel := d.config.DefaultKernel
	if !exists(rootfs) || !exists(kernel) {
		return model.Image{}, false
	}
	return model.Image{
		Name:         d.config.DefaultImageName,
		Managed:      false,
		ArtifactDir:  "",
		RootfsPath:   rootfs,
		KernelPath:   kernel,
		InitrdPath:   d.config.DefaultInitrd,
		ModulesDir:   d.config.DefaultModulesDir,
		PackagesPath: d.config.DefaultPackagesFile,
		Docker:       strings.Contains(filepath.Base(rootfs), "docker"),
	}, true
}

func defaultImageMatches(current, desired model.Image) bool {
	return current.Name == desired.Name &&
		current.Managed == desired.Managed &&
		current.ArtifactDir == desired.ArtifactDir &&
		current.RootfsPath == desired.RootfsPath &&
		current.KernelPath == desired.KernelPath &&
		current.InitrdPath == desired.InitrdPath &&
		current.ModulesDir == desired.ModulesDir &&
		current.PackagesPath == desired.PackagesPath &&
		current.Docker == desired.Docker
}

func (d *Daemon) reconcile(ctx context.Context) error {
	op := d.beginOperation("daemon.reconcile")
	vms, err := d.store.ListVMs(ctx)
	if err != nil {
		return op.fail(err)
	}
	for _, vm := range vms {
		if vm.State != model.VMStateRunning {
			continue
		}
		if system.ProcessRunning(vm.Runtime.PID, vm.Runtime.APISockPath) {
			continue
		}
		op.stage("stale_vm", vmLogAttrs(vm)...)
		_ = d.cleanupRuntime(ctx, vm, true)
		vm.State = model.VMStateStopped
		vm.Runtime.State = model.VMStateStopped
		vm.Runtime.PID = 0
		vm.Runtime.TapDevice = ""
		vm.Runtime.APISockPath = ""
		vm.Runtime.BaseLoop = ""
		vm.Runtime.COWLoop = ""
		vm.Runtime.DMName = ""
		vm.Runtime.DMDev = ""
		vm.UpdatedAt = model.Now()
		if err := d.store.UpsertVM(ctx, vm); err != nil {
			return op.fail(err, vmLogAttrs(vm)...)
		}
	}
	if err := d.rebuildDNS(ctx); err != nil {
		return op.fail(err)
	}
	op.done()
	return nil
}

func (d *Daemon) FindVM(ctx context.Context, idOrName string) (model.VMRecord, error) {
	if idOrName == "" {
		return model.VMRecord{}, errors.New("vm id or name is required")
	}
	if vm, err := d.store.GetVM(ctx, idOrName); err == nil {
		return vm, nil
	}
	vms, err := d.store.ListVMs(ctx)
	if err != nil {
		return model.VMRecord{}, err
	}
	matchCount := 0
	var match model.VMRecord
	for _, vm := range vms {
		if strings.HasPrefix(vm.ID, idOrName) || strings.HasPrefix(vm.Name, idOrName) {
			match = vm
			matchCount++
		}
	}
	if matchCount == 1 {
		return match, nil
	}
	if matchCount > 1 {
		return model.VMRecord{}, fmt.Errorf("multiple VMs match %q", idOrName)
	}
	return model.VMRecord{}, fmt.Errorf("vm %q not found", idOrName)
}

func (d *Daemon) FindImage(ctx context.Context, idOrName string) (model.Image, error) {
	if idOrName == "" {
		return model.Image{}, errors.New("image id or name is required")
	}
	if image, err := d.store.GetImageByName(ctx, idOrName); err == nil {
		return image, nil
	}
	if image, err := d.store.GetImageByID(ctx, idOrName); err == nil {
		return image, nil
	}
	images, err := d.store.ListImages(ctx)
	if err != nil {
		return model.Image{}, err
	}
	matchCount := 0
	var match model.Image
	for _, image := range images {
		if strings.HasPrefix(image.ID, idOrName) || strings.HasPrefix(image.Name, idOrName) {
			match = image
			matchCount++
		}
	}
	if matchCount == 1 {
		return match, nil
	}
	if matchCount > 1 {
		return model.Image{}, fmt.Errorf("multiple images match %q", idOrName)
	}
	return model.Image{}, fmt.Errorf("image %q not found", idOrName)
}

func (d *Daemon) TouchVM(ctx context.Context, idOrName string) (model.VMRecord, error) {
	d.mu.Lock()
	defer d.mu.Unlock()
	vm, err := d.FindVM(ctx, idOrName)
	if err != nil {
		return model.VMRecord{}, err
	}
	system.TouchNow(&vm)
	if err := d.store.UpsertVM(ctx, vm); err != nil {
		return model.VMRecord{}, err
	}
	return vm, nil
}

func marshalResultOrError(v any, err error) rpc.Response {
	if err != nil {
		return rpc.NewError("operation_failed", err.Error())
	}
	resp, marshalErr := rpc.NewResult(v)
	if marshalErr != nil {
		return rpc.NewError("marshal_failed", marshalErr.Error())
	}
	return resp
}

func exists(path string) bool {
	_, err := os.Stat(path)
	return err == nil
}