/* Copyright 1999-2009 Gentoo Foundation
 * Distributed under the terms of the GNU General Public License v2
 */

#include <dirent.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>

#define ENVD_CONFIG "/etc/env.d/python/config"

int valid_interpreter(const char* name) {
	/* name must match exactly "pythonX.Y", where the X is between 2 and 9,
	 * and Y is between 0 and 9
	 */
	if (!name || (strcmp(name, "python") == 0) || (strncmp(name, "python", 6) != 0) || strchr(name, '/') ||
			strlen(name) != 9 || name[6] < '2' || name[6] > '9' || name[7] != '.' || name[8] < '0' || name[8] > '9') {
		return 0;
	}
	return 1;
}

const char* find_latest()
{
	int major = -1;
	int minor = -1;
	DIR* d = opendir("/usr/bin");
	if (!d)
		return NULL;
	struct dirent *entry;
	while (entry = readdir(d))
	{
		const char* name = entry->d_name;
		if (valid_interpreter(name))
		{
			int newmajor = name[7];
			int newminor = name[9];
			/* prefer 2.* to anything later, but otherwise take the latest
			 * version
			 */
			if (newmajor == major && newminor > minor || newmajor == '2' && major != '2' || major != '2' && newmajor > major)
			{
				major = newmajor;
				minor = newminor;
			}
		}
	}
	if (major > 0 && minor > 0) {
		char pattern[10] = "python0.0";
		pattern[7] = major;
		pattern[9] = minor;
		char *ret = malloc(10);
		strncpy(ret, pattern, 10);
		return ret;
	}
	return NULL;
}

int main(int argc, char** argv)
{
	const char* EPYTHON = getenv("EPYTHON");
	if (!valid_interpreter(EPYTHON))
	{
		FILE* f = fopen(ENVD_CONFIG, "r");
		if (f)
		{
			struct stat st;
			fstat(fileno(f), &st);
			size_t size = st.st_size;
			char* cont = malloc(size + 1);
			fgets(cont, size + 1, f);
			fclose(f);
			size_t len = strlen(cont);
			if (len && cont[len - 1] == '\n')
				cont[len - 1] = 0;
			EPYTHON = cont;
		}
	}

	if (!valid_interpreter(EPYTHON))
		EPYTHON = find_latest();

	if (!EPYTHON)
		return 127;

	execvp(EPYTHON, argv);
	return 127;
}