/* Return the initial module search path. */

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

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

#ifdef __APPLE__
#  include <mach-o/dyld.h>
#endif

/* 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() carries out separate searches for prefix and exec_prefix.
 * Each search tries a number of different locations until a ``landmark''
 * file or directory is found.  If no prefix or exec_prefix is found, a
 * warning message is issued and the preprocessor defined PREFIX and
 * EXEC_PREFIX are used (even though they will not work); python carries on
 * as best as is possible, but most imports will fail.
 *
 * Before any searches are done, the location of the executable is
 * determined.  If argv[0] has one or more slashes in it, it is used
 * unchanged.  Otherwise, it must have been invoked from the shell's path,
 * so we search $PATH for the named executable and use that.  If the
 * executable was not found on $PATH (or there was no $PATH environment
 * variable), the original argv[0] string is used.
 *
 * Next, the executable location is examined to see if it is a symbolic
 * link.  If so, the link is chased (correctly interpreting a relative
 * pathname if one is found) and the directory of the link target is used.
 *
 * Finally, argv0_path is set to the directory containing the executable
 * (i.e. the last component is stripped).
 *
 * With argv0_path in hand, we perform a number of steps.  The same steps
 * are performed for prefix and for exec_prefix, but with a different
 * landmark.
 *
 * Step 1. Are we running python out of the build directory?  This is
 * checked by looking for a different kind of landmark relative to
 * argv0_path.  For prefix, the landmark's path is derived from the VPATH
 * preprocessor variable (taking into account that its value is almost, but
 * not quite, what we need).  For exec_prefix, the landmark is
 * pybuilddir.txt.  If the landmark is found, we're done.
 *
 * For the remaining steps, the prefix landmark will always be
 * lib/python$VERSION/os.py and the exec_prefix will always be
 * lib/python$VERSION/lib-dynload, where $VERSION is Python's version
 * number as supplied by the Makefile.  Note that this means that no more
 * build directory checking is performed; if the first step did not find
 * the landmarks, the assumption is that python is running from an
 * installed setup.
 *
 * Step 2. See if the $PYTHONHOME environment variable points to the
 * installed location of the Python libraries.  If $PYTHONHOME is set, then
 * it points to prefix and exec_prefix.  $PYTHONHOME can be a single
 * directory, which is used for both, or the prefix and exec_prefix
 * directories separated by a colon.
 *
 * Step 3. Try to find prefix and exec_prefix relative to argv0_path,
 * backtracking up the path until it is exhausted.  This is the most common
 * step to succeed.  Note that if prefix and exec_prefix are different,
 * exec_prefix is more likely to be found; however if exec_prefix is a
 * subdirectory of prefix, both will be found.
 *
 * Step 4. Search the directories pointed to by the preprocessor variables
 * PREFIX and EXEC_PREFIX.  These are supplied by the Makefile but can be
 * passed in as options to the configure script.
 *
 * That's it!
 *
 * Well, almost.  Once we have determined prefix and exec_prefix, the
 * preprocessor variable PYTHONPATH is used to construct a path.  Each
 * relative path on PYTHONPATH is prefixed with prefix.  Then the directory
 * containing the shared library modules is appended.  The environment
 * variable $PYTHONPATH is inserted in front of it all.  Finally, the
 * prefix and exec_prefix globals are tweaked so they reflect the values
 * expected by other code, by stripping the "lib/python$VERSION/..." stuff
 * off.  If either points to the build directory, the globals are reset to
 * the corresponding preprocessor variables (so sys.prefix will reflect the
 * installation location, even though sys.path points into the build
 * directory).  This seems to make more sense given that currently the only
 * known use of sys.prefix and sys.exec_prefix is for the ILU installation
 * process to find the installed Python tree.
 *
 * An embedding application can use Py_SetPath() to override all of
 * these authomatic path computations.
 *
 * NOTE: Windows MSVC builds use PC/getpathp.c instead!
 */

#ifdef __cplusplus
extern "C" {
#endif


#if !defined(PREFIX) || !defined(EXEC_PREFIX) || !defined(VERSION) || !defined(VPATH)
#error "PREFIX, EXEC_PREFIX, VERSION, and VPATH must be constant defined"
#endif

#ifndef LANDMARK
#define LANDMARK L"os.py"
#endif

typedef struct {
    wchar_t prefix[MAXPATHLEN+1];
    wchar_t exec_prefix[MAXPATHLEN+1];
    wchar_t progpath[MAXPATHLEN+1];
    wchar_t *module_search_path;
} PyPathConfig;

typedef struct {
    wchar_t *path_env;                 /* PATH environment variable */
    wchar_t *home;                     /* PYTHONHOME environment variable */
    wchar_t *module_search_path_env;   /* PYTHONPATH environment variable */
    wchar_t *module_search_path_buffer;

    wchar_t *prog;                     /* Program name */
    wchar_t *pythonpath;               /* PYTHONPATH define */
    wchar_t *prefix;                   /* PREFIX define */
    wchar_t *exec_prefix;              /* EXEC_PREFIX define */

    wchar_t *lib_python;               /* "lib/pythonX.Y" */
    wchar_t argv0_path[MAXPATHLEN+1];
    wchar_t zip_path[MAXPATHLEN+1];    /* ".../lib/pythonXY.zip" */

    int prefix_found;         /* found platform independent libraries? */
    int exec_prefix_found;    /* found the platform dependent libraries? */
} PyCalculatePath;

static const wchar_t delimiter[2] = {DELIM, '\0'};
static const wchar_t separator[2] = {SEP, '\0'};
static PyPathConfig path_config = {.module_search_path = NULL};


/* Get file status. Encode the path to the locale encoding. */
static int
_Py_wstat(const wchar_t* path, struct stat *buf)
{
    int err;
    char *fname;
    fname = Py_EncodeLocale(path, NULL);
    if (fname == NULL) {
        errno = EINVAL;
        return -1;
    }
    err = stat(fname, buf);
    PyMem_Free(fname);
    return err;
}


static void
reduce(wchar_t *dir)
{
    size_t i = wcslen(dir);
    while (i > 0 && dir[i] != SEP)
        --i;
    dir[i] = '\0';
}


static int
isfile(wchar_t *filename)          /* Is file, not directory */
{
    struct stat buf;
    if (_Py_wstat(filename, &buf) != 0) {
        return 0;
    }
    if (!S_ISREG(buf.st_mode)) {
        return 0;
    }
    return 1;
}


static int
ismodule(wchar_t *filename)        /* Is module -- check for .pyc too */
{
    if (isfile(filename)) {
        return 1;
    }

    /* Check for the compiled version of prefix. */
    if (wcslen(filename) < MAXPATHLEN) {
        wcscat(filename, L"c");
        if (isfile(filename)) {
            return 1;
        }
    }
    return 0;
}


/* Is executable file */
static int
isxfile(wchar_t *filename)
{
    struct stat buf;
    if (_Py_wstat(filename, &buf) != 0) {
        return 0;
    }
    if (!S_ISREG(buf.st_mode)) {
        return 0;
    }
    if ((buf.st_mode & 0111) == 0) {
        return 0;
    }
    return 1;
}


/* Is directory */
static int
isdir(wchar_t *filename)
{
    struct stat buf;
    if (_Py_wstat(filename, &buf) != 0) {
        return 0;
    }
    if (!S_ISDIR(buf.st_mode)) {
        return 0;
    }
    return 1;
}


/* 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
joinpath(wchar_t *buffer, wchar_t *stuff)
{
    size_t n, k;
    if (stuff[0] == SEP) {
        n = 0;
    }
    else {
        n = wcslen(buffer);
        if (n > 0 && buffer[n-1] != SEP && n < MAXPATHLEN) {
            buffer[n++] = SEP;
        }
    }
    if (n > MAXPATHLEN) {
        Py_FatalError("buffer overflow in getpath.c's joinpath()");
    }
    k = wcslen(stuff);
    if (n + k > MAXPATHLEN) {
        k = MAXPATHLEN - n;
    }
    wcsncpy(buffer+n, stuff, k);
    buffer[n+k] = '\0';
}


/* copy_absolute requires that path be allocated at least
   MAXPATHLEN + 1 bytes and that p be no more than MAXPATHLEN bytes. */
static void
copy_absolute(wchar_t *path, wchar_t *p, size_t pathlen)
{
    if (p[0] == SEP) {
        wcscpy(path, p);
    }
    else {
        if (!_Py_wgetcwd(path, pathlen)) {
            /* unable to get the current directory */
            wcscpy(path, p);
            return;
        }
        if (p[0] == '.' && p[1] == SEP) {
            p += 2;
        }
        joinpath(path, p);
    }
}


/* absolutize() requires that path be allocated at least MAXPATHLEN+1 bytes. */
static void
absolutize(wchar_t *path)
{
    wchar_t buffer[MAXPATHLEN+1];

    if (path[0] == SEP) {
        return;
    }
    copy_absolute(buffer, path, MAXPATHLEN+1);
    wcscpy(path, buffer);
}


/* search for a prefix value in an environment file. If found, copy it
   to the provided buffer, which is expected to be no more than MAXPATHLEN
   bytes long.
*/
static int
find_env_config_value(FILE * env_file, const wchar_t * key, wchar_t * value)
{
    int result = 0; /* meaning not found */
    char buffer[MAXPATHLEN*2+1];  /* allow extra for key, '=', etc. */

    fseek(env_file, 0, SEEK_SET);
    while (!feof(env_file)) {
        char * p = fgets(buffer, MAXPATHLEN*2, env_file);
        wchar_t tmpbuffer[MAXPATHLEN*2+1];
        PyObject * decoded;
        int n;

        if (p == NULL) {
            break;
        }
        n = strlen(p);
        if (p[n - 1] != '\n') {
            /* line has overflowed - bail */
            break;
        }
        if (p[0] == '#') {
            /* Comment - skip */
            continue;
        }
        decoded = PyUnicode_DecodeUTF8(buffer, n, "surrogateescape");
        if (decoded != NULL) {
            Py_ssize_t k;
            wchar_t * state;
            k = PyUnicode_AsWideChar(decoded,
                                     tmpbuffer, MAXPATHLEN * 2);
            Py_DECREF(decoded);
            if (k >= 0) {
                wchar_t * tok = wcstok(tmpbuffer, L" \t\r\n", &state);
                if ((tok != NULL) && !wcscmp(tok, key)) {
                    tok = wcstok(NULL, L" \t", &state);
                    if ((tok != NULL) && !wcscmp(tok, L"=")) {
                        tok = wcstok(NULL, L"\r\n", &state);
                        if (tok != NULL) {
                            wcsncpy(value, tok, MAXPATHLEN);
                            result = 1;
                            break;
                        }
                    }
                }
            }
        }
    }
    return result;
}


/* search_for_prefix requires that argv0_path be no more than MAXPATHLEN
   bytes long.
*/
static int
search_for_prefix(PyCalculatePath *calculate, PyPathConfig *config)
{
    size_t n;
    wchar_t *vpath;

    /* If PYTHONHOME is set, we believe it unconditionally */
    if (calculate->home) {
        wcsncpy(config->prefix, calculate->home, MAXPATHLEN);
        config->prefix[MAXPATHLEN] = L'\0';
        wchar_t *delim = wcschr(config->prefix, DELIM);
        if (delim) {
            *delim = L'\0';
        }
        joinpath(config->prefix, calculate->lib_python);
        joinpath(config->prefix, LANDMARK);
        return 1;
    }

    /* Check to see if argv[0] is in the build directory */
    wcsncpy(config->prefix, calculate->argv0_path, MAXPATHLEN);
    config->prefix[MAXPATHLEN] = L'\0';
    joinpath(config->prefix, L"Modules/Setup");
    if (isfile(config->prefix)) {
        /* Check VPATH to see if argv0_path is in the build directory. */
        vpath = Py_DecodeLocale(VPATH, NULL);
        if (vpath != NULL) {
            wcsncpy(config->prefix, calculate->argv0_path, MAXPATHLEN);
            config->prefix[MAXPATHLEN] = L'\0';
            joinpath(config->prefix, vpath);
            PyMem_RawFree(vpath);
            joinpath(config->prefix, L"Lib");
            joinpath(config->prefix, LANDMARK);
            if (ismodule(config->prefix)) {
                return -1;
            }
        }
    }

    /* Search from argv0_path, until root is found */
    copy_absolute(config->prefix, calculate->argv0_path, MAXPATHLEN+1);
    do {
        n = wcslen(config->prefix);
        joinpath(config->prefix, calculate->lib_python);
        joinpath(config->prefix, LANDMARK);
        if (ismodule(config->prefix)) {
            return 1;
        }
        config->prefix[n] = L'\0';
        reduce(config->prefix);
    } while (config->prefix[0]);

    /* Look at configure's PREFIX */
    wcsncpy(config->prefix, calculate->prefix, MAXPATHLEN);
    config->prefix[MAXPATHLEN] = L'\0';
    joinpath(config->prefix, calculate->lib_python);
    joinpath(config->prefix, LANDMARK);
    if (ismodule(config->prefix)) {
        return 1;
    }

    /* Fail */
    return 0;
}


static void
calculate_prefix(PyCalculatePath *calculate, PyPathConfig *config)
{
    calculate->prefix_found = search_for_prefix(calculate, config);
    if (!calculate->prefix_found) {
        if (!Py_FrozenFlag) {
            fprintf(stderr,
                "Could not find platform independent libraries <prefix>\n");
        }
        wcsncpy(config->prefix, calculate->prefix, MAXPATHLEN);
        joinpath(config->prefix, calculate->lib_python);
    }
    else {
        reduce(config->prefix);
    }
}


static void
calculate_reduce_prefix(PyCalculatePath *calculate, PyPathConfig *config)
{
    /* Reduce prefix and exec_prefix to their essence,
     * e.g. /usr/local/lib/python1.5 is reduced to /usr/local.
     * If we're loading relative to the build directory,
     * return the compiled-in defaults instead.
     */
    if (calculate->prefix_found > 0) {
        reduce(config->prefix);
        reduce(config->prefix);
        /* The prefix is the root directory, but reduce() chopped
         * off the "/". */
        if (!config->prefix[0]) {
            wcscpy(config->prefix, separator);
        }
    }
    else {
        wcsncpy(config->prefix, calculate->prefix, MAXPATHLEN);
    }
}


/* search_for_exec_prefix requires that argv0_path be no more than
   MAXPATHLEN bytes long.
*/
static int
search_for_exec_prefix(PyCalculatePath *calculate, PyPathConfig *config)
{
    size_t n;

    /* If PYTHONHOME is set, we believe it unconditionally */
    if (calculate->home) {
        wchar_t *delim = wcschr(calculate->home, DELIM);
        if (delim) {
            wcsncpy(config->exec_prefix, delim+1, MAXPATHLEN);
        }
        else {
            wcsncpy(config->exec_prefix, calculate->home, MAXPATHLEN);
        }
        config->exec_prefix[MAXPATHLEN] = L'\0';
        joinpath(config->exec_prefix, calculate->lib_python);
        joinpath(config->exec_prefix, L"lib-dynload");
        return 1;
    }

    /* Check to see if argv[0] is in the build directory. "pybuilddir.txt"
       is written by setup.py and contains the relative path to the location
       of shared library modules. */
    wcsncpy(config->exec_prefix, calculate->argv0_path, MAXPATHLEN);
    config->exec_prefix[MAXPATHLEN] = L'\0';
    joinpath(config->exec_prefix, L"pybuilddir.txt");
    if (isfile(config->exec_prefix)) {
        FILE *f = _Py_wfopen(config->exec_prefix, L"rb");
        if (f == NULL) {
            errno = 0;
        }
        else {
            char buf[MAXPATHLEN+1];
            PyObject *decoded;
            wchar_t rel_builddir_path[MAXPATHLEN+1];
            n = fread(buf, 1, MAXPATHLEN, f);
            buf[n] = '\0';
            fclose(f);
            decoded = PyUnicode_DecodeUTF8(buf, n, "surrogateescape");
            if (decoded != NULL) {
                Py_ssize_t k;
                k = PyUnicode_AsWideChar(decoded,
                                         rel_builddir_path, MAXPATHLEN);
                Py_DECREF(decoded);
                if (k >= 0) {
                    rel_builddir_path[k] = L'\0';
                    wcsncpy(config->exec_prefix, calculate->argv0_path, MAXPATHLEN);
                    config->exec_prefix[MAXPATHLEN] = L'\0';
                    joinpath(config->exec_prefix, rel_builddir_path);
                    return -1;
                }
            }
        }
    }

    /* Search from argv0_path, until root is found */
    copy_absolute(config->exec_prefix, calculate->argv0_path, MAXPATHLEN+1);
    do {
        n = wcslen(config->exec_prefix);
        joinpath(config->exec_prefix, calculate->lib_python);
        joinpath(config->exec_prefix, L"lib-dynload");
        if (isdir(config->exec_prefix)) {
            return 1;
        }
        config->exec_prefix[n] = L'\0';
        reduce(config->exec_prefix);
    } while (config->exec_prefix[0]);

    /* Look at configure's EXEC_PREFIX */
    wcsncpy(config->exec_prefix, calculate->exec_prefix, MAXPATHLEN);
    config->exec_prefix[MAXPATHLEN] = L'\0';
    joinpath(config->exec_prefix, calculate->lib_python);
    joinpath(config->exec_prefix, L"lib-dynload");
    if (isdir(config->exec_prefix)) {
        return 1;
    }

    /* Fail */
    return 0;
}


static void
calculate_exec_prefix(PyCalculatePath *calculate, PyPathConfig *config)
{
    calculate->exec_prefix_found = search_for_exec_prefix(calculate, config);
    if (!calculate->exec_prefix_found) {
        if (!Py_FrozenFlag) {
            fprintf(stderr,
                "Could not find platform dependent libraries <exec_prefix>\n");
        }
        wcsncpy(config->exec_prefix, calculate->exec_prefix, MAXPATHLEN);
        joinpath(config->exec_prefix, L"lib/lib-dynload");
    }
    /* If we found EXEC_PREFIX do *not* reduce it!  (Yet.) */
}


static void
calculate_reduce_exec_prefix(PyCalculatePath *calculate, PyPathConfig *config)
{
    if (calculate->exec_prefix_found > 0) {
        reduce(config->exec_prefix);
        reduce(config->exec_prefix);
        reduce(config->exec_prefix);
        if (!config->exec_prefix[0]) {
            wcscpy(config->exec_prefix, separator);
        }
    }
    else {
        wcsncpy(config->exec_prefix, calculate->exec_prefix, MAXPATHLEN);
    }
}


static void
calculate_progpath(PyCalculatePath *calculate, PyPathConfig *config)
{
    /* 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.
     */
    if (wcschr(calculate->prog, SEP)) {
        wcsncpy(config->progpath, calculate->prog, MAXPATHLEN);
    }

#ifdef __APPLE__
#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4
    uint32_t nsexeclength = MAXPATHLEN;
#else
    unsigned long nsexeclength = MAXPATHLEN;
#endif
    char execpath[MAXPATHLEN+1];

     /* On Mac OS X, if a script uses an interpreter of the form
      * "#!/opt/python2.3/bin/python", the kernel only passes "python"
      * as argv[0], which falls through to the $PATH search below.
      * If /opt/python2.3/bin isn't in your path, or is near the end,
      * this algorithm may incorrectly find /usr/bin/python. To work
      * around this, we can use _NSGetExecutablePath to get a better
      * hint of what the intended interpreter was, although this
      * will fail if a relative path was used. but in that case,
      * absolutize() should help us out below
      */
    else if(0 == _NSGetExecutablePath(execpath, &nsexeclength) && execpath[0] == SEP) {
        size_t r = mbstowcs(config->progpath, execpath, MAXPATHLEN+1);
        if (r == (size_t)-1 || r > MAXPATHLEN) {
            /* Could not convert execpath, or it's too long. */
            config->progpath[0] = '\0';
        }
    }
#endif /* __APPLE__ */
    else if (calculate->path_env) {
        wchar_t *path = calculate->path_env;
        while (1) {
            wchar_t *delim = wcschr(path, DELIM);

            if (delim) {
                size_t len = delim - path;
                if (len > MAXPATHLEN) {
                    len = MAXPATHLEN;
                }
                wcsncpy(config->progpath, path, len);
                *(config->progpath + len) = '\0';
            }
            else {
                wcsncpy(config->progpath, path, MAXPATHLEN);
            }

            joinpath(config->progpath, calculate->prog);
            if (isxfile(config->progpath)) {
                break;
            }

            if (!delim) {
                config->progpath[0] = L'\0';
                break;
            }
            path = delim + 1;
        }
    }
    else {
        config->progpath[0] = '\0';
    }
    if (config->progpath[0] != SEP && config->progpath[0] != '\0') {
        absolutize(config->progpath);
    }
}


static void
calculate_argv0_path(PyCalculatePath *calculate, PyPathConfig *config)
{
    wcsncpy(calculate->argv0_path, config->progpath, MAXPATHLEN);
    calculate->argv0_path[MAXPATHLEN] = '\0';

#ifdef WITH_NEXT_FRAMEWORK
    NSModule pythonModule;

    /* On Mac OS X we have a special case if we're running from a framework.
    ** This is because the python home should be set relative to the library,
    ** which is in the framework, not relative to the executable, which may
    ** be outside of the framework. Except when we're in the build directory...
    */
    pythonModule = NSModuleForSymbol(NSLookupAndBindSymbol("_Py_Initialize"));
    /* Use dylib functions to find out where the framework was loaded from */
    const char* modPath = NSLibraryNameForModule(pythonModule);
    if (modPath != NULL) {
        /* We're in a framework. */
        /* See if we might be in the build directory. The framework in the
        ** build directory is incomplete, it only has the .dylib and a few
        ** needed symlinks, it doesn't have the Lib directories and such.
        ** If we're running with the framework from the build directory we must
        ** be running the interpreter in the build directory, so we use the
        ** build-directory-specific logic to find Lib and such.
        */
        wchar_t* wbuf = Py_DecodeLocale(modPath, NULL);
        if (wbuf == NULL) {
            Py_FatalError("Cannot decode framework location");
        }

        wcsncpy(calculate->argv0_path, wbuf, MAXPATHLEN);
        reduce(calculate->argv0_path);
        joinpath(calculate->argv0_path, calculate->lib_python);
        joinpath(calculate->argv0_path, LANDMARK);
        if (!ismodule(calculate->argv0_path)) {
            /* We are in the build directory so use the name of the
               executable - we know that the absolute path is passed */
            wcsncpy(calculate->argv0_path, config->progpath, MAXPATHLEN);
        }
        else {
            /* Use the location of the library as the progpath */
            wcsncpy(calculate->argv0_path, wbuf, MAXPATHLEN);
        }
        PyMem_RawFree(wbuf);
    }
#endif

#if HAVE_READLINK
    wchar_t tmpbuffer[MAXPATHLEN+1];
    int linklen = _Py_wreadlink(config->progpath, tmpbuffer, MAXPATHLEN);
    while (linklen != -1) {
        if (tmpbuffer[0] == SEP) {
            /* tmpbuffer should never be longer than MAXPATHLEN,
               but extra check does not hurt */
            wcsncpy(calculate->argv0_path, tmpbuffer, MAXPATHLEN);
        }
        else {
            /* Interpret relative to progpath */
            reduce(calculate->argv0_path);
            joinpath(calculate->argv0_path, tmpbuffer);
        }
        linklen = _Py_wreadlink(calculate->argv0_path, tmpbuffer, MAXPATHLEN);
    }
#endif /* HAVE_READLINK */

    reduce(calculate->argv0_path);
    /* At this point, argv0_path is guaranteed to be less than
       MAXPATHLEN bytes long. */
}


/* Search for an "pyvenv.cfg" environment configuration file, first in the
   executable's directory and then in the parent directory.
   If found, open it for use when searching for prefixes.
*/
static void
calculate_read_pyenv(PyCalculatePath *calculate)
{
    wchar_t tmpbuffer[MAXPATHLEN+1];
    wchar_t *env_cfg = L"pyvenv.cfg";
    FILE *env_file;

    wcscpy(tmpbuffer, calculate->argv0_path);

    joinpath(tmpbuffer, env_cfg);
    env_file = _Py_wfopen(tmpbuffer, L"r");
    if (env_file == NULL) {
        errno = 0;

        reduce(tmpbuffer);
        reduce(tmpbuffer);
        joinpath(tmpbuffer, env_cfg);

        env_file = _Py_wfopen(tmpbuffer, L"r");
        if (env_file == NULL) {
            errno = 0;
        }
    }

    if (env_file == NULL) {
        return;
    }

    /* Look for a 'home' variable and set argv0_path to it, if found */
    if (find_env_config_value(env_file, L"home", tmpbuffer)) {
        wcscpy(calculate->argv0_path, tmpbuffer);
    }
    fclose(env_file);
}


static void
calculate_zip_path(PyCalculatePath *calculate, PyPathConfig *config)
{
    wcsncpy(calculate->zip_path, config->prefix, MAXPATHLEN);
    calculate->zip_path[MAXPATHLEN] = L'\0';

    if (calculate->prefix_found > 0) {
        /* Use the reduced prefix returned by Py_GetPrefix() */
        reduce(calculate->zip_path);
        reduce(calculate->zip_path);
    }
    else {
        wcsncpy(calculate->zip_path, calculate->prefix, MAXPATHLEN);
    }
    joinpath(calculate->zip_path, L"lib/python00.zip");

    /* Replace "00" with version */
    size_t bufsz = wcslen(calculate->zip_path);
    calculate->zip_path[bufsz - 6] = VERSION[0];
    calculate->zip_path[bufsz - 5] = VERSION[2];
}


static wchar_t *
calculate_module_search_path(PyCalculatePath *calculate, PyPathConfig *config)
{
    /* Calculate size of return buffer */
    size_t bufsz = 0;
    if (calculate->module_search_path_env != NULL) {
        bufsz += wcslen(calculate->module_search_path_env) + 1;
    }

    wchar_t *defpath = calculate->pythonpath;
    size_t prefixsz = wcslen(config->prefix) + 1;
    while (1) {
        wchar_t *delim = wcschr(defpath, DELIM);

        if (defpath[0] != SEP) {
            /* Paths are relative to prefix */
            bufsz += prefixsz;
        }

        if (delim) {
            bufsz += delim - defpath + 1;
        }
        else {
            bufsz += wcslen(defpath) + 1;
            break;
        }
        defpath = delim + 1;
    }

    bufsz += wcslen(calculate->zip_path) + 1;
    bufsz += wcslen(config->exec_prefix) + 1;

    /* Allocate the buffer */
    wchar_t *buf = PyMem_RawMalloc(bufsz * sizeof(wchar_t));
    if (buf == NULL) {
        Py_FatalError(
            "Not enough memory for dynamic PYTHONPATH");
    }
    buf[0] = '\0';

    /* Run-time value of $PYTHONPATH goes first */
    if (calculate->module_search_path_env) {
        wcscpy(buf, calculate->module_search_path_env);
        wcscat(buf, delimiter);
    }

    /* Next is the default zip path */
    wcscat(buf, calculate->zip_path);
    wcscat(buf, delimiter);

    /* Next goes merge of compile-time $PYTHONPATH with
     * dynamically located prefix.
     */
    defpath = calculate->pythonpath;
    while (1) {
        wchar_t *delim = wcschr(defpath, DELIM);

        if (defpath[0] != SEP) {
            wcscat(buf, config->prefix);
            if (prefixsz >= 2 && config->prefix[prefixsz - 2] != SEP &&
                defpath[0] != (delim ? DELIM : L'\0'))
            {
                /* not empty */
                wcscat(buf, separator);
            }
        }

        if (delim) {
            size_t len = delim - defpath + 1;
            size_t end = wcslen(buf) + len;
            wcsncat(buf, defpath, len);
            *(buf + end) = '\0';
        }
        else {
            wcscat(buf, defpath);
            break;
        }
        defpath = delim + 1;
    }
    wcscat(buf, delimiter);

    /* Finally, on goes the directory for dynamic-load modules */
    wcscat(buf, config->exec_prefix);

    return buf;
}


#define DECODE_FAILED(NAME, LEN) \
    ((LEN) == (size_t)-2) \
     ? _Py_INIT_ERR("failed to decode " #NAME) \
     : _Py_INIT_NO_MEMORY()


static _PyInitError
calculate_init(PyCalculatePath *calculate,
               const _PyMainInterpreterConfig *main_config)
{
    _PyInitError err;

    err = _Py_GetPythonHomeWithConfig(main_config, &calculate->home);
    if (_Py_INIT_FAILED(err)) {
        return err;
    }

    size_t len;
    char *path = getenv("PATH");
    if (path) {
        calculate->path_env = Py_DecodeLocale(path, &len);
        if (!calculate->path_env) {
            return DECODE_FAILED("PATH environment variable", len);
        }
    }

    calculate->prog = Py_GetProgramName();

    calculate->pythonpath = Py_DecodeLocale(PYTHONPATH, &len);
    if (!calculate->pythonpath) {
        return DECODE_FAILED("PYTHONPATH define", len);
    }
    calculate->prefix = Py_DecodeLocale(PREFIX, &len);
    if (!calculate->prefix) {
        return DECODE_FAILED("PREFIX define", len);
    }
    calculate->exec_prefix = Py_DecodeLocale(EXEC_PREFIX, &len);
    if (!calculate->prefix) {
        return DECODE_FAILED("EXEC_PREFIX define", len);
    }
    calculate->lib_python = Py_DecodeLocale("lib/python" VERSION, &len);
    if (!calculate->lib_python) {
        return DECODE_FAILED("EXEC_PREFIX define", len);
    }

    calculate->module_search_path_env = NULL;
    if (main_config) {
        if (main_config->module_search_path_env) {
            calculate->module_search_path_env = main_config->module_search_path_env;
        }

    }
    else {
        char *pythonpath = Py_GETENV("PYTHONPATH");
        if (pythonpath && pythonpath[0] != '\0') {
            calculate->module_search_path_buffer = Py_DecodeLocale(pythonpath, &len);
            if (!calculate->module_search_path_buffer) {
                return DECODE_FAILED("PYTHONPATH environment variable", len);
            }
            calculate->module_search_path_env = calculate->module_search_path_buffer;
        }
    }
    return _Py_INIT_OK();
}


static void
calculate_free(PyCalculatePath *calculate)
{
    PyMem_RawFree(calculate->pythonpath);
    PyMem_RawFree(calculate->prefix);
    PyMem_RawFree(calculate->exec_prefix);
    PyMem_RawFree(calculate->lib_python);
    PyMem_RawFree(calculate->path_env);
    PyMem_RawFree(calculate->module_search_path_buffer);
}


static void
calculate_path_impl(PyCalculatePath *calculate, PyPathConfig *config)
{
    calculate_progpath(calculate, config);
    calculate_argv0_path(calculate, config);
    calculate_read_pyenv(calculate);
    calculate_prefix(calculate, config);
    calculate_zip_path(calculate, config);
    calculate_exec_prefix(calculate, config);

    if ((!calculate->prefix_found || !calculate->exec_prefix_found) && !Py_FrozenFlag) {
        fprintf(stderr,
                "Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]\n");
    }

    config->module_search_path = calculate_module_search_path(calculate, config);
    calculate_reduce_prefix(calculate, config);
    calculate_reduce_exec_prefix(calculate, config);
}


static void
calculate_path(const _PyMainInterpreterConfig *main_config)
{
    PyCalculatePath calculate;
    memset(&calculate, 0, sizeof(calculate));

    _PyInitError err = calculate_init(&calculate, main_config);
    if (_Py_INIT_FAILED(err)) {
        calculate_free(&calculate);
        _Py_FatalInitError(err);
    }

    PyPathConfig new_path_config;
    memset(&new_path_config, 0, sizeof(new_path_config));

    calculate_path_impl(&calculate, &new_path_config);
    path_config = new_path_config;

    calculate_free(&calculate);
}


/* External interface */
void
Py_SetPath(const wchar_t *path)
{
    if (path_config.module_search_path != NULL) {
        PyMem_RawFree(path_config.module_search_path);
        path_config.module_search_path = NULL;
    }

    if (path == NULL) {
        return;
    }

    wchar_t *prog = Py_GetProgramName();
    wcsncpy(path_config.progpath, prog, MAXPATHLEN);
    path_config.exec_prefix[0] = path_config.prefix[0] = L'\0';
    path_config.module_search_path = PyMem_RawMalloc((wcslen(path) + 1) * sizeof(wchar_t));
    if (path_config.module_search_path != NULL) {
        wcscpy(path_config.module_search_path, path);
    }
}


wchar_t *
_Py_GetPathWithConfig(const _PyMainInterpreterConfig *main_config)
{
    if (!path_config.module_search_path) {
        calculate_path(main_config);
    }
    return path_config.module_search_path;
}


wchar_t *
Py_GetPath(void)
{
    if (!path_config.module_search_path) {
        calculate_path(NULL);
    }
    return path_config.module_search_path;
}


wchar_t *
Py_GetPrefix(void)
{
    if (!path_config.module_search_path) {
        calculate_path(NULL);
    }
    return path_config.prefix;
}


wchar_t *
Py_GetExecPrefix(void)
{
    if (!path_config.module_search_path) {
        calculate_path(NULL);
    }
    return path_config.exec_prefix;
}


wchar_t *
Py_GetProgramFullPath(void)
{
    if (!path_config.module_search_path) {
        calculate_path(NULL);
    }
    return path_config.progpath;
}

#ifdef __cplusplus
}
#endif