/**
 * This file is part of the Fun programming language.
 * https://hanez.org/project/fun/
 *
 * Copyright 2025 Johannes Findeisen <you@hanez.org>
 * Licensed under the terms of the ISC license.
 * https://opensource.org/license/isc-license-txt
 */

/**
* @file call.c
 * @brief Implements the OP_CALL opcode for function calls in the VM.
 *
 * This file handles the OP_CALL instruction, which calls a function with arguments.
 *
 * Behavior:
 * - operand specifies number of arguments
 * - Pops args and function from stack
 * - Creates new frame with args in locals
 * - Sets IP to start of function
 *
 * Error Handling:
 * - Exits with error if not enough args
 * - Exits if function isn't callable
 *
 * @author Johannes Findeisen
 * @date 2025-10-16
 */

case OP_CALL: {
    int argc = inst.operand;
    if (argc < 0) argc = 0;
    /* collect args in reverse (preserve order) */
    Value *args = NULL;
    if (argc > 0) {
        args = (Value*)malloc(sizeof(Value) * argc);
        /* pop args into array in reverse */
        for (int i = argc - 1; i >= 0; --i) {
            args[i] = pop_value(vm);
        }
    }
    /* pop function value */
    Value fnv = pop_value(vm);
    if (fnv.type != VAL_FUNCTION) {
        fprintf(stderr, "Runtime type error: CALL expects function\n");
        exit(1);
    }
    /* push new frame and transfer args */
    vm_push_frame(vm, fnv.fn, argc, args);
    /* free args array (locals moved), free fnv (no-op for function) */
    free(args);
    /* note: fnv contains a pointer to the Bytecode, don't free here */
    break;
}