package mangler

import (
	"reflect"
	"sync"
	"unsafe"
)

// manglers is a map of runtime
// type ptrs => Mangler functions.
var manglers sync.Map

// Mangler is a function that will take an input interface value of known
// type, and append it in mangled serialized form to the given byte buffer.
// While the value type is an interface, the Mangler functions are accessed
// by the value's runtime type pointer, allowing the input value type to be known.
type Mangler func(buf []byte, ptr unsafe.Pointer) []byte

// Get will fetch the Mangler function for given runtime type.
// Note that the returned mangler will be a no-op in the case
// that an incorrect type is passed as the value argument.
func Get(t reflect.Type) Mangler {
	var mng Mangler

	// Get raw runtime type ptr
	uptr := uintptr(eface_data(t))

	// Look for a cached mangler
	v, ok := manglers.Load(uptr)

	if !ok {
		// Load mangler function
		mng = loadMangler(t)
	} else {
		// cast cached value
		mng = v.(Mangler)
	}

	return func(buf []byte, ptr unsafe.Pointer) []byte {
		// First write the type ptr (this adds
		// a unique prefix for each runtime type).
		buf = append_uint64(buf, uint64(uptr))

		// Finally, mangle value
		return mng(buf, ptr)
	}
}

// Register will register the given Mangler function for use with vars of given runtime type. This allows
// registering performant manglers for existing types not implementing Mangled (e.g. std library types).
// NOTE: panics if there already exists a Mangler function for given type. Register on init().
func Register(t reflect.Type, m Mangler) {
	if t == nil {
		// Nil interface{} types cannot be searched by, do not accept
		panic("cannot register mangler for nil interface{} type")
	}

	// Get raw runtime type ptr
	uptr := uintptr(eface_data(t))

	// Ensure this is a unique encoder
	if _, ok := manglers.Load(uptr); ok {
		panic("already registered mangler for type: " + t.String())
	}

	// Cache this encoder func
	manglers.Store(uptr, m)
}

// Append will append the mangled form of input value 'a' to buffer 'b'.
// See mangler.String() for more information on mangled output.
func Append(b []byte, a any) []byte {
	var mng Mangler

	// Get reflect type of 'a'
	t := reflect.TypeOf(a)

	// Get raw runtime type ptr
	uptr := uintptr(eface_data(t))

	// Look for a cached mangler
	v, ok := manglers.Load(uptr)

	if !ok {
		// Load into cache
		mng = loadMangler(t)
		manglers.Store(uptr, mng)
	} else {
		// cast cached value
		mng = v.(Mangler)
	}

	// First write the type ptr (this adds
	// a unique prefix for each runtime type).
	b = append_uint64(b, uint64(uptr))

	// Finally, mangle value
	ptr := eface_data(a)
	return mng(b, ptr)
}

// String will return the mangled format of input value 'a'. This
// mangled output will be unique for all default supported input types
// during a single runtime instance. Uniqueness cannot be guaranteed
// between separate runtime instances (whether running concurrently, or
// the same application running at different times).
//
// The exact formatting of the output data should not be relied upon,
// only that it is unique given the above constraints. Generally though,
// the mangled output is the binary formatted text of given input data.
//
// Uniqueness is guaranteed for similar input data of differing types
// (e.g. string("hello world") vs. []byte("hello world")) by prefixing
// mangled output with the input data's runtime type pointer.
//
// Default supported types include:
// - string
// - bool
// - int,int8,int16,int32,int64
// - uint,uint8,uint16,uint32,uint64,uintptr
// - float32,float64
// - complex64,complex128
// - arbitrary structs
// - all type aliases of above
// - all pointers to the above
// - all slices / arrays of the above
func String(a any) string {
	b := Append(make([]byte, 0, 32), a)
	return *(*string)(unsafe.Pointer(&b))
}