package lmsprogress

import (
	"context"
	"errors"

	"Yimaru-Backend/internal/domain"
	"Yimaru-Backend/internal/repository"

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

const (
	errPrevProgram = "Complete the previous program before accessing this one."
	errPrevCourse  = "Complete the previous course in this program first."
	errPrevModule  = "Complete the previous module in this course first."
	errPrevLesson  = "Complete the previous lesson in this module first."
)

// Service enforces sequential LMS access for learners and records lesson progress.
type Service struct {
	store *repository.Store
}

func NewService(store *repository.Store) *Service {
	return &Service{store: store}
}

// CompleteLessonForUser records lesson completion and rolls up to module, course, and program when applicable.
func (s *Service) CompleteLessonForUser(ctx context.Context, userID, lessonID int64) error {
	return s.store.CompleteLessonForUser(ctx, userID, lessonID)
}

// CompletePracticeForUser records practice completion and rolls up to module, course, and program when applicable.
func (s *Service) CompletePracticeForUser(ctx context.Context, userID, questionSetID int64) error {
	return s.store.CompletePracticeForUser(ctx, userID, questionSetID)
}

// GetMyProgress returns completed lesson, module, course, and program IDs for the user.
func (s *Service) GetMyProgress(ctx context.Context, userID int64) (domain.LMSUserProgress, error) {
	return s.store.GetLMSUserProgressSnapshot(ctx, userID)
}

// CanAccessProgram returns whether the user may use content under this program (previous program must be fully completed if any).
func (s *Service) CanAccessProgram(ctx context.Context, userID, programID int64) (ok bool, reason string, err error) {
	if _, err := s.store.GetProgramByID(ctx, programID); err != nil {
		return false, "", err
	}
	prev, err := s.store.LmsGetPreviousProgram(ctx, programID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return true, "", nil
		}
		return false, "", err
	}
	has, err := s.store.LmsUserHasProgramProgress(ctx, userID, prev.ID)
	if err != nil {
		return false, "", err
	}
	if !has {
		return false, errPrevProgram, nil
	}
	return true, "", nil
}

// CanAccessCourse requires the parent program to be accessible and the previous course in the program to be completed.
func (s *Service) CanAccessCourse(ctx context.Context, userID, courseID int64) (ok bool, reason string, err error) {
	c, err := s.store.GetCourseByID(ctx, courseID)
	if err != nil {
		return false, "", err
	}
	ok, reason, err = s.CanAccessProgram(ctx, userID, c.ProgramID)
	if err != nil || !ok {
		return ok, reason, err
	}
	prev, err := s.store.LmsGetPreviousCourseInProgram(ctx, courseID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return true, "", nil
		}
		return false, "", err
	}
	has, err := s.store.LmsUserHasCourseProgress(ctx, userID, prev.ID)
	if err != nil {
		return false, "", err
	}
	if !has {
		return false, errPrevCourse, nil
	}
	return true, "", nil
}

// CanAccessModule requires the course (and its program chain) to be accessible and the previous module in the course to be completed.
func (s *Service) CanAccessModule(ctx context.Context, userID, moduleID int64) (ok bool, reason string, err error) {
	m, err := s.store.GetModuleByID(ctx, moduleID)
	if err != nil {
		return false, "", err
	}
	ok, reason, err = s.CanAccessCourse(ctx, userID, m.CourseID)
	if err != nil || !ok {
		return ok, reason, err
	}
	prev, err := s.store.LmsGetPreviousModuleInCourse(ctx, moduleID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return true, "", nil
		}
		return false, "", err
	}
	has, err := s.store.LmsUserHasModuleProgress(ctx, userID, prev.ID)
	if err != nil {
		return false, "", err
	}
	if !has {
		return false, errPrevModule, nil
	}
	return true, "", nil
}

// CanAccessLesson requires the module chain to be accessible and the previous lesson in the module to be completed.
func (s *Service) CanAccessLesson(ctx context.Context, userID, lessonID int64) (ok bool, reason string, err error) {
	lesson, err := s.store.GetLessonByID(ctx, lessonID)
	if err != nil {
		return false, "", err
	}
	ok, reason, err = s.CanAccessModule(ctx, userID, lesson.ModuleID)
	if err != nil || !ok {
		return ok, reason, err
	}
	prev, err := s.store.LmsGetPreviousLessonInModule(ctx, lessonID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return true, "", nil
		}
		return false, "", err
	}
	has, err := s.store.LmsUserHasLessonProgress(ctx, userID, prev.ID)
	if err != nil {
		return false, "", err
	}
	if !has {
		return false, errPrevLesson, nil
	}
	return true, "", nil
}

// ApplyAccessProgram sets p.Access for a learner. Non-learners: clears Access to omit from JSON.
func (s *Service) ApplyAccessProgram(ctx context.Context, role domain.Role, userID int64, p *domain.Program) error {
	if role != domain.RoleStudent {
		p.Access = nil
		return nil
	}
	ok, reason, err := s.CanAccessProgram(ctx, userID, p.ID)
	if err != nil {
		return err
	}
	done, err := s.store.LmsUserHasProgramProgress(ctx, userID, p.ID)
	if err != nil {
		return err
	}
	comp, tot, err := s.store.LmsUserLessonProgressInProgram(ctx, userID, p.ID)
	if err != nil {
		return err
	}
	c, t, pct := lmsProgressCounts(comp, tot, done)
	p.Access = &domain.LMSEntityAccess{
		IsAccessible: ok, IsCompleted: done, Reason: reasonIf(ok, reason),
		CompletedCount: c, TotalCount: t, ProgressPercent: pct,
	}
	return nil
}

// ApplyAccessCourse sets c.Access for a learner.
func (s *Service) ApplyAccessCourse(ctx context.Context, role domain.Role, userID int64, c *domain.Course) error {
	if role != domain.RoleStudent {
		c.Access = nil
		return nil
	}
	ok, reason, err := s.CanAccessCourse(ctx, userID, c.ID)
	if err != nil {
		return err
	}
	done, err := s.store.LmsUserHasCourseProgress(ctx, userID, c.ID)
	if err != nil {
		return err
	}
	comp, tot, err := s.store.LmsUserLessonProgressInCourse(ctx, userID, c.ID)
	if err != nil {
		return err
	}
	cc, tt, pct := lmsProgressCounts(comp, tot, done)
	c.Access = &domain.LMSEntityAccess{
		IsAccessible: ok, IsCompleted: done, Reason: reasonIf(ok, reason),
		CompletedCount: cc, TotalCount: tt, ProgressPercent: pct,
	}
	return nil
}

// ApplyAccessModule sets m.Access for a learner.
func (s *Service) ApplyAccessModule(ctx context.Context, role domain.Role, userID int64, m *domain.Module) error {
	if role != domain.RoleStudent {
		m.Access = nil
		return nil
	}
	ok, reason, err := s.CanAccessModule(ctx, userID, m.ID)
	if err != nil {
		return err
	}
	done, err := s.store.LmsUserHasModuleProgress(ctx, userID, m.ID)
	if err != nil {
		return err
	}
	comp, tot, err := s.store.LmsUserLessonProgressInModule(ctx, userID, m.ID)
	if err != nil {
		return err
	}
	cc, tt, pct := lmsProgressCounts(comp, tot, done)
	m.Access = &domain.LMSEntityAccess{
		IsAccessible: ok, IsCompleted: done, Reason: reasonIf(ok, reason),
		CompletedCount: cc, TotalCount: tt, ProgressPercent: pct,
	}
	return nil
}

// ApplyAccessLesson sets l.Access for a learner.
func (s *Service) ApplyAccessLesson(ctx context.Context, role domain.Role, userID int64, les *domain.Lesson) error {
	if role != domain.RoleStudent {
		les.Access = nil
		return nil
	}
	ok, reason, err := s.CanAccessLesson(ctx, userID, les.ID)
	if err != nil {
		return err
	}
	done, err := s.store.LmsUserHasLessonProgress(ctx, userID, les.ID)
	if err != nil {
		return err
	}
	var comp, tot int32
	if done {
		comp, tot = 1, 1
	} else {
		comp, tot = 0, 1
	}
	c, t, pct := lmsProgressCounts(comp, tot, done)
	les.Access = &domain.LMSEntityAccess{
		IsAccessible: ok, IsCompleted: done, Reason: reasonIf(ok, reason),
		CompletedCount: c, TotalCount: t, ProgressPercent: pct,
	}
	return nil
}

// lmsProgressCounts maps DB lesson completion counts to UI fields. Percent is 0–100; completed
// and total are aligned with isCompleted when the entity is fully done.
func lmsProgressCounts(completed, total int32, isCompleted bool) (c, t, pct int) {
	c, t = int(completed), int(total)
	if t < 0 {
		t = 0
	}
	if c < 0 {
		c = 0
	}
	if isCompleted {
		if t > 0 {
			return t, t, 100
		}
		return c, t, 100
	}
	if t == 0 {
		return 0, 0, 0
	}
	pct = (c * 100) / t
	if pct > 100 {
		pct = 100
	}
	return c, t, pct
}

func reasonIf(ok bool, r string) string {
	if ok {
		return ""
	}
	return r
}