// src/parser.rs
use regex::Regex;
use std::collections::HashSet;

pub struct ScriptParser {
    math_operators: Vec<(Regex, &'static str)>,
    number_re: Regex,
    variable_re: Regex,
}

impl ScriptParser {
    pub fn new() -> Self {
        let math_operators = vec![
            // Basic arithmetic
            (Regex::new(r"\(\s*\+\s+").unwrap(), "(decimal-add "),
            (Regex::new(r"\(\s*-\s+").unwrap(), "(decimal-sub "),
            (Regex::new(r"\(\s*\*\s+").unwrap(), "(decimal-mul "),
            (Regex::new(r"\(\s*/\s+").unwrap(), "(decimal-div "),

            // Power and advanced operations
            (Regex::new(r"\(\s*\^\s+").unwrap(), "(decimal-pow "),
            (Regex::new(r"\(\s*\*\*\s+").unwrap(), "(decimal-pow "),
            (Regex::new(r"\(\s*pow\s+").unwrap(), "(decimal-pow "),
            (Regex::new(r"\(\s*sqrt\s+").unwrap(), "(decimal-sqrt "),

            // Logarithmic functions
            (Regex::new(r"\(\s*ln\s+").unwrap(), "(decimal-ln "),
            (Regex::new(r"\(\s*log\s+").unwrap(), "(decimal-ln "),
            (Regex::new(r"\(\s*log10\s+").unwrap(), "(decimal-log10 "),
            (Regex::new(r"\(\s*exp\s+").unwrap(), "(decimal-exp "),

            // Trigonometric functions
            (Regex::new(r"\(\s*sin\s+").unwrap(), "(decimal-sin "),
            (Regex::new(r"\(\s*cos\s+").unwrap(), "(decimal-cos "),
            (Regex::new(r"\(\s*tan\s+").unwrap(), "(decimal-tan "),

            // Comparison operators
            (Regex::new(r"\(\s*>\s+").unwrap(), "(decimal-gt "),
            (Regex::new(r"\(\s*<\s+").unwrap(), "(decimal-lt "),
            (Regex::new(r"\(\s*=\s+").unwrap(), "(decimal-eq "),
            (Regex::new(r"\(\s*>=\s+").unwrap(), "(decimal-gte "),
            (Regex::new(r"\(\s*<=\s+").unwrap(), "(decimal-lte "),

            // Utility functions
            (Regex::new(r"\(\s*abs\s+").unwrap(), "(decimal-abs "),
            (Regex::new(r"\(\s*min\s+").unwrap(), "(decimal-min "),
            (Regex::new(r"\(\s*max\s+").unwrap(), "(decimal-max "),
            (Regex::new(r"\(\s*round\s+").unwrap(), "(decimal-round "),
        ];

        ScriptParser {
            math_operators,
            // VALID REGEX:
            // This captures the preceding delimiter (group 1) and the number (group 2) separately.
            // This avoids lookarounds and allows us to reconstruct the string correctly.
            number_re: Regex::new(r"(^|[\s\(])(-?\d+(?:\.\d+)?(?:[eE][+-]?\d+)?)").unwrap(),
            variable_re: Regex::new(r"\$([^\s)]+)").unwrap(),
        }
    }

    /// Transform a script by converting math operations and numbers to decimal functions
    pub fn transform(&self, script: &str) -> String {
        let mut transformed = script.to_string();

        // CORRECT ORDER: Functions first, then variables, then numbers.
        transformed = self.replace_math_functions(&transformed);
        transformed = self.replace_variable_references(&transformed);
        transformed = self.convert_numbers_to_strings(&transformed);

        transformed
    }

    /// Convert all unquoted numeric literals to quoted strings
    fn convert_numbers_to_strings(&self, script: &str) -> String {
        let parts: Vec<&str> = script.split('"').collect();
        let mut result = String::new();

        for (i, part) in parts.iter().enumerate() {
            if i % 2 == 0 {
                // Even indices are outside quotes - process them
                let processed = self.number_re.replace_all(part, |caps: &regex::Captures| {
                    // Reconstruct the string:
                    // caps[1] is the delimiter (space, '(', or start of string)
                    // caps[2] is the number itself
                    // We put the delimiter back and wrap the number in quotes.
                    format!("{}\"{}\"", &caps[1], &caps[2])
                });
                result.push_str(&processed);
            } else {
                // Odd indices are inside quotes - keep as is
                result.push_str(part);
            }

            if i < parts.len() - 1 {
                result.push('"');
            }
        }

        result
    }

    /// Replace math function calls with decimal equivalents
    fn replace_math_functions(&self, script: &str) -> String {
        let mut result = script.to_string();

        for (pattern, replacement) in &self.math_operators {
            result = pattern.replace_all(&result, *replacement).to_string();
        }

        result
    }

    /// Replace variable references ($var) with function calls
    fn replace_variable_references(&self, script: &str) -> String {
        self.variable_re.replace_all(script, |caps: &regex::Captures| {
            format!("(get-var \"{}\")", &caps[1])
        }).to_string()
    }

    /// Extract dependencies from script (useful for analysis)
    pub fn extract_dependencies(&self, script: &str) -> HashSet<String> {
        let mut dependencies = HashSet::new();

        for cap in self.variable_re.captures_iter(script) {
            dependencies.insert(cap[1].to_string());
        }

        dependencies
    }
}

impl Default for ScriptParser {
    fn default() -> Self {
        Self::new()
    }
}