package service

import (
	"context"
	"errors"
	"fmt"

	"gorm.io/gorm"

	"github.com/gochat/gochat/internal/model"
	"github.com/gochat/gochat/internal/repository"
	applogger "github.com/gochat/gochat/pkg/logger"
	pkgvalidator "github.com/gochat/gochat/pkg/validator"
)

// TeamService implements business logic for Team operations.
// Reference: Chatwoot app/controllers/api/v1/teams_controller.rb
type TeamService struct {
	teamRepo        *repository.TeamRepo
	teamMemberRepo  *repository.TeamMemberRepo
	db              *gorm.DB
}

// NewTeamService creates a new Team service.
func NewTeamService(teamRepo *repository.TeamRepo, teamMemberRepo *repository.TeamMemberRepo, db *gorm.DB) *TeamService {
	return &TeamService{teamRepo: teamRepo, teamMemberRepo: teamMemberRepo, db: db}
}

// CreateTeamRequest is the DTO for creating a team.
type CreateTeamRequest struct {
	Name               string `json:"name" validate:"required,min=2"`
	Description        string `json:"description,omitempty"`
	AllowAutoAssignment *bool  `json:"allow_auto_assignment,omitempty"`
}

// UpdateTeamRequest is the DTO for updating a team.
type UpdateTeamRequest struct {
	Name               string `json:"name,omitempty" validate:"omitempty,min=2"`
	Description        string `json:"description,omitempty"`
	AllowAutoAssignment *bool  `json:"allow_auto_assignment,omitempty"`
}

// TeamMemberRequest is the DTO for adding/removing team members.
type TeamMemberRequest struct {
	UserIDs []uint `json:"user_ids" validate:"required,min=1"`
}

// List retrieves all teams for an account.
func (s *TeamService) List(ctx context.Context, accountID uint, offset, limit int) ([]model.Team, int64, error) {
	return s.teamRepo.ListByAccount(ctx, accountID, offset, limit)
}

// Get retrieves a single team by ID scoped to an account.
func (s *TeamService) Get(ctx context.Context, id, accountID uint) (*model.Team, error) {
	team, err := s.teamRepo.FindByIDAndAccount(ctx, id, accountID)
	if err != nil {
		return nil, fmt.Errorf("team not found: %w", err)
	}
	return team, nil
}

// Create creates a new team within an account.
func (s *TeamService) Create(ctx context.Context, accountID uint, req CreateTeamRequest) (*model.Team, error) {
	if err := pkgvalidator.ValidateStruct(req); err != nil {
		return nil, err
	}

	autoAssign := true // default
	if req.AllowAutoAssignment != nil {
		autoAssign = *req.AllowAutoAssignment
	}

	team := &model.Team{
		AccountID:          accountID,
		Name:               req.Name,
		Description:        req.Description,
		AllowAutoAssignment: autoAssign,
	}

	if err := s.teamRepo.Create(ctx, team); err != nil {
		applogger.L().Errorf("failed to create team: %v", err)
		return nil, fmt.Errorf("failed to create team: %w", err)
	}
	return team, nil
}

// Update updates an existing team scoped to an account.
func (s *TeamService) Update(ctx context.Context, id, accountID uint, req UpdateTeamRequest) (*model.Team, error) {
	if err := pkgvalidator.ValidateStruct(req); err != nil {
		return nil, err
	}

	team, err := s.teamRepo.FindByIDAndAccount(ctx, id, accountID)
	if err != nil {
		return nil, fmt.Errorf("team not found: %w", err)
	}

	if req.Name != "" {
		team.Name = req.Name
	}
	// Allow empty description to clear it
	team.Description = req.Description
	if req.AllowAutoAssignment != nil {
		team.AllowAutoAssignment = *req.AllowAutoAssignment
	}

	if err := s.teamRepo.Update(ctx, team); err != nil {
		applogger.L().Errorf("failed to update team: %v", err)
		return nil, fmt.Errorf("failed to update team: %w", err)
	}
	return team, nil
}

// Delete soft-deletes a team scoped to an account.
func (s *TeamService) Delete(ctx context.Context, id, accountID uint) error {
	// Remove all members first
	if err := s.teamMemberRepo.DeleteByTeam(ctx, id); err != nil {
		applogger.L().Warnf("failed to remove team members during delete: %v", err)
	}

	if err := s.teamRepo.Delete(ctx, id, accountID); err != nil {
		return fmt.Errorf("failed to delete team: %w", err)
	}
	return nil
}

// AddMembers adds users to a team.
func (s *TeamService) AddMembers(ctx context.Context, teamID, accountID uint, userIDs []uint) ([]model.TeamMember, error) {
	// Verify team exists and belongs to account
	_, err := s.teamRepo.FindByIDAndAccount(ctx, teamID, accountID)
	if err != nil {
		return nil, fmt.Errorf("team not found: %w", err)
	}

	members := make([]model.TeamMember, 0, len(userIDs))
	for _, uid := range userIDs {
		// Skip if already a member
		existing, _ := s.teamMemberRepo.FindByTeamAndUser(ctx, teamID, uid)
		if existing != nil {
			continue
		}
		members = append(members, model.TeamMember{
			TeamID:            teamID,
			UserID:            uid,
			AvailabilityStatus: "offline",
		})
	}

	if len(members) == 0 {
		return nil, errors.New("all users are already team members")
	}

	if err := s.teamMemberRepo.CreateBatch(ctx, members); err != nil {
		applogger.L().Errorf("failed to add team members: %v", err)
		return nil, fmt.Errorf("failed to add team members: %w", err)
	}
	return members, nil
}

// RemoveMember removes a user from a team.
func (s *TeamService) RemoveMember(ctx context.Context, teamID, userID, accountID uint) error {
	// Verify team exists and belongs to account
	_, err := s.teamRepo.FindByIDAndAccount(ctx, teamID, accountID)
	if err != nil {
		return fmt.Errorf("team not found: %w", err)
	}

	if err := s.teamMemberRepo.Delete(ctx, teamID, userID); err != nil {
		return fmt.Errorf("failed to remove team member: %w", err)
	}
	return nil
}

// ListMembers retrieves all members of a team.
func (s *TeamService) ListMembers(ctx context.Context, teamID, accountID uint) ([]model.TeamMember, error) {
	// Verify team exists and belongs to account
	_, err := s.teamRepo.FindByIDAndAccount(ctx, teamID, accountID)
	if err != nil {
		return nil, fmt.Errorf("team not found: %w", err)
	}

	return s.teamMemberRepo.FindByTeam(ctx, teamID)
}

// UpdateMembers adds/removes members to match the provided user_ids list.
// Reference: Chatwoot team_members#update — calculates add/remove diffs from user_ids
func (s *TeamService) UpdateMembers(ctx context.Context, teamID, accountID uint, userIDs []uint) ([]model.TeamMember, error) {
	// Get current member IDs
	currentMembers, err := s.teamMemberRepo.FindByTeam(ctx, teamID)
	if err != nil {
		return nil, err
	}
	currentIDs := make([]uint, len(currentMembers))
	for i, m := range currentMembers {
		currentIDs[i] = m.UserID
	}

	// Calculate IDs to add and remove
	toAdd := difference(userIDs, currentIDs)
	toRemove := difference(currentIDs, userIDs)

	// Validate new user IDs belong to the account
	if len(toAdd) > 0 {
		// Chatwoot validates: invalid IDs (not in account) → 401
		if !s.validateUserIDsBelongToAccount(ctx, accountID, toAdd) {
			return nil, fmt.Errorf("unauthorized: invalid user IDs")
		}

		newMembers := make([]model.TeamMember, len(toAdd))
		for i, uid := range toAdd {
			newMembers[i] = model.TeamMember{TeamID: teamID, UserID: uid}
		}
		if err := s.teamMemberRepo.CreateBatch(ctx, newMembers); err != nil {
			return nil, err
		}
	}

	// Remove members not in the new list
	for _, uid := range toRemove {
		s.teamMemberRepo.Delete(ctx, teamID, uid)
	}

	// Return updated member list
	return s.teamMemberRepo.FindByTeam(ctx, teamID)
}

// difference returns elements in a that are not in b.
func difference(a, b []uint) []uint {
	bSet := make(map[uint]bool, len(b))
	for _, v := range b {
		bSet[v] = true
	}
	var result []uint
	for _, v := range a {
		if !bSet[v] {
			result = append(result, v)
		}
	}
	return result
}

// validateUserIDsBelongToAccount checks that all user IDs belong to the given account.
// Reference: Chatwoot team_members#validate_member_id_params — invalid IDs → 401
func (s *TeamService) validateUserIDsBelongToAccount(ctx context.Context, accountID uint, userIDs []uint) bool {
	for _, uid := range userIDs {
		var count int64
		s.db.WithContext(ctx).Model(&model.AccountUser{}).
			Where("account_id = ? AND user_id = ?", accountID, uid).
			Count(&count)
		if count == 0 {
			return false
		}
	}
	return true
}