// Package server wires HTTP routes, templates and handlers together.
package server

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"html/template"
	"io/fs"
	"log/slog"
	"net"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"

	"github.com/cdnutter/canon/internal/auth"
	"github.com/cdnutter/canon/internal/config"
	"github.com/cdnutter/canon/internal/imgcache"
	"github.com/cdnutter/canon/internal/providers"
	"github.com/cdnutter/canon/internal/store"
	"github.com/cdnutter/canon/web"
)

const (
	sessionCookie = "canon_session"
	sessionTTL    = 30 * 24 * time.Hour
)

type Server struct {
	cfg       config.Config
	store     *store.Store
	images    *imgcache.Cache
	providers *providers.Registry
	log       *slog.Logger

	pages      map[string]*template.Template
	static     fs.FS
	assetVer   string
	loginLimit *auth.Limiter
	setupCode  string
}

func New(cfg config.Config, st *store.Store, images *imgcache.Cache, log *slog.Logger, version string) (*Server, error) {
	s := &Server{
		cfg:        cfg,
		store:      st,
		images:     images,
		log:        log,
		assetVer:   version,
		loginLimit: auth.NewLimiter(10, 15*time.Minute),
	}
	s.providers = providers.NewRegistry(s.credentials)
	static, err := fs.Sub(web.FS, "static")
	if err != nil {
		return nil, err
	}
	s.static = static
	if err := s.parseTemplates(); err != nil {
		return nil, err
	}
	return s, nil
}

// SetSetupCode enables first-run account creation guarded by code.
func (s *Server) SetSetupCode(code string) { s.setupCode = code }

func (s *Server) credentials(ctx context.Context) providers.Credentials {
	set, err := s.store.Settings(ctx)
	if err != nil {
		s.log.Error("loading settings", "err", err)
		set = map[string]string{}
	}
	pick := func(env, key string) string {
		if env != "" {
			return env
		}
		return set[key]
	}
	return providers.Credentials{
		TMDBKey:          pick(s.cfg.TMDBKey, store.SettingTMDBKey),
		TVDBKey:          pick(s.cfg.TVDBKey, store.SettingTVDBKey),
		TVDBPin:          pick(s.cfg.TVDBPin, store.SettingTVDBPin),
		IGDBClientID:     pick(s.cfg.IGDBClientID, store.SettingIGDBClientID),
		IGDBClientSecret: pick(s.cfg.IGDBClientSecret, store.SettingIGDBClientSecret),
		MusicProvider:    set[store.SettingMusicProvider],
		TVProvider:       set[store.SettingTVProvider],
	}
}

func (s *Server) Handler() http.Handler {
	mux := http.NewServeMux()

	// Public
	mux.HandleFunc("GET /{$}", s.handleHome)
	mux.HandleFunc("GET /l/{slug}", s.handleList)
	mux.HandleFunc("GET /l/{slug}/export", s.handleExport)
	mux.HandleFunc("GET /images/{name}", s.handleImage)
	mux.HandleFunc("GET /custom.css", s.handleCustomCSS)
	mux.Handle("GET /static/", http.StripPrefix("/static/", s.staticHandler()))
	mux.HandleFunc("GET /favicon.ico", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, "/static/img/favicon.svg", http.StatusMovedPermanently)
	})
	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) { w.Write([]byte("ok")) })

	// Auth
	mux.HandleFunc("GET /login", s.handleLoginPage)
	mux.HandleFunc("POST /login", s.handleLogin)
	mux.HandleFunc("POST /logout", s.handleLogout)
	mux.HandleFunc("GET /setup", s.handleSetupPage)
	mux.HandleFunc("POST /setup", s.handleSetup)

	// Admin pages
	mux.HandleFunc("GET /admin", s.requireUser(s.handleAdminLists))
	mux.HandleFunc("GET /admin/lists/{id}", s.requireUser(s.handleAdminList))
	mux.HandleFunc("GET /admin/settings", s.requireUser(s.handleAdminSettings))

	// Admin JSON API
	api := func(pattern string, h http.HandlerFunc) { mux.HandleFunc(pattern, s.requireAPI(h)) }
	api("GET /api/lists", s.apiLists)
	api("POST /api/lists", s.apiCreateList)
	api("POST /api/lists/order", s.apiReorderLists)
	api("PUT /api/lists/{id}", s.apiUpdateList)
	api("DELETE /api/lists/{id}", s.apiDeleteList)
	api("GET /api/lists/{id}/items", s.apiItems)
	api("POST /api/lists/{id}/items", s.apiAddItem)
	api("PUT /api/items/{id}", s.apiUpdateItem)
	api("POST /api/items/{id}/image", s.apiUploadItemImage)
	api("POST /api/items/{id}/move", s.apiMoveItem)
	api("DELETE /api/items/{id}", s.apiDeleteItem)
	api("GET /api/search", s.apiSearch)
	api("GET /api/settings", s.apiSettings)
	api("PUT /api/settings", s.apiUpdateSettings)
	api("POST /api/settings/avatar", s.apiUploadAvatar)
	api("DELETE /api/settings/avatar", s.apiDeleteAvatar)
	api("POST /api/integrations/test", s.apiTestIntegration)
	api("PUT /api/account", s.apiUpdateAccount)

	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) { s.notFound(w, r) })

	return s.recoverer(s.securityHeaders(s.logRequests(mux)))
}

// ---- middleware ----

type statusWriter struct {
	http.ResponseWriter
	status int
}

func (w *statusWriter) WriteHeader(code int) {
	w.status = code
	w.ResponseWriter.WriteHeader(code)
}

func (s *Server) logRequests(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		sw := &statusWriter{ResponseWriter: w, status: 200}
		next.ServeHTTP(sw, r)
		if strings.HasPrefix(r.URL.Path, "/static/") || strings.HasPrefix(r.URL.Path, "/images/") {
			return
		}
		s.log.Debug("request", "method", r.Method, "path", r.URL.Path, "status", sw.status, "dur", time.Since(start).Round(time.Millisecond))
	})
}

func (s *Server) recoverer(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if v := recover(); v != nil {
				if v == http.ErrAbortHandler {
					panic(v)
				}
				s.log.Error("panic", "path", r.URL.Path, "err", v)
				http.Error(w, "Internal Server Error", http.StatusInternalServerError)
			}
		}()
		next.ServeHTTP(w, r)
	})
}

func (s *Server) securityHeaders(next http.Handler) http.Handler {
	// Remote https images are allowed so search results can preview art
	// before it's cached locally.
	const csp = "default-src 'self'; img-src 'self' data: blob: https:; style-src 'self' 'unsafe-inline'; script-src 'self'; " +
		"object-src 'none'; base-uri 'self'; form-action 'self'; frame-ancestors 'self'"
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := w.Header()
		h.Set("Content-Security-Policy", csp)
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("Referrer-Policy", "same-origin")
		h.Set("X-Frame-Options", "SAMEORIGIN")
		next.ServeHTTP(w, r)
	})
}

type ctxKey int

const userKey ctxKey = 0

type sessionUser struct {
	store.User
	TokenHash string
}

func (s *Server) currentUser(r *http.Request) (sessionUser, bool) {
	if u, ok := r.Context().Value(userKey).(sessionUser); ok {
		return u, true
	}
	c, err := r.Cookie(sessionCookie)
	if err != nil || c.Value == "" {
		return sessionUser{}, false
	}
	hash := auth.HashToken(c.Value)
	u, err := s.store.SessionUser(r.Context(), hash)
	if err != nil {
		return sessionUser{}, false
	}
	return sessionUser{User: u, TokenHash: hash}, true
}

func (s *Server) requireUser(h http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		u, ok := s.currentUser(r)
		if !ok {
			http.Redirect(w, r, "/login?next="+url.QueryEscape(r.URL.RequestURI()), http.StatusSeeOther)
			return
		}
		h(w, r.WithContext(context.WithValue(r.Context(), userKey, u)))
	}
}

// requireAPI guards JSON endpoints. Besides the session cookie, it requires a
// custom header that browsers won't send cross-site without a CORS
// preflight, which blocks CSRF.
func (s *Server) requireAPI(h http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Header.Get("X-Canon") != "1" || !s.sameOrigin(r) {
			writeError(w, http.StatusForbidden, "Missing request header")
			return
		}
		u, ok := s.currentUser(r)
		if !ok {
			writeError(w, http.StatusUnauthorized, "Your session expired. Please sign in again.")
			return
		}
		h(w, r.WithContext(context.WithValue(r.Context(), userKey, u)))
	}
}

// sameOrigin rejects requests whose Origin header names another site.
func (s *Server) sameOrigin(r *http.Request) bool {
	origin := r.Header.Get("Origin")
	if origin == "" || origin == "null" {
		return origin == "" // absent: non-browser or same-origin GET
	}
	u, err := url.Parse(origin)
	if err != nil {
		return false
	}
	host := r.Host
	if s.cfg.TrustProxy {
		if fh := r.Header.Get("X-Forwarded-Host"); fh != "" {
			host = fh
		}
	}
	return strings.EqualFold(u.Host, host)
}

func (s *Server) clientIP(r *http.Request) string {
	if s.cfg.TrustProxy {
		if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
			first, _, _ := strings.Cut(xff, ",")
			return strings.TrimSpace(first)
		}
		if xr := r.Header.Get("X-Real-IP"); xr != "" {
			return xr
		}
	}
	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		return r.RemoteAddr
	}
	return host
}

func (s *Server) isHTTPS(r *http.Request) bool {
	if s.cfg.SecureCookies || r.TLS != nil {
		return true
	}
	return s.cfg.TrustProxy && strings.EqualFold(r.Header.Get("X-Forwarded-Proto"), "https")
}

// ---- static files ----

func (s *Server) staticHandler() http.Handler {
	fsrv := http.FileServerFS(s.static)
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if strings.HasSuffix(r.URL.Path, "/") {
			s.notFound(w, r)
			return
		}
		if r.URL.Query().Get("v") != "" {
			w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
		} else {
			w.Header().Set("Cache-Control", "public, max-age=3600")
		}
		fsrv.ServeHTTP(w, r)
	})
}

func (s *Server) handleImage(w http.ResponseWriter, r *http.Request) {
	name := r.PathValue("name")
	if !imgcache.ValidName(name) {
		s.notFound(w, r)
		return
	}
	w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
	http.ServeFile(w, r, s.images.Dir()+"/"+name)
}

// ---- JSON helpers ----

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(v)
}

func writeError(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, map[string]string{"error": msg})
}

// writeErr maps store/provider errors to HTTP responses.
func (s *Server) writeErr(w http.ResponseWriter, err error) {
	var ve store.ValidationError
	var nc providers.NotConfiguredError
	switch {
	case errors.As(err, &ve):
		writeError(w, http.StatusBadRequest, ve.Msg)
	case errors.As(err, &nc):
		writeError(w, http.StatusFailedDependency, nc.Error())
	case errors.Is(err, store.ErrNotFound):
		writeError(w, http.StatusNotFound, "Not found")
	case errors.Is(err, imgcache.ErrNotImage):
		writeError(w, http.StatusBadRequest, err.Error())
	default:
		s.log.Error("request failed", "err", err)
		writeError(w, http.StatusInternalServerError, "Something went wrong: "+err.Error())
	}
}

func decodeJSON(r *http.Request, v any) error {
	dec := json.NewDecoder(http.MaxBytesReader(nil, r.Body, 1<<20))
	if err := dec.Decode(v); err != nil {
		return store.ValidationError{Msg: "Invalid request body"}
	}
	return nil
}

func pathID(r *http.Request) (int64, error) {
	id, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
	if err != nil || id <= 0 {
		return 0, store.ErrNotFound
	}
	return id, nil
}

func shortHash(s string) string {
	sum := sha256.Sum256([]byte(s))
	return hex.EncodeToString(sum[:])[:10]
}

func (s *Server) notFound(w http.ResponseWriter, r *http.Request) {
	if strings.HasPrefix(r.URL.Path, "/api/") {
		writeError(w, http.StatusNotFound, "Not found")
		return
	}
	s.render(w, r, http.StatusNotFound, "error", "Not found", errorPage{
		Code:    404,
		Message: "There's nothing ranked here.",
	})
}

type errorPage struct {
	Code    int
	Message string
}

func (s *Server) serverError(w http.ResponseWriter, r *http.Request, err error) {
	s.log.Error("page failed", "path", r.URL.Path, "err", err)
	s.render(w, r, http.StatusInternalServerError, "error", "Error", errorPage{
		Code:    500,
		Message: fmt.Sprintf("Something went wrong: %v", err),
	})
}