Add initial parsing

Signed-off-by: Marcel Müller <neikos@neikos.email>

src/cli.rs

@@ -0,0 +1,49 @@
+use camino::Utf8PathBuf;
+use clap::Parser;
+
+#[derive(Debug, Parser)]
+pub struct Args {
+    #[clap(short, long)]
+    pub expression: String,
+
+    #[clap(short, long, default_value_t = Utf8PathBuf::from("-"))]
+    input: Utf8PathBuf,
+
+    #[clap(short, long, group = "delimiters")]
+    lines: bool,
+
+    #[clap(short, long, group = "delimiters", default_value_t = true)]
+    words: bool,
+}
+
+pub enum InputDelimiter {
+    Lines,
+    Words,
+}
+
+pub enum Input {
+    Stdin,
+    FilePath(Utf8PathBuf),
+}
+
+impl Args {
+    pub fn delimiter(&self) -> InputDelimiter {
+        if self.lines {
+            return InputDelimiter::Lines;
+        }
+
+        if self.words {
+            return InputDelimiter::Words;
+        }
+
+        unreachable!("Either lines or words has to be true")
+    }
+
+    pub fn input(&self) -> Input {
+        if self.input == "-" {
+            Input::Stdin
+        } else {
+            Input::FilePath(self.input.clone())
+        }
+    }
+}