Add support for light colors

src/EventModal.svelte

@@ -18,7 +18,7 @@
 <Modal isOpen={open} {toggle} centered scrollable>
   <ModalHeader {toggle}>
     <span class="pe-3">
-      <Badge color="custom" style="background-color:{event.backgroundColor}">
+      <Badge color="custom" style="background-color:{event.backgroundColor}; color:{event.textColor}">
         {event.extendedProps.calendar}
       </Badge>
     </span>

src/calendar.js

@@ -1,3 +1,22 @@
+// https://stackoverflow.com/a/35970186
+function invertColor(hex) {
+  if (hex.indexOf('#') === 0) {
+    hex = hex.slice(1)
+  }
+  // convert 3-digit hex to 6-digits.
+  if (hex.length === 3) {
+    hex = hex[0] + hex[0] + hex[1] + hex[1] + hex[2] + hex[2]
+  }
+  if (hex.length !== 6) {
+    throw new Error('Invalid HEX color.')
+  }
+  var r = parseInt(hex.slice(0, 2), 16),
+    g = parseInt(hex.slice(2, 4), 16),
+    b = parseInt(hex.slice(4, 6), 16)
+  // https://stackoverflow.com/a/3943023/112731
+  return r * 0.299 + g * 0.587 + b * 0.114 > 186 ? '#000000' : '#FFFFFF'
+}
+
 const clouds = {
   KLUB_RESEAU: 'klub-reseau',
   ELEVES_ENS: 'eleves-ens',
@@ -140,6 +159,7 @@ function fcEventFromjCalEvent(cal) {
       start: evt.dtstart,
       end: evt.dtend,
       color: cal.color,
+      textColor: invertColor(cal.color),
       duration: end - start // in ms
     }