feat: Implement the prompt module for username (#56)

src/modules/directory.rs

@@ -40,6 +40,8 @@ pub fn segment(context: &Context) -> Option<Module> {
     let truncated_dir_string = truncate(dir_string, DIR_TRUNCATION_LENGTH);
     module.new_segment("path", truncated_dir_string);
 
+    module.get_prefix().set_value("in ");
+
     Some(module)
 }
 

src/modules/mod.rs

@@ -8,6 +8,7 @@ mod nodejs;
 mod package;
 mod python;
 mod rust;
+mod username;
 
 use crate::context::Context;
 use crate::module::Module;
@@ -24,6 +25,7 @@ pub fn handle(module: &str, context: &Context) -> Option<Module> {
         "package" => package::segment(context),
         "git_branch" => git_branch::segment(context),
         "git_status" => git_status::segment(context),
+        "username" => username::segment(context),
 
         _ => panic!("Unknown module: {}", module),
     }

src/modules/username.rs

@@ -0,0 +1,49 @@
+use ansi_term::{Color, Style};
+use std::env;
+use std::process::Command;
+
+use super::{Context, Module};
+
+/// Creates a segment with the current user's username
+///
+/// Will display the usename if any of the following criteria are met:
+///     - The current user isn't the same as the one that is logged in ($LOGNAME != $USER)
+///     - The current user is root (UID = 0)
+///     - The user is currently connected as an SSH session ($SSH_CONNECTION)
+pub fn segment(_context: &Context) -> Option<Module> {
+    let user = env::var("USER").ok();
+    let logname = env::var("LOGNAME").ok();
+    let ssh_connection = env::var("SSH_CONNECTION").ok();
+
+    let mut module_color = Color::Yellow.bold();
+
+    if user != logname || ssh_connection.is_some() || is_root(&mut module_color) {
+        let mut module = Module::new("username");
+        module.set_style(module_color);
+        module.new_segment("username", user?);
+
+        return Some(module);
+    }
+
+    None
+}
+
+fn get_uid() -> Option<u32> {
+    match Command::new("id").arg("-u").output() {
+        Ok(output) => String::from_utf8(output.stdout)
+            .map(|uid| uid.trim().parse::<u32>().ok())
+            .ok()?,
+        Err(_) => None,
+    }
+}
+
+fn is_root(style: &mut Style) -> bool {
+    match get_uid() {
+        Some(uid) if uid == 0 => {
+            style.clone_from(&Color::Red.bold());
+
+            true
+        }
+        _ => false,
+    }
+}

src/print.rs

@@ -8,6 +8,7 @@ use crate::modules;
 
 pub fn prompt(args: ArgMatches) {
     let prompt_order = vec![
+        "username",
         "directory",
         "git_branch",
         "git_status",