# Shellfish

Shellfish is a library to include interactive shells within a program. This may be useful when building terminal application where a persistent state is needed, so a basic cli is not enough; but a full tui is over the scope of the project. Shellfish provides a middle way, allowing interactive command editing whilst saving a state that all commands are given access to.

## The shell

By default the shell contains only 3 built-in commands:

 * `help` - displays help information.
 * `quit` - quits the shell.
 * `exit` - exits the shell.

The last two are identical, only the names differ.

When a command is added by the user (see bellow) the help is automatically generated and displayed. Keep in mind this help should be kept rather short, and any additional help should be through a dedicated help option.

## Features

The following features are available:
 * `rustyline`, for better input. This provides an `InputHandler`
 * `app`, for command line argument parsing.
 * `async`, for async. This can be coupled with `tokio` or `async_std`
 * [`clap`](#clap), for integration with the `clap` library.

## Example

The following code creates a basic shell, with the added commands:
 * `greet`, greets the user.
 * `echo`, echoes the input.
 * `count`, increments a counter.
 * `cat`, it is cat.

Also, if run with arguments than the shell is run non-interactvely.

```rust,compile_fail
use std::error::Error;
use std::fmt;
use std::ops::AddAssign;

use async_std::prelude::*;
use rustyline::DefaultEditor;
use shellfish::{app, handler::DefaultAsyncHandler, Command, Shell};

#[macro_use]
extern crate shellfish;

#[async_std::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Define a shell
    let mut shell = Shell::new_with_async_handler(
        0_u64,
        "<[Shellfish Example]>-$ ",
        DefaultAsyncHandler::default(),
        DefaultEditor::new()?,
    );

    // Add some commands
    shell
        .commands
        .insert("greet", Command::new("greets you.".to_string(), greet));

    shell
        .commands
        .insert("echo", Command::new("prints the input.".to_string(), echo));

    shell.commands.insert(
        "count",
        Command::new("increments a counter.".to_string(), count),
    );

    shell.commands.insert(
        "cat",
        Command::new_async(
            "Displays a plaintext file.".to_string(),
            async_fn!(u64, cat),
        ),
    );

    // Check if we have > 2 args, if so no need for interactive shell
    let mut args = std::env::args();
    if args.nth(1).is_some() {
        // Create the app from the shell.
        let mut app = app::App::try_from_async(shell)?;

        // Set the binary name
        app.handler.proj_name = Some("shellfish-example".to_string());
        app.load_cache()?;

        // Run it
        app.run_args_async().await?;
    } else {
        // Run the shell
        shell.run_async().await?;
    }
    Ok(())
}

/// Greets the user
fn greet(_state: &mut u64, args: Vec<String>) -> Result<(), Box<dyn Error>> {
    let arg = args.get(1).ok_or_else(|| Box::new(GreetingError))?;
    println!("Greetings {}, my good friend.", arg);
    Ok(())
}

/// Echos the input
fn echo(_state: &mut u64, args: Vec<String>) -> Result<(), Box<dyn Error>> {
    let mut args = args.iter();
    args.next();
    for arg in args {
        print!("{} ", arg);
    }
    println!();
    Ok(())
}

/// Acts as a counter
fn count(state: &mut u64, _args: Vec<String>) -> Result<(), Box<dyn Error>> {
    state.add_assign(1);
    println!("You have used this counter {} times", state);
    Ok(())
}

/// Asynchronously reads a file
async fn cat(
    _state: &mut u64,
    args: Vec<String>,
) -> Result<(), Box<dyn Error>> {
    use async_std::fs;

    if let Some(file) = args.get(1) {
        let mut contents = String::new();
        let mut file = fs::File::open(file).await?;
        file.read_to_string(&mut contents).await?;
        println!("{}", contents);
    }

    Ok(())
}

/// Greeting error
#[derive(Debug)]
pub struct GreetingError;

impl fmt::Display for GreetingError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "No name specified")
    }
}

impl Error for GreetingError {}
```

## Clap support

[`clap`](https://docs.rs/clap/3.2.16/clap/) allows for much
cleaner and easier handling of command line arguments, as can
be seen below:

```rust,compile_fail
// ... imports ...

/// Simple command to greet a person
///
/// This command will greet the person based of a multitide
/// of option flags, see below.
#[derive(Parser, Debug)]
#[clap(author, version, about)]
struct GreetArgs {
    /// Name of the person to greet
    name: String,

    /// Age of the person to greet
    #[clap(short, long)]
    age: Option<u8>,

    /// Whether to be formal or note
    #[clap(short, long)]
    formal: bool,
}

#[async_std::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Define a shell
    let mut shell = Shell::new_with_async_handler(
        (),
        "<[Shellfish Example]>-$ ",
        DefaultAsyncHandler::default(),
        DefaultEditor::new()?,
    );
    shell
        .commands
        .insert("greet", clap_command!((), GreetArgs, greet));
    shell.run_async().await?;

    Ok(())
}

fn greet(
    _state: &mut (),
    args: GreetArgs,
) -> Result<(), Box<dyn std::error::Error>> {

    // .. snip .. /
    
    Ok(())
}
```

For larger projects it is recommended to use clap to cut down on
boiler-plait.