package synth

import (
	"math"
	"testing"
)

func TestPanGainsCenter(t *testing.T) {
	gainL, gainR := PanGains(0.0)
	expected := math.Sqrt2 / 2 // cos(pi/4) = sin(pi/4) = 0.707...
	if math.Abs(gainL-expected) > 1e-9 {
		t.Errorf("PanGains(0.0) gainL = %v, want ~%v", gainL, expected)
	}
	if math.Abs(gainR-expected) > 1e-9 {
		t.Errorf("PanGains(0.0) gainR = %v, want ~%v", gainR, expected)
	}
}

func TestPanGainsFullLeft(t *testing.T) {
	gainL, gainR := PanGains(-1.0)
	if math.Abs(gainL-1.0) > 1e-9 {
		t.Errorf("PanGains(-1.0) gainL = %v, want ~1.0", gainL)
	}
	if math.Abs(gainR-0.0) > 1e-9 {
		t.Errorf("PanGains(-1.0) gainR = %v, want ~0.0", gainR)
	}
}

func TestPanGainsFullRight(t *testing.T) {
	gainL, gainR := PanGains(1.0)
	if math.Abs(gainL-0.0) > 1e-9 {
		t.Errorf("PanGains(1.0) gainL = %v, want ~0.0", gainL)
	}
	if math.Abs(gainR-1.0) > 1e-9 {
		t.Errorf("PanGains(1.0) gainR = %v, want ~1.0", gainR)
	}
}

func TestPanGainsPowerPreserved(t *testing.T) {
	pans := []float64{-1.0, -0.75, -0.5, -0.25, 0.0, 0.25, 0.5, 0.75, 1.0}
	for _, p := range pans {
		gainL, gainR := PanGains(p)
		power := gainL*gainL + gainR*gainR
		if math.Abs(power-1.0) > 1e-9 {
			t.Errorf("PanGains(%v) power = %v, want 1.0 (constant power law)", p, power)
		}
	}
}

func TestStereoFramesToInt16Bytes(t *testing.T) {
	frames := [][2]float64{{1.0, -1.0}}
	buf := StereoFramesToInt16Bytes(frames)
	if len(buf) != 4 {
		t.Fatalf("expected 4 bytes, got %d", len(buf))
	}
	// int16(32767) in little-endian = [0xFF, 0x7F]
	// int16(-32767) in little-endian = [0x01, 0x80]
	expectedL := int16(32767)
	expectedR := int16(-32767)
	gotL := int16(uint16(buf[0]) | uint16(buf[1])<<8)
	gotR := int16(uint16(buf[2]) | uint16(buf[3])<<8)
	if gotL != expectedL {
		t.Errorf("left channel = %d, want %d", gotL, expectedL)
	}
	if gotR != expectedR {
		t.Errorf("right channel = %d, want %d", gotR, expectedR)
	}
}

func TestStereoFramesToInt16BytesZero(t *testing.T) {
	frames := [][2]float64{{0.0, 0.0}}
	buf := StereoFramesToInt16Bytes(frames)
	if len(buf) != 4 {
		t.Fatalf("expected 4 bytes, got %d", len(buf))
	}
	for i, b := range buf {
		if b != 0 {
			t.Errorf("byte[%d] = %d, want 0", i, b)
		}
	}
}

func TestClampPreventsOverflow(t *testing.T) {
	// Values > 1.0 should be clamped to 1.0 before int16 conversion
	frames := [][2]float64{{2.0, -2.0}}
	buf := StereoFramesToInt16Bytes(frames)
	gotL := int16(uint16(buf[0]) | uint16(buf[1])<<8)
	gotR := int16(uint16(buf[2]) | uint16(buf[3])<<8)
	// Should be clamped to max int16 positive / negative
	if gotL != int16(32767) {
		t.Errorf("clamped left = %d, want 32767", gotL)
	}
	if gotR != int16(-32767) {
		t.Errorf("clamped right = %d, want -32767", gotR)
	}
}