// Package server exposes the session registry over HTTP.
package server

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strings"
	"syscall"

	"termd/internal/api"
	"termd/internal/keymap"
	"termd/internal/session"
)

// Server is the HTTP API over a session registry.
type Server struct {
	registry *session.Registry
	token    string
	mux      *http.ServeMux
}

// New builds the server. If token is non-empty, every request must carry
// "Authorization: Bearer <token>".
func New(reg *session.Registry, token string) *Server {
	s := &Server{registry: reg, token: token, mux: http.NewServeMux()}
	s.mux.HandleFunc("GET /healthz", s.handleHealthz)
	s.mux.HandleFunc("POST /sessions", s.handleCreate)
	s.mux.HandleFunc("GET /sessions", s.handleList)
	s.mux.HandleFunc("GET /sessions/{id}", s.handleInfo)
	s.mux.HandleFunc("DELETE /sessions/{id}", s.handleDelete)
	s.mux.HandleFunc("POST /sessions/{id}/resize", s.handleResize)
	s.mux.HandleFunc("POST /sessions/{id}/input", s.handleInput)
	s.mux.HandleFunc("POST /sessions/{id}/mouse", s.handleMouse)
	s.mux.HandleFunc("GET /sessions/{id}/screen", s.handleScreen)
	s.mux.HandleFunc("GET /sessions/{id}/attach", s.handleAttach)
	return s
}

func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if s.token != "" && r.Header.Get("Authorization") != "Bearer "+s.token {
		writeError(w, http.StatusUnauthorized, "missing or wrong bearer token", nil)
		return
	}
	s.mux.ServeHTTP(w, r)
}

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

func writeError(w http.ResponseWriter, status int, msg string, modes *api.Modes) {
	writeJSON(w, status, api.Error{Error: msg, Modes: modes})
}

// getSession resolves {id} or writes a 404 and returns nil.
func (s *Server) getSession(w http.ResponseWriter, r *http.Request) *session.Session {
	id := r.PathValue("id")
	sess := s.registry.Get(id)
	if sess == nil {
		writeError(w, http.StatusNotFound, fmt.Sprintf("no session %q", id), nil)
	}
	return sess
}

func decodeBody(w http.ResponseWriter, r *http.Request, v any) bool {
	dec := json.NewDecoder(http.MaxBytesReader(w, r.Body, 1<<20))
	dec.DisallowUnknownFields()
	if err := dec.Decode(v); err != nil {
		writeError(w, http.StatusBadRequest, "bad request body: "+err.Error(), nil)
		return false
	}
	return true
}

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

func (s *Server) handleCreate(w http.ResponseWriter, r *http.Request) {
	var req api.CreateSessionRequest
	if !decodeBody(w, r, &req) {
		return
	}
	sess, err := s.registry.Create(session.Options{
		Command: req.Command,
		Cwd:     req.Cwd,
		Env:     req.Env,
		Cols:    req.Cols,
		Rows:    req.Rows,
		Term:    req.Term,
	})
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error(), nil)
		return
	}
	writeJSON(w, http.StatusCreated, sess.Info())
}

func (s *Server) handleList(w http.ResponseWriter, _ *http.Request) {
	sessions := s.registry.List()
	list := api.SessionList{Sessions: make([]api.SessionInfo, 0, len(sessions))}
	for _, sess := range sessions {
		list.Sessions = append(list.Sessions, sess.Info())
	}
	writeJSON(w, http.StatusOK, list)
}

func (s *Server) handleInfo(w http.ResponseWriter, r *http.Request) {
	sess := s.getSession(w, r)
	if sess == nil {
		return
	}
	writeJSON(w, http.StatusOK, sess.Info())
}

var signals = map[string]syscall.Signal{
	"TERM": syscall.SIGTERM,
	"KILL": syscall.SIGKILL,
	"INT":  syscall.SIGINT,
	"HUP":  syscall.SIGHUP,
	"QUIT": syscall.SIGQUIT,
	"USR1": syscall.SIGUSR1,
	"USR2": syscall.SIGUSR2,
}

func (s *Server) handleDelete(w http.ResponseWriter, r *http.Request) {
	sess := s.getSession(w, r)
	if sess == nil {
		return
	}
	// Default to SIGHUP: it's what a closing terminal sends, and interactive
	// shells ignore SIGTERM (which would ride the 3s SIGKILL escalation).
	sigName := r.URL.Query().Get("signal")
	if sigName == "" {
		sigName = "HUP"
	}
	sig, ok := signals[strings.TrimPrefix(strings.ToUpper(sigName), "SIG")]
	if !ok {
		writeError(w, http.StatusBadRequest, fmt.Sprintf("unknown signal %q", sigName), nil)
		return
	}
	if err := sess.Kill(sig); err != nil {
		writeError(w, http.StatusInternalServerError, err.Error(), nil)
		return
	}
	s.registry.Remove(sess.ID)
	w.WriteHeader(http.StatusNoContent)
}

func (s *Server) handleResize(w http.ResponseWriter, r *http.Request) {
	sess := s.getSession(w, r)
	if sess == nil {
		return
	}
	var req api.ResizeRequest
	if !decodeBody(w, r, &req) {
		return
	}
	if err := sess.Resize(req.Cols, req.Rows); err != nil {
		writeError(w, http.StatusBadRequest, err.Error(), nil)
		return
	}
	writeJSON(w, http.StatusOK, map[string]int{"cols": req.Cols, "rows": req.Rows})
}

func (s *Server) handleInput(w http.ResponseWriter, r *http.Request) {
	sess := s.getSession(w, r)
	if sess == nil {
		return
	}
	var req api.InputRequest
	if !decodeBody(w, r, &req) {
		return
	}
	if len(req.Input) == 0 {
		writeError(w, http.StatusBadRequest, "input array is empty", nil)
		return
	}
	// Validate everything before sending anything: an input list is all or
	// nothing, never delivered halfway.
	type step struct {
		text string
		key  *keymap.Key
		raw  []byte
	}
	steps := make([]step, 0, len(req.Input))
	for i, item := range req.Input {
		set := 0
		for _, p := range []bool{item.Text != nil, item.Key != nil, item.Raw != nil} {
			if p {
				set++
			}
		}
		if set != 1 {
			writeError(w, http.StatusBadRequest,
				fmt.Sprintf("input[%d]: exactly one of text, key, raw must be set", i), nil)
			return
		}
		switch {
		case item.Text != nil:
			steps = append(steps, step{text: *item.Text})
		case item.Key != nil:
			k, err := keymap.Parse(*item.Key)
			if err != nil {
				writeError(w, http.StatusBadRequest, fmt.Sprintf("input[%d]: %s", i, err), nil)
				return
			}
			steps = append(steps, step{key: &k})
		case item.Raw != nil:
			steps = append(steps, step{raw: []byte(*item.Raw)})
		}
	}
	for i, st := range steps {
		var err error
		switch {
		case st.key != nil:
			err = sess.SendKey(*st.key)
		case st.raw != nil:
			err = sess.SendRaw(st.raw)
		default:
			err = sess.SendText(st.text)
		}
		if err != nil {
			status := http.StatusInternalServerError
			if errors.Is(err, session.ErrExited) {
				status = http.StatusConflict
			}
			writeError(w, status, fmt.Sprintf("input[%d]: %s", i, err), nil)
			return
		}
	}
	writeJSON(w, http.StatusOK, api.InputResponse{Written: len(steps)})
}

func (s *Server) handleMouse(w http.ResponseWriter, r *http.Request) {
	sess := s.getSession(w, r)
	if sess == nil {
		return
	}
	var req api.MouseRequest
	if !decodeBody(w, r, &req) {
		return
	}
	if err := sess.SendMouse(req); err != nil {
		var merr *session.MouseError
		switch {
		case errors.As(err, &merr):
			writeError(w, http.StatusConflict, merr.Reason, &merr.Modes)
		case errors.Is(err, session.ErrExited):
			writeError(w, http.StatusConflict, err.Error(), nil)
		default:
			writeError(w, http.StatusBadRequest, err.Error(), nil)
		}
		return
	}
	writeJSON(w, http.StatusOK, map[string]bool{"ok": true})
}

func (s *Server) handleScreen(w http.ResponseWriter, r *http.Request) {
	sess := s.getSession(w, r)
	if sess == nil {
		return
	}
	format := r.URL.Query().Get("format")
	switch format {
	case "", "text", "raw":
	default:
		writeError(w, http.StatusBadRequest, fmt.Sprintf("unknown format %q (want text or raw)", format), nil)
		return
	}
	writeJSON(w, http.StatusOK, sess.Snapshot(format == "raw"))
}