skip lines by counter alone

src/lib.rs

@@ -1,6 +1,8 @@
 use std::path::PathBuf;
 use std::fmt::Debug;
 use clap::Parser;
+use std::fs;
+use std::io;
 
 #[derive(Parser,Debug)]
 #[command(version)]
@@ -20,10 +22,24 @@ pub struct Cli {
     ignore_extras: bool,
 }
 
-pub fn skip<F>(cli: Cli, mut out: F) -> ()
+pub fn skip<F>(cli: Cli, mut out: F) -> io::Result<()>
     where F: FnMut(String) -> ()
 {
-    out(String::from("line 2"));
+    match &cli.file {
+        Some(file) => {
+            let content = fs::read_to_string(file).expect("Could not read file");
+            let mut counter = 0usize;
+            for current_line in content.lines() {
+                counter += 1;
+                if counter > cli.lines {
+                    out(String::from(current_line));
+                }
+            }
+        },
+        None => todo!("reading from stdin")
+    }
+
+    Ok(())
 }
 
 #[cfg(test)]
@@ -32,16 +48,31 @@ mod tests {
     use super::*;
 
     #[test]
-    fn skip_one_line() {
+    fn skip_one_line_from_two() -> io::Result<()> {
         //given
         let cli = Cli { lines: 1, file: Some(PathBuf::from("tests/two-lines.txt")), line: None, token: None, ignore_extras: false };
         let mut lines: Vec<String> = Vec::new();
 
         //when
-        skip(cli, |line| lines.push(line));
+        skip(cli, |line| lines.push(line))?;
 
         //then
         assert_eq!(lines, vec!["line 2"]);
+        Ok(())
+    }
+
+    #[test]
+    fn skip_two_lines_from_four() -> io::Result<()> {
+        //given
+        let cli = Cli { lines: 2, file: Some(PathBuf::from("tests/four-lines.txt")), line: None, token: None, ignore_extras: false };
+        let mut lines: Vec<String> = Vec::new();
+
+        //when
+        skip(cli, |line| lines.push(line))?;
+
+        //then
+        assert_eq!(lines, vec!["alpha", "gamma"]);
+        Ok(())
     }
 
 }

src/main.rs

@@ -2,16 +2,16 @@ use skip::{Cli, skip};
 use clap::Parser;
 use std::io::Write;
 
-fn main() {
+fn main() -> std::io::Result<()> {
     let args = Cli::parse();
+
     let stdout = std::io::stdout();
-    {
-        let mut output = stdout.lock();
-        skip(args, |line| {
-            match writeln!(output, "{}", line) {
-                Err(_) => (),
-                Ok(_) => ()
-            }
-        });
-    }
+    let mut output = stdout.lock();
+
+    skip(args, |line| {
+        match writeln!(output, "{}", line) {
+            Err(_) => (),
+            Ok(_) => ()
+        }
+    })
 }

tests/four-lines.txt

@@ -0,0 +1,4 @@
+alpha
+beta
+alpha
+gamma