3 files changed, 54 insertions, 14 deletions

diff --git a/Cargo.toml b/Cargo.toml
index d3ca6e4..d343a43 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,3 +7,5 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+byteorder = "1.4.2"
+bitvec = "0.21.0"
diff --git a/src/encode.rs b/src/encode.rs
new file mode 100644
index 0000000..24d3792
--- /dev/null
+++ b/src/encode.rs
@@ -0,0 +1,34 @@
+use std::io;
+
+use bitvec::prelude::*;
+use bitvec::slice::BitSlice;
+use byteorder::{LittleEndian, WriteBytesExt};
+
+use crate::Image;
+
+pub fn encode_image(obi_image: Image) -> io::Result<Vec<u8>> {
+    let mut obi_data = Vec::with_capacity(obi_image.file_header.file_size as usize);
+
+    // file header
+    let file_header = obi_image.file_header;
+    obi_data.write_u16::<LittleEndian>(file_header.version)?;
+    obi_data.write_u32::<LittleEndian>(file_header.file_size)?;
+    obi_data.write_u32::<LittleEndian>(file_header.data_offset)?;
+
+    // image info header
+    let image_info_header = obi_image.image_info_header;
+    obi_data.write_u32::<LittleEndian>(image_info_header.width)?;
+    obi_data.write_u32::<LittleEndian>(image_info_header.height)?;
+    obi_data.write_u32::<LittleEndian>(image_info_header.compression_type)?;
+    obi_data.write_u32::<LittleEndian>(image_info_header.post_compression_size)?;
+
+    // pixmap data
+    let pixmap = obi_image.data;
+    for byte in pixmap.chunks(8) {
+        let bits_as_u8 = byte.iter().map(|&e| e as u8).collect::<Vec<_>>();
+        let slice = BitSlice::<Lsb0, _>::from_slice(&bits_as_u8).unwrap();
+        obi_data.write_u8(slice.load::<u8>())?;
+    }
+
+    return Ok(obi_data);
+}
diff --git a/src/lib.rs b/src/lib.rs
index 1471aa8..61ca7a8 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,11 +1,7 @@
 #![allow(unreachable_patterns)]
 #![allow(non_snake_case)]
-#[non_exhaustive]
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
-pub enum Pixel {
-    On,
-    Off,
-}
+
+pub mod encode;
 
 #[non_exhaustive]
 #[derive(Copy, Clone, Debug, PartialEq)]
@@ -16,16 +12,16 @@ pub enum OBIVersion {
 impl OBIVersion {
     pub fn header_size(&self) -> u32 {
         match self {
-            One => 26,
+            OBIVersion::One => 26,
         }
     }
 }
 
 #[non_exhaustive]
 pub struct FileHeader {
-    pub version: u16,
     pub file_size: u32,
     pub data_offset: u32,
+    pub version: u16,
 }
 
 impl FileHeader {
@@ -82,15 +78,19 @@ impl CompressionType {
 pub struct Image {
     pub file_header: FileHeader,
     pub image_info_header: ImageInfoHeader,
-    pub data: Vec<Pixel>,
+    pub data: Vec<bool>,
 }
 
 impl Image {
     pub fn new(width: u32, height: u32) -> Self {
-        let data_size = width * height;
-        let data = vec![Pixel::Off; data_size as usize];
+        // round to the nearest multiple of 8
+        // convert to number of bytes by dividing by 8
+        let mut data_size = width * height + 7;
+        data_size = data_size - (data_size % 8);
+        let data = vec![false; data_size as usize];
+
         Self {
-            file_header: FileHeader::new(OBIVersion::One, data_size),
+            file_header: FileHeader::new(OBIVersion::One, data_size / 8),
             image_info_header: ImageInfoHeader::new(width, height),
             data,
         }
@@ -99,8 +99,12 @@ impl Image {
 
 #[cfg(test)]
 mod tests {
+    use super::*;
+    use std::mem::size_of;
+
     #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
+    fn size_of_image_info_header() {
+        let file_header_size = size_of::<ImageInfoHeader>();
+        assert_eq!(16, file_header_size);
     }
 }