package server

import (
	"encoding/json"
	"errors"
	"log/slog"
	"net/http"
	"time"

	"github.com/wzray/dns/internal/resolv"
)

type Server struct {
	mgr    *resolv.Manager
	log    *slog.Logger
	mux    *http.ServeMux
}

func New(mgr *resolv.Manager, log *slog.Logger) *Server {
	s := &Server{mgr: mgr, log: log, mux: http.NewServeMux()}
	s.routes()
	return s
}

func (s *Server) Handler() http.Handler {
	return s.withLogging(s.mux)
}

func (s *Server) routes() {
	s.mux.HandleFunc("GET /health", s.handleHealth)
	s.mux.HandleFunc("GET /dns", s.handleList)
	s.mux.HandleFunc("POST /dns", s.handleAdd)
	s.mux.HandleFunc("DELETE /dns/{address}", s.handleRemove)
}

type listResponse struct {
	Servers []string `json:"servers"`
}

type addRequest struct {
	Address string `json:"address"`
}

type errorResponse struct {
	Error string `json:"error"`
}

func (s *Server) handleHealth(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (s *Server) handleList(w http.ResponseWriter, r *http.Request) {
	servers, err := s.mgr.List()
	if err != nil {
		s.log.Error("list nameservers", "err", err)
		writeError(w, http.StatusInternalServerError, "failed to read nameservers")
		return
	}
	if servers == nil {
		servers = []string{}
	}
	writeJSON(w, http.StatusOK, listResponse{Servers: servers})
}

func (s *Server) handleAdd(w http.ResponseWriter, r *http.Request) {
	var req addRequest
	dec := json.NewDecoder(r.Body)
	dec.DisallowUnknownFields()
	if err := dec.Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid JSON body")
		return
	}
	if req.Address == "" {
		writeError(w, http.StatusBadRequest, "address is required")
		return
	}

	err := s.mgr.Add(req.Address)
	switch {
	case err == nil:
		writeJSON(w, http.StatusCreated, map[string]string{"address": req.Address})
	case errors.Is(err, resolv.ErrInvalidAddress):
		writeError(w, http.StatusBadRequest, err.Error())
	case errors.Is(err, resolv.ErrAlreadyExists):
		writeError(w, http.StatusConflict, err.Error())
	default:
		s.log.Error("add nameserver", "addr", req.Address, "err", err)
		writeError(w, http.StatusInternalServerError, "failed to add nameserver")
	}
}

func (s *Server) handleRemove(w http.ResponseWriter, r *http.Request) {
	addr := r.PathValue("address")
	if addr == "" {
		writeError(w, http.StatusBadRequest, "address is required")
		return
	}

	err := s.mgr.Remove(addr)
	switch {
	case err == nil:
		w.WriteHeader(http.StatusNoContent)
	case errors.Is(err, resolv.ErrInvalidAddress):
		writeError(w, http.StatusBadRequest, err.Error())
	case errors.Is(err, resolv.ErrNotFound):
		writeError(w, http.StatusNotFound, err.Error())
	default:
		s.log.Error("remove nameserver", "addr", addr, "err", err)
		writeError(w, http.StatusInternalServerError, "failed to remove nameserver")
	}
}

func writeJSON(w http.ResponseWriter, status int, body any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(body)
}

func writeError(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, errorResponse{Error: msg})
}

type statusRecorder struct {
	http.ResponseWriter
	status int
}

func (r *statusRecorder) WriteHeader(code int) {
	r.status = code
	r.ResponseWriter.WriteHeader(code)
}

func (s *Server) withLogging(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		rec := &statusRecorder{ResponseWriter: w, status: http.StatusOK}
		next.ServeHTTP(rec, r)
		s.log.Info("http request",
			"method", r.Method,
			"path", r.URL.Path,
			"status", rec.status,
			"duration_ms", time.Since(start).Milliseconds(),
			"remote", r.RemoteAddr,
		)
	})
}