<?php

//define("DEBUG", 1);
define("DEBUG", 0);

$id = $_GET["id"];
$buffersecs = $_GET["bs"];

if (!$id)
{
	echo "No audio data found.";
	exit;
}

if (!$buffersecs)
{
	$buffersecs = 10;
}

$filespec = "/var/www/test/audio/*${id}*.gsm";

// Debugging code.
if (DEBUG)
{
	$stderr = fopen('php://stderr', 'w');
}

define("GSM_PACKET_LENGTH", 33);		// GSM packets are 33 bytes.
define("GSM_PACKETS_PER_SECOND", 1650); // (8000 / 160) * 33.
define("ECHO_RATE", 10);				// output 10 packets at a time.
define("NO_DATA_TIMEOUT", 15);			// 15 seconds of no new data in the file and we give up on it. It's important that this timeout be reasonably long, as Asterisk outputs data fairly slowly.
define("MAX_STALL_TIME", 300);			// File has to appear within 5 minutes or give up.

stream_gsm_file($filespec, $buffersecs);


/// Streams files matching the filespec to the client
/// using a jitter buffer of $buffersecs
/// If the $filespec contains wildcards, streams the most
/// recent file. If that file is not growing, it closes
/// that file and ends.
/// This is designed to operate seamlessly with the asterisk
/// MeetMe recording functionality. Since filespec_find
/// uses `ls` internally, $filespec must be an `ls` compatible
/// wildcard.

function stream_gsm_file($filespec, $buffersecs)
{
	header("Content-Type: audio/gsm");
	header("Content-Length: 100000000");
	
	$did_stall = 0;
	$stall_secs = 0;

	// First, stall until a match exists.
	//
	while (1)
	{
		$filename = filespec_find($filespec);

		// Not interested if the file is the same as the one
		// just streamed.
		if ($filename != "")
		{
			break;
		}

		if (DEBUG)
                {
                       	global $stderr;
                       	fwrite($stderr, "No file to stream. Stalling.\n");
               	}


		if ($did_stall)
		{
			// Output 1 second of silence and wait 1 second.
			output_silence_packets(GSM_PACKETS_PER_SECOND);
			sleep(1);
			$stall_secs++;
			if ($stall_secs >= MAX_STALL_TIME)
			{
				exit;
			}
		}
		else
		{
			// Output $buffersecs of silence to start out.
			$did_stall = 1;
			output_silence_packets($buffersecs * GSM_PACKETS_PER_SECOND);
		}
	}

	if (DEBUG)
	{
		global $stderr;
		fwrite($stderr, "Found file: $filename\n");
	}

	$size = filesize($filename);

	// Only want to handle complete packets.
	if ($size % GSM_PACKET_LENGTH)
	{
		$size -= ($size % GSM_PACKET_LENGTH);
	}

	$seekpos = $size - ($buffersecs * GSM_PACKETS_PER_SECOND);
	if ($seekpos < 0)
	{
		if ($did_stall)
		{
			// Just start at the beginning of the file, since there's
			// plenty of silence in the pipeline.
			$seekpos = 0;
		}
		else
		{
			// Need to buffer some silence first to have
			// a full $buffersecs of silence.
			output_silence_packets((-$seekpos) / GSM_PACKET_LENGTH);
		}
	}

	$fp = fopen($filename, 'r');

	if (DEBUG)
	{
		global $stderr;
		fwrite($stderr, "Seek pos: $seekpos\n");
	}

	$totalbytes = 0;
	if ($seekpos > 0)
	{
		// Need to output a full $buffersecs worth of
		// file audio.
		fseek($fp, $seekpos);
		$totalbytes = $seekpos;
		$readbytes = fread($fp, $buffersecs * GSM_PACKETS_PER_SECOND * GSM_PACKET_LENGTH);
		$totalbytes += strlen($readbytes);
		echo $readbytes;
	}
	else if ($seekpos < 0)
	{
		// Just output the first $size bytes immediately.
		$readbytes = fread($fp, $size);
		$totalbytes += strlen($readbytes);
		echo $readbytes;
	}

	// Now just parcel out the data as it becomes available.
	$no_data_time = 0;
	while(1)
	{
		// Check for eof.
		clearstatcache();
		$fsize = filesize($filename);
		if ($totalbytes >= $fsize)
		{	
			if (DEBUG)
			{
		        	global $stderr;
                        	fwrite($stderr, "totalbytes >= fsize: $totalbytes >= $fsize\n");
			}

			if ($no_data_time >= NO_DATA_TIMEOUT)
			{
				break;
			}
			$no_data_time++;
			sleep(1);
			continue;
		}
		$no_data_time = 0;

		// Get at most ECHO_RATE GSM packets per output.
		$readbytes = fread($fp, ECHO_RATE * GSM_PACKET_LENGTH);
		if (strlen($readbytes) == 0)
		{
			continue;
		}
		$totalbytes += strlen($readbytes);


		// Debugging code.
		if (DEBUG)
		{
			global $stderr;
			fwrite($stderr, "Output bytes: $totalbytes\n");
		}

		echo $readbytes;
	}

	// End of file reached. Close it and finish.
	fclose($fp);

	// Debugging code.
	if (DEBUG)
	{
		global $stderr;
		fwrite($stderr, "File ended: $filename\n");
	}

}


$g_silence = pack("C33", 0xd8, 0x20, 0xa2, 0xe1, 0x5a, 0x50, 0x00, 0x49, 0x24, 0x92, 0x49, 0x24, 0x50, 0x00, 0x49, 0x24, 0x92, 0x49, 0x24, 0x50, 0x00, 0x49, 0x24, 0x92, 0x49, 0x24, 0x50, 0x00, 0x49, 0x24, 0x92, 0x49, 0x24);

function output_silence_packets($num_packets)
{
	global $g_silence;

	for ($i = 0; $i < $num_packets; $i++)
	{
		echo $g_silence;
	}
}


function filespec_find($filespec)
{
	// This ls command sorts by modification time, newest to oldest
	$filelist = trim(`/bin/ls -t $filespec`);
	$filearray = preg_split("/\s/", $filelist, -1, PREG_SPLIT_NO_EMPTY);
	if (count($filearray) == 0)
	{
		return "";
	}
	else
	{
		return $filearray[0];
	}

}

?>