[libcalamares] Move smart-string-truncation to library

Expand the API a little to support first-lines, last-lines,
and something of both. Use strong types to make the names
clear for each.

src/libcalamares/utils/String.cpp

@@ -121,4 +121,53 @@ obscure( const QString& string )
     return result;
 }
 
+
+QString
+truncateMultiLine( const QString& string, CalamaresUtils::LinesStartEnd lines, CalamaresUtils::CharCount chars )
+{
+    const int maxLines = lines.atStart + lines.atEnd;
+    if ( ( string.length() <= chars.total ) && ( string.count( '\n' ) <= maxLines ) )
+    {
+        return string;
+    }
+
+    QString shorter = string.simplified();
+    QString front, back;
+    if ( shorter.count( '\n' ) >= maxLines )
+    {
+        int from = -1;
+        for ( int i = 0; i < lines.atStart; ++i )
+        {
+            from = shorter.indexOf( '\n', from + 1 );
+            if ( from < 0 )
+            {
+                // That's strange, we counted at least maxLines newlines before
+                break;
+            }
+        }
+        if ( from > 0 )
+        {
+            front = shorter.left( from );
+        }
+
+        int lastNewLine = -1;
+        int lastCount = 0;
+        for ( auto i = shorter.rbegin(); i != shorter.rend() && lastCount < lines.atEnd; ++i )
+        {
+            if ( *i == '\n' )
+            {
+                ++lastCount;
+                lastNewLine = shorter.length() - int( i - shorter.rbegin() );
+            }
+        }
+        if ( ( lastNewLine >= 0 ) && ( lastCount >= lines.atEnd ) )
+        {
+            back = shorter.right( lastNewLine );
+        }
+    }
+
+    return front + back;
+}
+
+
 }  // namespace CalamaresUtils

src/libcalamares/utils/String.h

@@ -61,6 +61,36 @@ DLLEXPORT QString removeDiacritics( const QString& string );
  * @return the obfuscated string.
  */
 DLLEXPORT QString obscure( const QString& string );
+
+struct LinesStartEnd
+{
+    int atStart;
+    int atEnd;
+};
+
+struct CharCount
+{
+    int total;
+};
+
+/** @brief Truncate a string to some reasonable length for display
+ *
+ * Keep the first few, or last few (or both) lines of a possibly lengthy
+ * message @p string and reduce it to a displayable size (e.g. for
+ * pop-up windows that display the message). If the message is longer
+ * than @p chars, then characters are removed from the front (if
+ * @p lines.atStart is zero) or end (if @p lines.atEnd is zero) or in the middle
+ * (if both are nonzero).
+ *
+ * @param string the input string.
+ * @param lines number of lines to preserve.
+ * @param chars maximum number of characters in the returned string.
+ * @return a string built from parts of the input string.
+ */
+DLLEXPORT QString truncateMultiLine( const QString& string,
+                                     LinesStartEnd lines = LinesStartEnd { 3, 5 },
+                                     CharCount chars = CharCount { 812 } );
+
 }  // namespace CalamaresUtils
 
 #endif

src/libcalamaresui/ViewManager.cpp

@@ -19,6 +19,7 @@
 #include "utils/Logger.h"
 #include "utils/Paste.h"
 #include "utils/Retranslator.h"
+#include "utils/String.h"
 #include "viewpages/BlankViewStep.h"
 #include "viewpages/ExecutionViewStep.h"
 #include "viewpages/ViewStep.h"
@@ -136,41 +137,6 @@ ViewManager::insertViewStep( int before, ViewStep* step )
     emit endInsertRows();
 }
 
-/** Makes a long details message suitable for display
- *
- * @returns a (possibly shortened) version of @p text that
- *      will fit sensibly in a messagebox.
- */
-static QString
-simplifyText( const QString& text )
-{
-    constexpr const int maxLines = 8;
-    constexpr const int maxChars = 640;
-    QString shorter = text.simplified();
-    if ( shorter.count( '\n' ) >= maxLines )
-    {
-        int from = -1;
-        for ( int i = 0; i < maxLines; ++i )
-        {
-            from = shorter.indexOf( '\n', from + 1 );
-            if ( from < 0 )
-            {
-                // That's odd, we counted at least maxLines newlines before
-                break;
-            }
-        }
-        if ( from > 0 )
-        {
-            shorter.truncate( from );
-        }
-    }
-    if ( shorter.length() > maxChars )
-    {
-        shorter.truncate( maxChars );
-    }
-    return shorter;
-}
-
 void
 ViewManager::onInstallationFailed( const QString& message, const QString& details )
 {
@@ -186,7 +152,7 @@ ViewManager::onInstallationFailed( const QString& message, const QString& detail
     QString text = "<p>" + message + "</p>";
     if ( !details.isEmpty() )
     {
-        text += "<p>" + simplifyText( details ) + "</p>";
+        text += "<p>" + CalamaresUtils::truncateMultiLine( details, CalamaresUtils::LinesStartEnd{8, 0}) + "</p>";
     }
     if ( shouldOfferWebPaste )
     {