Add support for 3/4-bit colors

3-bit colors are added as an enum, and 4-bit colors a struct contains
this enum and a separate bright bit, which is not the most
space-efficient.

src/basic_color.rs

@@ -0,0 +1,78 @@
+use crate::{Canvas, Color};
+
+/// A 3-bit color type
+///
+/// The exact colors usually depend on the terminal color scheme.
+#[derive(Copy, Clone, Debug)]
+pub enum Color3 {
+    BLACK = 0,
+    RED = 1,
+    GREEN = 2,
+    YELLOW = 3,
+    BLUE = 4,
+    MAGENTA = 5,
+    CYAN = 6,
+    WHITE = 7,
+}
+
+impl Color for Color3 {
+    fn prelude(&self, f: &mut core::fmt::Formatter, canvas: crate::Canvas) -> core::fmt::Result {
+        match canvas {
+            Canvas::Foreground => write!(f, "\x1B[{}m", 30 + *self as u8),
+            Canvas::Background => write!(f, "\x1B[{}m", 40 + *self as u8),
+        }
+    }
+}
+
+/// A 4-bit color type
+///
+/// The different possibilities are available through associated constants;
+/// their exact colors usually depend on the terminal color scheme. A 4-bit
+/// color without its bright bit set is identical to its corresponding 3-bit
+/// color (not necessarily the one with the same name).
+#[derive(Copy, Clone, Debug)]
+pub struct Color4 {
+    color3: Color3,
+    bright: bool,
+}
+
+impl Color4 {
+    /// Build a Color4 based on [`Color3`] and a bright bit
+    pub const fn new(color3: Color3, bright: bool) -> Self {
+        Self { color3, bright }
+    }
+
+    pub const BLACK: Self = Self::new(Color3::BLACK, false);
+    pub const RED: Self = Self::new(Color3::RED, false);
+    pub const GREEN: Self = Self::new(Color3::GREEN, false);
+    pub const YELLOW: Self = Self::new(Color3::YELLOW, false);
+    pub const BLUE: Self = Self::new(Color3::BLUE, false);
+    pub const MAGENTA: Self = Self::new(Color3::MAGENTA, false);
+    pub const CYAN: Self = Self::new(Color3::CYAN, false);
+    pub const LIGHT_GRAY: Self = Self::new(Color3::WHITE, false);
+    pub const DARK_GRAY: Self = Self::new(Color3::BLACK, true);
+    pub const BRIGHT_RED: Self = Self::new(Color3::RED, true);
+    pub const BRIGHT_GREEN: Self = Self::new(Color3::GREEN, true);
+    pub const BRIGHT_YELLOW: Self = Self::new(Color3::YELLOW, true);
+    pub const BRIGHT_BLUE: Self = Self::new(Color3::BLUE, true);
+    pub const BRIGHT_MAGENTA: Self = Self::new(Color3::MAGENTA, true);
+    pub const BRIGHT_CYAN: Self = Self::new(Color3::CYAN, true);
+    pub const WHITE: Self = Self::new(Color3::WHITE, true);
+}
+
+impl Color for Color4 {
+    fn prelude(&self, f: &mut core::fmt::Formatter, canvas: crate::Canvas) -> core::fmt::Result {
+        match canvas {
+            Canvas::Foreground => write!(
+                f,
+                "\x1B[{}m",
+                if self.bright { 90 } else { 30 } + self.color3 as u8
+            ),
+            Canvas::Background => write!(
+                f,
+                "\x1B[{}m",
+                if self.bright { 100 } else { 40 } + self.color3 as u8
+            ),
+        }
+    }
+}

src/lib.rs

@@ -75,12 +75,14 @@ You need to [set your console mode](https://docs.microsoft.com/en-us/windows/con
  */
 
 mod background;
+mod basic_color;
 mod canvas;
 mod color;
 mod colors;
 mod foreground;
 
 pub use background::*;
+pub use basic_color::*;
 pub use canvas::*;
 pub use color::*;
 pub use colors::*;

tests/tests.rs

@@ -50,3 +50,20 @@ fn foo() {
     let foo = Foo(1, 2);
     println!("{:?}", foo.fg(green()));
 }
+
+#[test]
+fn color3() {
+    let hello_world = "Hello, world";
+    let formatted = hello_world.fg(Color3::BLUE);
+    assert_eq!("\u{1b}[34mHello, world\u{1b}[0m", format!("{}", formatted));
+}
+
+#[test]
+fn color4() {
+    let hello_world = "Hello, world";
+    let formatted = hello_world.fg(Color4::BLACK).bg(Color4::WHITE);
+    assert_eq!(
+        "\u{1b}[107m\u{1b}[30mHello, world\u{1b}[0m\u{1b}[0m",
+        format!("{}", formatted)
+    );
+}