calculator works pretty well minus the tearing

user-apps/calculator/src/main.rs

@@ -2,28 +2,21 @@
 #![no_main]
 
 extern crate alloc;
-use abi::{KeyCode, display::Display, get_key, print, sleep};
-use alloc::{boxed::Box, format, string::String, vec};
-use core::{panic::PanicInfo, pin::Pin};
+use abi::{KeyCode, display::Display, get_key, print};
+use alloc::{format, string::String, vec, vec::Vec};
+use core::panic::PanicInfo;
 use embedded_graphics::{
     Drawable,
     geometry::{Dimensions, Point},
-    mono_font::{
-        MonoTextStyle,
-        ascii::{self, FONT_6X10},
-        iso_8859_1::FONT_10X20,
-    },
+    mono_font::{MonoTextStyle, ascii::FONT_7X14, iso_8859_1::FONT_10X20},
     pixelcolor::Rgb565,
-    prelude::{Primitive, RgbColor, Size},
+    prelude::{Primitive, RgbColor},
     primitives::{PrimitiveStyle, Rectangle},
-    text::{Alignment, Text},
+    text::Text,
 };
 use embedded_layout::{
     align::{horizontal, vertical},
-    layout::linear::{
-        LinearLayout,
-        spacing::{DistributeFill, FixedMargin},
-    },
+    layout::linear::LinearLayout,
     object_chain::Chain,
     prelude::*,
 };
@@ -48,57 +41,63 @@ pub fn main() {
     let mut display = Display;
 
     let mut input = vec!['e', 'x', 'p', 'r', ':', ' '];
+    let input_min = input.len();
     let mut dirty = true;
-    let mut last_area: Option<Rectangle> = None;
+    let mut last_area: Option<(Rectangle, Rectangle)> = None;
+
+    LinearLayout::vertical(Chain::new(Text::new(
+        "Calculator!",
+        Point::zero(),
+        MonoTextStyle::new(&FONT_10X20, Rgb565::WHITE),
+    )))
+    .arrange()
+    .align_to(&display.bounding_box(), horizontal::Center, vertical::Top)
+    .draw(&mut display)
+    .expect("Failed to draw title");
 
     loop {
         if dirty {
+            let style = PrimitiveStyle::with_fill(Rgb565::BLACK);
             if let Some(area) = last_area {
-                Rectangle::new(area.top_left, area.size)
-                    .into_styled(PrimitiveStyle::with_fill(Rgb565::BLACK))
+                Rectangle::new(area.0.top_left, area.0.size)
+                    .into_styled(style)
+                    .draw(&mut display)
+                    .unwrap();
+
+                Rectangle::new(area.1.top_left, area.1.size)
+                    .into_styled(style)
                     .draw(&mut display)
                     .unwrap();
             }
 
             let text = input.iter().cloned().collect::<String>();
 
-            let expr = Text::new(
+            let style = MonoTextStyle::new(&FONT_7X14, Rgb565::WHITE);
+            let expr_layout = LinearLayout::vertical(Chain::new(Text::new(
                 &text,
                 display.bounding_box().center(),
-                MonoTextStyle::new(&FONT_6X10, Rgb565::WHITE),
-            );
-
-            let layout = LinearLayout::vertical(
-                Chain::new(Text::new(
-                    "Calculator!",
-                    Point::zero(),
-                    MonoTextStyle::new(&FONT_10X20, Rgb565::WHITE),
-                ))
-                .append(
-                    LinearLayout::horizontal(Chain::new(expr).append(Text::new(
-                        " = 901",
-                        Point::zero(),
-                        MonoTextStyle::new(&FONT_6X10, Rgb565::WHITE),
-                    )))
-                    .with_spacing(DistributeFill(expr.size().width))
-                    .arrange()
-                    .align_to(
-                        &display.bounding_box(),
-                        horizontal::Center,
-                        vertical::Center,
-                    ),
-                ),
-            )
-            .with_spacing(DistributeFill(50))
+                style,
+            )))
             .arrange()
-            .align_to(
-                &display.bounding_box(),
-                horizontal::Center,
-                vertical::Center,
-            );
+            .align_to(&display.bounding_box(), horizontal::Left, vertical::Center);
 
-            last_area = Some(layout.bounds());
-            layout.draw(&mut display).unwrap();
+            let result = if let Ok(result) = evaluate(&input[input_min..]) {
+                &format!(" = {}", result)
+            } else {
+                " = Error"
+            };
+
+            let eq_layout = LinearLayout::vertical(Chain::new(Text::new(
+                result,
+                display.bounding_box().center(),
+                style,
+            )))
+            .arrange()
+            .align_to(&display.bounding_box(), horizontal::Right, vertical::Center);
+
+            last_area = Some((expr_layout.bounds(), eq_layout.bounds()));
+            expr_layout.draw(&mut display).unwrap();
+            eq_layout.draw(&mut display).unwrap();
 
             dirty = false;
         }
@@ -109,10 +108,12 @@ pub fn main() {
                     input.push(ch);
                 }
                 KeyCode::Del => {
-                    input.clear();
+                    input.truncate(input_min);
                 }
                 KeyCode::Backspace => {
-                    input.pop();
+                    if input.len() > input_min {
+                        input.pop();
+                    }
                 }
                 KeyCode::Esc => return,
                 _ => (),
@@ -121,3 +122,77 @@ pub fn main() {
         }
     }
 }
+
+fn get_int(int: &[char]) -> Result<i32, ()> {
+    let mut output: i32 = 0;
+    for &c in int {
+        let digit = c.to_digit(10).ok_or(())? as i32;
+        output = output
+            .checked_mul(10)
+            .and_then(|v| v.checked_add(digit))
+            .ok_or(())?;
+    }
+    Ok(output)
+}
+
+fn primary(input: &[char], pos: &mut usize) -> Result<i32, ()> {
+    let mut digits = Vec::new();
+    while *pos < input.len() && input[*pos].is_ascii_digit() {
+        digits.push(input[*pos]);
+        *pos += 1;
+    }
+    if digits.is_empty() {
+        return Err(());
+    }
+    get_int(&digits)
+}
+
+fn mul_div(input: &[char], pos: &mut usize) -> Result<i32, ()> {
+    let mut value = primary(input, pos)?;
+    while *pos < input.len() {
+        let op = input[*pos];
+        if op != '*' && op != '/' {
+            break;
+        }
+        *pos += 1;
+        let rhs = primary(input, pos)?;
+        value = match op {
+            '*' => value.checked_mul(rhs).ok_or(())?,
+            '/' => {
+                if rhs == 0 {
+                    return Err(());
+                }
+                value.checked_div(rhs).ok_or(())?
+            }
+            _ => unreachable!(),
+        };
+    }
+    Ok(value)
+}
+
+fn add_sub(input: &[char], pos: &mut usize) -> Result<i32, ()> {
+    let mut value = mul_div(input, pos)?;
+    while *pos < input.len() {
+        let op = input[*pos];
+        if op != '+' && op != '-' {
+            break;
+        }
+        *pos += 1;
+        let rhs = mul_div(input, pos)?;
+        value = match op {
+            '+' => value.checked_add(rhs).ok_or(())?,
+            '-' => value.checked_sub(rhs).ok_or(())?,
+            _ => unreachable!(),
+        };
+    }
+    Ok(value)
+}
+
+fn evaluate(input: &[char]) -> Result<i32, ()> {
+    let mut pos = 0;
+    let result = add_sub(input, &mut pos)?;
+    if pos != input.len() {
+        return Err(());
+    }
+    Ok(result)
+}