/*
 * Copyright (C) 2015 Canonical Ltd
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
#include <errno.h>
#include <fcntl.h>
#include <regex.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include "cleanup-funcs.h"
#include "panic.h"
#include "utils.h"

void die(const char *msg, ...) {
    va_list ap;
    va_start(ap, msg);
    sc_panicv(msg, ap);
    va_end(ap);
}

struct sc_bool_name {
    const char *text;
    bool value;
};

static const struct sc_bool_name sc_bool_names[] = {
    {"yes", true}, {"no", false}, {"1", true}, {"0", false}, {"", false},
};

/**
 * Convert string to a boolean value, with a default.
 *
 * The return value is 0 in case of success or -1 when the string cannot be
 * converted correctly. In such case errno is set to indicate the problem and
 * the value is not written back to the caller-supplied pointer.
 *
 * If the text cannot be recognized, the default value is used.
 **/
static int parse_bool(const char *text, bool *value, bool default_value) {
    if (value == NULL) {
        errno = EFAULT;
        return -1;
    }
    if (text == NULL) {
        *value = default_value;
        return 0;
    }
    for (size_t i = 0; i < SC_ARRAY_SIZE(sc_bool_names); ++i) {
        if (strcmp(text, sc_bool_names[i].text) == 0) {
            *value = sc_bool_names[i].value;
            return 0;
        }
    }
    errno = EINVAL;
    return -1;
}

/**
 * Get an environment variable and convert it to a boolean.
 *
 * Supported values are those of parse_bool(), namely "yes", "no" as well as "1"
 * and "0". All other values are treated as false and a diagnostic message is
 * printed to stderr. If the environment variable is unset, set value to the
 * default_value as if the environment variable was set to default_value.
 **/
bool getenv_bool(const char *name, bool default_value) {
    const char *str_value = getenv(name);
    bool value = default_value;
    if (parse_bool(str_value, &value, default_value) < 0) {
        if (errno == EINVAL) {
            fprintf(stderr, "WARNING: unrecognized value of environment variable %s (expected yes/no or 1/0)\n", name);
            return false;
        } else {
            die("cannot convert value of environment variable %s to a boolean", name);
        }
    }
    return value;
}

bool sc_is_debug_enabled(void) { return getenv_bool("SNAP_CONFINE_DEBUG", false) || getenv_bool("SNAPD_DEBUG", false); }

bool sc_is_reexec_enabled(void) { return getenv_bool("SNAP_REEXEC", true); }

void debug(const char *msg, ...) {
    if (sc_is_debug_enabled()) {
        va_list va;
        va_start(va, msg);
        fprintf(stderr, "DEBUG: ");
        vfprintf(stderr, msg, va);
        fprintf(stderr, "\n");
        va_end(va);
    }
}

void write_string_to_file(const char *filepath, const char *buf) {
    debug("write_string_to_file %s %s", filepath, buf);
    FILE *f = fopen(filepath, "w");
    if (f == NULL) die("fopen %s failed", filepath);
    if (fwrite(buf, strlen(buf), 1, f) != 1) die("fwrite failed");
    if (fflush(f) != 0) die("fflush failed");
    if (fclose(f) != 0) die("fclose failed");
}

// TODO drop completely, not used by current code
sc_identity sc_set_effective_identity(sc_identity identity) {
    debug("set_effective_identity uid:%d (change: %s), gid:%d (change: %s)", identity.uid,
          identity.change_uid ? "yes" : "no", identity.gid, identity.change_gid ? "yes" : "no");
    /* We are being careful not to return a value instructing us to change GID
     * or UID by accident. */
    sc_identity old = {
        .change_gid = false,
        .change_uid = false,
    };

    if (identity.change_gid) {
        old.gid = getegid();
        old.change_gid = true;
        if (setegid(identity.gid) < 0) {
            die("cannot set effective group to %d", identity.gid);
        }
        if (getegid() != identity.gid) {
            die("effective group change from %d to %d has failed", old.gid, identity.gid);
        }
    }
    if (identity.change_uid) {
        old.uid = geteuid();
        old.change_uid = true;
        if (seteuid(identity.uid) < 0) {
            die("cannot set effective user to %d", identity.uid);
        }
        if (geteuid() != identity.uid) {
            die("effective user change from %d to %d has failed", old.uid, identity.uid);
        }
    }
    return old;
}

int sc_nonfatal_mkpath(const char *const path, mode_t mode, uid_t uid, uid_t gid) {
    // If asked to create an empty path, return immediately.
    if (strlen(path) == 0) {
        return 0;
    }
    // We're going to use strtok_r, which needs to modify the path, so we'll
    // make a copy of it.
    char *path_copy SC_CLEANUP(sc_cleanup_string) = NULL;
    path_copy = strdup(path);
    if (path_copy == NULL) {
        return -1;
    }
    // Open flags to use while we walk the user data path:
    // - Don't follow symlinks
    // - Don't allow child access to file descriptor
    // - Only open a directory (fail otherwise)
    const int open_flags = O_NOFOLLOW | O_CLOEXEC | O_DIRECTORY;

    // We're going to create each path segment via openat/mkdirat calls instead
    // of mkdir calls, to avoid following symlinks and placing the user data
    // directory somewhere we never intended for it to go. The first step is to
    // get an initial file descriptor.
    int fd SC_CLEANUP(sc_cleanup_close) = AT_FDCWD;
    if (path_copy[0] == '/') {
        fd = open("/", open_flags);
        if (fd < 0) {
            return -1;
        }
    }
    // strtok_r needs a pointer to keep track of where it is in the string.
    char *path_walker = NULL;

    // Initialize tokenizer and obtain first path segment.
    char *path_segment = strtok_r(path_copy, "/", &path_walker);
    while (path_segment) {
        // Try to create the directory.  It's okay if it already existed, but
        // return with error on any other error. Reset errno before attempting
        // this as it may stay stale (errno is not reset if mkdirat(2) returns
        // successfully).
        errno = 0;
        if (sc_ensure_mkdirat(fd, path_segment, mode, uid, gid) != 0) {
            return -1;
        }
        // Open the parent directory we just made (and close the previous one
        // (but not the special value AT_FDCWD) so we can continue down the
        // path.
        int previous_fd = fd;
        fd = openat(fd, path_segment, open_flags);
        if (previous_fd != AT_FDCWD && close(previous_fd) != 0) {
            return -1;
        }
        if (fd < 0) {
            return -1;
        }
        // Obtain the next path segment.
        path_segment = strtok_r(NULL, "/", &path_walker);
    }
    return 0;
}

bool sc_is_expected_path(const char *path) {
    const char *expected_path_re =
        "^((/var/lib/snapd)?/snap/(snapd|core)/x?[0-9]+/usr/lib|/usr/lib(exec)?)/snapd/snap-confine$";
    regex_t re;
    if (regcomp(&re, expected_path_re, REG_EXTENDED | REG_NOSUB) != 0)
        die("can not compile regex %s", expected_path_re);
    int status = regexec(&re, path, 0, NULL, 0);
    regfree(&re);
    return status == 0;
}

bool sc_wait_for_file(const char *path, size_t timeout_sec) {
    for (size_t i = 0; i < timeout_sec; ++i) {
        if (access(path, F_OK) == 0) {
            return true;
        }
        sleep(1);
    }
    return false;
}

const char *run_systemd_container = "/run/systemd/container";

static bool _sc_is_in_container(const char *p) {
    // see what systemd-detect-virt --container does in, see:
    // https://github.com/systemd/systemd/blob/5dcd6b1d55a1cfe247621d70f0e25d020de6e0ed/src/basic/virt.c#L749-L755
    // https://systemd.io/CONTAINER_INTERFACE/
    FILE *in SC_CLEANUP(sc_cleanup_file) = fopen(p, "r");
    if (in == NULL) {
        return false;
    }

    char container[128] = {0};

    if (fgets(container, sizeof(container), in) == NULL) {
        /* nothing read or other error? */
        return false;
    }

    size_t r = strnlen(container, sizeof container);
    // TODO add sc_str_chomp()?
    if (r > 0 && container[r - 1] == '\n') {
        /* replace trailing newline */
        container[r - 1] = 0;
        r--;
    }

    if (r == 0) {
        /* empty or just a newline */
        return false;
    }

    debug("detected container environment: %s", container);
    return true;
}

bool sc_is_in_container(void) { return _sc_is_in_container(run_systemd_container); }

static int compat_fchmodat_symlink_nofollow(int fd, const char *name, mode_t mode) {
    /* not all kernels support fchmodat(.., AT_SYMLINK_NOFOLLOW) (at least 4.14
     * on AMZN2 does not), attempt to handle that gracefully */
    int ret = fchmodat(fd, name, mode, AT_SYMLINK_NOFOLLOW);
    if (ret != 0 && (errno == ENOTSUP || errno == ENOSYS)) {
        /* reset errno */
        errno = 0;
        /* AT_SYMLINK_NOFOLLOW is not supported by the kernel */
        ret = fchmodat(fd, name, mode, 0);
    }
    return ret;
}

int sc_ensure_mkdirat(int fd, const char *name, mode_t mode, uid_t uid, uid_t gid) {
    /* Using 0000 permissions to avoid a race condition; we'll set the right
     * permissions after chown. */
    if (mkdirat(fd, name, 0000) < 0) {
        if (errno != EEXIST) {
            return -1;
        }
    } else {
        // new directory: set the right permissions and mode
        if (fchownat(fd, name, uid, gid, AT_SYMLINK_NOFOLLOW) < 0 ||
            compat_fchmodat_symlink_nofollow(fd, name, mode) < 0) {
            return -1;
        }
        /* as observed with certain combinations of new libc & old kernels,
         * glibc may have employed a fallback path for fchmodat() and left errno
         * in its original value of ENOSYS|ENOTSUP, let's reset it here such
         * that the caller can reliably probe for EEXIST to cath the mkdir()
         * branch if this function is successful, see glibc implementation for
         * details:
         * https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/fchmodat.c;h=dd1fa5db86bde99fe3eb4804b06c5adf11914b94;hb=HEAD#l31
         */
        errno = 0;
    }
    return 0;
}

int sc_ensure_mkdir(const char *path, mode_t mode, uid_t uid, uid_t gid) {
    return sc_ensure_mkdirat(AT_FDCWD, path, mode, uid, gid);
}