package lmsprogress

import (
	"context"
	"sort"
	"time"

	dbgen "Yimaru-Backend/gen/db"
	"Yimaru-Backend/internal/domain"

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

const (
	flatActivityLesson   = "lesson"
	flatActivityPractice = "practice"
	practiceScopeLesson  = "lesson"
	practiceScopeModule  = "module"
	practiceScopeCourse  = "course"
)

// AdminUserLearningActivityTree returns nested program → course → module → lesson/practice completions for a learner.
// The schema persists completion timestamps only (lesson completion, practice completion, rollup rows); partially started items do not appear.
func (s *Service) AdminUserLearningActivityTree(ctx context.Context, userID int64) (domain.AdminLMSUserLearningActivityTree, error) {
	rows, err := s.store.ListUserLMSFlatLearningActivity(ctx, userID)
	if err != nil {
		return domain.AdminLMSUserLearningActivityTree{}, err
	}
	return buildAdminLearningActivityTree(userID, rows), nil
}

type lessonAccum struct {
	id          int64
	title       string
	sortOrder   int32
	completedAt *time.Time
	practices   []domain.AdminLMSPracticeLearningEntry
	practiceDed map[int64]struct{}
}

type moduleAccum struct {
	id                 int64
	name               string
	sortOrder          int32
	rollup             *time.Time
	lessons            map[int64]*lessonAccum
	lessonOrder        []int64
	modulePractices    []domain.AdminLMSPracticeLearningEntry
	modulePracticeSeen map[int64]struct{}
}

type courseAccum struct {
	id                 int64
	name               string
	sortOrder          int32
	rollup             *time.Time
	modules            map[int64]*moduleAccum
	moduleOrder        []int64
	coursePractices    []domain.AdminLMSPracticeLearningEntry
	coursePracticeSeen map[int64]struct{}
}

type programAccum struct {
	id          int64
	name        string
	sortOrder   int32
	rollup      *time.Time
	courses     map[int64]*courseAccum
	courseOrder []int64
}

type adminActivityTreeBuilder struct {
	programs     map[int64]*programAccum
	programOrder []int64
}

func newAdminActivityTreeBuilder() *adminActivityTreeBuilder {
	return &adminActivityTreeBuilder{
		programs: make(map[int64]*programAccum),
	}
}

func (b *adminActivityTreeBuilder) ensureProgram(row dbgen.ListUserLMSFlatLearningActivityByUserRow) *programAccum {
	pa, ok := b.programs[row.ProgramID]
	if !ok {
		pa = &programAccum{
			id:      row.ProgramID,
			courses: make(map[int64]*courseAccum),
		}
		b.programs[row.ProgramID] = pa
		b.programOrder = append(b.programOrder, row.ProgramID)
	}
	pa.name = row.ProgramName
	pa.sortOrder = row.ProgramSortOrder
	if t := pgTimestamptzPtr(row.ProgramCompletedAt); t != nil {
		pa.rollup = t
	}
	return pa
}

func (pa *programAccum) ensureCourse(row dbgen.ListUserLMSFlatLearningActivityByUserRow) *courseAccum {
	ca, ok := pa.courses[row.CourseID]
	if !ok {
		ca = &courseAccum{
			id:                 row.CourseID,
			modules:            make(map[int64]*moduleAccum),
			coursePracticeSeen: make(map[int64]struct{}),
		}
		pa.courses[row.CourseID] = ca
		pa.courseOrder = append(pa.courseOrder, row.CourseID)
	}
	ca.name = row.CourseName
	ca.sortOrder = row.CourseSortOrder
	if t := pgTimestamptzPtr(row.CourseCompletedAt); t != nil {
		ca.rollup = t
	}
	return ca
}

func (ca *courseAccum) ensureModule(row dbgen.ListUserLMSFlatLearningActivityByUserRow) *moduleAccum {
	ma, ok := ca.modules[row.ModuleID]
	if !ok {
		ma = &moduleAccum{
			id:                 row.ModuleID,
			lessons:            make(map[int64]*lessonAccum),
			modulePracticeSeen: make(map[int64]struct{}),
		}
		ca.modules[row.ModuleID] = ma
		ca.moduleOrder = append(ca.moduleOrder, row.ModuleID)
	}
	ma.name = row.ModuleName
	ma.sortOrder = row.ModuleSortOrder
	if t := pgTimestamptzPtr(row.ModuleCompletedAt); t != nil {
		ma.rollup = t
	}
	return ma
}

func (ma *moduleAccum) ensureLesson(id int64, title string, sortOrder int32) *lessonAccum {
	la, ok := ma.lessons[id]
	if !ok {
		la = &lessonAccum{
			id:          id,
			title:       title,
			sortOrder:   sortOrder,
			practiceDed: make(map[int64]struct{}),
		}
		ma.lessons[id] = la
		ma.lessonOrder = append(ma.lessonOrder, id)
	}
	if title != "" {
		la.title = title
	}
	return la
}

func (la *lessonAccum) addPractice(p domain.AdminLMSPracticeLearningEntry) {
	if _, dup := la.practiceDed[p.LMSPracticeID]; dup {
		return
	}
	la.practiceDed[p.LMSPracticeID] = struct{}{}
	la.practices = append(la.practices, p)
}

func (ma *moduleAccum) addModulePractice(p domain.AdminLMSPracticeLearningEntry) {
	if _, dup := ma.modulePracticeSeen[p.LMSPracticeID]; dup {
		return
	}
	ma.modulePracticeSeen[p.LMSPracticeID] = struct{}{}
	ma.modulePractices = append(ma.modulePractices, p)
}

func (ca *courseAccum) addCoursePractice(p domain.AdminLMSPracticeLearningEntry) {
	if _, dup := ca.coursePracticeSeen[p.LMSPracticeID]; dup {
		return
	}
	ca.coursePracticeSeen[p.LMSPracticeID] = struct{}{}
	ca.coursePractices = append(ca.coursePractices, p)
}

func (b *adminActivityTreeBuilder) ingest(row dbgen.ListUserLMSFlatLearningActivityByUserRow) {
	switch row.ActivityKind {
	case flatActivityLesson:
		if row.LessonID == 0 {
			return
		}
		p := b.ensureProgram(row)
		c := p.ensureCourse(row)
		m := c.ensureModule(row)
		l := m.ensureLesson(row.LessonID, row.LessonTitle, row.LessonSortOrder)
		if t := pgTimestamptzPtr(row.LessonCompletedAt); t != nil {
			l.completedAt = t
		}
	case flatActivityPractice:
		if row.LmsPracticeID == 0 {
			return
		}
		at, ok := pgTimestamptzTime(row.ActivityAt)
		if !ok {
			return
		}
		pr := domain.AdminLMSPracticeLearningEntry{
			LMSPracticeID: row.LmsPracticeID,
			Title:         row.PracticeTitle,
			CompletedAt:   at,
		}
		p := b.ensureProgram(row)
		c := p.ensureCourse(row)
		switch {
		case row.LessonID != 0:
			pr.Scope = practiceScopeLesson
			m := c.ensureModule(row)
			l := m.ensureLesson(row.LessonID, row.LessonTitle, row.LessonSortOrder)
			l.addPractice(pr)
		case row.ModuleID != 0:
			pr.Scope = practiceScopeModule
			m := c.ensureModule(row)
			m.addModulePractice(pr)
		default:
			pr.Scope = practiceScopeCourse
			c.addCoursePractice(pr)
		}
	}
}

func sortPracticeSlice(ps []domain.AdminLMSPracticeLearningEntry) {
	sort.Slice(ps, func(i, j int) bool {
		if !ps[i].CompletedAt.Equal(ps[j].CompletedAt) {
			return ps[i].CompletedAt.Before(ps[j].CompletedAt)
		}
		return ps[i].LMSPracticeID < ps[j].LMSPracticeID
	})
}

func buildAdminLearningActivityTree(userID int64, rows []dbgen.ListUserLMSFlatLearningActivityByUserRow) domain.AdminLMSUserLearningActivityTree {
	b := newAdminActivityTreeBuilder()
	for i := range rows {
		b.ingest(rows[i])
	}

	sort.Slice(b.programOrder, func(i, j int) bool {
		a := b.programs[b.programOrder[i]]
		cc := b.programs[b.programOrder[j]]
		if a.sortOrder != cc.sortOrder {
			return a.sortOrder < cc.sortOrder
		}
		return a.id < cc.id
	})

	outPrograms := make([]domain.AdminLMSProgramLearningEntry, 0, len(b.programOrder))
	for _, pid := range b.programOrder {
		pa := b.programs[pid]
		sort.Slice(pa.courseOrder, func(i, j int) bool {
			a := pa.courses[pa.courseOrder[i]]
			c := pa.courses[pa.courseOrder[j]]
			if a.sortOrder != c.sortOrder {
				return a.sortOrder < c.sortOrder
			}
			return a.id < c.id
		})
		courses := make([]domain.AdminLMSCourseLearningEntry, 0, len(pa.courseOrder))
		for _, cid := range pa.courseOrder {
			ca := pa.courses[cid]
			sort.Slice(ca.moduleOrder, func(i, j int) bool {
				a := ca.modules[ca.moduleOrder[i]]
				c := ca.modules[ca.moduleOrder[j]]
				if a.sortOrder != c.sortOrder {
					return a.sortOrder < c.sortOrder
				}
				return a.id < c.id
			})
			modules := make([]domain.AdminLMSModuleLearningEntry, 0, len(ca.moduleOrder))
			for _, mid := range ca.moduleOrder {
				ma := ca.modules[mid]
				sort.Slice(ma.lessonOrder, func(i, j int) bool {
					a := ma.lessons[ma.lessonOrder[i]]
					c := ma.lessons[ma.lessonOrder[j]]
					if a.sortOrder != c.sortOrder {
						return a.sortOrder < c.sortOrder
					}
					return a.id < c.id
				})
				lessons := make([]domain.AdminLMSLessonLearningEntry, 0, len(ma.lessonOrder))
				for _, lid := range ma.lessonOrder {
					la := ma.lessons[lid]
					sortPracticeSlice(la.practices)
					entry := domain.AdminLMSLessonLearningEntry{
						ID:                    la.id,
						Title:                 la.title,
						SortOrder:             la.sortOrder,
						CompletedAt:           la.completedAt,
						LessonScopedPractices: la.practices,
					}
					lessons = append(lessons, entry)
				}
				mod := domain.AdminLMSModuleLearningEntry{
					ID:                     ma.id,
					Name:                   ma.name,
					SortOrder:              ma.sortOrder,
					RollupFullyCompletedAt: ma.rollup,
				}
				if len(lessons) > 0 {
					mod.Lessons = lessons
				}
				if len(ma.modulePractices) > 0 {
					sortPracticeSlice(ma.modulePractices)
					mod.ModuleScopedPractices = ma.modulePractices
				}
				modules = append(modules, mod)
			}
			cr := domain.AdminLMSCourseLearningEntry{
				ID:                     ca.id,
				Name:                   ca.name,
				SortOrder:              ca.sortOrder,
				RollupFullyCompletedAt: ca.rollup,
				Modules:                modules,
			}
			if len(ca.coursePractices) > 0 {
				sortPracticeSlice(ca.coursePractices)
				cr.CourseLevelPractices = ca.coursePractices
			}
			courses = append(courses, cr)
		}
		outPrograms = append(outPrograms, domain.AdminLMSProgramLearningEntry{
			ID:                     pa.id,
			Name:                   pa.name,
			SortOrder:              pa.sortOrder,
			RollupFullyCompletedAt: pa.rollup,
			Courses:                courses,
		})
	}
	return domain.AdminLMSUserLearningActivityTree{
		UserID:   userID,
		Programs: outPrograms,
	}
}

func pgTimestamptzPtr(t pgtype.Timestamptz) *time.Time {
	if !t.Valid {
		return nil
	}
	tt := t.Time
	return &tt
}

func pgTimestamptzTime(t pgtype.Timestamptz) (time.Time, bool) {
	if !t.Valid {
		return time.Time{}, false
	}
	return t.Time, true
}