// Package policy defines sanction, limit, and eligibility-domain entities used
// by User Service.
package policy

import (
	"fmt"
	"slices"
	"strings"
	"time"

	"galaxy/user/internal/domain/common"
)

// SanctionCode identifies one supported sanction in the v1 policy catalog.
type SanctionCode string

const (
	// SanctionCodeLoginBlock denies login.
	SanctionCodeLoginBlock SanctionCode = "login_block"

	// SanctionCodePrivateGameCreateBlock denies private-game creation.
	SanctionCodePrivateGameCreateBlock SanctionCode = "private_game_create_block"

	// SanctionCodePrivateGameManageBlock denies private-game management.
	SanctionCodePrivateGameManageBlock SanctionCode = "private_game_manage_block"

	// SanctionCodeGameJoinBlock denies game joining.
	SanctionCodeGameJoinBlock SanctionCode = "game_join_block"

	// SanctionCodeProfileUpdateBlock denies self-service profile/settings
	// mutations.
	SanctionCodeProfileUpdateBlock SanctionCode = "profile_update_block"
)

// IsKnown reports whether SanctionCode belongs to the frozen v1 catalog.
func (code SanctionCode) IsKnown() bool {
	switch code {
	case SanctionCodeLoginBlock,
		SanctionCodePrivateGameCreateBlock,
		SanctionCodePrivateGameManageBlock,
		SanctionCodeGameJoinBlock,
		SanctionCodeProfileUpdateBlock:
		return true
	default:
		return false
	}
}

// LimitCode identifies one user-specific limit code recognized by User
// Service.
type LimitCode string

const (
	// LimitCodeMaxOwnedPrivateGames limits how many private games the user may
	// own while the current entitlement is paid.
	LimitCodeMaxOwnedPrivateGames LimitCode = "max_owned_private_games"

	// LimitCodeMaxPendingPublicApplications stores the total public-games budget
	// consumed together with current active public memberships when Game Lobby
	// derives remaining pending application headroom.
	LimitCodeMaxPendingPublicApplications LimitCode = "max_pending_public_applications"

	// LimitCodeMaxActiveGameMemberships limits how many active public-game
	// memberships the user may hold at once.
	LimitCodeMaxActiveGameMemberships LimitCode = "max_active_game_memberships"
)

const (
	// LimitCodeMaxActivePrivateGames is a retired legacy code recognized only
	// so old stored records do not break current reads.
	LimitCodeMaxActivePrivateGames LimitCode = "max_active_private_games"

	// LimitCodeMaxPendingPrivateJoinRequests is a retired legacy code
	// recognized only so old stored records do not break current reads.
	LimitCodeMaxPendingPrivateJoinRequests LimitCode = "max_pending_private_join_requests"

	// LimitCodeMaxPendingPrivateInvitesSent is a retired legacy code
	// recognized only so old stored records do not break current reads.
	LimitCodeMaxPendingPrivateInvitesSent LimitCode = "max_pending_private_invites_sent"
)

// IsKnown reports whether LimitCode belongs to the current supported write/API
// catalog.
func (code LimitCode) IsKnown() bool {
	return code.IsSupported()
}

// IsSupported reports whether LimitCode belongs to the current supported
// write/API catalog.
func (code LimitCode) IsSupported() bool {
	switch code {
	case LimitCodeMaxOwnedPrivateGames,
		LimitCodeMaxPendingPublicApplications,
		LimitCodeMaxActiveGameMemberships:
		return true
	default:
		return false
	}
}

// IsRetired reports whether LimitCode is a retired legacy code recognized
// only for read compatibility with already stored history records.
func (code LimitCode) IsRetired() bool {
	switch code {
	case LimitCodeMaxActivePrivateGames,
		LimitCodeMaxPendingPrivateJoinRequests,
		LimitCodeMaxPendingPrivateInvitesSent:
		return true
	default:
		return false
	}
}

// IsRecognized reports whether LimitCode is either currently supported or
// retired-but-recognized for read compatibility.
func (code LimitCode) IsRecognized() bool {
	return code.IsSupported() || code.IsRetired()
}

// EligibilityMarker identifies one derived eligibility boolean that may be
// indexed for admin listing.
type EligibilityMarker string

const (
	// EligibilityMarkerCanLogin tracks whether the user may currently log in.
	EligibilityMarkerCanLogin EligibilityMarker = "can_login"

	// EligibilityMarkerCanCreatePrivateGame tracks whether the user may create
	// a private game.
	EligibilityMarkerCanCreatePrivateGame EligibilityMarker = "can_create_private_game"

	// EligibilityMarkerCanManagePrivateGame tracks whether the user may manage
	// a private game.
	EligibilityMarkerCanManagePrivateGame EligibilityMarker = "can_manage_private_game"

	// EligibilityMarkerCanJoinGame tracks whether the user may join a game.
	EligibilityMarkerCanJoinGame EligibilityMarker = "can_join_game"

	// EligibilityMarkerCanUpdateProfile tracks whether the user may update
	// self-service profile/settings fields.
	EligibilityMarkerCanUpdateProfile EligibilityMarker = "can_update_profile"
)

// IsKnown reports whether EligibilityMarker belongs to the frozen v1 set.
func (marker EligibilityMarker) IsKnown() bool {
	switch marker {
	case EligibilityMarkerCanLogin,
		EligibilityMarkerCanCreatePrivateGame,
		EligibilityMarkerCanManagePrivateGame,
		EligibilityMarkerCanJoinGame,
		EligibilityMarkerCanUpdateProfile:
		return true
	default:
		return false
	}
}

// SanctionRecordID identifies one sanction history record.
type SanctionRecordID string

// String returns SanctionRecordID as its stored identifier string.
func (id SanctionRecordID) String() string {
	return string(id)
}

// IsZero reports whether SanctionRecordID does not contain a usable value.
func (id SanctionRecordID) IsZero() bool {
	return strings.TrimSpace(string(id)) == ""
}

// Validate reports whether SanctionRecordID is non-empty, normalized, and
// uses the frozen Stage 02 prefix.
func (id SanctionRecordID) Validate() error {
	return validatePrefixedRecordID("sanction record id", string(id), "sanction-")
}

// LimitRecordID identifies one limit history record.
type LimitRecordID string

// String returns LimitRecordID as its stored identifier string.
func (id LimitRecordID) String() string {
	return string(id)
}

// IsZero reports whether LimitRecordID does not contain a usable value.
func (id LimitRecordID) IsZero() bool {
	return strings.TrimSpace(string(id)) == ""
}

// Validate reports whether LimitRecordID is non-empty, normalized, and uses
// the frozen Stage 02 prefix.
func (id LimitRecordID) Validate() error {
	return validatePrefixedRecordID("limit record id", string(id), "limit-")
}

// SanctionRecord stores one sanction history record.
type SanctionRecord struct {
	// RecordID identifies the sanction history record.
	RecordID SanctionRecordID

	// UserID identifies the account that owns the sanction.
	UserID common.UserID

	// SanctionCode stores the sanction applied to the account.
	SanctionCode SanctionCode

	// Scope stores the machine-readable scope attached to the sanction.
	Scope common.Scope

	// ReasonCode stores the reason for the sanction mutation.
	ReasonCode common.ReasonCode

	// Actor stores the audit actor metadata for the apply mutation.
	Actor common.ActorRef

	// AppliedAt stores when the sanction becomes effective.
	AppliedAt time.Time

	// ExpiresAt stores the optional planned expiry of the sanction.
	ExpiresAt *time.Time

	// RemovedAt stores when the sanction was later removed explicitly.
	RemovedAt *time.Time

	// RemovedBy stores the audit actor metadata for the remove mutation.
	RemovedBy common.ActorRef

	// RemovedReasonCode stores the reason for the remove mutation.
	RemovedReasonCode common.ReasonCode
}

// Validate reports whether SanctionRecord satisfies the frozen structural
// invariants that do not depend on a caller-supplied clock.
func (record SanctionRecord) Validate() error {
	if err := record.RecordID.Validate(); err != nil {
		return fmt.Errorf("sanction record id: %w", err)
	}
	if err := record.UserID.Validate(); err != nil {
		return fmt.Errorf("sanction user id: %w", err)
	}
	if !record.SanctionCode.IsKnown() {
		return fmt.Errorf("sanction code %q is unsupported", record.SanctionCode)
	}
	if err := record.Scope.Validate(); err != nil {
		return fmt.Errorf("sanction scope: %w", err)
	}
	if err := record.ReasonCode.Validate(); err != nil {
		return fmt.Errorf("sanction reason code: %w", err)
	}
	if err := record.Actor.Validate(); err != nil {
		return fmt.Errorf("sanction actor: %w", err)
	}
	if err := common.ValidateTimestamp("sanction applied at", record.AppliedAt); err != nil {
		return err
	}
	if record.ExpiresAt != nil && !record.ExpiresAt.After(record.AppliedAt) {
		return common.ErrInvertedTimeRange
	}
	if record.RemovedAt == nil {
		if !record.RemovedBy.IsZero() {
			return fmt.Errorf("sanction removed by must be empty when removed at is absent")
		}
		if !record.RemovedReasonCode.IsZero() {
			return fmt.Errorf("sanction removed reason code must be empty when removed at is absent")
		}
		return nil
	}
	if record.RemovedAt.Before(record.AppliedAt) {
		return fmt.Errorf("sanction removed at must not be before applied at")
	}
	if err := record.RemovedBy.Validate(); err != nil {
		return fmt.Errorf("sanction removed by: %w", err)
	}
	if err := record.RemovedReasonCode.Validate(); err != nil {
		return fmt.Errorf("sanction removed reason code: %w", err)
	}

	return nil
}

// ValidateAt reports whether SanctionRecord also satisfies the current-time
// Stage 02 invariant that `applied_at` must not be in the future.
func (record SanctionRecord) ValidateAt(now time.Time) error {
	if err := record.Validate(); err != nil {
		return err
	}
	if now.IsZero() {
		return fmt.Errorf("sanction validation time must not be zero")
	}
	if record.AppliedAt.After(now.UTC()) {
		return fmt.Errorf("sanction applied at must not be in the future")
	}

	return nil
}

// IsActiveAt reports whether SanctionRecord is active at now according to the
// frozen Stage 02 rules.
func (record SanctionRecord) IsActiveAt(now time.Time) bool {
	now = now.UTC()
	switch {
	case now.IsZero():
		return false
	case record.AppliedAt.After(now):
		return false
	case record.RemovedAt != nil:
		return false
	case record.ExpiresAt != nil && !record.ExpiresAt.After(now):
		return false
	default:
		return true
	}
}

// LimitRecord stores one user-specific limit history record.
type LimitRecord struct {
	// RecordID identifies the limit history record.
	RecordID LimitRecordID

	// UserID identifies the account that owns the limit.
	UserID common.UserID

	// LimitCode stores which count-based limit is overridden.
	LimitCode LimitCode

	// Value stores the override value.
	Value int

	// ReasonCode stores the reason for the limit mutation.
	ReasonCode common.ReasonCode

	// Actor stores the audit actor metadata for the set mutation.
	Actor common.ActorRef

	// AppliedAt stores when the limit becomes effective.
	AppliedAt time.Time

	// ExpiresAt stores the optional planned expiry of the limit.
	ExpiresAt *time.Time

	// RemovedAt stores when the limit was later removed explicitly.
	RemovedAt *time.Time

	// RemovedBy stores the audit actor metadata for the remove mutation.
	RemovedBy common.ActorRef

	// RemovedReasonCode stores the reason for the remove mutation.
	RemovedReasonCode common.ReasonCode
}

// Validate reports whether LimitRecord satisfies the structural invariants
// that do not depend on a caller-supplied clock. Retired legacy limit codes
// remain recognized here so already stored records still decode safely.
func (record LimitRecord) Validate() error {
	if err := record.RecordID.Validate(); err != nil {
		return fmt.Errorf("limit record id: %w", err)
	}
	if err := record.UserID.Validate(); err != nil {
		return fmt.Errorf("limit user id: %w", err)
	}
	if !record.LimitCode.IsRecognized() {
		return fmt.Errorf("limit code %q is unsupported", record.LimitCode)
	}
	if record.Value < 0 {
		return fmt.Errorf("limit value must not be negative")
	}
	if err := record.ReasonCode.Validate(); err != nil {
		return fmt.Errorf("limit reason code: %w", err)
	}
	if err := record.Actor.Validate(); err != nil {
		return fmt.Errorf("limit actor: %w", err)
	}
	if err := common.ValidateTimestamp("limit applied at", record.AppliedAt); err != nil {
		return err
	}
	if record.ExpiresAt != nil && !record.ExpiresAt.After(record.AppliedAt) {
		return common.ErrInvertedTimeRange
	}
	if record.RemovedAt == nil {
		if !record.RemovedBy.IsZero() {
			return fmt.Errorf("limit removed by must be empty when removed at is absent")
		}
		if !record.RemovedReasonCode.IsZero() {
			return fmt.Errorf("limit removed reason code must be empty when removed at is absent")
		}
		return nil
	}
	if record.RemovedAt.Before(record.AppliedAt) {
		return fmt.Errorf("limit removed at must not be before applied at")
	}
	if err := record.RemovedBy.Validate(); err != nil {
		return fmt.Errorf("limit removed by: %w", err)
	}
	if err := record.RemovedReasonCode.Validate(); err != nil {
		return fmt.Errorf("limit removed reason code: %w", err)
	}

	return nil
}

// ValidateAt reports whether LimitRecord also satisfies the current-time Stage
// 02 invariant that `applied_at` must not be in the future.
func (record LimitRecord) ValidateAt(now time.Time) error {
	if err := record.Validate(); err != nil {
		return err
	}
	if now.IsZero() {
		return fmt.Errorf("limit validation time must not be zero")
	}
	if record.AppliedAt.After(now.UTC()) {
		return fmt.Errorf("limit applied at must not be in the future")
	}

	return nil
}

// IsActiveAt reports whether LimitRecord is active at now according to the
// frozen Stage 02 rules.
func (record LimitRecord) IsActiveAt(now time.Time) bool {
	now = now.UTC()
	switch {
	case now.IsZero():
		return false
	case record.AppliedAt.After(now):
		return false
	case record.RemovedAt != nil:
		return false
	case record.ExpiresAt != nil && !record.ExpiresAt.After(now):
		return false
	default:
		return true
	}
}

// ActiveSanctionsAt returns the active sanctions at now, sorted
// deterministically by `sanction_code`. The function returns an error when the
// input contains structurally invalid records or more than one active sanction
// for the same `user_id + sanction_code`.
func ActiveSanctionsAt(records []SanctionRecord, now time.Time) ([]SanctionRecord, error) {
	active := make([]SanctionRecord, 0, len(records))
	seen := make(map[SanctionCode]struct{}, len(records))

	for _, record := range records {
		if err := record.ValidateAt(now); err != nil {
			return nil, err
		}
		if !record.IsActiveAt(now) {
			continue
		}
		if _, ok := seen[record.SanctionCode]; ok {
			return nil, fmt.Errorf("multiple active sanctions for code %q", record.SanctionCode)
		}
		seen[record.SanctionCode] = struct{}{}
		active = append(active, record)
	}

	slices.SortFunc(active, func(left SanctionRecord, right SanctionRecord) int {
		return strings.Compare(string(left.SanctionCode), string(right.SanctionCode))
	})

	return active, nil
}

// ActiveLimitsAt returns the active limits at now, sorted deterministically by
// `limit_code`. Retired legacy limit codes are ignored so historical records
// stored under the old catalog do not affect current effective reads. The
// function returns an error when the input contains structurally invalid
// records or more than one active current limit for the same
// `user_id + limit_code`.
func ActiveLimitsAt(records []LimitRecord, now time.Time) ([]LimitRecord, error) {
	active := make([]LimitRecord, 0, len(records))
	seen := make(map[LimitCode]struct{}, len(records))

	for _, record := range records {
		if err := record.ValidateAt(now); err != nil {
			return nil, err
		}
		if !record.IsActiveAt(now) {
			continue
		}
		if !record.LimitCode.IsSupported() {
			continue
		}
		if _, ok := seen[record.LimitCode]; ok {
			return nil, fmt.Errorf("multiple active limits for code %q", record.LimitCode)
		}
		seen[record.LimitCode] = struct{}{}
		active = append(active, record)
	}

	slices.SortFunc(active, func(left LimitRecord, right LimitRecord) int {
		return strings.Compare(string(left.LimitCode), string(right.LimitCode))
	})

	return active, nil
}

func validatePrefixedRecordID(name string, value string, prefix string) error {
	switch {
	case strings.TrimSpace(value) == "":
		return fmt.Errorf("%s must not be empty", name)
	case strings.TrimSpace(value) != value:
		return fmt.Errorf("%s must not contain surrounding whitespace", name)
	case !strings.HasPrefix(value, prefix):
		return fmt.Errorf("%s must start with %q", name, prefix)
	case len(value) == len(prefix):
		return fmt.Errorf("%s must contain opaque data after %q", name, prefix)
	default:
		return nil
	}
}