//! A command to execute (port of `config/command.zig`).

use crate::cli_args::{ArgError, ConfigField};
use crate::formatter::EntryFormatter;
use std::fmt;

/// A command to execute (argv0 and args).
///
/// A command is specified as a simple string such as "nvim a b c".
/// By default, we expect the downstream to do some sort of shell expansion
/// on this string.
///
/// If a command is already expanded and the user does NOT want to do
/// shell expansion (because this usually requires a round trip into
/// /bin/sh or equivalent), specify a `direct:`-prefix. e.g.
/// `direct:nvim a b c`.
///
/// The whitespace before or around the prefix is ignored. For example,
/// `  direct:nvim a b c` and `direct: nvim a b c` are equivalent.
///
/// If the command is not absolute, it'll be looked up via the PATH.
/// For the shell-expansion case, we let the shell do this. For the
/// direct case, we do this directly.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Command {
    /// Execute a command directly, e.g. via `exec`. The format here
    /// is already structured to be ready to passed directly to `exec`
    /// with index zero being the command to execute.
    ///
    /// Index zero is not guaranteed to be an absolute path, and may require
    /// PATH lookup. It is up to the downstream to do this, usually via
    /// delegation to something like `execvp`.
    Direct(Vec<String>),

    /// Execute a command via shell expansion. This provides the command
    /// as a single string that is expected to be expanded in some way
    /// (up to the downstream). Usually `/bin/sh -c`.
    Shell(String),
}

impl Default for Command {
    fn default() -> Self {
        Command::Shell(String::new())
    }
}

/// Iterates over each argument in the command.
#[derive(Debug, Clone)]
pub struct ArgIterator {
    args: std::vec::IntoIter<String>,
}

impl Iterator for ArgIterator {
    type Item = String;

    fn next(&mut self) -> Option<String> {
        self.args.next()
    }
}

/// Best-effort shell string splitter matching Zig's
/// `std.process.ArgIteratorGeneral(.{})` (whitespace separated, double
/// quotes group, backslashes only special before a double quote).
fn split_general(s: &str) -> Vec<String> {
    let b = s.as_bytes();
    let mut out = vec![];
    let mut i = 0;
    loop {
        // skip whitespace
        while i < b.len() && (b[i] == b' ' || b[i] == b'\t') {
            i += 1;
        }
        if i >= b.len() {
            break;
        }

        let mut cur: Vec<u8> = vec![];
        let mut quoted = false;
        while i < b.len() {
            match b[i] {
                b' ' | b'\t' if !quoted => break,
                b'\\' => {
                    let mut n = 0;
                    while i < b.len() && b[i] == b'\\' {
                        n += 1;
                        i += 1;
                    }
                    if i < b.len() && b[i] == b'"' {
                        cur.extend(std::iter::repeat_n(b'\\', n / 2));
                        if n % 2 == 1 {
                            cur.push(b'"');
                            i += 1;
                        }
                    } else {
                        cur.extend(std::iter::repeat_n(b'\\', n));
                    }
                }
                b'"' => {
                    quoted = !quoted;
                    i += 1;
                }
                c => {
                    cur.push(c);
                    i += 1;
                }
            }
        }
        out.push(String::from_utf8_lossy(&cur).into_owned());
    }
    out
}

impl Command {
    /// Creates a command as a single string, joining arguments as
    /// necessary with spaces. Its not guaranteed that this is a valid
    /// command; it is only meant to be human readable.
    #[must_use]
    pub fn string(&self) -> String {
        match self {
            Command::Shell(v) => v.clone(),
            Command::Direct(v) => v.join(" "),
        }
    }

    /// Get an iterator over the arguments array.
    ///
    /// For direct commands this just iterates over the array. For shell
    /// commands this uses a best effort shell string parser (like Zig's
    /// `ArgIteratorGeneral`). This is not guaranteed to be 100% accurate,
    /// but it works for common cases.
    #[must_use]
    pub fn arg_iterator(&self) -> ArgIterator {
        let args = match self {
            Command::Direct(v) => v.clone(),
            Command::Shell(v) => split_general(v),
        };
        ArgIterator {
            args: args.into_iter(),
        }
    }
}

impl ConfigField for Command {
    fn parse_cli(&mut self, input: Option<&str>) -> Result<(), ArgError> {
        // Input is required. Whitespace on the edges isn't needed.
        // Commands must be non-empty.
        let input = input.ok_or(ArgError::ValueRequired)?;
        let trimmed = input.trim_matches(' ');
        if trimmed.is_empty() {
            return Err(ArgError::ValueRequired);
        }

        // If we have a `:` then we MIGHT have a prefix to specify what
        // tag we should use.
        let (direct, str) = match trimmed.find(':') {
            Some(idx) if &trimmed[..idx] == "direct" => (true, &trimmed[idx + 1..]),
            Some(idx) if &trimmed[..idx] == "shell" => (false, &trimmed[idx + 1..]),
            _ => (false, trimmed),
        };

        let str = str.trim_matches(' ');
        *self = if direct {
            // We're not shell expanding, so the arguments are naively
            // split on spaces.
            Command::Direct(str.split(' ').map(str::to_string).collect())
        } else {
            Command::Shell(str.to_string())
        };
        Ok(())
    }

    fn format_entry(&self, f: &mut EntryFormatter<'_>) -> fmt::Result {
        match self {
            Command::Shell(v) => writeln!(f.writer, "{} = {v}", f.name),
            Command::Direct(v) => writeln!(f.writer, "{} = direct:{}", f.name, v.join(" ")),
        }
    }
}

#[cfg(test)]
#[allow(clippy::unwrap_used)]
mod tests {
    use super::*;
    use crate::formatter::format_entry;

    #[test]
    fn command_parse_cli_errors() {
        let mut v = Command::default();
        assert_eq!(v.parse_cli(None), Err(ArgError::ValueRequired));
        assert_eq!(v.parse_cli(Some("")), Err(ArgError::ValueRequired));
        assert_eq!(v.parse_cli(Some(" ")), Err(ArgError::ValueRequired));
    }

    #[test]
    fn command_parse_cli_shell_expanded() {
        let mut v = Command::default();
        v.parse_cli(Some("echo hello")).unwrap();
        assert_eq!(v, Command::Shell("echo hello".into()));

        // Spaces are stripped
        v.parse_cli(Some(" echo hello ")).unwrap();
        assert_eq!(v, Command::Shell("echo hello".into()));
    }

    #[test]
    fn command_parse_cli_direct() {
        let mut v = Command::default();
        v.parse_cli(Some("direct:echo hello")).unwrap();
        assert_eq!(v, Command::Direct(vec!["echo".into(), "hello".into()]));

        // Spaces around the prefix
        v.parse_cli(Some(" direct:  echo hello")).unwrap();
        assert_eq!(v, Command::Direct(vec!["echo".into(), "hello".into()]));
    }

    #[test]
    fn command_arg_iterator_shell() {
        let v = Command::Shell("echo hello world".into());
        let mut it = v.arg_iterator();
        assert_eq!(it.next().unwrap(), "echo");
        assert_eq!(it.next().unwrap(), "hello");
        assert_eq!(it.next().unwrap(), "world");
        assert!(it.next().is_none());
    }

    #[test]
    fn command_arg_iterator_shell_quotes() {
        let v = Command::Shell("echo \"hello world\" a\\\"b".into());
        let args: Vec<String> = v.arg_iterator().collect();
        assert_eq!(args, ["echo", "hello world", "a\"b"]);
    }

    #[test]
    fn command_arg_iterator_direct() {
        let v = Command::Direct(vec!["echo".into(), "hello world".into()]);
        let mut it = v.arg_iterator();
        assert_eq!(it.next().unwrap(), "echo");
        assert_eq!(it.next().unwrap(), "hello world");
        assert!(it.next().is_none());
    }

    #[test]
    fn command_string_shell() {
        let v = Command::Shell("echo hello world".into());
        assert_eq!(v.string(), "echo hello world");
    }

    #[test]
    fn command_string_direct() {
        let v = Command::Direct(vec!["echo".into(), "hello world".into()]);
        assert_eq!(v.string(), "echo hello world");
    }

    #[test]
    fn command_format_config_shell() {
        let mut v = Command::default();
        v.parse_cli(Some("echo hello")).unwrap();
        let mut s = String::new();
        format_entry("a", &v, &mut s).unwrap();
        assert_eq!(s, "a = echo hello\n");
    }

    #[test]
    fn command_format_config_direct() {
        let mut v = Command::default();
        v.parse_cli(Some("direct: echo hello")).unwrap();
        let mut s = String::new();
        format_entry("a", &v, &mut s).unwrap();
        assert_eq!(s, "a = direct:echo hello\n");
    }
}