/*
  ICFS: Interactively Controlled File System
  Copyright (C) 2024-2025  Fedir Kovalov

  This program can be distributed under the terms of the GNU GPLv2.
  See the file LICENSE.
*/

#include "proc_operations.h"
#include <linux/limits.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

/**
 * @brief Returns the PID of the main thread (i.e., the process ID) of the
 * process that the given thread ID (tid) belongs to.
 *
 * @param tid The thread ID (TID) of any thread in the process.
 * @return pid_t The process ID (main thread's PID), or -1 on error.
 */
pid_t get_main_thread_pid(pid_t tid) {
  // Validate input
  if (tid <= 0) {
    // errno = EINVAL;
    return 0;
  }

  char path[PATH_MAX];
  snprintf(path, sizeof(path), "/proc/%d/status", tid);

  FILE *fp = fopen(path, "r");
  if (!fp) {
    return 0; // Could not open the file
  }

  pid_t tgid = 0;
  char line[256];

  while (fgets(line, sizeof(line), fp)) {
    if (sscanf(line, "Tgid: %d", &tgid) == 1) {
      break;
    }
  }

  fclose(fp);
  if (tgid != tid) {
    fprintf(stderr, "The tid and and pid wasn't equal. tid:%d, pid:%d.\n", tid,
            tgid);
  }
  return tgid;
}

char *get_process_name_by_pid(const int pid) {
  char path[1024];
  sprintf(path, "/proc/%d/exe", pid);

  size_t size = 128;
  char *name = malloc(size);
  if (name == NULL) {
    fprintf(stderr, "Could not get process name by pid %d", pid);
    perror("");
    return NULL;
  }

  while (1) {
    ssize_t len = readlink(path, name, size);

    if (len == -1) {
      fprintf(stderr, "Could not get process name by pid %d", pid);
      perror("");
      free(name);
      return NULL;
    }
    if ((size_t)len >= size) {
      size *= 2;
      char *new_name = realloc(name, size);
      if (!new_name) {
        free(name);
        return NULL;
      }
      name = new_name;
    } else {
      // readlink does not set the null character
      name[len] = 0;
      break;
    }
  }

  return name;
}

/**
 * Finds the parent process ID of a given process.
 *
 * @param pid: The process ID of the process to find the parent of
 * @return: The parent process ID, or 0 if the parent process ID could not be
 * found
 */
pid_t get_parent_pid(pid_t pid) {
  pid_t ppid = 0;
  char path[256];
  snprintf(path, sizeof(path), "/proc/%u/status", pid);

  FILE *file = fopen(path, "r");
  if (file == NULL) {
    perror("Failed to open /proc/<pid>/status");
    return 0;
  }

  char line[256];
  while (fgets(line, sizeof(line), file)) {
    if (sscanf(line, "PPid:\t%d", &ppid) == 1) {
      fclose(file);
      return ppid;
    }
  }

  fclose(file);
  return 0; // Parent PID not found
}