2 files changed, 80 insertions, 8 deletions

diff --git a/src/bin/prepare-commit-msg.rs b/src/bin/prepare-commit-msg.rs
index 8118374..63edba0 100644
--- a/src/bin/prepare-commit-msg.rs
+++ b/src/bin/prepare-commit-msg.rs
@@ -1,14 +1,55 @@
+extern crate rust_git_hooks;
+
+use rust_git_hooks::*;
+use std::fs::File;
+use std::io::Write;
+use std::io::Read;
+use std::process;
 use std::env;
-use std::io::{stdin, BufRead};
 
 fn main() {
-    let args: Vec<_> = env::args().skip(1).collect();
-    println!("prepare-commit-msg called with {:?}", args);
+    log();
+
+    let current_branch = get_current_branch();
+    let commit_filename = env::args().nth(1);
 
-    println!("BEGIN STDIN for prepare-commit-msg");
-    let stdin = stdin();
-    for line in stdin.lock().lines() {
-        println!("{:?}", line);
+    
+    match (current_branch, commit_filename) {
+        (Ok(branch), Some(filename)) => {
+            let write_result = prepend_branch_name(branch, filename);
+            match write_result {
+                Ok(_) => {},
+                Err(e) => {
+                    eprintln!("Failed to prepend message. {}", e);
+                    process::exit(2);
+                }
+            };
+        },
+        (Err(e), _) => {
+            eprintln!("Failed to find current branch. {}", e);
+            process::exit(1);
+        },
+        (_, None) => {
+            eprintln!("Commit file was not provided");
+            process::exit(2);
+        }
     }
-    println!("END STDIN");
+}
+
+fn prepend_branch_name(branch_name: String, commit_filename: String) -> Result<(), std::io::Error> {
+    // It turns out that prepending a string to a file is not an
+    // obvious action. You can only write to the end of a file :(
+    //
+    // The solution is to read the existing contents, then write a new
+    // file starting with the branch name, and then writing the rest
+    // of the file.
+    
+    let mut read_commit_file = File::open(commit_filename.clone())?;
+    let mut current_message = String::new();
+    read_commit_file.read_to_string(&mut current_message)?;
+    
+    let mut commit_file = File::create(commit_filename)?;
+
+    writeln!(commit_file, "{}:", branch_name)?;
+    write!(commit_file, "{}", current_message)
 }
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..18b3476
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,31 @@
+extern crate git2;
+
+use std::env;
+use std::io::{stdin, BufRead};
+
+use git2::Repository;
+
+
+pub fn log() {
+    let name_arg = env::args().nth(0).unwrap_or(String::from("unknown"));
+    let args: Vec<_> = env::args().skip(1).collect();
+    println!("{} called with {:?}", name_arg, args);
+
+    println!("BEGIN STDIN");
+    let stdin = stdin();
+    for line in stdin.lock().lines() {
+        println!("{:?}", line);
+    }
+    println!("END STDIN");
+}
+
+pub fn get_current_branch() -> Result<String, git2::Error> {
+    let git_repo = Repository::discover("./")?;
+    let head = git_repo.head()?;
+    let head_name =  head.shorthand();
+    match head_name {
+        Some(name) => Ok(name.to_string()),
+        None => Err(git2::Error::from_str("No branch name found"))
+    }
+}
+