From 7e20da97efd5796154d0b5570f307c49f1f4e307 Mon Sep 17 00:00:00 2001
From: Benjamin Saunders <ben.e.saunders@gmail.com>
Date: Sat, 23 Nov 2019 11:03:39 -0800
Subject: [PATCH] Widget adaptor for string parsing

---
 druid/examples/parse.rs        | 37 +++++++++++++++++++
 druid/src/widget/mod.rs        |  3 ++
 druid/src/widget/parse.rs      | 65 ++++++++++++++++++++++++++++++++++
 druid/src/widget/widget_ext.rs | 10 +++++-
 4 files changed, 114 insertions(+), 1 deletion(-)
 create mode 100644 druid/examples/parse.rs
 create mode 100644 druid/src/widget/parse.rs

diff --git a/druid/examples/parse.rs b/druid/examples/parse.rs
new file mode 100644
index 0000000000..0c620179bd
--- /dev/null
+++ b/druid/examples/parse.rs
@@ -0,0 +1,37 @@
+// Copyright 2019 The xi-editor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use druid::widget::{Align, Column, DynLabel, Padding, Parse, TextBox};
+use druid::{AppLauncher, Widget, WindowDesc};
+
+fn main() {
+    let main_window = WindowDesc::new(ui_builder);
+    let data = Some(0);
+    AppLauncher::with_window(main_window)
+        .use_simple_logger()
+        .launch(data)
+        .expect("launch failed");
+}
+
+fn ui_builder() -> impl Widget<Option<u32>> {
+    let label = DynLabel::new(|data: &Option<u32>, _env| {
+        data.map_or_else(|| "Invalid input".into(), |x| x.to_string())
+    });
+    let input = Parse::new(TextBox::new());
+
+    let mut col = Column::new();
+    col.add_child(Align::centered(Padding::new(5.0, label)), 1.0);
+    col.add_child(Padding::new(5.0, input), 1.0);
+    col
+}
diff --git a/druid/src/widget/mod.rs b/druid/src/widget/mod.rs
index df0bb589aa..e1f177981c 100644
--- a/druid/src/widget/mod.rs
+++ b/druid/src/widget/mod.rs
@@ -70,3 +70,6 @@ pub use widget_ext::WidgetExt;
 
 mod list;
 pub use crate::widget::list::{List, ListIter};
+
+mod parse;
+pub use crate::widget::parse::Parse;
diff --git a/druid/src/widget/parse.rs b/druid/src/widget/parse.rs
new file mode 100644
index 0000000000..f0e227fa9f
--- /dev/null
+++ b/druid/src/widget/parse.rs
@@ -0,0 +1,65 @@
+use std::fmt::Display;
+use std::mem;
+use std::str::FromStr;
+
+use crate::kurbo::Size;
+use crate::{
+    BaseState, BoxConstraints, Data, Env, Event, EventCtx, LayoutCtx, PaintCtx, UpdateCtx, Widget,
+};
+
+/// Converts a `Widget<String>` to a `Widget<Option<T>>`, mapping parse errors to None
+pub struct Parse<T> {
+    widget: T,
+    state: String,
+}
+
+impl<T> Parse<T> {
+    pub fn new(widget: T) -> Self {
+        Self {
+            widget,
+            state: String::new(),
+        }
+    }
+}
+
+impl<T: FromStr + Display + Data, W: Widget<String>> Widget<Option<T>> for Parse<W> {
+    fn update(
+        &mut self,
+        ctx: &mut UpdateCtx,
+        old_data: Option<&Option<T>>,
+        data: &Option<T>,
+        env: &Env,
+    ) {
+        let old = match *data {
+            None => return, // Don't clobber the input
+            Some(ref x) => mem::replace(&mut self.state, x.to_string()),
+        };
+        let old = old_data.map(|_| old);
+        self.widget.update(ctx, old.as_ref(), &self.state, env)
+    }
+
+    fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut Option<T>, env: &Env) {
+        self.widget.event(ctx, event, &mut self.state, env);
+        *data = self.state.parse().ok();
+    }
+
+    fn layout(
+        &mut self,
+        ctx: &mut LayoutCtx,
+        bc: &BoxConstraints,
+        _data: &Option<T>,
+        env: &Env,
+    ) -> Size {
+        self.widget.layout(ctx, bc, &self.state, env)
+    }
+
+    fn paint(
+        &mut self,
+        paint: &mut PaintCtx,
+        base_state: &BaseState,
+        _data: &Option<T>,
+        env: &Env,
+    ) {
+        self.widget.paint(paint, base_state, &self.state, env)
+    }
+}
diff --git a/druid/src/widget/widget_ext.rs b/druid/src/widget/widget_ext.rs
index a36074f023..2005dceff0 100644
--- a/druid/src/widget/widget_ext.rs
+++ b/druid/src/widget/widget_ext.rs
@@ -17,7 +17,7 @@
 use crate::kurbo::Insets;
 use crate::piet::{PaintBrush, UnitPoint};
 
-use super::{Align, Container, EnvScope, Padding, SizedBox};
+use super::{Align, Container, EnvScope, Padding, Parse, SizedBox};
 use crate::{Data, Env, Lens, LensWrap, Widget};
 
 /// A trait that provides extra methods for combining `Widget`s.
@@ -116,6 +116,14 @@ pub trait WidgetExt<T: Data>: Widget<T> + Sized + 'static {
     fn lens<U: Data, L: Lens<T, U>>(self, lens: L) -> LensWrap<U, L, Self> {
         LensWrap::new(self, lens)
     }
+
+    /// Parse a `Widget<String>`'s contents
+    fn parse(self) -> Parse<Self>
+    where
+        Self: Widget<String>,
+    {
+        Parse::new(self)
+    }
 }
 
 impl<T: Data + 'static, W: Widget<T> + 'static> WidgetExt<T> for W {}