add a basic .ics file parser implementation

app/src/main/kotlin/com/simplemobiletools/calendar/helpers/IcsParser.kt

@@ -0,0 +1,56 @@
+package com.simplemobiletools.calendar.helpers
+
+import android.content.Context
+import com.simplemobiletools.calendar.R
+import com.simplemobiletools.calendar.models.Event
+
+object IcsParser {
+    private val BEGIN_EVENT = "BEGIN:VEVENT"
+    private val BEGIN_ALARM = "BEGIN:VALARM"
+    private val END = "END:VEVENT"
+    private val DTSTART = "DTSTART:"
+    private val DTEND = "DTEND:"
+    private val SUMMARY = "SUMMARY:"
+    private val DESCRIPTION = "DESCRIPTION:"
+
+    var curStart = -1
+    var curEnd = -1
+    var curTitle = ""
+    var curDescription = ""
+
+    fun parseIcs(context: Context) {
+        val inputStream = context.resources.openRawResource(R.raw.sample)
+
+        inputStream.bufferedReader().use {
+            while (true) {
+                val line = it.readLine()?.trim() ?: break
+                if (line == BEGIN_EVENT) {
+                    resetValues()
+                } else if (line.startsWith(DTSTART)) {
+                    val datetime = line.substring(DTSTART.length)
+                    curStart = 0
+                } else if (line.startsWith(DTEND)) {
+                    val datetime = line.substring(DTEND.length)
+                    curEnd = 0
+                } else if (line.startsWith(SUMMARY)) {
+                    curTitle = line.substring(SUMMARY.length)
+                } else if (line.startsWith(DESCRIPTION)) {
+                    curDescription = line.substring(DESCRIPTION.length)
+                } else if (line == END || line == BEGIN_ALARM) {
+                    if (curTitle.isEmpty() || curStart == -1 || curEnd == -1)
+                        continue
+
+                    val event = Event(0, 0, 0, curTitle, curDescription)
+                    resetValues()
+                }
+            }
+        }
+    }
+
+    fun resetValues() {
+        curStart = -1
+        curEnd = -1
+        curTitle = ""
+        curDescription = ""
+    }
+}