// Fenrir console screen reader.
// Copyright (c) 2026 Storm Dragon
// SPDX-License-Identifier: GPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option)
// any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
// more details.
//
// You should have received a copy of the GNU General Public License along with
// this program. If not, see <https://www.gnu.org/licenses/gpl-3.0.html>.

//go:build linux && cgo

package terminal

import (
	"bytes"
	"errors"
	"os"
	"syscall"
	"testing"
)

func TestTerminalOutputBackpressurePreservesBytes(t *testing.T) {
	var pipeFds [2]int
	if err := syscall.Pipe2(pipeFds[:], syscall.O_NONBLOCK|syscall.O_CLOEXEC); err != nil {
		t.Fatal(err)
	}
	defer func() {
		if pipeFds[0] >= 0 {
			syscall.Close(pipeFds[0])
		}
	}()
	output := os.NewFile(uintptr(pipeFds[1]), "terminal-output")
	defer output.Close()
	want := bytes.Repeat([]byte("\x1b[1mredraw é界\x1b[0m\r\n"), 16384)
	session := &Session{output: output, outputPending: bytes.Clone(want)}
	if err := session.flush_output(); err != nil {
		t.Fatal(err)
	}
	remaining := len(session.outputPending)
	if remaining == 0 || remaining == len(want) {
		t.Fatalf("expected partial write, %d of %d bytes remain", remaining, len(want))
	}
	if err := session.flush_output(); err != nil || len(session.outputPending) != remaining {
		t.Fatalf("full output must defer without losing data: remaining=%d err=%v", len(session.outputPending), err)
	}
	var got []byte
	var buffer [4096]byte
	for {
		n, err := syscall.Read(pipeFds[0], buffer[:])
		if n > 0 {
			got = append(got, buffer[:n]...)
		}
		if errors.Is(err, syscall.EAGAIN) {
			if len(session.outputPending) == 0 {
				break
			}
			if err := session.flush_output(); err != nil {
				t.Fatal(err)
			}
		} else if err != nil {
			t.Fatal(err)
		}
	}
	if !bytes.Equal(got, want) {
		t.Fatalf("terminal output changed: got %d bytes, want %d", len(got), len(want))
	}
	// A closed terminal remains an error; only temporary fullness is retried.
	syscall.Close(pipeFds[0])
	pipeFds[0] = -1
	session.outputPending = []byte("closed")
	if err := session.flush_output(); !errors.Is(err, syscall.EPIPE) {
		t.Fatalf("closed output: %v", err)
	}
}