add crate cli_helpers with option and config parsing; use in aquatic

Putting cli functionality into its own crate will allow using it
from aquatic_bench and possibly other programs.

cli_helpers/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "cli_helpers"
+version = "0.1.0"
+authors = ["Joakim Frostegård <joakim.frostegard@gmail.com>"]
+edition = "2018"
+
+[dependencies]
+anyhow = "1"
+gumdrop = "0.7"
+serde = { version = "1", features = ["derive"] }
+toml = "0.5"

cli_helpers/src/lib.rs

@@ -0,0 +1,80 @@
+use std::fs::File;
+use std::io::Read;
+
+use anyhow;
+use gumdrop::Options;
+use serde::{Serialize, de::DeserializeOwned};
+use toml;
+
+
+#[derive(Debug, Options)]
+struct AppOptions {
+    #[options(help = "run with config file", short = "c", meta = "PATH")]
+    config_file: Option<String>,
+    #[options(help = "print default config file")]
+    print_config: bool,
+    #[options(help = "print help message")]
+    help: bool,
+}
+
+
+fn config_from_toml_file<T>(path: String) -> anyhow::Result<T>
+    where T: DeserializeOwned
+{
+    let mut file = File::open(path)?;
+    let mut data = String::new();
+    file.read_to_string(&mut data)?;
+
+    toml::from_str(&data).map_err(|e| anyhow::anyhow!("Parse failed: {}", e))
+}
+
+fn default_config_as_toml<T>() -> String
+    where T: Default + Serialize
+{
+    toml::to_string_pretty(&T::default())
+        .expect("Could not serialize default config to toml")
+}
+
+
+pub fn run_with_cli_and_config<T, F>(
+    title: &str,
+    // Function that takes config file and runs application
+    f: F,
+) where T: Default + Serialize + DeserializeOwned, F: Fn(T) {
+    let args: Vec<String> = ::std::env::args().collect();
+
+    match AppOptions::parse_args_default(&args[1..]){
+        Ok(opts) => {
+            if opts.help_requested(){
+                print_help(title, None);
+            } else if opts.print_config {
+                print!("{}", default_config_as_toml::<T>());
+            } else if let Some(config_file) = opts.config_file {
+                match config_from_toml_file(config_file){
+                    Ok(config) => f(config),
+                    Err(err) => {
+                        eprintln!("Error while reading config file: {}", err);
+
+                        ::std::process::exit(1);
+                    }
+                }
+            } else {
+                f(T::default())
+            }
+        },
+        Err(err) => {
+            print_help(title, Some(&format!("{}", err)))
+        }
+    }
+}
+
+
+fn print_help(title: &str, opt_error: Option<&str>){
+    println!("{}", title);
+
+    if let Some(error) = opt_error {
+        println!("\nError: {}.", error);
+    }
+
+    println!("\n{}", AppOptions::usage());
+}