Implement rupsc, clone of upsc (#5)

Fixes #4

rupsc/src/main.rs

@@ -0,0 +1,85 @@
+///! # rupsc
+///! A demo program to display UPS variables.
+///! This a Rust clone of [upsc](https://github.com/networkupstools/nut/blob/master/clients/upsc.c).
+///!
+///! P.S.: pronounced "r-oopsie".
+mod cmd;
+mod parser;
+
+use crate::parser::UpsdName;
+use anyhow::Context;
+use clap::{App, Arg};
+use core::convert::TryInto;
+
+fn main() -> anyhow::Result<()> {
+    let args = App::new(clap::crate_name!())
+        .version(clap::crate_version!())
+        .author(clap::crate_authors!())
+        .about(clap::crate_description!())
+        .arg(
+            Arg::with_name("list")
+                .short("l")
+                .conflicts_with_all(&["list-full", "clients"])
+                .takes_value(false)
+                .help("Lists each UPS on <hostname>, one per line."),
+        )
+        .arg(
+            Arg::with_name("list-full")
+                .short("L")
+                .conflicts_with_all(&["list", "clients"])
+                .takes_value(false)
+                .help("Lists each UPS followed by its description (from ups.conf)."),
+        )
+        .arg(
+            Arg::with_name("clients")
+                .short("c")
+                .conflicts_with_all(&["list", "list-full"])
+                .takes_value(false)
+                .help("Lists each client connected on <upsname>, one per line."),
+        )
+        .arg(
+            Arg::with_name("debug")
+                .short("D")
+                .takes_value(false)
+                .help("Enables debug mode (logs network commands to stderr)."),
+        )
+        .arg(
+            Arg::with_name("upsd-server")
+                .required(false)
+                .value_name("[upsname][@<hostname>[:<port>]]")
+                .help("upsd server (with optional upsname, if applicable)."),
+        )
+        .arg(
+            Arg::with_name("variable")
+                .required(false)
+                .value_name("variable")
+                .help("Optional, display this variable only."),
+        )
+        .get_matches();
+
+    let server: parser::UpsdName = args.value_of("upsd-server").map_or_else(
+        || Ok(UpsdName::default()),
+        |s| s.try_into().with_context(|| "Invalid upsd server name"),
+    )?;
+
+    let debug = args.is_present("debug");
+
+    if args.is_present("list") {
+        return cmd::list_devices(server, false, debug);
+    }
+
+    if args.is_present("list-full") {
+        return cmd::list_devices(server, true, debug);
+    }
+
+    if args.is_present("clients") {
+        return cmd::list_clients(server, debug);
+    }
+
+    // Fallback: prints one variable (or all of them)
+    if let Some(variable) = args.value_of("variable") {
+        cmd::print_variable(server, variable, debug)
+    } else {
+        cmd::list_variables(server, debug)
+    }
+}