#include "parser.h"
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <memory>
#include <stdexcept>
#include <sstream>
#include <vector>
#include <regex>
#include <array>

namespace nix_irc {

static std::string trim(const std::string& s) {
    size_t start = s.find_first_not_of(" \t\n\r");
    if (start == std::string::npos) return "";
    size_t end = s.find_last_not_of(" \t\n\r");
    return s.substr(start, end - start + 1);
}

static std::string read_file(const std::string& path) {
    FILE* f = fopen(path.c_str(), "r");
    if (!f) {
        throw std::runtime_error("Cannot open file: " + path);
    }
    fseek(f, 0, SEEK_END);
    long size = ftell(f);
    fseek(f, 0, SEEK_SET);
    std::string content(size, '\0');
    if (fread(content.data(), 1, size, f) != static_cast<size_t>(size)) {
        fclose(f);
        throw std::runtime_error("Failed to read file: " + path);
    }
    fclose(f);
    return content;
}

static std::pair<std::string, std::string> run_command(const std::string& cmd) {
    std::array<char, 256> buffer;
    std::string result;
    std::string error;

    FILE* pipe = popen(cmd.c_str(), "r");
    if (!pipe) throw std::runtime_error("popen failed");

    while (fgets(buffer.data(), buffer.size(), pipe) != nullptr) {
        result += buffer.data();
    }

    int status = pclose(pipe);
    if (status != 0) {
        throw std::runtime_error("Command failed: " + cmd);
    }
    return {result, error};
}

struct Token {
    enum Type {
        LPAREN, RPAREN, LBRACE, RBRACE, LBRACKET, RBRACKET,
        IDENT, STRING, STRING_INTERP, PATH, INT, BOOL,
        LET, IN, REC, IF, THEN, ELSE, ASSERT, WITH, INHERIT,
        DOT, SEMICOLON, COLON, EQUALS, AT, COMMA, QUESTION, ELLIPSIS,
        // Operators
        PLUS, MINUS, STAR, SLASH, CONCAT,
        EQEQ, NE, LT, GT, LE, GE,
        AND, OR, IMPL, NOT,
        EOF_
    } type;
    std::string value;
    size_t line;
    size_t col;
};

class Lexer {
public:
    Lexer(const std::string& input) : input(input), pos(0), line(1), col(1) {}

    std::vector<Token> tokenize() {
        #define TOKEN(t) Token{Token::t, "", line, col}

        while (pos < input.size()) {
            skip_whitespace();
            if (pos >= input.size()) break;

            char c = input[pos];

            if (c == '(') { emit(TOKEN(LPAREN)); }
            else if (c == ')') { emit(TOKEN(RPAREN)); }
            else if (c == '{') { emit(TOKEN(LBRACE)); }
            else if (c == '}') { emit(TOKEN(RBRACE)); }
            else if (c == '[') { emit(TOKEN(LBRACKET)); }
            else if (c == ']') { emit(TOKEN(RBRACKET)); }
            else if (c == ';') { emit(TOKEN(SEMICOLON)); }
            else if (c == ':') { emit(TOKEN(COLON)); }
            else if (c == '@') { emit(TOKEN(AT)); }
            else if (c == ',') { emit(TOKEN(COMMA)); }
            else if (c == '"') { tokenize_string(); }
            // Two-char operators
            else if (c == '=' && pos + 1 < input.size() && input[pos + 1] == '=') {
                tokens.push_back(TOKEN(EQEQ));
                pos += 2; col += 2;
            }
            else if (c == '=') { emit(TOKEN(EQUALS)); }
            else if (c == '!' && pos + 1 < input.size() && input[pos + 1] == '=') {
                tokens.push_back(TOKEN(NE));
                pos += 2; col += 2;
            }
            else if (c == '<' && pos + 1 < input.size() && input[pos + 1] == '=') {
                tokens.push_back(TOKEN(LE));
                pos += 2; col += 2;
            }
            else if (c == '>' && pos + 1 < input.size() && input[pos + 1] == '=') {
                tokens.push_back(TOKEN(GE));
                pos += 2; col += 2;
            }
            else if (c == '+' && pos + 1 < input.size() && input[pos + 1] == '+') {
                tokens.push_back(TOKEN(CONCAT));
                pos += 2; col += 2;
            }
            else if (c == '&' && pos + 1 < input.size() && input[pos + 1] == '&') {
                tokens.push_back(TOKEN(AND));
                pos += 2; col += 2;
            }
            else if (c == '|' && pos + 1 < input.size() && input[pos + 1] == '|') {
                tokens.push_back(TOKEN(OR));
                pos += 2; col += 2;
            }
            else if (c == '-' && pos + 1 < input.size() && input[pos + 1] == '>') {
                tokens.push_back(TOKEN(IMPL));
                pos += 2; col += 2;
            }
            // Single-char operators
            else if (c == '+') { emit(TOKEN(PLUS)); }
            else if (c == '*') { emit(TOKEN(STAR)); }
            else if (c == '/') {
                // Check if it's a path or division
                if (pos + 1 < input.size() && (isalnum(input[pos + 1]) || input[pos + 1] == '.')) {
                    tokenize_path();
                } else {
                    emit(TOKEN(SLASH));
                }
            }
            else if (c == '<') { emit(TOKEN(LT)); }
            else if (c == '>') { emit(TOKEN(GT)); }
            else if (c == '!') { emit(TOKEN(NOT)); }
            else if (c == '.') {
                // Check for ellipsis (...)
                if (pos + 2 < input.size() && input[pos + 1] == '.' && input[pos + 2] == '.') {
                    tokens.push_back(TOKEN(ELLIPSIS));
                    pos += 3; col += 3;
                } else {
                    emit(TOKEN(DOT));
                }
            }
            else if (c == '?') { emit(TOKEN(QUESTION)); }
            else if (c == '-') {
                // Check if it's a negative number or minus operator
                if (pos + 1 < input.size() && isdigit(input[pos + 1])) {
                    tokenize_int();
                } else {
                    emit(TOKEN(MINUS));
                }
            }
            else if (isdigit(c)) { tokenize_int(); }
            else if (isalpha(c) || c == '_') { tokenize_ident(); }
            else { pos++; col++; }
        }
        tokens.push_back({Token::EOF_, "", line, col});

        #undef TOKEN
        return tokens;
    }

private:
    std::vector<Token> tokens;
    const std::string& input;
    size_t pos;
    size_t line;
    size_t col;

    void emit(Token t) {
        tokens.push_back(t);
        pos++;
        col++;
    }

    void skip_whitespace() {
        while (pos < input.size()) {
            char c = input[pos];
            if (c == ' ' || c == '\t' || c == '\n' || c == '\r') {
                if (c == '\n') { line++; col = 1; }
                else { col++; }
                pos++;
            } else if (c == '#') {
                while (pos < input.size() && input[pos] != '\n') pos++;
            } else {
                break;
            }
        }
    }

    void tokenize_string() {
        pos++;
        std::string s;
        bool has_interp = false;

        while (pos < input.size() && input[pos] != '"') {
            if (input[pos] == '\\' && pos + 1 < input.size()) {
                pos++;
                switch (input[pos]) {
                    case 'n': s += '\n'; break;
                    case 't': s += '\t'; break;
                    case 'r': s += '\r'; break;
                    case '"': s += '"'; break;
                    case '\\': s += '\\'; break;
                    case '$': s += '$'; break;  // Escaped $
                    default: s += input[pos]; break;
                }
                pos++;
            } else if (input[pos] == '$' && pos + 1 < input.size() && input[pos + 1] == '{') {
                // Found interpolation marker
                has_interp = true;
                s += input[pos];  // Keep $ in raw string
                pos++;
            } else {
                s += input[pos];
                pos++;
            }
        }
        pos++;

        Token::Type type = has_interp ? Token::STRING_INTERP : Token::STRING;
        tokens.push_back({type, s, line, col});
        col += s.size() + 2;
    }

    void tokenize_path() {
        size_t start = pos;
        while (pos < input.size() && !isspace(input[pos]) &&
               input[pos] != '(' && input[pos] != ')' &&
               input[pos] != '{' && input[pos] != '}' &&
               input[pos] != '[' && input[pos] != ']') {
            pos++;
        }
        std::string path = input.substr(start, pos - start);
        tokens.push_back({Token::PATH, path, line, col});
        col += path.size();
    }

    void tokenize_int() {
        size_t start = pos;
        if (input[pos] == '-') pos++;
        while (pos < input.size() && isdigit(input[pos])) pos++;
        std::string num = input.substr(start, pos - start);
        tokens.push_back({Token::INT, num, line, col});
        col += num.size();
    }

    void tokenize_ident() {
        size_t start = pos;
        while (pos < input.size() && (isalnum(input[pos]) || input[pos] == '_' || input[pos] == '-')) pos++;
        std::string ident = input.substr(start, pos - start);

        Token::Type type = Token::IDENT;
        if (ident == "let") type = Token::LET;
        else if (ident == "in") type = Token::IN;
        else if (ident == "rec") type = Token::REC;
        else if (ident == "if") type = Token::IF;
        else if (ident == "then") type = Token::THEN;
        else if (ident == "else") type = Token::ELSE;
        else if (ident == "assert") type = Token::ASSERT;
        else if (ident == "with") type = Token::WITH;
        else if (ident == "inherit") type = Token::INHERIT;
        else if (ident == "true") type = Token::BOOL;
        else if (ident == "false") type = Token::BOOL;

        tokens.push_back({type, ident, line, col});
        col += ident.size();
    }
};

class Parser::Impl {
public:
    std::vector<Token> tokens;
    size_t pos = 0;
    std::string current_file;

    const Token& current() {
        if (pos < tokens.size()) return tokens[pos];
        static Token eof{Token::EOF_, "", 0, 0};
        return eof;
    }

    void advance() { pos++; }

    bool consume(Token::Type type) {
        if (current().type == type) {
            advance();
            return true;
        }
        return false;
    }

    bool expect(Token::Type type) {
        if (current().type != type) {
            std::cerr << "Expected token " << type << " but got " << current().type
                      << " at " << current().line << ":" << current().col << "\n";
            return false;
        }
        advance();
        return true;
    }

    // Get operator precedence (higher = tighter binding)
    int get_precedence(Token::Type type) {
        switch (type) {
            case Token::OR: return 1;
            case Token::AND: return 2;
            case Token::IMPL: return 3;
            case Token::EQEQ: case Token::NE: return 4;
            case Token::LT: case Token::GT: case Token::LE: case Token::GE: return 5;
            case Token::CONCAT: return 6;
            case Token::PLUS: case Token::MINUS: return 7;
            case Token::STAR: case Token::SLASH: return 8;
            default: return 0;
        }
    }

    // Convert token type to binary operator
    BinaryOp token_to_binop(Token::Type type) {
        switch (type) {
            case Token::PLUS: return BinaryOp::ADD;
            case Token::MINUS: return BinaryOp::SUB;
            case Token::STAR: return BinaryOp::MUL;
            case Token::SLASH: return BinaryOp::DIV;
            case Token::CONCAT: return BinaryOp::CONCAT;
            case Token::EQEQ: return BinaryOp::EQ;
            case Token::NE: return BinaryOp::NE;
            case Token::LT: return BinaryOp::LT;
            case Token::GT: return BinaryOp::GT;
            case Token::LE: return BinaryOp::LE;
            case Token::GE: return BinaryOp::GE;
            case Token::AND: return BinaryOp::AND;
            case Token::OR: return BinaryOp::OR;
            case Token::IMPL: return BinaryOp::IMPL;
            default: throw std::runtime_error("Invalid binary operator");
        }
    }

    std::shared_ptr<Node> parse_expr() {
        // Try to parse lambda
        auto lambda = try_parse_lambda();
        if (lambda) return lambda;

        if (consume(Token::IF)) {
            auto cond = parse_expr();
            expect(Token::THEN);
            auto then = parse_expr();
            expect(Token::ELSE);
            auto else_ = parse_expr();
            return std::make_shared<Node>(IfNode(cond, then, else_));
        }
        if (consume(Token::LET)) {
            bool is_rec = consume(Token::REC);
            std::vector<std::pair<std::string, std::shared_ptr<Node>>> bindings;
            parse_bindings(bindings);
            expect(Token::IN);
            auto body = parse_expr();

            if (is_rec) {
                auto letrec = LetRecNode(body);
                letrec.bindings = std::move(bindings);
                return std::make_shared<Node>(std::move(letrec));
            } else {
                auto let = LetNode(body);
                let.bindings = std::move(bindings);
                return std::make_shared<Node>(std::move(let));
            }
        }
        if (consume(Token::ASSERT)) {
            auto cond = parse_expr();
            expect(Token::SEMICOLON);
            auto body = parse_expr();
            return std::make_shared<Node>(AssertNode(cond, body));
        }
        if (consume(Token::WITH)) {
            auto attrs = parse_expr();
            expect(Token::SEMICOLON);
            auto body = parse_expr();
            return std::make_shared<Node>(WithNode(attrs, body));
        }

        return parse_expr1();
    }

    std::shared_ptr<Node> parse_expr1() {
        return parse_binary_op(0);
    }

    // Precedence climbing for binary operators
    std::shared_ptr<Node> parse_binary_op(int min_prec) {
        auto left = parse_selection();

        while (true) {
            int prec = get_precedence(current().type);
            if (prec == 0 || prec < min_prec) break;

            Token op_token = current();
            advance();

            auto right = parse_binary_op(prec + 1);
            left = std::make_shared<Node>(BinaryOpNode(
                token_to_binop(op_token.type),
                left,
                right
            ));
        }

        return left;
    }

    std::shared_ptr<Node> parse_selection() {
        auto left = parse_expr2();

        while (current().type == Token::DOT) {
            advance();
            Token name = current();
            if (name.type == Token::IDENT) {
                advance();
                auto attr = std::make_shared<Node>(ConstStringNode(name.value));
                auto result = std::make_shared<Node>(SelectNode(left, attr));

                if (consume(Token::DOT)) {
                    Token name2 = current();
                    if (name2.type == Token::IDENT) {
                        advance();
                        auto attr2 = std::make_shared<Node>(ConstStringNode(name2.value));
                        auto* curr = result->get_if<SelectNode>();
                        while (curr && consume(Token::DOT)) {
                            Token n = current();
                            expect(Token::IDENT);
                            auto a = std::make_shared<Node>(ConstStringNode(n.value));
                            curr->attr = std::make_shared<Node>(AppNode(
                                std::make_shared<Node>(AppNode(curr->attr, a)),
                                std::make_shared<Node>(ConstNullNode())
                            ));
                        }
                    }
                }
                return result;
            } else if (consume(Token::LBRACE)) {
                auto result = std::make_shared<Node>(SelectNode(left, std::make_shared<Node>(ConstStringNode(name.value))));
                parse_expr_attrs(result);
                expect(Token::RBRACE);
                return result;
            }
            return left;
        }

        return left;
    }

    void parse_expr_attrs(std::shared_ptr<Node>&) {
        // Extended selection syntax
    }

    std::shared_ptr<Node> parse_expr2() {
        std::shared_ptr<Node> left = parse_expr3();

        while (true) {
            if (current().type == Token::LBRACKET) {
                advance();
                auto arg = parse_expr();
                expect(Token::RBRACKET);
                left = std::make_shared<Node>(AppNode(left, arg));
            } else if (current().type == Token::STRING) {
                Token s = current();
                advance();
                auto arg = std::make_shared<Node>(ConstStringNode(s.value));
                left = std::make_shared<Node>(AppNode(left, arg));
            } else {
                break;
            }
        }

        return left;
    }

    std::shared_ptr<Node> parse_expr3() {
        // Handle unary operators
        if (consume(Token::MINUS)) {
            auto operand = parse_expr3();
            return std::make_shared<Node>(UnaryOpNode(UnaryOp::NEG, operand));
        }

        if (consume(Token::NOT)) {
            auto operand = parse_expr3();
            return std::make_shared<Node>(UnaryOpNode(UnaryOp::NOT, operand));
        }

        if (consume(Token::LPAREN)) {
            auto expr = parse_expr();
            expect(Token::RPAREN);
            return expr;
        }

        if (consume(Token::LBRACE)) {
            return parse_attrs();
        }

        if (consume(Token::LBRACKET)) {
            return parse_list();
        }

        Token t = current();

        if (t.type == Token::IDENT) {
            advance();
            return std::make_shared<Node>(VarNode(0, t.value));
        }

        if (t.type == Token::INT) {
            advance();
            return std::make_shared<Node>(ConstIntNode(std::stoll(t.value)));
        }

        if (t.type == Token::STRING) {
            advance();
            return std::make_shared<Node>(ConstStringNode(t.value));
        }

        if (t.type == Token::STRING_INTERP) {
            Token str_token = current();
            advance();
            return parse_string_interp(str_token.value);
        }

        if (t.type == Token::PATH) {
            advance();
            return std::make_shared<Node>(ConstPathNode(t.value));
        }

        if (t.type == Token::BOOL) {
            advance();
            return std::make_shared<Node>(ConstBoolNode(t.value == "true"));
        }

        std::cerr << "Unknown token: " << t.value << " (type " << t.type << ")\n";
        advance();
        return std::make_shared<Node>(ConstNullNode());
    }

    std::shared_ptr<Node> parse_attrs() {
        auto attrs = AttrsetNode(false);

        while (current().type != Token::RBRACE && current().type != Token::EOF_) {
            if (consume(Token::REC)) {
                attrs.recursive = true;
                continue;
            }

            // Handle inherit keyword
            if (consume(Token::INHERIT)) {
                std::shared_ptr<Node> source;

                // Check for (expr) form
                if (consume(Token::LPAREN)) {
                    source = parse_expr();
                    expect(Token::RPAREN);
                }

                // Parse identifier list
                while (current().type == Token::IDENT) {
                    Token name = current();
                    advance();

                    if (source) {
                        // inherit (expr) x → x = expr.x
                        auto select = std::make_shared<Node>(SelectNode(
                            source,
                            std::make_shared<Node>(ConstStringNode(name.value))
                        ));
                        attrs.attrs.push_back({name.value, select});
                    } else {
                        // inherit x → x = x
                        auto var = std::make_shared<Node>(VarNode(0, name.value));
                        attrs.attrs.push_back({name.value, var});
                    }
                }

                expect(Token::SEMICOLON);
                continue;
            }

            if (current().type == Token::IDENT || current().type == Token::STRING) {
                Token key = current();
                advance();
                std::string key_str = key.value;

                if (consume(Token::EQUALS)) {
                    auto value = parse_expr();
                    attrs.attrs.push_back({key_str, value});
                } else if (consume(Token::AT)) {
                    auto pattern = parse_expr();
                    auto value = parse_expr();
                    attrs.attrs.push_back({key_str, value});
                }
            }

            if (consume(Token::COMMA)) continue;
            if (consume(Token::SEMICOLON)) continue;

            // If we get here and haven't handled the token, break
            if (current().type != Token::RBRACE && current().type != Token::EOF_) {
                break;
            }
        }

        expect(Token::RBRACE);
        return std::make_shared<Node>(std::move(attrs));
    }

    std::shared_ptr<Node> parse_list() {
        std::shared_ptr<Node> list = std::make_shared<Node>(ConstNullNode());

        if (consume(Token::RBRACKET)) {
            return list;
        }

        std::vector<std::shared_ptr<Node>> elements;
        while (current().type != Token::RBRACKET) {
            elements.push_back(parse_expr());
            if (!consume(Token::COMMA)) break;
        }
        expect(Token::RBRACKET);

        for (auto it = elements.rbegin(); it != elements.rend(); ++it) {
            list = std::make_shared<Node>(AppNode(
                std::make_shared<Node>(AppNode(
                    std::make_shared<Node>(VarNode(0, "__list")),
                    *it
                )),
                list
            ));
        }

        return list;
    }

    void parse_bindings(std::vector<std::pair<std::string, std::shared_ptr<Node>>>& bindings) {
        while (current().type == Token::IDENT || current().type == Token::INHERIT) {
            // Handle inherit keyword
            if (consume(Token::INHERIT)) {
                std::shared_ptr<Node> source;

                // Check for (expr) form
                if (consume(Token::LPAREN)) {
                    source = parse_expr();
                    expect(Token::RPAREN);
                }

                // Parse identifier list
                while (current().type == Token::IDENT) {
                    Token name = current();
                    advance();

                    if (source) {
                        // inherit (expr) x → x = expr.x
                        auto select = std::make_shared<Node>(SelectNode(
                            source,
                            std::make_shared<Node>(ConstStringNode(name.value))
                        ));
                        bindings.push_back({name.value, select});
                    } else {
                        // inherit x → x = x
                        auto var = std::make_shared<Node>(VarNode(0, name.value));
                        bindings.push_back({name.value, var});
                    }
                }

                expect(Token::SEMICOLON);
                continue;
            }

            if (current().type != Token::IDENT) break;
            Token key = current();
            advance();

            if (consume(Token::AT)) {
                auto pattern = parse_expr();
                auto value = parse_expr();
                bindings.push_back({key.value, value});
            } else {
                expect(Token::EQUALS);
                auto value = parse_expr();
                bindings.push_back({key.value, value});
            }

            if (!consume(Token::SEMICOLON)) break;
        }
    }

    // Try to parse lambda, return nullptr if not a lambda
    std::shared_ptr<Node> try_parse_lambda() {
        size_t saved_pos = pos;

        // Check for named pattern: arg@{ ... }:
        std::optional<std::string> named_arg;
        if (current().type == Token::IDENT) {
            Token name = current();
            advance();
            if (consume(Token::AT)) {
                named_arg = name.value;
            } else if (consume(Token::COLON)) {
                // Simple lambda: x: body
                auto body = parse_expr();
                auto lambda = LambdaNode(1, body);
                lambda.param_name = name.value;
                return std::make_shared<Node>(std::move(lambda));
            } else {
                // Not a lambda, restore position
                pos = saved_pos;
                return nullptr;
            }
        }

        // Check for pattern: { ... }:
        if (current().type == Token::LBRACE) {
            advance();

            // Parse pattern fields
            struct Field {
                std::string name;
                std::optional<std::shared_ptr<Node>> default_val;
            };
            std::vector<Field> fields;
            bool has_ellipsis = false;

            while (current().type != Token::RBRACE && current().type != Token::EOF_) {
                if (consume(Token::ELLIPSIS)) {
                    has_ellipsis = true;
                    if (consume(Token::COMMA)) continue;
                    break;
                }

                if (current().type == Token::IDENT) {
                    Token field_name = current();
                    advance();

                    Field field;
                    field.name = field_name.value;

                    // Check for default value
                    if (consume(Token::QUESTION)) {
                        field.default_val = parse_expr();
                    }

                    fields.push_back(field);

                    if (consume(Token::COMMA)) continue;
                    break;
                } else {
                    break;
                }
            }

            if (!consume(Token::RBRACE)) {
                // Not a lambda pattern, restore
                pos = saved_pos;
                return nullptr;
            }

            if (!consume(Token::COLON)) {
                // Not a lambda, restore
                pos = saved_pos;
                return nullptr;
            }

            // Parse body
            auto body = parse_expr();

            // Desugar pattern to lambda with let bindings
            // { a, b ? x }: body → arg: let a = arg.a; b = if arg ? a then arg.a else x; in body

            std::string arg_name = named_arg.value_or("_arg");
            auto arg_var = std::make_shared<Node>(VarNode(0, arg_name));

            std::vector<std::pair<std::string, std::shared_ptr<Node>>> bindings;

            for (const auto& field : fields) {
                // Create arg.field selection
                auto select = std::make_shared<Node>(SelectNode(
                    arg_var,
                    std::make_shared<Node>(ConstStringNode(field.name))
                ));

                if (field.default_val) {
                    // if arg ? field then arg.field else default
                    auto has_attr = std::make_shared<Node>(HasAttrNode(
                        arg_var,
                        std::make_shared<Node>(ConstStringNode(field.name))
                    ));
                    auto if_node = std::make_shared<Node>(IfNode(
                        has_attr,
                        select,
                        *field.default_val
                    ));
                    bindings.push_back({field.name, if_node});
                } else {
                    bindings.push_back({field.name, select});
                }
            }

            // If named pattern, also bind the argument name
            if (named_arg) {
                bindings.push_back({*named_arg, arg_var});
            }

            // Create let expression
            auto let = LetNode(body);
            let.bindings = std::move(bindings);
            auto let_node = std::make_shared<Node>(std::move(let));

            // Create lambda
            auto lambda = LambdaNode(1, let_node);
            lambda.param_name = arg_name;
            lambda.strict_pattern = !has_ellipsis;
            return std::make_shared<Node>(std::move(lambda));
        }

        // Not a lambda
        pos = saved_pos;
        return nullptr;
    }

    std::shared_ptr<Node> parse_string_interp(const std::string& raw) {
        std::vector<std::shared_ptr<Node>> parts;
        size_t i = 0;
        std::string current_str;

        while (i < raw.size()) {
            if (raw[i] == '$' && i + 1 < raw.size() && raw[i + 1] == '{') {
                // Save current string part if any
                if (!current_str.empty()) {
                    parts.push_back(std::make_shared<Node>(ConstStringNode(current_str)));
                    current_str.clear();
                }

                // Find matching }
                i += 2;  // Skip ${
                int depth = 1;
                size_t expr_start = i;
                bool in_string = false;
                char string_quote = 0;

                while (i < raw.size() && depth > 0) {
                    if (!in_string) {
                        if (raw[i] == '"' || raw[i] == '\'') {
                            in_string = true;
                            string_quote = raw[i];
                        } else if (raw[i] == '{') {
                            depth++;
                        } else if (raw[i] == '}') {
                            depth--;
                        }
                    } else {
                        if (raw[i] == string_quote && (i == 0 || raw[i-1] != '\\')) {
                            in_string = false;
                        } else if (raw[i] == '\\') {
                            i++;
                        }
                    }
                    if (depth > 0) i++;
                }

                if (depth > 0) {
                    throw std::runtime_error("unterminated ${ in string interpolation");
                }

                // Parse the expression
                std::string expr_str = raw.substr(expr_start, i - expr_start);

                // Tokenize and parse the expression
                Lexer lexer(expr_str);
                auto expr_tokens = lexer.tokenize();

                // Save current state
                auto saved_tokens = tokens;
                auto saved_pos = pos;

                // Parse expression
                tokens = expr_tokens;
                pos = 0;
                auto expr = parse_expr();

                // Restore state
                tokens = saved_tokens;
                pos = saved_pos;

                // Convert to string using toString builtin
                auto to_string = std::make_shared<Node>(VarNode(0, "toString"));
                auto str_expr = std::make_shared<Node>(AppNode(to_string, expr));
                parts.push_back(str_expr);

                i++;  // Skip }
            } else {
                current_str += raw[i];
                i++;
            }
        }

        // Add remaining string part
        if (!current_str.empty()) {
            parts.push_back(std::make_shared<Node>(ConstStringNode(current_str)));
        }

        // Build concatenation tree
        if (parts.empty()) {
            return std::make_shared<Node>(ConstStringNode(""));
        }

        auto result = parts[0];
        for (size_t j = 1; j < parts.size(); j++) {
            // Use ADD (+) for string concatenation; CONCAT (++) is Nix list concatenation
            result = std::make_shared<Node>(BinaryOpNode(BinaryOp::ADD, result, parts[j]));
        }

        return result;
    }
};

Parser::Parser() : pImpl(std::make_unique<Impl>()) {}
Parser::~Parser() = default;

std::shared_ptr<Node> Parser::parse(const std::string& source, const std::string& path) {
    pImpl->current_file = path;

    Lexer lexer(source);
    pImpl->tokens = lexer.tokenize();
    pImpl->pos = 0;

    return pImpl->parse_expr();
}

std::shared_ptr<Node> Parser::parse_file(const std::string& path) {
    std::string content = read_file(path);
    return parse(content, path);
}

}