// Package game defines the game record domain model, status machine, and
// sentinel errors owned by Game Lobby Service.
package game

import (
	"fmt"
	"strings"
	"time"

	"galaxy/cronutil"
	"galaxy/lobby/internal/domain/common"

	"golang.org/x/mod/semver"
)

// GameType identifies the admission model of one game record.
type GameType string

const (
	// GameTypePublic reports that the game uses the application flow and
	// is administered by system administrators.
	GameTypePublic GameType = "public"

	// GameTypePrivate reports that the game uses the invite flow and is
	// administered by its owner.
	GameTypePrivate GameType = "private"
)

// IsKnown reports whether value belongs to the frozen game type
// vocabulary.
func (value GameType) IsKnown() bool {
	switch value {
	case GameTypePublic, GameTypePrivate:
		return true
	default:
		return false
	}
}

// RuntimeSnapshot stores the denormalized runtime snapshot imported from
// Game Master.
type RuntimeSnapshot struct {
	// CurrentTurn stores the last observed turn number. Zero means not
	// yet running.
	CurrentTurn int

	// RuntimeStatus stores the last observed runtime status string from
	// Game Master. Empty means not yet running.
	RuntimeStatus string

	// EngineHealthSummary stores the last observed engine health summary
	// string from Game Master. Empty means not yet running.
	EngineHealthSummary string
}

// RuntimeBinding stores the runtime binding metadata produced by Runtime
// Manager after a successful container start. The binding is required to
// register the running game with Game Master and to correlate the game
// record with the source job-result event for audit purposes.
type RuntimeBinding struct {
	// ContainerID identifies the engine container assigned by Runtime
	// Manager.
	ContainerID string

	// EngineEndpoint stores the network address Game Master uses to
	// reach the engine container.
	EngineEndpoint string

	// RuntimeJobID stores the source `runtime:job_results` Redis Stream
	// message id (in `<ms>-<seq>` form) that produced this binding. It
	// gives operators a back-reference from the game record to the
	// originating Runtime Manager event when investigating incidents.
	RuntimeJobID string

	// BoundAt stores when the binding was persisted.
	BoundAt time.Time
}

// Validate reports whether binding contains the structural invariants
// required for a runtime binding produced by success-path
// processing.
func (binding RuntimeBinding) Validate() error {
	if strings.TrimSpace(binding.ContainerID) == "" {
		return fmt.Errorf("runtime binding container id must not be empty")
	}
	if strings.TrimSpace(binding.EngineEndpoint) == "" {
		return fmt.Errorf("runtime binding engine endpoint must not be empty")
	}
	if strings.TrimSpace(binding.RuntimeJobID) == "" {
		return fmt.Errorf("runtime binding runtime job id must not be empty")
	}
	if binding.BoundAt.IsZero() {
		return fmt.Errorf("runtime binding bound at must not be zero")
	}
	return nil
}

// Game stores one durable game record owned by Game Lobby Service.
type Game struct {
	// GameID identifies the record.
	GameID common.GameID

	// GameName stores the human-readable game name.
	GameName string

	// Description stores the optional human-readable description.
	Description string

	// GameType stores the admission model.
	GameType GameType

	// OwnerUserID stores the platform user id of the private-game owner.
	// It must be empty for public games.
	OwnerUserID string

	// Status stores the current lifecycle state.
	Status Status

	// MinPlayers stores the minimum approved participants required
	// before the game may start.
	MinPlayers int

	// MaxPlayers stores the target roster size that activates the gap
	// window.
	MaxPlayers int

	// StartGapHours stores the length of the gap window in hours after
	// max_players is reached.
	StartGapHours int

	// StartGapPlayers stores the number of additional participants
	// admitted during the gap window.
	StartGapPlayers int

	// EnrollmentEndsAt stores the UTC deadline at which enrollment closes
	// automatically.
	EnrollmentEndsAt time.Time

	// TurnSchedule stores the five-field cron expression passed to
	// Game Master at registration.
	TurnSchedule string

	// TargetEngineVersion stores the semver string of the engine to
	// launch.
	TargetEngineVersion string

	// CreatedAt stores when the record was created.
	CreatedAt time.Time

	// UpdatedAt stores when the record was last mutated.
	UpdatedAt time.Time

	// StartedAt stores when the record entered the running status.
	StartedAt *time.Time

	// FinishedAt stores when the record entered the finished status.
	FinishedAt *time.Time

	// RuntimeSnapshot stores the denormalized runtime snapshot from
	// Game Master.
	RuntimeSnapshot RuntimeSnapshot

	// RuntimeBinding stores the runtime binding metadata produced by
	// Runtime Manager after a successful container start. It is nil
	// before the start succeeds and non-nil afterwards.
	RuntimeBinding *RuntimeBinding
}

// NewGameInput groups all fields required to create a draft game record.
type NewGameInput struct {
	// GameID identifies the draft record.
	GameID common.GameID

	// GameName stores the human-readable game name.
	GameName string

	// Description stores the optional human-readable description.
	Description string

	// GameType stores the admission model.
	GameType GameType

	// OwnerUserID stores the owner id for private games. It must be empty
	// for public games.
	OwnerUserID string

	// MinPlayers stores the minimum approved participants required
	// before the game may start.
	MinPlayers int

	// MaxPlayers stores the target roster size that activates the gap
	// window.
	MaxPlayers int

	// StartGapHours stores the gap window length in hours.
	StartGapHours int

	// StartGapPlayers stores the number of additional participants
	// admitted during the gap window.
	StartGapPlayers int

	// EnrollmentEndsAt stores the enrollment deadline.
	EnrollmentEndsAt time.Time

	// TurnSchedule stores the five-field cron expression.
	TurnSchedule string

	// TargetEngineVersion stores the semver of the engine to launch.
	TargetEngineVersion string

	// Now stores the creation wall-clock used for CreatedAt and
	// UpdatedAt.
	Now time.Time
}

// New validates input and returns a draft Game record. Validation errors
// are returned verbatim so callers can surface them as invalid_request.
func New(input NewGameInput) (Game, error) {
	if err := input.Validate(); err != nil {
		return Game{}, err
	}

	record := Game{
		GameID:              input.GameID,
		GameName:            input.GameName,
		Description:         input.Description,
		GameType:            input.GameType,
		OwnerUserID:         input.OwnerUserID,
		Status:              StatusDraft,
		MinPlayers:          input.MinPlayers,
		MaxPlayers:          input.MaxPlayers,
		StartGapHours:       input.StartGapHours,
		StartGapPlayers:     input.StartGapPlayers,
		EnrollmentEndsAt:    input.EnrollmentEndsAt.UTC(),
		TurnSchedule:        input.TurnSchedule,
		TargetEngineVersion: input.TargetEngineVersion,
		CreatedAt:           input.Now.UTC(),
		UpdatedAt:           input.Now.UTC(),
	}

	if err := record.Validate(); err != nil {
		return Game{}, err
	}

	return record, nil
}

// Validate reports whether input satisfies the frozen game-record
// invariants required to construct a draft record.
func (input NewGameInput) Validate() error {
	if err := input.GameID.Validate(); err != nil {
		return fmt.Errorf("game id: %w", err)
	}
	if strings.TrimSpace(input.GameName) == "" {
		return fmt.Errorf("game name must not be empty")
	}
	if !input.GameType.IsKnown() {
		return fmt.Errorf("game type %q is unsupported", input.GameType)
	}
	switch input.GameType {
	case GameTypePrivate:
		if strings.TrimSpace(input.OwnerUserID) == "" {
			return fmt.Errorf("owner user id must not be empty for private games")
		}
	case GameTypePublic:
		if input.OwnerUserID != "" {
			return fmt.Errorf("owner user id must be empty for public games")
		}
	}
	if input.MinPlayers <= 0 {
		return fmt.Errorf("min players must be positive")
	}
	if input.MaxPlayers <= 0 {
		return fmt.Errorf("max players must be positive")
	}
	if input.MaxPlayers < input.MinPlayers {
		return fmt.Errorf("max players must not be less than min players")
	}
	if input.StartGapHours <= 0 {
		return fmt.Errorf("start gap hours must be positive")
	}
	if input.StartGapPlayers <= 0 {
		return fmt.Errorf("start gap players must be positive")
	}
	if input.Now.IsZero() {
		return fmt.Errorf("now must not be zero")
	}
	if input.EnrollmentEndsAt.IsZero() {
		return fmt.Errorf("enrollment ends at must not be zero")
	}
	if !input.EnrollmentEndsAt.After(input.Now) {
		return fmt.Errorf("enrollment ends at must be after now")
	}
	if err := validateCronExpression(input.TurnSchedule); err != nil {
		return err
	}
	if err := validateSemver(input.TargetEngineVersion); err != nil {
		return err
	}

	return nil
}

// Validate reports whether record satisfies the full invariants.
// Every marshal and unmarshal round-trip calls Validate to guarantee that
// the Redis store never exposes malformed records.
func (record Game) Validate() error {
	if err := record.GameID.Validate(); err != nil {
		return fmt.Errorf("game id: %w", err)
	}
	if strings.TrimSpace(record.GameName) == "" {
		return fmt.Errorf("game name must not be empty")
	}
	if !record.GameType.IsKnown() {
		return fmt.Errorf("game type %q is unsupported", record.GameType)
	}
	switch record.GameType {
	case GameTypePrivate:
		if strings.TrimSpace(record.OwnerUserID) == "" {
			return fmt.Errorf("owner user id must not be empty for private games")
		}
	case GameTypePublic:
		if record.OwnerUserID != "" {
			return fmt.Errorf("owner user id must be empty for public games")
		}
	}
	if !record.Status.IsKnown() {
		return fmt.Errorf("status %q is unsupported", record.Status)
	}
	if record.MinPlayers <= 0 {
		return fmt.Errorf("min players must be positive")
	}
	if record.MaxPlayers <= 0 {
		return fmt.Errorf("max players must be positive")
	}
	if record.MaxPlayers < record.MinPlayers {
		return fmt.Errorf("max players must not be less than min players")
	}
	if record.StartGapHours <= 0 {
		return fmt.Errorf("start gap hours must be positive")
	}
	if record.StartGapPlayers <= 0 {
		return fmt.Errorf("start gap players must be positive")
	}
	if record.EnrollmentEndsAt.IsZero() {
		return fmt.Errorf("enrollment ends at must not be zero")
	}
	if err := validateCronExpression(record.TurnSchedule); err != nil {
		return err
	}
	if err := validateSemver(record.TargetEngineVersion); err != nil {
		return err
	}
	if record.CreatedAt.IsZero() {
		return fmt.Errorf("created at must not be zero")
	}
	if record.UpdatedAt.IsZero() {
		return fmt.Errorf("updated at must not be zero")
	}
	if record.UpdatedAt.Before(record.CreatedAt) {
		return fmt.Errorf("updated at must not be before created at")
	}
	if record.StartedAt != nil {
		if record.StartedAt.IsZero() {
			return fmt.Errorf("started at must not be zero when present")
		}
		if record.StartedAt.Before(record.CreatedAt) {
			return fmt.Errorf("started at must not be before created at")
		}
	}
	if record.FinishedAt != nil {
		if record.FinishedAt.IsZero() {
			return fmt.Errorf("finished at must not be zero when present")
		}
		if record.FinishedAt.Before(record.CreatedAt) {
			return fmt.Errorf("finished at must not be before created at")
		}
	}
	if record.RuntimeSnapshot.CurrentTurn < 0 {
		return fmt.Errorf("runtime snapshot current turn must not be negative")
	}
	if record.RuntimeBinding != nil {
		if err := record.RuntimeBinding.Validate(); err != nil {
			return err
		}
		if record.RuntimeBinding.BoundAt.Before(record.CreatedAt) {
			return fmt.Errorf("runtime binding bound at must not be before created at")
		}
	}

	return nil
}

func validateCronExpression(value string) error {
	if strings.TrimSpace(value) == "" {
		return fmt.Errorf("turn schedule must not be empty")
	}
	if _, err := cronutil.Parse(value); err != nil {
		return fmt.Errorf("turn schedule must be a valid five-field cron expression: %w", err)
	}
	return nil
}

func validateSemver(value string) error {
	if strings.TrimSpace(value) == "" {
		return fmt.Errorf("target engine version must not be empty")
	}
	candidate := value
	if !strings.HasPrefix(candidate, "v") {
		candidate = "v" + candidate
	}
	if !semver.IsValid(candidate) {
		return fmt.Errorf("target engine version %q must be a valid semver string", value)
	}
	return nil
}