// Package docker provides the production Docker SDK adapter that
// implements `galaxy/rtmanager/internal/ports.DockerClient`. The
// adapter is the single component allowed to talk to the local Docker
// daemon; every Runtime Manager service path that needs container
// lifecycle operations goes through this surface.
//
// The adapter is intentionally narrow — it does not orchestrate, log,
// or retry. Cross-cutting concerns (lease coordination, durable state,
// notification side-effects) live in the service layer.
package docker

import (
	"context"
	"errors"
	"fmt"
	"io"
	"maps"
	"strings"
	"sync"
	"time"

	cerrdefs "github.com/containerd/errdefs"
	"github.com/docker/docker/api/types/container"
	"github.com/docker/docker/api/types/events"
	"github.com/docker/docker/api/types/filters"
	"github.com/docker/docker/api/types/image"
	"github.com/docker/docker/api/types/network"
	dockerclient "github.com/docker/docker/client"
	"github.com/docker/go-units"

	"galaxy/rtmanager/internal/ports"
)

// EnginePort is the in-container HTTP port the engine listens on. The
// value is fixed by `rtmanager/README.md §Container Model` and by the
// engine's Dockerfile (`game/Dockerfile`); RTM never publishes the port
// to the host. Keeping the constant here lets the adapter own the URL
// shape so the start service does not have to know it.
const EnginePort = 8080

// Config groups the dependencies and per-process defaults required to
// construct a Client. The struct is value-typed so wiring code can
// build it inline without intermediate variables.
type Config struct {
	// Docker stores the SDK client this adapter wraps. It must be
	// non-nil; callers typically construct it via `client.NewClientWithOpts`.
	Docker *dockerclient.Client

	// LogDriver stores the Docker logging driver applied to every
	// container the adapter creates (e.g. `json-file`).
	LogDriver string

	// LogOpts stores the comma-separated `key=value` driver options
	// forwarded to Docker. Empty disables driver-specific options.
	LogOpts string

	// Clock supplies the wall-clock used for `RunResult.StartedAt`.
	// Defaults to `time.Now` when nil.
	Clock func() time.Time
}

// Client is the production adapter implementing `ports.DockerClient`.
// Construct it via NewClient; do not zero-initialise.
type Client struct {
	docker    *dockerclient.Client
	logDriver string
	logOpts   string
	clock     func() time.Time
}

// NewClient constructs a Client from cfg. It returns an error if cfg
// does not carry the minimum collaborator set the adapter needs to
// function.
func NewClient(cfg Config) (*Client, error) {
	if cfg.Docker == nil {
		return nil, errors.New("new docker adapter: nil docker client")
	}
	if strings.TrimSpace(cfg.LogDriver) == "" {
		return nil, errors.New("new docker adapter: log driver must not be empty")
	}
	clock := cfg.Clock
	if clock == nil {
		clock = time.Now
	}
	return &Client{
		docker:    cfg.Docker,
		logDriver: cfg.LogDriver,
		logOpts:   cfg.LogOpts,
		clock:     clock,
	}, nil
}

// EnsureNetwork verifies the user-defined Docker network is present.
// The adapter never creates networks; provisioning is the operator's
// job per `rtmanager/README.md §Container Model`.
func (client *Client) EnsureNetwork(ctx context.Context, name string) error {
	if _, err := client.docker.NetworkInspect(ctx, name, network.InspectOptions{}); err != nil {
		if cerrdefs.IsNotFound(err) {
			return ports.ErrNetworkMissing
		}
		return fmt.Errorf("ensure network %q: %w", name, err)
	}
	return nil
}

// PullImage pulls ref according to policy. The pull stream is drained
// to completion because the Docker SDK only finishes the underlying
// pull when the body is consumed.
func (client *Client) PullImage(ctx context.Context, ref string, policy ports.PullPolicy) error {
	if !policy.IsKnown() {
		return fmt.Errorf("pull image %q: unknown pull policy %q", ref, policy)
	}
	switch policy {
	case ports.PullPolicyAlways:
		return client.runPull(ctx, ref)
	case ports.PullPolicyIfMissing:
		if present, err := client.imagePresent(ctx, ref); err != nil {
			return err
		} else if present {
			return nil
		}
		return client.runPull(ctx, ref)
	case ports.PullPolicyNever:
		present, err := client.imagePresent(ctx, ref)
		if err != nil {
			return err
		}
		if !present {
			return ports.ErrImageNotFound
		}
		return nil
	default:
		return fmt.Errorf("pull image %q: unsupported pull policy %q", ref, policy)
	}
}

// InspectImage returns image metadata for ref. RTM only reads labels
// at start time; the broader inspect struct stays accessible for
// diagnostics.
func (client *Client) InspectImage(ctx context.Context, ref string) (ports.ImageInspect, error) {
	inspect, err := client.docker.ImageInspect(ctx, ref)
	if err != nil {
		if cerrdefs.IsNotFound(err) {
			return ports.ImageInspect{}, ports.ErrImageNotFound
		}
		return ports.ImageInspect{}, fmt.Errorf("inspect image %q: %w", ref, err)
	}
	var labels map[string]string
	if inspect.Config != nil {
		labels = copyStringMap(inspect.Config.Labels)
	}
	return ports.ImageInspect{Ref: ref, Labels: labels}, nil
}

// InspectContainer returns container metadata for containerID. The
// adapter best-effort decodes Docker timestamps; malformed values map
// to the zero time so callers do not have to defend against nil
// pointers in the SDK response.
func (client *Client) InspectContainer(ctx context.Context, containerID string) (ports.ContainerInspect, error) {
	inspect, err := client.docker.ContainerInspect(ctx, containerID)
	if err != nil {
		if cerrdefs.IsNotFound(err) {
			return ports.ContainerInspect{}, ports.ErrContainerNotFound
		}
		return ports.ContainerInspect{}, fmt.Errorf("inspect container %q: %w", containerID, err)
	}

	result := ports.ContainerInspect{ID: inspect.ID}
	if inspect.ContainerJSONBase != nil {
		result.RestartCount = inspect.RestartCount
		if inspect.State != nil {
			result.Status = string(inspect.State.Status)
			result.OOMKilled = inspect.State.OOMKilled
			result.ExitCode = inspect.State.ExitCode
			result.StartedAt = parseDockerTime(inspect.State.StartedAt)
			result.FinishedAt = parseDockerTime(inspect.State.FinishedAt)
			if inspect.State.Health != nil {
				result.Health = string(inspect.State.Health.Status)
			}
		}
	}
	if inspect.Config != nil {
		result.ImageRef = inspect.Config.Image
		result.Hostname = inspect.Config.Hostname
		result.Labels = copyStringMap(inspect.Config.Labels)
	}
	return result, nil
}

// Run creates and starts one container according to spec. On
// `ContainerStart` failure the adapter best-effort removes the partial
// container so the start service never has to clean up after a failed
// start path.
func (client *Client) Run(ctx context.Context, spec ports.RunSpec) (ports.RunResult, error) {
	if err := spec.Validate(); err != nil {
		return ports.RunResult{}, fmt.Errorf("run container: %w", err)
	}
	memoryBytes, err := units.RAMInBytes(spec.Memory)
	if err != nil {
		return ports.RunResult{}, fmt.Errorf("run container %q: parse memory %q: %w", spec.Name, spec.Memory, err)
	}
	pidsLimit := int64(spec.PIDsLimit)

	containerCfg := &container.Config{
		Image:    spec.Image,
		Hostname: spec.Hostname,
		Env:      envMapToSlice(spec.Env),
		Labels:   copyStringMap(spec.Labels),
		Cmd:      append([]string(nil), spec.Cmd...),
	}
	hostCfg := &container.HostConfig{
		Binds: bindMountsToBinds(spec.BindMounts),
		LogConfig: container.LogConfig{
			Type:   client.logDriver,
			Config: parseLogOpts(client.logOpts),
		},
		Resources: container.Resources{
			NanoCPUs:  int64(spec.CPUQuota * 1e9),
			Memory:    memoryBytes,
			PidsLimit: &pidsLimit,
		},
	}
	netCfg := &network.NetworkingConfig{
		EndpointsConfig: map[string]*network.EndpointSettings{
			spec.Network: {
				Aliases: []string{spec.Hostname},
			},
		},
	}

	created, err := client.docker.ContainerCreate(ctx, containerCfg, hostCfg, netCfg, nil, spec.Name)
	if err != nil {
		return ports.RunResult{}, fmt.Errorf("create container %q: %w", spec.Name, err)
	}

	if err := client.docker.ContainerStart(ctx, created.ID, container.StartOptions{}); err != nil {
		client.cleanupAfterFailedStart(created.ID)
		return ports.RunResult{}, fmt.Errorf("start container %q: %w", spec.Name, err)
	}

	return ports.RunResult{
		ContainerID:    created.ID,
		EngineEndpoint: fmt.Sprintf("http://%s:%d", spec.Hostname, EnginePort),
		StartedAt:      client.clock(),
	}, nil
}

// Stop bounds graceful shutdown by timeout. A missing container is
// surfaced as ErrContainerNotFound so the service layer can treat it
// as already-stopped per `rtmanager/README.md §Lifecycles → Stop`.
func (client *Client) Stop(ctx context.Context, containerID string, timeout time.Duration) error {
	seconds := max(int(timeout.Round(time.Second).Seconds()), 0)
	if err := client.docker.ContainerStop(ctx, containerID, container.StopOptions{Timeout: &seconds}); err != nil {
		if cerrdefs.IsNotFound(err) {
			return ports.ErrContainerNotFound
		}
		return fmt.Errorf("stop container %q: %w", containerID, err)
	}
	return nil
}

// Remove removes the container without forcing kill. A missing
// container is reported as success so callers can treat the operation
// as idempotent.
func (client *Client) Remove(ctx context.Context, containerID string) error {
	if err := client.docker.ContainerRemove(ctx, containerID, container.RemoveOptions{}); err != nil {
		if cerrdefs.IsNotFound(err) {
			return nil
		}
		return fmt.Errorf("remove container %q: %w", containerID, err)
	}
	return nil
}

// List returns container summaries that match filter. Empty Labels
// match every container; the reconciler always passes
// `com.galaxy.owner=rtmanager`.
func (client *Client) List(ctx context.Context, filter ports.ListFilter) ([]ports.ContainerSummary, error) {
	args := filters.NewArgs()
	for key, value := range filter.Labels {
		args.Add("label", key+"="+value)
	}
	summaries, err := client.docker.ContainerList(ctx, container.ListOptions{All: true, Filters: args})
	if err != nil {
		return nil, fmt.Errorf("list containers: %w", err)
	}
	out := make([]ports.ContainerSummary, 0, len(summaries))
	for _, summary := range summaries {
		hostname := ""
		if len(summary.Names) > 0 {
			hostname = strings.TrimPrefix(summary.Names[0], "/")
		}
		out = append(out, ports.ContainerSummary{
			ID:        summary.ID,
			ImageRef:  summary.Image,
			Hostname:  hostname,
			Labels:    copyStringMap(summary.Labels),
			Status:    string(summary.State),
			StartedAt: time.Unix(summary.Created, 0).UTC(),
		})
	}
	return out, nil
}

// EventsListen subscribes to the Docker events stream and returns a
// typed channel of decoded container events plus an asynchronous
// error channel. The caller cancels ctx to terminate the subscription;
// the goroutine closes both channels on termination.
func (client *Client) EventsListen(ctx context.Context) (<-chan ports.DockerEvent, <-chan error, error) {
	msgs, sdkErrs := client.docker.Events(ctx, events.ListOptions{})
	out := make(chan ports.DockerEvent)
	outErrs := make(chan error, 1)

	var closeOnce sync.Once
	closeAll := func() {
		closeOnce.Do(func() {
			close(out)
			close(outErrs)
		})
	}

	go func() {
		defer closeAll()
		for {
			select {
			case <-ctx.Done():
				return
			case msg, ok := <-msgs:
				if !ok {
					return
				}
				if msg.Type != events.ContainerEventType {
					continue
				}
				select {
				case <-ctx.Done():
					return
				case out <- decodeEvent(msg):
				}
			case err, ok := <-sdkErrs:
				if !ok {
					return
				}
				if err == nil {
					continue
				}
				select {
				case <-ctx.Done():
				case outErrs <- err:
				}
				return
			}
		}
	}()

	return out, outErrs, nil
}

func (client *Client) cleanupAfterFailedStart(containerID string) {
	cleanupCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	_ = client.docker.ContainerRemove(cleanupCtx, containerID, container.RemoveOptions{Force: true})
}

func (client *Client) imagePresent(ctx context.Context, ref string) (bool, error) {
	if _, err := client.docker.ImageInspect(ctx, ref); err != nil {
		if cerrdefs.IsNotFound(err) {
			return false, nil
		}
		return false, fmt.Errorf("inspect image %q: %w", ref, err)
	}
	return true, nil
}

func (client *Client) runPull(ctx context.Context, ref string) error {
	body, err := client.docker.ImagePull(ctx, ref, image.PullOptions{})
	if err != nil {
		if cerrdefs.IsNotFound(err) {
			return ports.ErrImageNotFound
		}
		return fmt.Errorf("pull image %q: %w", ref, err)
	}
	defer body.Close()
	if _, err := io.Copy(io.Discard, body); err != nil {
		return fmt.Errorf("drain pull stream for %q: %w", ref, err)
	}
	return nil
}

func envMapToSlice(envMap map[string]string) []string {
	if len(envMap) == 0 {
		return nil
	}
	out := make([]string, 0, len(envMap))
	for key, value := range envMap {
		out = append(out, key+"="+value)
	}
	return out
}

func bindMountsToBinds(mounts []ports.BindMount) []string {
	if len(mounts) == 0 {
		return nil
	}
	binds := make([]string, 0, len(mounts))
	for _, mount := range mounts {
		bind := mount.HostPath + ":" + mount.MountPath
		if mount.ReadOnly {
			bind += ":ro"
		}
		binds = append(binds, bind)
	}
	return binds
}

func parseLogOpts(raw string) map[string]string {
	if strings.TrimSpace(raw) == "" {
		return nil
	}
	out := make(map[string]string)
	for part := range strings.SplitSeq(raw, ",") {
		entry := strings.TrimSpace(part)
		if entry == "" {
			continue
		}
		index := strings.IndexByte(entry, '=')
		if index <= 0 {
			continue
		}
		out[entry[:index]] = entry[index+1:]
	}
	if len(out) == 0 {
		return nil
	}
	return out
}

func parseDockerTime(raw string) time.Time {
	if raw == "" {
		return time.Time{}
	}
	parsed, err := time.Parse(time.RFC3339Nano, raw)
	if err != nil {
		return time.Time{}
	}
	return parsed.UTC()
}

func copyStringMap(in map[string]string) map[string]string {
	if in == nil {
		return nil
	}
	out := make(map[string]string, len(in))
	maps.Copy(out, in)
	return out
}

func decodeEvent(msg events.Message) ports.DockerEvent {
	occurredAt := time.Time{}
	switch {
	case msg.TimeNano != 0:
		occurredAt = time.Unix(0, msg.TimeNano).UTC()
	case msg.Time != 0:
		occurredAt = time.Unix(msg.Time, 0).UTC()
	}
	exitCode := 0
	if raw, ok := msg.Actor.Attributes["exitCode"]; ok {
		if value, err := parseExitCode(raw); err == nil {
			exitCode = value
		}
	}
	return ports.DockerEvent{
		Action:      string(msg.Action),
		ContainerID: msg.Actor.ID,
		Labels:      copyStringMap(msg.Actor.Attributes),
		ExitCode:    exitCode,
		OccurredAt:  occurredAt,
	}
}

func parseExitCode(raw string) (int, error) {
	value := 0
	for _, r := range raw {
		if r < '0' || r > '9' {
			return 0, fmt.Errorf("non-numeric exit code %q", raw)
		}
		value = value*10 + int(r-'0')
	}
	return value, nil
}

// Compile-time assertion: Client implements ports.DockerClient.
var _ ports.DockerClient = (*Client)(nil)