lust/vm/

stdlib.rs

use super::corelib::{string_key, unwrap_lua_value};
use super::VM;
use crate::bytecode::value::ValueKey;
use crate::bytecode::{NativeCallResult, Value};
use crate::config::LustConfig;
use crate::lua_compat::register_lust_function;
use crate::LustInt;
use rand::rngs::StdRng;
use rand::{Rng, SeedableRng};
use regex::Regex;
use std::fs;
use std::io::{self, Read, Write};
use std::rc::Rc;
use std::sync::{Mutex, OnceLock};
use std::thread;
use std::time::{Duration, SystemTime, UNIX_EPOCH};

static RNG: OnceLock<Mutex<StdRng>> = OnceLock::new();
pub fn create_stdlib(config: &LustConfig, vm: &VM) -> Vec<(&'static str, Value)> {
    let mut stdlib = vec![
        ("print", create_print_fn()),
        ("println", create_println_fn()),
        ("type", create_type_fn()),
        ("select", create_select_fn()),
        ("random", create_math_random_fn()),
        ("randomseed", create_math_randomseed_fn()),
    ];
    if config.is_module_enabled("io") {
        stdlib.push(("io", create_io_module(vm)));
    }

    if config.is_module_enabled("string") {
        stdlib.push(("string", create_string_module(vm)));
    }

    if config.is_module_enabled("os") {
        stdlib.push(("os", create_os_module(vm)));
    }

    stdlib
}

fn create_print_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        for (i, arg) in args.iter().enumerate() {
            if i > 0 {
                print!("\t");
            }

            print!("{}", arg);
        }

        Ok(NativeCallResult::Return(Value::Nil))
    }))
}

fn create_println_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        for (i, arg) in args.iter().enumerate() {
            if i > 0 {
                print!("\t");
            }

            print!("{}", arg);
        }

        println!();
        Ok(NativeCallResult::Return(Value::Nil))
    }))
}

fn create_type_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.is_empty() {
            return Err("type() requires at least one argument".to_string());
        }

        let value = &args[0];

        // Special handling for LuaValue enum - return Lua type names
        if let Value::Enum { enum_name, variant, .. } = value {
            if enum_name == "LuaValue" {
                let lua_type = match variant.as_str() {
                    "Nil" => "nil",
                    "Bool" => "boolean",
                    "Int" | "Float" => "number",
                    "String" => "string",
                    "Table" => "table",
                    "Function" => "function",
                    "Userdata" | "LightUserdata" => "userdata",
                    "Thread" => "thread",
                    _ => "unknown",
                };
                return Ok(NativeCallResult::Return(Value::enum_variant(
                    "LuaValue",
                    "String",
                    vec![Value::string(lua_type)],
                )));
            }
        }

        // Regular Lust types - also wrap in LuaValue for Lua compat
        let type_name = match value {
            Value::Nil => "nil",
            Value::Bool(_) => "bool",
            Value::Int(_) => "int",
            Value::Float(_) => "float",
            Value::String(_) => "string",
            Value::Array(_) => "array",
            Value::Tuple(_) => "tuple",
            Value::Map(_) => "map",
            Value::Struct { .. } | Value::WeakStruct(_) => "struct",
            Value::Enum { .. } => "enum",
            Value::Function(_) => "function",
            Value::NativeFunction(_) => "function",
            Value::Closure { .. } => "function",
            Value::Iterator(_) => "iterator",
            Value::Task(_) => "task",
        };
        Ok(NativeCallResult::Return(Value::enum_variant(
            "LuaValue",
            "String",
            vec![Value::string(type_name)],
        )))
    }))
}

pub(crate) fn create_select_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.is_empty() {
            return Err("select expects at least one argument".to_string());
        }
        let selector = unwrap_lua_value(args[0].clone());
        let mut values: Vec<Value> = Vec::new();
        for arg in args.iter().skip(1) {
            let val = unwrap_lua_value(arg.clone());
            if let Some(arr) = val.as_array() {
                values.extend(arr.into_iter());
            } else {
                values.push(val);
            }
        }
        if let Some(s) = selector.as_string() {
            if s == "#" {
                return Ok(NativeCallResult::Return(Value::Int(values.len() as LustInt)));
            } else {
                return Err("select expects '#' or an index as the first argument".to_string());
            }
        }
        let raw_idx = if let Some(i) = selector.as_int() {
            i
        } else if let Some(f) = selector.as_float() {
            f as LustInt
        } else {
            return Err("select expects '#' or an integer as the first argument".to_string());
        };
        let len = values.len() as isize;
        let mut start = if raw_idx < 0 {
            len + raw_idx as isize + 1
        } else {
            raw_idx as isize
        };
        if start < 1 {
            start = 1;
        }
        let start_idx = (start - 1) as usize;
        if start_idx >= values.len() {
            return return_lua_values(Vec::new());
        }
        return_lua_values(values[start_idx..].to_vec())
    }))
}

fn create_io_module(vm: &VM) -> Value {
    let entries = [
        (string_key("read_file"), create_io_read_file_fn()),
        (
            string_key("read_file_bytes"),
            create_io_read_file_bytes_fn(),
        ),
        (string_key("write_file"), create_io_write_file_fn()),
        (string_key("read_stdin"), create_io_read_stdin_fn()),
        (string_key("read_line"), create_io_read_line_fn()),
        (string_key("write_stdout"), create_io_write_stdout_fn()),
    ];
    vm.map_with_entries(entries)
}

fn create_io_read_file_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.len() != 1 {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "io.read_file(path) requires a single string path",
            ))));
        }

        let path = match args[0].as_string() {
            Some(p) => p,
            None => {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    "io.read_file(path) requires a string path",
                ))))
            }
        };
        match fs::read_to_string(path) {
            Ok(contents) => Ok(NativeCallResult::Return(Value::ok(Value::string(contents)))),
            Err(err) => Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            )))),
        }
    }))
}

fn create_io_read_file_bytes_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.len() != 1 {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "io.read_file_bytes(path) requires a single string path",
            ))));
        }

        let path = match args[0].as_string() {
            Some(p) => p,
            None => {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    "io.read_file_bytes(path) requires a string path",
                ))))
            }
        };

        match fs::read(path) {
            Ok(bytes) => {
                let values: Vec<Value> = bytes
                    .into_iter()
                    .map(|b| Value::Int(b as LustInt))
                    .collect();
                Ok(NativeCallResult::Return(Value::ok(Value::array(values))))
            }

            Err(err) => Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            )))),
        }
    }))
}

fn create_io_write_file_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.len() < 2 {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "io.write_file(path, contents) requires a path and value",
            ))));
        }

        let path = match args[0].as_string() {
            Some(p) => p,
            None => {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    "io.write_file(path, contents) requires a string path",
                ))))
            }
        };
        let contents = if let Some(s) = args[1].as_string() {
            s.to_string()
        } else {
            format!("{}", args[1])
        };
        match fs::write(path, contents) {
            Ok(_) => Ok(NativeCallResult::Return(Value::ok(Value::Nil))),
            Err(err) => Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            )))),
        }
    }))
}

fn create_io_read_stdin_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if !args.is_empty() {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "io.read_stdin() takes no arguments",
            ))));
        }

        let mut buffer = String::new();
        match io::stdin().read_to_string(&mut buffer) {
            Ok(_) => Ok(NativeCallResult::Return(Value::ok(Value::string(buffer)))),
            Err(err) => Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            )))),
        }
    }))
}

fn create_io_read_line_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if !args.is_empty() {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "io.read_line() takes no arguments",
            ))));
        }

        let mut line = String::new();
        match io::stdin().read_line(&mut line) {
            Ok(_) => Ok(NativeCallResult::Return(Value::ok(Value::string(line)))),
            Err(err) => Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            )))),
        }
    }))
}

fn create_io_write_stdout_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let mut stdout = io::stdout();
        for arg in args {
            if let Err(err) = write!(stdout, "{}", arg) {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    err.to_string(),
                ))));
            }
        }

        if let Err(err) = stdout.flush() {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            ))));
        }

        Ok(NativeCallResult::Return(Value::ok(Value::Nil)))
    }))
}

fn create_os_module(vm: &VM) -> Value {
    let entries = [
        (string_key("time"), create_os_time_fn()),
        (string_key("sleep"), create_os_sleep_fn()),
        (string_key("create_file"), create_os_create_file_fn()),
        (string_key("create_dir"), create_os_create_dir_fn()),
        (string_key("remove_file"), create_os_remove_file_fn()),
        (string_key("remove_dir"), create_os_remove_dir_fn()),
        (string_key("rename"), create_os_rename_fn()),
    ];
    vm.map_with_entries(entries)
}

fn create_os_time_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if !args.is_empty() {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "os.time() takes no arguments",
            ))));
        }

        let now = SystemTime::now();
        let seconds = match now.duration_since(UNIX_EPOCH) {
            Ok(duration) => duration.as_secs_f64(),
            Err(err) => -(err.duration().as_secs_f64()),
        };

        Ok(NativeCallResult::Return(Value::Float(seconds)))
    }))
}

fn create_os_sleep_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.len() != 1 {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "os.sleep(seconds) requires a single float duration",
            ))));
        }

        let seconds = match args[0].as_float() {
            Some(value) => value,
            None => {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    "os.sleep(seconds) requires a float duration",
                ))))
            }
        };

        if !seconds.is_finite() || seconds < 0.0 {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "os.sleep(seconds) requires a finite, non-negative duration",
            ))));
        }

        if seconds > (u64::MAX as f64) {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "os.sleep(seconds) duration is too large",
            ))));
        }

        thread::sleep(Duration::from_secs_f64(seconds));

        Ok(NativeCallResult::Return(Value::ok(Value::Nil)))
    }))
}

fn create_os_create_file_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.len() != 1 {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "os.create_file(path) requires a single string path",
            ))));
        }

        let path = match args[0].as_string() {
            Some(p) => p,
            None => {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    "os.create_file(path) requires a string path",
                ))))
            }
        };
        match fs::OpenOptions::new().write(true).create(true).open(path) {
            Ok(_) => Ok(NativeCallResult::Return(Value::ok(Value::Nil))),
            Err(err) => Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            )))),
        }
    }))
}

fn create_os_create_dir_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.len() != 1 {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "os.create_dir(path) requires a single string path",
            ))));
        }

        let path = match args[0].as_string() {
            Some(p) => p,
            None => {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    "os.create_dir(path) requires a string path",
                ))))
            }
        };
        match fs::create_dir_all(path) {
            Ok(_) => Ok(NativeCallResult::Return(Value::ok(Value::Nil))),
            Err(err) => Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            )))),
        }
    }))
}

fn create_os_remove_file_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.len() != 1 {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "os.remove_file(path) requires a single string path",
            ))));
        }

        let path = match args[0].as_string() {
            Some(p) => p,
            None => {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    "os.remove_file(path) requires a string path",
                ))))
            }
        };
        match fs::remove_file(path) {
            Ok(_) => Ok(NativeCallResult::Return(Value::ok(Value::Nil))),
            Err(err) => Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            )))),
        }
    }))
}

fn create_os_remove_dir_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.len() != 1 {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "os.remove_dir(path) requires a single string path",
            ))));
        }

        let path = match args[0].as_string() {
            Some(p) => p,
            None => {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    "os.remove_dir(path) requires a string path",
                ))))
            }
        };
        match fs::remove_dir_all(path) {
            Ok(_) => Ok(NativeCallResult::Return(Value::ok(Value::Nil))),
            Err(err) => Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            )))),
        }
    }))
}

fn create_os_rename_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.len() != 2 {
            return Ok(NativeCallResult::Return(Value::err(Value::string(
                "os.rename(from, to) requires two string paths",
            ))));
        }

        let from = match args[0].as_string() {
            Some(f) => f,
            None => {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    "os.rename(from, to) requires string paths",
                ))))
            }
        };
        let to = match args[1].as_string() {
            Some(t) => t,
            None => {
                return Ok(NativeCallResult::Return(Value::err(Value::string(
                    "os.rename(from, to) requires string paths",
                ))))
            }
        };
        match fs::rename(from, to) {
            Ok(_) => Ok(NativeCallResult::Return(Value::ok(Value::Nil))),
            Err(err) => Ok(NativeCallResult::Return(Value::err(Value::string(
                err.to_string(),
            )))),
        }
    }))
}

fn create_string_module(vm: &VM) -> Value {
    let entries = [
        (string_key("len"), create_string_len_fn()),
        (string_key("lower"), create_string_lower_fn()),
        (string_key("upper"), create_string_upper_fn()),
        (string_key("sub"), create_string_sub_fn()),
        (string_key("byte"), create_string_byte_fn()),
        (string_key("char"), create_string_char_fn()),
        (string_key("find"), create_string_find_fn()),
        (string_key("match"), create_string_match_fn()),
        (string_key("gsub"), create_string_gsub_fn()),
        (string_key("format"), create_string_format_fn()),
    ];
    vm.map_with_entries(entries)
}

fn create_string_len_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let input = args.get(0).cloned().unwrap_or(Value::Nil);
        let value = unwrap_lua_value(input);
        match value {
            Value::Nil => Ok(NativeCallResult::Return(Value::Int(0))), // Nil has length 0
            Value::String(s) => Ok(NativeCallResult::Return(Value::Int(s.len() as LustInt))),
            other => Err(format!("string.len expects a string, got {:?}", other)),
        }
    }))
}

fn create_string_lower_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let value = unwrap_lua_value(args.get(0).cloned().unwrap_or(Value::Nil));
        let s = value
            .as_string()
            .ok_or_else(|| "string.lower expects a string".to_string())?;
        Ok(NativeCallResult::Return(Value::string(&s.to_lowercase())))
    }))
}

fn create_string_upper_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let value = unwrap_lua_value(args.get(0).cloned().unwrap_or(Value::Nil));
        let s = value
            .as_string()
            .ok_or_else(|| "string.upper expects a string".to_string())?;
        Ok(NativeCallResult::Return(Value::string(&s.to_uppercase())))
    }))
}

fn create_string_sub_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let value = unwrap_lua_value(args.get(0).cloned().unwrap_or(Value::Nil));
        let source = value
            .as_string()
            .ok_or_else(|| "string.sub expects a string".to_string())?;
        let start = args
            .get(1)
            .map(|v| unwrap_lua_value(v.clone()).as_int().unwrap_or(1))
            .unwrap_or(1);
        let end = args
            .get(2)
            .map(|v| unwrap_lua_value(v.clone()).as_int().unwrap_or(source.len() as LustInt));
        let (start_idx, end_idx) = normalize_range(start, end, source.len());
        if start_idx >= source.len() || start_idx >= end_idx {
            return Ok(NativeCallResult::Return(Value::string("")));
        }
        let slice = &source.as_bytes()[start_idx..end_idx.min(source.len())];
        Ok(NativeCallResult::Return(Value::string(
            String::from_utf8_lossy(slice),
        )))
    }))
}

fn create_string_byte_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let value = unwrap_lua_value(args.get(0).cloned().unwrap_or(Value::Nil));
        let source = value
            .as_string()
            .ok_or_else(|| "string.byte expects a string".to_string())?;
        let start = args
            .get(1)
            .map(|v| unwrap_lua_value(v.clone()).as_int().unwrap_or(1))
            .unwrap_or(1);
        let end = args
            .get(2)
            .map(|v| unwrap_lua_value(v.clone()).as_int().unwrap_or(start));
        let (start_idx, end_idx) = normalize_range(start, end, source.len());
        let bytes = source.as_bytes();
        if start_idx >= bytes.len() || start_idx >= end_idx {
            return return_lua_values(vec![lua_nil()]);
        }
        let mut values = Vec::new();
        for b in &bytes[start_idx..end_idx.min(bytes.len())] {
            values.push(Value::Int(*b as LustInt));
        }
        return_lua_values(values)
    }))
}

fn create_string_char_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let mut output = String::new();
        for arg in args {
            let raw = unwrap_lua_value(arg.clone());
            let code = raw
                .as_int()
                .or_else(|| raw.as_float().map(|f| f as LustInt))
                .ok_or_else(|| "string.char expects numeric arguments".to_string())?;
            if code < 0 || code > 255 {
                return Err("string.char codepoints must be in [0,255]".to_string());
            }
            if let Some(ch) = char::from_u32(code as u32) {
                output.push(ch);
            }
        }
        Ok(NativeCallResult::Return(Value::string(output)))
    }))
}

fn create_string_find_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let subject = unwrap_lua_value(args.get(0).cloned().unwrap_or(Value::Nil));
        let pattern_val = unwrap_lua_value(args.get(1).cloned().unwrap_or(Value::Nil));
        let haystack = subject
            .as_string()
            .ok_or_else(|| "string.find expects a string subject".to_string())?;
        let pattern = pattern_val
            .as_string()
            .ok_or_else(|| "string.find expects a pattern string".to_string())?;
        let start = args
            .get(2)
            .map(|v| unwrap_lua_value(v.clone()).as_int().unwrap_or(1))
            .unwrap_or(1);
        let plain = args
            .get(3)
            .map(|v| matches!(unwrap_lua_value(v.clone()), Value::Bool(true)))
            .unwrap_or(false);
        let (offset, _) = normalize_range(start, None, haystack.len());
        if offset > haystack.len() {
            return return_lua_values(vec![lua_nil()]);
        }
        let slice = haystack.get(offset..).unwrap_or("");
        if plain {
            if let Some(pos) = slice.find(pattern) {
                let begin = offset + pos;
                let end = begin + pattern.len().saturating_sub(1);
                return return_lua_values(vec![
                    Value::Int((begin as LustInt) + 1),
                    Value::Int((end as LustInt) + 1),
                ]);
            }
            return return_lua_values(vec![lua_nil()]);
        }
        let regex = lua_pattern_to_regex(pattern)?;
        if let Some(caps) = regex.captures(slice) {
            if let Some(mat) = caps.get(0) {
                let begin = offset + mat.start();
                let end = offset + mat.end().saturating_sub(1);
                let mut results: Vec<Value> = vec![
                    Value::Int((begin as LustInt) + 1),
                    Value::Int((end as LustInt) + 1),
                ];
                for idx in 1..caps.len() {
                    if let Some(c) = caps.get(idx) {
                        results.push(Value::string(c.as_str()));
                    } else {
                        results.push(lua_nil());
                    }
                }
                return return_lua_values(results);
            }
        }
        return_lua_values(vec![lua_nil()])
    }))
}

fn create_string_match_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let subject = unwrap_lua_value(args.get(0).cloned().unwrap_or(Value::Nil));
        let pattern_val = unwrap_lua_value(args.get(1).cloned().unwrap_or(Value::Nil));
        let haystack = subject
            .as_string()
            .ok_or_else(|| "string.match expects a string subject".to_string())?;
        let pattern = pattern_val
            .as_string()
            .ok_or_else(|| "string.match expects a pattern string".to_string())?;
        let start = args
            .get(2)
            .map(|v| unwrap_lua_value(v.clone()).as_int().unwrap_or(1))
            .unwrap_or(1);
        let (offset, _) = normalize_range(start, None, haystack.len());
        if offset > haystack.len() {
            return Ok(NativeCallResult::Return(Value::Nil));
        }
        let slice = haystack.get(offset..).unwrap_or("");
        let regex = lua_pattern_to_regex(pattern)?;
        let Some(caps) = regex.captures(slice) else {
            return Ok(NativeCallResult::Return(Value::Nil));
        };
        let Some(mat) = caps.get(0) else {
            return Ok(NativeCallResult::Return(Value::Nil));
        };

        let capture_count = caps.len().saturating_sub(1);
        if capture_count == 0 {
            return Ok(NativeCallResult::Return(Value::string(mat.as_str())));
        }
        if capture_count == 1 {
            if let Some(c) = caps.get(1) {
                return Ok(NativeCallResult::Return(Value::string(c.as_str())));
            }
            return Ok(NativeCallResult::Return(Value::Nil));
        }

        let mut results = Vec::with_capacity(capture_count);
        for idx in 1..caps.len() {
            if let Some(c) = caps.get(idx) {
                results.push(Value::string(c.as_str()));
            } else {
                results.push(Value::Nil);
            }
        }
        return_lua_values(results)
    }))
}

fn create_string_gsub_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let subject = unwrap_lua_value(args.get(0).cloned().unwrap_or(Value::Nil));
        let pattern_val = unwrap_lua_value(args.get(1).cloned().unwrap_or(Value::Nil));
        let repl = args.get(2).cloned().unwrap_or(Value::Nil);
        let limit = args
            .get(3)
            .map(|v| unwrap_lua_value(v.clone()).as_int().unwrap_or(-1))
            .unwrap_or(-1);
        let text = subject
            .as_string()
            .ok_or_else(|| "string.gsub expects a string subject".to_string())?;
        let pattern = pattern_val
            .as_string()
            .ok_or_else(|| "string.gsub expects a pattern string".to_string())?;
        let regex = lua_pattern_to_regex(pattern)?;
        let max_repls = if limit < 0 { i64::MAX } else { limit };
        enum Replacer {
            String(String),
            Func(Value),
            Other(Value),
        }
        let replacer = match &repl {
            Value::Enum { enum_name, variant, .. }
                if enum_name == "LuaValue" && variant == "Function" =>
            {
                Replacer::Func(repl.clone())
            }
            Value::Function(_) | Value::NativeFunction(_) | Value::Closure { .. } => {
                Replacer::Func(repl.clone())
            }
            _ => {
                let unwrapped = unwrap_lua_value(repl.clone());
                match unwrapped {
                    Value::String(s) => Replacer::String(s.to_string()),
                    other => Replacer::Other(other),
                }
            }
        };
        let mut last_end = 0;
        let mut count: i64 = 0;
        let mut output = String::new();
        for caps in regex.captures_iter(text) {
            if count >= max_repls {
                break;
            }
            let mat = caps.get(0).unwrap();
            output.push_str(&text[last_end..mat.start()]);
            let replacement = match &replacer {
                Replacer::String(template) => build_template_replacement(template.as_str(), &caps),
                Replacer::Func(func_val) => {
                    VM::with_current(|vm| {
                        let mut call_args = Vec::new();
                        if caps.len() > 1 {
                            for idx in 1..caps.len() {
                                if let Some(c) = caps.get(idx) {
                                    call_args.push(to_lua_value(vm, Value::string(c.as_str()))?);
                                } else {
                                    call_args.push(lua_nil());
                                }
                            }
                        } else if let Some(m) = caps.get(0) {
                            call_args.push(to_lua_value(vm, Value::string(m.as_str()))?);
                        }
                        let result = vm
                            .call_value(func_val, call_args)
                            .map_err(|e| e.to_string())?;
                        let first = unwrap_first_return(result);
                        Ok(first.to_string())
                    })?
                }
                Replacer::Other(other) => other.to_string(),
            };
            output.push_str(&replacement);
            last_end = mat.end();
            count += 1;
        }
        output.push_str(&text[last_end..]);
        return_lua_values(vec![Value::string(output), Value::Int(count)])
    }))
}

fn create_string_format_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.is_empty() {
            return Err("string.format requires a format string".to_string());
        }
        let fmt_val = unwrap_lua_value(args[0].clone());
        let fmt = fmt_val
            .as_string()
            .ok_or_else(|| "string.format expects a string format".to_string())?;
        let rendered = render_format(fmt, &args[1..])?;
        Ok(NativeCallResult::Return(Value::string(rendered)))
    }))
}

#[derive(Clone)]
enum TableData {
    Array(Value),
    Map(Value),
}

fn table_data(value: &Value) -> Option<TableData> {
    if value.as_array().is_some() {
        return Some(TableData::Array(value.clone()));
    }

    if value.as_map().is_some() {
        return Some(TableData::Map(value.clone()));
    }

    if let Some(map) = value.struct_get_field("table") {
        if map.as_map().is_some() {
            return Some(TableData::Map(map));
        }
    }

    None
}

fn read_sequence(data: &TableData) -> Vec<Value> {
    match data {
        TableData::Array(val) => val.as_array().unwrap_or_default(),
        TableData::Map(val) => {
            let map = val.as_map().unwrap_or_default();
            let mut seq: Vec<Value> = Vec::new();
            let mut idx: LustInt = 1;
            loop {
                let key = ValueKey::from_value(&Value::Int(idx));
                if let Some(val) = map.get(&key) {
                    seq.push(val.clone());
                    idx += 1;
                } else {
                    break;
                }
            }
            seq
        }
    }
}

pub(crate) fn create_table_unpack_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        if args.is_empty() {
            return Err("table.unpack expects a table/array".to_string());
        }
        let table_val = unwrap_lua_value(args[0].clone());
        let Some(data) = table_data(&table_val) else {
            return Err("table.unpack expects a table/array".to_string());
        };
        let seq = read_sequence(&data);
        let start = args
            .get(1)
            .and_then(|v| unwrap_lua_value(v.clone()).as_int())
            .unwrap_or(1);
        let end = args
            .get(2)
            .and_then(|v| unwrap_lua_value(v.clone()).as_int())
            .unwrap_or(seq.len() as LustInt);
        let start_idx = (start - 1).max(0) as usize;
        let end_idx = end.max(0) as usize;
        let mut values: Vec<Value> = Vec::new();
        for (i, val) in seq.iter().enumerate() {
            if i < start_idx || i >= end_idx {
                continue;
            }
            values.push(val.clone());
        }
        return_lua_values(values)
    }))
}

fn create_math_random_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let lower = args
            .get(0)
            .map(|v| unwrap_lua_value(v.clone()))
            .and_then(|v| if matches!(v, Value::Nil) { None } else { Some(v) });
        let upper = args
            .get(1)
            .map(|v| unwrap_lua_value(v.clone()))
            .and_then(|v| if matches!(v, Value::Nil) { None } else { Some(v) });
        let value = with_rng_mut(|rng| match (lower.as_ref(), upper.as_ref()) {
            (None, _) => Value::Float(rng.gen::<f64>()),
            (Some(max), None) => {
                let hi = coerce_int(max).unwrap_or(1);
                let upper_bound = if hi < 1 { 1 } else { hi };
                Value::Int(rng.gen_range(1..=upper_bound))
            }
            (Some(min), Some(max)) => {
                let lo = coerce_int(min).unwrap_or(1);
                let hi = coerce_int(max).unwrap_or(lo);
                let (start, end) = if lo <= hi { (lo, hi) } else { (hi, lo) };
                Value::Int(rng.gen_range(start..=end))
            }
        })?;
        Ok(NativeCallResult::Return(value))
    }))
}

fn create_math_randomseed_fn() -> Value {
    Value::NativeFunction(Rc::new(|args: &[Value]| {
        let seed_val = args
            .get(0)
            .map(|v| unwrap_lua_value(v.clone()))
            .unwrap_or(Value::Int(0));
        let seed = coerce_int(&seed_val).unwrap_or(0) as u64;
        let mutex = RNG.get_or_init(|| Mutex::new(StdRng::from_entropy()));
        *mutex.lock().map_err(|e| e.to_string())? = StdRng::seed_from_u64(seed);
        Ok(NativeCallResult::Return(Value::Nil))
    }))
}

fn coerce_int(value: &Value) -> Option<LustInt> {
    match value {
        Value::Int(i) => Some(*i),
        Value::Float(f) => Some(*f as LustInt),
        Value::Bool(b) => Some(if *b { 1 } else { 0 }),
        _ => None,
    }
}

fn with_rng_mut<F, R>(f: F) -> Result<R, String>
where
    F: FnOnce(&mut StdRng) -> R,
{
    let mutex = RNG.get_or_init(|| Mutex::new(StdRng::from_entropy()));
    mutex
        .lock()
        .map_err(|e| e.to_string())
        .map(|mut guard| f(&mut *guard))
}

fn render_format(fmt: &str, args: &[Value]) -> Result<String, String> {
    let mut out = String::new();
    let mut arg_idx = 0;
    let mut chars = fmt.chars().peekable();
    while let Some(ch) = chars.next() {
        if ch != '%' {
            out.push(ch);
            continue;
        }
        if let Some('%') = chars.peek() {
            chars.next();
            out.push('%');
            continue;
        }
        let mut zero_pad = false;
        if let Some('0') = chars.peek() {
            zero_pad = true;
            chars.next();
        }
        let mut width_str = String::new();
        while let Some(next) = chars.peek() {
            if next.is_ascii_digit() {
                width_str.push(*next);
                chars.next();
            } else {
                break;
            }
        }
        let mut precision: Option<usize> = None;
        if let Some('.') = chars.peek() {
            chars.next();
            let mut prec = String::new();
            while let Some(next) = chars.peek() {
                if next.is_ascii_digit() {
                    prec.push(*next);
                    chars.next();
                } else {
                    break;
                }
            }
            if !prec.is_empty() {
                precision = prec.parse().ok();
            }
        }
        let spec = chars
            .next()
            .ok_or_else(|| "incomplete format specifier".to_string())?;
        let width = if width_str.is_empty() {
            None
        } else {
            width_str.parse().ok()
        };
        let arg = args
            .get(arg_idx)
            .cloned()
            .unwrap_or(Value::Nil);
        arg_idx += 1;
        let raw = unwrap_lua_value(arg);
        let formatted = match spec {
            's' => raw.to_string(),
            'd' | 'i' | 'u' => {
                let num = raw
                    .as_int()
                    .or_else(|| raw.as_float().map(|f| f as LustInt))
                    .unwrap_or(0);
                pad_value(format!("{}", num), width, zero_pad)
            }
            'x' => {
                let num = raw
                    .as_int()
                    .or_else(|| raw.as_float().map(|f| f as LustInt))
                    .unwrap_or(0);
                pad_value(format!("{:x}", num), width, zero_pad)
            }
            'X' => {
                let num = raw
                    .as_int()
                    .or_else(|| raw.as_float().map(|f| f as LustInt))
                    .unwrap_or(0);
                pad_value(format!("{:X}", num), width, zero_pad)
            }
            'c' => {
                let num = raw
                    .as_int()
                    .or_else(|| raw.as_float().map(|f| f as LustInt))
                    .unwrap_or(0);
                if let Some(ch) = char::from_u32(num as u32) {
                    ch.to_string()
                } else {
                    "".to_string()
                }
            }
            'f' | 'g' => {
                let num = raw
                    .as_float()
                    .or_else(|| raw.as_int().map(|i| i as f64))
                    .unwrap_or(0.0);
                if let Some(p) = precision {
                    pad_value(format!("{:.*}", p, num), width, zero_pad)
                } else {
                    pad_value(format!("{}", num), width, zero_pad)
                }
            }
            other => {
                pad_value(format!("{}", other), width, zero_pad)
            }
        };
        out.push_str(&formatted);
    }
    Ok(out)
}

fn pad_value(value: String, width: Option<usize>, zero_pad: bool) -> String {
    if let Some(w) = width {
        if value.len() < w {
            let mut padded = String::new();
            let pad_char = if zero_pad { '0' } else { ' ' };
            for _ in 0..(w - value.len()) {
                padded.push(pad_char);
            }
            padded.push_str(&value);
            return padded;
        }
    }
    value
}

fn normalize_range(start: LustInt, end: Option<LustInt>, len: usize) -> (usize, usize) {
    let len_i = len as LustInt;
    let mut s = if start < 0 { len_i + start + 1 } else { start };
    let mut e = end.unwrap_or(len_i);
    if e < 0 {
        e = len_i + e + 1;
    }
    if s < 1 {
        s = 1;
    }
    if e < 0 {
        e = 0;
    }
    if e > len_i {
        e = len_i;
    }
    if s > e {
        return (len, len);
    }
    (
        s.saturating_sub(1) as usize,
        e.max(0) as usize,
    )
}

fn lua_pattern_to_regex(pattern: &str) -> Result<Regex, String> {
    fn is_regex_meta(ch: char) -> bool {
        matches!(ch, '.' | '+' | '*' | '?' | '^' | '$' | '(' | ')' | '[' | ']' | '{' | '}' | '|' | '\\')
    }
    let mut out = String::new();
    let mut chars = pattern.chars().peekable();
    let mut in_class = false;
    while let Some(ch) = chars.next() {
        match ch {
            '%' => {
                if let Some(next) = chars.next() {
                    let translated = match next {
                        'a' => Some(if in_class { "A-Za-z" } else { "[A-Za-z]" }),
                        'c' => Some(if in_class { "\\p{Cc}" } else { "[\\p{Cc}]" }),
                        'd' => Some(if in_class { "0-9" } else { "[0-9]" }),
                        'l' => Some(if in_class { "a-z" } else { "[a-z]" }),
                        'u' => Some(if in_class { "A-Z" } else { "[A-Z]" }),
                        'w' => Some(if in_class { "A-Za-z0-9_" } else { "[A-Za-z0-9_]" }),
                        'x' => Some(if in_class { "A-Fa-f0-9" } else { "[A-Fa-f0-9]" }),
                        's' => Some(if in_class { "\\s" } else { "[\\s]" }),
                        'p' => Some(if in_class { "\\p{P}" } else { "[\\p{P}]" }),
                        'z' => Some(if in_class { "\\x00" } else { "[\\x00]" }),
                        '%' => Some("%"),
                        _ => None,
                    };
                    if let Some(rep) = translated {
                        out.push_str(rep);
                    } else {
                        if is_regex_meta(next) {
                            out.push('\\');
                        }
                        out.push(next);
                    }
                } else {
                    out.push('%');
                }
            }
            '[' => {
                in_class = true;
                out.push('[');
            }
            ']' => {
                in_class = false;
                out.push(']');
            }
            '.' | '+' | '*' | '?' => out.push(ch),
            '^' | '$' | '(' | ')' => out.push(ch),
            '{' | '}' | '|' | '\\' => {
                out.push('\\');
                out.push(ch);
            }
            '-' => {
                if in_class {
                    out.push('-');
                } else {
                    out.push_str("*?");
                }
            }
            other => {
                if !in_class && is_regex_meta(other) {
                    out.push('\\');
                }
                out.push(other);
            }
        }
    }
    Regex::new(&out).map_err(|e| e.to_string())
}

fn build_template_replacement(template: &str, caps: &regex::Captures) -> String {
    let mut out = String::new();
    let mut chars = template.chars().peekable();
    while let Some(ch) = chars.next() {
        if ch == '%' {
            if let Some(next) = chars.next() {
                if next == '%' {
                    out.push('%');
                    continue;
                }
                if let Some(d) = next.to_digit(10) {
                    let idx = d as usize;
                    if idx == 0 {
                        if let Some(m) = caps.get(0) {
                            out.push_str(m.as_str());
                        }
                    } else if let Some(m) = caps.get(idx) {
                        out.push_str(m.as_str());
                    }
                    continue;
                }
                out.push(next);
            } else {
                out.push('%');
            }
        } else {
            out.push(ch);
        }
    }
    out
}

fn to_lua_value(vm: &VM, value: Value) -> Result<Value, String> {
    if let Value::Enum { enum_name, .. } = &value {
        if enum_name == "LuaValue" {
            return Ok(value);
        }
    }
    Ok(match value.clone() {
        Value::Nil => Value::enum_unit("LuaValue", "Nil"),
        Value::Bool(b) => Value::enum_variant("LuaValue", "Bool", vec![Value::Bool(b)]),
        Value::Int(i) => Value::enum_variant("LuaValue", "Int", vec![Value::Int(i)]),
        Value::Float(f) => Value::enum_variant("LuaValue", "Float", vec![Value::Float(f)]),
        Value::String(s) => Value::enum_variant("LuaValue", "String", vec![Value::String(s)]),
        Value::Map(map) => {
            let table = Value::Map(map.clone());
            let metamethods = vm.new_map_value();
            let lua_table = vm
                .instantiate_struct(
                    "LuaTable",
                    vec![
                        (Rc::new("table".to_string()), table),
                        (Rc::new("metamethods".to_string()), metamethods),
                    ],
                )
                .map_err(|e| e.to_string())?;
            Value::enum_variant("LuaValue", "Table", vec![lua_table])
        }
        Value::Function(_) | Value::Closure { .. } | Value::NativeFunction(_) => {
            let handle = register_lust_function(value.clone());
            let lua_fn = vm
                .instantiate_struct(
                    "LuaFunction",
                    vec![(Rc::new("handle".to_string()), Value::Int(handle as LustInt))],
                )
                .map_err(|e| e.to_string())?;
            Value::enum_variant("LuaValue", "Function", vec![lua_fn])
        }
        other => Value::enum_variant(
            "LuaValue",
            "LightUserdata",
            vec![Value::Int(other.type_of() as LustInt)],
        ),
    })
}

fn return_lua_values(values: Vec<Value>) -> Result<NativeCallResult, String> {
    VM::with_current(|vm| pack_lua_values(vm, values).map(NativeCallResult::Return))
}

fn pack_lua_values(vm: &VM, values: Vec<Value>) -> Result<Value, String> {
    let mut packed = Vec::with_capacity(values.len());
    for value in values {
        packed.push(to_lua_value(vm, value)?);
    }
    Ok(Value::array(packed))
}

fn unwrap_first_return(value: Value) -> Value {
    if let Value::Array(arr) = value {
        if let Some(first) = arr.borrow().get(0) {
            return unwrap_lua_value(first.clone());
        }
        return Value::Nil;
    }
    unwrap_lua_value(value)
}

fn lua_nil() -> Value {
    Value::enum_unit("LuaValue", "Nil")
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn stdlib_defaults_without_optional_modules() {
        let vm = VM::with_config(&LustConfig::default());
        let stdlib = create_stdlib(&LustConfig::default(), &vm);
        assert!(!stdlib.iter().any(|(name, _)| *name == "io"));
        assert!(!stdlib.iter().any(|(name, _)| *name == "os"));
        assert!(!stdlib.iter().any(|(name, _)| *name == "string"));
    }

    #[test]
    fn stdlib_includes_optional_modules_when_configured() {
        let cfg = LustConfig::from_toml_str(
            r#"
                [settings]
                stdlib_modules = ["io", "os", "string"]
            "#,
        )
        .expect("parse");
        let vm = VM::with_config(&cfg);
        let stdlib = create_stdlib(&cfg, &vm);
        assert!(stdlib.iter().any(|(name, _)| *name == "io"));
        assert!(stdlib.iter().any(|(name, _)| *name == "os"));
        assert!(stdlib.iter().any(|(name, _)| *name == "string"));
    }
}