add option to lookup multiple coordinates from stdin (#166)

README.md

@@ -130,6 +130,18 @@ Rust port's Python binding; you can view it
 - Python, see [`ringsaturn/tzfpy`](https://github.com/ringsaturn/tzfpy)
 - Wasm, see [`ringsaturn/tzf-wasm`](https://github.com/ringsaturn/tzf-wasm)
 
+## Command line
+
+The binary helps in debugging tzf-rs and using it in (scripting) languages
+without bindings. Either specify the coordinates as parameters to get a single
+time zone, or to look up multiple coordinates efficiently specify the ordering
+and pipe them to the binary one pair of coordinates per line.
+
+```shell
+tzf --lng 116.3883 --lat 39.9289
+echo -e "116.3883 39.9289\n116.3883, 39.9289" | tzf --stdin-order lng-lat
+```
+
 ## LICENSE
 
 This project is licensed under the [MIT license](./LICENSE). The data is

src/bin/tzf.rs

@@ -1,23 +1,69 @@
 #![cfg(feature = "clap")]
 
-use clap::Parser;
+use clap::{Args, Parser, ValueEnum};
+use std::error::Error;
+use std::io::{self, BufRead, Write};
 use tzf_rs::DefaultFinder;
 
 #[derive(Parser, Debug)]
 #[command(name = "tzf")]
 struct Cli {
-    /// longitude
+    #[command(flatten)]
+    params: Option<Params>,
+
+    /// Read multiple coordinates from stdin in given order
+    #[arg(long, conflicts_with("Params"))]
+    stdin_order: Option<StdinOrder>,
+}
+
+#[derive(Args, Debug)]
+struct Params {
+    /// Longitude
     #[arg(long, allow_negative_numbers(true), alias("lon"))]
     lng: f64,
 
-    /// latitude
+    /// Latitude
     #[arg(long, allow_negative_numbers(true))]
     lat: f64,
 }
 
-pub fn main() {
+#[derive(Clone, Debug, ValueEnum)]
+enum StdinOrder {
+    #[value(alias("lon-lat"))]
+    LngLat,
+    #[value(alias("lat-lon"))]
+    LatLng,
+}
+
+fn is_delimiter(c: char) -> bool {
+    matches!(c, ' ' | '\t' | ',' | ';')
+}
+
+pub fn main() -> Result<(), Box<dyn Error>> {
     let cli = Cli::parse();
     let finder = DefaultFinder::new();
-    let tz_name = finder.get_tz_name(cli.lng, cli.lat);
-    println!("{tz_name:?}");
+    if let Some(params) = cli.params {
+        println!("{:?}", finder.get_tz_name(params.lng, params.lat));
+    } else if let Some(stdin_order) = cli.stdin_order {
+        let (mut stdin, mut stdout) = (io::stdin().lock(), io::stdout().lock());
+        let mut line = String::new();
+        while stdin.read_line(&mut line)? != 0 && line.ends_with("\n") {
+            let mut iter = line.chars().skip(1);
+            let i = 1 + iter.position(is_delimiter).expect("Missing delimiter");
+            let j = i
+                + 1
+                + iter
+                    .position(|c| !is_delimiter(c))
+                    .expect("Missing second coordinate");
+            let k = line.len() - if line.ends_with("\r\n") { 2 } else { 1 };
+            let (a, b) = (line[0..i].parse::<f64>()?, line[j..k].parse::<f64>()?);
+            let (lng, lat) = match stdin_order {
+                StdinOrder::LngLat => (a, b),
+                StdinOrder::LatLng => (b, a),
+            };
+            writeln!(stdout, "{:?}", finder.get_tz_name(lng, lat))?;
+            line.clear();
+        }
+    }
+    Ok(())
 }