// Package healtheventspublisher provides the Redis-Streams-backed
// publisher for `runtime:health_events`. Every Publish call upserts the
// latest `health_snapshots` row before XADDing the event so consumers
// observing the snapshot store can never lag the event stream by more
// than the duration of one network call.
//
// The publisher is shared across `ports.HealthEventPublisher` callers:
// the start service emits `container_started`; the probe, inspect, and
// events-listener workers emit the rest. The publisher's surface is
// stable across all of them.
package healtheventspublisher

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"strconv"

	"galaxy/rtmanager/internal/domain/health"
	"galaxy/rtmanager/internal/ports"

	"github.com/redis/go-redis/v9"
)

// emptyDetails is the canonical JSON payload installed when the caller
// supplies an empty Details slice. Matches the SQL DEFAULT for
// `health_snapshots.details`.
const emptyDetails = "{}"

// Wire field names used by the Redis Streams payload. Frozen by
// `rtmanager/api/runtime-health-asyncapi.yaml`; renaming any of them
// breaks consumers.
const (
	fieldGameID       = "game_id"
	fieldContainerID  = "container_id"
	fieldEventType    = "event_type"
	fieldOccurredAtMS = "occurred_at_ms"
	fieldDetails      = "details"
)

// Config groups the dependencies and stream name required to construct
// a Publisher.
type Config struct {
	// Client appends entries to the Redis Stream. Must be non-nil.
	Client *redis.Client

	// Snapshots upserts the latest health snapshot. Must be non-nil.
	Snapshots ports.HealthSnapshotStore

	// Stream stores the Redis Stream key events are published to (e.g.
	// `runtime:health_events`). Must not be empty.
	Stream string
}

// Publisher implements `ports.HealthEventPublisher` on top of a shared
// Redis client and the production `health_snapshots` store.
type Publisher struct {
	client    *redis.Client
	snapshots ports.HealthSnapshotStore
	stream    string
}

// NewPublisher constructs one Publisher from cfg. Validation errors
// surface the missing collaborator verbatim.
func NewPublisher(cfg Config) (*Publisher, error) {
	if cfg.Client == nil {
		return nil, errors.New("new rtmanager health events publisher: nil redis client")
	}
	if cfg.Snapshots == nil {
		return nil, errors.New("new rtmanager health events publisher: nil snapshot store")
	}
	if cfg.Stream == "" {
		return nil, errors.New("new rtmanager health events publisher: stream must not be empty")
	}
	return &Publisher{
		client:    cfg.Client,
		snapshots: cfg.Snapshots,
		stream:    cfg.Stream,
	}, nil
}

// Publish upserts the matching health_snapshots row and then XADDs the
// envelope to the configured Redis Stream. Both side effects are
// required; the snapshot upsert runs first so a successful Publish
// always leaves the snapshot store at least as fresh as the stream.
func (publisher *Publisher) Publish(ctx context.Context, envelope ports.HealthEventEnvelope) error {
	if publisher == nil || publisher.client == nil || publisher.snapshots == nil {
		return errors.New("publish health event: nil publisher")
	}
	if ctx == nil {
		return errors.New("publish health event: nil context")
	}
	if err := envelope.Validate(); err != nil {
		return fmt.Errorf("publish health event: %w", err)
	}

	details := envelope.Details
	if len(details) == 0 {
		details = json.RawMessage(emptyDetails)
	}

	status, source := snapshotMappingFor(envelope.EventType)
	snapshot := health.HealthSnapshot{
		GameID:      envelope.GameID,
		ContainerID: envelope.ContainerID,
		Status:      status,
		Source:      source,
		Details:     details,
		ObservedAt:  envelope.OccurredAt.UTC(),
	}
	if err := publisher.snapshots.Upsert(ctx, snapshot); err != nil {
		return fmt.Errorf("publish health event: upsert snapshot: %w", err)
	}

	occurredAtMS := envelope.OccurredAt.UTC().UnixMilli()
	values := map[string]any{
		fieldGameID:       envelope.GameID,
		fieldContainerID:  envelope.ContainerID,
		fieldEventType:    string(envelope.EventType),
		fieldOccurredAtMS: strconv.FormatInt(occurredAtMS, 10),
		fieldDetails:      string(details),
	}
	if err := publisher.client.XAdd(ctx, &redis.XAddArgs{
		Stream: publisher.stream,
		Values: values,
	}).Err(); err != nil {
		return fmt.Errorf("publish health event: xadd: %w", err)
	}
	return nil
}

// snapshotMappingFor returns the SnapshotStatus and SnapshotSource that
// match eventType per `rtmanager/README.md §Health Monitoring`.
//
// `container_started` is observed when the start service successfully
// runs the container; the snapshot collapses it to `healthy`.
// `probe_recovered` collapses to `healthy` per
// `rtmanager/docs/domain-and-ports.md` §4: it does not have its own
// snapshot status; the next observation overwrites the prior
// `probe_failed` with `healthy`.
func snapshotMappingFor(eventType health.EventType) (health.SnapshotStatus, health.SnapshotSource) {
	switch eventType {
	case health.EventTypeContainerStarted:
		return health.SnapshotStatusHealthy, health.SnapshotSourceDockerEvent
	case health.EventTypeContainerExited:
		return health.SnapshotStatusExited, health.SnapshotSourceDockerEvent
	case health.EventTypeContainerOOM:
		return health.SnapshotStatusOOM, health.SnapshotSourceDockerEvent
	case health.EventTypeContainerDisappeared:
		return health.SnapshotStatusContainerDisappeared, health.SnapshotSourceDockerEvent
	case health.EventTypeInspectUnhealthy:
		return health.SnapshotStatusInspectUnhealthy, health.SnapshotSourceInspect
	case health.EventTypeProbeFailed:
		return health.SnapshotStatusProbeFailed, health.SnapshotSourceProbe
	case health.EventTypeProbeRecovered:
		return health.SnapshotStatusHealthy, health.SnapshotSourceProbe
	default:
		return "", ""
	}
}

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