package api

import (
    "math"
    "os"

    "github.com/go-audio/wav"
)

func waveformFromWav(path string, buckets int) ([]float64, error) {
    if buckets <= 0 {
        buckets = 256
    }
    f, err := os.Open(path)
    if err != nil {
        return nil, err
    }
    defer f.Close()
    dec := wav.NewDecoder(f)
    buf, err := dec.FullPCMBuffer()
    if err != nil {
        return nil, err
    }
    samples := buf.AsFloat32Buffer().Data
    if len(samples) == 0 {
        return make([]float64, buckets), nil
    }
    chunk := len(samples) / buckets
    if chunk < 1 {
        chunk = 1
    }
    out := make([]float64, 0, buckets)
    for i := 0; i < len(samples) && len(out) < buckets; i += chunk {
        end := i + chunk
        if end > len(samples) {
            end = len(samples)
        }
        peak := 0.0
        for _, s := range samples[i:end] {
            v := math.Abs(float64(s))
            if v > peak {
                peak = v
            }
        }
        out = append(out, math.Round(peak*1000)/1000)
    }
    return out, nil
}