validate_registry Subroutine

    subroutine validate_registry(registry_path, is_valid, error_message)
        character(len=*), intent(in) :: registry_path
        logical, intent(out) :: is_valid
        character(len=*), intent(out) :: error_message

        integer :: unit, iostat, line_num
        character(len=512) :: line
        logical :: in_packages_section, in_package, has_packages_section
        character(len=128) :: current_package

        is_valid = .true.
        error_message = ''
        line_num = 0
        has_packages_section = .false.

        open (newunit=unit, file=registry_path, status='old', iostat=iostat)
        if (iostat /= 0) then
            is_valid = .false.
            error_message = 'Cannot open registry file: '//trim(registry_path)
            return
        end if

        in_packages_section = .false.
        in_package = .false.
        current_package = ''

        do
            read (unit, '(a)', iostat=iostat) line
            if (iostat /= 0) exit

            line_num = line_num + 1
            line = adjustl(line)

            ! Skip empty lines and comments
            if (len_trim(line) == 0) cycle
            if (line(1:1) == '#') cycle

            ! Check for [packages] section
            if (line == '[packages]') then
                has_packages_section = .true.
                in_packages_section = .true.
                in_package = .false.
                cycle
            end if

            ! Check for package sections
            if (line(1:10) == '[packages.' .and. index(line, ']') > 0) then
                if (.not. in_packages_section) then
                    is_valid = .false.
          write(error_message, '(a,i0)') 'Package section found before [packages] section at line ', line_num
                    close (unit)
                    return
                end if

                current_package = extract_between(line, '[packages.', ']')
                if (len_trim(current_package) == 0) then
                    is_valid = .false.
                 write (error_message, '(a,i0)') 'Empty package name at line ', line_num
                    close (unit)
                    return
                end if

                in_package = .true.
                cycle
            end if

            ! Validate package properties
            if (in_package .and. index(line, '=') > 0) then
                if (index(line, 'git =') > 0) then
                    ! Check if git URL is properly quoted
                    if (index(line, '"') == 0) then
                        is_valid = .false.
            write(error_message, '(a,i0,a)') 'Git URL not properly quoted at line ', line_num, ' in package ', trim(current_package)
                        close (unit)
                        return
                    end if
                else if (index(line, 'version =') > 0) then
                    ! Check if version is properly quoted
                    if (index(line, '"') == 0) then
                        is_valid = .false.
            write(error_message, '(a,i0,a)') 'Version not properly quoted at line ', line_num, ' in package ', trim(current_package)
                        close (unit)
                        return
                    end if
                else if (index(line, 'prefix =') > 0) then
                    ! Check if prefix is properly quoted
                    if (index(line, '"') == 0) then
                        is_valid = .false.
            write(error_message, '(a,i0,a)') 'Prefix not properly quoted at line ', line_num, ' in package ', trim(current_package)
                        close (unit)
                        return
                    end if
                end if
            end if
        end do

        close (unit)

        if (.not. has_packages_section) then
            is_valid = .false.
            error_message = 'Registry file missing [packages] section'
            return
        end if

    end subroutine validate_registry