package ptrproxy

//#include <stdlib.h>
import (
	"C"
)
import (
	"sync"
	"unsafe"
)

// PtrProxy creates a safe pointer registry. It hangs on to an unsafe.Pointer and
// returns a totally-safe unsafe.Pointer ID that can be used to look up the original
// pointer by using it.
var (
	mutex  sync.RWMutex
	lookup map[unsafe.Pointer]unsafe.Pointer = map[unsafe.Pointer]unsafe.Pointer{}
)

// Ref registers the given pointer and returns a corresponding id that can be
// used to retrieve it later.
func Ref(ptr unsafe.Pointer) unsafe.Pointer {
	if ptr == nil {
		return nil
	}
	var cptr unsafe.Pointer = C.malloc(C.size_t(1))
	if cptr == nil {
		return nil
	}
	mutex.Lock()
	lookup[cptr] = ptr
	mutex.Unlock()
	return cptr
}

// Deref takes an id and returns the corresponding pointer if it exists.
func Deref(ptr unsafe.Pointer) (unsafe.Pointer, bool) {
	if ptr == nil {
		return nil, false
	}
	mutex.RLock()
	val, ok := lookup[ptr]
	mutex.RUnlock()
	return val, ok
}

// Deref and Free
func Move(ptr unsafe.Pointer) (unsafe.Pointer, bool) {
	if ptr == nil {
		return nil, false
	}
	mutex.Lock()
	val, ok := lookup[ptr]
	if ok == false {
		mutex.Unlock()
		return nil, false
	} else {
		delete(lookup, ptr)
		mutex.Unlock()
		C.free(ptr)

		return val, true
	}
}

// Free releases a registered pointer by its id.
func Free(ptr unsafe.Pointer) {
	if ptr == nil {
		return
	}
	mutex.Lock()
	delete(lookup, ptr)
	mutex.Unlock()

	C.free(ptr)
}

// This like https://github.com/mattn/go-pointer
// https://github.com/shazow/gohttplib/blob/master/ptrproxy.go