func ReadLastNLines()

in internal/utils/file/file.go [227:282]

• 46 lines of code
• 12 McCabe index (conditional complexity)

func ReadLastNLines(path string, n int) ([]string, error) {
	galog.Debugf("Reading last %d lines of file %q", n, path)

	f, err := os.Open(path)
	if err != nil {
		return nil, fmt.Errorf("failed to open file %q: %w", path, err)
	}
	defer f.Close()

	stat, err := f.Stat()
	if err != nil {
		return nil, fmt.Errorf("failed to stat file %q: %w", path, err)
	}

	size := stat.Size()
	bufferSize := int64(1024)

	buffer := make([]byte, bufferSize)
	var lines []string
	var chunk []byte

	for offset := size - 1; offset >= 0; offset -= bufferSize {
		start := offset - bufferSize
		if start < 0 {
			start = 0
		}

		readSize := int(offset - start + 1)

		_, err := f.ReadAt(buffer[:readSize], start)
		if err != nil && !errors.Is(err, io.ErrUnexpectedEOF) {
			return nil, err
		}

		for i := readSize - 1; i >= 0; i-- {
			if buffer[i] == '\n' {
				lines = append([]string{string(chunk)}, lines...)
				chunk = nil
				if len(lines) >= n {
					return lines, nil
				}
			} else {
				chunk = append([]byte{buffer[i]}, chunk...)
			}
		}

		if len(chunk) > 0 {
			lines = append([]string{string(chunk)}, lines...)
		}

		if len(lines) >= n {
			return lines[len(lines)-n:], nil
		}
	}
	return lines, nil
}