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/*
 * This tool is meant to wrap the other Qt tools by searching for different
 * instances of Qt on the system. It's mostly destined to be used on Unix
 * systems other than Mac OS X. For that reason, it uses POSIX APIs and does
 * not try to be compatible with the DOS or Win32 APIs. In particular, it uses
 * opendir(3) and readdir(3) as well as paths exclusively separated by slashes.
 */

#define _CRT_SECURE_NO_WARNINGS
#define _POSIX_C_SOURCE 200809L

#include <set>
#include <string>
#include <vector>

#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#if defined(_WIN32) || defined(__WIN32__)
#  include <process.h>
#  define execv _execv
#  define PATH_SEP "\\"
#  define EXE_SUFFIX ".exe"
#else
#  include <sys/types.h>
#  include <dirent.h>
#  include <libgen.h>
#  include <pwd.h>
#  include <unistd.h>
#  define PATH_SEP "/"
#  define EXE_SUFFIX ""
#endif

using namespace std;

static const char myName[] = "qtchooser" EXE_SUFFIX;

static const char *argv0;
enum Mode {
    Unknown,
    PrintHelp,
    RunTool,
    ListVersions,
    PrintEnvironment
};

struct Sdk
{
    string name;
    string configFile;
    string toolsPath;
    string librariesPath;

    bool isValid() const { return !toolsPath.empty(); }
};

struct ToolWrapper
{
    int printHelp();
    int listVersions();
    int printEnvironment(const string &targetSdk);
    int runTool(const string &targetSdk, const string &targetTool, char **argv);

private:
    vector<string> searchPaths() const;

    typedef bool (ToolWrapper:: *VisitFunction)(const string &targetSdk, Sdk &item);
    Sdk iterateSdks(const string &targetSdk, VisitFunction visit);
    Sdk selectSdk(const string &targetSdk);

    bool printSdk(const string &, Sdk &sdk);
    bool matchSdk(const string &targetSdk, Sdk &sdk);
};

int ToolWrapper::printHelp()
{
    puts("Usage:\n"
         "  qtchooser { -l | -list-versions | -print-env }\n"
         "  qtchooser -run-tool=<tool name> [-qt=<Qt version>] [program arguments]\n"
         "  <executable name> [-qt=<Qt version>] [program arguments]\n"
         "\n"
         "Environment variables accepted:\n"
         " QTCHOOSER_RUNTOOL  name of the tool to be run (same as the -run-tool argument)\n"
         " QT_SELECT          version of Qt to be run (same as the -qt argument)\n");
    return 0;
}

int ToolWrapper::listVersions()
{
    iterateSdks(string(), &ToolWrapper::printSdk);
    return 0;
}

int ToolWrapper::printEnvironment(const string &targetSdk)
{
    Sdk sdk = selectSdk(targetSdk);
    if (!sdk.isValid())
        return 1;

    // ### The paths and the name are not escaped, so hopefully no one will be
    // installing Qt on paths containing backslashes or quotes on Unix. Paths
    // with spaces are taken into account by surrounding the arguments with
    // quotes.

    printf("QT_SELECT=\"%s\"\n", sdk.name.c_str());
    printf("QTTOOLDIR=\"%s\"\n", sdk.toolsPath.c_str());
    printf("QTLIBDIR=\"%s\"\n", sdk.librariesPath.c_str());
    return 0;
}

static string userHome()
{
    const char *value = getenv("HOME");
    if (value)
        return value;

#if defined(_WIN32) || defined(__WIN32__)
    // ### FIXME: some Windows-specific code to get the user's home directory
    // using GetUserProfileDirectory (userenv.h / dll)
    return "C:";
#else
    struct passwd *pwd = getpwuid(getuid());
    if (pwd && pwd->pw_dir)
        return pwd->pw_dir;
    return string();
#endif
}

static inline bool beginsWith(const char *haystack, const char *needle)
{
    return strncmp(haystack, needle, strlen(needle)) == 0;
}

static inline bool endsWith(const char *haystack, const char *needle)
{
    size_t haystackLen = strlen(haystack);
    size_t needleLen = strlen(needle);
    if (needleLen > haystackLen)
        return false;
    return strcmp(haystack + haystackLen - needleLen, needle) == 0;
}

bool linksBackToSelf(const char *link, const char *target)
{
#if !defined(_WIN32) && !defined(__WIN32__)
    char buf[512];
    int count = readlink(link, buf, sizeof(buf));
    if (count >= 0) {
        buf[count] = '\0';
        if (endsWith(buf, target) == 0) {
            fprintf(stderr, "%s: could not exec '%s' since it links to %s itself. Check your installation.\n",
                    target, link, target);
            return true;
        }
    }
#endif
    return false;
}

int ToolWrapper::runTool(const string &targetSdk, const string &targetTool, char **argv)
{
    Sdk sdk = selectSdk(targetSdk);
    if (!sdk.isValid())
        return 1;

    string tool = sdk.toolsPath + PATH_SEP + targetTool;
    if (tool[0] == '~')
        tool = userHome() + tool.substr(1);

    // check if the tool is a symlink to ourselves
    if (linksBackToSelf(tool.c_str(), argv0))
        return 1;

    argv[0] = &tool[0];
#ifdef QTCHOOSER_TEST_MODE
    while (*argv)
        printf("%s\n", *argv++);
    return 0;
#else
    execv(argv[0], argv);
#ifdef __APPLE__
    // failed; see if we have a .app package by the same name
    {
        char appPath[PATH_MAX];
        snprintf(appPath, PATH_MAX, "%s.app/Contents/MacOS/%s",
                 argv[0], basename(argv[0]));
        execv(appPath, argv);
    }
#endif
    fprintf(stderr, "%s: could not exec '%s': %s\n",
            argv0, argv[0], strerror(errno));
    return 1;
#endif
}

static vector<string> stringSplit(const char *source)
{
#if defined(_WIN32) || defined(__WIN32__)
    char listSeparator = ';';
#else
    char listSeparator = ':';
#endif

    vector<string> result;
    if (!*source)
        return result;

    while (true) {
        const char *p = strchr(source, listSeparator);
        if (!p) {
            result.push_back(source);
            return result;
        }

        result.push_back(string(source, p - source));
        source = p + 1;
    }
    return result;
}

static string qgetenv(const char *env, const string &defaultValue = string())
{
    const char *value = getenv(env);
    return value ? string(value) : defaultValue;
}

vector<string> ToolWrapper::searchPaths() const
{
    vector<string> paths;

    // search the XDG config location directories
    paths = stringSplit(qgetenv("XDG_CONFIG_DIRS", "/etc/xdg").c_str());

    string localDir = qgetenv("XDG_CONFIG_HOME", userHome() + PATH_SEP ".config");
    paths.push_back(localDir);

    for (vector<string>::iterator it = paths.begin(); it != paths.end(); ++it)
        *it += "/qtchooser/";

    return paths;
}

Sdk ToolWrapper::iterateSdks(const string &targetSdk, VisitFunction visit)
{
    vector<string> paths = searchPaths();
    set<string> seenNames;
    Sdk sdk;
    for (vector<string>::iterator it = paths.begin(); it != paths.end(); ++it) {
        const string &path = *it;

        // no ISO C++ or ISO C API for listing directories, so use POSIX
        DIR *dir = opendir(path.c_str());
        if (!dir)
            continue;  // no such dir or not a dir, doesn't matter

        while (struct dirent *d = readdir(dir)) {
#ifdef _DIRENT_HAVE_D_TYPE
            if (d->d_type == DT_DIR)
                continue;
#endif

            static const char wantedSuffix[] = ".conf";
            size_t fnamelen = strlen(d->d_name);
            if (fnamelen < sizeof(wantedSuffix))
                continue;
            if (memcmp(d->d_name + fnamelen + 1 - sizeof(wantedSuffix), wantedSuffix, sizeof wantedSuffix - 1) != 0)
                continue;

            if (seenNames.find(d->d_name) != seenNames.end())
                continue;

            seenNames.insert(d->d_name);
            sdk.name = d->d_name;
            sdk.name.resize(fnamelen + 1 - sizeof wantedSuffix);
            sdk.configFile = path + PATH_SEP + d->d_name;
            if ((this->*visit)(targetSdk, sdk))
                return sdk;
        }

        closedir(dir);
    }
    return Sdk();
}

Sdk ToolWrapper::selectSdk(const string &targetSdk)
{
    Sdk matchedSdk = iterateSdks(targetSdk, &ToolWrapper::matchSdk);
    if (!matchedSdk.isValid()) {
        fprintf(stderr, "%s: could not find a Qt installation of '%s'\n", argv0, targetSdk.c_str());
    }
    return matchedSdk;
}

bool ToolWrapper::printSdk(const string &, Sdk &sdk)
{
    printf("%s\n", sdk.name.c_str());
    return false; // continue
}

bool ToolWrapper::matchSdk(const string &targetSdk, Sdk &sdk)
{
    if (targetSdk == sdk.name || (targetSdk.empty() && sdk.name == "default")) {
        FILE *f = fopen(sdk.configFile.c_str(), "r");
        if (!f) {
            fprintf(stderr, "%s: could not open config file '%s': %s\n",
                    argv0, sdk.configFile.c_str(), strerror(errno));
            exit(1);
        }

        // read the first two lines.
        // 1) the first line contains the path to the Qt tools like qmake
        // 2) the second line contains the path to the Qt libraries
        // further lines are reserved for future enhancement
#if _POSIX_VERSION >= 200809L
        size_t len = 0;
        char *line = 0;
        ssize_t read = getline(&line, &len, f);
        if (read < 0) {
            free(line);
            fclose(f);
            return false;
        }
        sdk.toolsPath = line;

        read = getline(&line, &len, f);
        if (read < 0) {
            free(line);
            fclose(f);
            return false;
        }
        sdk.librariesPath = line;

        free(line);
#elif defined(PATH_MAX)
        char buf[PATH_MAX];
        if (!fgets(buf, PATH_MAX - 1, f)) {
            fclose(f);
            return false;
        }
        sdk.toolsPath = buf;

        if (!fgets(buf, PATH_MAX - 1, f)) {
            fclose(f);
            return false;
        }
        sdk.librariesPath = buf;
#else
# error "POSIX < 2008 and no PATH_MAX, fix me"
#endif
        sdk.toolsPath.erase(sdk.toolsPath.size() - 1); // drop newline
        sdk.librariesPath.erase(sdk.librariesPath.size() - 1); // drop newline

        fclose(f);
        return true;
    }

    return false;
}

int main(int argc, char **argv)
{
    // search the environment for defaults
    Mode operatingMode = Unknown;
    argv0 = basename(argv[0]);
    const char *targetSdk = getenv("QT_SELECT");

    // the default tool is the one in argv[0]
    const char *targetTool = argv0;

    // if argv[0] points back to us, use the environment
    if (strcmp(targetTool, myName) == 0)
        targetTool = getenv("QTCHOOSER_RUNTOOL");
    else
        operatingMode = RunTool;

    // check the arguments to see if there's an override
    int optind = 1;
    for ( ; optind < argc; ++optind) {
        char *arg = argv[optind];
        if (*arg == '-') {
            ++arg;
            if (*arg == '-')
                ++arg;
            if (!*arg) {
                // -- argument, ends our processing
                // but skip this dash-dash argument
                ++optind;
                break;
            } else if (beginsWith(arg, "qt")) {
                // -qtX or -qt=X argument
                arg += 2;
                targetSdk = *arg == '=' ? arg + 1 : arg;
            } else if (!targetTool && beginsWith(arg, "run-tool=")) {
                // -run-tool= argument
                targetTool = arg + strlen("run-tool=");
                operatingMode = RunTool;
            } else {
                // not one of our arguments, must be for the target tool
                break;
            }
        } else {
            // not one of our arguments, must be for the target tool
            break;
        }
    }

    if (!targetSdk)
        targetSdk = "";

    ToolWrapper wrapper;
    if (operatingMode == RunTool || targetTool) {
        if (!targetTool) {
            fprintf(stderr, "%s: no tool selected. Stop.\n", argv0);
            return 1;
        }
        return wrapper.runTool(targetSdk,
                               targetTool,
                               argv + optind - 1);
    }

    // running qtchooser itself
    // check for our arguments
    operatingMode = PrintHelp;
    for ( ; optind < argc; ++optind) {
        char *arg = argv[optind];
        if (*arg == '-') {
            ++arg;
            if (*arg == '-')
                ++arg;
            // double-dash arguments are OK too
            if (*arg == '-')
                ++arg;
            if (strcmp(arg, "list-versions") == 0 || strcmp(arg, "l") == 0) {
                operatingMode = ListVersions;
            } else if (beginsWith(arg, "print-env")) {
                operatingMode = PrintEnvironment;
            } else if (strcmp(arg, "help") != 0) {
                fprintf(stderr, "%s: unknown option: %s\n", argv0, arg - 1);
                return 1;
            }
        } else {
            fprintf(stderr, "%s: unknown argument: %s\n", argv0, arg);
            return 1;
        }
    }

    // dispatch
    switch (operatingMode) {
    case RunTool:
    case Unknown:
        // can't happen!
        assert(false);
        return 127;

    case PrintHelp:
        return wrapper.printHelp();

    case PrintEnvironment:
        return wrapper.printEnvironment(targetSdk);

    case ListVersions:
        return wrapper.listVersions();
    }
}