/*
 * gg - Grokkin' Grep: a minimal, fast, portable grep-like file finder
 *
 * Usage: gg SEARCH_TERM [FILE_OR_DIRECTORY]
 *
 * Created by Luxferre in 2026, released into the public domain
 */
#ifndef _POSIX_C_SOURCE
#define _POSIX_C_SOURCE 200809L
#endif
#ifndef _DEFAULT_SOURCE
#define _DEFAULT_SOURCE
#endif

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>

#ifndef PATH_MAX
#define PATH_MAX 4096
#endif

#define IO_BUFSZ (32u * 1024) /* per-thread read buffer */

/* ---------- shared scan state ---------- */
static const char *needle;
static size_t needle_len;
static int found_any = 0;
static pthread_mutex_t found_mx = PTHREAD_MUTEX_INITIALIZER;
/* ---------- directory work queue (parallel walk + scan) ---------- */
typedef struct DirJob {
  char *path;
  struct DirJob *next;
} DirJob;

static DirJob *dir_stack = NULL;
static pthread_mutex_t dir_mx = PTHREAD_MUTEX_INITIALIZER;

static void push_dir(const char *path) {
  DirJob *j = malloc(sizeof *j);
  if (j == NULL)
    return;
  j->path = strdup(path);
  if (j->path == NULL) {
    free(j);
    return;
  }
  pthread_mutex_lock(&dir_mx);
  j->next = dir_stack;
  dir_stack = j;
  pthread_mutex_unlock(&dir_mx);
}

static void die(const char *msg) {
  perror(msg);
  exit(2);
}

static char *pop_dir(void) {
  pthread_mutex_lock(&dir_mx);
  DirJob *j = dir_stack;
  if (j != NULL)
    dir_stack = j->next;
  pthread_mutex_unlock(&dir_mx);
  if (j == NULL)
    return NULL;
  char *p = j->path;
  free(j);
  return p;
}

/* ---------- scan one open fd (chunked read + memmem, binary-skipping) ---------- */
typedef struct {
  char *buf;
  char *carry;
} ScanBufs;

static int scan_fd(int fd, ScanBufs *sb) {
  char *buf = sb->buf;
  char *carry = sb->carry;
  size_t carryn = 0;
  int hit = 0;

  for (;;) {
    ssize_t r = read(fd, buf + carryn, IO_BUFSZ);
    if (r < 0) {
      if (errno == EINTR)
        continue;
      break;
    }
    if (r == 0)
      break; /* EOF */
    size_t wn = carryn + (size_t)r;

    /* Binary detection: a NUL byte marks a binary file, which we skip (like
     * ripgrep). Stop reading the moment we see one so we do not waste
     * bandwidth scanning the rest of a large binary file. If a needle occurs
     * before the first NUL it is still a valid text match. */
    void *nul = memchr(buf, '\0', wn);
    size_t text_end = (nul != NULL) ? (size_t)((const char *)nul - buf) : wn;
    if (text_end >= needle_len) {
      if (memmem(buf, text_end, needle, needle_len) != NULL) {
        hit = 1;
        break;
      }
    }
    if (nul != NULL)
      break; /* binary file: no further scanning */

    /* No NUL and no match yet: carry the tail across chunks. */
    if (wn >= needle_len)
      carryn = needle_len - 1;
    else
      carryn = wn;
    memcpy(carry, buf + wn - carryn, carryn);
    memcpy(buf, carry, carryn);
  }

  return hit;
}

static void report_match(const char *path) {
  pthread_mutex_lock(&found_mx);
  found_any = 1;
  puts(path);
  pthread_mutex_unlock(&found_mx);
}

static void scan_file(const char *path, ScanBufs *sb) {
  int fd = open(path, O_RDONLY | O_CLOEXEC);
  if (fd < 0)
    return; /* unreadable entries are silently skipped */
  if (scan_fd(fd, sb))
    report_match(path);
  close(fd);
}

/* ---------- worker: pop a directory, scan its files, enqueue subdirs ---------- */
static void *worker(void *arg) {
  (void)arg;
  ScanBufs sb;
  sb.buf = malloc(IO_BUFSZ + needle_len);
  sb.carry = malloc(needle_len);
  if (sb.buf == NULL || sb.carry == NULL) {
    free(sb.buf);
    free(sb.carry);
    return NULL;
  }
  char child[PATH_MAX];
  for (;;) {
    char *dir = pop_dir();
    if (dir == NULL)
      break;
    DIR *d = opendir(dir);
    if (d != NULL) {
      struct dirent *ent;
      while ((ent = readdir(d)) != NULL) {
        if (strcmp(ent->d_name, ".") == 0 ||
            strcmp(ent->d_name, "..") == 0)
          continue;
        int n = snprintf(child, sizeof child, "%s/%s", dir, ent->d_name);
        if (n < 0 || (size_t)n >= sizeof child)
          continue;
        if (ent->d_type == DT_REG) {
          scan_file(child, &sb);
        } else if (ent->d_type == DT_DIR) {
          push_dir(child);
        } else if (ent->d_type == DT_LNK) {
          continue; /* do not follow symlinks: avoids cycles */
        } else {
          struct stat st;
          if (lstat(child, &st) != 0)
            continue;
          if (S_ISDIR(st.st_mode))
            push_dir(child);
          else if (S_ISREG(st.st_mode))
            scan_file(child, &sb);
        }
      }
      closedir(d);
    }
    free(dir);
  }
  free(sb.buf);
  free(sb.carry);
  return NULL;
}

int main(int argc, char **argv) {
  if (argc < 2 || argc > 3) {
    fprintf(stderr, "usage: %s SEARCH_TERM [FILE_OR_DIRECTORY]\n", argv[0]);
    return 2;
  }

  needle = argv[1];
  needle_len = strlen(needle);
  if (needle_len == 0) {
    fprintf(stderr, "gg: empty search term\n");
    return 2;
  }

  char cwd[PATH_MAX];
  const char *root;
  if (argc == 3) {
    struct stat st;
    if (stat(argv[2], &st) != 0) {
      fprintf(stderr, "gg: %s: %s\n", argv[2], strerror(errno));
      return 2;
    }
    if (!S_ISDIR(st.st_mode) && !S_ISREG(st.st_mode)) {
      fprintf(stderr, "gg: %s: not a regular file or directory\n", argv[2]);
      return 2;
    }
    root = argv[2];
  } else {
    if (getcwd(cwd, sizeof cwd) == NULL)
      die("getcwd");
    root = cwd;
  }

  struct stat st;
  if (stat(root, &st) != 0) {
    fprintf(stderr, "gg: %s: %s\n", root, strerror(errno));
    return 2;
  }

  /* Seed the directory work queue, then let the workers walk and scan in
   * parallel: each worker pops a directory, scans its regular files inline,
   * and pushes any sub-directories it finds. This overlaps the (metadata)
   * walk with the (data) scan across all online CPUs. */
  if (S_ISREG(st.st_mode)) {
    scan_file(root, &(ScanBufs){ malloc(IO_BUFSZ + needle_len),
                                 malloc(needle_len) });
  } else {
    push_dir(root);
  }

  long nproc = sysconf(_SC_NPROCESSORS_ONLN);
  if (nproc < 1)
    nproc = 1;
  int nth = (int)nproc;
  if (nth > 256)
    nth = 256;

  pthread_t t[256];
  int started = 0;
  for (int i = 0; i < nth; i++) {
    if (pthread_create(&t[i], NULL, worker, NULL) != 0)
      break;
    started++;
  }
  for (int i = 0; i < started; i++)
    pthread_join(t[i], NULL);

  return found_any ? 0 : 1;
}