Clean up and simplify the code.

1 files changed, 192 insertions, 62 deletions

diff --git a/src/main.rs b/src/main.rs
index 37adc6f..ffa6320 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,22 +1,172 @@
-mod rand;
-mod sc;
-
-use rand::Gen;
-use sc::{Key, Screen};
+use libc::termios;
 use std::error::Error;
-use std::io::{stderr, stdout, Write};
+use std::io::{stderr, stdout, Read, Write};
+use std::sync::mpsc::{Receiver, SyncSender, TryRecvError};
 use std::time::{Duration, SystemTime};
 
+#[derive(Debug)]
+struct Gen {
+    state: u64,
+}
+
+impl Gen {
+    fn new() -> Gen {
+        Gen {
+            state: SystemTime::now()
+                .duration_since(SystemTime::UNIX_EPOCH)
+                .unwrap()
+                .as_nanos() as u64,
+        }
+    }
+
+    fn rand(&mut self, max: i32) -> i32 {
+        // https://en.wikipedia.org/wiki/Linear_congruential_generator
+        self.state = self.state.wrapping_mul(6364136223846793005).wrapping_add(1);
+        (self.state >> 33 & 0x7fffffff) as i32 % max
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 struct Pos {
     row: u16,
     col: u16,
 }
 
+fn pos(row: u16, col: u16) -> Pos {
+    Pos { row, col }
+}
+
+// https://en.wikipedia.org/wiki/ANSI_escape_code
+fn move_cursor(pos: Pos) -> Result<(), Box<dyn Error>> {
+    write!(stdout(), "\x1b[{};{}H", pos.row + 1, pos.col + 1)?;
+    Ok(())
+}
+
+fn clear() -> Result<(), Box<dyn Error>> {
+    write!(stdout(), "\x1b[2J")?;
+    Ok(())
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Dir {
+    Up,
+    Down,
+    Left,
+    Right,
+}
+
+impl Dir {
+    fn opposite(self) -> Dir {
+        match self {
+            Dir::Up => Dir::Down,
+            Dir::Down => Dir::Up,
+            Dir::Left => Dir::Right,
+            Dir::Right => Dir::Left,
+        }
+    }
+}
+
+struct Screen {
+    old_attr: termios,
+    keys: Receiver<Dir>,
+    cancel: SyncSender<()>,
+}
+
+impl Screen {
+    const ROWS: u16 = 25;
+    const COLS: u16 = 50;
+
+    fn init() -> Result<Screen, Box<dyn Error>> {
+        // Get current terminal attrs.
+        let mut attr;
+        unsafe {
+            attr = std::mem::zeroed();
+            if libc::tcgetattr(1, &mut attr) < 0 {
+                return Err(Box::from("tcgetattr failed"));
+            }
+        }
+
+        // Put the terminal into raw mode.
+        unsafe {
+            let mut raw = std::mem::zeroed();
+            libc::cfmakeraw(&mut raw);
+            raw.c_cc[libc::VMIN] = 0;
+            raw.c_cc[libc::VTIME] = 1; // 100ms timeout
+            if libc::tcsetattr(1, libc::TCSANOW, &raw) < 0 {
+                return Err(Box::from("tcsetattr failed"));
+            }
+        }
+
+        let (key_tx, key_rx) = std::sync::mpsc::sync_channel(4);
+        let (cancel_tx, cancel_rx) = std::sync::mpsc::sync_channel(0);
+        std::thread::spawn(move || {
+            let mut stdin = std::io::stdin().lock();
+            let mut buf = [0; 3];
+            while let Err(TryRecvError::Empty) = cancel_rx.try_recv() {
+                let Ok(n) = stdin.read(&mut buf) else {
+                    continue;
+                };
+                if n < 3 || buf[0] != 27 || buf[1] != b'[' {
+                    continue;
+                }
+                let key = match buf[2] {
+                    b'A' => Dir::Up,
+                    b'B' => Dir::Down,
+                    b'C' => Dir::Right,
+                    b'D' => Dir::Left,
+                    _ => {
+                        continue;
+                    }
+                };
+                let _ = key_tx.try_send(key);
+            }
+        });
+
+        clear()?;
+        move_cursor(pos(0, 0))?;
+        for _ in 0..Screen::COLS {
+            write!(stdout(), "-")?;
+        }
+        for i in 1..Screen::ROWS - 1 {
+            move_cursor(pos(i, 0))?;
+            write!(stdout(), "|")?;
+            move_cursor(pos(i, Screen::COLS - 1))?;
+            write!(stdout(), "|")?;
+        }
+        move_cursor(pos(Screen::ROWS - 1, 0))?;
+        for _ in 0..Screen::COLS {
+            write!(stdout(), "-")?;
+        }
+
+        Ok(Screen {
+            old_attr: attr,
+            keys: key_rx,
+            cancel: cancel_tx,
+        })
+    }
+
+    fn read_key(&self) -> Option<Dir> {
+        self.keys.try_recv().ok()
+    }
+}
+
+impl Drop for Screen {
+    fn drop(&mut self) {
+        self.cancel.send(()).unwrap();
+        unsafe {
+            libc::tcsetattr(1, libc::TCSANOW, &self.old_attr);
+        }
+    }
+}
+
+fn in_bounds(pos: Pos) -> bool {
+    (1..Screen::ROWS - 1).contains(&pos.row) && (1..Screen::COLS - 1).contains(&pos.col)
+}
+
 #[derive(Debug)]
 struct Snake {
     body: Vec<Pos>,
-    direction: Key,
+    direction: Dir,
     growing: i64,
 }
 
@@ -24,38 +174,38 @@ impl Snake {
     fn next(&self) -> Pos {
         let mut pos = self.body[0];
         match self.direction {
-            Key::Up => pos.row -= 1,
-            Key::Down => pos.row += 1,
-            Key::Left => pos.col -= 1,
-            Key::Right => pos.col += 1,
+            Dir::Up => pos.row -= 1,
+            Dir::Down => pos.row += 1,
+            Dir::Left => pos.col -= 1,
+            Dir::Right => pos.col += 1,
         }
         pos
     }
 
-    fn erase(&self, screen: &Screen) -> Result<(), Box<dyn Error>> {
+    fn erase(&self) -> Result<(), Box<dyn Error>> {
         let pos = self.next();
-        if screen.in_bounds(pos.row, pos.col) {
-            sc::move_cursor(pos.row, pos.col)?;
+        if in_bounds(pos) {
+            move_cursor(pos)?;
             write!(stdout(), " ")?;
         }
         for &pos in self.body.iter() {
-            sc::move_cursor(pos.row, pos.col)?;
+            move_cursor(pos)?;
             write!(stdout(), " ")?;
         }
         Ok(())
     }
 
-    fn print(&self, g: &mut Gen, screen: &Screen) -> Result<(), Box<dyn Error>> {
+    fn print(&self, g: &mut Gen) -> Result<(), Box<dyn Error>> {
         let next = self.next();
-        if (self.direction == Key::Left || self.direction == Key::Right)
-            && screen.in_bounds(next.row, next.col)
+        if (self.direction == Dir::Left || self.direction == Dir::Right)
+            && in_bounds(next)
             && g.rand(40) == 0
         {
-            sc::move_cursor(next.row, next.col)?;
+            move_cursor(next)?;
             write!(stdout(), "~")?;
         }
         for (i, &pos) in self.body.iter().enumerate() {
-            sc::move_cursor(pos.row, pos.col)?;
+            move_cursor(pos)?;
             if i == 0 {
                 write!(stdout(), "O")?;
                 continue;
@@ -113,70 +263,52 @@ impl Snake {
     }
 }
 
+#[derive(Debug)]
 struct Fruit {
     pos: Pos,
 }
 
 impl Fruit {
     fn print(&self) -> Result<(), Box<dyn Error>> {
-        sc::move_cursor(self.pos.row, self.pos.col)?;
+        move_cursor(self.pos)?;
         write!(stdout(), "@")?;
         Ok(())
     }
 
-    fn new_pos(&mut self, g: &mut Gen, screen: &Screen) {
-        self.pos.row = g.rand(i32::from(screen.rows) - 4) as u16 + 2;
-        self.pos.col = g.rand(i32::from(screen.cols) - 4) as u16 + 2;
+    fn new_pos(&mut self, g: &mut Gen) {
+        self.pos.row = g.rand(i32::from(Screen::ROWS) - 4) as u16 + 2;
+        self.pos.col = g.rand(i32::from(Screen::COLS) - 4) as u16 + 2;
     }
 }
 
 fn snake() -> Result<i64, Box<dyn Error>> {
     let screen = Screen::init()?;
-    let mut g = rand::new(
-        SystemTime::now()
-            .duration_since(SystemTime::UNIX_EPOCH)
-            .unwrap()
-            .as_nanos() as i64,
-    );
+    let mut g = Gen::new();
     let mut snake = Snake {
-        body: vec![Pos {
-            row: screen.rows / 2,
-            col: screen.cols / 2,
-        }],
-        direction: Key::Right,
+        body: vec![pos(Screen::ROWS / 2, Screen::COLS / 2)],
+        direction: Dir::Right,
         growing: 0,
     };
-    let mut fruit = Fruit {
-        pos: Pos { row: 0, col: 0 },
-    };
-    fruit.new_pos(&mut g, &screen);
+    let mut fruit = Fruit { pos: pos(0, 0) };
+    fruit.new_pos(&mut g);
     let mut score: i64 = 0;
     let mut real_score: i64 = 0;
     let mut delay = Duration::from_millis(200);
 
     loop {
-        sc::move_cursor(0, 3)?;
+        move_cursor(pos(0, 3))?;
         write!(stdout(), " Score: {} ", score)?;
-        snake.print(&mut g, &screen)?;
+        snake.print(&mut g)?;
         fruit.print()?;
 
-        sc::move_cursor(screen.rows - 1, screen.cols - 1)?;
+        move_cursor(pos(Screen::ROWS - 1, Screen::COLS - 1))?;
         stdout().flush()?;
-        let mut d = delay;
-        if snake.direction == Key::Up || snake.direction == Key::Down {
-            d = d * 5 / 4;
-        }
-        std::thread::sleep(d);
+        std::thread::sleep(delay);
 
-        snake.erase(&screen)?;
-        if let Some(key) = screen.read_key() {
-            if !(snake.direction == Key::Up && key == Key::Down
-                || snake.direction == Key::Down && key == Key::Up
-                || snake.direction == Key::Left && key == Key::Right
-                || snake.direction == Key::Right && key == Key::Left)
-                || snake.body.len() == 1
-            {
-                snake.direction = key;
+        snake.erase()?;
+        if let Some(dir) = screen.read_key() {
+            if dir != snake.direction.opposite() || snake.body.len() == 1 {
+                snake.direction = dir;
             }
         };
         snake.step();
@@ -184,7 +316,7 @@ fn snake() -> Result<i64, Box<dyn Error>> {
         if snake.body[0] == fruit.pos {
             snake.growing += 6;
             loop {
-                fruit.new_pos(&mut g, &screen);
+                fruit.new_pos(&mut g);
                 if !snake.body.contains(&fruit.pos) {
                     break;
                 }
@@ -194,9 +326,7 @@ fn snake() -> Result<i64, Box<dyn Error>> {
             real_score += 1;
             delay = delay * 14 / 15;
         }
-        if !screen.in_bounds(snake.body[0].row, snake.body[0].col)
-            || snake.body[1..].contains(&snake.body[0])
-        {
+        if !in_bounds(snake.body[0]) || snake.body[1..].contains(&snake.body[0]) {
             return Ok(score);
         }
     }
@@ -210,7 +340,7 @@ fn main() {
             std::process::exit(1);
         }
     };
-    let _ = sc::clear();
-    let _ = sc::move_cursor(0, 0);
+    let _ = clear();
+    let _ = move_cursor(pos(0, 0));
     let _ = writeln!(stdout(), "Score: {}", score);
 }