add option to list timezones

src/cli.rs

@@ -4,6 +4,7 @@ use chrono::Local;
 use chrono::NaiveDate;
 use chrono::NaiveTime;
 use chrono::TimeZone;
+use chrono_tz::TZ_VARIANTS;
 use chrono_tz::Tz;
 use clap::Parser;
 use colored::Colorize;
@@ -28,7 +29,10 @@ pub struct Args {
     #[arg(short, long, default_value = "Local")]
     pub local: String,
 
-    pub time: String,
+    #[arg(long)]
+    pub list: bool,
+
+    pub time: Option<String>,
 }
 
 #[derive(PartialEq, Debug)]
@@ -60,13 +64,15 @@ impl Error for CliError {}
 
 pub fn print_timezones(
     timezones: &Vec<String>,
-    time: &String,
+    time: Option<&String>,
     date: Option<&String>,
     local_timezone: &String,
     padding_hours: i8,
 ) -> Result<(), CliError> {
     let todays_date = &get_todays_date();
     let date = date.unwrap_or(todays_date);
+    let time_now = Local::now().format("%H:%M").to_string();
+    let time = time.unwrap_or(&time_now);
 
     let parsed_time = if let Ok(hour) = time.parse::<u32>() {
         NaiveTime::from_hms_opt(hour, 0, 0).ok_or(CliError::CouldNotParseTime)?
@@ -194,3 +200,9 @@ fn print_timetable(name: &String, name_padding_len: u32, timetable: &Vec<NaiveTi
 
     println!("{}:{}\t{}", name, name_padding, formatted.join("\t"));
 }
+
+pub fn list_timezones() {
+    for tz in TZ_VARIANTS {
+        println!("{}", tz.name())
+    }
+}

src/main.rs

@@ -4,13 +4,17 @@ mod cli;
 use clap::Parser;
 use cli::{Args, print_timezones};
 
+use crate::cli::list_timezones;
+
 fn main() {
     let args = Args::parse();
 
-    if args.timezone.len() > 0 {
+    if args.list {
+        list_timezones();
+    } else if args.timezone.len() > 0 {
         let res = print_timezones(
             &args.timezone,
-            &args.time,
+            args.time.as_ref(),
             args.date.as_ref(),
             &args.local,
             5,