//! Quote strings for use with Bash, the GNU Bourne-Again Shell.
//!
//! # ⚠️ Warning
//!
//! It is _possible_ to encode NUL in a Bash string, but Bash appears to then
//! truncate the rest of the string after that point, likely because NUL is the
//! C string terminator. This appears to be a bug in Bash or at least a serious
//! limitation.
//!
//! If you're quoting UTF-8 content this may not be a problem since there is
//! only one code point – the null character itself – that will ever produce a
//! NUL byte. To avoid this problem entirely, consider using [Modified
//! UTF-8][modified-utf-8] so that the NUL byte can never appear in a valid byte
//! stream.
//!
//! [modified-utf-8]: https://en.wikipedia.org/wiki/UTF-8#Modified_UTF-8
//!
//! # 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
//!   ```
//!
//! Bash allows, in newer versions, for non-ASCII Unicode characters with
//! `\uHHHH` and `\UXXXXXXXX` syntax inside these [ANSI C quoted
//! strings][ansi-c-quoting], 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.
//!
//! [ansi-c-quoting]:
//!     https://www.gnu.org/software/bash/manual/html_node/ANSI_002dC-Quoting.html
//!

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

use crate::ascii::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 `$'foo\nbar'`.
///
/// See [`escape_into`] for a variant that extends an existing `Vec` instead of
/// allocating a new one.
///
/// # Examples
///
/// ```
/// # use shell_quote::bash;
/// assert_eq!(bash::escape("foobar"), b"foobar");
/// assert_eq!(bash::escape("foo bar"), b"$'foo bar'");
/// ```
///
/// The input argument 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 a new `OsString`.
///
/// Same as [`escape`], but returns an `OsString`.
///
pub fn quote<T: Into<OsString>>(s: T) -> OsString {
    OsString::from_vec(escape(s))
}

/// 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_inert) {
        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"),
            Control(ch) => sout.extend(format!("\\x{:02X}", ch).bytes()),
            Backslash => sout.extend(b"\\\\"),
            SingleQuote => sout.extend(b"\\'"),
            DoubleQuote => sout.extend(b"\""),
            Delete => sout.extend(b"\\x7F"),
            PrintableInert(ch) => sout.push(ch),
            Printable(ch) => sout.push(ch),
            Extended(ch) => sout.extend(format!("\\x{:02X}", ch).bytes()),
        }
    }
    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,
        Control(_) => 4,
        Backslash => 2,
        SingleQuote => 2,
        DoubleQuote => 1,
        Delete => 4,
        PrintableInert(_) => 1,
        Printable(_) => 1,
        Extended(_) => 4,
    }
}

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

    use crate::find_bins;

    use super::{escape, escape_into, quote};

    #[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);
        }
    }

    #[test]
    fn test_quote() {
        assert_eq!(
            quote("abcdefghijklmnopqrstuvwxyz"),
            OsString::from("abcdefghijklmnopqrstuvwxyz"),
        );
    }
}