Add basic parts editing to work editor

The work editor contains a ReorderableList view now. This list consists
of instances of the new PartTile widget, which only supports editing the
parts title and its level (meaning how deep it is down the tree) for
now.

lib/editors/work.dart

@@ -5,11 +5,14 @@ import '../database.dart';
 import '../selectors/instruments.dart';
 import '../selectors/person.dart';
 
-class WorkData {
-  String title = '';
+class PartData {
+  final titleController = TextEditingController();
+
+  int level;
   Person composer;
   List<Instrument> instruments = [];
-  List<WorkData> parts = [];
+
+  PartData(this.level);
 }
 
 class WorkProperties extends StatelessWidget {
@@ -83,6 +86,97 @@ class WorkProperties extends StatelessWidget {
   }
 }
 
+class PartTile extends StatefulWidget {
+  final PartData part;
+  final void Function() onMore;
+  final void Function() onAdd;
+  final void Function() onDelete;
+  final void Function(int levels) onMove;
+
+  PartTile({
+    Key key,
+    @required this.part,
+    @required this.onMore,
+    @required this.onAdd,
+    @required this.onDelete,
+    @required this.onMove,
+  }) : super(key: key);
+
+  @override
+  _PartTileState createState() => _PartTileState();
+}
+
+class _PartTileState extends State<PartTile> {
+  static const unit = 16.0;
+  static const iconShrink = 4.0;
+
+  double dragStart;
+  double dragDelta = 0.0;
+
+  @override
+  Widget build(BuildContext context) {
+    final padding = widget.part.level * unit + dragDelta;
+    final iconSize = 24 - widget.part.level * iconShrink;
+
+    return GestureDetector(
+      child: Padding(
+        padding: EdgeInsets.only(left: padding > 0.0 ? padding : 0.0),
+        child: Row(
+          children: <Widget>[
+            Padding(
+              padding: const EdgeInsets.only(left: 16.0, right: 8.0),
+              child: Icon(
+                Icons.drag_handle,
+                size: iconSize,
+              ),
+            ),
+            Expanded(
+              child: TextField(
+                controller: widget.part.titleController,
+                decoration: InputDecoration(
+                  border: InputBorder.none,
+                  hintText: 'Part title',
+                ),
+              ),
+            ),
+            IconButton(
+              icon: const Icon(Icons.more_horiz),
+              iconSize: iconSize,
+              onPressed: widget.onMore,
+            ),
+            IconButton(
+              icon: const Icon(Icons.add),
+              iconSize: iconSize,
+              onPressed: widget.onAdd,
+            ),
+            IconButton(
+              icon: const Icon(Icons.delete),
+              iconSize: iconSize,
+              onPressed: widget.onDelete,
+            ),
+          ],
+        ),
+      ),
+      onHorizontalDragStart: (details) {
+        dragStart = details.localPosition.dx;
+      },
+      onHorizontalDragUpdate: (details) {
+        setState(() {
+          dragDelta = details.localPosition.dx - dragStart;
+        });
+      },
+      onHorizontalDragEnd: (details) {
+        if (dragDelta.abs() >= unit) {
+          widget.onMove((dragDelta / unit).round());
+        }
+        setState(() {
+          dragDelta = 0.0;
+        });
+      },
+    );
+  }
+}
+
 class WorkEditor extends StatefulWidget {
   final Work work;
 
@@ -98,7 +192,11 @@ class _WorkEditorState extends State<WorkEditor> {
   final titleController = TextEditingController();
 
   Backend backend;
-  final WorkData data = WorkData();
+
+  String title = '';
+  Person composer;
+  List<Instrument> instruments = [];
+  List<PartData> parts = [];
 
   @override
   void initState() {
@@ -115,6 +213,7 @@ class _WorkEditorState extends State<WorkEditor> {
 
     backend = Backend.of(context);
 
+    // TODO: Initialize parts
     if (widget.work != null) {
       if (widget.work.composer != null) {
         () async {
@@ -122,9 +221,9 @@ class _WorkEditorState extends State<WorkEditor> {
               await backend.db.personById(widget.work.composer).getSingle();
 
           // We don't want to override a newly selected composer.
-          if (data.composer != null) {
+          if (composer != null) {
             setState(() {
-              data.composer = person;
+              composer = person;
             });
           }
         }();
@@ -135,17 +234,63 @@ class _WorkEditorState extends State<WorkEditor> {
             await backend.db.instrumentsByWork(widget.work.id).get();
 
         // We don't want to override already selected instruments.
-        if (data.instruments.isEmpty) {
+        if (instruments.isEmpty) {
           setState(() {
-            data.instruments = selection;
+            instruments = selection;
           });
         }
       }();
     }
   }
 
+  void cleanLevels() {
+    var previousLevel = -1;
+    for (var i = 0; i < parts.length; i++) {
+      final part = parts[i];
+      if (part.level > previousLevel + 1) {
+        part.level = previousLevel + 1;
+      }
+      previousLevel = part.level;
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
+    final List<Widget> partTiles = [];
+    for (var i = 0; i < parts.length; i++) {
+      final part = parts[i];
+
+      partTiles.add(PartTile(
+        key: Key(part.hashCode.toString()),
+        part: part,
+        // TODO: Make part details editable
+        onMore: () {},
+        onAdd: () {
+          setState(() {
+            parts.insert(i + 1, PartData(part.level + 1));
+          });
+        },
+        onDelete: () {
+          setState(() {
+            parts.removeAt(i);
+            cleanLevels();
+          });
+        },
+        onMove: (levels) {
+          if (levels > 0 && i > 0 && parts[i - 1].level >= part.level) {
+            setState(() {
+              part.level++;
+            });
+          } else if (levels < 0) {
+            final newLevel = part.level + levels;
+            setState(() {
+              part.level = newLevel > 0 ? newLevel : 0;
+            });
+          }
+        },
+      ));
+    }
+
     return Scaffold(
       appBar: AppBar(
         title: Text('Work'),
@@ -156,25 +301,56 @@ class _WorkEditorState extends State<WorkEditor> {
           ),
         ],
       ),
-      body: ListView(
+      body: ReorderableListView(
+        header: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
           children: <Widget>[
             WorkProperties(
               titleController: titleController,
-            composer: data.composer,
-            instruments: data.instruments,
-            onComposerChanged: (composer) {
+              composer: composer,
+              instruments: instruments,
+              onComposerChanged: (newComposer) {
                 setState(() {
-                data.composer = composer;
+                  composer = newComposer;
                 });
               },
-            onInstrumentsChanged: (instruments) {
+              onInstrumentsChanged: (newInstruments) {
                 setState(() {
-                data.instruments = instruments;
+                  instruments = newInstruments;
                 });
               },
             ),
+            if (parts.length > 0)
+              Padding(
+                padding: const EdgeInsets.only(left: 16.0, top: 16.0),
+                child: Text(
+                  'Parts',
+                  style: Theme.of(context).textTheme.subhead,
+                ),
+              ),
           ],
         ),
+        children: partTiles,
+        onReorder: (i1, i2) {
+          setState(() {
+            final part = parts.removeAt(i1);
+            final newIndex = i2 > i1 ? i2 - 1 : i2;
+
+            parts.insert(newIndex, part);
+
+            cleanLevels();
+          });
+        },
+      ),
+      floatingActionButton: FloatingActionButton.extended(
+        icon: const Icon(Icons.add),
+        label: Text('Add part'),
+        onPressed: () {
+          setState(() {
+            parts.add(PartData(0));
+          });
+        },
+      ),
     );
   }
 }