package modules

import (
	"Yimaru-Backend/internal/domain"
	"Yimaru-Backend/internal/ports"
	"Yimaru-Backend/internal/services/courses"
	"context"
	"errors"

	"github.com/jackc/pgx/v5"
)

var ErrModuleNotFound = errors.New("module not found")

type Service struct {
	modules ports.ModuleStore
	courses ports.CourseStore
}

func NewService(modules ports.ModuleStore, courses ports.CourseStore) *Service {
	return &Service{modules: modules, courses: courses}
}

func (s *Service) getCourseOrErr(ctx context.Context, courseID int64) (domain.Course, error) {
	c, err := s.courses.GetCourseByID(ctx, courseID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return domain.Course{}, courses.ErrCourseNotFound
		}
		return domain.Course{}, err
	}
	return c, nil
}

// Create loads the course and stores program_id from it (parent program is not taken from the URL).
func (s *Service) Create(ctx context.Context, courseID int64, input domain.CreateModuleInput) (domain.Module, error) {
	c, err := s.getCourseOrErr(ctx, courseID)
	if err != nil {
		return domain.Module{}, err
	}
	return s.modules.CreateModule(ctx, c.ProgramID, courseID, input)
}

func (s *Service) GetByID(ctx context.Context, id int64) (domain.Module, error) {
	m, err := s.modules.GetModuleByID(ctx, id)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return domain.Module{}, ErrModuleNotFound
		}
		return domain.Module{}, err
	}
	return m, nil
}

// ListByCourse loads the course and lists modules for its program_id and course_id.
func (s *Service) ListByCourse(ctx context.Context, courseID int64, limit, offset int32) ([]domain.Module, int64, error) {
	c, err := s.getCourseOrErr(ctx, courseID)
	if err != nil {
		return nil, 0, err
	}
	if limit <= 0 {
		limit = 20
	}
	if limit > 200 {
		limit = 200
	}
	if offset < 0 {
		offset = 0
	}
	return s.modules.ListModulesByProgramAndCourse(ctx, c.ProgramID, courseID, limit, offset)
}

func (s *Service) Update(ctx context.Context, id int64, input domain.UpdateModuleInput) (domain.Module, error) {
	m, err := s.modules.UpdateModule(ctx, id, input)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return domain.Module{}, ErrModuleNotFound
		}
		return domain.Module{}, err
	}
	return m, nil
}

func (s *Service) Delete(ctx context.Context, id int64) error {
	if _, err := s.modules.GetModuleByID(ctx, id); err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return ErrModuleNotFound
		}
		return err
	}
	return s.modules.DeleteModule(ctx, id)
}

// ReorderInCourse sets module sort_order under a course. ordered must list every module id in that course
// exactly once (e.g. from GET /courses/{id}/modules) in the desired order.
func (s *Service) ReorderInCourse(ctx context.Context, courseID int64, ordered []int64) error {
	if _, err := s.getCourseOrErr(ctx, courseID); err != nil {
		return err
	}
	expected, err := s.modules.ListModuleIDsByCourse(ctx, courseID)
	if err != nil {
		return err
	}
	if err := domain.ValidateReorderPermutation(ordered, expected); err != nil {
		return err
	}
	if len(ordered) == 0 {
		return nil
	}
	return s.modules.ReorderModulesInCourse(ctx, courseID, ordered)
}