Attempt to calculate context lines for #460

Author: scottchiefbaker

diff-so-fancy

@@ -26,6 +26,7 @@ my $use_unicode_dash_for_ruler = git_config_boolean("diff-so-fancy.useUnicodeRul
 my $ruler_width                = git_config("diff-so-fancy.rulerWidth", undef);
 my $git_strip_prefix           = git_config_boolean("diff.noprefix","false");
 my $has_stdin                  = has_stdin();
+my $CONTEXT_LINES              = undef; # Number of lines of context diff used
 
 my $ansi_regex = qr/\e\[([0-9]{1,3}(;[0-9]{1,3}){0,10})[mK]/;
 my $ansi_color_regex = qr/(${ansi_regex})?/;
@@ -139,6 +140,11 @@ do_dsf_stuff(\@lines);
 sub do_dsf_stuff {
 	my $input = shift();
 
+	# Calculate the context lines the first time
+	if (!defined $CONTEXT_LINES) {
+		$CONTEXT_LINES = calculate_context_lines(@lines);
+	}
+
 	#print STDERR "START -------------------------------------------------\n";
 	#print STDERR join("",@$input);
 	#print STDERR "END ---------------------------------------------------\n";
@@ -534,16 +540,14 @@ sub start_line_calc {
 		return 1;
 	}
 
-	# Git defaults to three lines of context
-	my $default_context_lines = 3;
 	# Three lines on either side, and the line itself = 7
-	my $expected_context      = ($default_context_lines * 2 + 1);
+	my $expected_context = ($CONTEXT_LINES * 2 + 1);
 
 	# The first three lines
 	if ($line_num == 1 && $diff_context < $expected_context) {
-		$ret = $diff_context - $default_context_lines;
+		$ret = $diff_context - $CONTEXT_LINES;
 	} else {
-		$ret = $line_num + $default_context_lines;
+		$ret = $line_num + $CONTEXT_LINES;
 	}
 
 	if ($ret < 1) {
@@ -1081,6 +1085,27 @@ sub debug_log {
 	return 1;
 }
 
+sub calculate_context_lines {
+	my @lines     = @_;
+	my $count     = 0;
+	my $hunk_line = 0;
+
+	foreach my $line (@lines) {
+		if ($line =~ /^${ansi_color_regex}(@@@* .+? @@@*)(.*)/) {
+			$hunk_line = $count;
+		} elsif ($hunk_line && $line =~ /^${ansi_color_regex}[+-]/) {
+			my $diff = $count - $hunk_line - 1;
+			#print "Hunk: $hunk_line, ChangedLine: $count ($diff context)\n";
+			return $diff;
+		}
+
+		$count++;
+	};
+
+	# If for some reason we can't figure it out, assume 3
+	return 3;
+}
+
 # Borrowed from: https://www.perturb.org/display/1097_Perl_detect_if_a_module_is_installed_before_using_it.html
 sub AUTOLOAD {
 	our $AUTOLOAD; # keep 'use strict' happy