package service

import (
	"context"
	"errors"
	"fmt"
	"net/url"
	"strconv"
	"strings"

	"github.com/prabhupadasays/spsays-bff/internal/model"
	"github.com/prabhupadasays/spsays-bff/internal/repository"
)

const (
	maxQuizQuestions = 100
	minQuizOptions   = 2
	maxQuizOptions   = 5
	maxQuizTitle     = 200
)

var (
	ErrQuizTitle       = errors.New("a quiz needs a title")
	ErrQuizNoQuestions = errors.New("a quiz needs at least one question")
	ErrQuizTooMany     = fmt.Errorf("a quiz can have at most %d questions", maxQuizQuestions)
	ErrQuizPrompt      = errors.New("every question needs a prompt")
	ErrQuizOptionCount = fmt.Errorf("each question needs %d to %d options", minQuizOptions, maxQuizOptions)
	ErrQuizOptionBody  = errors.New("every option needs text")
	ErrQuizOneCorrect  = errors.New("a single-answer question needs exactly one correct option")
	ErrQuizNoCorrect   = errors.New("a multiple-answer question needs at least one correct option")
	ErrQuizLocked      = errors.New("people have already taken this quiz, so its questions can't change")
	ErrQuizTarget      = errors.New("that link isn't a book chapter, lecture or conversation")
	ErrQuizUnpublished = errors.New("this quiz isn't available")
)

// QuizService is both sides of quizzes: authoring for staff, taking for users.
type QuizService struct {
	quizzes *repository.QuizRepo
	// content resolves a pasted link into a target title and kind.
	content *repository.VaniRepo
}

func NewQuizService(quizzes *repository.QuizRepo, content *repository.VaniRepo) *QuizService {
	return &QuizService{quizzes: quizzes, content: content}
}

// QuizDraft is what the admin editor submits. TargetURL is pasted from the
// app; empty means a stand-alone quiz.
type QuizDraft struct {
	Title       string
	Description string
	TargetURL   string
	// TargetTitle overrides the resolved content title when set.
	TargetTitle string
	Questions   []repository.QuestionInput
}

// NormalizeContentPath reduces a pasted link to the path a content page
// reports for itself: no scheme, host, query, fragment or trailing slash.
// Both sides normalise identically, so "https://…/books/bg/2/?x" and the
// page's own "/books/bg/2" meet.
func NormalizeContentPath(raw string) string {
	p := strings.TrimSpace(raw)
	if u, err := url.Parse(p); err == nil && u.Host != "" {
		p = u.Path
	}
	p = strings.SplitN(strings.SplitN(p, "?", 2)[0], "#", 2)[0]
	p = "/" + strings.Trim(p, "/")
	if p == "/" {
		return ""
	}
	return p
}

// resolveTarget works out what a link points at.
func (s *QuizService) resolveTarget(ctx context.Context, raw, override string) (kind string, path *string, title string, err error) {
	p := NormalizeContentPath(raw)
	if p == "" {
		return model.QuizStandalone, nil, "", nil
	}
	parts := strings.Split(strings.Trim(p, "/"), "/")

	switch {
	case len(parts) == 2 && parts[0] == "transcriptions":
		t, err := s.content.TranscriptBySlug(ctx, parts[1])
		if err != nil {
			return "", nil, "", ErrQuizTarget
		}
		kind = model.QuizLecture
		if t.Type == "conversation" {
			kind = model.QuizConversation
		}
		title = t.Name

	case len(parts) >= 3 && parts[0] == "books":
		kind = model.QuizChapter
		book := parts[1]
		bookTitle := s.content.BookTitle(ctx, book)
		if bookTitle == "" {
			bookTitle = strings.ToUpper(book)
		}
		last := parts[len(parts)-1]
		if _, numErr := strconv.Atoi(last); numErr == nil {
			// /books/bg/2, /books/sb/1/2, /books/cc/adi/3 — a numbered chapter.
			title = bookTitle + " — Chapter " + last
		} else if pr, err := s.content.ProseBySlug(ctx, book, last); err == nil {
			title = pr.Title
		} else {
			title = bookTitle
		}

	default:
		return "", nil, "", ErrQuizTarget
	}

	if o := strings.TrimSpace(override); o != "" {
		title = o
	}
	return kind, &p, title, nil
}

func validateQuestions(qs []repository.QuestionInput) ([]repository.QuestionInput, error) {
	if len(qs) == 0 {
		return nil, ErrQuizNoQuestions
	}
	if len(qs) > maxQuizQuestions {
		return nil, ErrQuizTooMany
	}
	out := make([]repository.QuestionInput, 0, len(qs))
	for _, q := range qs {
		q.Prompt = strings.TrimSpace(q.Prompt)
		q.Explanation = strings.TrimSpace(q.Explanation)
		if q.Prompt == "" {
			return nil, ErrQuizPrompt
		}
		if len(q.Options) < minQuizOptions || len(q.Options) > maxQuizOptions {
			return nil, ErrQuizOptionCount
		}
		correct := 0
		for i := range q.Options {
			q.Options[i].Body = strings.TrimSpace(q.Options[i].Body)
			if q.Options[i].Body == "" {
				return nil, ErrQuizOptionBody
			}
			if q.Options[i].IsCorrect {
				correct++
			}
		}
		if q.Multi && correct == 0 {
			return nil, ErrQuizNoCorrect
		}
		if !q.Multi && correct != 1 {
			return nil, ErrQuizOneCorrect
		}
		out = append(out, q)
	}
	return out, nil
}

func (s *QuizService) toInput(ctx context.Context, d QuizDraft, withQuestions bool) (repository.QuizInput, error) {
	in := repository.QuizInput{
		Title:       strings.TrimSpace(d.Title),
		Description: strings.TrimSpace(d.Description),
	}
	if in.Title == "" || len([]rune(in.Title)) > maxQuizTitle {
		return in, ErrQuizTitle
	}
	var err error
	if in.TargetKind, in.TargetPath, in.TargetTitle, err = s.resolveTarget(ctx, d.TargetURL, d.TargetTitle); err != nil {
		return in, err
	}
	if withQuestions {
		if in.Questions, err = validateQuestions(d.Questions); err != nil {
			return in, err
		}
	}
	return in, nil
}

// ── Admin ─────────────────────────────────────────────────────────────────

func (s *QuizService) ListAdmin(ctx context.Context) ([]model.Quiz, error) {
	return s.quizzes.ListAdmin(ctx)
}

func (s *QuizService) GetAdmin(ctx context.Context, id string) (*model.Quiz, error) {
	q, err := s.quizzes.Get(ctx, id, true)
	if err != nil {
		return nil, err
	}
	if q.AttemptCount, err = s.quizzes.AttemptCount(ctx, id); err != nil {
		return nil, err
	}
	return q, nil
}

func (s *QuizService) Create(ctx context.Context, actorID string, d QuizDraft) (*model.Quiz, error) {
	in, err := s.toInput(ctx, d, true)
	if err != nil {
		return nil, err
	}
	id, err := s.quizzes.Create(ctx, in, actorID)
	if err != nil {
		return nil, err
	}
	return s.GetAdmin(ctx, id)
}

// Update rewrites a quiz. Once anyone has attempted it, its questions are
// frozen — their answers reference those exact questions and options — and
// only the title, description and target may change. Sending questions then
// is refused rather than silently ignored.
func (s *QuizService) Update(ctx context.Context, id string, d QuizDraft) (*model.Quiz, error) {
	attempts, err := s.quizzes.AttemptCount(ctx, id)
	if err != nil {
		return nil, err
	}
	locked := attempts > 0
	if locked && len(d.Questions) > 0 {
		return nil, ErrQuizLocked
	}
	in, err := s.toInput(ctx, d, !locked)
	if err != nil {
		return nil, err
	}
	if err := s.quizzes.Update(ctx, id, in, !locked); err != nil {
		return nil, err
	}
	return s.GetAdmin(ctx, id)
}

func (s *QuizService) SetPublished(ctx context.Context, id string, published bool) (*model.Quiz, error) {
	if published {
		q, err := s.quizzes.Get(ctx, id, false)
		if err != nil {
			return nil, err
		}
		if len(q.Questions) == 0 {
			return nil, ErrQuizNoQuestions
		}
	}
	if err := s.quizzes.SetPublished(ctx, id, published); err != nil {
		return nil, err
	}
	return s.GetAdmin(ctx, id)
}

func (s *QuizService) Delete(ctx context.Context, id string) error {
	return s.quizzes.Delete(ctx, id)
}

func (s *QuizService) Participants(ctx context.Context, id string) ([]model.QuizParticipant, error) {
	if _, err := s.quizzes.Get(ctx, id, false); err != nil {
		return nil, err
	}
	return s.quizzes.Participants(ctx, id)
}

func (s *QuizService) Responses(ctx context.Context, id string) ([]model.QuizQuestionStat, error) {
	if _, err := s.quizzes.Get(ctx, id, false); err != nil {
		return nil, err
	}
	return s.quizzes.QuestionStats(ctx, id)
}

// ParticipantResult is one person's answers, for the admin — including an
// attempt still in progress, which a user can never see of their own.
func (s *QuizService) ParticipantResult(ctx context.Context, quizID, userID string) (*model.QuizResult, error) {
	return s.quizzes.Result(ctx, quizID, userID, true)
}

// ResetParticipant wipes one participant's attempt; the quiz becomes pending
// for them. Works on unpublished quizzes too — staff may tidy results up
// while a quiz is offline.
func (s *QuizService) ResetParticipant(ctx context.Context, quizID, userID string) error {
	if _, err := s.quizzes.Get(ctx, quizID, false); err != nil {
		return err
	}
	return s.quizzes.ResetAttempt(ctx, quizID, userID)
}

// ── Taking ────────────────────────────────────────────────────────────────

// published loads a quiz that users may see.
func (s *QuizService) published(ctx context.Context, id string) (*model.Quiz, error) {
	q, err := s.quizzes.Get(ctx, id, false)
	if err != nil {
		return nil, err
	}
	if q.PublishedAt == nil {
		return nil, ErrQuizUnpublished
	}
	return q, nil
}

func (s *QuizService) withStatus(ctx context.Context, userID string, qs []model.Quiz) ([]model.QuizCard, error) {
	ids := make([]string, len(qs))
	for i, q := range qs {
		ids[i] = q.ID
	}
	st, err := s.quizzes.Statuses(ctx, userID, ids)
	if err != nil {
		return nil, err
	}
	out := make([]model.QuizCard, len(qs))
	for i, q := range qs {
		q.Questions = nil
		my, ok := st[q.ID]
		if !ok {
			my = model.QuizStatus{State: model.QuizNotStarted, Total: q.QuestionCount}
		}
		out[i] = model.QuizCard{Quiz: q, My: my}
	}
	return out, nil
}

// ForPath returns the quiz on a content page with the caller's progress, or
// nil when the page has none. userID may be empty for signed-out readers.
func (s *QuizService) ForPath(ctx context.Context, userID, rawPath string) (*model.QuizCard, error) {
	p := NormalizeContentPath(rawPath)
	if p == "" {
		return nil, nil
	}
	q, err := s.quizzes.PublishedForPath(ctx, p)
	if err != nil || q == nil {
		return nil, err
	}
	cards, err := s.withStatus(ctx, userID, []model.Quiz{*q})
	if err != nil {
		return nil, err
	}
	return &cards[0], nil
}

func (s *QuizService) ListPublished(ctx context.Context, userID string) ([]model.QuizCard, error) {
	qs, err := s.quizzes.ListPublished(ctx)
	if err != nil {
		return nil, err
	}
	return s.withStatus(ctx, userID, qs)
}

func (s *QuizService) Card(ctx context.Context, userID, id string) (*model.QuizCard, error) {
	q, err := s.published(ctx, id)
	if err != nil {
		return nil, err
	}
	cards, err := s.withStatus(ctx, userID, []model.Quiz{*q})
	if err != nil {
		return nil, err
	}
	return &cards[0], nil
}

// Start opens (or resumes) the caller's attempt and returns where they are.
func (s *QuizService) Start(ctx context.Context, userID, id string) (*model.QuizPlay, error) {
	q, err := s.published(ctx, id)
	if err != nil {
		return nil, err
	}
	if err := s.quizzes.Start(ctx, id, userID, len(q.Questions)); err != nil {
		return nil, err
	}
	return s.next(ctx, userID, q)
}

func (s *QuizService) next(ctx context.Context, userID string, q *model.Quiz) (*model.QuizPlay, error) {
	play, err := s.quizzes.Next(ctx, q.ID, userID)
	if err != nil {
		return nil, err
	}
	play.Title = q.Title
	return play, nil
}

// Answer records a choice — one option, or several on a multi question — and
// returns the next step.
func (s *QuizService) Answer(ctx context.Context, userID, id, questionID string, optionIDs []string) (*model.QuizPlay, error) {
	q, err := s.published(ctx, id)
	if err != nil {
		return nil, err
	}
	if err := s.quizzes.Answer(ctx, id, userID, questionID, optionIDs); err != nil {
		return nil, err
	}
	return s.next(ctx, userID, q)
}

// Result is the caller's OWN finished attempt — the only result a user can
// read. The user id comes from the session, never the request.
func (s *QuizService) Result(ctx context.Context, userID, id string) (*model.QuizResult, error) {
	if _, err := s.quizzes.Get(ctx, id, false); err != nil {
		return nil, err
	}
	return s.quizzes.Result(ctx, id, userID, false)
}