making it usable from cli

src/args.rs

@@ -0,0 +1,39 @@
+use clap::{Parser, ValueEnum};
+
+#[derive(Parser, Debug)]
+#[command(version, about)]
+pub struct Args {
+    #[arg(long, value_enum, required = true)]
+    pub mode: Mode,
+
+    #[arg(
+        short,
+        long,
+        required = true,
+    )]
+    pub input_file: Option<String>,
+
+    #[arg(
+        short,
+        long,
+        required_if_eq("mode", "Mode::Encode"),
+        required_if_eq("mode", "Mode::Decode"),
+        required_if_eq("mode", "Mode::Remove")
+    )]
+    pub chunk_type: Option<String>,
+
+    #[arg(
+        short,
+        long,
+        required_if_eq("mode", "Mode::Encode")
+    )]
+    pub message: Option<String>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, ValueEnum)]
+pub enum Mode {
+    Encode,
+    Decode,
+    Print,
+    Remove
+}

src/main.rs

@@ -4,9 +4,58 @@ mod chunk_type;
 mod commands;
 mod png;
 
+use core::panic;
+use std::path::PathBuf;
+use std::fs::File;
+
+use args::Mode;
+use chunk_type::ChunkType;
+use clap::Parser;
+use crate::args::Args;
+
 pub type Error = Box<dyn std::error::Error>;
 pub type Result<T> = std::result::Result<T, Error>;
 
-fn main() -> Result<()> {
+fn get_image(path: &str) -> File {
+    let image_path: PathBuf = PathBuf::from(path);
+    let path_display = image_path.display();
+
+    let image = match File::open(&image_path) {
+        Err(why) => panic!("couldn't open {}: {}", path_display, why),
+        Ok(file) => file
+    };
+
+    image
+}
+
+fn encode(image: File, chunk_type: ChunkType, message: &str) {
     todo!()
 }
+
+fn decode(image: File, chunk_type: ChunkType) {
+    todo!()
+}
+
+fn print_message(image: File) {
+    todo!()
+}
+
+fn remove_message(image: File, chunk_type: ChunkType) {
+    todo!()
+}
+
+fn main() -> Result<()> {
+    let args = Args::parse();
+
+    let image = get_image(&args.input_file.unwrap());
+
+    match args.mode {
+        Mode::Encode    => todo!(),
+        Mode::Decode    => todo!(),
+        Mode::Print     => todo!(),
+        Mode::Remove    => todo!(),
+        _               => Err("not a valid mode")?
+    }
+
+    Ok(())
+}