3 files changed, 180 insertions, 0 deletions
diff --git a/gifed/src/block/extension/application.rs b/gifed/src/block/extension/application.rs
new file mode 100644
index 0000000..9ec1814
--- /dev/null
+++ b/gifed/src/block/extension/application.rs
@@ -0,0 +1,15 @@
+pub struct Application {
+	pub(crate) identifier: String, // max len 8
+	pub(crate) authentication_code: [u8; 3],
+	pub(crate) data: Vec<u8>,
+}
+
+impl Application {
+	pub fn identifier(&self) -> &str {
+		&self.identifier
+	}
+
+	pub fn authentication_code(&self) -> &[u8] {
+		&self.authentication_code
+	}
+}
diff --git a/gifed/src/block/extension/graphiccontrol.rs b/gifed/src/block/extension/graphiccontrol.rs
new file mode 100644
index 0000000..b595554
--- /dev/null
+++ b/gifed/src/block/extension/graphiccontrol.rs
@@ -0,0 +1,116 @@
+use std::{convert::TryInto, fmt};
+
+#[derive(Clone, Debug)]
+pub struct GraphicControl {
+	pub(crate) packed: u8,
+	pub(crate) delay_time: u16,
+	pub(crate) transparency_index: u8,
+}
+
+impl GraphicControl {
+	pub fn new(
+		disposal_method: DisposalMethod,
+		user_input_flag: bool,
+		transparency_flag: bool,
+		delay_time: u16,
+		transparency_index: u8,
+	) -> Self {
+		let mut ret = Self {
+			packed: 0,
+			delay_time,
+			transparency_index,
+		};
+
+		ret.set_disposal_method(disposal_method);
+		ret.user_input(user_input_flag);
+		ret.transparency(transparency_flag);
+
+		ret
+	}
+
+	pub fn disposal_method(&self) -> Option<DisposalMethod> {
+		match self.packed & 0b000_111_00 {
+			0b000_000_00 => Some(DisposalMethod::NoAction),
+			0b000_100_00 => Some(DisposalMethod::DoNotDispose),
+			0b000_010_00 => Some(DisposalMethod::RestoreBackground),
+			0b000_110_00 => Some(DisposalMethod::RestorePrevious),
+			_ => None,
+		}
+	}
+
+	pub fn set_disposal_method(&mut self, method: DisposalMethod) {
+		match method {
+			DisposalMethod::NoAction => self.packed &= 0b111_000_1_1,
+			DisposalMethod::DoNotDispose => self.packed |= 0b000_100_0_0,
+			DisposalMethod::RestoreBackground => self.packed |= 0b000_010_0_0,
+			DisposalMethod::RestorePrevious => self.packed |= 0b000_110_0_0,
+		};
+	}
+
+	pub fn transparency_index(&self) -> u8 {
+		self.transparency_index
+	}
+
+	pub fn user_input(&mut self, flag: bool) {
+		if flag {
+			self.packed |= 0b000_000_1_0;
+		} else {
+			self.packed &= 0b111_111_0_1;
+		}
+	}
+
+	pub fn transparency(&mut self, flag: bool) {
+		if flag {
+			self.packed |= 0b000_000_0_1;
+		} else {
+			self.packed &= 0b111_111_1_0;
+		}
+	}
+
+	pub fn delay_time(&self) -> u16 {
+		self.delay_time
+	}
+
+	pub fn delay_time_mut(&mut self) -> &mut u16 {
+		&mut self.delay_time
+	}
+
+	pub fn is_transparent(&self) -> bool {
+		self.packed & 0b000_000_0_1 > 0
+	}
+}
+
+impl From<[u8; 4]> for GraphicControl {
+	fn from(arr: [u8; 4]) -> Self {
+		let packed = arr[0];
+		let delay_time = u16::from_le_bytes(arr[1..3].try_into().unwrap());
+		let transparency_index = arr[3];
+
+		Self {
+			packed,
+			delay_time,
+			transparency_index,
+		}
+	}
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum DisposalMethod {
+	NoAction,
+	DoNotDispose,
+	RestoreBackground,
+	RestorePrevious,
+}
+
+impl fmt::Display for DisposalMethod {
+	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+		let st = match self {
+			DisposalMethod::NoAction => "Dispose as Normal",
+			DisposalMethod::DoNotDispose => "No Dispose",
+			DisposalMethod::RestoreBackground => "Restore to background",
+			DisposalMethod::RestorePrevious => "Restore previous image",
+		};
+
+		write!(f, "{}", st)
+	}
+}
diff --git a/gifed/src/block/extension/mod.rs b/gifed/src/block/extension/mod.rs
new file mode 100644
index 0000000..fb5eb20
--- /dev/null
+++ b/gifed/src/block/extension/mod.rs
@@ -0,0 +1,49 @@
+mod application;
+mod graphiccontrol;
+
+pub use graphiccontrol::{DisposalMethod, GraphicControl};
+
+pub use self::application::Application;
+
+pub enum Extension {
+	GraphicControl(GraphicControl),
+	Looping(u16),
+	Comment(Vec<u8>), // Plain Text
+	Application(Application),
+}
+
+impl From<&Extension> for Box<[u8]> {
+	fn from(ext: &Extension) -> Self {
+		let mut vec = vec![];
+		vec.push(0x21); // Push the extension introducer
+
+		match ext {
+			Extension::GraphicControl(gc) => {
+				vec.push(0xF9); // Graphic control label
+				vec.push(0x04); // Block size for this extension is always 4
+				vec.push(gc.packed);
+				vec.extend_from_slice(&gc.delay_time.to_le_bytes());
+				vec.push(gc.transparency_index);
+			}
+			Extension::Looping(count) => {
+				vec.push(0xFF); // Application extension label
+				vec.push(0x0B); // 11 bytes in this block
+				vec.extend_from_slice(b"NETSCAPE2.0"); // App. ident. and "auth code"
+				vec.push(0x03); // Sub-block length
+				vec.push(0x01); // Identifies netscape looping extension
+				vec.extend_from_slice(&count.to_le_bytes());
+			}
+			Extension::Comment(_) => todo!(),
+			Extension::Application(_) => todo!(),
+		}
+
+		vec.push(0x00); // Zero-length data block indicates end of extension
+		vec.into_boxed_slice()
+	}
+}
+
+impl From<GraphicControl> for Extension {
+	fn from(gce: GraphicControl) -> Self {
+		Extension::GraphicControl(gce)
+	}
+}