/* Return the initial module search path. */
/* Used by DOS, OS/2, Windows 3.1.  Works on NT too. */

#include "Python.h"
#include "osdefs.h"

#ifdef MS_WIN32
#include <windows.h>
extern BOOL PyWin_IsWin32s(void);
#endif

#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>

#if HAVE_UNISTD_H
#include <unistd.h>
#endif /* HAVE_UNISTD_H */

/* Search in some common locations for the associated Python libraries.
 *
 * Two directories must be found, the platform independent directory
 * (prefix), containing the common .py and .pyc files, and the platform
 * dependent directory (exec_prefix), containing the shared library
 * modules.  Note that prefix and exec_prefix can be the same directory,
 * but for some installations, they are different.
 *
 * Py_GetPath() tries to return a sensible Python module search path.
 *
 * First, we look to see if the executable is in a subdirectory of
 * the Python build directory.  We calculate the full path of the
 * directory containing the executable as progpath.  We work backwards
 * along progpath and look for $dir/Modules/Setup.in, a distinctive
 * landmark.  If found, we use $dir/Lib as $root.  The returned
 * Python path is the compiled #define PYTHONPATH with all the initial
 * "./lib" replaced by $root.
 *
 * Otherwise, if there is a PYTHONPATH environment variable, we return that.
 *
 * Otherwise we try to find $progpath/lib/os.py, and if found, then
 * root is $progpath/lib, and we return Python path as compiled PYTHONPATH
 * with all "./lib" replaced by $root (as above).
 *
 */

#ifndef LANDMARK
#define LANDMARK "lib\\os.py"
#endif

static char prefix[MAXPATHLEN+1];
static char exec_prefix[MAXPATHLEN+1];
static char progpath[MAXPATHLEN+1];
static char *module_search_path = NULL;


static int
is_sep(char ch)	/* determine if "ch" is a separator character */
{
#ifdef ALTSEP
	return ch == SEP || ch == ALTSEP;
#else
	return ch == SEP;
#endif
}


static void
reduce(char *dir)
{
	int i = strlen(dir);
	while (i > 0 && !is_sep(dir[i]))
		--i;
	dir[i] = '\0';
}
	

static int
exists(char *filename)
{
	struct stat buf;
	return stat(filename, &buf) == 0;
}


/* Add a path component, by appending stuff to buffer.
   buffer must have at least MAXPATHLEN + 1 bytes allocated, and contain a
   NUL-terminated string with no more than MAXPATHLEN characters (not counting
   the trailing NUL).  It's a fatal error if it contains a string longer than
   that (callers must be careful!).  If these requirements are met, it's
   guaranteed that buffer will still be a NUL-terminated string with no more
   than MAXPATHLEN characters at exit.  If stuff is too long, only as much of
   stuff as fits will be appended.
*/
static void
join(char *buffer, char *stuff)
{
	int n, k;
	if (is_sep(stuff[0]))
		n = 0;
	else {
		n = strlen(buffer);
		if (n > 0 && !is_sep(buffer[n-1]) && n < MAXPATHLEN)
			buffer[n++] = SEP;
	}
	if (n > MAXPATHLEN)
		Py_FatalError("buffer overflow in getpathp.c's joinpath()");
	k = strlen(stuff);
	if (n + k > MAXPATHLEN)
		k = MAXPATHLEN - n;
	strncpy(buffer+n, stuff, k);
	buffer[n+k] = '\0';
}


static int
search_for_prefix(char *argv0_path, char *landmark)
{
	int n;

	/* Search from argv0_path, until root is found */
	strcpy(prefix, argv0_path);
	do {
		n = strlen(prefix);
		join(prefix, landmark);
		if (exists(prefix)) {
			prefix[n] = '\0';
			return 1;
		}
		prefix[n] = '\0';
		reduce(prefix);
	} while (prefix[0]);
	return 0;
}

#ifdef MS_WIN32
#include "malloc.h" // for alloca - see comments below!
extern const char *PyWin_DLLVersionString; // a string loaded from the DLL at startup.


/* Load a PYTHONPATH value from the registry.
   Load from either HKEY_LOCAL_MACHINE or HKEY_CURRENT_USER.

   Returns NULL, or a pointer that should be freed.
*/

static char *
getpythonregpath(HKEY keyBase, BOOL bWin32s)
{
	HKEY newKey = 0;
	DWORD nameSize = 0;
	DWORD dataSize = 0;
	DWORD numEntries = 0;
	LONG rc;
	char *retval = NULL;
	char *dataBuf;
	const char keyPrefix[] = "Software\\Python\\PythonCore\\";
	const char keySuffix[] = "\\PythonPath";
	int versionLen;
	char *keyBuf;

	// Tried to use sysget("winver") but here is too early :-(
	versionLen = strlen(PyWin_DLLVersionString);
	// alloca == no free required, but memory only local to fn.
	// also no heap fragmentation!  Am I being silly?
	keyBuf = alloca(sizeof(keyPrefix)-1 + versionLen + sizeof(keySuffix)); // chars only, plus 1 NULL.
	// lots of constants here for the compiler to optimize away :-)
	memcpy(keyBuf, keyPrefix, sizeof(keyPrefix)-1);
	memcpy(keyBuf+sizeof(keyPrefix)-1, PyWin_DLLVersionString, versionLen);
	memcpy(keyBuf+sizeof(keyPrefix)-1+versionLen, keySuffix, sizeof(keySuffix)); // NULL comes with this one!

	rc=RegOpenKey(keyBase,
		      keyBuf,
		      &newKey);
	if (rc==ERROR_SUCCESS) {
		RegQueryInfoKey(newKey, NULL, NULL, NULL, NULL, NULL, NULL, 
		                &numEntries, &nameSize, &dataSize, NULL, NULL);
	}
	if (bWin32s && numEntries==0 && dataSize==0) {
		/* must hardcode for Win32s */
		numEntries = 1;
		dataSize = 511;
	}
	if (numEntries) {
		/* Loop over all subkeys. */
		/* Win32s doesnt know how many subkeys, so we do
		   it twice */
		char keyBuf[MAX_PATH+1];
		int index = 0;
		int off = 0;
		for(index=0;;index++) {
			long reqdSize = 0;
			DWORD rc = RegEnumKey(newKey,
					      index, keyBuf, MAX_PATH+1);
			if (rc) break;
			rc = RegQueryValue(newKey, keyBuf, NULL, &reqdSize);
			if (rc) break;
			if (bWin32s && reqdSize==0) reqdSize = 512;
			dataSize += reqdSize + 1; /* 1 for the ";" */
		}
		dataBuf = malloc(dataSize+1);
		if (dataBuf==NULL)
			return NULL; /* pretty serious?  Raise error? */
		/* Now loop over, grabbing the paths.
		   Subkeys before main library */
		for(index=0;;index++) {
			int adjust;
			long reqdSize = dataSize;
			DWORD rc = RegEnumKey(newKey,
					      index, keyBuf,MAX_PATH+1);
			if (rc) break;
			rc = RegQueryValue(newKey,
					   keyBuf, dataBuf+off, &reqdSize);
			if (rc) break;
			if (reqdSize>1) {
				/* If Nothing, or only '\0' copied. */
				adjust = strlen(dataBuf+off);
				dataSize -= adjust;
				off += adjust;
				dataBuf[off++] = ';';
				dataBuf[off] = '\0';
				dataSize--;
			}
		}
		/* Additionally, win32s doesnt work as expected, so
		   the specific strlen() is required for 3.1. */
		rc = RegQueryValue(newKey, "", dataBuf+off, &dataSize);
		if (rc==ERROR_SUCCESS) {
			if (strlen(dataBuf)==0)
				free(dataBuf);
			else
				retval = dataBuf; /* caller will free */
		}
		else
			free(dataBuf);
	}

	if (newKey)
		RegCloseKey(newKey);
	return retval;
}
#endif /* MS_WIN32 */

static void
get_progpath(void)
{
	extern char *Py_GetProgramName(void);
	char *path = getenv("PATH");
	char *prog = Py_GetProgramName();

#ifdef MS_WIN32
	if (GetModuleFileName(NULL, progpath, MAXPATHLEN))
		return;
#endif
	if (prog == NULL || *prog == '\0')
		prog = "python";

	/* If there is no slash in the argv0 path, then we have to
	 * assume python is on the user's $PATH, since there's no
	 * other way to find a directory to start the search from.  If
	 * $PATH isn't exported, you lose.
	 */
#ifdef ALTSEP
	if (strchr(prog, SEP) || strchr(prog, ALTSEP))
#else
	if (strchr(prog, SEP))
#endif
		strcpy(progpath, prog);
	else if (path) {
		while (1) {
			char *delim = strchr(path, DELIM);

			if (delim) {
				int len = delim - path;
				strncpy(progpath, path, len);
				*(progpath + len) = '\0';
			}
			else
				strcpy(progpath, path);

			join(progpath, prog);
			if (exists(progpath))
				break;

			if (!delim) {
				progpath[0] = '\0';
				break;
			}
			path = delim + 1;
		}
	}
	else
		progpath[0] = '\0';
}

static void
calculate_path(void)
{
	char argv0_path[MAXPATHLEN+1];
	char *buf;
	int bufsz;
	char *pythonhome = Py_GetPythonHome();
	char *envpath = Py_GETENV("PYTHONPATH");
#ifdef MS_WIN32
	char *machinepath, *userpath;

	/* Are we running under Windows 3.1(1) Win32s? */
	if (PyWin_IsWin32s()) {
		/* Only CLASSES_ROOT is supported */
		machinepath = getpythonregpath(HKEY_CLASSES_ROOT, TRUE); 
		userpath = NULL;
	} else {
		machinepath = getpythonregpath(HKEY_LOCAL_MACHINE, FALSE);
		userpath = getpythonregpath(HKEY_CURRENT_USER, FALSE);
	}
#endif

	get_progpath();
	strcpy(argv0_path, progpath);
	reduce(argv0_path);
	if (pythonhome == NULL || *pythonhome == '\0') {
		if (search_for_prefix(argv0_path, LANDMARK))
			pythonhome = prefix;
		else
			pythonhome = NULL;
	}
	else {
        char *delim;

		strcpy(prefix, pythonhome);

        /* Extract Any Optional Trailing EXEC_PREFIX */
        /* e.g. PYTHONHOME=<prefix>:<exec_prefix>   */
        delim = strchr(prefix, DELIM);
        if (delim) {
            *delim = '\0';
            strcpy(exec_prefix, delim+1);
        } else
            strcpy(exec_prefix, EXEC_PREFIX);
    }

	if (envpath && *envpath == '\0')
		envpath = NULL;

	/* We need to construct a path from the following parts:
	   (1) the PYTHONPATH environment variable, if set;
	   (2) for Win32, the machinepath and userpath, if set;
	   (3) the PYTHONPATH config macro, with the leading "."
	       of each component replaced with pythonhome, if set;
	   (4) the directory containing the executable (argv0_path).
	   The length calculation calculates #3 first.
	*/

	/* Calculate size of return buffer */
	if (pythonhome != NULL) {
		char *p;
		bufsz = 1;	
		for (p = PYTHONPATH; *p; p++) {
			if (*p == DELIM)
				bufsz++; /* number of DELIM plus one */
		}
		bufsz *= strlen(pythonhome);
	}
	else
		bufsz = 0;
	bufsz += strlen(PYTHONPATH) + 1;
	if (envpath != NULL)
		bufsz += strlen(envpath) + 1;
	bufsz += strlen(argv0_path) + 1;
#ifdef MS_WIN32
	if (machinepath)
		bufsz += strlen(machinepath) + 1;
	if (userpath)
		bufsz += strlen(userpath) + 1;
#endif

	module_search_path = buf = malloc(bufsz);
	if (buf == NULL) {
		/* We can't exit, so print a warning and limp along */
		fprintf(stderr, "Can't malloc dynamic PYTHONPATH.\n");
		if (envpath) {
			fprintf(stderr, "Using default static $PYTHONPATH.\n");
			module_search_path = envpath;
		}
		else {
			fprintf(stderr, "Using environment $PYTHONPATH.\n");
			module_search_path = PYTHONPATH;
		}
		return;
	}

	if (envpath) {
		strcpy(buf, envpath);
		buf = strchr(buf, '\0');
		*buf++ = DELIM;
	}
#ifdef MS_WIN32
	if (machinepath) {
		strcpy(buf, machinepath);
		buf = strchr(buf, '\0');
		*buf++ = DELIM;
	}
	if (userpath) {
		strcpy(buf, userpath);
		buf = strchr(buf, '\0');
		*buf++ = DELIM;
	}
#endif
	if (pythonhome == NULL) {
		strcpy(buf, PYTHONPATH);
		buf = strchr(buf, '\0');
	}
	else {
		char *p = PYTHONPATH;
		char *q;
		int n;
		for (;;) {
			q = strchr(p, DELIM);
			if (q == NULL)
				n = strlen(p);
			else
				n = q-p;
			if (p[0] == '.' && is_sep(p[1])) {
				strcpy(buf, pythonhome);
				buf = strchr(buf, '\0');
				p++;
				n--;
			}
			strncpy(buf, p, n);
			buf += n;
			if (q == NULL)
				break;
			*buf++ = DELIM;
			p = q+1;
		}
	}
	if (argv0_path) {
		*buf++ = DELIM;
		strcpy(buf, argv0_path);
		buf = strchr(buf, '\0');
	}
	*buf = '\0';
}


/* External interface */

char *
Py_GetPath(void)
{
	if (!module_search_path)
		calculate_path();

	return module_search_path;
}

char *
Py_GetPrefix(void)
{
	if (!module_search_path)
		calculate_path();

	return prefix;
}

char *
Py_GetExecPrefix(void)
{
	if (!module_search_path)
		calculate_path();

	return exec_prefix;
}

char *
Py_GetProgramFullPath(void)
{
	if (!module_search_path)
		calculate_path();

	return progpath;
}