package audio

// DefaultMaxSampleRate is the maximum sample rate for spectrograms.
const DefaultMaxSampleRate = 16000

// ResampleRate converts samples from one sample rate to another using linear interpolation.
// This is used to downsample high sample rate audio for spectrogram visualization.
// fromRate: original sample rate (e.g., 250000)
// toRate: target sample rate (e.g., 16000)
func ResampleRate(samples []float64, fromRate, toRate int) []float64 {
	if fromRate == toRate || len(samples) == 0 {
		return samples
	}
	// speed = fromRate/toRate: e.g. 250000/16000 = 15.625 (skip samples to downsample)
	return Resample(samples, float64(fromRate)/float64(toRate))
}

// Resample changes playback speed using linear interpolation.
// speed > 1.0 = faster (fewer samples), speed < 1.0 = slower (more samples).
// For half-speed playback, use speed=0.5 which doubles the sample count.
func Resample(samples []float64, speed float64) []float64 {
	if speed == 1.0 || len(samples) == 0 {
		return samples
	}

	// Calculate new length: slower speed = more samples
	newLen := int(float64(len(samples)) / speed)
	if newLen <= 0 {
		return samples
	}

	result := make([]float64, newLen)

	for i := range newLen {
		// Source index in original samples (floating point)
		srcIdx := float64(i) * speed
		idx0 := int(srcIdx)
		idx1 := idx0 + 1

		// Clamp to valid range
		if idx0 >= len(samples) {
			idx0 = len(samples) - 1
		}
		if idx1 >= len(samples) {
			idx1 = len(samples) - 1
		}

		// Linear interpolation between adjacent samples
		frac := srcIdx - float64(idx0)
		result[i] = samples[idx0]*(1-frac) + samples[idx1]*frac
	}

	return result
}