package handlers

import (
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"log/slog"
	"math/rand"
	"net/http"
	"os"
	"strconv"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"

	"qbank/internal/auth"
	"qbank/internal/db"
	"qbank/internal/models"
	"qbank/internal/sampling"
)

// happyCatThreshold is the minimum score percentage to show a happy cat.
const happyCatThreshold = 60

type TestHandler struct {
	auth   *auth.Manager
	repo   *db.Repo
	render *Renderer
}

func NewTestHandler(a *auth.Manager, repo *db.Repo, r *Renderer) *TestHandler {
	return &TestHandler{auth: a, repo: repo, render: r}
}

func (h *TestHandler) NewGet(w http.ResponseWriter, r *http.Request) {
	totalQ, _ := h.repo.CountQuestions()
	sourceCounts, _ := h.repo.CountBySource()

	data := BaseData(h.auth, r)
	data["TotalQ"] = totalQ
	data["SourceStats"] = sourceCounts
	h.render.Render(w, http.StatusOK, "test_new", data)
}

func (h *TestHandler) NewPost(w http.ResponseWriter, r *http.Request) {
	if !h.auth.CheckCSRF(r) {
		HTTPError(w, http.StatusForbidden)
		return
	}
	r.Body = http.MaxBytesReader(w, r.Body, 4096)
	if err := r.ParseForm(); err != nil {
		HTTPError(w, http.StatusBadRequest)
		return
	}

	user := auth.UserFromCtx(r.Context())
	source := r.FormValue("source")
	mode := r.FormValue("mode")

	n, _ := strconv.Atoi(r.FormValue("n"))
	if n <= 0 {
		n = 10
	}

	questions, err := h.repo.ListQuestions(db.ListFilter{Source: source})
	if err != nil {
		slog.Error("list questions for test", "err", err)
		HTTPError(w, http.StatusInternalServerError)
		return
	}

	if len(questions) == 0 {
		totalQ, _ := h.repo.CountQuestions()
		sourceCounts, _ := h.repo.CountBySource()
		data := BaseData(h.auth, r)
		data["TotalQ"] = totalQ
		data["SourceStats"] = sourceCounts
		data["Error"] = "No questions available for the selected filter."
		h.render.Render(w, http.StatusOK, "test_new", data)
		return
	}

	if n > len(questions) {
		n = len(questions)
	}

	ids := make([]string, len(questions))
	for i, q := range questions {
		ids[i] = q.ID
	}

	var candidates []sampling.Candidate
	if mode == "uniform" {
		candidates = make([]sampling.Candidate, len(questions))
		for i, q := range questions {
			candidates[i] = sampling.Candidate{ID: q.ID, Weight: 1.0}
		}
	} else {
		stats, err := h.repo.GetStatsForUser(user.ID, ids)
		if err != nil {
			slog.Error("get stats for test", "err", err)
			HTTPError(w, http.StatusInternalServerError)
			return
		}
		now := time.Now()
		candidates = make([]sampling.Candidate, len(questions))
		for i, q := range questions {
			candidates[i] = sampling.Candidate{
				ID:     q.ID,
				Weight: sampling.ComputeWeight(stats[q.ID], now),
			}
		}
	}

	rng := rand.New(rand.NewSource(time.Now().UnixNano()))
	picked := sampling.SelectWeighted(candidates, n, rng)
	// Shuffle presentation order independently of selection order.
	rng.Shuffle(len(picked), func(i, j int) { picked[i], picked[j] = picked[j], picked[i] })

	pickedIDs := make([]string, len(picked))
	for i, c := range picked {
		pickedIDs[i] = c.ID
	}

	testID, err := h.repo.CreateTest(user.ID, pickedIDs)
	if err != nil {
		slog.Error("create test", "err", err)
		HTTPError(w, http.StatusInternalServerError)
		return
	}

	http.Redirect(w, r, fmt.Sprintf("/test/%d/q/1", testID), http.StatusSeeOther)
}

func (h *TestHandler) QuestionGet(w http.ResponseWriter, r *http.Request) {
	n, test, ok := h.loadTestAndN(w, r)
	if !ok {
		return
	}

	questionID := test.QuestionIDs[n-1]
	q, answers, err := h.repo.GetQuestion(questionID)
	if err != nil {
		slog.Error("get question for test", "err", err)
		HTTPError(w, http.StatusInternalServerError)
		return
	}

	data := BaseData(h.auth, r)
	data["TestID"] = test.ID
	data["N"] = n
	data["Total"] = test.NQuestions
	data["Question"] = q
	data["Answers"] = deterministicShuffle(answers, test.ID, questionID)
	data["ProgressPct"] = (n - 1) * 100 / test.NQuestions

	h.render.Render(w, http.StatusOK, "test_question", data)
}

func (h *TestHandler) QuestionPost(w http.ResponseWriter, r *http.Request) {
	n, test, ok := h.loadTestAndN(w, r)
	if !ok {
		return
	}

	if !h.auth.CheckCSRF(r) {
		HTTPError(w, http.StatusForbidden)
		return
	}
	r.Body = http.MaxBytesReader(w, r.Body, 4096)
	if err := r.ParseForm(); err != nil {
		HTTPError(w, http.StatusBadRequest)
		return
	}

	user := auth.UserFromCtx(r.Context())
	questionID := test.QuestionIDs[n-1]

	_, answers, err := h.repo.GetQuestion(questionID)
	if err != nil {
		slog.Error("get question for answer", "err", err)
		HTTPError(w, http.StatusInternalServerError)
		return
	}

	var selectedID *int64
	var isCorrect bool
	if rawID := r.FormValue("answer_id"); rawID != "" {
		id, err := strconv.ParseInt(rawID, 10, 64)
		if err == nil {
			selectedID = &id
			for _, a := range answers {
				if a.ID == id && a.IsCorrect {
					isCorrect = true
					break
				}
			}
		}
	}

	if err := h.repo.RecordAnswer(test.ID, questionID, selectedID, isCorrect); err != nil {
		slog.Error("record answer", "err", err)
		HTTPError(w, http.StatusInternalServerError)
		return
	}
	if err := h.repo.UpsertStat(user.ID, questionID, isCorrect); err != nil {
		slog.Error("upsert stat", "err", err)
	}

	if n < test.NQuestions {
		http.Redirect(w, r, fmt.Sprintf("/test/%d/q/%d", test.ID, n+1), http.StatusSeeOther)
		return
	}

	if err := h.repo.FinishTest(test.ID); err != nil {
		slog.Error("finish test", "err", err)
	}
	http.Redirect(w, r, fmt.Sprintf("/test/%d/results", test.ID), http.StatusSeeOther)
}

// ResultItem holds per-question data for the results page.
type ResultItem struct {
	Question   *models.Question
	Answers    []*ResultAnswer
	UserRight  bool // user selected the correct answer
	Unanswered bool // user skipped without selecting
}

// ResultAnswer annotates each answer with display markers.
type ResultAnswer struct {
	*models.Answer
	UserPicked bool // user selected this answer
}

func (h *TestHandler) ResultsGet(w http.ResponseWriter, r *http.Request) {
	user := auth.UserFromCtx(r.Context())
	testID, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
	if err != nil {
		HTTPError(w, http.StatusNotFound)
		return
	}
	test, err := h.repo.GetTest(testID)
	if err != nil || test.UserID != user.ID {
		HTTPError(w, http.StatusNotFound)
		return
	}

	testAnswers, err := h.repo.GetTestAnswers(testID)
	if err != nil {
		slog.Error("get test answers", "err", err)
		HTTPError(w, http.StatusInternalServerError)
		return
	}
	// Index test answers by question ID for quick lookup.
	taByQ := make(map[string]*models.TestAnswer, len(testAnswers))
	for _, ta := range testAnswers {
		taByQ[ta.QuestionID] = ta
	}

	var items []ResultItem
	nCorrect := 0
	for _, qid := range test.QuestionIDs {
		q, answers, err := h.repo.GetQuestion(qid)
		if err != nil {
			slog.Error("get question for results", "qid", qid, "err", err)
			HTTPError(w, http.StatusInternalServerError)
			return
		}
		ta := taByQ[qid]
		var selectedID int64
		unanswered := ta == nil || !ta.SelectedAnswerID.Valid
		if !unanswered {
			selectedID = ta.SelectedAnswerID.Int64
		}
		userRight := ta != nil && ta.IsCorrect.Valid && ta.IsCorrect.Bool
		if userRight {
			nCorrect++
		}
		ra := make([]*ResultAnswer, len(answers))
		for i, a := range answers {
			ra[i] = &ResultAnswer{
				Answer:     a,
				UserPicked: !unanswered && a.ID == selectedID,
			}
		}
		items = append(items, ResultItem{
			Question:   q,
			Answers:    ra,
			UserRight:  userRight,
			Unanswered: unanswered,
		})
	}

	var timeTaken string
	if test.CompletedAt.Valid {
		d := test.CompletedAt.Time.Sub(test.CreatedAt).Round(time.Second)
		h := int(d.Hours())
		m := int(d.Minutes()) % 60
		s := int(d.Seconds()) % 60
		if h > 0 {
			timeTaken = fmt.Sprintf("%dh %dm %ds", h, m, s)
		} else if m > 0 {
			timeTaken = fmt.Sprintf("%dm %ds", m, s)
		} else {
			timeTaken = fmt.Sprintf("%ds", s)
		}
	}

	mood := "sad"
	if test.NQuestions > 0 && nCorrect*100/test.NQuestions >= happyCatThreshold {
		mood = "happy"
	}
	catURL := randomCatURL(mood)

	data := BaseData(h.auth, r)
	data["Test"] = test
	data["Items"] = items
	data["NCorrect"] = nCorrect
	data["TimeTaken"] = timeTaken
	data["CatURL"] = catURL
	h.render.Render(w, http.StatusOK, "test_results", data)
}

// loadTestAndN extracts and validates the test ID and question number (n) from
// URL params. Returns the 1-based question index and the test, or writes an
// error and returns false.
func (h *TestHandler) loadTestAndN(w http.ResponseWriter, r *http.Request) (int, *models.Test, bool) {
	user := auth.UserFromCtx(r.Context())

	testID, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
	if err != nil {
		HTTPError(w, http.StatusNotFound)
		return 0, nil, false
	}

	n, err := strconv.Atoi(chi.URLParam(r, "n"))
	if err != nil {
		HTTPError(w, http.StatusNotFound)
		return 0, nil, false
	}

	test, err := h.repo.GetTest(testID)
	if err != nil || test.UserID != user.ID {
		HTTPError(w, http.StatusNotFound)
		return 0, nil, false
	}

	if n < 1 || n > test.NQuestions {
		HTTPError(w, http.StatusNotFound)
		return 0, nil, false
	}

	return n, test, true
}

// randomCatURL picks a random image from web/static/cats/<mood>/ and returns
// its URL path, or an empty string if the folder is missing or empty.
func randomCatURL(mood string) string {
	dir := "web/static/cats/" + mood
	entries, err := os.ReadDir(dir)
	if err != nil {
		return ""
	}
	var images []string
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		n := strings.ToLower(e.Name())
		if strings.HasSuffix(n, ".jpg") || strings.HasSuffix(n, ".jpeg") ||
			strings.HasSuffix(n, ".png") || strings.HasSuffix(n, ".gif") ||
			strings.HasSuffix(n, ".webp") {
			images = append(images, e.Name())
		}
	}
	if len(images) == 0 {
		return ""
	}
	return "/static/cats/" + mood + "/" + images[rand.Intn(len(images))]
}

// deterministicShuffle returns a copy of answers shuffled by a seed derived
// from the test ID and question ID, so the order is stable across page reloads.
func deterministicShuffle(answers []*models.Answer, testID int64, questionID string) []*models.Answer {
	b, _ := hex.DecodeString(questionID)
	qInt := int64(binary.BigEndian.Uint64(b))
	rng := rand.New(rand.NewSource(testID ^ qInt))
	out := make([]*models.Answer, len(answers))
	copy(out, answers)
	rng.Shuffle(len(out), func(i, j int) { out[i], out[j] = out[j], out[i] })
	return out
}