fm-rds-tx/internal/rds/encoder_test.go

package rds

import (
	"math"
	"strings"
	"testing"
)

func TestCRC10KnownVector(t *testing.T) {
	// Verify the CRC polynomial produces 10-bit outputs
	c := crc10(0x1234)
	if c > 0x3FF {
		t.Fatalf("CRC exceeds 10 bits: %x", c)
	}
}

func TestEncodeBlockProduces26Bits(t *testing.T) {
	block := encodeBlock(0x1234, 'A')
	// Must fit in 26 bits
	if block>>26 != 0 {
		t.Fatalf("block exceeds 26 bits: %x", block)
	}
	// Data portion should be the original word
	data := uint16(block >> 10)
	if data != 0x1234 {
		t.Fatalf("data mismatch: got %x want %x", data, 0x1234)
	}
}

func TestBuildGroup0ABlockCount(t *testing.T) {
	g := buildGroup0A(0x1234, 0, false, false, 0, "TESTFM")
	// Block A must be PI
	if g[0] != 0x1234 {
		t.Fatalf("block A not PI: %x", g[0])
	}
	// Block D should contain first two PS chars 'T','E'
	ch0 := byte(g[3] >> 8)
	ch1 := byte(g[3] & 0xFF)
	if ch0 != 'T' || ch1 != 'E' {
		t.Fatalf("unexpected PS chars: %c %c", ch0, ch1)
	}
}

func TestBuildGroup2ABlockCount(t *testing.T) {
	g := buildGroup2A(0x1234, 0, false, false, 0, "Hello World")
	if g[0] != 0x1234 {
		t.Fatalf("block A not PI: %x", g[0])
	}
	// Group type field in block B should have type 2 in bits 15..12
	groupType := (g[1] >> 12) & 0x0F
	if groupType != 2 {
		t.Fatalf("unexpected group type: %d", groupType)
	}
}

func TestEncoderGenerate(t *testing.T) {
	cfg := DefaultConfig()
	cfg.SampleRate = 228000
	enc, err := NewEncoder(cfg)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}

	samples := enc.Generate(1024)
	if len(samples) != 1024 {
		t.Fatalf("expected 1024 samples, got %d", len(samples))
	}

	var maxAbs float64
	var energy float64
	for _, s := range samples {
		a := math.Abs(s)
		energy += s * s
		if a > maxAbs {
			maxAbs = a
		}
	}

	if energy == 0 {
		t.Fatal("expected non-zero energy in RDS output")
	}
	if maxAbs > defaultAmplitude*1.01 {
		t.Fatalf("samples exceed configured amplitude: %.6f", maxAbs)
	}
}

func TestEncoderReset(t *testing.T) {
	cfg := DefaultConfig()
	cfg.SampleRate = 228000
	enc, err := NewEncoder(cfg)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}

	sampleA := enc.Generate(1)[0]
	enc.Generate(100)
	enc.Reset()
	sampleB := enc.Generate(1)[0]
	if math.Abs(sampleA-sampleB) > 1e-9 {
		t.Fatalf("expected reset to replay initial sample: %v vs %v", sampleA, sampleB)
	}
}

func TestGroupSchedulerCycles(t *testing.T) {
	cfg := DefaultConfig()
	cfg.PS = "TESTPS"
	cfg.RT = "short"
	gs := newGroupScheduler(cfg)

	// Should get 4 PS groups then RT groups then cycle
	for i := 0; i < 40; i++ {
		_ = gs.NextGroup()
	}
	// No panic = success
}

func TestNormalizePS(t *testing.T) {
	got := normalizePS("radiox")
	if got != "RADIOX  " {
		t.Fatalf("unexpected PS: %q", got)
	}
}

func TestNormalizeRT(t *testing.T) {
	long := strings.Repeat("a", 80)
	got := normalizeRT(long)
	if len(got) != 64 {
		t.Fatalf("unexpected RT length: %d", len(got))
	}
}

func TestDifferentialEncoder(t *testing.T) {
	d := diffEncoder{}
	// Input: 0 -> out = 0^0 = 0, prev=0
	// Input: 1 -> out = 0^1 = 1, prev=1
	// Input: 0 -> out = 1^0 = 1, prev=1
	// Input: 1 -> out = 1^1 = 0, prev=0
	expected := []uint8{0, 1, 1, 0}
	input := []uint8{0, 1, 0, 1}
	for i, in := range input {
		got := d.encode(in)
		if got != expected[i] {
			t.Fatalf("step %d: input=%d expected=%d got=%d", i, in, expected[i], got)
		}
	}
}

func TestRTSegmentCount(t *testing.T) {
	if n := rtSegmentCount("Hi"); n != 1 {
		t.Fatalf("expected 1, got %d", n)
	}
	if n := rtSegmentCount("Hello World!"); n != 3 {
		t.Fatalf("expected 3, got %d", n)
	}
	if n := rtSegmentCount(strings.Repeat("x", 64)); n != 16 {
		t.Fatalf("expected 16, got %d", n)
	}
}