#!/usr/bin/perl -w
# $Id: github_md2html 1189 2019-07-13 16:41:07Z mueller $
# SPDX-License-Identifier: GPL-3.0-or-later
# Copyright 2016-2019 by Walter F.J. Mueller <W.F.J.Mueller@gsi.de>
#
#  Revision History:
# Date         Rev Version  Comment
# 2019-07-13  1189   1.1.5  drop superfluous exists for $opts
# 2018-12-18  1089   1.1.4  add and use bailout
# 2018-10-19  1057   1.1.3  add --verbose; don't list up-to-date files anymore
# 2018-07-02  1033   1.1.2  use non-greedy match in -stand code
# 2018-05-13  1021   1.1.1  handle fragment identifiers in -standalone mapping
# 2017-01-02   837   1.1    add -standalone and -trace; add rate wait
# 2016-12-17   823   1.0    Initial version
#

use 5.14.0;                                 # require Perl 5.14 or higher
use strict;                                 # require strict checking
use Getopt::Long;
use LWP::UserAgent;
use JSON::XS;

my %opts = ();

GetOptions(\%opts,
           "context:s", "force", "standalone", "trace", "verbose",
           "dump", "help")
  or bailout("bad command options");

my $url_ghapi_md     = "https://api.github.com/markdown";
my $url_ghapi_mdraw  = "https://api.github.com/markdown/raw";
my $url_css_ghmd     = "https://wfjm.github.io/css/github-markdown.css";
my $url_css_ghmdbody = "https://wfjm.github.io/css/github-markdown-body.css";

autoflush STDOUT 1 if (-p STDOUT);          # autoflush if output into pipe
autoflush STDOUT 1 if (-t STDOUT);          # autoflush if output into term

if ($opts{help}) {
  print_help();
  exit 0;
}

my @flist;
foreach my $arg (@ARGV) {
  if  (! -e $arg) {
    print STDERR "github_md2html-E: file or directory '$arg' not found\n";
  } elsif (-f $arg) {
    push @flist, $arg;
  } elsif (-d $arg) {
    open (FFILE, "find $arg -name '*.md' -type f | sort |")
      or bailout("Failed to run 'find $arg': $!");
    while (<FFILE>) {
      chomp;
      push @flist, $_;
    }
    close FFILE;
  } elsif (-l $arg) {
    print STDERR "github_md2html-W: symlink '$arg' ignored\n";
  } else {
    print STDERR "github_md2html-E: '$arg' not file or directory, ignored\n";
  }
}

unless (scalar @flist) {
  print STDERR "github_md2html-E: no files specified of found\n";
  print_help();
  exit 1;
}

foreach my $file (@flist) {
  do_md2html($file);
}

#-------------------------------------------------------------------------------

sub do_request {
  my ($ifile,$ua,$req) = @_;
  for (my $nretry=0; $nretry<10; $nretry++) {
    my $res  = $ua->request($req);

    if ($opts{dump}) {
      print "------------------------------------------------------\n";
      print "response for $ifile\n";
      print $res->as_string,"\n";
      print "------------------------------------------------------\n";
    }

    return $res if $res->is_success;

    my $rate_limit  = $res->header('X-RateLimit-Limit');
    my $rate_remain = $res->header('X-RateLimit-Remaining');
    my $rate_reset  = $res->header('X-RateLimit-Reset');
    if ($res->status_line eq '403 Forbidden' &&
        defined $rate_limit && defined $rate_remain && defined $rate_reset &&
        $rate_remain == 0) {
      my $twait  = $rate_reset - time;
      my $twait_min = $twait / 60;
      my $twait_sec = $twait % 60;
      printf "github_md2html-I: rate limit %d/hr reached, wait %2dm%02ds\n",
        $rate_limit,
          $twait_min, $twait_sec;
      sleep $twait+1;
    } else {
      print STDERR "github_md2html-E: api error:'" . $res->status_line . "'\n";
      print STDERR "response for $ifile\n";
      print STDERR $res->as_string,"\n";
      return undef;
    }
  }
  print STDERR "github_md2html-E: retry limit reached\n";
  return undef;
}

#-------------------------------------------------------------------------------

sub do_md2html {
  my ($ifile) = @_;
  my $ofile = "$ifile.html";
  my $doit = $opts{force} || (not -e $ofile);

  unless ($doit) {
    # -M returns <script_start_time> - <file_modify_time> in fractional days
    # --> thus file age in days relative to now
    $doit = -M $ofile > -M $ifile;      # output older than input
  }

  unless ($doit) {
    print "$ifile: ok\n" if $opts{verbose};
    return;
  }

  # get file path and name
  my $ifile_path = '.';
  my $ifile_name = $ifile;
  if ($ifile =~ m|^(.+)/(.+)|) {
    $ifile_path = $1;
    $ifile_name = $2;
  }

  # read input file
  my $idata;
  {
    local $/;                               # slurp file ...
    open IFILE, $ifile or bailout("file read open for '$ifile' failed: $!");
    $idata = <IFILE>;
    close IFILE;
  }

  # prepare request
  my $ua = LWP::UserAgent->new;
  my $req;

  # with context --> use markdown api (json based)
  if (exists $opts{context}) {
    $req = HTTP::Request->new('POST', $url_ghapi_md);
    my %apireq = ('mode'    => 'gfm',
                  'context' => $opts{context},
                  'text'    => $idata
                 );
    my $apireq_json = encode_json(\%apireq);
    $req->content($apireq_json);

  # no context --> use markdown/raw api
  } else {
    $req = HTTP::Request->new('POST', $url_ghapi_mdraw);
    $req->content_type('text/x-markdown');
    $req->content($idata);
  }

  if ($opts{dump}) {
    print "------------------------------------------------------\n";
    print "request for $ifile\n";
    print $req->as_string,"\n";
  }

  my $res  = do_request($ifile, $ua, $req);
  return unless defined $res;

  my $html = $res->decoded_content;

  if ($opts{standalone}) {
    $html =~ s{<a(.*?)href="(.+?)"}{        # non-greedy matches !!
      my $hopt = $1;
      my $href = "$2";
      unless ($href =~ m|^https?://|) {
        if ($href =~ m|^(.+\.md)(#.*)?$|) {
          $href  = $1 . '.html';
          $href .= $2 if defined $2;
          print "  hmap: $href\n" if $opts{trace};
        } else {
          if (-d "$ifile_path/$href") {
            $href =~ s|/$||;                # drop trailing '/'
            if (-r "$ifile_path/$href/README.md") {
              $href .= '/README.md.html';
              print "  dmap: $href: ok\n" if $opts{trace};
            } else {
              print "  dmap: $href: skipped\n" if $opts{trace};
            }
          }
        }
      }
      "<a${hopt}href=\"$href\"";
    }gex;
  }

  open OFILE, ">$ofile" or bailout("file write open for '$ofile' failed: $!");
  print OFILE '<!DOCTYPE html>',"\n";
  print OFILE '<html>',"\n";
  print OFILE '<head>',"\n";
  print OFILE '  <meta http-equiv="Content-Type"',
                       ' content="text/html; charset=UTF-8">',"\n";
  print OFILE '  <meta name="generator"',
                       ' content="github_md2html via github api">',"\n";
  print OFILE '  <link rel="stylesheet"',
                       ' href="',$url_css_ghmd,'">',"\n";
  print OFILE '  <link rel="stylesheet"',
                       ' href="',$url_css_ghmdbody,'">',"\n";
  print OFILE '</head>',"\n";
  print OFILE '<body class="markdown-body">',"\n";
  if ($opts{standalone} && $ifile_name eq 'README.md') {
    print OFILE '<p><i>Directory README.',"\n";
    print OFILE 'To <a href=".">local directory listing</a></i>.</p>',"\n";
  }
  print OFILE $html,"\n";
  print OFILE '</body>',"\n";
  print OFILE '</html>',"\n";
  close OFILE;

  my $rate_limit  = $res->header('X-RateLimit-Limit');
  my $rate_remain = $res->header('X-RateLimit-Remaining');
  my $rate_reset  = $res->header('X-RateLimit-Reset');
  my $time_reset  = $rate_reset - time;
  my $reset_min   = $time_reset / 60;
  my $reset_sec   = $time_reset % 60;

  printf "%s: done, rate %d of %d for %2dm%02ds\n",
    $ifile, $rate_remain, $rate_limit, $reset_min, $reset_sec;
}

#-------------------------------------------------------------------------------

sub bailout {
  my ($msg) = @_;
  print STDERR "github_md2html-F: $msg\n";
  exit 1;
}

#-------------------------------------------------------------------------------

sub print_help {
  print "usage: github_md2html [opts] files...\n";
  print "  --force        update all (default: check timestamps)\n";
  print "  --standalone   modify links for local browser usage\n";
  print "  --trace        trace link mapping in standalone mode\n";
  print "  --context c    uses context and markdown api (default: raw api)\n";
  print "  --dump         print HTTP request and response\n";
  print "  --help         this message\n";
}