// Copyright 2018 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.

package convert_test

import (
	"bytes"
	"io"
	"math"
	"testing"

	"github.com/hajimehoshi/ebiten/v2/audio/internal/convert"
)

func soundAt(timeInSecond float64) float64 {
	const freq = 220

	amp := []float64{1.0, 0.8, 0.6, 0.4, 0.2}
	v := 0.0
	for j := 0; j < len(amp); j++ {
		v += amp[j] * math.Sin(2.0*math.Pi*timeInSecond*freq*float64(j+1))
	}
	if v > 1 {
		v = 1
	}
	if v < -1 {
		v = -1
	}
	return v
}

func newSoundBytes(sampleRate int) []byte {
	b := make([]byte, sampleRate*4) // 1 second
	for i := 0; i < len(b)/4; i++ {
		v := soundAt(float64(i) / float64(sampleRate))
		v16 := int16(v * (1<<15 - 1))
		b[4*i] = byte(v16)
		b[4*i+1] = byte(v16 >> 8)
		b[4*i+2] = byte(v16)
		b[4*i+3] = byte(v16 >> 8)
	}
	return b
}

func TestResampling(t *testing.T) {
	cases := []struct {
		In  int
		Out int
	}{
		{
			In:  44100,
			Out: 48000,
		},
		{
			In:  48000,
			Out: 44100,
		},
	}
	for _, c := range cases {
		inB := newSoundBytes(c.In)
		outS := convert.NewResampling(bytes.NewReader(inB), int64(len(inB)), c.In, c.Out)
		gotB, err := io.ReadAll(outS)
		if err != nil {
			t.Fatal(err)
		}
		wantB := newSoundBytes(c.Out)
		if len(gotB) != len(wantB) {
			t.Errorf("len(gotB) == %d but len(wantB) == %d", len(gotB), len(wantB))
		}
		for i := 0; i < len(gotB)/2; i++ {
			got := float64(int16(gotB[2*i])|(int16(gotB[2*i+1])<<8)) / (1<<15 - 1)
			want := float64(int16(wantB[2*i])|(int16(wantB[2*i+1])<<8)) / (1<<15 - 1)
			if math.Abs(got-want) > 0.025 {
				t.Errorf("sample rate: %d, index: %d: got: %f, want: %f", c.Out, i, got, want)
			}
		}
	}
}