package admin

import (
	"context"
	"encoding/json"
	"strings"

	"github.com/google/uuid"

	"github.com/yuxingu/digital-psychology/apps/api/internal/repository"
)

var (
	ErrInvalidStatusEdge = errString("invalid status transition")
	ErrReasonRequired    = errString("reason required")
)

var allowedStatusEdges = map[string]map[string]struct{}{
	"active":    {"disabled": {}, "banned": {}, "suspended": {}},
	"disabled":  {"active": {}, "banned": {}},
	"suspended": {"active": {}, "banned": {}, "disabled": {}},
	"banned":    {"active": {}, "disabled": {}},
}

// TransitionUserStatus migrates UserStatus with audit.
func (s *Service) TransitionUserStatus(ctx context.Context, adminID, userID uuid.UUID, toStatus, reason string) error {
	toStatus = strings.TrimSpace(toStatus)
	reason = strings.TrimSpace(reason)
	if reason == "" {
		return ErrReasonRequired
	}
	ok, err := s.Repo.UserExists(ctx, userID)
	if err != nil {
		return err
	}
	if !ok {
		return ErrUserNotFound
	}
	from, err := s.Repo.GetUserStatus(ctx, userID)
	if err != nil || from == "" {
		return ErrUserNotFound
	}
	if from == toStatus {
		return ErrInvalidStatusEdge
	}
	next, okEdge := allowedStatusEdges[from]
	if !okEdge {
		return ErrInvalidStatusEdge
	}
	if _, okEdge = next[toStatus]; !okEdge {
		return ErrInvalidStatusEdge
	}
	meta, _ := json.Marshal(map[string]string{
		"from": from, "to": toStatus, "reason": reason,
	})
	return s.Repo.TransitionUserStatusWithAudit(ctx, adminID, userID, from, toStatus, reason, meta)
}

// ListStatusTransitions returns recent transitions.
func (s *Service) ListStatusTransitions(ctx context.Context, userID uuid.UUID, limit int) ([]repository.AccountTransition, error) {
	ok, err := s.Repo.UserExists(ctx, userID)
	if err != nil {
		return nil, err
	}
	if !ok {
		return nil, ErrUserNotFound
	}
	items, err := s.Repo.ListStatusTransitions(ctx, userID, limit)
	if err != nil {
		return nil, err
	}
	if items == nil {
		items = []repository.AccountTransition{}
	}
	return items, nil
}