Add help text and configurable buckets to CLI tool

src/bin/histo.rs

@@ -14,8 +14,101 @@ fn main() {
     }
 }
 
+fn io_error(error: impl Into<Box<dyn std::error::Error + Send + Sync>>) -> io::Error {
+    io::Error::new(io::ErrorKind::Other, error)
+}
+
+const HELP_TEXT: &'static str = "\
+Reads data from `stdin` and prints a histogram of the data to `stdout`.
+
+The input data format must be one unsigned 64-bit integer per line.
+
+USAGE:
+    histo [OPTIONS] [FLAGS]
+
+OPTIONS:
+    -n, --buckets BUCKETS
+        Configure the number of buckets in the histogram
+
+FLAGS:
+    -h, --help
+        Prints help information
+
+    -V, --version
+        Prints version information
+
+EXAMPLE:
+
+    $ head data.txt
+    3
+    1
+    50
+    38
+    1
+    38
+    1
+    38
+    39
+    4
+    $ histo < data.txt
+    # Number of samples = 154653
+    # Min = 1
+    # Max = 58
+    #
+    # Mean = 4.407945529669717
+    # Standard deviation = 5.8241339617399985
+    # Variance = 33.92053640429325
+    #
+    # Each ∎ is a count of 2484
+    #
+     1 ..  7 [ 124222 ]: ∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎
+     7 .. 13 [  18556 ]: ∎∎∎∎∎∎∎
+    13 .. 19 [   7117 ]: ∎∎
+    19 .. 25 [   2059 ]:
+    25 .. 31 [   1245 ]:
+    31 .. 37 [    284 ]:
+    37 .. 43 [    882 ]:
+    43 .. 49 [    122 ]:
+    49 .. 55 [    135 ]:
+    55 .. 61 [     31 ]:
+";
+
+fn help_text() {
+    eprintln!("histo {}\n\n{}", env!("CARGO_PKG_VERSION"), HELP_TEXT);
+}
+
+fn fail_with_help_text(msg: impl AsRef<str>) -> ! {
+    eprintln!("{}", msg.as_ref());
+    eprintln!();
+    help_text();
+    process::exit(1)
+}
+
 fn try_main() -> io::Result<()> {
-    let mut hist = histo::Histogram::with_buckets(10);
+    let mut buckets = 10;
+
+    let mut args = std::env::args().skip(1);
+    while let Some(arg) = args.next() {
+        match arg.as_str() {
+            "-n" | "--buckets" => {
+                let arg = args.next().unwrap_or_else(|| {
+                    fail_with_help_text(format!("missing number of buckets for `{arg}`"))
+                });
+                buckets = arg.parse().map_err(|e| io_error(e))?;
+            }
+            "-h" | "--help" => {
+                help_text();
+                process::exit(0);
+            }
+            "-V" | "--version" => {
+                println!("histo {}", env!("CARGO_PKG_VERSION"));
+                process::exit(0);
+            }
+            _ => fail_with_help_text(format!("unknown CLI argument: `{arg}`")),
+        }
+    }
+
+    let mut hist = histo::Histogram::with_buckets(buckets);
 
     let stdin = io::stdin();
     let mut stdin = stdin.lock();
@@ -27,9 +120,7 @@ fn try_main() -> io::Result<()> {
             if line.is_empty() {
                 continue;
             }
-            let sample: u64 = line.trim()
-                .parse()
-                .map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
+            let sample: u64 = line.trim().parse().map_err(|e| io_error(e))?;
 
             hist.add(sample);
         }