rson-core 1.0.0

//! RSON parser implementation using nom.
//!
//! This module provides functions to parse RSON text into `RsonValue` structures.
//! The parser is built with nom for efficient, zero-copy parsing where possible.

use crate::{RsonValue, RsonError, RsonResult};
use indexmap::IndexMap;
use nom::{
    branch::alt,
    bytes::complete::{tag, take_while, take_while1},
    character::complete::{
        char, multispace1, none_of, 
        alpha1, digit1
    },
    combinator::{map, map_res, opt, recognize, value},
    multi::separated_list0,
    number::complete::recognize_float,
    sequence::{delimited, pair, preceded, separated_pair, terminated, tuple},
    IResult,
};

#[cfg(not(feature = "std"))]
use alloc::{
    string::{String, ToString},
    vec::Vec,
};

/// Parse a complete RSON document.
pub fn parse_rson(input: &str) -> RsonResult<RsonValue> {
    let result = terminated(
        preceded(ws_and_comments, parse_value),
        preceded(ws_and_comments, nom::combinator::eof)
    )(input);
    
    match result {
        Ok((_, value)) => Ok(value),
        Err(e) => Err(RsonError::from(e)),
    }
}

/// Parse a single RSON value (may not consume entire input).
pub fn parse_rson_value(input: &str) -> RsonResult<RsonValue> {
    let result = preceded(ws_and_comments, parse_value)(input);
    
    match result {
        Ok((_, value)) => Ok(value),
        Err(e) => Err(RsonError::from(e)),
    }
}

/// Parse any RSON value.
fn parse_value(input: &str) -> IResult<&str, RsonValue> {
    alt((
        parse_null,
        parse_bool,
        parse_option,
        parse_enum,
        parse_struct,
        parse_tuple,
        parse_number,
        parse_char,
        parse_string,
        parse_array,
        parse_map,
    ))(input)
}

/// Parse whitespace and comments.
fn ws_and_comments(input: &str) -> IResult<&str, ()> {
    value(
        (),
        nom::multi::many0(alt((
            value((), multispace1),
            parse_line_comment,
            parse_block_comment,
        )))
    )(input)
}

/// Parse a line comment: // comment text
fn parse_line_comment(input: &str) -> IResult<&str, ()> {
    value(
        (),
        tuple((
            tag("//"),
            take_while(|c| c != '\n'),
            opt(char('\n')),
        ))
    )(input)
}

/// Parse a block comment: /* comment text */
fn parse_block_comment(input: &str) -> IResult<&str, ()> {
    value(
        (),
        tuple((
            tag("/*"),
            take_while(|c| c != '*'),
            tag("*/"),
        ))
    )(input)
}

/// Parse null value.
fn parse_null(input: &str) -> IResult<&str, RsonValue> {
    value(RsonValue::Null, tag("null"))(input)
}

/// Parse boolean value.
fn parse_bool(input: &str) -> IResult<&str, RsonValue> {
    alt((
        value(RsonValue::Bool(true), tag("true")),
        value(RsonValue::Bool(false), tag("false")),
    ))(input)
}

/// Parse Option value: Some(value) or None
fn parse_option(input: &str) -> IResult<&str, RsonValue> {
    alt((
        map(
            preceded(
                tag("Some"),
                delimited(
                    preceded(ws_and_comments, char('(')),
                    preceded(ws_and_comments, parse_value),
                    preceded(ws_and_comments, char(')')),
                )
            ),
            |v| RsonValue::Option(Some(Box::new(v)))
        ),
        value(RsonValue::Option(None), tag("None")),
    ))(input)
}

/// Parse a number (integer or float).
fn parse_number(input: &str) -> IResult<&str, RsonValue> {
    // First try to parse as float
    let float_result: IResult<&str, &str> = recognize_float(input);
    if let Ok((remaining, number_str)) = float_result {
        if number_str.contains('.') || number_str.contains('e') || number_str.contains('E') {
            if let Ok(f) = number_str.parse::<f64>() {
                return Ok((remaining, RsonValue::Float(f)));
            }
        }
    }
    
    // Try to parse as integer
    map_res(
        recognize(pair(opt(char('-')), digit1)),
        |s: &str| s.parse::<i64>().map(RsonValue::Int)
    )(input)
}

/// Parse a character literal: 'c'
fn parse_char(input: &str) -> IResult<&str, RsonValue> {
    map(
        delimited(char('\''), parse_char_content, char('\'')),
        RsonValue::Char
    )(input)
}

/// Parse the content of a character literal.
fn parse_char_content(input: &str) -> IResult<&str, char> {
    alt((
        none_of("'\\"),
        preceded(char('\\'), parse_escape_char),
    ))(input)
}

/// Parse an escape character.
fn parse_escape_char(input: &str) -> IResult<&str, char> {
    alt((
        value('\n', char('n')),
        value('\r', char('r')),
        value('\t', char('t')),
        value('\\', char('\\')),
        value('\'', char('\'')),
        value('\"', char('\"')),
        value('\0', char('0')),
        parse_unicode_escape,
    ))(input)
}

/// Parse Unicode escape: \uXXXX
fn parse_unicode_escape(input: &str) -> IResult<&str, char> {
    map_res(
        preceded(char('u'), take_while1(|c: char| c.is_ascii_hexdigit())),
        |hex_str: &str| {
            u32::from_str_radix(hex_str, 16)
                .ok()
                .and_then(char::from_u32)
                .ok_or("Invalid Unicode codepoint")
        }
    )(input)
}

/// Parse a string literal: "string content"
fn parse_string(input: &str) -> IResult<&str, RsonValue> {
    map(
        delimited(char('"'), parse_string_content, char('"')),
        |s| RsonValue::String(s.to_string())
    )(input)
}

/// Parse the content of a string literal.
fn parse_string_content(input: &str) -> IResult<&str, String> {
    let mut result = String::new();
    let mut remaining = input;
    
    while !remaining.is_empty() {
        if remaining.starts_with('"') {
            break;
        } else if remaining.starts_with('\\') {
            let (rest, escaped_char) = preceded(char('\\'), parse_escape_char)(remaining)?;
            result.push(escaped_char);
            remaining = rest;
        } else {
            let (rest, ch) = nom::character::complete::anychar(remaining)?;
            result.push(ch);
            remaining = rest;
        }
    }
    
    Ok((remaining, result))
}

/// Parse an identifier (unquoted key or type name).
fn parse_identifier(input: &str) -> IResult<&str, String> {
    map(
        recognize(pair(
            alt((alpha1, tag("_"))),
            take_while(|c: char| c.is_alphanumeric() || c == '_')
        )),
        |s: &str| s.to_string()
    )(input)
}

/// Parse an array: [value1, value2, ...]
fn parse_array(input: &str) -> IResult<&str, RsonValue> {
    map(
        delimited(
            char('['),
            terminated(
                separated_list0(
                    preceded(ws_and_comments, char(',')),
                    preceded(ws_and_comments, parse_value)
                ),
                opt(preceded(ws_and_comments, char(',')))
            ),
            preceded(ws_and_comments, char(']'))
        ),
        RsonValue::Array
    )(input)
}

/// Parse a map: { key: value, ... }
fn parse_map(input: &str) -> IResult<&str, RsonValue> {
    map(
        delimited(
            char('{'),
            terminated(
                separated_list0(
                    preceded(ws_and_comments, char(',')),
                    preceded(
                        ws_and_comments,
                        separated_pair(
                            parse_map_key,
                            preceded(ws_and_comments, char(':')),
                            preceded(ws_and_comments, parse_value)
                        )
                    )
                ),
                opt(preceded(ws_and_comments, char(',')))
            ),
            preceded(ws_and_comments, char('}'))
        ),
        |pairs| {
            let mut map = IndexMap::new();
            for (key, value) in pairs {
                map.insert(key, value);
            }
            RsonValue::Map(map)
        }
    )(input)
}

/// Parse a map key (identifier or string).
fn parse_map_key(input: &str) -> IResult<&str, String> {
    alt((
        parse_identifier,
        map(
            delimited(char('"'), parse_string_content, char('"')),
            |s| s
        ),
    ))(input)
}

/// Parse a struct: StructName(field: value, ...)
fn parse_struct(input: &str) -> IResult<&str, RsonValue> {
    map(
        pair(
            parse_identifier,
            delimited(
                char('('),
                terminated(
                    separated_list0(
                        preceded(ws_and_comments, char(',')),
                        preceded(
                            ws_and_comments,
                            separated_pair(
                                parse_identifier,
                                preceded(ws_and_comments, char(':')),
                                preceded(ws_and_comments, parse_value)
                            )
                        )
                    ),
                    opt(preceded(ws_and_comments, char(',')))
                ),
                preceded(ws_and_comments, char(')'))
            )
        ),
        |(name, fields)| {
            let mut field_map = IndexMap::new();
            for (field_name, value) in fields {
                field_map.insert(field_name, value);
            }
            RsonValue::Struct {
                name,
                fields: field_map,
            }
        }
    )(input)
}

/// Parse a tuple: (value1, value2, ...)
fn parse_tuple(input: &str) -> IResult<&str, RsonValue> {
    // Only parse as tuple if it doesn't look like a struct
    let lookahead = preceded(
        ws_and_comments,
        alt((
            // Check if next thing after '(' is an identifier followed by ':'
            value(false, tuple((parse_identifier, preceded(ws_and_comments, char(':'))))),
            // Otherwise it could be a tuple
            value(true, take_while(|_| true))
        ))
    );
    
    // If lookahead suggests this might be a struct field, don't parse as tuple
    if let Ok((_, false)) = preceded(char('('), lookahead)(input) {
        return Err(nom::Err::Error(nom::error::Error::new(input, nom::error::ErrorKind::Alt)));
    }
    
    map(
        delimited(
            char('('),
            terminated(
                separated_list0(
                    preceded(ws_and_comments, char(',')),
                    preceded(ws_and_comments, parse_value)
                ),
                opt(preceded(ws_and_comments, char(',')))
            ),
            preceded(ws_and_comments, char(')'))
        ),
        RsonValue::Tuple
    )(input)
}

/// Parse an enum: EnumName::Variant or EnumName::Variant(value)
fn parse_enum(input: &str) -> IResult<&str, RsonValue> {
    map(
        tuple((
            parse_identifier,
            preceded(tag("::"), parse_identifier),
            opt(delimited(
                char('('),
                preceded(ws_and_comments, parse_value),
                preceded(ws_and_comments, char(')'))
            ))
        )),
        |(enum_name, variant, value)| RsonValue::Enum {
            name: enum_name,
            variant,
            value: value.map(Box::new),
        }
    )(input)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_parse_null() {
        assert_eq!(parse_rson("null").unwrap(), RsonValue::Null);
    }

    #[test]
    fn test_parse_bool() {
        assert_eq!(parse_rson("true").unwrap(), RsonValue::Bool(true));
        assert_eq!(parse_rson("false").unwrap(), RsonValue::Bool(false));
    }

    #[test]
    fn test_parse_numbers() {
        assert_eq!(parse_rson("42").unwrap(), RsonValue::Int(42));
        assert_eq!(parse_rson("-17").unwrap(), RsonValue::Int(-17));
        assert_eq!(parse_rson("3.14").unwrap(), RsonValue::Float(3.14));
        assert_eq!(parse_rson("-2.5").unwrap(), RsonValue::Float(-2.5));
    }

    #[test]
    fn test_parse_string() {
        assert_eq!(parse_rson(r#""hello""#).unwrap(), RsonValue::String("hello".to_string()));
        assert_eq!(parse_rson(r#""hello\nworld""#).unwrap(), RsonValue::String("hello\nworld".to_string()));
    }

    #[test]
    fn test_parse_char() {
        assert_eq!(parse_rson("'a'").unwrap(), RsonValue::Char('a'));
        assert_eq!(parse_rson(r"'\n'").unwrap(), RsonValue::Char('\n'));
    }

    #[test]
    fn test_parse_array() {
        assert_eq!(
            parse_rson("[1, 2, 3]").unwrap(),
            RsonValue::Array(vec![
                RsonValue::Int(1),
                RsonValue::Int(2),
                RsonValue::Int(3),
            ])
        );
        
        // With trailing comma
        assert_eq!(
            parse_rson("[1, 2, 3,]").unwrap(),
            RsonValue::Array(vec![
                RsonValue::Int(1),
                RsonValue::Int(2),
                RsonValue::Int(3),
            ])
        );
    }

    #[test]
    fn test_parse_map() {
        let mut expected = IndexMap::new();
        expected.insert("name".to_string(), RsonValue::String("Alice".to_string()));
        expected.insert("age".to_string(), RsonValue::Int(30));
        
        assert_eq!(
            parse_rson(r#"{ name: "Alice", age: 30 }"#).unwrap(),
            RsonValue::Map(expected)
        );
    }

    #[test]
    fn test_parse_struct() {
        let mut expected = IndexMap::new();
        expected.insert("x".to_string(), RsonValue::Int(10));
        expected.insert("y".to_string(), RsonValue::Int(20));
        
        assert_eq!(
            parse_rson("Point(x: 10, y: 20)").unwrap(),
            RsonValue::Struct {
                name: "Point".to_string(),
                fields: expected,
            }
        );
    }

    #[test]
    fn test_parse_tuple() {
        assert_eq!(
            parse_rson("(1, 2, 3)").unwrap(),
            RsonValue::Tuple(vec![
                RsonValue::Int(1),
                RsonValue::Int(2),
                RsonValue::Int(3),
            ])
        );
    }

    #[test]
    fn test_parse_enum() {
        assert_eq!(
            parse_rson("Color::Red").unwrap(),
            RsonValue::Enum {
                name: "Color".to_string(),
                variant: "Red".to_string(),
                value: None,
            }
        );
        
        assert_eq!(
            parse_rson(r#"Result::Ok("success")"#).unwrap(),
            RsonValue::Enum {
                name: "Result".to_string(),
                variant: "Ok".to_string(),
                value: Some(Box::new(RsonValue::String("success".to_string()))),
            }
        );
    }

    #[test]
    fn test_parse_option() {
        assert_eq!(
            parse_rson("None").unwrap(),
            RsonValue::Option(None)
        );
        
        assert_eq!(
            parse_rson("Some(42)").unwrap(),
            RsonValue::Option(Some(Box::new(RsonValue::Int(42))))
        );
    }

    #[test]
    fn test_parse_with_comments() {
        let input = r#"
        // This is a user struct
        User(
            id: 1, // user ID
            name: "Alice", /* user name */
            active: true,
        )
        "#;
        
        let mut expected = IndexMap::new();
        expected.insert("id".to_string(), RsonValue::Int(1));
        expected.insert("name".to_string(), RsonValue::String("Alice".to_string()));
        expected.insert("active".to_string(), RsonValue::Bool(true));
        
        assert_eq!(
            parse_rson(input).unwrap(),
            RsonValue::Struct {
                name: "User".to_string(),
                fields: expected,
            }
        );
    }

    #[test]
    fn test_json_compatibility() {
        // Test that valid JSON parses correctly
        let json_input = r#"{
            "name": "Alice",
            "age": 30,
            "active": true,
            "score": 95.5,
            "tags": ["admin", "user"],
            "metadata": null
        }"#;
        
        let result = parse_rson(json_input);
        assert!(result.is_ok());
        
        let value = result.unwrap();
        match value {
            RsonValue::Map(_) => {}
            _ => panic!("Expected map"),
        }
    }
}