Implement cursor movement in `TextInput`

4 files changed, 175 insertions, 49 deletions

diff --git a/core/src/widget/text_input.rs b/core/src/widget/text_input.rs
index e0f0744b..95064ab3 100644
--- a/core/src/widget/text_input.rs
+++ b/core/src/widget/text_input.rs
@@ -1,9 +1,11 @@
 use crate::Length;
 
+use std::ops::{Index, RangeTo};
+
 pub struct TextInput<'a, Message> {
     pub state: &'a mut State,
     pub placeholder: String,
-    pub value: String,
+    pub value: Value,
     pub width: Length,
     pub max_width: Length,
     pub padding: u16,
@@ -12,11 +14,6 @@ pub struct TextInput<'a, Message> {
     pub on_submit: Option<Message>,
 }
 
-#[derive(Debug, Default)]
-pub struct State {
-    pub is_focused: bool,
-}
-
 impl<'a, Message> TextInput<'a, Message> {
     pub fn new<F>(
         state: &'a mut State,
@@ -30,7 +27,7 @@ impl<'a, Message> TextInput<'a, Message> {
         Self {
             state,
             placeholder: String::from(placeholder),
-            value: String::from(value),
+            value: Value::new(value),
             width: Length::Fill,
             max_width: Length::Shrink,
             padding: 0,
@@ -84,3 +81,84 @@ where
         f.debug_struct("TextInput").finish()
     }
 }
+
+#[derive(Debug, Default)]
+pub struct State {
+    pub is_focused: bool,
+    cursor_position: usize,
+}
+
+impl State {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn focused() -> Self {
+        Self {
+            is_focused: true,
+            ..Self::default()
+        }
+    }
+
+    pub fn move_cursor_right(&mut self, value: &Value) {
+        let current = self.cursor_position(value);
+
+        if current < value.len() {
+            self.cursor_position = current + 1;
+        }
+    }
+
+    pub fn move_cursor_left(&mut self, value: &Value) {
+        let current = self.cursor_position(value);
+
+        if current > 0 {
+            self.cursor_position = current - 1;
+        }
+    }
+
+    pub fn cursor_position(&self, value: &Value) -> usize {
+        self.cursor_position.min(value.len())
+    }
+}
+
+pub struct Value(Vec<char>);
+
+impl Value {
+    pub fn new(string: &str) -> Self {
+        Self(string.chars().collect())
+    }
+
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    pub fn until(&self, index: usize) -> Self {
+        Self(self.0[..index].iter().cloned().collect())
+    }
+
+    pub fn to_string(&self) -> String {
+        let mut string = String::new();
+
+        for c in self.0.iter() {
+            string.push(*c);
+        }
+
+        string
+    }
+
+    pub fn insert(&mut self, index: usize, c: char) {
+        self.0.insert(index, c);
+    }
+
+    pub fn remove(&mut self, index: usize) {
+        self.0.remove(index);
+    }
+}
+
+impl Index<RangeTo<usize>> for Value {
+    type Output = [char];
+
+    fn index(&self, index: RangeTo<usize>) -> &[char] {
+        &self.0[index]
+    }
+}
diff --git a/examples/todos.rs b/examples/todos.rs
index 6189c8db..9581262a 100644
--- a/examples/todos.rs
+++ b/examples/todos.rs
@@ -15,26 +15,6 @@ struct Todos {
     tasks: Vec<Task>,
 }
 
-#[derive(Debug)]
-struct Task {
-    description: String,
-    completed: bool,
-}
-
-impl Task {
-    fn new(description: String) -> Self {
-        Task {
-            description,
-            completed: false,
-        }
-    }
-
-    fn view(&mut self) -> Element<bool> {
-        Checkbox::new(self.completed, &self.description, |checked| checked)
-            .into()
-    }
-}
-
 #[derive(Debug, Clone)]
 pub enum Message {
     InputChanged(String),
@@ -107,6 +87,26 @@ impl Application for Todos {
     }
 }
 
+#[derive(Debug)]
+struct Task {
+    description: String,
+    completed: bool,
+}
+
+impl Task {
+    fn new(description: String) -> Self {
+        Task {
+            description,
+            completed: false,
+        }
+    }
+
+    fn view(&mut self) -> Element<bool> {
+        Checkbox::new(self.completed, &self.description, |checked| checked)
+            .into()
+    }
+}
+
 // Colors
 const GRAY: Color = Color {
     r: 0.5,
diff --git a/native/src/widget/text_input.rs b/native/src/widget/text_input.rs
index 976ca995..d9837b61 100644
--- a/native/src/widget/text_input.rs
+++ b/native/src/widget/text_input.rs
@@ -45,28 +45,55 @@ where
             Event::Keyboard(keyboard::Event::CharacterReceived(c))
                 if self.state.is_focused && !c.is_control() =>
             {
-                self.value.push(c);
+                let cursor_position = self.state.cursor_position(&self.value);
 
-                let message = (self.on_change)(self.value.clone());
-                messages.push(message);
-            }
-            Event::Keyboard(keyboard::Event::Input {
-                key_code: keyboard::KeyCode::Backspace,
-                state: ButtonState::Pressed,
-            }) => {
-                let _ = self.value.pop();
+                self.value.insert(cursor_position, c);
+                self.state.move_cursor_right(&self.value);
 
-                let message = (self.on_change)(self.value.clone());
+                let message = (self.on_change)(self.value.to_string());
                 messages.push(message);
             }
             Event::Keyboard(keyboard::Event::Input {
-                key_code: keyboard::KeyCode::Enter,
+                key_code,
                 state: ButtonState::Pressed,
-            }) => {
-                if let Some(on_submit) = self.on_submit.clone() {
-                    messages.push(on_submit);
+            }) if self.state.is_focused => match key_code {
+                keyboard::KeyCode::Enter => {
+                    if let Some(on_submit) = self.on_submit.clone() {
+                        messages.push(on_submit);
+                    }
                 }
-            }
+                keyboard::KeyCode::Backspace => {
+                    let cursor_position =
+                        self.state.cursor_position(&self.value);
+
+                    if cursor_position > 0 {
+                        self.state.move_cursor_left(&self.value);
+
+                        let _ = self.value.remove(cursor_position - 1);
+
+                        let message = (self.on_change)(self.value.to_string());
+                        messages.push(message);
+                    }
+                }
+                keyboard::KeyCode::Delete => {
+                    let cursor_position =
+                        self.state.cursor_position(&self.value);
+
+                    if cursor_position < self.value.len() {
+                        let _ = self.value.remove(cursor_position);
+
+                        let message = (self.on_change)(self.value.to_string());
+                        messages.push(message);
+                    }
+                }
+                keyboard::KeyCode::Left => {
+                    self.state.move_cursor_left(&self.value);
+                }
+                keyboard::KeyCode::Right => {
+                    self.state.move_cursor_right(&self.value);
+                }
+                _ => {}
+            },
             _ => {}
         }
     }
diff --git a/wgpu/src/renderer/text_input.rs b/wgpu/src/renderer/text_input.rs
index 30e06878..f119ae6a 100644
--- a/wgpu/src/renderer/text_input.rs
+++ b/wgpu/src/renderer/text_input.rs
@@ -55,17 +55,18 @@ impl text_input::Renderer for Renderer {
         };
 
         let size = f32::from(text_input.size.unwrap_or(self.default_size()));
+        let text = text_input.value.to_string();
 
         let value = Primitive::Clip {
             bounds: text_bounds,
             offset: 0,
             content: Box::new(Primitive::Text {
-                content: if text_input.value.is_empty() {
+                content: if text.is_empty() {
                     text_input.placeholder.clone()
                 } else {
-                    text_input.value.clone()
+                    text.clone()
                 },
-                color: if text_input.value.is_empty() {
+                color: if text.is_empty() {
                     Color {
                         r: 0.7,
                         g: 0.7,
@@ -95,11 +96,18 @@ impl text_input::Renderer for Renderer {
                 primitives: if text_input.state.is_focused {
                     use wgpu_glyph::{GlyphCruncher, Scale, Section};
 
+                    let text_before_cursor = &text_input
+                        .value
+                        .until(
+                            text_input.state.cursor_position(&text_input.value),
+                        )
+                        .to_string();
+
                     let mut text_value_width = self
                         .glyph_brush
                         .borrow_mut()
                         .glyph_bounds(Section {
-                            text: &text_input.value,
+                            text: text_before_cursor,
                             bounds: (f32::INFINITY, text_bounds.height),
                             scale: Scale { x: size, y: size },
                             ..Default::default()
@@ -107,11 +115,24 @@ impl text_input::Renderer for Renderer {
                         .map(|bounds| bounds.width().round())
                         .unwrap_or(0.0);
 
-                    let spaces_at_the_end = text_input.value.len()
-                        - text_input.value.trim_end().len();
+                    let spaces_at_the_end = text_before_cursor.len()
+                        - text_before_cursor.trim_end().len();
 
                     if spaces_at_the_end > 0 {
-                        text_value_width += spaces_at_the_end as f32 * 5.0;
+                        let space_width = {
+                            let glyph_brush = self.glyph_brush.borrow();
+
+                            // TODO: Select appropriate font
+                            let font = &glyph_brush.fonts()[0];
+
+                            font.glyph(' ')
+                                .scaled(Scale { x: size, y: size })
+                                .h_metrics()
+                                .advance_width
+                        };
+
+                        text_value_width +=
+                            spaces_at_the_end as f32 * space_width;
                     }
 
                     let cursor = Primitive::Quad {