%D \module
%D   [       file=m-system-readers,
%D        version=2021.02.13,
%D          title=\CONTEXT\ Modules,
%D       subtitle=Reading from files,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA ADE \& \CONTEXT\ Development Team}]

%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

\startmodule[system-readers]

% \unprotect
%
% \installcorenamespace {markedlines}
%
% \permanent\protected\def\startmarkedlines[#1]%
%   {\edef\scratchstring{#1}%
%    \scratchcounter\numexpr\inputlineno+\plusone\relax
%    \gobbleuntilandfinalize\stopmarkedlines}
%
% \permanent\protected\def\stopmarkedlines
%   {\edefcsname\??markedlines\scratchstring\endcsname
%      {{\the\scratchcounter}{\the\numexpr\inputlineno+\minusone\relax}}}
%
% \protected\def\firstmarkedline#1%
%   {\numexpr
%      \ifcsname\??markedlines#1\endcsname
%        \expanded{\noexpand\firstoftwoarguments\lastnamedcs}%
%      \else
%        \zerocount
%     \fi
%    \relax}
%
% \protected\def\lastmarkedline#1%
%   {\numexpr
%      \ifcsname\??markedlines#1\endcsname
%        \expanded{\noexpand\secondoftwoarguments\lastnamedcs}%
%      \else
%        \zerocount
%     \fi
%    \relax}
%
% \protected\def\markedlines#1%
%   {\ifcsname\??markedlines\scratchstring\endcsname\lastnamedcs\else{0}{0}\fi}
%
% \protect

\startluacode

    local createtoken   = tokens.create
    local gobbletoken   = tokens.gobble
    local integer_value = tokens.values.integer

    local marked = { }

    interfaces.implement {
        name      = "startmarkedlines",
        public    = true,
        protected = true,
        arguments = "optional",
        actions   = function(tag)
            local start = status.readstate.linenumber + 1
            gobbletoken(createtoken("startmarkedlines"),createtoken("stopmarkedlines"))
            local state = status.readstate
            marked[tag] = { state.filename, start, state.linenumber - 1 }
        end
    }


    interfaces.implement {
        name      = "markedfilename",
        public    = true,
     -- usage     = "value",
        arguments = "string",
        actions   = function(tag)
            local m = marked[tag]
         -- return m and m[1] or ""
            context(m and m[1] or "")
        end
    }

    interfaces.implement {
        name      = "firstmarkedline",
        public    = true,
        usage     = "value",
        arguments = "string",
        actions   = function(tag)
            local m = marked[tag]
            return integer_value, m and m[2] or 0
        end
    }

    interfaces.implement {
        name      = "lastmarkedline",
        public    = true,
        usage     = "value",
        arguments = "string",
        actions   = function(tag)
            local m = marked[tag]
            return integer_value, m and m[3] or 0
        end
    }

\stopluacode

\continueifinputfile{m-system-readers.mkxl}

\starttext

\startmarkedlines[test]
SOME LINE 1
SOME LINE 2
SOME LINE 3
SOME LINE 4
\stopmarkedlines

\startmarkedlines[more]
SOME MORE 1
SOME MORE 2
SOME MORE 3
SOME MORE 4
\stopmarkedlines

\begingroup
    \newlocalread\myreada
    \immediate\openin\myreada {\markedfilename{test}}
    \dostepwiserecurse{\lastmarkedline{test}}{\firstmarkedline{test}}{-1}{
        \readline\myreada line #1 to \scratchstring #1 : \scratchstring \par
    }
    \immediate\closein\myreada
\endgroup

\blank

\begingroup
    \newlocalread\myreada
    \immediate\openin\myreada {\markedfilename{more}}
    \dostepwiserecurse{\firstmarkedline{more}}{\lastmarkedline{more}}{1}{
        \read    \myreada line #1 to \scratchstring #1 : \scratchstring \par
    }
    \immediate\closein\myreada
\endgroup

\stoptext