package daemon

import (
	"context"
	"errors"
	"fmt"
	"io/fs"
	"net/http"
	"os"
	"path/filepath"
	"slices"

	"github.com/containerd/log"
	"github.com/moby/extensions"
	"github.com/moby/extensions/grpcproxy"
	"github.com/moby/extensions/host"
	"github.com/moby/moby/v2/daemon/config"
	"github.com/moby/moby/v2/daemon/internal/rootless"
	servicegrpcv0 "github.com/moby/moby/v2/extpoints/servicegrpc/v0"
	"github.com/moby/moby/v2/pkg/homedir"
	"google.golang.org/grpc"
)

// newExtensionHost builds the daemon's extension host.
func (daemon *Daemon) newExtensionHost(ctx context.Context) (*host.Host, error) {
	cfg := daemon.Config()
	runtimeDir := extensionRuntimeDir(&cfg)
	if err := os.MkdirAll(runtimeDir, 0o700); err != nil {
		return nil, fmt.Errorf("create extension runtime directory: %w", err)
	}
	if err := os.Chmod(runtimeDir, 0o700); err != nil {
		return nil, fmt.Errorf("set permissions on extension runtime directory: %w", err)
	}
	// A crashed daemon leaves its API socket behind. Opening the socket
	// replaces it, but a daemon whose extensions never use the API would
	// otherwise keep the dead socket around.
	if err := os.Remove(extensionAPISocket(&cfg)); err != nil && !errors.Is(err, fs.ErrNotExist) {
		log.G(ctx).WithError(err).Warn("failed to remove stale extension API socket")
	}
	defaults := slices.Concat(builtinExtensions, daemon.daemonExtensions())
	exts, err := selectBuiltinExtensions(cfg.Extensions, defaults, daemon.optionalExtensions())
	if err != nil {
		return nil, err
	}
	return host.New(ctx,
		host.WithRuntimeDir(runtimeDir),
		host.WithExtensions(exts...),
		host.WithDirs(extensionDirs(&cfg)...),
		host.WithClientProviders(clientProviders()...),
		host.WithProviderPolicy(host.PointPolicyFunc(func(extensions.ExtensionIdentity, extensions.PointID) host.PointPolicyResult {
			return host.Allow()
		})),
		host.WithDependencyProviders(dependencyProviders()...),
		host.WithPointServers(offeredPointServers()...),
		host.WithExtensionConfig(extensionConfig(&cfg)),
	)
}

// extensionRuntimeDir holds the extension sockets.
// It is private to the daemon user.
func extensionRuntimeDir(cfg *config.Config) string {
	return filepath.Join(cfg.ExecRoot, "extensions")
}

// extensionAPISocket is the path of the API socket for extensions.
func extensionAPISocket(cfg *config.Config) string {
	return filepath.Join(extensionRuntimeDir(cfg), "api.sock")
}

// extensionAPIEndpoint provides the daemon.api point.
// It opens the API socket for extensions when an extension first asks for the
// endpoint, so daemons without such extensions expose no extra API endpoint.
// The socket is separate from the configured hosts, which may be TLS-only TCP
// or socket-activated and so unusable by extensions.
func (daemon *Daemon) extensionAPIEndpoint(ctx context.Context) (string, error) {
	cfg := daemon.Config()
	path := extensionAPISocket(&cfg)
	if err := daemon.apiSockets.Open(ctx, path); err != nil {
		return "", err
	}
	return "unix://" + path, nil
}

// StartAPISockets serves h on the API sockets the daemon creates for its own
// consumers, such as extensions.
func (daemon *Daemon) StartAPISockets(h http.Handler) {
	daemon.apiSockets.Start(h)
}

// extensionConfig converts daemon.json's extensions.configs entries to host form.
func extensionConfig(cfg *config.Config) map[extensions.ExtensionID]extensions.Config {
	if len(cfg.Extensions.Configs) == 0 {
		return nil
	}
	out := make(map[extensions.ExtensionID]extensions.Config, len(cfg.Extensions.Configs))
	for _, extensionConfig := range cfg.Extensions.Configs {
		out[extensionConfig.ID] = extensionConfig.Config
	}
	return out
}

// extensionDirs are the directories scanned for out-of-process extension
// binaries: the ones configured with --extension-dir, or the default location
// when none are configured.
func extensionDirs(cfg *config.Config) []string {
	if len(cfg.Extensions.Dirs) > 0 {
		return cfg.Extensions.Dirs
	}
	dir, err := defaultExtensionDir()
	if err != nil {
		// Only rootless without a home directory reaches here; without a default
		// the daemon simply loads no extensions rather than failing to start.
		log.G(context.TODO()).WithError(err).Debug("extensions: no default directory")
		return nil
	}
	return []string{dir}
}

// defaultExtensionDir is the standard location for extension binaries:
// /usr/libexec/docker/moby-extensions, or the rootless equivalent under the
// user's libexec home.
func defaultExtensionDir() (string, error) {
	libexecDir := "/usr/libexec"
	if rootless.RunningWithRootlessKit() {
		var err error
		libexecDir, err = homedir.GetLibexecHome()
		if err != nil {
			return "", err
		}
	}
	return filepath.Join(libexecDir, "docker", "moby-extensions"), nil
}

// ExposeExtensionServices publishes service.grpc services and points offered
// through service.v0 on the API socket.
// In-process services are registered on gs; out-of-process services are proxied.
// Service-name collisions fail startup.
func (daemon *Daemon) ExposeExtensionServices(gs *grpc.Server) (*grpcproxy.Proxy, error) {
	if daemon.extensionHost == nil {
		return nil, nil
	}
	reserved := make(map[string]struct{})
	for name := range gs.GetServiceInfo() {
		reserved[name] = struct{}{}
	}

	inproc, err := servicegrpcv0.Collect(daemon.extensionHost)
	if err != nil {
		return nil, err
	}
	// Include offered points in the service-name collision check.
	var offered offeredServices
	daemon.extensionHost.RegisterInProcessServices(&offered)
	inproc = append(inproc, offered...)
	for _, svc := range inproc {
		if _, taken := reserved[svc.Name]; taken {
			return nil, fmt.Errorf("in-process extension cannot expose gRPC service %q: it is already served", svc.Name)
		}
		reserved[svc.Name] = struct{}{}
	}
	for _, svc := range inproc {
		gs.RegisterService(svc.Desc, svc.Impl)
	}

	var backends []grpcproxy.Backend
	for ext, names := range daemon.extensionHost.PublishedServicesForPoint(servicegrpcv0.Point.ID()) {
		if conn, ok := daemon.extensionHost.Conn(ext); ok {
			backends = append(backends, grpcproxy.Backend{ID: string(ext), Conn: conn, Services: names})
		}
	}
	routes, err := grpcproxy.BuildRoutes(backends, reserved)
	if err != nil {
		return nil, err
	}
	if len(routes) == 0 {
		return nil, nil
	}
	return grpcproxy.New(routes), nil
}

// offeredServices collects in-process services for validation before registration.
type offeredServices []servicegrpcv0.Service

func (s *offeredServices) RegisterService(desc *grpc.ServiceDesc, impl any) {
	*s = append(*s, servicegrpcv0.Service{Name: desc.ServiceName, Desc: desc, Impl: impl})
}