#ifndef _DEFAULT_SOURCE
#define _DEFAULT_SOURCE
#endif
#ifndef _XOPEN_SOURCE
#define _XOPEN_SOURCE 700
#endif

#include "cst_skills.h"

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>

#ifndef _WIN32
#include <dirent.h>
#include <pthread.h>
#endif

#include "cst_tools.h"
#include "cst_util.h"

#define SKILL_MD_MAX (256 * 1024)
#define SKILL_FILE_MAX (256 * 1024)
#define SKILL_LIST_FILES 60
#define EXTRA_ROOTS 16

/* --- frontmatter --------------------------------------------------------- */

static const char *skip_bom(const char *s) {
  if ((unsigned char)s[0] == 0xEF && (unsigned char)s[1] == 0xBB &&
      (unsigned char)s[2] == 0xBF)
    return s + 3;
  return s;
}

/* Start of the frontmatter lines and of the closing fence, or NULL. */
static const char *fm_bounds(const char *text, const char **end) {
  const char *s = skip_bom(text);
  if (strncmp(s, "---", 3) != 0)
    return NULL;
  const char *p = s + 3;
  while (*p == ' ' || *p == '\t' || *p == '\r')
    p++;
  if (*p != '\n')
    return NULL;
  const char *start = ++p;
  while (*p) {
    if (strncmp(p, "---", 3) == 0) {
      const char *q = p + 3;
      while (*q == ' ' || *q == '\t' || *q == '\r')
        q++;
      if (*q == '\n' || !*q) {
        *end = p;
        return start;
      }
    }
    const char *nl = strchr(p, '\n');
    if (!nl)
      break;
    p = nl + 1;
  }
  return NULL;
}

const char *cst_fm_body(const char *text) {
  const char *end = NULL;
  if (!text || !fm_bounds(text, &end))
    return text ? skip_bom(text) : "";
  const char *nl = strchr(end, '\n');
  if (!nl)
    return end + strlen(end);
  nl++;
  while (*nl == '\n' || *nl == '\r')
    nl++;
  return nl;
}

static void trim_into(const char *s, size_t n, char *out, size_t on) {
  while (n && isspace((unsigned char)*s))
    s++, n--;
  while (n && isspace((unsigned char)s[n - 1]))
    n--;
  if (n >= 2 && ((s[0] == '"' && s[n - 1] == '"') ||
                 (s[0] == '\'' && s[n - 1] == '\''))) {
    s++;
    n -= 2;
  }
  if (n >= on)
    n = on - 1;
  memcpy(out, s, n);
  out[n] = 0;
}

static void append_part(char *out, size_t n, const char *sep,
                        const char *part) {
  size_t used = strlen(out);
  if (used + 1 >= n || !part[0])
    return;
  snprintf(out + used, n - used, "%s%s", used ? sep : "", part);
}

int cst_fm_get(const char *text, const char *key, char *out, size_t n) {
  if (!out || !n)
    return 0;
  out[0] = 0;
  const char *end = NULL;
  const char *p = text ? fm_bounds(text, &end) : NULL;
  if (!p)
    return 0;
  size_t kl = strlen(key);
  while (p < end) {
    const char *nl = memchr(p, '\n', (size_t)(end - p));
    const char *le = nl ? nl : end;
    if ((size_t)(le - p) > kl && strncmp(p, key, kl) == 0 && p[kl] == ':') {
      char val[1024];
      trim_into(p + kl + 1, (size_t)(le - p - kl - 1), val, sizeof(val));
      const char *q = nl ? nl + 1 : end;
      int folded = strcmp(val, ">") == 0 || strcmp(val, ">-") == 0;
      int literal = strcmp(val, "|") == 0 || strcmp(val, "|-") == 0;
      if (val[0] == '[') {
        size_t vl = strlen(val);
        if (vl && val[vl - 1] == ']')
          val[--vl] = 0;
        char *tok = strtok(val + 1, ",");
        while (tok) {
          char item[256];
          trim_into(tok, strlen(tok), item, sizeof(item));
          append_part(out, n, ",", item);
          tok = strtok(NULL, ",");
        }
        return 1;
      }
      if (!folded && !literal && val[0]) {
        snprintf(out, n, "%s", val);
        return 1;
      }
      /* block value: following indented lines (or "- item" list) */
      while (q < end && (*q == ' ' || *q == '\t')) {
        const char *qn = memchr(q, '\n', (size_t)(end - q));
        const char *qe = qn ? qn : end;
        char line[1024];
        trim_into(q, (size_t)(qe - q), line, sizeof(line));
        if (!folded && !literal && line[0] == '-' &&
            (line[1] == ' ' || !line[1])) {
          char item[1024];
          trim_into(line + 1, strlen(line + 1), item, sizeof(item));
          append_part(out, n, ",", item);
        } else {
          append_part(out, n, literal ? "\n" : " ", line);
        }
        q = qn ? qn + 1 : end;
      }
      return 1;
    }
    p = nl ? nl + 1 : end;
  }
  return 0;
}

/* --- discovery ----------------------------------------------------------- */

static struct {
  char dir[OS_PATH_MAX];
  char source[48];
} g_roots[EXTRA_ROOTS];
static int g_nroots;
#ifndef _WIN32
static pthread_mutex_t g_mu = PTHREAD_MUTEX_INITIALIZER;
#define LOCK() pthread_mutex_lock(&g_mu)
#define UNLOCK() pthread_mutex_unlock(&g_mu)
#else
#define LOCK() ((void)0)
#define UNLOCK() ((void)0)
#endif

void cst_skills_add_root(const char *dir, const char *source) {
  if (!dir || !dir[0])
    return;
  LOCK();
  int dup = 0;
  for (int i = 0; i < g_nroots; i++)
    dup |= strcmp(g_roots[i].dir, dir) == 0;
  if (!dup && g_nroots < EXTRA_ROOTS) {
    snprintf(g_roots[g_nroots].dir, sizeof(g_roots[0].dir), "%s", dir);
    snprintf(g_roots[g_nroots].source, sizeof(g_roots[0].source), "%s",
             source ? source : "plugin");
    g_nroots++;
  }
  UNLOCK();
}

void cst_skills_clear_roots(const char *prefix) {
  LOCK();
  int k = 0;
  size_t pl = prefix ? strlen(prefix) : 0;
  for (int i = 0; i < g_nroots; i++) {
    if (pl && strncmp(g_roots[i].source, prefix, pl) != 0)
      g_roots[k++] = g_roots[i];
  }
  g_nroots = k;
  UNLOCK();
}

static char *slurp(const char *path, size_t max, size_t *len) {
  FILE *fp = fopen(path, "rb");
  if (!fp)
    return NULL;
  cst_buf_t b = {0};
  char tmp[8192];
  size_t n;
  int big = 0;
  while ((n = fread(tmp, 1, sizeof(tmp), fp)) > 0) {
    if (b.len + n > max) {
      big = 1;
      break;
    }
    cst_buf_append(&b, tmp, n);
  }
  fclose(fp);
  if (big) {
    cst_buf_free(&b);
    return NULL;
  }
  if (!b.buf)
    cst_buf_puts(&b, "");
  if (len)
    *len = b.len;
  return cst_buf_steal(&b);
}

static int skill_cmp(const void *a, const void *b) {
  return strcmp(((const cst_skill_t *)a)->name, ((const cst_skill_t *)b)->name);
}

static int have(const cst_skill_t *v, int n, const char *name) {
  for (int i = 0; i < n; i++)
    if (strcmp(v[i].name, name) == 0)
      return 1;
  return 0;
}

static int scan_root(const char *root, const char *source, cst_skill_t *out,
                     int n, int max) {
#ifndef _WIN32
  DIR *d = opendir(root);
  if (!d)
    return n;
  struct dirent *de;
  while (n < max && (de = readdir(d)) != NULL) {
    if (de->d_name[0] == '.')
      continue;
    char dir[OS_PATH_MAX], md[OS_PATH_MAX + 16];
    if (snprintf(dir, sizeof(dir), "%s/%s", root, de->d_name) >=
        (int)sizeof(dir))
      continue;
    snprintf(md, sizeof(md), "%s/SKILL.md", dir);
    char *text = slurp(md, SKILL_MD_MAX, NULL);
    if (!text)
      continue;
    cst_skill_t s;
    memset(&s, 0, sizeof(s));
    if (!cst_fm_get(text, "name", s.name, sizeof(s.name)) || !s.name[0])
      snprintf(s.name, sizeof(s.name), "%.63s", de->d_name);
    cst_fm_get(text, "description", s.desc, sizeof(s.desc));
    if (!s.desc[0]) {
      /* first prose line of the body */
      const char *b = cst_fm_body(text);
      for (;;) {
        while (*b == ' ' || *b == '\t' || *b == '\n' || *b == '\r')
          b++;
        if (*b != '#')
          break;
        b += strcspn(b, "\n");
      }
      trim_into(b, strcspn(b, "\r\n"), s.desc, sizeof(s.desc));
    }
    free(text);
    snprintf(s.dir, sizeof(s.dir), "%s", dir);
    snprintf(s.source, sizeof(s.source), "%s", source);
    if (!have(out, n, s.name))
      out[n++] = s;
  }
  closedir(d);
#else
  (void)root;
  (void)source;
  (void)out;
  (void)max;
#endif
  return n;
}

int cst_skills_list(const char *ws, cst_skill_t *out, int max) {
  if (!out || max <= 0)
    return 0;
  int n = 0;
  char p[OS_PATH_MAX];
  if (ws && ws[0]) {
    snprintf(p, sizeof(p), "%s/.agent/skills", ws);
    n = scan_root(p, "workspace", out, n, max);
    snprintf(p, sizeof(p), "%s/.claude/skills", ws);
    n = scan_root(p, "claude", out, n, max);
  }
  char cfg[OS_PATH_MAX];
  if (os_config_dir(cfg, sizeof(cfg)) == 0) {
    snprintf(p, sizeof(p), "%.4000s/skills", cfg);
    n = scan_root(p, "user", out, n, max);
  }
  LOCK();
  int nr = g_nroots;
  char roots[EXTRA_ROOTS][OS_PATH_MAX], srcs[EXTRA_ROOTS][48];
  for (int i = 0; i < nr; i++) {
    memcpy(roots[i], g_roots[i].dir, sizeof(roots[i]));
    memcpy(srcs[i], g_roots[i].source, sizeof(srcs[i]));
  }
  UNLOCK();
  for (int i = 0; i < nr; i++)
    n = scan_root(roots[i], srcs[i], out, n, max);
  qsort(out, (size_t)n, sizeof(*out), skill_cmp);
  return n;
}

char *cst_skills_index(const char *ws) {
  cst_skill_t *v = calloc(CST_SKILLS_MAX, sizeof(*v));
  if (!v)
    return NULL;
  int n = cst_skills_list(ws, v, CST_SKILLS_MAX);
  if (n == 0) {
    free(v);
    return NULL;
  }
  cst_buf_t b = {0};
  cst_buf_puts(&b, "\nSkills (call skill(name) to load one before working on a "
                   "task that matches its description):\n");
  int shown = 0;
  for (int i = 0; i < n; i++) {
    char line[400];
    size_t dl = strlen(v[i].desc);
    size_t keep = cst_utf8_floor(v[i].desc, dl > 240 ? 240 : dl);
    snprintf(line, sizeof(line), "- %s: %.*s%s\n", v[i].name, (int)keep,
             v[i].desc, keep < dl ? "…" : "");
    if (b.len + strlen(line) > CST_SKILL_INDEX_MAX - 64)
      break;
    cst_buf_puts(&b, line);
    shown++;
  }
  if (shown < n)
    cst_buf_printf(&b, "- … %d more (see /skills)\n", n - shown);
  free(v);
  return cst_buf_steal(&b);
}

/* --- loading ------------------------------------------------------------- */

static int find_skill(const char *ws, const char *name, cst_skill_t *out) {
  cst_skill_t *v = calloc(CST_SKILLS_MAX, sizeof(*v));
  if (!v)
    return 0;
  int n = cst_skills_list(ws, v, CST_SKILLS_MAX), hit = 0;
  for (int i = 0; i < n && !hit; i++) {
    if (strcmp(v[i].name, name) == 0) {
      *out = v[i];
      hit = 1;
    }
  }
  free(v);
  return hit;
}

static void list_files(const char *dir, const char *rel, int depth,
                       cst_buf_t *b, int *count) {
#ifndef _WIN32
  char full[OS_PATH_MAX];
  if (snprintf(full, sizeof(full), "%s%s%s", dir, rel[0] ? "/" : "", rel) >=
      (int)sizeof(full))
    return;
  DIR *d = opendir(full);
  if (!d)
    return;
  char *names[256];
  int nn = 0;
  struct dirent *de;
  while (nn < 256 && (de = readdir(d)) != NULL) {
    if (de->d_name[0] == '.')
      continue;
    names[nn] = strdup(de->d_name);
    if (names[nn])
      nn++;
  }
  closedir(d);
  for (int i = 1; i < nn; i++) {
    for (int j = i; j > 0 && strcmp(names[j - 1], names[j]) > 0; j--) {
      char *tmp = names[j];
      names[j] = names[j - 1];
      names[j - 1] = tmp;
    }
  }
  for (int i = 0; i < nn; i++) {
    char crel[OS_PATH_MAX], cfull[OS_PATH_MAX + 2];
    snprintf(crel, sizeof(crel), "%s%s%.255s", rel, rel[0] ? "/" : "",
             names[i]);
    snprintf(cfull, sizeof(cfull), "%s/%s", dir, crel);
    struct stat st;
    if (stat(cfull, &st) != 0)
      continue;
    if (S_ISDIR(st.st_mode)) {
      if (depth < 3)
        list_files(dir, crel, depth + 1, b, count);
    } else if (strcmp(crel, "SKILL.md") != 0) {
      if (*count < SKILL_LIST_FILES)
        cst_buf_printf(b, "- %s\n", crel);
      (*count)++;
    }
  }
  for (int i = 0; i < nn; i++)
    free(names[i]);
#else
  (void)dir;
  (void)rel;
  (void)depth;
  (void)b;
  (void)count;
#endif
}

static char *errf(int *code, const char *fmt, const char *a, const char *b) {
  char msg[1200];
  snprintf(msg, sizeof(msg), fmt, a, b);
  *code = 1;
  return strdup(msg);
}

static char *names_list(const char *ws) {
  cst_skill_t *v = calloc(CST_SKILLS_MAX, sizeof(*v));
  cst_buf_t b = {0};
  int n = v ? cst_skills_list(ws, v, CST_SKILLS_MAX) : 0;
  for (int i = 0; i < n; i++)
    cst_buf_printf(&b, "%s%s", i ? ", " : "", v[i].name);
  free(v);
  if (!b.buf)
    cst_buf_puts(&b, "(none)");
  return cst_buf_steal(&b);
}

char *cst_skill_read(const char *ws, const char *name, const char *file,
                     int *exit_code) {
  int dummy;
  if (!exit_code)
    exit_code = &dummy;
  *exit_code = 0;
  cst_skill_t s;
  if (!name || !name[0] || !find_skill(ws, name, &s)) {
    char *names = names_list(ws);
    char *r = errf(exit_code, "error: no skill named \"%.100s\" (available: %.900s)",
                   name ? name : "", names ? names : "");
    free(names);
    return r;
  }
  if (file && file[0]) {
    char want[OS_PATH_MAX * 2], real[OS_PATH_MAX], root[OS_PATH_MAX];
    snprintf(want, sizeof(want), "%s/%s", s.dir, file);
    if (os_realpath(s.dir, root, sizeof(root)) != 0 ||
        os_realpath(want, real, sizeof(real)) != 0)
      return errf(exit_code, "error: skill %s has no file %.300s", s.name,
                  file);
    if (!os_path_under(root, real))
      return errf(exit_code, "error: %.300s is outside the skill %s directory",
                  file, s.name);
    size_t n = 0;
    char *body = slurp(real, SKILL_FILE_MAX, &n);
    if (!body)
      return errf(exit_code, "error: cannot read %.300s of skill %s (missing, "
                  "a directory, or over 256 KiB)", file, s.name);
    if (memchr(body, 0, n)) {
      free(body);
      return errf(exit_code, "error: %.300s of skill %s is binary", file,
                  s.name);
    }
    cst_buf_t b = {0};
    cst_buf_printf(&b, "skill %s · %s\n", s.name, file);
    cst_buf_append(&b, body, n);
    free(body);
    return cst_buf_steal(&b);
  }
  char md[OS_PATH_MAX + 16];
  snprintf(md, sizeof(md), "%s/SKILL.md", s.dir);
  char *text = slurp(md, SKILL_MD_MAX, NULL);
  if (!text)
    return errf(exit_code, "error: cannot read %.300s%.1s", md, "");
  cst_buf_t b = {0};
  cst_buf_printf(&b, "skill %s (%s) · %s\n\n", s.name, s.source, s.dir);
  cst_buf_puts(&b, cst_fm_body(text));
  free(text);
  if (b.len && b.buf[b.len - 1] != '\n')
    cst_buf_puts(&b, "\n");
  cst_buf_t files = {0};
  int count = 0;
  list_files(s.dir, "", 0, &files, &count);
  if (count) {
    cst_buf_printf(&b, "\nFiles in this skill (read with skill(name=\"%s\", "
                       "file=...); paths are relative to %s):\n",
                   s.name, s.dir);
    cst_buf_append(&b, files.buf, files.len);
    if (count > SKILL_LIST_FILES)
      cst_buf_printf(&b, "- … %d more\n", count - SKILL_LIST_FILES);
  }
  cst_buf_free(&files);
  return cst_buf_steal(&b);
}

char *cst_skill_prompt(const char *ws, const char *name, const char *task) {
  int code = 0;
  char *body = cst_skill_read(ws, name, NULL, &code);
  if (!body || code != 0) {
    free(body);
    return NULL;
  }
  cst_buf_t b = {0};
  cst_buf_printf(&b, "Use the \"%s\" skill for this task. Its instructions "
                     "(already loaded):\n\n<skill>\n",
                 name);
  cst_buf_puts(&b, body);
  cst_buf_puts(&b, "</skill>\n\n");
  cst_buf_puts(&b, task && task[0] ? task : "Apply this skill now.");
  free(body);
  return cst_buf_steal(&b);
}

/* --- tool ---------------------------------------------------------------- */

static const char *arg_of(const ctl_tool_call_t *c, const char *key) {
  for (int i = 0; i < c->nargs; i++)
    if (strcmp(c->args[i].key, key) == 0)
      return c->args[i].value ? c->args[i].value : "";
  return NULL;
}

static int skill_tool(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,
                      cst_tool_result_t *r, void *ud) {
  (void)ud;
  int code = 0;
  char *out = cst_skill_read(ctx->workspace_root, arg_of(c, "name"),
                             arg_of(c, "file"), &code);
  r->out = out ? out : strdup("error: out of memory");
  r->out_len = r->out ? strlen(r->out) : 0;
  r->exit_code = out ? code : 1;
  return 0;
}

static int always(const ctl_tool_call_t *c, void *ud) {
  (void)c;
  (void)ud;
  return 1;
}

int cst_skills_register_tool(void) {
  if (cst_tool_find("skill"))
    return 0;
  cst_tool_def_t d;
  memset(&d, 0, sizeof(d));
  d.name = "skill";
  d.desc = "Load a skill from the Skills list: its instructions (SKILL.md) "
           "and the list of its files. Load the matching skill before "
           "starting such a task; pass file to read one of its files.";
  d.schema_json =
      "{\"type\":\"object\",\"properties\":{"
      "\"name\":{\"type\":\"string\",\"description\":\"skill name\"},"
      "\"file\":{\"type\":\"string\",\"description\":\"a file inside the "
      "skill directory (optional)\"}},\"required\":[\"name\"]}";
  d.perm = CST_TP_META;
  d.run_ex = skill_tool;
  d.parallel = always;
  d.owner = "builtin:skills";
  return cst_tool_register(&d);
}