Update RocketChatUserAvatar.

Since it is a helper, we don't need to instantiate the RocketChatUserAvatar to each use. This commit adds methods to get a drawable with username initials.

app/src/main/java/chat/rocket/android/helper/RocketChatUserAvatar.kt

 package chat.rocket.android.helper
 
+import android.content.Context
+import android.graphics.Typeface
+import android.graphics.drawable.Drawable
+import com.amulyakhare.textdrawable.TextDrawable
 import java.net.URLEncoder
 
-class RocketChatUserAvatar(val hostname: String, val username: String) {
+object RocketChatUserAvatar {
 
-    val imageUri: String
-        /** REMARK
-         * This is often a SVG image (see Rocket.Chat:server/startup/avatar.js).
+    /**
+     * Returns the user avatar URI.
+     *
+     * REMARK: This is often a SVG image (Rocket.Chat:server/startup/avatar.js).
+     *
+     * @param hostname The server's hostname.
+     * @param username The username.
+     * @return The user avatar URI.
+     * @see getImageFormat
      */
-        get() {
+    fun getUri(hostname : String, username: String): String {
         return "https://" +
                 hostname.replace("http://", "").replace("https://", "") +
                 "/avatar/" +
                 URLEncoder.encode(username, "UTF-8")
     }
+
+    /**
+     * Returns the user avatar image format.
+     *
+     * @param uri The user avatar image URI to get the image format.
+     * @return The user avatar image format. Possible values are: "image/jpeg", "image/png" and "image/svg+xml".
+     * @see getUri
+     */
+    fun getImageFormat(uri: String): String {
+        return OkHttpHelper.getContentType(uri)
+    }
+
+    /**
+     * Returns a drawable with username initials.
+     *
+     * @param username The username.
+     * @param context The context.
+     * @return A drawable with username initials.
+     * @see getUsernameInitials
+     */
+    fun getTextDrawable(username: String, context: Context): Drawable {
+        val round = (4 * context.resources.displayMetrics.density).toInt()
+
+        return TextDrawable.builder()
+                .beginConfig()
+                .useFont(Typeface.SANS_SERIF)
+                .endConfig()
+                .buildRoundRect(getUsernameInitials(username), getUserAvatarBackgroundColor(username), round)
+    }
+
+    /**
+     * Returns a string with the username initials. For example: username John Doe returns JD initials.
+     *
+     * @param username The username.
+     * @return A string with username initials.
+     */
+    fun getUsernameInitials(username: String): String {
+        val name = username
+                .replace("[^A-Za-z0-9]", ".")
+                .replace("\\.+", ".")
+                .replace("(^\\.)|(\\.$)", "")
+        val initials = name.split(".")
+        if (initials.size > 1) {
+            return (initials[0].substring(0, 1) + initials[initials.size - 1].substring(0, 1)).toUpperCase()
+        } else {
+            return (name.replace("[^A-Za-z0-9]", "").substring(0, 2)).toUpperCase()
+        }
+    }
+
+    /**
+     * Returns a background color to be rendered on the user avatar (Rocket.Chat:server/startup/avatar.js).
+     *
+     * @param username The username.
+     * @return A hexadecimal color.
+     */
+    fun getUserAvatarBackgroundColor(username: String): Int {
+        return COLORS[username.length % COLORS.size]
+    }
+
+    private val COLORS = intArrayOf(
+            0xFFF44336.toInt(), 0xFFE91E63.toInt(), 0xFF9C27B0.toInt(), 0xFF673AB7.toInt(), 0xFF3F51B5.toInt(),
+            0xFF2196F3.toInt(), 0xFF03A9F4.toInt(), 0xFF00BCD4.toInt(), 0xFF009688.toInt(), 0xFF4CAF50.toInt(),
+            0xFF8BC34A.toInt(), 0xFFCDDC39.toInt(), 0xFFFFC107.toInt(), 0xFFFF9800.toInt(), 0xFFFF5722.toInt(),
+            0xFF795548.toInt(), 0xFF9E9E9E.toInt(), 0xFF607D8B.toInt())
 }
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