// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

package server

import (
	"context"
	"errors"
	"io"
	"net"
	"testing"
	"time"
)

func dial(t *testing.T, addr string) net.Conn {
	t.Helper()
	conn, err := net.Dial("tcp", addr)
	if err != nil {
		t.Fatalf("dial %s: %v", addr, err)
	}
	t.Cleanup(func() { conn.Close() })
	return conn
}

func TestServeHandsConnectionsToHandle(t *testing.T) {
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("listen: %v", err)
	}

	accepted := make(chan net.Conn, 2)
	s := &Server{Handle: func(conn net.Conn) {
		accepted <- conn
		conn.Close()
	}}

	ctx, cancel := context.WithCancel(context.Background())
	serveErr := make(chan error, 1)
	go func() { serveErr <- s.Serve(ctx, ln) }()

	for range 2 {
		conn := dial(t, ln.Addr().String())
		select {
		case got := <-accepted:
			if got.RemoteAddr() == nil {
				t.Fatal("a connection without a remote address arrived")
			}
		case <-time.After(2 * time.Second):
			t.Fatal("the connection did not reach Handle")
		}
		// Handle closed the connection, so the next read reports it.
		if _, err := conn.Read(make([]byte, 1)); !errors.Is(err, io.EOF) {
			t.Fatalf("read after Handle returned: %v", err)
		}
	}

	cancel()
	select {
	case err := <-serveErr:
		if err != nil {
			t.Fatalf("Serve returned %v after cancellation", err)
		}
	case <-time.After(2 * time.Second):
		t.Fatal("Serve did not return after cancellation")
	}
}

func TestServeClosesWithoutHandle(t *testing.T) {
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("listen: %v", err)
	}

	s := &Server{}
	ctx, cancel := context.WithCancel(context.Background())
	serveErr := make(chan error, 1)
	go func() { serveErr <- s.Serve(ctx, ln) }()

	conn := dial(t, ln.Addr().String())
	if _, err := conn.Read(make([]byte, 1)); !errors.Is(err, io.EOF) {
		t.Fatalf("a connection without Handle read %v, want EOF", err)
	}

	cancel()
	select {
	case err := <-serveErr:
		if err != nil {
			t.Fatalf("Serve returned %v after cancellation", err)
		}
	case <-time.After(2 * time.Second):
		t.Fatal("Serve did not return after cancellation")
	}
}

func TestServeListenerFailure(t *testing.T) {
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("listen: %v", err)
	}
	if err := ln.Close(); err != nil {
		t.Fatalf("close: %v", err)
	}

	// A closed listener is a stop, not a failure: the shutdown raced the
	// accept loop, and the daemon exits cleanly either way.
	s := &Server{}
	if err := s.Serve(context.Background(), ln); err != nil {
		t.Fatalf("Serve returned %v for a closed listener, want nil", err)
	}
}

func TestServeCapsConnections(t *testing.T) {
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("listen: %v", err)
	}

	// The first connection holds its slot until released, so the state of
	// the cap is deterministic for the second.
	release := make(chan struct{})
	s := &Server{MaxConns: 1, Handle: func(conn net.Conn) {
		<-release
		conn.Close()
	}}

	ctx, cancel := context.WithCancel(context.Background())
	serveErr := make(chan error, 1)
	go func() { serveErr <- s.Serve(ctx, ln) }()

	first := dial(t, ln.Addr().String())
	// The refused connection ends at once: the read sees the close, not a
	// timeout.
	refused := dial(t, ln.Addr().String())
	refused.SetReadDeadline(time.Now().Add(2 * time.Second))
	if _, err := refused.Read(make([]byte, 1)); !errors.Is(err, io.EOF) {
		t.Fatalf("a connection above the cap read %v, want the immediate end", err)
	}
	close(release)
	first.Close()

	cancel()
	select {
	case err := <-serveErr:
		if err != nil {
			t.Fatalf("Serve returned %v after cancellation", err)
		}
	case <-time.After(2 * time.Second):
		t.Fatal("Serve did not return after cancellation")
	}
}