// Package api expõe a camada HTTP da aplicação de notas.
package api

import (
	"crypto/subtle"
	"encoding/json"
	"errors"
	"io/fs"
	"log/slog"
	"net/http"
	"strings"
	"time"

	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/extension"
	htmlr "github.com/yuin/goldmark/renderer/html"

	"github.com/lgcosta/notas-online/internal/store"
)

// CookieName é o cookie HttpOnly onde o token de sessão é guardado.
const CookieName = "notas_token"

const cookieMaxAge = 30 * 24 * time.Hour

// Server agrupa dependências e rotas.
type Server struct {
	st    *store.Store
	token string
	webFS fs.FS
	md    goldmark.Markdown
}

// New cria o servidor da API. webFS é o filesystem embutido do frontend
// (raiz contém index.html, css/, js/).
func New(st *store.Store, token string, webFS fs.FS) *Server {
	return &Server{
		st:    st,
		token: token,
		webFS: webFS,
		md: goldmark.New(
			goldmark.WithExtensions(extension.GFM),
			goldmark.WithRendererOptions(htmlr.WithHardWraps()),
		),
	}
}

// Handler monta o mux completo (rotas públicas, autenticadas e estáticas).
func (s *Server) Handler() http.Handler {
	mux := http.NewServeMux()

	mux.HandleFunc("POST /api/login", s.handleLogin)
	mux.HandleFunc("POST /api/logout", s.handleLogout)
	mux.HandleFunc("GET /api/me", s.handleMe)

	mux.HandleFunc("GET /api/notes", s.auth(s.handleListNotes))
	mux.HandleFunc("POST /api/notes", s.auth(s.handleCreateNote))
	mux.HandleFunc("GET /api/notes/{id}", s.auth(s.handleGetNote))
	mux.HandleFunc("PUT /api/notes/{id}", s.auth(s.handleUpdateNote))
	mux.HandleFunc("DELETE /api/notes/{id}", s.auth(s.handleDeleteNote))
	mux.HandleFunc("GET /api/notes/{id}/raw", s.auth(s.handleRaw))
	mux.HandleFunc("GET /api/notes/{id}/revisions", s.auth(s.handleListRevisions))
	mux.HandleFunc("GET /api/notes/{id}/revisions/{hash}", s.auth(s.handleGetRevision))
	mux.HandleFunc("GET /api/notes/{id}/revisions/{hash}/diff", s.auth(s.handleRevisionDiff))
	mux.HandleFunc("POST /api/notes/{id}/revisions/{hash}/restore", s.auth(s.handleRestore))

	mux.HandleFunc("GET /api/tags", s.auth(s.handleTags))
	mux.HandleFunc("GET /api/categories", s.auth(s.handleCategories))
	mux.HandleFunc("POST /api/categories", s.auth(s.handleCreateCategory))
	mux.HandleFunc("PUT /api/categories/{id}", s.auth(s.handleUpdateCategory))
	mux.HandleFunc("DELETE /api/categories/{id}", s.auth(s.handleDeleteCategory))
	mux.HandleFunc("POST /api/render", s.auth(s.handleRender))

	mux.HandleFunc("GET /{$}", s.serveIndex)
	mux.Handle("GET /", http.FileServerFS(s.webFS))

	return s.wrap(mux)
}

// wrap aplica middlewares globais: recuperação, headers de segurança e log.
func (s *Server) wrap(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if rec := recover(); rec != nil {
				slog.Error("panic atendendo requisição", "path", r.URL.Path, "panic", rec)
				http.Error(w, `{"error":"erro interno"}`, http.StatusInternalServerError)
			}
		}()
		h := w.Header()
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("X-Frame-Options", "DENY")
		h.Set("Referrer-Policy", "no-referrer")
		h.Set("Content-Security-Policy",
			"default-src 'self'; img-src 'self' data:; style-src 'self'; "+
				"script-src 'self'; frame-src 'self'; connect-src 'self'")
		next.ServeHTTP(w, r)
	})
}

// ---------------------------------------------------------------------------
// Autenticação
// ---------------------------------------------------------------------------

func (s *Server) presentedToken(r *http.Request) string {
	if v, ok := strings.CutPrefix(r.Header.Get("Authorization"), "Bearer "); ok {
		return strings.TrimSpace(v)
	}
	if c, err := r.Cookie(CookieName); err == nil {
		return c.Value
	}
	return ""
}

func (s *Server) validToken(candidate string) bool {
	if s.token == "" || candidate == "" {
		return false
	}
	return subtle.ConstantTimeCompare([]byte(candidate), []byte(s.token)) == 1
}

func (s *Server) auth(h http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if !s.validToken(s.presentedToken(r)) {
			writeError(w, http.StatusUnauthorized, "token inválido ou ausente")
			return
		}
		h(w, r)
	}
}

type loginRequest struct {
	Token string `json:"token"`
}

func (s *Server) handleLogin(w http.ResponseWriter, r *http.Request) {
	var req loginRequest
	if err := decodeJSON(r, &req, 1<<16); err != nil {
		writeError(w, http.StatusBadRequest, "corpo JSON inválido")
		return
	}
	if !s.validToken(strings.TrimSpace(req.Token)) {
		writeError(w, http.StatusUnauthorized, "token inválido")
		return
	}
	secure := r.TLS != nil || r.Header.Get("X-Forwarded-Proto") == "https"
	http.SetCookie(w, &http.Cookie{
		Name:     CookieName,
		Value:    strings.TrimSpace(req.Token),
		Path:     "/",
		MaxAge:   int(cookieMaxAge.Seconds()),
		HttpOnly: true,
		Secure:   secure,
		SameSite: http.SameSiteLaxMode,
	})
	writeJSON(w, http.StatusOK, map[string]any{"authed": true})
}

func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
	http.SetCookie(w, &http.Cookie{Name: CookieName, Value: "", Path: "/", MaxAge: -1,
		HttpOnly: true, SameSite: http.SameSiteLaxMode})
	writeJSON(w, http.StatusOK, map[string]any{"authed": false})
}

func (s *Server) handleMe(w http.ResponseWriter, r *http.Request) {
	if !s.validToken(s.presentedToken(r)) {
		writeError(w, http.StatusUnauthorized, "não autenticado")
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"authed": true})
}

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

func decodeJSON(r *http.Request, v any, maxBytes int64) error {
	defer r.Body.Close()
	dec := json.NewDecoder(http.MaxBytesReader(nil, r.Body, maxBytes))
	dec.DisallowUnknownFields()
	if err := dec.Decode(v); err != nil {
		return err
	}
	return nil
}

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

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

// mapStoreError converte erros da store para códigos HTTP.
func mapStoreError(w http.ResponseWriter, err error) {
	switch {
	case errors.Is(err, store.ErrNotFound):
		writeError(w, http.StatusNotFound, "nota não encontrada")
	case errors.Is(err, store.ErrRevision):
		writeError(w, http.StatusNotFound, "revisão não encontrada")
	case errors.Is(err, store.ErrInvalid):
		writeError(w, http.StatusBadRequest, err.Error())
	case errors.Is(err, store.ErrTooLarge):
		writeError(w, http.StatusRequestEntityTooLarge, "conteúdo excede 2 MiB")
	case errors.Is(err, store.ErrUnchanged):
		writeError(w, http.StatusConflict, "o conteúdo dessa revisão já está ativo")
	default:
		slog.Error("erro interno da store", "err", err)
		writeError(w, http.StatusInternalServerError, "erro interno")
	}
}