#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h> 
#include <sys/socket.h>
#include <netinet/in.h>

#define	PORT	31337
#define OUT_FILE	"junk"
//#define	HOST	192.
//#define	flen	53851
#define	BUFLEN	65536		//65536-20 is the maximum udp packet size, looks like a nice maximum for server.

/**
 * TODO:
 * 	Make sure data is fetched from same client.
 **/
int main(void){
	int sockHandle;
	//int port;
	struct sockaddr_in *sock_server, *sock_client;
	char buf[BUFLEN];
	unsigned int downloaded=0;
	unsigned int sequence=0;
	unsigned int fileSize=0;
	int packetCount=-1;
	int received=0;
	FILE *fileHandle;
	socklen_t socklen=sizeof(struct sockaddr_in);
    printf("datasink\n");
	sock_server = malloc(socklen);
	sock_client = malloc(socklen);
	if(!sock_server || !sock_client){
		printf("Cannot allocate memory for socket.\n");
	}

	sockHandle=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
	if(sockHandle<0){
		printf("Cannot get socket\n");
		return 0;
	}
	
	sock_server->sin_family = AF_INET;
	sock_server->sin_addr.s_addr=htonl(INADDR_ANY);
	sock_server->sin_port = htons(PORT);
	if(bind(sockHandle, (struct sockaddr *)sock_server, socklen)<0){
		printf("Error, cannot bind socket\n");
		return 0;
	}

	fileHandle=fopen(OUT_FILE, "wb");
	if(fileHandle==NULL){
		printf("Cannot open file for writing\n");
		return 0;
	}
	printf("ready for data\n"); 
	while(1){
		received=recvfrom(sockHandle, buf, BUFLEN, 0, (struct sockaddr *)sock_client, &socklen);
		if(received<0){
			printf("Error, cannot receive data\n");
			return 0;
		}
		if(packetCount==-1){
			sequence = buf[0]<<8;
			sequence |= buf[1];
			sequence &= 0x0000ffff;
			if(sequence!=0){
				printf("Caught packet in middle of stream, ignoring\n");
				continue;
			}else{
				printf("Caught first packet, starting capture.\n");
				packetCount=0;
				fileSize = (buf[2] & 0x000000ff)<<8;
				fileSize |= buf[3] & 0x000000ff;
				fileSize &= 0x0000ffff;
				printf("File size is: %u\n", fileSize);
				fwrite(buf+4, 1, received-4, fileHandle);
				downloaded=received-4;
			}
		}else{
			sequence = buf[0]<<8;
			sequence |= buf[1];
			sequence &= 0x0000ffff;
			if(sequence!=packetCount+1){
				printf("Missed a packet, bumping sequence. Expecting %u, got %u. Waiting for new sequence.\n", packetCount+1, sequence);
				fseek(fileHandle, 0, SEEK_SET);
				packetCount=0;
				downloaded=0;
			}else{
				fwrite(buf+2, 1, received-2, fileHandle);
				packetCount++;
				downloaded += received-2;
				printf("Downloaded: %i\n", downloaded);
			}
		}
		if(downloaded>=fileSize){
			printf("Download complete. %i out of %i bytes.\n", downloaded, fileSize);
			break;
		}

	}
	fclose(fileHandle);
	//listen(sockHandle)

}