// Copyright (c) 2026 Charles KWON OhJun (charleskwonohjun@gmail.com)
// All rights reserved.

package hbrt

import "strings"

// pendingCall stores the symbol for the next Function/Do call.
// This avoids storing Go pointers in Value.data (which GC can't trace).

// PushSymbol records the function symbol for the next call.
// The actual symbol is stored in Thread, not on the eval stack.
// A marker NIL is pushed to keep stack positions correct.
// Harbour: hb_xvmPushSymbol
func (t *Thread) PushSymbol(sym *Symbol) {
	t.pushPendingSym(sym)
	t.push(MakeNil()) // placeholder for symbol position
}

// Function calls the function with nArgs arguments.
// Stack layout before: [sym_placeholder] [nil/self] [arg1] ... [argN]
// Stack after: [retval]
// Harbour: hb_xvmFunction
func (t *Thread) Function(nArgs int) {
	sym := t.popPendingSym()

	if sym == nil {
		panic(t.runtimeError("no function symbol for call"))
	}

	// Resolve function
	fn := sym.Func
	if fn == nil && t.vm != nil {
		found := t.vm.FindSymbol(strings.ToUpper(sym.Name))
		if found != nil {
			fn = found.Func
		}
	}
	if fn == nil {
		panic(t.runtimeError("undefined function: " + sym.Name))
	}

	// Collect args from stack
	args := make([]Value, nArgs)
	for i := nArgs - 1; i >= 0; i-- {
		args[i] = t.pop()
	}
	t.pop() // pop NIL/self placeholder
	t.pop() // pop symbol placeholder

	// Push args back for Frame() to pick up
	for _, arg := range args {
		t.push(arg)
	}

	// Set pending params count and symbol for Frame()
	t.pendingParams = nArgs
	t.pendingCallSym = sym

	// Call
	fn(t)

	// Push return value
	t.push(t.retVal)
}

// Do calls the function but discards the return value.
// Harbour: hb_xvmDo
func (t *Thread) Do(nArgs int) {
	t.Function(nArgs)
	t.pop() // discard return value
}