package console

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/novox/mesh-tools/node-tools/internal/wire"
)

// bodyLimit is the most a request body may be.
const bodyLimit = 1 << 20

var loopback = map[string]bool{"127.0.0.1": true, "::1": true, "localhost": true, "[::1]": true}

// Listening is a console that listens: where, with the port the machine gave, and how to stop it.
type Listening struct {
	Address string
	Close   func() error
}

// Serve listens on host:port, refused unless the host is loopback — said before binding, so a
// console that would open to a network is a startup failure (ADR 0152).
func Serve(s *Surface, listen string) (*Listening, error) {
	at := strings.LastIndex(listen, ":")
	if at < 0 {
		return nil, fmt.Errorf("%q is not host:port", listen)
	}
	host, portText := listen[:at], listen[at+1:]
	if !loopback[host] {
		return nil, fmt.Errorf(`the console listens on loopback and nowhere else (novox/hq ADR 0152): %q is not this `+
			"machine's own address — whoever is on the machine owns the mesh there, and nobody else may reach this", host)
	}
	port, err := strconv.Atoi(portText)
	if err != nil || port < 0 || port > 65535 {
		return nil, fmt.Errorf("%q is not a port", portText)
	}
	ln, err := net.Listen("tcp", net.JoinHostPort(strings.Trim(host, "[]"), portText))
	if err != nil {
		return nil, err
	}
	// Every request's context ends when the console is closed, so a mesh_wait in flight ends at once rather
	// than holding a stop or a restart for up to its ten minutes (the review of issue 745).
	base, cancel := context.WithCancel(context.Background())
	server := &http.Server{Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { route(w, r, s) }),
		BaseContext: func(net.Listener) context.Context { return base }}
	go func() { _ = server.Serve(ln) }()
	bound := ln.Addr().(*net.TCPAddr).Port
	return &Listening{Address: host + ":" + strconv.Itoa(bound), Close: func() error {
		cancel()
		// A backstop: what is still answering after the cancel is cut off, never waited on for long.
		ctx, done := context.WithTimeout(context.Background(), ShutdownWithin)
		defer done()
		err := server.Shutdown(ctx)
		if errors.Is(err, context.DeadlineExceeded) {
			return server.Close()
		}
		return err
	}}, nil
}

// ShutdownWithin is how long closing the console waits for the requests still being answered after their
// context was cancelled.
var ShutdownWithin = 5 * time.Second

func route(w http.ResponseWriter, r *http.Request, s *Surface) {
	switch r.URL.Path {
	case "/":
		w.Header().Set("content-type", "text/plain; charset=utf-8")
		_, _ = io.WriteString(w, "the mesh's console: MCP over HTTP at POST /mcp (novox/hq design 34)\n")
		return
	case "/mcp":
	default:
		writeJSON(w, 404, map[string]any{"error": "the console serves /mcp and nothing else"})
		return
	}
	switch r.Method {
	case http.MethodPost:
	case http.MethodDelete:
		w.WriteHeader(204) // no session to end
		return
	default:
		w.Header().Set("allow", "POST, DELETE")
		w.WriteHeader(405)
		return
	}
	body, err := io.ReadAll(io.LimitReader(r.Body, bodyLimit+1))
	if err != nil || len(body) > bodyLimit {
		if err == nil {
			err = fmt.Errorf("the request is larger than %d bytes", bodyLimit)
		}
		writeJSON(w, 413, map[string]any{"jsonrpc": "2.0", "id": nil, "error": map[string]any{"code": -32600, "message": err.Error()}})
		return
	}
	trimmed := strings.TrimSpace(string(body))
	if strings.HasPrefix(trimmed, "[") {
		var batch []Request
		if err := json.Unmarshal(body, &batch); err != nil {
			writeJSON(w, 400, map[string]any{"jsonrpc": "2.0", "id": nil, "error": map[string]any{"code": -32700, "message": "the body is not JSON"}})
			return
		}
		replies := []*Reply{}
		for _, req := range batch {
			if reply := s.HandleContext(r.Context(), req); reply != nil {
				replies = append(replies, reply)
			}
		}
		if len(replies) == 0 {
			w.WriteHeader(202)
			return
		}
		writeJSON(w, 200, replies)
		return
	}
	var req Request
	if err := json.Unmarshal(body, &req); err != nil {
		writeJSON(w, 400, map[string]any{"jsonrpc": "2.0", "id": nil, "error": map[string]any{"code": -32700, "message": "the body is not JSON"}})
		return
	}
	reply := s.HandleContext(r.Context(), req)
	if reply == nil {
		w.WriteHeader(202)
		return
	}
	writeJSON(w, 200, reply)
}

func writeJSON(w http.ResponseWriter, status int, body any) {
	text, err := wire.Marshal(body)
	if err != nil {
		text, _ = json.Marshal(map[string]any{"error": errors.New("unencodable answer").Error()})
	}
	w.Header().Set("content-type", "application/json; charset=utf-8")
	w.Header().Set("content-length", strconv.Itoa(len(text)))
	w.WriteHeader(status)
	_, _ = w.Write(text)
}