trjhtr

I'm learning Rust by learning the Rust programming language book. I'm now implementing the solution for the third challenge.

Using a hash map and vectors, create a text interface to allow a user to add employee names to a department in a company. For example, "Add Sally to Engineering" or "Add Amir to Sales." Then let the user retrieve a list of all people in a department or all people in the company by department, sorted alphabetically.

I decided to do a simple UI to enter commands, but the implementation is very naive overall.

Rust is my first systems language. My background is in Ruby and Javascript.

use std::collections::HashMap;
use std::io::self, Write;
use std::str::SplitWhitespace;

fn main() 
 println!("Welcome to the department interface. Please run a command:");
 help();

 let mut departments: HashMap<String, Vec<String>> = HashMap::new();

 loop 
 print_promt();
 let command = get_command();
 let mut command_iter = command.split_whitespace();

 match command_iter.next() 
 Some("add") => match process_add(&mut command_iter) 
 Ok((employee, department)) => 
 let mut employees = departments.entry(department).or_insert(Vec::new());
 employees.push(employee);
 
 Err(err) => println!("Error: ", err),
 ,
 Some("help") => help(),
 Some("list") => println!(":#?", &departments),
 Some("exit") => break,
 Some(_) => println!(": Command unknown. Try `help`", command),
 None => panic!("We shouldn't be here"),
 
 


fn help() 
 println!("help: show this help.");
 println!("exit: exits this program.");
 println!("show: shows the deparment structure.");
 println!("add: adds an employee to a department");
 println!(" - usage: `add <employee name> to <department_name>`");


fn print_promt() 
 print!("> ");
 io::stdout().flush().ok().expect("Couldn't flush stdout!");


// I think this can be made better returning an Enum/Struct with a parsed command.
fn get_command() -> String 
 let mut command = String::new();
 io::stdin()
 .read_line(&mut command)
 .expect("Couldn't read command!");
 command



// The compiler told me to add the lifetime, but I don't understand why (I haven't reached that
// part of the book yet.)
// FIXME `SplitWhitespace` is too specific.
fn process_add<'a>(command: &mut SplitWhitespace) -> Result<(String, String), &'a str> 
 let mut employee = String::new();
 let mut department = String::new();

 // For a command "add Ronald Reagan to Old Presidents"
 // - Consume the iterator onto `employee` until you find "to""
 // - Consume the rest of the iterator onto `department`
 // Using two loops feels naive though. I don't like the duplication inside them.
 //
 // Maybe `String` can be extended and I could add a `push_str_with_separator` method that does
 // the extra check.
 // 
 // employee.push_str_with_separator(word);
 //
 while let Some(word) = command.next() 
 if word == "to" 
 break;
 

 if employee.len() > 0 
 employee.push_str(" ");
 
 employee.push_str(word)
 

 for word in command 
 if department.len() > 0 
 department.push_str(" ");
 
 department.push_str(word);
 

 if employee.len() > 0 && department.len() > 0 
 Ok((employee, department))
 else 
 Err("Could not parse command. Try `add <employee name> to <department name>")