/*
 * 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 <fnmatch.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;
static int git_all = 0; /* if set, ignore .gitignore / .git entirely */

/* ---------- .gitignore handling ---------- */
typedef struct Pattern {
  int negate;     /* pattern began with '!' */
  int dir_only;   /* pattern ended with '/' (matches dirs only) */
  int has_slash;  /* pattern contains a '/' (anchored to its .gitignore dir) */
  char *pat;      /* pattern text (without '!' / trailing '/') */
  size_t pat_len;
} Pattern;

typedef struct GitIgnore {
  Pattern *pats;
  size_t npats;
  const char *rel;       /* directory this ignore governs, relative to root */
  struct GitIgnore *parent;
  struct GitIgnore *gnext; /* global list, for cleanup */
} GitIgnore;

static GitIgnore *gi_all = NULL;

/* ---------- directory work queue (parallel walk + scan) ---------- */
typedef struct DirJob {
  char *path; /* full path for opendir/open */
  char *rel;  /* path relative to the search root ("" for root) */
  GitIgnore *gi; /* active ignore set for this directory's children */
  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, const char *rel, GitIgnore *gi) {
  DirJob *j = malloc(sizeof *j);
  if(j == NULL)
    return;
  j->path = strdup(path);
  if(j->path == NULL) {
    free(j);
    return;
  }
  j->rel = strdup(rel);
  if(j->rel == NULL) {
    free(j->path);
    free(j);
    return;
  }
  j->gi = gi;
  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 void pop_dir(char **path, char **rel, GitIgnore **gi) {
  pthread_mutex_lock(&dir_mx);
  DirJob *j = dir_stack;
  if(j != NULL)
    dir_stack = j->next;
  pthread_mutex_unlock(&dir_mx);
  if(j == NULL) {
    *path = NULL;
    *rel = NULL;
    *gi = NULL;
    return;
  }
  *path = j->path;
  *rel = j->rel;
  *gi = j->gi;
  free(j);
}

/* Read an entire fd into a malloc'd, NUL-terminated buffer. Returns the buffer
 * (caller frees) and stores the length in *len, or NULL on error. */
static char *read_all(int fd, size_t *len) {
  size_t cap = 4096, n = 0;
  char *buf = malloc(cap);
  if(buf == NULL)
    return NULL;
  for(;;) {
    if(n == cap) {
      cap *= 2;
      char *nb = realloc(buf, cap);
      if(nb == NULL) {
        free(buf);
        return NULL;
      }
      buf = nb;
    }
    ssize_t r = read(fd, buf + n, cap - n);
    if(r < 0) {
      if(errno == EINTR)
        continue;
      free(buf);
      return NULL;
    }
    if(r == 0)
      break;
    n += (size_t)r;
  }
  buf = realloc(buf, n + 1);
  if(buf == NULL)
    return NULL;
  buf[n] = '\0';
  *len = n;
  return buf;
}

/* Parse a .gitignore buffer into patterns, chained under `parent`. Returns the
 * new GitIgnore node (sharing `parent` if the file is empty/absent). */
static GitIgnore *load_gitignore(const char *dir, GitIgnore *parent,
                                 const char *rel) {
  char path[PATH_MAX];
  int n = snprintf(path, sizeof path, "%s/.gitignore", dir);
  if(n < 0 || (size_t)n >= sizeof path)
    return parent;
  int fd = open(path, O_RDONLY | O_CLOEXEC);
  if(fd < 0)
    return parent;

  size_t len = 0;
  char *buf = read_all(fd, &len);
  close(fd);
  if(buf == NULL)
    return parent;

  Pattern *pa = NULL;
  size_t np = 0, cap = 0;
  char *p = buf, *end = buf + len;
  while(p < end) {
    char *nl = memchr(p, '\n', (size_t)(end - p));
    size_t llen = (nl != NULL) ? (size_t)(nl - p) : (size_t)(end - p);
    if(llen > 0 && p[llen - 1] == '\r')
      llen--;
    size_t s = 0;
    while(s < llen && (p[s] == ' ' || p[s] == '\t'))
      s++;
    size_t e = llen;
    while(e > s && (p[e - 1] == ' ' || p[e - 1] == '\t'))
      e--;
    if(s >= e || p[s] == '#') {
      p = (nl != NULL) ? nl + 1 : end;
      continue;
    }
    char *t = malloc(e - s + 1);
    if(t == NULL)
      break;
    memcpy(t, p + s, e - s);
    t[e - s] = '\0';

    int negate = 0, dir_only = 0;
    if(t[0] == '!') {
      negate = 1;
      memmove(t, t + 1, strlen(t));
    }
    size_t tl = strlen(t);
    if(tl > 0 && t[tl - 1] == '/') {
      dir_only = 1;
      t[tl - 1] = '\0';
      tl--;
    }
    int has_slash = (strchr(t, '/') != NULL);

    if(np == cap) {
      cap = cap ? cap * 2 : 16;
      Pattern *na = realloc(pa, cap * sizeof *pa);
      if(na == NULL) {
        free(t);
        break;
      }
      pa = na;
    }
    pa[np].negate = negate;
    pa[np].dir_only = dir_only;
    pa[np].has_slash = has_slash;
    pa[np].pat = t;
    pa[np].pat_len = tl;
    np++;
    p = (nl != NULL) ? nl + 1 : end;
  }
  free(buf);

  if(np == 0) {
    free(pa);
    return parent;
  }

  GitIgnore *g = malloc(sizeof *g);
  if(g == NULL) {
    for(size_t i = 0; i < np; i++)
      free(pa[i].pat);
    free(pa);
    return parent;
  }
  g->pats = pa;
  g->npats = np;
  g->rel = strdup(rel);
  g->parent = parent;
  g->gnext = gi_all;
  gi_all = g;
  return g;
}

/* Match a single path segment `s` (len sl) against a glob `p` (len pl) where
 * '*' matches a run of non-'/' chars and '?' matches one char. */
static int seg_eq(const char *p, size_t pl, const char *s, size_t sl) {
  size_t i = 0, j = 0;
  size_t star = SIZE_MAX, si = 0, sj = 0;
  while(i < pl || j < sl) {
    if(i < pl && p[i] == '*') {
      star = i;
      si = i + 1;
      sj = j;
      i++;
      continue;
    }
    if(i < pl && (p[i] == '?' || (j < sl && p[i] == s[j]))) {
      i++;
      j++;
      continue;
    }
    if(star != SIZE_MAX) {
      /* Extend what the '*' matches by one more char of s, if possible. */
      if(sj + 1 > sl)
        break;
      i = si;
      sj++;
      j = sj;
      continue;
    }
    return 0;
  }
  return i == pl && j == sl;
}

/* Match a slash-separated pattern `p` against path `s`, supporting `**`. */
static int match_path(const char *p, const char *s) {
  for(;;) {
    if(p[0] == '*' && p[1] == '*') {
      p += 2;
      while(*p == '/')
        p++;
      if(*p == '\0')
        return 1;
      const char *sp = s;
      for(;;) {
        if(match_path(p, sp))
          return 1;
        while(*sp && *sp != '/')
          sp++;
        if(*sp == '\0')
          break;
        sp++;
      }
      return 0;
    }
    if(*p == '\0')
      return *s == '\0';
    if(*p == '/') {
      if(*s != '/')
        return 0;
      p++;
      s++;
      continue;
    }
    const char *pe = p;
    while(*pe && *pe != '/')
      pe++;
    const char *se = s;
    while(*se && *se != '/')
      se++;
    if(!seg_eq(p, (size_t)(pe - p), s, (size_t)(se - s)))
      return 0;
    p = pe;
    s = se;
  }
}

/* Match a gitignore pattern against a path (path relative to the owning
 * .gitignore directory). A leading '/' only marks the pattern as anchored to
 * that directory (it is already implied by `path`), so it is stripped before
 * matching. Falls back to fnmatch for patterns without `**`. */
static int git_match(const char *pat, const char *path) {
  while(*pat == '/')
    pat++;
  if(*pat == '\0')
    return *path == '\0';
  if(strstr(pat, "**") == NULL)
    return fnmatch(pat, path, FNM_PATHNAME) == 0;
  return match_path(pat, path);
}

/* Decide whether an entry named `name` (full relative path `entry_rel`, a
 * directory iff `is_dir`) is ignored by the active ignore set `gi`. The
 * deepest matching rule wins (git semantics). */
static int is_ignored(const char *entry_rel, const char *name, GitIgnore *gi,
                      int is_dir) {
  GitIgnore *chain[1024];
  int n = 0;
  for(GitIgnore *g = gi; g != NULL && n < 1024; g = g->parent)
    chain[n++] = g;

  int ignored = 0;
  for(int i = n - 1; i >= 0; i--) { /* root -> child (deepest wins) */
    GitIgnore *g = chain[i];
    for(size_t p = 0; p < g->npats; p++) {
      Pattern *pat = &g->pats[p];
      int m;
      if(pat->has_slash) {
        const char *rp;
        if(g->rel[0] == '\0') {
          rp = entry_rel;
        } else {
          size_t rl = strlen(g->rel);
          if(strncmp(entry_rel, g->rel, rl) != 0)
            continue;
          if(entry_rel[rl] != '/')
            continue;
          rp = entry_rel + rl + 1;
        }
        m = git_match(pat->pat, rp);
      } else {
        if(pat->dir_only && !is_dir)
          continue;
        m = git_match(pat->pat, name);
      }
      if(m)
        ignored = pat->negate ? 0 : 1;
    }
  }
  return ignored;
}

/* ---------- 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];
  char relbuf[PATH_MAX];

  for(;;) {
    char *dir, *rel;
    GitIgnore *parent_gi;
    pop_dir(&dir, &rel, &parent_gi);
    if(dir == NULL)
      break;

    GitIgnore *my_gi = parent_gi;
    if(!git_all)
      my_gi = load_gitignore(dir, parent_gi, rel);

    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;
        const char *name = ent->d_name;

        int n = snprintf(child, sizeof child, "%s/%s", dir, name);
        if(n < 0 || (size_t)n >= sizeof child)
          continue;
        n = snprintf(relbuf, sizeof relbuf, "%s%s%s",
                     rel, (rel[0] == '\0') ? "" : "/", name);
        if(n < 0 || (size_t)n >= sizeof relbuf)
          continue;

        int is_dir = (ent->d_type == DT_DIR);
        if(ent->d_type == DT_UNKNOWN) {
          struct stat st;
          if(lstat(child, &st) == 0)
            is_dir = S_ISDIR(st.st_mode);
        }

        if(!git_all) {
          /* Always skip .git directories, just like git. */
          if(strcmp(name, ".git") == 0 && is_dir)
            continue;
          if(is_ignored(relbuf, name, my_gi, is_dir))
            continue;
        }

        if(ent->d_type == DT_REG) {
          scan_file(child, &sb);
        } else if(ent->d_type == DT_DIR) {
          push_dir(child, relbuf, my_gi);
        } 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, relbuf, my_gi);
          else if(S_ISREG(st.st_mode))
            scan_file(child, &sb);
        }
      }
      closedir(d);
    }
    free(dir);
    free(rel);
  }
  free(sb.buf);
  free(sb.carry);
  return NULL;
}

static void free_gitignores(void) {
  GitIgnore *g = gi_all;
  while(g != NULL) {
    GitIgnore *next = g->gnext;
    for(size_t i = 0; i < g->npats; i++)
      free(g->pats[i].pat);
    free(g->pats);
    free((void *)g->rel);
    free(g);
    g = next;
  }
  gi_all = 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;
  }

  git_all = (getenv("GG_GIT_ALL") != NULL);

  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, "", NULL);
  }

  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);

  free_gitignores();
  return found_any ? 0 : 1;
}