Ignore "@instance..." part of username when computing status length (#3392)

* Move compose.* tests to own namespace

* Ignore "@instance..." part of username when computing status length

In a status with a mention ("@foo@example.org") only the "@foo" part should
be included in the calculated status length. It wasn't, so the app was
prevening people from posting statuses that should have been allowed.

Fix this.

- Lift the length calculation code in to a separate static function (easier
  and faster to test)
- Add a `MentionSpan` type, to reuse existing code for detecting mentions
- Fix a bug in `FakeSpannable.getSpans()` (it was returning the outer type,
  not the wrapped inner span)
- Add additional fast tests

The tests made sense under the `components.compose.ComposeActivity` package,
so I also created that and moved the existing ComposeActivity tests there.

Fixes https://github.com/tuskyapp/Tusky/issues/3339

* Static import assertEquals

app/src/main/java/com/keylesspalace/tusky/components/compose/ComposeActivity.kt

@@ -31,6 +31,8 @@ import android.os.Build
 import android.os.Bundle
 import android.os.Parcelable
 import android.provider.MediaStore
+import android.text.Spanned
+import android.text.style.URLSpan
 import android.util.Log
 import android.view.KeyEvent
 import android.view.MenuItem
@@ -91,6 +93,7 @@ import com.keylesspalace.tusky.entity.NewPoll
 import com.keylesspalace.tusky.entity.Status
 import com.keylesspalace.tusky.settings.PrefKeys
 import com.keylesspalace.tusky.util.APP_THEME_DEFAULT
+import com.keylesspalace.tusky.util.MentionSpan
 import com.keylesspalace.tusky.util.PickMediaFiles
 import com.keylesspalace.tusky.util.getInitialLanguages
 import com.keylesspalace.tusky.util.getLocaleList
@@ -883,20 +886,11 @@ class ComposeActivity :
 
     @VisibleForTesting
     fun calculateTextLength(): Int {
-        var offset = 0
-        val urlSpans = binding.composeEditField.urls
-        if (urlSpans != null) {
-            for (span in urlSpans) {
-                // it's expected that this will be negative
-                // when the url length is less than the reserved character count
-                offset += (span.url.length - charactersReservedPerUrl)
-            }
-        }
-        var length = binding.composeEditField.length() - offset
-        if (viewModel.showContentWarning.value) {
-            length += binding.composeContentWarningField.length()
-        }
-        return length
+        return statusLength(
+            binding.composeEditField.text,
+            binding.composeContentWarningField.text,
+            charactersReservedPerUrl
+        )
     }
 
     @VisibleForTesting
@@ -1352,5 +1346,53 @@ class ComposeActivity :
         fun canHandleMimeType(mimeType: String?): Boolean {
             return mimeType != null && (mimeType.startsWith("image/") || mimeType.startsWith("video/") || mimeType.startsWith("audio/") || mimeType == "text/plain")
         }
+
+        /**
+         * Calculate the effective status length.
+         *
+         * Some text is counted differently:
+         *
+         * In the status body:
+         *
+         * - URLs always count for [urlLength] characters irrespective of their actual length
+         *   (https://docs.joinmastodon.org/user/posting/#links)
+         * - Mentions ("@user@some.instance") only count the "@user" part
+         *   (https://docs.joinmastodon.org/user/posting/#mentions)
+         * - Hashtags are always treated as their actual length, including the "#"
+         *   (https://docs.joinmastodon.org/user/posting/#hashtags)
+         *
+         * Content warning text is always treated as its full length, URLs and other entities
+         * are not treated differently.
+         *
+         * @param body status body text
+         * @param contentWarning optional content warning text
+         * @param urlLength the number of characters attributed to URLs
+         * @return the effective status length
+         */
+        @JvmStatic
+        fun statusLength(body: Spanned, contentWarning: Spanned?, urlLength: Int): Int {
+            var length = body.length - body.getSpans(0, body.length, URLSpan::class.java)
+                .fold(0) { acc, span ->
+                    // Accumulate a count of characters to be *ignored* in the final length
+                    acc + when (span) {
+                        is MentionSpan -> {
+                            // Ignore everything from the second "@" (if present)
+                            span.url.length - (
+                                span.url.indexOf("@", 1).takeIf { it >= 0 }
+                                    ?: span.url.length
+                                )
+                        }
+                        else -> {
+                            // Expected to be negative if the URL length < maxUrlLength
+                            span.url.length - urlLength
+                        }
+                    }
+                }
+
+            // Content warning text is treated as is, URLs or mentions there are not special
+            contentWarning?.let { length += it.length }
+
+            return length
+        }
     }
 }

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

@@ -156,7 +156,7 @@ private fun getCustomSpanForMention(mentions: List<Mention>, span: URLSpan, list
 }
 
 private fun getCustomSpanForMentionUrl(url: String, mentionId: String, listener: LinkListener): ClickableSpan {
-    return object : NoUnderlineURLSpan(url) {
+    return object : MentionSpan(url) {
         override fun onClick(view: View) = listener.onViewAccount(mentionId)
     }
 }

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

@@ -19,9 +19,14 @@ import android.text.TextPaint
 import android.text.style.URLSpan
 import android.view.View
 
-open class NoUnderlineURLSpan(
-    url: String
-) : URLSpan(url) {
+open class NoUnderlineURLSpan constructor(val url: String) : URLSpan(url) {
+
+    // This should not be necessary. But if you don't do this the [StatusLengthTest] tests
+    // fail. Without this, accessing the `url` property, or calling `getUrl()` (which should
+    // automatically call through to [UrlSpan.getURL]) returns null.
+    override fun getURL(): String {
+        return url
+    }
 
     override fun updateDrawState(ds: TextPaint) {
         super.updateDrawState(ds)
@@ -32,3 +37,8 @@ open class NoUnderlineURLSpan(
         view.context.openLink(url)
     }
 }
+
+/**
+ * Mentions of other users ("@user@example.org")
+ */
+open class MentionSpan(url: String) : NoUnderlineURLSpan(url)

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

@@ -131,6 +131,7 @@ private fun getSpan(matchType: FoundMatchType, string: String, colour: Int, star
     return when (matchType) {
         FoundMatchType.HTTP_URL -> NoUnderlineURLSpan(string.substring(start, end))
         FoundMatchType.HTTPS_URL -> NoUnderlineURLSpan(string.substring(start, end))
+        FoundMatchType.MENTION -> MentionSpan(string.substring(start, end))
         else -> ForegroundColorSpan(colour)
     }
 }