patch lab 1 feedback + do lab 02

labs/02/cut.rs

@@ -0,0 +1,106 @@
+use std::env;
+use std::io;
+use std::process;
+
+enum Range {
+    Nth(usize),
+    From(usize),
+    Between(usize, usize),
+    To(usize),
+}
+
+impl Range {
+    fn parse(s: &str) -> Option<Range> {
+        match s.split_once('-') {
+            None => Some(Range::Nth(number(s)?)),
+            Some(("", m)) => Some(Range::To(number(m)?)),
+            Some((n, "")) => Some(Range::From(number(n)?)),
+            Some((n, m)) => {
+                let (n, m) = (number(n)?, number(m)?);
+                if n > m {
+                    return None;
+                }
+                Some(Range::Between(n, m))
+            }
+        }
+    }
+
+    fn contains(&self, n: usize) -> bool {
+        match *self {
+            Range::Nth(x) => n == x,
+            Range::From(x) => n >= x,
+            Range::Between(x, y) => n >= x && n <= y,
+            Range::To(y) => n <= y,
+        }
+    }
+}
+
+// str::parse accepts a leading '+', so check digits ourselves
+fn number(s: &str) -> Option<usize> {
+    if s.is_empty() || !s.chars().all(|c| c.is_ascii_digit()) {
+        return None;
+    }
+
+    let n: usize = s.parse().ok()?;
+    if n == 0 {
+        return None;
+    }
+
+    Some(n)
+}
+
+fn parse_args(arg: &str) -> Option<(bool, Vec<Range>)> {
+    let fields = match arg.get(..2)? {
+        "-c" => false,
+        "-f" => true,
+        _ => return None,
+    };
+
+    let ranges = arg[2..]
+        .split(',')
+        .map(Range::parse)
+        .collect::<Option<Vec<_>>>()?;
+
+    Some((fields, ranges))
+}
+
+fn selected(ranges: &[Range], n: usize) -> bool {
+    ranges.iter().any(|r| r.contains(n))
+}
+
+fn cut(line: &str, fields: bool, ranges: &[Range]) -> String {
+    if fields {
+        line.split('\t')
+            .enumerate()
+            .filter(|(i, _)| selected(ranges, i + 1))
+            .map(|(_, f)| f)
+            .collect::<Vec<_>>()
+            .join("\t")
+    } else {
+        line.chars()
+            .enumerate()
+            .filter(|(i, _)| selected(ranges, i + 1))
+            .map(|(_, c)| c)
+            .collect()
+    }
+}
+
+fn main() {
+    let args: Vec<String> = env::args().skip(1).collect();
+
+    let (fields, ranges) = match args.as_slice() {
+        [arg] => parse_args(arg),
+        _ => None,
+    }
+    .unwrap_or_else(|| {
+        eprintln!("usage: cut -c<ranges> | -f<ranges>");
+        process::exit(1);
+    });
+
+    let input = io::read_to_string(io::stdin()).unwrap_or_default();
+
+    for line in input.split_inclusive('\n') {
+        let body = line.trim_end_matches(['\n', '\r']);
+        print!("{}{}", cut(body, fields, &ranges), &line[body.len()..]);
+    }
+}