patharg 0.3.0

Treat "-" (hyphen/dash) arguments as stdin/stdout
Documentation 
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//! An example of using patharg with clap and tokio
//!
//! Run with `cargo run --example tokio-flipcase --features examples,tokio`
//!
//! Say you're using clap to write a command named "tokio-flipcase" that flips
//! the cases of all the letters in a file, changing uppercase to lowercase and
//! lowercase to uppercase, and you want this command to take a path to a file
//! to read input from and another path for the file to write the output to.
//! By using `patharg::InputArg` and `patharg::OutputArg` as the types of the
//! arguments in your `clap::Parser`, tokio-flipcase will treat a '-' argument
//! as referring to stdin/stdout, and you'll be able to use the types' methods
//! to read or write from any filepath or standard stream given on the command
//! line.
//!
//! tokio-flipcase can then be invoked in the following ways:
//!
//! - `tokio-flipcase` — Read input from stdin, write output to stdout
//! - `tokio-flipcase file.txt` — Read input from `file.txt`, write output to
//!   stdout
//! - `tokio-flipcase -` — Read input from stdin, write output to stdout
//! - `tokio-flipcase -o out.txt` — Read input from stdin, write output to
//!   `out.txt`
//! - `tokio-flipcase -o -` — Read input from stdin, write output to stdout
//! - `tokio-flipcase -o out.txt file.txt` — Read input from `file.txt`, write
//!   output to `out.txt`
//! - `tokio-flipcase -o out.txt -` — Read input from stdin, write output to
//!   `out.txt`
//! - `tokio-flipcase -o - file.txt` — Read input from `file.txt`, write output
//!   to stdout
//! - `tokio-flipcase -o - -` — Read input from stdin, write output to stdout

use clap::Parser;
use patharg::{InputArg, OutputArg};
use tokio::io::AsyncWriteExt;
use tokio_stream::StreamExt;

/// Flip the cases of all the letters in a file.
#[derive(Parser)]
struct Arguments {
    /// The file to write the case-flipped text to.
    #[clap(short = 'o', long, default_value_t)]
    // The `default_value_t` attribute causes the default value of the argument
    // to be `OutputArg::default()`, which equals `OutputArg::Stdout`.
    outfile: OutputArg,

    /// The file to read the text to case-flip from.
    #[clap(default_value_t)]
    // The `default_value_t` attribute causes the default value of the argument
    // to be `InputArg::default()`, which equals `InputArg::Stdin`.
    infile: InputArg,
}

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let args = Arguments::parse();
    let mut output = args.outfile.async_create().await?;
    let mut stream = args.infile.async_lines().await?;
    while let Some(r) = stream.next().await {
        let line = r?;
        let mut flipped = flipcase(line);
        flipped.push('\n');
        output.write_all(flipped.as_ref()).await?;
    }
    Ok(())
}

fn flipcase(s: String) -> String {
    let mut out = String::with_capacity(s.len());
    for c in s.chars() {
        if c.is_uppercase() {
            out.extend(c.to_lowercase());
        } else if c.is_lowercase() {
            out.extend(c.to_uppercase());
        } else {
            out.push(c);
        }
    }
    out
}