//! Quote strings for use with Bash, the GNU Bourne-Again Shell.

use std::ffi::OsString;
use std::os::unix::ffi::OsStringExt;

use crate::scan::Char;

/// Escape a string of *bytes* into a new `Vec<u8>`.
///
/// This will return one of the following:
/// - The string as-is, if no escaping is necessary.
/// - An [ANSI-C escaped string][ansi-c-quoting], like `$'foo bar'`.
///
/// **NOTE:** It is _possible_ to encode NUL in this syntax as `$'\x00'`, but
/// Bash appears to then truncate the rest of the string after that point,
/// likely because NUL is the C string terminator. This seems like a **bug** in
/// Bash.
///
/// See [`escape_into`][] for a variant that extends an existing `Vec` instead
/// of allocating a new one.
///
/// [`escape_into`]: ./fn.escape_into.html
///
/// # Examples
///
/// ```
/// # use shell_quote::bash;
/// assert_eq!(bash::escape("foobar"), b"foobar");
/// assert_eq!(bash::escape("foo bar"), b"$'foo bar'");
/// ```
///
/// # Notes
///
/// From bash(1):
///
///   Words of the form $'string' are treated specially. The word expands to
///   string, with backslash- escaped characters replaced as specified by the
///   ANSI C standard. Backslash escape sequences, if present, are decoded as
///   follows:
///
///   ```text
///   \a     alert (bell)
///   \b     backspace
///   \e     an escape character
///   \f     form feed
///   \n     new line
///   \r     carriage return
///   \t     horizontal tab
///   \v     vertical tab
///   \\     backslash
///   \'     single quote
///   \nnn   the eight-bit character whose value is the
///          octal value nnn (one to three digits)
///   \xHH   the eight-bit character whose value is the
///          hexadecimal value HH (one or two hex digits)
///   \cx    a control-x character
///   ```
///
/// You can see that Bash allows (maybe only in newer versions?) for non-ASCII
/// Unicode characters with `\uHHHH` and `\UXXXXXXXX` syntax, but we avoid this
/// and work only with bytes. Part of the problem is that it's not clear how
/// Bash then works with these strings. Does it encode these characters into
/// bytes according to the user's current locale? Are strings in Bash now
/// natively Unicode?
///
/// For now it's up to the caller to figure out encoding. A significant use case
/// for this code is to escape filenames into scripts, and on *nix variants I
/// understand that filenames are essentially arrays of bytes, even if the OS
/// adds some normalisation and case-insensitivity on top.
///
/// If you have some expertise in this area I would love to hear from you.
///
/// The argument passed into `escape` is `Into<OsString>`, so you can pass in
/// regular Rust strings, `PathBuf`, and so on. For a regular Rust string it
/// will be quoted byte for byte
///
/// [ansi-c-quoting]:
///     https://www.gnu.org/software/bash/manual/html_node/ANSI_002dC-Quoting.html
///
pub fn escape<T: Into<OsString>>(s: T) -> Vec<u8> {
    let sin = s.into().into_vec();
    if let Some(esc) = escape_prepare(&sin) {
        // Maybe pointless optimisation, but here we calculate the memory we need to
        // avoid reallocations as we construct the output string. Since we now know
        // we're going to use Bash's $'...' string notation, we also add 3 bytes.
        let size: usize = esc.iter().map(escape_size).sum();
        let mut sout = Vec::with_capacity(size + 3);
        escape_chars(esc, &mut sout); // Do the work.
        sout
    } else {
        sin
    }
}

/// Escape a string of *bytes* into an existing `Vec<u8>`.
///
/// See [`escape`][] for more details.
///
/// [`escape`]: ./fn.escape.html
///
/// # Examples
///
/// ```
/// # use shell_quote::bash;
/// let mut buf = Vec::with_capacity(128);
/// bash::escape_into("foobar", &mut buf);
/// buf.push(b' ');  // Add a space.
/// bash::escape_into("foo bar", &mut buf);
/// assert_eq!(buf, b"foobar $'foo bar'");
/// ```
///
pub fn escape_into<T: Into<OsString>>(s: T, sout: &mut Vec<u8>) {
    let sin = s.into().into_vec();
    if let Some(esc) = escape_prepare(&sin) {
        // Maybe pointless optimisation, but here we calculate the memory we need to
        // avoid reallocations as we construct the output string. Since we now know
        // we're going to use Bash's $'...' string notation, we also add 3 bytes.
        let size: usize = esc.iter().map(escape_size).sum();
        sout.reserve(size + 3);
        escape_chars(esc, sout); // Do the work.
    } else {
        sout.extend(sin);
    }
}

fn escape_prepare(sin: &[u8]) -> Option<Vec<Char>> {
    let esc: Vec<_> = sin.iter().map(Char::from).collect();
    // An optimisation: if the string only contains "safe" characters we can
    // avoid further work.
    if esc.iter().all(Char::is_literal) {
        None
    } else {
        Some(esc)
    }
}

fn escape_chars(esc: Vec<Char>, sout: &mut Vec<u8>) {
    // Push a Bash-style $'...' escaped string into `sout`.
    sout.extend(b"$'");
    for mode in esc {
        use Char::*;
        match mode {
            Bell => sout.extend(b"\\a"),
            Backspace => sout.extend(b"\\b"),
            Escape => sout.extend(b"\\e"),
            FormFeed => sout.extend(b"\\f"),
            NewLine => sout.extend(b"\\n"),
            CarriageReturn => sout.extend(b"\\r"),
            HorizontalTab => sout.extend(b"\\t"),
            VerticalTab => sout.extend(b"\\v"),
            Backslash => sout.extend(b"\\\\"),
            SingleQuote => sout.extend(b"\\'"),
            ByValue(ch) if ch < 0o177 => sout.extend(format!("\\x{:02X}", ch).bytes()),
            ByValue(ch) => sout.push(ch),
            Literal(ch) => sout.push(ch),
            Quoted(ch) => sout.push(ch),
        }
    }
    sout.push(b'\'');
}

fn escape_size(char: &Char) -> usize {
    use Char::*;
    match char {
        Bell => 2,
        Backspace => 2,
        Escape => 2,
        FormFeed => 2,
        NewLine => 2,
        CarriageReturn => 2,
        HorizontalTab => 2,
        VerticalTab => 2,
        Backslash => 2,
        SingleQuote => 2,
        ByValue(_) => 4,
        Literal(_) => 1,
        Quoted(_) => 1,
    }
}

#[cfg(test)]
mod tests {
    use std::ffi::OsString;
    use std::os::unix::prelude::OsStringExt;

    use crate::find_bins;

    use super::escape;
    use super::escape_into;

    #[test]
    fn test_lowercase_ascii() {
        assert_eq!(
            escape("abcdefghijklmnopqrstuvwxyz"),
            b"abcdefghijklmnopqrstuvwxyz"
        );
    }

    #[test]
    fn test_uppercase_ascii() {
        assert_eq!(
            escape("ABCDEFGHIJKLMNOPQRSTUVWXYZ"),
            b"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        );
    }

    #[test]
    fn test_numbers() {
        assert_eq!(escape("0123456789"), b"0123456789");
    }

    #[test]
    fn test_punctuation() {
        assert_eq!(escape("-_=/,.+"), b"$'-_=/,.+'");
    }

    #[test]
    fn test_basic_escapes() {
        assert_eq!(escape(r#"woo"wah""#), br#"$'woo"wah"'"#);
    }

    #[test]
    #[allow(non_snake_case)]
    fn test_control_characters() {
        assert_eq!(escape(&"\x00"), b"$'\\x00'");
        assert_eq!(escape(&"\x07"), b"$'\\a'");
        assert_eq!(escape(&"\x00"), b"$'\\x00'");
        assert_eq!(escape(&"\x06"), b"$'\\x06'");
        assert_eq!(escape(&"\x7F"), b"$'\x7F'");
    }

    #[test]
    fn test_escape_into_plain() {
        let mut buffer = Vec::new();
        escape_into("hello", &mut buffer);
        assert_eq!(buffer, b"hello");
    }

    #[test]
    fn test_escape_into_with_escapes() {
        let mut buffer = Vec::new();
        escape_into("-_=/,.+", &mut buffer);
        assert_eq!(buffer, b"$'-_=/,.+'");
    }

    #[test]
    fn test_roundtrip() {
        use std::process::Command;
        let mut script = b"echo -n ".to_vec();
        // It doesn't seem possible to roundtrip NUL, probably because it is the
        // string terminator character in C. To me this seems like a bug in Bash.
        let string: OsString = OsString::from_vec((1u8..=u8::MAX).collect());
        escape_into(&string, &mut script);
        let script = OsString::from_vec(script);
        // Test with every version of `bash` we find on `PATH`.
        for bin in find_bins("bash") {
            let output = Command::new(bin).arg("-c").arg(&script).output().unwrap();
            let result = OsString::from_vec(output.stdout);
            assert_eq!(result, string);
        }
    }
}