add: rewriter logic and tests

src/main.rs

@@ -0,0 +1,51 @@
+use clap::Parser;
+
+mod rewriter;
+
+use env_logger::Env;
+use log::info;
+use rewriter::Rewriter;
+
+/// Implements a HTTP server which allows clients to 'register'
+/// themselves. Their IP address will be used to replace a
+/// needle in a set of config files. This is intended to be
+/// used as a low-cost way of enabling Kubernetes ingress
+/// using nginx running on a machine that has a public port.
+/// 
+/// The needle is expected to be a dummy IP address; something
+/// fairly unique. The goal is to replace nginx files, where
+/// we often repeat lines if we want nginx to load balance between
+/// multiple destination IPs.
+#[derive(Parser, Debug)]
+#[command(version, about, long_about = None)]
+struct Args {
+    /// The needle that will be replaced. Anytime a line
+    /// is encountered with this needle, the line is dropped
+    /// and instead N lines (one per replacement) is added to
+    /// the output.
+    #[arg(short, long)]
+    rewrite_string: String,
+
+    /// The folder which contains the templates that
+    /// will be be searched for the needle.
+    #[arg(short, long)]
+    source_folder: String,
+
+    /// Where to write the replaced lines.
+    #[arg(short, long)]
+    dest_folder: String,
+}
+
+fn main() {
+    // Log info and above by default
+    env_logger::Builder::from_env(Env::default().default_filter_or("info")).init();
+    let args = Args::parse();
+
+    let mut rewriter = Rewriter::new(args.rewrite_string);
+
+    rewriter.add_replacement(String::from("abc"));
+    rewriter
+        .rewrite_folder(&args.source_folder, &args.dest_folder)
+        .unwrap();
+    info!("Finished writing new config to {}", args.dest_folder);
+}