[gnome-todo] todoist: Add auxiliary methods for color conversion

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 1db51e85723184a33b1537375efe91c0453b07be
Author: Rohit Kaushik <kaushikrohit325 gmail com>
Date:   Fri Jun 16 00:13:49 2017 +0530

    todoist: Add auxiliary methods for color conversion
    
    Since Todoist uses an integer mapped to hex code for list color,
    but To Do uses GdkRGBA we need function that will do the necessary
    conversion from one to other.
    This patch add following method:
      1)convert_color_code: This converts todoist supported int code to
        To Do  supported GdkRGBA color.
    
      2)get_color_code_index: This returns index for To Do supported GdkRGBA
        color which maps correctly to todoist color codes (hex).
    
      3)optimized_eucledian_color_distance: Required by 2nd method to find
        To Do color closed to todoist predifined color codes.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=772278

 plugins/todoist/gtd-provider-todoist.c |   85 ++++++++++++++++++++++++++++++++
 1 files changed, 85 insertions(+), 0 deletions(-)
---
diff --git a/plugins/todoist/gtd-provider-todoist.c b/plugins/todoist/gtd-provider-todoist.c
index 341542a..929e679 100644
--- a/plugins/todoist/gtd-provider-todoist.c
+++ b/plugins/todoist/gtd-provider-todoist.c
@@ -52,6 +52,32 @@ enum {
   LAST_PROP
 };
 
+static const gchar *colormap[] =
+{
+  "#95ef63",
+  "#ff8581",
+  "#ffc471",
+  "#f9ec75",
+  "#a8c8e4",
+  "#d2b8a3",
+  "#e2a8e4",
+  "#cccccc",
+  "#fb886e",
+  "#ffcc00",
+  "#74e8d3",
+  "#3bd5fb",
+  "#dc4fad",
+  "#ac193d",
+  "#d24726",
+  "#82ba00",
+  "#03b3b2",
+  "#008299",
+  "#5db2ff",
+  "#0072c6",
+  "#000000",
+  "#777777"
+};
+
 /*
  * GtdProviderInterface implementation
  */
@@ -101,6 +127,65 @@ gtd_provider_todoist_get_goa_object (GtdProviderTodoist  *self)
 {
   return self->account_object;
 }
+
+static gint
+optimized_eucledian_color_distance (GdkRGBA *color1,
+                                    GdkRGBA *color2)
+{
+  gdouble red_diff;
+  gdouble green_diff;
+  gdouble blue_diff;
+  gdouble red_mean_level;
+
+  red_mean_level = (color1->red + color2->red) / 2;
+  red_diff = color1->red - color2->red;
+  green_diff = color1->green - color2->green;
+  blue_diff = color1->blue - color2->blue;
+
+  return (red_diff * red_diff * (2 + red_mean_level) +
+          green_diff * green_diff * 4 +
+          blue_diff * blue_diff * ((1 - red_mean_level) + 2));
+}
+
+static GdkRGBA*
+convert_color_code (gint index)
+{
+  GdkRGBA rgba;
+
+  gdk_rgba_parse (&rgba, colormap [index]);
+
+  return gdk_rgba_copy (&rgba);
+}
+
+static gint
+get_color_code_index (GdkRGBA *rgba)
+{
+  guint nearest_color_index;
+  guint min_color_diff;
+  guint i;
+
+  nearest_color_index = 0;
+  min_color_diff = G_MAXUINT;
+
+  for (i = 0; i < G_N_ELEMENTS (colormap); i++)
+    {
+      GdkRGBA color;
+      guint distance;
+
+      gdk_rgba_parse (&color, colormap [i]);
+
+      distance = optimized_eucledian_color_distance (rgba, &color);
+
+      if (min_color_diff > distance)
+        {
+          min_color_diff = distance;
+          nearest_color_index = i;
+        }
+    }
+
+  return nearest_color_index;
+}
+
 static void
 gtd_provider_todoist_create_task (GtdProvider *provider,
                                    GtdTask     *task)