feat: cw decoder

internal/cwdecode/cwdecode_test.go

@@ -0,0 +1,98 @@
+package cwdecode
+
+import (
+	"math"
+	"strings"
+	"testing"
+)
+
+// reverse Morse map for the synthesizer.
+func charToMorse() map[byte]string {
+	m := map[byte]string{}
+	for code, ch := range morse {
+		m[ch] = code
+	}
+	return m
+}
+
+// keyMessage synthesizes a clean keyed tone for msg at the given WPM/pitch.
+func keyMessage(msg string, fs, wpm int, pitch float64) []int16 {
+	dot := fs * 1200 / (wpm * 1000) // samples per dot
+	c2m := charToMorse()
+	var out []int16
+	phase := 0.0
+	dphi := 2 * math.Pi * pitch / float64(fs)
+
+	tone := func(n int) {
+		for i := 0; i < n; i++ {
+			out = append(out, int16(9000*math.Sin(phase)))
+			phase += dphi
+		}
+	}
+	silence := func(n int) {
+		for i := 0; i < n; i++ {
+			out = append(out, 0)
+		}
+	}
+
+	silence(fs / 4) // 250 ms lead-in for AGC warmup
+	for i := 0; i < len(msg); i++ {
+		ch := msg[i]
+		if ch == ' ' {
+			silence(7 * dot)
+			continue
+		}
+		code := c2m[ch]
+		for j := 0; j < len(code); j++ {
+			if code[j] == '.' {
+				tone(dot)
+			} else {
+				tone(3 * dot)
+			}
+			silence(dot) // inter-element gap
+		}
+		silence(3 * dot) // inter-character gap (on top of the trailing element gap)
+	}
+	silence(fs / 4)
+	return out
+}
+
+func TestDecodeCleanSignal(t *testing.T) {
+	const fs = 16000
+	var sb strings.Builder
+	d := New(fs, func(s string) { sb.WriteString(s) }, nil)
+
+	// Repeat so AGC warm-up only costs the first word.
+	samples := keyMessage("PARIS PARIS PARIS", fs, 22, 700)
+	// Feed in small chunks like the live capture would.
+	for i := 0; i < len(samples); i += 256 {
+		end := i + 256
+		if end > len(samples) {
+			end = len(samples)
+		}
+		d.Process(samples[i:end])
+	}
+
+	got := strings.ToUpper(sb.String())
+	if !strings.Contains(got, "PARIS") {
+		t.Fatalf("decoded %q, want it to contain PARIS", got)
+	}
+}
+
+func TestDecodeNumbersAndProsign(t *testing.T) {
+	const fs = 16000
+	var sb strings.Builder
+	d := New(fs, func(s string) { sb.WriteString(s) }, nil)
+	samples := keyMessage("TEST 599 TEST", fs, 18, 650)
+	for i := 0; i < len(samples); i += 200 {
+		end := i + 200
+		if end > len(samples) {
+			end = len(samples)
+		}
+		d.Process(samples[i:end])
+	}
+	got := strings.ToUpper(sb.String())
+	if !strings.Contains(got, "599") {
+		t.Fatalf("decoded %q, want it to contain 599", got)
+	}
+}