path: root/src/poem/anthology.rs

mod alias;
mod cd;
mod exit;
mod export;
mod source;
mod which;
use crate::compose::Environment;
use std::io;
use std::process::{Output, Stdio};

/// A static list of all the built-in commands
static INDEX: [&str; 8] = [
    "alias", "cd", "exit", "export", "source", "unalias", "unset", "which",
];

/// Lookup the index of a built-in command
///
/// Looks up the index of a built-in command in [INDEX], accounting for
/// aliases.
///
/// # Aliases
/// * quit -> exit
/// * set -> export
pub fn lookup(verb: &str) -> Option<usize> {
    let verb = match verb {
        "quit" => "exit",  // Alias 'quit' to 'exit'
        "set" => "export", // Alias 'set' to 'export'
        _ => verb,
    };
    INDEX.iter().position(|v| v.to_string() == verb)
}

/// Dummy interface for STDIN
///
/// A helper struct for dealing with STDIN in built-in commands.
/// Currently, there are no built-in commands that actually use this,
/// but it needs to exist for the `incant!()` macro to function
/// properly. See [Anthology] for more details.
#[derive(Debug, PartialEq, Eq, Clone)]
pub struct AnthologyStdin {
    /// Bytes
    data: Vec<u8>,
}

impl AnthologyStdin {
    /// Create a new instance of AnthologyStdin
    pub fn new() -> Self {
        AnthologyStdin { data: Vec::new() }
    }

    /// Return a mutable version of self
    pub fn as_mut(&mut self) -> Option<&mut Self> {
        Some(self)
    }

    /// Write bytes specified by data into STDIN
    pub fn write_all(&mut self, data: &[u8]) -> Result<(), io::Error> {
        self.data.append(&mut data.to_vec());
        Ok(())
    }
}

/// Interface for built-in commands
///
/// The implementation of [Anthology] is designed to mimic
/// [std::process::Command], in order to avoid code redundancy. The
/// internal structure of [Anthology] is fairly irrelevant to this
/// `impl`, with the exception of the `stdin`, and `output` fields. In
/// addition to the documentation below, it may also be helpful to read
/// through the `incant!()` macro, so see how processes are actually
/// forked.
#[derive(Debug, Clone)]
pub struct Anthology {
    /// Name of the built-in command (see [lookup()] and/or [INDEX])
    verb: String,

    /// Arguments to pass to the built-in command
    clause: Option<Vec<String>>,

    /// Indicates STDIN should be read in (but no built-ins use STDIN)
    uin: bool,

    /// Indicates STDOUT should be captured
    uout: bool,

    /// Indicates STDERR should be captured
    uerr: bool,

    /// Compatability with [std::process::Command]
    pub stdin: AnthologyStdin,

    /// Stores the built-in output (return code, STDOUT, STDERR), also
    /// needed for compatability with [std::process::Command]
    output: Option<Output>,
}

impl Anthology {
    /// Create a new instance of a built-in command
    ///
    /// Sets up a built-in command with default values.
    ///
    /// # Examples
    /// ```
    /// let mut command = Anthology::new("alias");
    /// ```
    pub fn new(i: usize) -> Self {
        Anthology {
            verb: INDEX[i].to_string(),
            clause: None,
            uin: false,
            uout: false,
            uerr: false,
            stdin: AnthologyStdin::new(),
            output: None,
        }
    }

    /// Setup arguments to the built-in command
    ///
    /// Sets the 'clause' field of the [Anthology] struct, which are arguments
    /// to be passed to the built-in command.
    pub fn args(&mut self, clause: Vec<String>) {
        self.clause = match clause.is_empty() {
            true => None,
            false => Some(clause.clone()),
        };
    }

    /// Read to STDIN
    ///
    /// None of the built-in commands will currently read from STDIN for any
    /// reason, so this is just a dummy function.
    pub fn stdin(&mut self, _stdin: Stdio) {
        self.uin = true;
    }

    /// Capture STDOUT
    pub fn stdout(&mut self, _stdout: Stdio) {
        self.uout = true;
    }

    /// Capture STDERR
    pub fn stderr(&mut self, _stderr: Stdio) {
        self.uerr = true;
    }

    /// Set the process group
    ///
    /// This is only needed if a process is forked into the background.
    /// Technically this is possible with the built-ins, but not really
    /// useful, so this function simply does nothing. As a result,
    /// built-ins that get forked into the background always return
    /// immediately.
    pub fn process_group(&mut self, _id: usize) {}

    /// Get the process id
    ///
    /// This is only needed if a process is forked into the background.
    /// Will always return `0` for built-in commands. Also see
    /// [process_group()][Anthology::process_group].
    pub fn id(&mut self) -> i32 {
        0
    }

    /// Run a built-in command
    ///
    /// Runs a built-in command based on the `verb`, appropriately
    /// passing arguments and [Environment] fields as necessary.
    pub fn spawn(&mut self, env: &mut Environment) -> Result<Self, io::Error> {
        // Incant the built-in and set the output
        self.output = Some(match self.verb.as_str() {
            "alias" => alias::incant(&self.clause, self.uout, &mut env.aliases),
            "cd" => cd::incant(&self.clause, self.uerr),
            "exit" => exit::incant(),
            "export" => export::incant(&self.clause, self.uout),
            "source" => source::incant(&self.clause, self.uout, self.uerr, env),
            "unalias" => alias::unincant(&self.clause, self.uerr, &mut env.aliases),
            "unset" => export::unincant(&self.clause, self.uerr),
            "which" => which::incant(&self.clause, self.uout, self.uerr, env),
            _ => unreachable!(),
        });

        Ok(self.clone())
    }

    /// Get the output of a built-in
    ///
    /// Return the [Output] of a built-in command. This function needed
    /// for compatibility with [std::process::Command].
    pub fn wait_with_output(&self) -> Result<Output, io::Error> {
        match &self.output {
            Some(output) => Ok(output.clone()),
            None => Err(io::Error::new(io::ErrorKind::Other, "not spawned")),
        }
    }
}