// Copyright 2019 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// +build go1.13

package jsutil

import (
	"fmt"
	"reflect"
	"runtime"
	"syscall/js"
	"unsafe"
)

func Uint8ArrayToSlice(value js.Value) []byte {
	s := make([]byte, value.Get("byteLength").Int())
	js.CopyBytesToGo(s, value)
	return s
}

func ArrayBufferToSlice(value js.Value) []byte {
	return Uint8ArrayToSlice(js.Global().Get("Uint8Array").New(value))
}

func sliceToByteSlice(s interface{}) []byte {
	switch s := s.(type) {
	case []int8:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		return *(*[]byte)(unsafe.Pointer(h))
	case []int16:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 2
		h.Cap *= 2
		return *(*[]byte)(unsafe.Pointer(h))
	case []int32:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 4
		h.Cap *= 4
		return *(*[]byte)(unsafe.Pointer(h))
	case []int64:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 8
		h.Cap *= 8
		return *(*[]byte)(unsafe.Pointer(h))
	case []uint8:
		return s
	case []uint16:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 2
		h.Cap *= 2
		return *(*[]byte)(unsafe.Pointer(h))
	case []uint32:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 4
		h.Cap *= 4
		return *(*[]byte)(unsafe.Pointer(h))
	case []uint64:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 8
		h.Cap *= 8
		return *(*[]byte)(unsafe.Pointer(h))
	case []float32:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 4
		h.Cap *= 4
		return *(*[]byte)(unsafe.Pointer(h))
	case []float64:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 8
		h.Cap *= 8
		return *(*[]byte)(unsafe.Pointer(h))
	default:
		panic(fmt.Sprintf("jsutil: unexpected value at sliceToBytesSlice: %T", s))
	}
}

func SliceToTypedArray(s interface{}) (js.Value, func()) {
	switch s := s.(type) {
	case []int8:
		a := js.Global().Get("Uint8Array").New(len(s))
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Int8Array").New(buf, a.Get("byteOffset"), a.Get("byteLength")), func() {}
	case []int16:
		a := js.Global().Get("Uint8Array").New(len(s) * 2)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Int16Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/2), func() {}
	case []int32:
		a := js.Global().Get("Uint8Array").New(len(s) * 4)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Int32Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/4), func() {}
	case []uint8:
		a := js.Global().Get("Uint8Array").New(len(s))
		js.CopyBytesToJS(a, s)
		runtime.KeepAlive(s)
		return a, func() {}
	case []uint16:
		a := js.Global().Get("Uint8Array").New(len(s) * 2)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Uint16Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/2), func() {}
	case []uint32:
		a := js.Global().Get("Uint8Array").New(len(s) * 4)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Uint32Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/4), func() {}
	case []float32:
		a := js.Global().Get("Uint8Array").New(len(s) * 4)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Float32Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/4), func() {}
	case []float64:
		a := js.Global().Get("Uint8Array").New(len(s) * 8)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Float64Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/8), func() {}
	default:
		panic(fmt.Sprintf("jsutil: unexpected value at SliceToTypedArray: %T", s))
	}
}