package web

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"html/template"
	"io/fs"
	"log"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/alexedwards/scs/v2"
	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"

	"plumber/internal/blob"
	"plumber/internal/geo"
	"plumber/internal/pacific"
	"plumber/internal/store"
)

type Config struct {
	AdminUsername string
	SecureCookie  bool
	Blob          blob.Uploader
}

type Server struct {
	store    store.Store
	sessions *scs.SessionManager
	tmpl     *template.Template
	cfg      Config
	static   http.Handler
}

type page struct {
	User      *store.User
	CSRF      string
	Flash     string
	Title     string
	Today     string
	Yesterday string
}

type huntPage struct {
	page
	Date        string
	Label       string
	IsToday     bool
	IsYesterday bool
	Questions   []store.RankedQuestion
}

type questionPage struct {
	page
	Question *store.RankedQuestion
	Answer   *store.Answer
}

type submitPage struct {
	page
	TitleVal string
	BodyVal  string
	CityVal  string
	Error    string
}

type authPage struct {
	page
	Username string
	Error    string
	Next     string
}

type voteCtx struct {
	User     *store.User
	CSRF     string
	View     string
	Date     string
	Question store.RankedQuestion
}

func New(st store.Store, sessionStore scs.Store, templateFS fs.FS, staticFS fs.FS, cfg Config) (*Server, error) {
	if cfg.Blob == nil {
		cfg.Blob = blob.Disabled{}
	}
	funcMap := template.FuncMap{
		"voteCtx": func(user *store.User, csrf, view, date string, q store.RankedQuestion) voteCtx {
			return voteCtx{User: user, CSRF: csrf, View: view, Date: date, Question: q}
		},
		"add":          func(a, b int) int { return a + b },
		"rank":         func(i int) int { return i + 1 },
		"isAdmin":      func(u *store.User) bool { return u.Admin() },
		"pacificLabel": pacific.Label,
		"locationTag": func(u *store.User) string {
			if u != nil {
				if name := geo.StateName(u.State); name != "" {
					return name
				}
			}
			return "Bay Area"
		},
	}
	tmpl, err := template.New("").Funcs(funcMap).ParseFS(templateFS, "templates/*.html", "templates/partials/*.html")
	if err != nil {
		return nil, fmt.Errorf("parse templates: %w", err)
	}
	sessions := scs.New()
	sessions.Store = sessionStore
	sessions.Lifetime = 30 * 24 * time.Hour
	sessions.Cookie.Name = "plumber_session"
	sessions.Cookie.HttpOnly = true
	sessions.Cookie.SameSite = http.SameSiteLaxMode
	sessions.Cookie.Secure = cfg.SecureCookie
	sessions.Cookie.Path = "/"

	sub, err := fs.Sub(staticFS, "static")
	if err != nil {
		return nil, err
	}

	return &Server{
		store:    st,
		sessions: sessions,
		tmpl:     tmpl,
		cfg:      cfg,
		static:   http.StripPrefix("/static/", http.FileServer(http.FS(sub))),
	}, nil
}

func (s *Server) Handler() http.Handler {
	r := chi.NewRouter()
	r.Use(middleware.RequestID)
	r.Use(middleware.RealIP)
	r.Use(middleware.Logger)
	r.Use(middleware.Recoverer)
	r.Use(func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			r.Body = http.MaxBytesReader(w, r.Body, 3<<20)
			next.ServeHTTP(w, r)
		})
	})
	r.Use(s.sessions.LoadAndSave)
	r.Use(s.withUser)
	r.Handle("/static/*", s.static)
	r.Get("/", s.handleToday)
	r.Get("/archive", s.handleArchive)
	r.Get("/hunt/{date}", s.handleHunt)
	r.Get("/submit", s.handleSubmitForm)
	r.Post("/submit", s.handleSubmit)
	r.Get("/questions/{id}", s.handleQuestion)
	r.Post("/questions/{id}/vote", s.handleVote)
	r.Post("/questions/{id}/answer", s.handleAnswer)
	r.Post("/questions/{id}/hide", s.handleHide)
	r.Get("/login", s.handleLoginForm)
	r.Post("/login", s.handleLogin)
	r.Get("/register", s.handleRegisterForm)
	r.Post("/register", s.handleRegister)
	r.Get("/auth/prompt", s.handleAuthPrompt)
	r.Post("/logout", s.handleLogout)
	r.Get("/admin/users", s.handleAdminUsers)
	r.Post("/admin/users/{id}/role", s.handleAdminSetRole)
	r.Get("/profile", s.handleProfileForm)
	r.Post("/profile", s.handleProfile)
	return r
}

type ctxKey int

const userKey ctxKey = 1

func (s *Server) withUser(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if s.sessions.GetString(r.Context(), "csrf") == "" {
			s.sessions.Put(r.Context(), "csrf", randomHex(16))
		}
		id := s.sessions.GetString(r.Context(), "user_id")
		if id != "" {
			u, err := s.store.UserByID(r.Context(), id)
			if err == nil {
				r = r.WithContext(context.WithValue(r.Context(), userKey, u))
			}
		}
		next.ServeHTTP(w, r)
	})
}

func currentUser(r *http.Request) *store.User {
	u, _ := r.Context().Value(userKey).(*store.User)
	return u
}

func (s *Server) basePage(r *http.Request, title string) page {
	return page{
		User:      currentUser(r),
		CSRF:      s.sessions.GetString(r.Context(), "csrf"),
		Flash:     s.sessions.PopString(r.Context(), "flash"),
		Title:     title,
		Today:     pacific.Today(),
		Yesterday: pacific.Yesterday(),
	}
}

func isHTMX(r *http.Request) bool {
	return r.Header.Get("HX-Request") == "true"
}

func (s *Server) requireCSRF(w http.ResponseWriter, r *http.Request) bool {
	if err := r.ParseForm(); err != nil {
		http.Error(w, "bad form", http.StatusBadRequest)
		return false
	}
	want := s.sessions.GetString(r.Context(), "csrf")
	got := r.PostFormValue("_csrf")
	if want == "" || got != want {
		http.Error(w, "invalid csrf token", http.StatusForbidden)
		return false
	}
	return true
}

func (s *Server) handleToday(w http.ResponseWriter, r *http.Request) {
	s.renderHunt(w, r, pacific.Today())
}

func (s *Server) handleArchive(w http.ResponseWriter, r *http.Request) {
	date := r.URL.Query().Get("date")
	if date == "" || date == pacific.Today() {
		http.Redirect(w, r, "/", http.StatusSeeOther)
		return
	}
	if _, err := pacific.Parse(date); err != nil || date > pacific.Today() {
		http.Redirect(w, r, "/", http.StatusSeeOther)
		return
	}
	http.Redirect(w, r, "/hunt/"+url.PathEscape(date), http.StatusSeeOther)
}

func (s *Server) handleHunt(w http.ResponseWriter, r *http.Request) {
	date := chi.URLParam(r, "date")
	if _, err := pacific.Parse(date); err != nil {
		http.NotFound(w, r)
		return
	}
	if date >= pacific.Today() {
		http.Redirect(w, r, "/", http.StatusSeeOther)
		return
	}
	s.renderHunt(w, r, date)
}

func (s *Server) renderHunt(w http.ResponseWriter, r *http.Request, date string) {
	viewer := ""
	if u := currentUser(r); u != nil {
		viewer = u.ID
	}
	questions, err := s.store.ListHunt(r.Context(), date, viewer)
	if err != nil {
		http.Error(w, "could not load questions", http.StatusInternalServerError)
		return
	}
	label := pacific.Label(date)
	title := label
	if pacific.IsToday(date) {
		title = "Today"
	}
	s.exec(w, "hunt", huntPage{
		page:        s.basePage(r, title),
		Date:        date,
		Label:       label,
		IsToday:     pacific.IsToday(date),
		IsYesterday: pacific.IsYesterday(date),
		Questions:   questions,
	})
}

func (s *Server) handleSubmitForm(w http.ResponseWriter, r *http.Request) {
	if currentUser(r) == nil {
		s.sessions.Put(r.Context(), "flash", "Sign in to ask a question.")
		http.Redirect(w, r, "/login?next=/submit", http.StatusSeeOther)
		return
	}
	s.exec(w, "submit", submitPage{page: s.basePage(r, "Ask a question")})
}

func (s *Server) handleSubmit(w http.ResponseWriter, r *http.Request) {
	if !s.requireCSRF(w, r) {
		return
	}
	u := currentUser(r)
	if u == nil {
		http.Redirect(w, r, "/login?next=/submit", http.StatusSeeOther)
		return
	}
	title := strings.TrimSpace(r.PostFormValue("title"))
	body := strings.TrimSpace(r.PostFormValue("body"))
	city := strings.TrimSpace(r.PostFormValue("city"))
	if title == "" || body == "" {
		s.exec(w, "submit", submitPage{
			page:     s.basePage(r, "Ask a question"),
			TitleVal: title,
			BodyVal:  body,
			CityVal:  city,
			Error:    "Title and description are required.",
		})
		return
	}
	if len(title) > 120 {
		title = truncateRunes(title, 120)
	}
	if len(body) > 8000 {
		body = truncateRunes(body, 8000)
	}
	if len(city) > 80 {
		city = truncateRunes(city, 80)
	}
	q := &store.RankedQuestion{
		AuthorID: u.ID,
		Title:    title,
		Body:     body,
		City:     city,
	}
	if err := s.store.CreateQuestion(r.Context(), q); err != nil {
		http.Error(w, "could not save question", http.StatusInternalServerError)
		return
	}
	http.Redirect(w, r, "/questions/"+url.PathEscape(q.ID), http.StatusSeeOther)
}

func (s *Server) handleQuestion(w http.ResponseWriter, r *http.Request) {
	id := chi.URLParam(r, "id")
	viewer := ""
	if u := currentUser(r); u != nil {
		viewer = u.ID
	}
	q, err := s.store.GetQuestion(r.Context(), id, viewer)
	if err != nil || (q.Hidden && !currentUser(r).Admin()) {
		http.NotFound(w, r)
		return
	}
	var ans *store.Answer
	if q.Answered {
		ans, _ = s.store.GetAnswer(r.Context(), q.ID)
	}
	s.exec(w, "question", questionPage{
		page:     s.basePage(r, q.Title),
		Question: q,
		Answer:   ans,
	})
}

func (s *Server) handleVote(w http.ResponseWriter, r *http.Request) {
	if !s.requireCSRF(w, r) {
		return
	}
	u := currentUser(r)
	if u == nil {
		if isHTMX(r) {
			s.exec(w, "signin-prompt", s.basePage(r, ""))
			return
		}
		http.Redirect(w, r, "/login", http.StatusSeeOther)
		return
	}
	id := chi.URLParam(r, "id")
	value := 0
	switch r.PostFormValue("value") {
	case "1":
		value = 1
	case "-1":
		value = -1
	default:
		http.Error(w, "invalid vote", http.StatusBadRequest)
		return
	}
	if err := s.store.Vote(r.Context(), u.ID, id, value); err != nil {
		http.Error(w, "could not vote", http.StatusInternalServerError)
		return
	}
	view := r.PostFormValue("view")
	date := r.PostFormValue("date")
	if isHTMX(r) {
		if view == "list" {
			s.renderLeaderboard(w, r, date)
			return
		}
		q, err := s.store.GetQuestion(r.Context(), id, u.ID)
		if err != nil {
			http.Error(w, "not found", http.StatusNotFound)
			return
		}
		s.exec(w, "vote", voteCtx{
			User:     u,
			CSRF:     s.sessions.GetString(r.Context(), "csrf"),
			View:     "question",
			Date:     q.HuntDate,
			Question: *q,
		})
		return
	}
	if view == "question" {
		http.Redirect(w, r, "/questions/"+url.PathEscape(id), http.StatusSeeOther)
		return
	}
	if date != "" && date != pacific.Today() {
		http.Redirect(w, r, "/hunt/"+url.PathEscape(date), http.StatusSeeOther)
		return
	}
	http.Redirect(w, r, "/", http.StatusSeeOther)
}

func (s *Server) renderLeaderboard(w http.ResponseWriter, r *http.Request, date string) {
	if date == "" {
		date = pacific.Today()
	}
	viewer := ""
	if u := currentUser(r); u != nil {
		viewer = u.ID
	}
	questions, err := s.store.ListHunt(r.Context(), date, viewer)
	if err != nil {
		http.Error(w, "could not load questions", http.StatusInternalServerError)
		return
	}
	s.exec(w, "leaderboard", huntPage{
		page:      s.basePage(r, ""),
		Date:      date,
		Questions: questions,
	})
}

func (s *Server) handleAnswer(w http.ResponseWriter, r *http.Request) {
	if !s.requireCSRF(w, r) {
		return
	}
	u := currentUser(r)
	if !u.Admin() {
		http.Error(w, "forbidden", http.StatusForbidden)
		return
	}
	id := chi.URLParam(r, "id")
	body := strings.TrimSpace(r.PostFormValue("body"))
	if body == "" {
		http.Error(w, "answer required", http.StatusBadRequest)
		return
	}
	if len(body) > 12000 {
		body = truncateRunes(body, 12000)
	}
	ans := &store.Answer{
		QuestionID: id,
		AuthorID:   u.ID,
		Body:       body,
	}
	if err := s.store.UpsertAnswer(r.Context(), ans); err != nil {
		http.Error(w, "could not save answer", http.StatusInternalServerError)
		return
	}
	saved, err := s.store.GetAnswer(r.Context(), id)
	if err != nil {
		http.Error(w, "could not load answer", http.StatusInternalServerError)
		return
	}
	if isHTMX(r) {
		s.exec(w, "answer", questionPage{page: s.basePage(r, ""), Answer: saved})
		return
	}
	http.Redirect(w, r, "/questions/"+url.PathEscape(id), http.StatusSeeOther)
}

func (s *Server) handleHide(w http.ResponseWriter, r *http.Request) {
	if !s.requireCSRF(w, r) {
		return
	}
	u := currentUser(r)
	if !u.Admin() {
		http.Error(w, "forbidden", http.StatusForbidden)
		return
	}
	id := chi.URLParam(r, "id")
	q, err := s.store.GetQuestion(r.Context(), id, u.ID)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	if err := s.store.HideQuestion(r.Context(), id); err != nil {
		http.Error(w, "could not hide", http.StatusInternalServerError)
		return
	}
	if isHTMX(r) && r.PostFormValue("view") == "list" {
		s.renderLeaderboard(w, r, q.HuntDate)
		return
	}
	if isHTMX(r) {
		w.Header().Set("HX-Redirect", "/")
		w.WriteHeader(http.StatusSeeOther)
		return
	}
	http.Redirect(w, r, "/", http.StatusSeeOther)
}

func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
	if !s.requireCSRF(w, r) {
		return
	}
	s.sessions.Remove(r.Context(), "user_id")
	http.Redirect(w, r, "/", http.StatusSeeOther)
}

func (s *Server) exec(w http.ResponseWriter, name string, data any) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := s.tmpl.ExecuteTemplate(w, name, data); err != nil {
		log.Printf("template %s: %v", name, err)
		http.Error(w, "template error", http.StatusInternalServerError)
	}
}

// truncateRunes shortens s to at most max runes without splitting a code point.
func truncateRunes(s string, max int) string {
	if max <= 0 {
		return ""
	}
	n := 0
	for byteIdx := range s {
		if n == max {
			return s[:byteIdx]
		}
		n++
	}
	return s
}

func randomHex(n int) string {
	b := make([]byte, n)
	if _, err := rand.Read(b); err != nil {
		panic(err)
	}
	return hex.EncodeToString(b)
}