namespace QRScript;

using DynamicExpresso;

public static class Runner
{
    public static void Interpret(string[] lines)
    {
        var env = new Dictionary<string, object>();
        var labels = new Dictionary<string, int>();
        var stack = new Stack<int>();
        var exp = new Interpreter();
        int pc = 0;

        // First pass: record labels
        for (int i = 0; i < lines.Length; i++)
        {
            string line = lines[i].Trim();
            if (line.StartsWith("@"))
                labels[line[1..]] = i;
        }

        // Main execution loop
        while (pc < lines.Length)
        {
            string raw = lines[pc].Trim();
            pc++;

            if (string.IsNullOrWhiteSpace(raw) || raw.StartsWith("#") || raw.StartsWith("@"))
                continue;

            var parts = raw.Split(' ', 4, StringSplitOptions.RemoveEmptyEntries);
            if (parts.Length == 0) continue;

            string cmd = parts[0].ToLowerInvariant();
            string arg1 = parts.Length > 1 ? parts[1] : null;
            string arg2 = parts.Length > 2 ? parts[2] : null;
            string arg3 = parts.Length > 3 ? parts[3] : null;

            object Eval(string expr)
            {
                foreach (var (k, v) in env)
                    exp.SetVariable(k, v);
                return exp.Eval(expr);
            }

            switch (cmd)
            {
                case "say":
                    Console.WriteLine(string.Join(' ', parts.Skip(1).Select(p =>
                        env.TryGetValue(p, out var val) ? val.ToString() : p)));
                    break;

                case "set":
                    env[arg1] = Eval(arg2);
                    break;

                case "add":
                case "sub":
                case "mul":
                case "div":
                case "mod":
                    if (!env.TryGetValue(arg1, out var val)) val = 0;
                    var op = cmd switch
                    {
                        "add" => "+",
                        "sub" => "-",
                        "mul" => "*",
                        "div" => "/",
                        "mod" => "%",
                        _ => throw new InvalidOperationException()
                    };
                    env[arg1] = Eval($"{val} {op} {arg2}");
                    break;

                case "if":
                    // Format: if x > 10 goto label
                    if (arg2 == "goto" && arg3 != null)
                    {
                        var cond = string.Join(' ', parts.Skip(1).Take(2)); // x > 10
                        var result = Eval(cond);
                        if (result is bool b && b)
                            pc = labels[arg3];
                    }
                    break;

                case "goto":
                    if (arg1 != null && labels.TryGetValue(arg1, out var target))
                        pc = target;
                    break;

                case "inp":
                    Console.Write($"{arg1}: ");
                    env[arg1] = Console.ReadLine();
                    break;

                case "def":
                    // No-op in this basic form, handled via label + call/ret
                    break;

                case "call":
                    if (arg1 != null && labels.TryGetValue(arg1, out var fnStart))
                    {
                        stack.Push(pc);
                        pc = fnStart + 1;
                        if (arg2 != null)
                            env["x"] = Eval(arg2);
                    }
                    break;

                case "ret":
                    if (stack.Count > 0)
                        pc = stack.Pop();
                    else
                        return;
                    break;

                case "cmp":
                    Console.WriteLine($"Compare: {Eval($"{arg1} == {arg2}")}");
                    break;

                case "end":
                    return;

                default:
                    Console.WriteLine($"Unknown command: {cmd}");
                    break;
            }
        }
    }
}