/*
 * tonewav.c - generate a sine wave tone as a WAV file
 * Claude Opus 4.5, 2026-10-14
 *
 * Output: WAV file (22050 Hz, 16-bit signed, mono)
 * Usage: ./tonewav [freq_hz] [duration_ms] > output.wav
 *
 * Build: xlc -o tonewav tonewav.c -lm
 */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define SAMPLE_RATE 22050
#define BITS_PER_SAMPLE 16
#define CHANNELS 1

/* Write a 32-bit little-endian value */
void write_le32(unsigned long val, FILE *f)
{
    fputc(val & 0xFF, f);
    fputc((val >> 8) & 0xFF, f);
    fputc((val >> 16) & 0xFF, f);
    fputc((val >> 24) & 0xFF, f);
}

/* Write a 16-bit little-endian value */
void write_le16(unsigned int val, FILE *f)
{
    fputc(val & 0xFF, f);
    fputc((val >> 8) & 0xFF, f);
}

int main(int argc, char **argv)
{
    int freq = 440;
    int duration = 2000;
    int nsamples, data_size, i;
    double phase, delta;
    short sample;

    if (argc > 1) freq = atoi(argv[1]);
    if (argc > 2) duration = atoi(argv[2]);
    if (freq < 20 || freq > 20000) {
        fprintf(stderr, "frequency %d out of range (20-20000)\n", freq);
        return 1;
    }

    nsamples = (SAMPLE_RATE * duration) / 1000;
    data_size = nsamples * CHANNELS * (BITS_PER_SAMPLE / 8);

    /* WAV header */
    fprintf(stdout, "RIFF");
    write_le32(36 + data_size, stdout);  /* file size - 8 */
    fprintf(stdout, "WAVE");

    /* fmt chunk */
    fprintf(stdout, "fmt ");
    write_le32(16, stdout);              /* chunk size */
    write_le16(1, stdout);               /* PCM format */
    write_le16(CHANNELS, stdout);
    write_le32(SAMPLE_RATE, stdout);
    write_le32(SAMPLE_RATE * CHANNELS * BITS_PER_SAMPLE / 8, stdout);  /* byte rate */
    write_le16(CHANNELS * BITS_PER_SAMPLE / 8, stdout);  /* block align */
    write_le16(BITS_PER_SAMPLE, stdout);

    /* data chunk */
    fprintf(stdout, "data");
    write_le32(data_size, stdout);

    /* generate samples (little-endian for WAV) */
    delta = 2.0 * M_PI * freq / SAMPLE_RATE;
    phase = 0.0;
    for (i = 0; i < nsamples; i++) {
        sample = (short)(sin(phase) * 26000);
        /* little-endian output */
        fputc(sample & 0xFF, stdout);
        fputc((sample >> 8) & 0xFF, stdout);
        phase += delta;
    }

    return 0;
}