#!/usr/bin/env perl
# TODO:
# implement -s and -r flags
# implement --timeout flag in main loop
# possibly create a man page
#
# listen: a simple configurable build system
# created by Bryson Steck, @brysonsteck on GitHub
# free and open source under the GPL Version 3
# 
# Usage
# listen [flags] [file(s) to watch] [command(s) to run on file changes]
# 
# Flags
# -a, --all if all of the files have changed, required if multiple files
# -o, --any if any one of the files have changed, required if multiple files
# -s to use checksum on file change instead of when the file was modified
# -r, --run immediately run exec command, then start listening
# --timeout=[time] change timeout time in whole seconds (DEFAULT 1 SECOND)
# --help prints help

# GLOBALS
local $| = 1;
my $VERSION = "0.1.0";
my $ARGC = scalar @ARGV;
my $TIMEOUT = 1;
my $START_LISTEN = 0;
my $EXEC_POSITION = $ARGC - 1;
my $EXEC_LISTEN = undef;
my $ALL_FLAG = undef;
my $ANY_FLAG = undef;
my $MULTI_FILES = undef;
my $CHECKSUM_FLAG = undef;
my $CHECKSUM_COMMAND = "/usr/bin/env cksum";
my $RUN_NOW = undef;
my $black = "\033[0;90m";
my $nocolor = "\033[0m";

sub flags {
  if ($ARGC == 0) {
    print "listen: To what?\n";
    exit 2;
  }

  my $current_arg = 0;

  foreach $arg (@ARGV) {
    if ($arg =~ m/-[aosrhv]/) {
      if ($arg =~ m/a/) {
        $ALL_FLAG = "def";
      } 
      if ($arg =~ m/o/) {
        $ANY_FLAG = "def";
      }
      if ($arg =~ m/s/) {
        $CHECKSUM_FLAG = "def";
      }
      if ($arg =~ m/r/) {
        $RUN_NOW = "def";
      }
      if ($arg =~ m/h/) {
        print "\nlisten v$VERSION - a simple automation system\n";
        print "Copyright 2022 Bryson Steck\n";
        print "Free and open source under the GNU General Public License v3.\n";
        print "Run 'listen --license' to view the license and warranty disclaimer.\n\n";
        print "usage: listen [-v | --version] [-h | --help] [-a | --all]\n";
        print "              [-o | --any] [-s] [-r | --run] FILE1 [FILE2 ...]\n";
        print "              COMMAND\n\n";
        print "informational flags:\n";
        print "  -h | --help    -> Print this message\n";
        print "  -v | --version -> Print the version of listen\n";
        print "  --license      -> Print the license/warranty disclaimer\n";
        print "                    (GNU General Public License v3)\n\n";
        print "multiple file flags:\n";
        print "  -a | --all     -> Run COMMAND if ALL of the files have been modified\n";
        print "  -o | --any     -> Run COMMAND if ANY of the files have been modified\n\n";
        print "other flags:\n";
        print "  -r | --run     -> Run COMMAND before starting listen\n";
        print "  -s             -> Check for file modification based on cksum\n";
        print "                    (as opposed to the files' modified timestamp)\n\n";
        exit 1;
      }
      if ($arg =~ m/v/) {
        print "listen v$VERSION\n";
      }
    } elsif ($arg =~ m/--timeout=/) {
      my @timeout_split = split /\=/, $arg;
      if (scalar @timeout_split == 1) {
        print "timeout flag invalid\n";
        exit 2;
      } elsif (int($timeout_split[1]) > 0) {
        $TIMEOUT = $timeout_split[1];
        print "timeout is now $TIMEOUT seconds\n";
      } else {
        print "timeout flag invalid\n";
        exit 2;
      }
    } elsif ($arg =~ m/--help/) {
      print "\nlisten v$VERSION - a simple automation system\n";
      print "Copyright 2022 Bryson Steck\n";
      print "Free and open source under the GNU General Public License v3.\n";
      print "Run 'listen --license' to view the license and warranty disclaimer.\n\n";
      print "usage: listen [-v | --version] [-h | --help] [-a | --all]\n";
      print "              [-o | --any] [-s] [-r | --run] FILE1 [FILE2 ...]\n";
      print "              COMMAND\n\n";
      print "informational flags:\n";
      print "  -h | --help    -> Print this message\n";
      print "  -v | --version -> Print the version of listen\n";
      print "  --license      -> Print the license/warranty disclaimer\n";
      print "                    (GNU General Public License v3)\n\n";
      print "multiple file flags:\n";
      print "  -a | --all     -> Run COMMAND if ALL of the files have been modified\n";
      print "  -o | --any     -> Run COMMAND if ANY of the files have been modified\n\n";
      print "other flags:\n";
      print "  -r | --run     -> Run COMMAND before starting listen\n";
      print "  -s             -> Check for file modification based on cksum\n";
      print "                    (as opposed to the files' modified timestamp)\n\n";
      exit 1;
    } elsif ($arg =~ m/--version/) {
      print "listen v$VERSION\n";
      exit 1;
    } elsif ($arg =~ m/--license/) {
      print "listen is free and open source under the GNU GPL Version 3.0.\n\n";
      print "This program is free software: you can redistribute it and/or modify\n";
      print "it under the terms of the GNU General Public License as published by\n";
      print "the Free Software Foundation, either version 3 of the License, or\n";
      print "(at your option) any later version.\n\n";
      print "This program is distributed in the hope that it will be useful,\n";
      print "but WITHOUT ANY WARRANTY; without even the implied warranty of\n";
      print "MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the\n";
      print "GNU General Public License for more details.\n\n";
      print "You should have received a copy of the GNU General Public License\n";
      print "along with this program.  If not, see <https://www.gnu.org/licenses/>.\n";
      exit 1;
    } elsif ($arg =~ m/--all/) {
      $ALL_FLAG = "def";
    } elsif ($arg =~ m/--any/) {
      $ANY_FLAG = "def";
    } elsif ($arg =~ m/--run/) {
      $RUN_NOW = "def";
    } else {
      last;
    }
    $current_arg++;
  }

  $START_LISTEN = $current_arg;
}

sub get_exec {
  if ($START_LISTEN + 1 == $ARGC) {
    print "listen: Not enough arguments\n";
    exit 3;
  }

  $EXEC_LISTEN = $ARGV[-1];
}

sub require_flags {
  if ($EXEC_POSITION - $START_LISTEN != 1) {
    if (!$ALL_FLAG and !$ANY_FLAG) {
      print "listen: Either -a or -o must be specified with multiple files to watch\n";
      exit 4;
    } elsif ($ALL_FLAG and $ANY_FLAG) {
      print "listen: You must specify either -a or -o for multiple files, not both\n";
      exit 4;
    }

    $MULTI_FILES = "def";
  }
}

sub check_files {
  for (my $i = $START_LISTEN; $i < $EXEC_POSITION; $i++) {
    if (not -e $ARGV[$i]) {
      print "listen: $ARGV[$i]: No such file or directory\n";
      exit 5;
    } elsif (not -r $ARGV[$i]) {
      print "listen: $ARGV[$i]: Permission denied (warning)\n";
    }
  }
}

sub diff {
  if ($CHECKSUM_FLAG) {
    #my $checksum_files;
    #for (my $i = $START_LISTEN; $i < $EXEC_POSITION; $i++) {
    #  $checksum_files = $checksum_files + " $ARGV[$i]";
    #}
    #print "$CHECKSUM_COMMAND $checksum_files";
    #return `$CHECKSUM_COMMAND $checksum_files`
  } else {
    my @return;

    for (my $i = $START_LISTEN; $i < $EXEC_POSITION; $i++) {
      push @return, (stat($ARGV[$i]))[9];
    }

    return @return;
  }
}

sub start {
  if (!$MULTI_FILES) {
    if ($EXEC_LISTEN =~ m/ _ /) {
      $EXEC_LISTEN =~ s/ _ / $ARGV[$START_LISTEN] /g;
    } elsif ($EXEC_LISTEN =~ m/ _/) {
      $EXEC_LISTEN =~ s/ _/ $ARGV[$START_LISTEN] /g;
    } elsif ($EXEC_LISTEN =~ m/_ /) {
      $EXEC_LISTEN =~ s/_ / $ARGV[$START_LISTEN] /g;
    }
  }

  print "$black& listen $VERSION\n";
  print "& This program is free software, and comes with ABSOLUTELY NO WARRANTY.\n";
  print "& Run 'listen --license' for details.\n&\n";
  print "& This shell command will run:\n";
  print "&   $EXEC_LISTEN\n";

  if ($MULTI_FILES) {
    if ($ALL_FLAG) {
      print "& When all the files below have been modified:\n";
      for (my $i = $START_LISTEN; $i < $EXEC_POSITION; $i++) {
        print "&   $ARGV[$i]\n";
      }
    } elsif ($ANY_FLAG) {
      print "& When any of the files below have been modified:\n";
      for (my $i = $START_LISTEN; $i < $EXEC_POSITION; $i++) {
        print "&   $ARGV[$i]\n";
      }
    }
  } else {
    print "& When this file has been modified:\n";
    print "&   $ARGV[$START_LISTEN]\n";
  }

  if ($RUN_NOW) {
    print "${black}& Running now, then starting listen...${nocolor}\n";
    system $EXEC_LISTEN;
    my $status = $? >> 8;
    if (int($status) != 0) {
      print "$black& WARNING: Exit code is $status. Returned to listen...$nocolor\n";
    } else {
      print "$black& Returned to listen...$nocolor\n";
    }
  } else {
    print "${black}& Starting now...${nocolor}\n";
  }

  my @previous_epoch = diff();
  my @current_epoch = diff();
  my @modified_files;

  for (my $i = $START_LISTEN; $i < $EXEC_POSITION; $i++) {
    push @modified_files, "no";
  }

  while (1) {
    my $run = undef;
    my $file_changed = undef;
    @current_epoch = diff();

    if ($MULTI_FILES) {
      if ($ALL_FLAG) {
        my $counter = 0;

        foreach $modified (@modified_files) {
          if (@current_epoch[$counter] != @previous_epoch[$counter]) {
            $modified = "yes";
          }
          $counter++;
        }
        foreach $modified (@modified_files) {
          my $run = 'def';
          if ($modified !~ "yes") {
            $run = undef;
          }
        }
      } else {
        my $counter = 0;

        foreach (@current_epoch) {
          if ($current_epoch[$counter] != $previous_epoch[$counter]) {
            $run = "def";
            $file_changed = $counter;
          }
          $counter++;
        }
      }
    } else {
      if ($current_epoch[0] != $previous_epoch[0]) {
        $run = "def";
        $file_changed = 0;
      }
    }

    if ($run) {
      if ($MULTI_FILES) {
        print "$black& File \"$ARGV[$file_changed + 1]\" modified. Running command...$nocolor\n";
      } else {
        print "$black& File \"$ARGV[$START_LISTEN]\" modified. Running command...$nocolor\n";
      }
      system $EXEC_LISTEN;
      my $status = $? >> 8;
      if (int($status) != 0) {
        print "$black& WARNING: Exit code is $status. Returned to listen...$nocolor\n";
      } else {
        print "$black& Returned to listen...$nocolor\n";
      }

      @previous_epoch = @current_epoch;
    }

    sleep(1);
  }
}

# ---- START OF SCRIPT ----
# start by checking flags
flags();

# get executable to run on trigger
get_exec();

# check if additional flags are needed 
# because multiple files are being listened to
require_flags();

# check if file(s) exist
check_files();

# start listen
start();