vertical pattern repeat

this contains awful hacks, the structure of

    print_next_colour(), and
    display()

Really needs to be reworked because they share a lot of state about the
pattern (whether it is forwards or backwards, horizontally and
vertically), but don't explicitly pass any of it between them. I
literally only need to give print_next_colour() two variables (x and y) for it
to get the correct colour, without needing to share super ugly state.

A better option might just be to generate the rainbow in 2x length and
store forwards+reverse. That would save a lot of runtime arithmetic.

Makefile

@@ -16,6 +16,5 @@ debug: colcat.c
 	gcc -g -c c-colours/colours.c -o bin/colours.o 
 	gcc -g -lm bin/colcat.o bin/colours.o -o bin/colcat
 
-
 clean:
 	rm bin/*

colcat.c

@@ -18,6 +18,7 @@ int num_colours;        // the length of the rainbow
 // start_hue and end_hue hue values
 int start_hue = -1;
 int end_hue = -1;
+bool reverse = false;
 
 char help_text[] = "\nUsage: colcat [args] [--] [FILES] \n"
                      "\n"
@@ -35,14 +36,10 @@ char help_text[] = "\nUsage: colcat [args] [--] [FILES] \n"
 
 /* Print the nth colour of the <rainbow_len> chars long rainbow */
 void print_next_colour(int current) {
-    static bool reverse = false;
 
-    if (current % rainbow_len == 0) {
+    if (current % (num_colours) == 0 && current > 0) {
         reverse = !reverse;
     }
-    if (current == 0) {
-        reverse = false;
-    }
 
     int index = 0;
     if (!reverse) {
@@ -72,12 +69,31 @@ bool end_hue_ansi_code(char c) {
 int display(FILE *file) {
     char c = fgetc(file);
 
-    int start_hue = 0;
+    int start = 0;
+    int end;
     int counter = 0;
+    if (frequency) 
+        end = num_colours / frequency - 1;
+    else {
+        end = 0;
+        counter = num_colours; // so that print starts at reverse=true
+    }
     bool in_escape = false;
+    bool vert_reverse = false;
     while (c != EOF) {
         if (c == '\n') {
-            counter = (start_hue += frequency);
+            if (frequency) {
+                if (counter % (end) == 0) {
+                    vert_reverse = !vert_reverse;
+                }
+                counter = start += (vert_reverse ? -1 : 1) * frequency;
+                if (counter < 0) {
+                    counter = -counter;
+                }
+            } else {
+                counter = num_colours;
+            }
+            reverse = false;
         }
         if (c == '\033') {
             in_escape = true;
@@ -156,6 +172,9 @@ int generate_rainbow() {
         colours[i] = get_rgb(c);
     }
 
+    c.h = end_hue;
+    colours[num_colours - 1] = get_rgb(c);
+
     return 0;
 }