add days placeholder

- days placeholder <days:yyyy-mm-dd> pattern added.

src/main/kotlin/space/mori/chzzk_bot/chzzk/MessageHandler.kt

@@ -25,6 +25,7 @@ class MessageHandler(
     private val dailyCounterPattern = Regex("<daily_counter:([^>]+)>")
     private val namePattern = Regex("<name>")
     private val followPattern = Regex("<following>")
+    private val daysPattern = """<days:(\d{4})-(\d{2})-(\d{2})>""".toRegex()
 
     init {
         reloadCommand()
@@ -162,6 +163,16 @@ class MessageHandler(
             }
         }
 
+        result = daysPattern.replace(result) {
+            val (year, month, day) = it.destructured
+            val pastDate = LocalDateTime.of(year.toInt(), month.toInt(), day.toInt(), 0, 0, 0)
+            val today = LocalDateTime.now()
+
+            val daysBetween = ChronoUnit.DAYS.between(pastDate, today)
+
+            daysBetween.toString()
+        }
+
         result = counterPattern.replace(result) {
             val name = it.groupValues[1]
             CounterService.updateCounterValue(name, 1, user).toString()