#!/usr/bin/env perl

use strict;
use warnings;
use List::Util qw(first);

# On-the-fly urxvt font resizing.  Like ⌘{+,-}, on mac computers, just
# way more complicated.
#
# Noah K. Tilton <lists@tilton.co>
#
# What it does:
#
# 1) Emits escape sequences to change the font size in the running console;
# 2) Persists the changed font size to xresources file.
#
# Note: For the time being, the Monaco font is treated as a special
# case, due to Unicode compatibility issues.  Other fonts may need
# special treatment, but I'm not using them.  In particular, Monaco only
# supports unicode in certain pixel sizes.  9, 10, 12, 14 are embedded
# bitmaps, which means (Except for 10) that they lack certain unicode
# charmaps.
#
# Note: the regexes will only work on xft xrdb entries

#   For this script to work, ~/.Xdefauls should probably contain at
#   least the following:
#
#       urxvt*font
#       urxvt*boldFont
#       urxvt*boldColors: on
#
# References: man 3 urxvtperl
#
#  Debugging:   urxvt --perl-lib ${HOME}/.urxvt -pe font


use constant X_RESOURCES => "~/.config/xresources/fonts";

# Whether to restrict Monaco to using only point sizes that support
# unicode.
use constant UNICODE_ONLY => 0;
use constant ENABLE_DPI_SCALING => 1;

use constant FONT_PROPS => qw/font imFont boldFont italicFont boldItalicFont/;
use constant STANDARD_DPI => 75;
use constant MM_TO_INCH => 0.0393701;

sub _resize_xft_string
{
  my ($self, $key, $delta)      = @_;
  my (@pieces)                  = split /:/, $self->{fonts}{$key};
  my (@resized)                 = ();
  my ($monaco)                  = undef;

  foreach my $piece (@pieces)
  {
    # Assumption: xft:fontname comes before pixelsize=whatever
    $monaco ||= $piece =~ /^Monaco/i;

    # matching string
    if ($piece =~ /pixelsize=(\d*)/)
    {
      my ($old_size)    =  $1;
      my ($new_size)    =  $old_size;

      # monaco font
      if ($monaco)
      {
        my (@monaco_unicode_sizes) = UNICODE_ONLY 
                                        ? (8, 9, 10, 11, 13, 15, 16, 18, 21, 22, 28)
                                        : (1 .. 72) ;

        my ($monaco_default_size) = &{ sub {  my @a = sort { $a <=> $b } @_;
                                            return ($a[$#a/2] + $a[@a/2]) / 2;}
        }(@monaco_unicode_sizes); # median ...
        my ($old_size_index) = first {
          $monaco_unicode_sizes[$_] eq $old_size } 0..$#monaco_unicode_sizes;

        # old font size is valid
        if (defined($old_size_index))
        {
          # Do bounds checking:
          #
          # 1) avoid decrement of smallest font size index to a negative
          # value --which would undesirably wrap around and set font to
          # larger size
          if ($old_size_index > 0 || $delta > 0)
          {
            my ($new_size_index)  = $old_size_index + $delta; # +1, equivalently
            # 2) avoid increment of largest to non-existent larger
            $new_size             = exists($monaco_unicode_sizes[$new_size_index])
                                            ? $monaco_unicode_sizes[$new_size_index]
                                            : $old_size;
          }
        }
        else
        {
          # user had an invalid/non-unicode monaco size, reset to default
          $new_size  = $monaco_default_size;
        }
      }
      else
      {
        $new_size += $delta;
      }
      $piece =~ s/pixelsize=$old_size/pixelsize=$new_size/;
    }
    push @resized, $piece;
  }
  return join (":", @resized);
}

sub _scale_xft_string
{
  my ($self, $str) = @_;

  $str =~ s/pixelsize=(\d+)/"pixelsize=" . ($1 * $self->{dpi} \/ STANDARD_DPI)/eg;
  return $str;
}

sub update_display
{
  my ($self) = @_;

  # Update internal urxvt resource hash
  #     This is necessary or else the next resize won't have an updated
  #     value. "font" key is updated by urxvt when cmd_parse is called,
  #     but boldFont is *not*, at least with the escape sequences I'm
  #     emitting.
  foreach my $res (FONT_PROPS) {
    $self->{term}->resource($res, $self->_scale_xft_string($self->{fonts}{$res}));
  }

  my $scaled = $self->{term}->resource("font");
  $self->{term}->cmd_parse("\e]710;$scaled\007");
}

sub change_size
{
  my ($self, $delta) = @_;

  # Update xft strings with font size {+/-}1
  foreach (FONT_PROPS) {
    $self->{fonts}{$_} = $self->_resize_xft_string($_, $delta);
  }

  # Emit escape sequence to change fonts in rxvt runtime
  $self->update_display;

  # Persist the changes to xrdb
  system("xrdb -load " . X_RESOURCES);
  open(XRDB_MERGE, "| xrdb -merge") || die "can't fork: $!";
  local $SIG{PIPE} = sub { die "xrdb pipe broke" };
  foreach (FONT_PROPS) {
    print XRDB_MERGE "urxvt\*$_: $self->{fonts}{$_}\n"
  }
  close XRDB_MERGE || die "bad xrdb: $! $?";
  system("xrdb -edit " . X_RESOURCES);
}

sub on_user_command
{
  # This function is called whenever some urxvt.keysym.*: perl:x:y
  # mapped in X_RESOURCES is called; where x is this "module" (file,
  # translation unit...), y is some function in this file (and this
  # function, if defined), and $cmd is the argument z.
  #
  my ($self, $cmd) = @_;

  if ($cmd =~ /font:(..crement)/)   # {in, de, ex}
  {
    $self->change_size(($1 eq "increment") ? +1 : -1);
  }
}

sub on_init
{
  my ($self) = @_;

  ($self->{winx}, $self->{winy}) = (0, 0);

  # Get current font settings
  foreach (FONT_PROPS) {
    $self->{fonts}{$_} = $self->{term}->resource($_);
  }
  $self->{dpi} = STANDARD_DPI;
}

sub get_dpi_at
{
  my ($px, $py) = @_;

  foreach (grep {m/ connected /} `xrandr 2> /dev/null`) {
    # Parse monitor dimensions from xrandr output, and skip if the given point
    # is not on this monitor
    my ($w, $h, $x, $y, $rot, $wmm, $hmm) = m/\b(\d+)x(\d+)([-+]\d+)([-+]\d+) (\w*).* (\d+)mm x (\d+)mm\b/;
    next if $px < $x or $py < $y or $px >= $x + $w or $py >= $y + $h;
    ($wmm, $hmm) = ($hmm, $wmm) if $rot eq "left" or $rot eq "right";

    # Calculate DPI based on width alone for now:
    #   screen width in pixels / screen width in inches
    return $w / ($wmm * MM_TO_INCH);
  }
  return 0;
}

sub on_configure_notify
{
  my ($self, $event) = @_;
  my $term = $self->{term};

  return unless ENABLE_DPI_SCALING;

  my ($newx, $newy) = $term->XTranslateCoordinates($term->vt, $term->DefaultRootWindow, 0, 0);
  $newx += $event->{width}/2;
  $newy += $event->{height}/2;

  return if $newx == $self->{winx} and $newy == $self->{winy};

  ($self->{winx}, $self->{winy}) = ($newx, $newy);
  my $dpi = get_dpi_at($newx, $newy);
  return if $dpi == 0 or $self->{dpi} == $dpi;
  $self->{dpi} = $dpi;
  $self->update_display;

  $term->XMoveResizeWindow($term->vt, $event->{x}, $event->{y}, $event->{width}, $event->{height});
}