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! Copyright (c) 2020 Jeffrey Armstrong <jeff@rainbow-100.com>
!
! Permission is hereby granted, free of charge, to any person obtaining a copy
! of this software and associated documentation files (the "Software"), to deal
! in the Software without restriction, including without limitation the rights
! to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
! copies of the Software, and to permit persons to whom the Software is
! furnished to do so, subject to the following conditions:
!
! The above copyright notice and this permission notice shall be included in
! all copies or substantial portions of the Software.
!
! The Software shall be used for Good, not Evil.
!
! THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
! IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
! FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
! AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
! LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
! OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
! SOFTWARE.

module file_handling

    integer, parameter::file_type_plain_text    = 1
    integer, parameter::file_type_gemini        = 2

    character(17), parameter::end_indicator = "** END OF FILE **"

contains

    subroutine mark_file_end(unit_number)
    implicit none
    
        integer, intent(in)::unit_number
        Write(unit_number, '(A1)', advance='no') new_line('a')
        Write(unit_number, '(A17)') end_indicator
        
    end subroutine mark_file_end

    function is_file_end_marker(text)
    implicit none
    
        character(*), intent(in)::text
        logical::is_file_end_marker
        
        is_file_end_marker = (index(text, end_indicator) > 0)
        
    end function is_file_end_marker
    
    subroutine skip_line(unit_number)
    implicit none
    
        integer, intent(in)::unit_number
        
        character::c
        integer::iostatus
        
        read(unit_number, '(A1)', advance='no', iostat=iostatus) c
        do while(c /= CHAR(10) .AND. iostatus == 0)
            read(unit_number, '(A1)', advance='no', iostat=iostatus) c
        end do
        
    end subroutine skip_line
    
    subroutine read_line_text(unit_number, res, iostatus)
    implicit none
    
        character(len=:), allocatable, intent(out)::res
        integer, intent(in)::unit_number
        integer, intent(out)::iostatus
        integer::startpos, endpos, length, i
        character::c
        
        inquire(unit=unit_number, pos=startpos)
        
        endpos = startpos
        read(unit_number, '(A1)', advance='no', iostat=iostatus) c
        do while(c /= CHAR(10) .AND. iostatus == 0)
            endpos = endpos + 1
            read(unit_number, '(A1)', advance='no', iostat=iostatus) c
        end do
        
        length = (endpos - startpos + 1)
        
        allocate(character(len=length) :: res)
        res = repeat(' ', length)
        
        ! Rewind seems necessary, especially on non-Windows...
        rewind(unit_number)
        
        read(unit_number, '(A1)', pos=startpos, advance='no', iostat=iostatus) c
        if(iostatus == 0) then
            res(1:1) = c
            do i=2, length
                read(unit_number, '(A1)', advance='no', iostat=iostatus) c
                
                if(iostatus /= 0) then
                    exit
                end if
                
                res(i:i) = c
            end do
        end if
        
    end subroutine read_line_text
    
    subroutine replace_tabs(text)
    implicit none
    
        character(*), intent(inout)::text
        integer::i
        
        i = index(text, char(9))
        do while(i > 0)
            text(i:i) = ' '
            i = index(text, char(9))
        end do
    
    end subroutine replace_tabs
    
    subroutine process_line(single_line, file_type, preformatted_on)
    use layout
    implicit none
    
        type(line), intent(inout)::single_line
        integer, intent(in)::file_type
        logical, intent(inout)::preformatted_on
        
        integer::line_length

        if(file_type == file_type_plain_text) then
        
            single_line%line_type = line_type_preformatted
            preformatted_on = .TRUE.
        
        else if(file_type == file_type_gemini) then
            
            line_length = len_trim(single_line%text)
            
            if((.not. preformatted_on) .AND. line_length > 2 .AND. &
               single_line%text(1:2) == "=>") then
                
                single_line%line_type = line_type_link
                single_line%text(1:2) = "  "
                call replace_tabs(single_line%text)
                single_line%text = adjustl(single_line%text)
                
            else if(line_length >= 3 .AND. single_line%text(1:3) == "```") then
            
                preformatted_on = .not. preformatted_on
                single_line%line_type = line_type_indicator
                
            else if(preformatted_on) then
                
                single_line%line_type = line_type_preformatted
                
            else
            
                single_line%line_type = line_type_text
                
            end if
            
        end if
        
    end subroutine process_line
    
    function load_unit(unit_number, file_type) result(first_line)
    use layout
    implicit none

        integer, intent(in)::unit_number, file_type
        type(line), pointer::first_line

        type(line), pointer::walker, next_line
        integer::iostatus
        logical::preformatted_on
        
        preformatted_on = .FALSE.
        
        allocate(first_line)

        ! Skip the first line - it has the status code
        rewind(unit_number)
        call skip_line(unit_number)

        call read_line_text(unit_number, first_line%text, iostatus)
        first_line%next => null()
        first_line%breaks => null()
        
        walker=>first_line
        
        do while(iostatus /= -1 .and. .not. is_file_end_marker(walker%text))  ! -1 should be end of file
            
            call process_line(walker, file_type, preformatted_on)
            
            allocate(next_line)
            next_line%next => null()
            next_line%breaks => null()
            
            walker%next => next_line
            next_line => null()
            walker => walker%next
            
            call read_line_text(unit_number, walker%text, iostatus)
            
        end do

        if(is_file_end_marker(walker%text)) then
            walker%text = " "
        end if
    
    end function load_unit

    function load_filename(filename, iostatus, mimetype) result(first_line)
    use layout, only: line
    implicit none
    
        character(*), intent(in)::filename
        integer, intent(out)::iostatus
        character(*), intent(in), optional::mimetype
        
        type(line), pointer::first_line
        
        integer::filetype
        
        open(unit=1097, file=filename, access='stream', iostat=iostatus, form='FORMATTED')
        if(iostatus == 0) then
        
            if(present(mimetype)) then
                if(trim(mimetype) == 'text/gemini') then
                    filetype = file_type_gemini
                else
                    filetype = file_type_plain_text
                end if
            else
                filetype = file_type_plain_text
            end if
            
            first_line => load_unit(1097, filetype)
        end if
    
    end function load_filename
    
end module file_handling