#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <libgen.h>
#include <openssl/sha.h>

#define nil NULL

int
main(int argc, char **argv)
{
	char *path, *e, *origexe, *s, exe[4096], *argv0, *in, *out, *dirout, dhh[SHA256_DIGEST_LENGTH*2+1];
	uint8_t tmp[65536], dh[SHA256_DIGEST_LENGTH];
	int d, f, i, argout;
	SHA256_CTX shactx;
	struct stat st;
	ssize_t n;
	pid_t pid;

	if((dirout = getenv("LLCACHE_DIR")) == nil){
		fprintf(stderr, "LLCACHE_DIR not set\n");
		goto err;
	}
	if((argv0 = basename(argv[0])) == nil){
		fprintf(stderr, "argv[0] is not a proper path\n");
		goto err;
	}

	if((n = readlink("/proc/self/exe", exe, sizeof(exe))) >= (ssize_t)sizeof(exe)){
exesmall:
		fprintf(stderr, "exe buffer too small\n");
		goto err;
	}else if(n < 0){
		perror("exe buffer");
		goto err;
	}
	exe[n] = 0;
	origexe = realpath(exe, nil);

	path = strdup(getenv("PATH"));
	for(s = path; s != nil; s = e ? e + 1 : nil){
		if((e = strchr(s, ':')) != nil)
			*e = 0;
		if((d = open(s, O_DIRECTORY|O_RDONLY)) < 0)
			continue;
		n = readlinkat(d, argv0, exe, sizeof(exe));
		if(n >= (ssize_t)sizeof(exe))
			goto exesmall;
		if(n < 0){
			if((n = fstatat(d, argv0, &st, 0)) == 0)
				exe[0] = 0;
		}
		close(d);
		if(n < 0 || strcmp(origexe, exe) == 0)
			continue;
		if(snprintf(exe, sizeof(exe), "%s/%s", s, argv0) >= (int)sizeof(exe))
			goto exesmall;
		if((s = realpath(exe, nil)) == nil || strcmp(origexe, s) == 0){
			free(s);
			continue;
		}

		break;
	}
	if(s == nil){
		fprintf(stderr, "%s: not found\n", argv0);
		goto err;
	}

	SHA256_Init(&shactx);
	SHA256_Update(&shactx, s, strlen(s)+1);

	in = nil;
	out = nil;
	argout = -1;
	for(i = 1; i < argc; i++){
		if(argv[i][0] == '/'){
			if(strcmp(argv[i-1], "-o") == 0){
				out = argv[i];
				argout = i;
			}else{
				in = argv[i];
			}
		}else{
			SHA256_Update(&shactx, argv[i], strlen(argv[i])+1);
		}
	}
	if(in == nil || out == nil)
		goto run;

	if((f = open(in, O_RDONLY)) < 0){
inerr:
		perror("input");
		goto err;
	}
	for(;;){
		if((n = read(f, tmp, sizeof(tmp))) == 0)
			break;
		if(n < 0)
			goto inerr;
		SHA256_Update(&shactx, tmp, n);
	}
	close(f);

	SHA256_Final(dh, &shactx);
	for(i = 0; i < (int)sizeof(dh); i++)
		sprintf(&dhh[i*2], "%02x", dh[i]);

	pid = 0;
copy:
	if((d = open(dirout, O_DIRECTORY)) >= 0 && (f = openat(d, dhh, O_RDONLY)) >= 0 && fstat(f, &st) == 0){
		close(d);
		if((d = creat(out, st.st_mode)) < 0){
			perror("creat");
			goto err;
		}
		for(;;){
			if((n = read(f, tmp, sizeof(tmp))) == 0)
				break;
			if(n < 0)
				goto inerr;
			if(write(d, tmp, n) != n){
				perror("output");
				goto err;
			}
		}
		close(f);
		close(d);
		return 0;
	}

	if(pid != 0){
		fprintf(stderr, "endless loop?\n");
		goto err;
	}

run:
	if((pid = fork()) < 0){
		perror("fork");
		goto err;
	}else if(pid == 0){
		if(argout > 0){
			snprintf((char*)tmp, sizeof(tmp), "%s/%s", dirout, dhh);
			argv[argout] = (char*)tmp;
		}
		execvp(s, argv);
		perror("exec");
		goto err;
	}

	if(waitpid(pid, &i, 0) < 0){
		perror("waitpid");
		goto err;
	}
	if(i == 0)
		goto copy;
err:
	return 1;
}