package daemon

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"net"
	"os"
	"sync"
	"time"

	"banger/internal/api"
	"banger/internal/buildinfo"
	"banger/internal/config"
	ws "banger/internal/daemon/workspace"
	"banger/internal/model"
	"banger/internal/paths"
	"banger/internal/rpc"
	"banger/internal/store"
	"banger/internal/system"
	"banger/internal/vmdns"
)

// Daemon is the composition root: shared infrastructure (store,
// runner, logger, layout, config) plus pointers to the four focused
// services that own behavior. Open wires the services; the dispatch
// loop forwards RPCs to them. No lifecycle / image / workspace /
// networking behavior lives on *Daemon itself — it's wiring.
type Daemon struct {
	layout paths.Layout
	config model.DaemonConfig
	store  *store.Store
	runner system.CommandRunner
	logger *slog.Logger

	net *HostNetwork
	img *ImageService
	ws  *WorkspaceService
	vm  *VMService

	closing         chan struct{}
	once            sync.Once
	pid             int
	listener        net.Listener
	vmCaps          []vmCapability
	requestHandler  func(context.Context, rpc.Request) rpc.Response
	guestWaitForSSH func(context.Context, string, string, time.Duration) error
	guestDial       func(context.Context, string, string) (guestSSHClient, error)
}

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
	}
	closing := make(chan struct{})
	runner := system.NewRunner()
	d = &Daemon{
		layout:  layout,
		config:  cfg,
		store:   db,
		runner:  runner,
		logger:  logger,
		closing: closing,
		pid:     os.Getpid(),
	}
	wireServices(d)
	// From here on, every failure path must run Close() so the host
	// state we touched (DNS listener goroutine, resolvectl routing,
	// SQLite handle, future side effects) gets unwound. Close is
	// idempotent + nil-guarded so it's safe to call on a partially
	// initialised daemon — `d.vmDNS == nil` and friends short-circuit
	// the teardown of components we never set up.
	defer func() {
		if err != nil {
			_ = d.Close()
		}
	}()

	d.ensureVMSSHClientConfig()
	d.logger.Info("daemon opened", "socket", layout.SocketPath, "state_dir", layout.StateDir, "log_level", cfg.LogLevel)
	if err = d.net.startVMDNS(vmdns.DefaultListenAddr); err != nil {
		d.logger.Error("daemon open failed", "stage", "start_vm_dns", "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
	}
	d.net.ensureVMDNSResolverRouting(ctx)
	// Seed HostNetwork's pool index from taps already claimed by VMs
	// on disk so newly warmed pool entries don't collide with them.
	if d.config.TapPoolSize > 0 && d.store != nil {
		vms, listErr := d.store.ListVMs(ctx)
		if listErr != nil {
			d.logger.Error("daemon open failed", "stage", "initialize_tap_pool", "error", listErr.Error())
			return nil, listErr
		}
		used := make([]string, 0, len(vms))
		for _, vm := range vms {
			if tap := d.vm.vmHandles(vm.ID).TapDevice; tap != "" {
				used = append(used, tap)
			}
		}
		d.net.initializeTapPool(used)
	}
	go d.net.ensureTapPool(context.Background())
	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()
		}
		var closeErr error
		if d.store != nil {
			closeErr = d.store.Close()
		}
		err = errors.Join(d.net.clearVMDNSResolverRouting(context.Background()), d.net.stopVMDNS(), closeErr)
	})
	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 _, ok := err.(net.Error); ok {
				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":
		info := buildinfo.Current()
		result, _ := rpc.NewResult(api.PingResult{
			Status:  "ok",
			PID:     d.pid,
			Version: info.Version,
			Commit:  info.Commit,
			BuiltAt: info.BuiltAt,
		})
		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.vm.CreateVM(ctx, params)
		return marshalResultOrError(api.VMShowResult{VM: vm}, err)
	case "vm.create.begin":
		params, err := rpc.DecodeParams[api.VMCreateParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		op, err := d.vm.BeginVMCreate(ctx, params)
		return marshalResultOrError(api.VMCreateBeginResult{Operation: op}, err)
	case "vm.create.status":
		params, err := rpc.DecodeParams[api.VMCreateStatusParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		op, err := d.vm.VMCreateStatus(ctx, params.ID)
		return marshalResultOrError(api.VMCreateStatusResult{Operation: op}, err)
	case "vm.create.cancel":
		params, err := rpc.DecodeParams[api.VMCreateStatusParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		err = d.vm.CancelVMCreate(ctx, params.ID)
		return marshalResultOrError(api.Empty{}, 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.vm.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.vm.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.vm.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.vm.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.vm.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.vm.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.vm.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.vm.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.vm.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.vm.TouchVM(ctx, params.IDOrName)
		if err != nil {
			return rpc.NewError("not_found", err.Error())
		}
		if !d.vm.vmAlive(vm) {
			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 "vm.health":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		result, err := d.vm.HealthVM(ctx, params.IDOrName)
		return marshalResultOrError(result, err)
	case "vm.ping":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		result, err := d.vm.PingVM(ctx, params.IDOrName)
		return marshalResultOrError(result, err)
	case "vm.ports":
		params, err := rpc.DecodeParams[api.VMRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		result, err := d.vm.PortsVM(ctx, params.IDOrName)
		return marshalResultOrError(result, err)
	case "vm.workspace.prepare":
		params, err := rpc.DecodeParams[api.VMWorkspacePrepareParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		workspace, err := d.ws.PrepareVMWorkspace(ctx, params)
		return marshalResultOrError(api.VMWorkspacePrepareResult{Workspace: workspace}, err)
	case "vm.workspace.export":
		params, err := rpc.DecodeParams[api.WorkspaceExportParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		result, err := d.ws.ExportVMWorkspace(ctx, params)
		return marshalResultOrError(result, err)
	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.img.FindImage(ctx, params.IDOrName)
		return marshalResultOrError(api.ImageShowResult{Image: image}, err)
	case "image.register":
		params, err := rpc.DecodeParams[api.ImageRegisterParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		image, err := d.img.RegisterImage(ctx, params)
		return marshalResultOrError(api.ImageShowResult{Image: image}, err)
	case "image.promote":
		params, err := rpc.DecodeParams[api.ImageRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		image, err := d.img.PromoteImage(ctx, params.IDOrName)
		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.img.DeleteImage(ctx, params.IDOrName)
		return marshalResultOrError(api.ImageShowResult{Image: image}, err)
	case "image.pull":
		params, err := rpc.DecodeParams[api.ImagePullParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		image, err := d.img.PullImage(ctx, params)
		return marshalResultOrError(api.ImageShowResult{Image: image}, err)
	case "kernel.list":
		return marshalResultOrError(d.img.KernelList(ctx))
	case "kernel.show":
		params, err := rpc.DecodeParams[api.KernelRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		entry, err := d.img.KernelShow(ctx, params.Name)
		return marshalResultOrError(api.KernelShowResult{Entry: entry}, err)
	case "kernel.delete":
		params, err := rpc.DecodeParams[api.KernelRefParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		err = d.img.KernelDelete(ctx, params.Name)
		return marshalResultOrError(api.Empty{}, err)
	case "kernel.import":
		params, err := rpc.DecodeParams[api.KernelImportParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		entry, err := d.img.KernelImport(ctx, params)
		return marshalResultOrError(api.KernelShowResult{Entry: entry}, err)
	case "kernel.pull":
		params, err := rpc.DecodeParams[api.KernelPullParams](req)
		if err != nil {
			return rpc.NewError("bad_request", err.Error())
		}
		entry, err := d.img.KernelPull(ctx, params)
		return marshalResultOrError(api.KernelShowResult{Entry: entry}, err)
	case "kernel.catalog":
		return marshalResultOrError(d.img.KernelCatalog(ctx))
	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.vm.pollStats(context.Background()); err != nil && d.logger != nil {
				d.logger.Error("background stats poll failed", "error", err.Error())
			}
		case <-staleTicker.C:
			if err := d.vm.stopStaleVMs(context.Background()); err != nil && d.logger != nil {
				d.logger.Error("background stale sweep failed", "error", err.Error())
			}
			d.vm.pruneVMCreateOperations(time.Now().Add(-10 * time.Minute))
		}
	}
}

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 err := d.vm.withVMLockByIDErr(ctx, vm.ID, func(vm model.VMRecord) error {
			if vm.State != model.VMStateRunning {
				// Belt-and-braces: a stopped VM should never have a
				// scratch file or a cache entry. Clean up anything
				// left by an ungraceful previous daemon crash.
				d.vm.clearVMHandles(vm)
				return nil
			}
			// Rebuild the in-memory handle cache by loading the per-VM
			// scratch file and verifying the firecracker process is
			// still alive.
			h, alive, err := d.vm.rediscoverHandles(ctx, vm)
			if err != nil && d.logger != nil {
				d.logger.Warn("rediscover handles failed", "vm_id", vm.ID, "error", err.Error())
			}
			// Either way, seed the cache with what the scratch file
			// claimed. If alive, subsequent vmAlive() calls pass; if
			// not, cleanupRuntime needs these handles to know which
			// kernel resources (DM / loops / tap) to tear down.
			d.vm.setVMHandlesInMemory(vm.ID, h)
			if alive {
				return nil
			}
			op.stage("stale_vm", vmLogAttrs(vm)...)
			_ = d.vm.cleanupRuntime(ctx, vm, true)
			vm.State = model.VMStateStopped
			vm.Runtime.State = model.VMStateStopped
			d.vm.clearVMHandles(vm)
			vm.UpdatedAt = model.Now()
			return d.store.UpsertVM(ctx, vm)
		}); err != nil {
			return op.fail(err, "vm_id", vm.ID)
		}
	}
	if err := d.vm.rebuildDNS(ctx); err != nil {
		return op.fail(err)
	}
	op.done()
	return nil
}

// FindVM stays on Daemon as a thin forwarder to the VM service lookup.
// Dispatch code reads the facade directly; tests that pre-date the
// service split keep compiling.
func (d *Daemon) FindVM(ctx context.Context, idOrName string) (model.VMRecord, error) {
	return d.vm.FindVM(ctx, idOrName)
}

// FindImage stays on Daemon as a thin forwarder to the image service
// lookup so callers reading dispatch code see the obvious facade, and
// tests that pre-date the service split still compile.
func (d *Daemon) FindImage(ctx context.Context, idOrName string) (model.Image, error) {
	return d.img.FindImage(ctx, idOrName)
}

func (d *Daemon) TouchVM(ctx context.Context, idOrName string) (model.VMRecord, error) {
	return d.vm.TouchVM(ctx, idOrName)
}

// wireServices populates the four focused services and their peer
// references from the infrastructure already on d (runner, logger,
// config, layout, store, closing, plus the SSH-client test seams).
// Idempotent: each service is skipped if the field is already non-nil,
// so tests can preinstall stubs for the services they want to fake and
// let wireServices fill the rest. The peer-service closures on
// WorkspaceService capture d rather than a direct *VMService pointer so
// the ws↔vm construction order doesn't recurse: the closures read d.vm
// at call time, by which point it is populated.
func wireServices(d *Daemon) {
	if d.net == nil {
		d.net = newHostNetwork(hostNetworkDeps{
			runner:  d.runner,
			logger:  d.logger,
			config:  d.config,
			layout:  d.layout,
			closing: d.closing,
		})
	}
	if d.img == nil {
		d.img = newImageService(imageServiceDeps{
			runner: d.runner,
			logger: d.logger,
			config: d.config,
			layout: d.layout,
			store:  d.store,
			beginOperation: func(name string, attrs ...any) *operationLog {
				return d.beginOperation(name, attrs...)
			},
		})
	}
	if d.ws == nil {
		d.ws = newWorkspaceService(workspaceServiceDeps{
			runner:        d.runner,
			logger:        d.logger,
			config:        d.config,
			layout:        d.layout,
			store:         d.store,
			repoInspector: ws.NewInspector(),
			vmResolver: func(ctx context.Context, idOrName string) (model.VMRecord, error) {
				return d.vm.FindVM(ctx, idOrName)
			},
			aliveChecker: func(vm model.VMRecord) bool {
				return d.vm.vmAlive(vm)
			},
			waitGuestSSH: d.waitForGuestSSH,
			dialGuest:    d.dialGuest,
			imageResolver: func(ctx context.Context, idOrName string) (model.Image, error) {
				return d.FindImage(ctx, idOrName)
			},
			imageWorkSeed: func(ctx context.Context, image model.Image, fingerprint string) error {
				return d.img.refreshManagedWorkSeedFingerprint(ctx, image, fingerprint)
			},
			withVMLockByRef: func(ctx context.Context, idOrName string, fn func(model.VMRecord) (model.VMRecord, error)) (model.VMRecord, error) {
				return d.vm.withVMLockByRef(ctx, idOrName, fn)
			},
			beginOperation: d.beginOperation,
		})
	}
	if d.vm == nil {
		d.vm = newVMService(vmServiceDeps{
			runner:          d.runner,
			logger:          d.logger,
			config:          d.config,
			layout:          d.layout,
			store:           d.store,
			net:             d.net,
			img:             d.img,
			ws:              d.ws,
			capHooks:        d.buildCapabilityHooks(),
			beginOperation:  d.beginOperation,
			vsockHostDevice: defaultVsockHostDevice,
		})
	}
	if len(d.vmCaps) == 0 {
		d.vmCaps = d.defaultCapabilities()
	}
}

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
}