Fix incorrectly incrementing IDs before sending to server. (#1026)

* Fix incorrectly incrementing IDs before sending to server.

* Add TimelineRepositoryTest, fix adding placeholder, fix String#dec()

* Add more TimelineRepository tests, fix bugs

* Add tests for adding statuses from DB.

app/src/main/java/com/keylesspalace/tusky/util/HtmlConverter.kt

@@ -0,0 +1,22 @@
+package com.keylesspalace.tusky.util
+
+import android.text.Spanned
+
+/**
+ * Abstracting away Android-specific things.
+ */
+interface HtmlConverter {
+    fun fromHtml(html: String): Spanned
+
+    fun toHtml(text: Spanned): String
+}
+
+internal class HtmlConverterImpl : HtmlConverter {
+    override fun fromHtml(html: String): Spanned {
+        return HtmlUtils.fromHtml(html)
+    }
+
+    override fun toHtml(text: Spanned): String {
+        return HtmlUtils.toHtml(text)
+    }
+}

app/src/main/java/com/keylesspalace/tusky/util/StringUtils.kt

@@ -25,7 +25,7 @@ fun randomAlphanumericString(count: Int): String {
 fun String.inc(): String {
     // We assume that we will stay in the safe range for now
     val builder = this.toCharArray()
-    builder.last().inc()
+    builder[lastIndex] = builder[lastIndex].inc()
     return String(builder)
 }
 
@@ -34,24 +34,25 @@ fun String.inc(): String {
  * "Decrement" string so that during sorting it's smaller than [this].
  */
 fun String.dec(): String {
+    if (this.isEmpty()) return this
+
     val builder = this.toCharArray()
     var i = builder.lastIndex
     while (i > 0) {
         if (builder[i] > '0') {
             builder[i] = builder[i].dec()
-            break
+            return String(builder)
         } else {
             builder[i] = 'z'
         }
         i--
     }
-    // All characters were '0'
-    if (i == 0 && this.isNotEmpty()) {
-        // Remove one character
-        return String(builder.copyOfRange(1, builder.size))
+    return if (builder[0] > '1') {
+        builder[0] = builder[0].dec()
+        String(builder)
+    } else {
+        String(builder.copyOfRange(1, builder.size))
     }
-
-    return String(builder)
 }
 
 /**