From a3807311cb6873dc6c13effca26afdeccb278400 Mon Sep 17 00:00:00 2001
From: Marcin Szalek <marcin.szalek1@gmail.com>
Date: Sat, 18 Nov 2017 09:12:56 +0100
Subject: [PATCH] Handled empty dataset scenario

---
 lib/screens/history_page.dart   | 37 +++++++++++++++-----------
 lib/widgets/progress_chart.dart | 47 +++++++++++++++++++++++++--------
 2 files changed, 57 insertions(+), 27 deletions(-)

diff --git a/lib/screens/history_page.dart b/lib/screens/history_page.dart
index 92c5d94..e41daef 100644
--- a/lib/screens/history_page.dart
+++ b/lib/screens/history_page.dart
@@ -37,22 +37,27 @@ class HistoryPage extends StatelessWidget {
         );
       },
       builder: (context, viewModel) {
-        return new ListView.builder(
-          shrinkWrap: true,
-          itemCount: viewModel.entries.length,
-          itemBuilder: (buildContext, index) {
-            //calculating difference
-            double difference = index == viewModel.entries.length - 1
-                ? 0.0
-                : viewModel.entries[index].weight -
-                    viewModel.entries[index + 1].weight;
-            return new InkWell(
-                onTap: () => _openEditEntryDialog(viewModel.entries[index],
-                    context, viewModel.editEntryCallback),
-                child:
-                    new WeightListItem(viewModel.entries[index], difference));
-          },
-        );
+        if (viewModel.entries.isEmpty) {
+          return new Center(child: new Text("Add your weight to see history"),);
+        } else {
+          return new ListView.builder(
+            shrinkWrap: true,
+            itemCount: viewModel.entries.length,
+            itemBuilder: (buildContext, index) {
+              //calculating difference
+              double difference = index == viewModel.entries.length - 1
+                  ? 0.0
+                  : viewModel.entries[index].weight -
+                  viewModel.entries[index + 1].weight;
+              return new InkWell(
+                  onTap: () =>
+                      _openEditEntryDialog(viewModel.entries[index],
+                          context, viewModel.editEntryCallback),
+                  child:
+                  new WeightListItem(viewModel.entries[index], difference));
+            },
+          );
+        }
       },
     );
   }
diff --git a/lib/widgets/progress_chart.dart b/lib/widgets/progress_chart.dart
index aa38702..7a52e53 100644
--- a/lib/widgets/progress_chart.dart
+++ b/lib/widgets/progress_chart.dart
@@ -111,15 +111,16 @@ class ChartPainter extends CustomPainter {
     drawingWidth = size.width * 0.95;
     drawingHeight = topOffsetEnd;
 
-    if (entries.isNotEmpty) {
+    if (entries.isEmpty) {
+      _drawParagraphInsteadOfChart(
+          canvas, size, "Add your weight to see history");
+    } else {
       Tuple2<int, int> borderLineValues = _getMinAndMaxValues(entries);
       _drawHorizontalLinesAndLabels(
           canvas, size, borderLineValues.item1, borderLineValues.item2);
       _drawBottomLabels(canvas, size);
 
       _drawLines(canvas, borderLineValues.item1, borderLineValues.item2);
-    } else {
-      //TODO: I think it should be handled at higher level
     }
   }
 
@@ -241,15 +242,22 @@ class ChartPainter extends CustomPainter {
     double maxWeight = entries.map((entry) => entry.weight).reduce(math.max);
     double minWeight = entries.map((entry) => entry.weight).reduce(math.min);
 
-    int maxLineValue = maxWeight.ceil();
-    int difference = maxLineValue - minWeight.floor();
-    int toSubtract = (NUMBER_OF_HORIZONTAL_LINES - 1) -
-        (difference % (NUMBER_OF_HORIZONTAL_LINES - 1));
-    if (toSubtract == NUMBER_OF_HORIZONTAL_LINES - 1) {
-      toSubtract = 0;
-    }
-    int minLineValue = minWeight.floor() - toSubtract;
+    int maxLineValue;
+    int minLineValue;
 
+    if (maxWeight == minWeight) {
+      maxLineValue = maxWeight.ceil() + 1;
+      minLineValue = maxLineValue - 4;
+    } else {
+      maxLineValue = maxWeight.ceil();
+      int difference = maxLineValue - minWeight.floor();
+      int toSubtract = (NUMBER_OF_HORIZONTAL_LINES - 1) -
+          (difference % (NUMBER_OF_HORIZONTAL_LINES - 1));
+      if (toSubtract == NUMBER_OF_HORIZONTAL_LINES - 1) {
+        toSubtract = 0;
+      }
+      minLineValue = minWeight.floor() - toSubtract;
+    }
     return new Tuple2(minLineValue, maxLineValue);
   }
 
@@ -266,6 +274,23 @@ class ChartPainter extends CustomPainter {
     double yOffset = 5 + drawingHeight - relativeYposition * drawingHeight;
     return new Offset(xOffset, yOffset);
   }
+
+  _drawParagraphInsteadOfChart(ui.Canvas canvas, ui.Size size, String text) {
+    double fontSize = 14.0;
+    ui.ParagraphBuilder builder = new ui.ParagraphBuilder(
+      new ui.ParagraphStyle(
+        fontSize: fontSize,
+        textAlign: TextAlign.center,
+      ),
+    )
+      ..pushStyle(new ui.TextStyle(color: Colors.black))
+      ..addText(text);
+    final ui.Paragraph paragraph = builder.build()
+      ..layout(new ui.ParagraphConstraints(width: size.width));
+
+    canvas.drawParagraph(
+        paragraph, new Offset(0.0, size.height / 2 - fontSize));
+  }
 }
 
 DateTime _getStartDateOfChart() {