[WIP] truncate long text posts

lib/widgets/post.dart

@@ -1,3 +1,5 @@
+import 'dart:ui' as ui;
+
 import 'package:cached_network_image/cached_network_image.dart';
 import 'package:esys_flutter_share/esys_flutter_share.dart';
 import 'package:flutter/cupertino.dart';
@@ -97,11 +99,35 @@ class PostWidget extends HookWidget {
     );
   }
 
+  List<ui.LineMetrics> postNeedsToTruncate(
+    String body,
+    Size size,
+    ui.TextDirection textDirection,
+  ) {
+    final span = TextSpan(
+      text: body,
+    );
+    final tp = TextPainter(
+      text: span,
+      maxLines: 20,
+      textDirection: textDirection,
+    )..layout(maxWidth: size.width - 20);
+
+    return tp.computeLineMetrics();
+  }
+
   // == UI ==
 
   @override
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
+    final textPostData = post.post.body == null
+        ? []
+        : postNeedsToTruncate(
+            post.post.body,
+            MediaQuery.of(context).size,
+            Directionality.of(context),
+          );
     void _openLink() => linkLauncher(
         context: context, url: post.post.url, instanceHost: instanceHost);
 
@@ -419,12 +445,54 @@ class PostWidget extends HookWidget {
               postImage()
             else if (post.post.url != null && post.post.url.isNotEmpty)
               linkPreview(),
-            if (post.post.body != null)
+            if (post.post.body != null && fullPost)
               // TODO: trim content
               Padding(
                   padding: const EdgeInsets.all(10),
                   child:
                       MarkdownText(post.post.body, instanceHost: instanceHost)),
+            if (post.post.body != null && !fullPost && textPostData.length < 20)
+              // TODO: trim content
+              Padding(
+                  padding: const EdgeInsets.all(10),
+                  child:
+                      MarkdownText(post.post.body, instanceHost: instanceHost)),
+            if (post.post.body != null &&
+                !fullPost &&
+                textPostData.length >= 20)
+              Container(
+                constraints: BoxConstraints(
+                    maxHeight:
+                        (textPostData.first as ui.LineMetrics).height * 20),
+                child: Stack(
+                  alignment: Alignment.bottomCenter,
+                  children: [
+                    ClipRect(
+                      child: Align(
+                        alignment: Alignment.topCenter,
+                        heightFactor: 0.8,
+                        child: Padding(
+                            padding: const EdgeInsets.all(10),
+                            child: MarkdownText(post.post.body,
+                                instanceHost: instanceHost)),
+                      ),
+                    ),
+                    Container(
+                      height: (textPostData.first as ui.LineMetrics).height * 4,
+                      decoration: BoxDecoration(
+                        gradient: LinearGradient(
+                          begin: Alignment.topCenter,
+                          end: Alignment.bottomCenter,
+                          colors: [
+                            Colors.transparent,
+                            theme.cardColor,
+                          ],
+                        ),
+                      ),
+                    ),
+                  ],
+                ),
+              ),
             actions(),
           ],
         ),