//! Implements a parser for readline binding syntax.

use crate::error;

/// Represents a key-sequence-to-shell-command binding.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(test, derive(serde::Serialize, serde::Deserialize))]
pub struct KeySequenceShellCommandBinding {
    /// Key sequence to bind
    pub seq: KeySequence,
    /// Shell command to bind to the sequence
    pub shell_cmd: String,
}

/// Represents a key-sequence-to-readline-command binding.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(test, derive(serde::Serialize, serde::Deserialize))]
pub struct KeySequenceReadlineBinding {
    /// Key sequence to bind
    pub seq: KeySequence,
    /// Readline target to bind to the sequence
    pub target: ReadlineTarget,
}

/// Represents a readline target.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(test, derive(serde::Serialize, serde::Deserialize))]
pub enum ReadlineTarget {
    /// A named readline function.
    Function(String),
    /// A readline command macro.
    Macro(String),
}

/// Represents a key sequence.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(test, derive(serde::Serialize, serde::Deserialize))]
pub struct KeySequence(pub Vec<KeySequenceItem>);

/// Represents an element of a key sequence.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(test, derive(serde::Serialize, serde::Deserialize))]
pub enum KeySequenceItem {
    /// Control
    Control,
    /// Meta
    Meta,
    /// Regular character
    Byte(u8),
}

/// Represents a single key stroke.
#[derive(Debug, Default, Clone, PartialEq, Eq)]
#[cfg_attr(test, derive(serde::Serialize, serde::Deserialize))]
pub struct KeyStroke {
    /// Meta key is held down
    pub meta: bool,
    /// Control key is held down
    pub control: bool,
    /// Primary key code
    pub key_code: Vec<u8>,
}

/// Parses a key sequence.
///
/// # Arguments
///
/// * `input` - The input string to parse
pub fn parse_key_sequence(input: &str) -> Result<KeySequence, error::BindingParseError> {
    readline_binding::key_sequence(input)
        .map_err(|_err| error::BindingParseError::Unknown(input.to_owned()))
}

/// Parses a binding specification that maps a key sequence
/// to a shell command.
///
/// # Arguments
///
/// * `input` - The input string to parse
pub fn parse_key_sequence_shell_cmd_binding(
    input: &str,
) -> Result<KeySequenceShellCommandBinding, error::BindingParseError> {
    readline_binding::key_sequence_shell_cmd_binding(input)
        .map_err(|_err| error::BindingParseError::Unknown(input.to_owned()))
}

/// Parses a binding specification that maps a key sequence
/// to a readline target.
///
/// # Arguments
///
/// * `input` - The input string to parse
pub fn parse_key_sequence_readline_binding(
    input: &str,
) -> Result<KeySequenceReadlineBinding, error::BindingParseError> {
    readline_binding::key_sequence_readline_binding(input)
        .map_err(|_err| error::BindingParseError::Unknown(input.to_owned()))
}

/// Converts a `KeySequence` to a vector of `KeyStroke`.
///
/// # Arguments
///
/// * `seq` - The key sequence to convert
pub fn key_sequence_to_strokes(
    seq: &KeySequence,
) -> Result<Vec<KeyStroke>, error::BindingParseError> {
    let mut strokes = vec![];
    let mut current_stroke = KeyStroke::default();

    for item in &seq.0 {
        if matches!(
            item,
            KeySequenceItem::Control | KeySequenceItem::Meta | KeySequenceItem::Byte(b'\x1b')
        ) && !current_stroke.key_code.is_empty()
        {
            strokes.push(current_stroke);
            current_stroke = KeyStroke::default();
        }

        match item {
            KeySequenceItem::Control => current_stroke.control = true,
            KeySequenceItem::Meta => current_stroke.meta = true,
            KeySequenceItem::Byte(b) => {
                current_stroke.key_code.push(*b);
                // If this is a control or meta stroke, the modifier only applies to this one byte,
                // so we need to push the stroke and start fresh for subsequent bytes.
                if current_stroke.control || current_stroke.meta {
                    strokes.push(current_stroke);
                    current_stroke = KeyStroke::default();
                }
            }
        }
    }

    if current_stroke.key_code.is_empty() {
        if current_stroke.control || current_stroke.meta {
            return Err(error::BindingParseError::MissingKeyCode);
        }
    } else {
        strokes.push(current_stroke);
    }

    Ok(strokes)
}

peg::parser! {
    grammar readline_binding() for str {
        rule _() = [' ' | '\t' | '\n']*

        pub rule key_sequence_shell_cmd_binding() -> KeySequenceShellCommandBinding =
            _ "\"" seq:key_sequence() "\"" _ ":" _ cmd:shell_cmd() _ { KeySequenceShellCommandBinding { seq, shell_cmd: cmd } }

        pub rule key_sequence_readline_binding() -> KeySequenceReadlineBinding =
            _ "\"" seq:key_sequence() "\"" _ ":" _ "\"" cmd:readline_cmd() "\"" _ {
                KeySequenceReadlineBinding { seq, target: ReadlineTarget::Macro(cmd) }
            } /
            _ "\"" seq:key_sequence() "\"" _ ":" _ func:readline_function() _ {
                KeySequenceReadlineBinding { seq, target: ReadlineTarget::Function(func) }
            }

        rule readline_cmd() -> String = s:$([^'"']*) { s.to_string() }
        rule shell_cmd() -> String = s:$([_]*) { s.to_string() }
        rule readline_function() -> String = s:$([_]*) { s.to_string() }

        // Main rule for parsing a key sequence
        pub rule key_sequence() -> KeySequence =
            items:key_sequence_item()* { KeySequence(items) }

        rule key_sequence_item() -> KeySequenceItem =
            "\\C-" { KeySequenceItem::Control } /
            "\\M-" { KeySequenceItem::Meta } /
            "\\e" { KeySequenceItem::Byte(b'\x1b') } /
            "\\\\" { KeySequenceItem::Byte(b'\\') } /
            "\\\"" { KeySequenceItem::Byte(b'"') } /
            "\\'" { KeySequenceItem::Byte(b'\'') } /
            "\\a" { KeySequenceItem::Byte(b'\x07') } /
            "\\b" { KeySequenceItem::Byte(b'\x08') } /
            "\\d" { KeySequenceItem::Byte(b'\x7f') } /
            "\\f" { KeySequenceItem::Byte(b'\x0c') } /
            "\\n" { KeySequenceItem::Byte(b'\n') } /
            "\\r" { KeySequenceItem::Byte(b'\r') } /
            "\\t" { KeySequenceItem::Byte(b'\t') } /
            "\\v" { KeySequenceItem::Byte(b'\x0b') } /
            "\\" n:octal_number() { KeySequenceItem::Byte(n) } /
            "\\" n:hex_number() { KeySequenceItem::Byte(n) } /
            [c if c != '"'] { KeySequenceItem::Byte(c as u8) }

        rule octal_number() -> u8 =
            s:$(['0'..='7']*<1,3>) {? u8::from_str_radix(s, 8).or(Err("invalid octal number")) }

        rule hex_number() -> u8 =
            s:$(['0'..='9' | 'a'..='f' | 'A'..='F']*<1,2>) {? u8::from_str_radix(s, 16).or(Err("invalid hex number")) }
    }
}

#[cfg(test)]
#[expect(clippy::panic_in_result_fn)]
mod tests {
    use super::*;
    use anyhow::Result;

    #[test]
    fn test_basic_shell_cmd_binding_parse() -> Result<()> {
        let binding = parse_key_sequence_shell_cmd_binding(r#""\C-k": xyz"#)?;
        assert_eq!(
            binding.seq.0,
            [KeySequenceItem::Control, KeySequenceItem::Byte(b'k')]
        );
        assert_eq!(binding.shell_cmd, "xyz");

        Ok(())
    }

    #[test]
    fn test_basic_readline_func_binding_parse() -> Result<()> {
        let binding = parse_key_sequence_readline_binding(r#""\M-x": some-function"#)?;
        assert_eq!(
            binding.seq.0,
            [KeySequenceItem::Meta, KeySequenceItem::Byte(b'x')]
        );
        assert_eq!(
            binding.target,
            ReadlineTarget::Function("some-function".to_string())
        );

        Ok(())
    }

    #[test]
    fn test_basic_readline_cmd_binding_parse() -> Result<()> {
        let binding = parse_key_sequence_readline_binding(r#""\C-k": "xyz""#)?;
        assert_eq!(
            binding.seq.0,
            [KeySequenceItem::Control, KeySequenceItem::Byte(b'k')]
        );
        assert_eq!(binding.target, ReadlineTarget::Macro(String::from("xyz")));

        Ok(())
    }
}