#define _GNU_SOURCE

#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static void fail(const char *message)
{
    fprintf(stderr, "embedded PostgreSQL launcher: %s\n", message);
    exit(127);
}

static void join_path(char *destination, size_t capacity, const char *left, const char *right)
{
    int length = snprintf(destination, capacity, "%s/%s", left, right);
    if (length < 0 || (size_t) length >= capacity)
        fail("installation path is too long");
}

int main(int argc, char **argv)
{
    char executable[PATH_MAX];
    ssize_t executable_length = readlink("/proc/self/exe", executable, sizeof(executable) - 1);
    if (executable_length < 0) {
        perror("embedded PostgreSQL launcher: /proc/self/exe");
        return 127;
    }
    executable[executable_length] = '\0';

    char *tool = strrchr(executable, '/');
    if (tool == NULL || tool[1] == '\0')
        fail("cannot determine the requested PostgreSQL tool");
    tool++;

    char root[PATH_MAX];
    if ((size_t) executable_length >= sizeof(root))
        fail("installation path is too long");
    memcpy(root, executable, (size_t) executable_length + 1);

    char *bin_separator = strrchr(root, '/');
    if (bin_separator == NULL)
        fail("cannot determine the PostgreSQL installation directory");
    *bin_separator = '\0';
    char *root_separator = strrchr(root, '/');
    if (root_separator == NULL)
        fail("cannot determine the PostgreSQL installation directory");
    *root_separator = '\0';

    char loader[PATH_MAX];
    char library_path[PATH_MAX];
    char real_tool[PATH_MAX];
    join_path(loader, sizeof(loader), root, "lib/ld-musl-x86_64.so.1");
    join_path(library_path, sizeof(library_path), root, "lib");

    char real_tool_relative[PATH_MAX];
    int relative_length = snprintf(
        real_tool_relative,
        sizeof(real_tool_relative),
        "libexec/%s",
        tool
    );
    if (relative_length < 0 || (size_t) relative_length >= sizeof(real_tool_relative))
        fail("tool path is too long");
    join_path(real_tool, sizeof(real_tool), root, real_tool_relative);

    char **loader_argv = calloc((size_t) argc + 6, sizeof(char *));
    if (loader_argv == NULL) {
        perror("embedded PostgreSQL launcher: calloc");
        return 127;
    }

    loader_argv[0] = loader;
    loader_argv[1] = "--library-path";
    loader_argv[2] = library_path;
    loader_argv[3] = "--argv0";
    loader_argv[4] = executable;
    loader_argv[5] = real_tool;
    for (int index = 1; index < argc; index++)
        loader_argv[index + 5] = argv[index];

    execv(loader, loader_argv);
    fprintf(
        stderr,
        "embedded PostgreSQL launcher: cannot execute %s: %s\n",
        real_tool,
        strerror(errno)
    );
    return 127;
}