Add detailed comments to Goertzel and two-tone detector functions for improved code clarity

main.go

@@ -1,10 +1,9 @@
-// -wav=output.wav -minA=500 -minB=2000 -rms=10 -ratio=0.3
 package main
 
 import (
 	"flag"
 	"fmt"
-    "log"
+	"log/slog"
 	"math"
 	"os"
 	"time"
@@ -23,6 +22,7 @@ var (
 	hopMs       = flag.Int("hop", 50, "Hop size (ms)")
 	ratioThresh = flag.Float64("ratio", 0.65, "Power ratio threshold for tone detection")
 	rmsThresh   = flag.Float64("rms", 300.0, "Minimum RMS for valid signal")
+	verbose     = flag.Bool("verbose", false, "Enable debug logging")
 )
 
 // Goertzel struct for frequency detection
@@ -33,6 +33,11 @@ type goertzel struct {
 	coeff float64
 }
 
+// newGoertzel initializes and returns a new Goertzel filter configured to detect a specific target frequency.
+// targetHz specifies the frequency to detect in Hertz.
+// fs is the sampling rate in Hertz.
+// N is the number of samples to process.
+// The function calculates the filter coefficients based on the provided parameters.
 func newGoertzel(targetHz float64, fs float64, N int) *goertzel {
 	g := &goertzel{N: N, fs: fs}
 	g.k = int(0.5 + (float64(g.N)*targetHz)/fs)
@@ -41,6 +46,10 @@ func newGoertzel(targetHz float64, fs float64, N int) *goertzel {
 	return g
 }
 
+// Power computes the power of the target frequency in the input signal x using the Goertzel algorithm.
+// It processes the input slice x of length g.N, applying the Goertzel recurrence to accumulate state.
+// The function returns the squared magnitude (power) of the frequency bin specified by g.k.
+// x should be a slice of float64 samples, typically representing a windowed segment of a signal.
 func (g *goertzel) Power(x []float64) float64 {
 	var s0, s1, s2 float64
 	for i := 0; i < g.N; i++ {
@@ -54,6 +63,10 @@ func (g *goertzel) Power(x []float64) float64 {
 	return real*real + imag*imag
 }
 
+// windowHann applies a Hann window to the input slice x in place.
+// The Hann window is commonly used in signal processing to reduce spectral leakage
+// by tapering the beginning and end of the signal to zero.
+// The function modifies the input slice directly.
 func windowHann(x []float64) {
 	n := float64(len(x))
 	for i := range x {
@@ -61,6 +74,9 @@ func windowHann(x []float64) {
 	}
 }
 
+// pcmToFloat converts a slice of 16-bit PCM audio samples (buf) to a slice of float64 values.
+// The output slice has length N, and each element is the float64 representation of the corresponding PCM sample.
+// If N is greater than the length of buf, the output slice will contain zero values for the remaining elements.
 func pcmToFloat(buf []int16, N int) []float64 {
 	out := make([]float64, N)
 	for i := 0; i < N && i < len(buf); i++ {
@@ -69,6 +85,9 @@ func pcmToFloat(buf []int16, N int) []float64 {
 	return out
 }
 
+// rmsPCM calculates the root mean square (RMS) value of a slice of 16-bit PCM audio samples.
+// It returns the RMS as a float64, which represents the signal's effective amplitude.
+// If the input slice is empty, it returns 0.
 func rmsPCM(buf []int16) float64 {
 	var s float64
 	for _, v := range buf {
@@ -97,15 +116,34 @@ type twoToneDetector struct {
 	aFreq       float64
 	aAccumMs    int
 	aStart      time.Time
+	aEnd        time.Time
 	waitingB    bool
 	bFreq       float64
 	bAccumMs    int
 	bStart      time.Time
+	bEnd        time.Time
 	gapRemainMs int
+	logger      *slog.Logger
 }
 
-func newTwoToneDetector(fs, winN, hopN int, ratioThresh, rmsThresh float64, minAms, minBms, gapMaxMs int) *twoToneDetector {
-    // Frequency range: 300–3000 Hz, 10 Hz steps
+// newTwoToneDetector creates and initializes a new twoToneDetector instance.
+// It sets up a bank of Goertzel filters for frequencies ranging from 300 Hz to 3000 Hz in 10 Hz steps.
+// Parameters:
+//
+//	fs         - Sample rate in Hz.
+//	winN       - Window size for analysis.
+//	hopN       - Hop size between windows.
+//	ratioThresh- Threshold for tone ratio detection.
+//	rmsThresh  - RMS threshold for signal detection.
+//	minAms     - Minimum duration of tone A in milliseconds.
+//	minBms     - Minimum duration of tone B in milliseconds.
+//	gapMaxMs   - Maximum allowed gap between tones in milliseconds.
+//	logger     - Logger for diagnostic output.
+//
+// Returns:
+//
+//	Pointer to a twoToneDetector configured with the specified parameters.
+func newTwoToneDetector(fs, winN, hopN int, ratioThresh, rmsThresh float64, minAms, minBms, gapMaxMs int, logger *slog.Logger) *twoToneDetector {
 	freqs := make([]float64, 0)
 	for f := 300.0; f <= 3000.0; f += 10.0 {
 		freqs = append(freqs, f)
@@ -125,10 +163,31 @@ func newTwoToneDetector(fs, winN, hopN int, ratioThresh, rmsThresh float64, minA
 		gapMaxMs:    gapMaxMs,
 		freqs:       freqs,
 		gzBank:      gzBank,
+		logger:      logger,
 	}
 }
 
-func (d *twoToneDetector) stepWindow(pcms []int16, t0 time.Time) (event string, aFreq, aDur, bFreq, bDur float64) {
+// stepWindow processes a window of PCM audio samples to detect a two-tone sequence.
+// It applies a Hann window to the samples, computes RMS and power ratios, and tracks
+// the presence and duration of two distinct tones (A and B) according to configured thresholds.
+// The function returns an event string (e.g., "TWO_TONE_DETECTED") when a valid two-tone
+// sequence is detected, along with the frequencies and durations (in milliseconds) of both tones,
+// and the timestamp of detection.
+//
+// Parameters:
+//
+//	pcms    - Slice of int16 PCM audio samples for the current window.
+//	t0      - Start time of the current window.
+//
+// Returns:
+//
+//	event     - Event string indicating detection status (e.g., "TWO_TONE_DETECTED" or "").
+//	aFreq     - Frequency of detected Tone A (Hz).
+//	aDur      - Duration of Tone A (milliseconds).
+//	bFreq     - Frequency of detected Tone B (Hz).
+//	bDur      - Duration of Tone B (milliseconds).
+//	timestamp - Timestamp of detection (time.Time). Zero value if no event detected.
+func (d *twoToneDetector) stepWindow(pcms []int16, t0 time.Time) (event string, aFreq, aDur, bFreq, bDur float64, timestamp time.Time) {
 	xi := pcmToFloat(pcms, d.winN)
 	windowHann(xi)
 
@@ -138,9 +197,16 @@ func (d *twoToneDetector) stepWindow(pcms []int16, t0 time.Time) (event string,
 	}
 
 	r := rmsPCM(pcms)
+	hopDur := time.Millisecond * time.Duration(int(float64(d.hopN)*1000.0/float64(d.fs)))
+	now := t0
+
 	if r < d.rmsThresh {
+		d.logger.Debug("RMS below threshold, resetting",
+			"time", now.Format(time.RFC3339),
+			"rms", fmt.Sprintf("%.2f", r),
+			"threshold", d.rmsThresh)
 		d.reset()
-	return "", 0, 0, 0, 0
+		return "", 0, 0, 0, 0, time.Time{}
 	}
 
 	// Find frequency with highest power
@@ -155,98 +221,143 @@ func (d *twoToneDetector) stepWindow(pcms []int16, t0 time.Time) (event string,
 	}
 	ratio := bestPow / (total + 1e-12)
 	if ratio < d.ratioThresh {
+		d.logger.Debug("Ratio below threshold, resetting",
+			"time", now.Format(time.RFC3339),
+			"ratio", fmt.Sprintf("%.3f", ratio),
+			"threshold", d.ratioThresh)
 		d.reset()
-	return "", 0, 0, 0, 0
+		return "", 0, 0, 0, 0, time.Time{}
 	}
 	freq := d.freqs[bestIdx]
 
-    hopDur := time.Millisecond * time.Duration(int(float64(d.hopN)*1000.0/float64(d.fs)))
-    now := t0
-
 	if !d.inA && !d.waitingB {
 		// Looking for Tone A
 		d.inA = true
 		d.aFreq = freq
-	d.aAccumMs = int(hopDur.Milliseconds())
 		d.aStart = now
 	} else if d.inA && !d.waitingB {
 		// Confirming Tone A
 		if math.Abs(freq-d.aFreq) <= 10.0 {
 			d.aAccumMs += int(hopDur.Milliseconds())
+			d.aEnd = now.Add(hopDur)
 			if d.aAccumMs >= d.minAms {
 				d.inA = false
 				d.waitingB = true
 				d.gapRemainMs = d.gapMaxMs
 			}
 		} else {
+			d.logger.Debug("Frequency differs from Tone A, resetting",
+				"time", now.Format(time.RFC3339),
+				"freq", fmt.Sprintf("%.1f", freq),
+				"tone_a_freq", fmt.Sprintf("%.1f", d.aFreq))
 			d.reset()
 		}
 	} else if d.waitingB {
 		d.gapRemainMs -= int(hopDur.Milliseconds())
 		if d.gapRemainMs <= 0 {
+			d.logger.Debug("Gap exceeded max duration, resetting",
+				"time", now.Format(time.RFC3339),
+				"gap_max_ms", d.gapMaxMs)
 			d.reset()
 		} else if math.Abs(freq-d.aFreq) > 10.0 {
-	    // Check for Tone B (different frequency)
+			// Check for Tone B
 			if d.bAccumMs == 0 {
 				d.bFreq = freq
 				d.bStart = now
 			} else if math.Abs(freq-d.bFreq) > 10.0 {
-		// Switched to a different frequency, reset B
+				d.logger.Debug("Frequency differs from Tone B, resetting B",
+					"time", now.Format(time.RFC3339),
+					"freq", fmt.Sprintf("%.1f", freq),
+					"tone_b_freq", fmt.Sprintf("%.1f", d.bFreq))
 				d.bFreq = freq
 				d.bAccumMs = 0
 				d.bStart = now
 			}
 			d.bAccumMs += int(hopDur.Milliseconds())
+			d.bEnd = now.Add(hopDur)
 			if d.bAccumMs >= d.minBms {
 				event = "TWO_TONE_DETECTED"
-		return event, d.aFreq, float64(d.aAccumMs), d.bFreq, float64(d.bAccumMs)
+				aDurMs := float64(d.aEnd.Sub(d.aStart).Milliseconds())
+				bDurMs := float64(d.bEnd.Sub(d.bStart).Milliseconds())
+				d.logger.Info("Two-tone detected",
+					"time", now.Format(time.RFC3339),
+					"tone_a_freq", fmt.Sprintf("%.1f", d.aFreq),
+					"tone_a_duration_ms", fmt.Sprintf("%.0f", aDurMs),
+					"tone_b_freq", fmt.Sprintf("%.1f", d.bFreq),
+					"tone_b_duration_ms", fmt.Sprintf("%.0f", bDurMs))
+				return event, d.aFreq, aDurMs, d.bFreq, bDurMs, now
 			}
 		}
 	}
-    return "", 0, 0, 0, 0
+	return "", 0, 0, 0, 0, time.Time{}
 }
 
+// reset reinitializes all internal state fields of the twoToneDetector,
+// clearing any ongoing detection data and preparing the detector for a new
+// detection sequence. This includes resetting flags, frequency values,
+// accumulated durations, start/end timestamps, and gap tracking.
 func (d *twoToneDetector) reset() {
 	d.inA = false
 	d.aFreq = 0
 	d.aAccumMs = 0
 	d.aStart = time.Time{}
+	d.aEnd = time.Time{}
 	d.waitingB = false
 	d.bFreq = 0
 	d.bAccumMs = 0
 	d.bStart = time.Time{}
+	d.bEnd = time.Time{}
 	d.gapRemainMs = 0
 }
 
 func main() {
 	flag.Parse()
+
+	// Initialize slog logger
+	logLevel := &slog.LevelVar{}
+	logLevel.Set(slog.LevelInfo)
+	if *verbose {
+		logLevel.Set(slog.LevelDebug)
+	}
+	logger := slog.New(slog.NewJSONHandler(os.Stderr, &slog.HandlerOptions{
+		Level: logLevel,
+	}))
+
 	if *wavFile == "" {
-	log.Fatal("WAV file path is required (use -wav flag)")
+		logger.Error("WAV file path is required", "flag", "-wav")
+		os.Exit(1)
 	}
 
 	file, err := os.Open(*wavFile)
 	if err != nil {
-	log.Fatalf("Failed to open WAV file: %v", err)
+		logger.Error("Failed to open WAV file", "error", err)
+		os.Exit(1)
 	}
 	defer file.Close()
 
 	decoder := wav.NewDecoder(file)
 	if !decoder.IsValidFile() {
-	log.Fatal("Invalid WAV file")
+		logger.Error("Invalid WAV file")
+		os.Exit(1)
 	}
 	if decoder.Format().SampleRate != 8000 || decoder.Format().NumChannels != 1 {
-	log.Fatalf("WAV file must be mono 8kHz, got %d Hz, %d channels",
-	    decoder.Format().SampleRate, decoder.Format().NumChannels)
+		logger.Error("WAV file must be mono 8kHz",
+			"sample_rate", decoder.Format().SampleRate,
+			"channels", decoder.Format().NumChannels)
+		os.Exit(1)
 	}
 
 	const fs = 8000
 	winN := int(float64(fs) * float64(*winMs) / 1000.0)
 	hopN := int(float64(fs) * float64(*hopMs) / 1000.0)
 	if winN <= 0 || hopN <= 0 || hopN > winN {
-	log.Fatalf("Invalid window/hop: winN=%d, hopN=%d", winN, hopN)
+		logger.Error("Invalid window/hop parameters",
+			"winN", winN,
+			"hopN", hopN)
+		os.Exit(1)
 	}
 
-    det := newTwoToneDetector(fs, winN, hopN, *ratioThresh, *rmsThresh, *minAms, *minBms, *gapMaxMs)
+	det := newTwoToneDetector(fs, winN, hopN, *ratioThresh, *rmsThresh, *minAms, *minBms, *gapMaxMs, logger)
 
 	buf := &audio.IntBuffer{
 		Format:         &audio.Format{SampleRate: fs, NumChannels: 1},
@@ -256,11 +367,13 @@ func main() {
 	sampleCount := 0
 	startTime := time.Now()
 
-    log.Println("Processing WAV file...")
+	logger.Info("Processing WAV file")
 	for {
 		n, err := decoder.PCMBuffer(buf)
 		if err != nil || n == 0 || len(buf.Data) == 0 {
-	    log.Printf("Finished processing %d samples (%.2f seconds)", sampleCount, float64(sampleCount)/float64(fs))
+			logger.Info("Finished processing",
+				"samples", sampleCount,
+				"duration_sec", fmt.Sprintf("%.2f", float64(sampleCount)/float64(fs)))
 			break
 		}
 
@@ -273,9 +386,9 @@ func main() {
 		for offset := 0; offset <= len(pcm)-winN; offset += hopN {
 			win := pcm[offset:min(offset+winN, len(pcm))]
 			t := startTime.Add(time.Duration(sampleCount-len(pcm)+offset) * time.Second / time.Duration(fs))
-	    event, aFreq, aDur, bFreq, bDur := det.stepWindow(win, t)
+			event, aFreq, aDur, bFreq, bDur, timestamp := det.stepWindow(win, t)
 			if event != "" {
-		fmt.Printf("Detected two-tone sequence:\n")
+				fmt.Printf("Detected two-tone sequence at %s:\n", timestamp.Format(time.RFC3339))
 				fmt.Printf("  Tone A: %.1f Hz, duration %.0f ms\n", aFreq, aDur)
 				fmt.Printf("  Tone B: %.1f Hz, duration %.0f ms\n", bFreq, bDur)
 				det.reset()
@@ -284,6 +397,7 @@ func main() {
 	}
 }
 
+// min returns the smaller of two integer values a and b.
 func min(a, b int) int {
 	if a < b {
 		return a