refactor: migrate MapFragment to Composable (#647)

app/src/main/java/com/geeksville/mesh/util/CustomRecentEmojiProvider.kt

@@ -0,0 +1,48 @@
+package com.geeksville.mesh.util
+
+import android.content.Context
+import androidx.emoji2.emojipicker.RecentEmojiAsyncProvider
+import com.google.common.util.concurrent.Futures
+import com.google.common.util.concurrent.ListenableFuture
+
+/**
+ * Define a custom recent emoji provider which shows most frequently used emoji
+ */
+class CustomRecentEmojiProvider(
+    context: Context
+) : RecentEmojiAsyncProvider {
+
+    private val sharedPreferences =
+        context.getSharedPreferences(RECENT_EMOJI_LIST_FILE_NAME, Context.MODE_PRIVATE)
+
+    private val emoji2Frequency: MutableMap<String, Int> by lazy {
+        sharedPreferences.getString(PREF_KEY_CUSTOM_EMOJI_FREQ, null)?.split(SPLIT_CHAR)
+            ?.associate { entry ->
+                entry.split(KEY_VALUE_DELIMITER, limit = 2).takeIf { it.size == 2 }
+                    ?.let { it[0] to it[1].toInt() } ?: ("" to 0)
+            }?.toMutableMap() ?: mutableMapOf()
+    }
+
+    override fun getRecentEmojiListAsync(): ListenableFuture<List<String>> =
+        Futures.immediateFuture(emoji2Frequency.toList().sortedByDescending { it.second }
+            .map { it.first })
+
+    override fun recordSelection(emoji: String) {
+        emoji2Frequency[emoji] = (emoji2Frequency[emoji] ?: 0) + 1
+        saveToPreferences()
+    }
+
+    private fun saveToPreferences() {
+        sharedPreferences
+            .edit()
+            .putString(PREF_KEY_CUSTOM_EMOJI_FREQ, emoji2Frequency.entries.joinToString(SPLIT_CHAR))
+            .apply()
+    }
+
+    companion object {
+        private const val PREF_KEY_CUSTOM_EMOJI_FREQ = "pref_key_custom_emoji_freq"
+        private const val RECENT_EMOJI_LIST_FILE_NAME = "org.geeksville.emoji.prefs"
+        private const val SPLIT_CHAR = ","
+        private const val KEY_VALUE_DELIMITER = "="
+    }
+}