/* WebUI: the HTTP + SSE front end (see include/cst_webui.h).
 *
 * Threading: every HTTP connection runs on its own thread (src/http_srv.c),
 * a turn runs on its own worker thread, and the agent itself is only ever
 * touched from the turn thread or while holding w->mu. The hooks the agent
 * calls live on the turn thread: they append to the event ring, wake the
 * event-stream threads and, for permission/ask_user, block until the
 * browser answers (or the timeout denies it). Nothing in the engine was
 * changed to make this work - the hooks are the interface the TUI uses too. */

#ifndef _DEFAULT_SOURCE
#define _DEFAULT_SOURCE
#endif

#include "cst_agent.h"
#include "cst_attach.h"
#include "cst_http.h"
#include "cst_util.h"
#include "cst_web_md.h"
#include "cst_webui.h"
#include "cJSON.h"
#include "os_compat.h"

#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#define WUI_RING 2000
#define WUI_TOOL_OUT 32768
#define WUI_ASK_MAX 1024

typedef struct {
  const char *name;
  const char *ctype;
  const unsigned char *data;
  size_t len;
} wui_asset_t;

#include "web_assets.inc"

typedef struct wui_sse {
  struct wui *w;
  cst_http_conn_t *c;
  uint64_t cursor;
  pthread_mutex_t mu;
  pthread_cond_t cv;
  int closed;
  struct wui_sse *next;
} wui_sse_t;

typedef struct wui {
  cst_agent_t *agent;
  cst_http_server_t *srv;
  char host[64];
  char token[64];
  int need_auth;
  const char *root; /* --web-dev: serve assets from disk */
  int perm_timeout_s;

  pthread_mutex_t mu;
  pthread_cond_t cv; /* permission / ask_user answers */
  cst_web_md_t *md; /* live markdown for the running turn */
  /* event ring */
  uint64_t seq;
  struct {
    uint64_t seq;
    char *frame;
  } ring[WUI_RING];
  wui_sse_t *subs;

  int busy;
  uint64_t req_id; /* permission/ask id counter */
  uint64_t perm_id;
  int perm_active, perm_answer;
  uint64_t ask_id;
  int ask_active, ask_rc;
  char ask_ans[WUI_ASK_MAX];

  volatile int stopping;
} wui_t;

/* --- events --------------------------------------------------------------- */

static uint64_t wui_first_seq(const wui_t *w) {
  return w->seq > WUI_RING ? w->seq - WUI_RING + 1 : 1;
}

/* Owns data (a cJSON object). */
static void wui_emit(wui_t *w, const char *type, cJSON *data) {
  if (!data)
    data = cJSON_CreateObject();
  if (!data)
    return;
  cJSON_AddStringToObject(data, "type", type);
  cJSON_AddNumberToObject(data, "seq", (double)(w->seq + 1));
  char *json = cJSON_PrintUnformatted(data);
  cJSON_Delete(data);
  if (!json)
    return;
  cst_buf_t f = {0};
  cst_buf_printf(&f, "event: %s\ndata: %s\n\n", type, json);
  free(json);
  if (!f.buf) {
    cst_buf_free(&f);
    return;
  }
  pthread_mutex_lock(&w->mu);
  w->seq++;
  int slot = (int)(w->seq % WUI_RING);
  free(w->ring[slot].frame);
  w->ring[slot].frame = f.buf; /* stolen */
  w->ring[slot].seq = w->seq;
  f.buf = NULL;
  for (wui_sse_t *s = w->subs; s; s = s->next)
    pthread_cond_broadcast(&s->cv);
  pthread_mutex_unlock(&w->mu);
  cst_buf_free(&f);
}

static void wui_emit_str(wui_t *w, const char *type, const char *key,
                         const char *val) {
  cJSON *o = cJSON_CreateObject();
  if (!o)
    return;
  cJSON_AddStringToObject(o, key, val ? val : "");
  wui_emit(w, type, o);
}

static void wui_emit_text(wui_t *w, const char *type, const char *text,
                          size_t len) {
  cJSON *o = cJSON_CreateObject();
  if (!o)
    return;
  char *s = malloc(len + 1);
  if (!s) {
    cJSON_Delete(o);
    return;
  }
  memcpy(s, text, len);
  s[len] = 0;
  cJSON_AddStringToObject(o, "text", s);
  free(s);
  wui_emit(w, type, o);
}

/* --- state --------------------------------------------------------------- */

static cJSON *wui_state_new(wui_t *w) {
  const cst_agent_config_t *cfg = cst_agent_config(w->agent);
  cJSON *o = cJSON_CreateObject();
  if (!o || !cfg) {
    cJSON_Delete(o);
    return NULL;
  }
  char sid[128] = "";
  cst_agent_session_id(w->agent, sid, sizeof(sid));
  cst_usage_t sess = {0}, turn = {0};
  cst_agent_usage(w->agent, &sess, &turn);
  cJSON_AddStringToObject(o, "protocol", "cst-webui/1");
  cJSON_AddStringToObject(o, "workspace", cfg->workspace_root);
  cJSON_AddStringToObject(o, "session", sid);
  cJSON_AddStringToObject(o, "provider", cfg->provider);
  cJSON_AddStringToObject(o, "model", cfg->model);
  cJSON_AddStringToObject(o, "effort", cfg->effort);
  cJSON_AddStringToObject(o, "approval", cst_approval_name(cfg->approval));
  cJSON_AddStringToObject(o, "protocol_tools", cst_protocol_name(cfg->protocol));
  cJSON_AddBoolToObject(o, "plan_mode", cfg->plan_mode);
  cJSON_AddBoolToObject(o, "status_busy", w->busy);
  cJSON_AddStringToObject(o, "todo", cst_agent_todo(w->agent)
                                       ? cst_agent_todo(w->agent)
                                       : "");
  cJSON_AddNumberToObject(o, "context_tokens",
                          (double)cst_agent_last_prompt_tokens(w->agent));
  cJSON_AddBoolToObject(o, "undo_available",
                        cst_agent_undo_available(w->agent) != 0);
  cJSON *u = cJSON_AddObjectToObject(o, "usage");
  if (u) {
    cJSON_AddNumberToObject(u, "requests", sess.requests);
    cJSON_AddNumberToObject(u, "prompt_tokens", (double)sess.prompt);
    cJSON_AddNumberToObject(u, "completion_tokens", (double)sess.out);
    cJSON_AddNumberToObject(u, "cached_tokens", (double)sess.cached);
    cJSON_AddNumberToObject(u, "cache_miss_tokens", (double)sess.miss);
    cJSON_AddNumberToObject(u, "cost", sess.cost);
    cJSON_AddBoolToObject(u, "priced", sess.priced != 0);
    cJSON_AddStringToObject(u, "currency", sess.currency);
  }
  cJSON *imgs = cJSON_AddArrayToObject(o, "pending_images");
  int n = cst_agent_pending_count(w->agent);
  for (int i = 0; i < n && imgs; i++) {
    char line[160];
    if (cst_agent_pending_describe(w->agent, i, line, sizeof(line)) == 0)
      cJSON_AddItemToArray(imgs, cJSON_CreateString(line));
  }
  return o;
}

static void wui_emit_state(wui_t *w) {
  cJSON *o = wui_state_new(w);
  if (o)
    wui_emit(w, "state", o);
}

/* --- session -------------------------------------------------------------- */

static cJSON *msg_json(const cst_message_t *m) {
  cJSON *o = cJSON_CreateObject();
  if (!o)
    return NULL;
  const char *role = "user";
  switch (m->role) {
  case CST_ROLE_SYSTEM: role = "system"; break;
  case CST_ROLE_ASSISTANT: role = "assistant"; break;
  case CST_ROLE_TOOL: role = "tool"; break;
  default: role = "user"; break;
  }
  cJSON_AddStringToObject(o, "role", role);
  cJSON_AddStringToObject(o, "content", m->content ? m->content : "");
  if (m->role == CST_ROLE_ASSISTANT && m->content && m->content[0]) {
    char *html = cst_web_md_html(m->content, strlen(m->content));
    if (html) {
      cJSON_AddStringToObject(o, "html", html);
      free(html);
    }
  }
  if (m->reasoning && m->reasoning[0])
    cJSON_AddStringToObject(o, "reasoning", m->reasoning);
  if (m->tool_call_id[0])
    cJSON_AddStringToObject(o, "tool_call_id", m->tool_call_id);
  if (m->tool_name[0])
    cJSON_AddStringToObject(o, "tool_name", m->tool_name);
  if (m->tool_calls_json && m->tool_calls_json[0]) {
    cJSON *tc = cJSON_Parse(m->tool_calls_json);
    if (tc) {
      cJSON_AddItemToObject(o, "tool_calls", tc);
    }
  }
  if (m->nattach > 0) {
    cJSON *arr = cJSON_AddArrayToObject(o, "attach");
    for (int i = 0; arr && i < m->nattach; i++) {
      cJSON *a = cJSON_CreateObject();
      if (!a)
        continue;
      cJSON_AddStringToObject(a, "name", m->attach[i].name);
      cJSON_AddStringToObject(a, "mime", m->attach[i].mime);
      cJSON_AddStringToObject(a, "rel", m->attach[i].rel);
      cJSON_AddNumberToObject(a, "bytes", (double)m->attach[i].bytes);
      cJSON_AddItemToArray(arr, a);
    }
  }
  return o;
}

static char *wui_session_json(wui_t *w, int from) {
  cst_session_t *s = cst_agent_session(w->agent);
  if (!s)
    return NULL;
  cJSON *root = cJSON_CreateObject();
  if (!root)
    return NULL;
  cJSON *arr = cJSON_AddArrayToObject(root, "messages");
  cst_session_lock(s);
  int n = cst_session_count(s);
  for (int i = from; i < n; i++) {
    const cst_message_t *m = cst_session_get(s, i);
    if (!m)
      continue;
    cJSON *j = msg_json(m);
    if (j && arr)
      cJSON_AddItemToArray(arr, j);
    else
      cJSON_Delete(j);
  }
  cst_session_unlock(s);
  char *out = cJSON_PrintUnformatted(root);
  cJSON_Delete(root);
  return out;
}

/* --- hooks --------------------------------------------------------------- */

static int wui_md_emit(const char *html, size_t len, void *ud) {
  wui_t *w = ud;
  if (len)
    wui_emit_text(w, "assistant_html", html, len);
  return 0;
}

static void on_status(const char *msg, void *ud) {
  wui_emit_str((wui_t *)ud, "status", "message", msg);
}

static void on_assistant_delta(const char *text, size_t len, void *ud) {
  wui_t *w = ud;
  if (!w->md)
    w->md = cst_web_md_new(wui_md_emit, w);
  if (w->md)
    cst_web_md_feed(w->md, text, len);
  wui_emit_text(w, "assistant_delta", text, len);
}

static void on_think_delta(const char *text, size_t len, void *ud) {
  wui_emit_text((wui_t *)ud, "think_delta", text, len);
}

static cJSON *call_json(const ctl_tool_call_t *call) {
  cJSON *o = cJSON_CreateObject();
  if (!o)
    return NULL;
  cJSON_AddStringToObject(o, "id", call->id);
  cJSON_AddStringToObject(o, "name", call->name);
  cJSON *args = cJSON_AddObjectToObject(o, "args");
  for (int i = 0; args && i < call->nargs; i++) {
    cJSON *v = cJSON_CreateString(call->args[i].value ? call->args[i].value : "");
    if (v)
      cJSON_AddItemToObject(args, call->args[i].key, v);
  }
  return o;
}

static void on_tool_event(const char *phase, const ctl_tool_call_t *call,
                          const char *detail, void *ud) {
  wui_t *w = ud;
  cJSON *o = call ? call_json(call) : cJSON_CreateObject();
  if (!o)
    return;
  cJSON_AddStringToObject(o, "phase", phase ? phase : "");
  if (detail)
    cJSON_AddStringToObject(o, "detail", detail);
  wui_emit(w, "tool", o);
}

static void on_tool_result(const ctl_tool_call_t *call, const char *out,
                           size_t len, int exit_code, void *ud) {
  wui_t *w = ud;
  cJSON *o = call ? call_json(call) : cJSON_CreateObject();
  if (!o)
    return;
  size_t shown = len > WUI_TOOL_OUT ? WUI_TOOL_OUT : len;
  char *s = malloc(shown + 1);
  if (!s) {
    cJSON_Delete(o);
    return;
  }
  memcpy(s, out, shown);
  s[shown] = 0;
  cJSON_AddStringToObject(o, "out", s);
  cJSON_AddBoolToObject(o, "truncated", len > shown);
  cJSON_AddNumberToObject(o, "bytes", (double)len);
  free(s);
  cJSON_AddNumberToObject(o, "exit", exit_code);
  wui_emit(w, "tool_result", o);
}

static void on_todo(const char *text, void *ud) {
  wui_emit_str((wui_t *)ud, "todo", "text", text ? text : "");
}

static int wui_wait_permission(wui_t *w, const char *tool, const char *detail,
                               const char *preview) {
  pthread_mutex_lock(&w->mu);
  w->req_id++;
  uint64_t id = w->req_id;
  w->perm_id = id;
  w->perm_active = 1;
  w->perm_answer = -1;
  int has_client = w->subs != NULL;
  pthread_mutex_unlock(&w->mu);

  cJSON *o = cJSON_CreateObject();
  if (o) {
    cJSON_AddNumberToObject(o, "id", (double)id);
    cJSON_AddStringToObject(o, "tool", tool ? tool : "tool");
    cJSON_AddStringToObject(o, "detail", detail ? detail : "");
    cJSON_AddStringToObject(o, "preview", preview ? preview : "");
    cJSON_AddBoolToObject(o, "sandbox", detail &&
                                           strncmp(detail, CST_PERM_SANDBOX,
                                                   strlen(CST_PERM_SANDBOX)) ==
                                               0);
    wui_emit(w, "permission", o);
  }
  int timeout = w->perm_timeout_s > 0 ? w->perm_timeout_s : 600;
  /* Nobody is watching: do not hang the turn for ten minutes. */
  if (!has_client)
    timeout = 3;
  int answer = CST_PERM_DENY;
  struct timespec deadline;
  clock_gettime(CLOCK_REALTIME, &deadline);
  deadline.tv_sec += timeout;
  pthread_mutex_lock(&w->mu);
  for (;;) {
    if (w->perm_active && w->perm_id == id && w->perm_answer >= 0) {
      answer = w->perm_answer;
      w->perm_active = 0;
      break;
    }
    if (w->stopping)
      break;
    int rc = pthread_cond_timedwait(&w->cv, &w->mu, &deadline);
    if (rc != 0) {
      w->perm_active = 0;
      break;
    }
  }
  pthread_mutex_unlock(&w->mu);
  cJSON *e = cJSON_CreateObject();
  if (e) {
    cJSON_AddNumberToObject(e, "id", (double)id);
    cJSON_AddNumberToObject(e, "answer", answer);
    wui_emit(w, "permission_done", e);
  }
  return answer;
}

static int on_permission(const char *tool_name, const char *detail,
                         const char *preview, void *ud) {
  return wui_wait_permission((wui_t *)ud, tool_name, detail, preview);
}

static int on_ask_user(const char *question, const char *options, char *ans,
                       size_t ans_sz, void *ud) {
  wui_t *w = ud;
  pthread_mutex_lock(&w->mu);
  w->req_id++;
  uint64_t id = w->req_id;
  w->ask_id = id;
  w->ask_active = 1;
  w->ask_rc = -1;
  w->ask_ans[0] = 0;
  int has_client = w->subs != NULL;
  pthread_mutex_unlock(&w->mu);

  cJSON *o = cJSON_CreateObject();
  if (o) {
    cJSON_AddNumberToObject(o, "id", (double)id);
    cJSON_AddStringToObject(o, "question", question ? question : "");
    cJSON *arr = cJSON_AddArrayToObject(o, "options");
    for (const char *p = options; arr && p && *p;) {
      const char *nl = strchr(p, '\n');
      size_t n = nl ? (size_t)(nl - p) : strlen(p);
      char *tmp = malloc(n + 1);
      if (tmp) {
        memcpy(tmp, p, n);
        tmp[n] = 0;
        cJSON_AddItemToArray(arr, cJSON_CreateString(tmp));
        free(tmp);
      }
      p = nl ? nl + 1 : NULL;
    }
    wui_emit(w, "ask_user", o);
  }
  int timeout = has_client ? 600 : 3;
  int rc = -1;
  struct timespec deadline;
  clock_gettime(CLOCK_REALTIME, &deadline);
  deadline.tv_sec += timeout;
  pthread_mutex_lock(&w->mu);
  for (;;) {
    if (w->ask_active && w->ask_id == id && w->ask_rc != 0) {
      rc = w->ask_rc == 1 ? 0 : -1;
      snprintf(ans, ans_sz, "%s", w->ask_ans);
      w->ask_active = 0;
      break;
    }
    if (w->stopping)
      break;
    int wrc = pthread_cond_timedwait(&w->cv, &w->mu, &deadline);
    if (wrc != 0) {
      w->ask_active = 0;
      break;
    }
  }
  pthread_mutex_unlock(&w->mu);
  return rc;
}

/* --- routes -------------------------------------------------------------- */

static int read_file_all(const char *path, char **out, size_t *out_len) {
  FILE *fp = fopen(path, "rb");
  if (!fp)
    return -1;
  cst_buf_t b = {0};
  char tmp[8192];
  size_t n;
  while ((n = fread(tmp, 1, sizeof(tmp), fp)) > 0) {
    if (cst_buf_append(&b, tmp, n) != 0) {
      fclose(fp);
      cst_buf_free(&b);
      return -1;
    }
  }
  fclose(fp);
  size_t total = b.len;
  *out = cst_buf_steal(&b);
  if (!*out)
    return -1;
  *out_len = total;
  return 0;
}

static int wui_serve_file(cst_http_conn_t *c, wui_t *w, const char *path) {
  if (!w->root || !path || !path[0] || strstr(path, ".."))
    return -1;
  char full[4096];
  const char *rel = path[0] == '/' ? path + 1 : path;
  if (!rel[0])
    rel = "index.html";
  if (snprintf(full, sizeof(full), "%s/%s", w->root, rel) >=
      (int)sizeof(full))
    return -1;
  char *data = NULL;
  size_t len = 0;
  if (read_file_all(full, &data, &len) != 0)
    return -1;
  const char *ctype = "application/octet-stream";
  size_t n = strlen(rel);
  if (n > 5 && strcmp(rel + n - 5, ".html") == 0)
    ctype = "text/html; charset=utf-8";
  else if (n > 3 && strcmp(rel + n - 3, ".js") == 0)
    ctype = "text/javascript; charset=utf-8";
  else if (n > 4 && strcmp(rel + n - 4, ".css") == 0)
    ctype = "text/css; charset=utf-8";
  else if (n > 4 && strcmp(rel + n - 4, ".svg") == 0)
    ctype = "image/svg+xml";
  int rc = cst_http_send(c, 200, ctype, data, len);
  free(data);
  return rc;
}

static int wui_serve_asset(cst_http_conn_t *c, wui_t *w, const char *path) {
  const char *rel = path[0] == '/' ? path + 1 : path;
  if (!rel[0])
    rel = "index.html";
  if (w->root)
    return wui_serve_file(c, w, path);
  for (int i = 0; i < wui_asset_count; i++) {
    if (strcmp(wui_assets[i].name, rel) == 0)
      return cst_http_send(c, 200, wui_assets[i].ctype, wui_assets[i].data,
                           wui_assets[i].len);
  }
  return -1;
}

static int h_asset(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  const cst_http_req_t *req = cst_http_request(c);
  /* Stored session images: /api/attach/<rel>. The name is validated before
   * it can touch the filesystem, and only the session's own directory is
   * reachable. */
  static const char prefix[] = "/api/attach/";
  if (strncmp(req->path, prefix, sizeof(prefix) - 1) == 0) {
    const char *rel = req->path + sizeof(prefix) - 1;
    if (!cst_attach_rel_ok(rel))
      return -1;
    const char *sess = cst_agent_session_path(w->agent);
    char dir[OS_PATH_MAX], full[OS_PATH_MAX];
    if (!sess || cst_attach_dir(sess, dir, sizeof(dir)) != 0)
      return -1;
    if (snprintf(full, sizeof(full), "%s/%s", dir, rel) >= (int)sizeof(full))
      return -1;
    char *data = NULL;
    size_t len = 0;
    if (read_file_all(full, &data, &len) != 0)
      return -1;
    const char *ctype = "application/octet-stream";
    size_t n = strlen(rel);
    if (n > 4 && strcmp(rel + n - 4, ".png") == 0)
      ctype = "image/png";
    else if (n > 4 && (strcmp(rel + n - 4, ".jpg") == 0 ||
                       strcmp(rel + n - 4, ".jpeg") == 0))
      ctype = "image/jpeg";
    else if (n > 4 && strcmp(rel + n - 4, ".gif") == 0)
      ctype = "image/gif";
    else if (n > 5 && strcmp(rel + n - 5, ".webp") == 0)
      ctype = "image/webp";
    else if (n > 4 && strcmp(rel + n - 4, ".bmp") == 0)
      ctype = "image/bmp";
    int rc = cst_http_send(c, 200, ctype, data, len);
    free(data);
    return rc;
  }
  return wui_serve_asset(c, w, req->path);
}

/* --- API handlers -------------------------------------------------------- */

static int h_state(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  pthread_mutex_lock(&w->mu);
  cJSON *o = wui_state_new(w);
  pthread_mutex_unlock(&w->mu);
  if (!o)
    return cst_http_send_err(c, 500, "out of memory");
  char *json = cJSON_PrintUnformatted(o);
  cJSON_Delete(o);
  if (!json)
    return cst_http_send_err(c, 500, "out of memory");
  int rc = cst_http_send_json(c, 200, json);
  free(json);
  return rc;
}

static int h_session(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  char buf[32];
  int from = 0;
  if (cst_http_query(cst_http_request(c), "from", buf, sizeof(buf)) == 0)
    from = atoi(buf);
  if (from < 0)
    from = 0;
  char *json = wui_session_json(w, from);
  if (!json)
    return cst_http_send_err(c, 500, "out of memory");
  int rc = cst_http_send_json(c, 200, json);
  free(json);
  return rc;
}

static int h_events(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  const cst_http_req_t *req = cst_http_request(c);
  wui_sse_t s;
  memset(&s, 0, sizeof(s));
  s.w = w;
  s.c = c;
  s.cursor = 0;
  char buf[32];
  if (cst_http_query(req, "since", buf, sizeof(buf)) == 0)
    s.cursor = (uint64_t)strtoull(buf, NULL, 10);
  pthread_mutex_init(&s.mu, NULL);
  pthread_cond_init(&s.cv, NULL);
  pthread_mutex_lock(&w->mu);
  if (s.cursor == 0)
    s.cursor = w->seq; /* a fresh client wants new events only */
  if (s.cursor < wui_first_seq(w) - 1)
    s.cursor = wui_first_seq(w) - 1; /* too far behind: resume at the head */
  s.next = w->subs;
  w->subs = &s;
  pthread_mutex_unlock(&w->mu);

  if (cst_http_stream_begin(c, "text/event-stream; charset=utf-8") != 0) {
    goto done;
  }
  cst_http_stream_write(c, ": cst-agent webui\n\n", 19);
  for (;;) {
    if (cst_http_stopping(w->srv) || w->stopping || s.closed)
      break;
    cst_buf_t out = {0};
    pthread_mutex_lock(&w->mu);
    uint64_t last = w->seq;
    uint64_t first = wui_first_seq(w);
    int n = 0;
    for (uint64_t q = s.cursor + 1; q <= last && n < 256; q++) {
      if (q < first)
        continue;
      char *frame = w->ring[q % WUI_RING].frame;
      if (!frame)
        continue;
      cst_buf_printf(&out, "id: %llu\n%s", (unsigned long long)q, frame);
      n++;
      s.cursor = q;
    }
    pthread_mutex_unlock(&w->mu);
    if (n == 0) {
      struct timespec ts;
      clock_gettime(CLOCK_REALTIME, &ts);
      ts.tv_sec += 1;
      pthread_mutex_lock(&s.mu);
      if (!s.closed)
        pthread_cond_timedwait(&s.cv, &s.mu, &ts);
      pthread_mutex_unlock(&s.mu);
      cst_buf_free(&out);
      if (cst_http_stream_write(c, ": ping\n\n", 8) != 0)
        break;
      continue;
    }
    int rc = cst_http_stream_write(c, out.buf, out.len);
    cst_buf_free(&out);
    if (rc != 0)
      break;
  }
done:
  pthread_mutex_lock(&w->mu);
  wui_sse_t **pp = &w->subs;
  while (*pp && *pp != &s)
    pp = &(*pp)->next;
  if (*pp == &s)
    *pp = s.next;
  pthread_mutex_unlock(&w->mu);
  pthread_mutex_destroy(&s.mu);
  pthread_cond_destroy(&s.cv);
  return 0;
}

typedef struct {
  wui_t *w;
  char *prompt;
} wui_turn_t;

static void wui_end_turn(wui_t *w, int rc, const char *err) {
  /* Flush the markdown *outside* the lock: flushing emits the last HTML
   * chunks, and wui_emit takes w->mu itself. */
  pthread_mutex_lock(&w->mu);
  cst_web_md_t *md = w->md;
  w->md = NULL;
  w->busy = 0;
  pthread_mutex_unlock(&w->mu);
  if (md) {
    cst_web_md_finish(md);
    cst_web_md_free(md);
  }
  cJSON *o = cJSON_CreateObject();
  if (o) {
    cJSON_AddNumberToObject(o, "rc", rc);
    cJSON_AddStringToObject(o, "error", err ? err : "");
    wui_emit(w, "turn_end", o);
  }
  wui_emit_state(w);
}

static void *wui_turn_main(void *arg) {
  wui_turn_t *t = arg;
  wui_t *w = t->w;
  cst_agent_hooks_t hooks;
  memset(&hooks, 0, sizeof(hooks));
  hooks.on_status = on_status;
  hooks.on_assistant_delta = on_assistant_delta;
  hooks.on_think_delta = on_think_delta;
  hooks.on_tool_event = on_tool_event;
  hooks.on_tool_result = on_tool_result;
  hooks.on_permission = on_permission;
  hooks.on_ask_user = on_ask_user;
  hooks.on_todo = on_todo;
  hooks.userdata = w;
  char err[512];
  err[0] = 0;
  int rc = cst_agent_run_turn_ex(w->agent, t->prompt, &hooks, err, sizeof(err));
  wui_end_turn(w, rc, err);
  free(t->prompt);
  free(t);
  return NULL;
}

static int wui_start_turn(wui_t *w, const char *text, char *err, size_t err_sz) {
  pthread_mutex_lock(&w->mu);
  if (w->busy) {
    pthread_mutex_unlock(&w->mu);
    snprintf(err, err_sz, "a turn is already running");
    return -1;
  }
  w->busy = 1;
  if (w->md) {
    cst_web_md_free(w->md);
    w->md = NULL;
  }
  pthread_mutex_unlock(&w->mu);
  wui_turn_t *t = calloc(1, sizeof(*t));
  if (!t) {
    pthread_mutex_lock(&w->mu);
    w->busy = 0;
    pthread_mutex_unlock(&w->mu);
    snprintf(err, err_sz, "out of memory");
    return -1;
  }
  t->w = w;
  t->prompt = strdup(text ? text : "");
  if (!t->prompt) {
    free(t);
    pthread_mutex_lock(&w->mu);
    w->busy = 0;
    pthread_mutex_unlock(&w->mu);
    snprintf(err, err_sz, "out of memory");
    return -1;
  }
  pthread_t th;
  if (pthread_create(&th, NULL, wui_turn_main, t) != 0) {
    free(t->prompt);
    free(t);
    pthread_mutex_lock(&w->mu);
    w->busy = 0;
    pthread_mutex_unlock(&w->mu);
    snprintf(err, err_sz, "cannot start the turn thread");
    return -1;
  }
  pthread_detach(th);
  wui_emit_state(w);
  return 0;
}

static int h_turn(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  const cst_http_req_t *req = cst_http_request(c);
  cJSON *body = req->body_len ? cJSON_Parse(req->body) : NULL;
  const cJSON *text = body ? cJSON_GetObjectItem(body, "text") : NULL;
  if (!body || !cJSON_IsString(text)) {
    cJSON_Delete(body);
    return cst_http_send_err(c, 400, "expected {\"text\": \"...\"}");
  }
  char err[256] = "";
  int rc = wui_start_turn(w, text->valuestring, err, sizeof(err));
  cJSON_Delete(body);
  if (rc != 0)
    return cst_http_send_err(c, 409, err);
  return cst_http_send_str(c, 202, "application/json; charset=utf-8",
                           "{\"ok\":true}");
}

static int h_cancel(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  cst_agent_request_cancel(w->agent);
  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
                           "{\"ok\":true}");
}

static int h_permission(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  const cst_http_req_t *req = cst_http_request(c);
  cJSON *body = req->body_len ? cJSON_Parse(req->body) : NULL;
  const cJSON *id = body ? cJSON_GetObjectItem(body, "id") : NULL;
  const cJSON *ans = body ? cJSON_GetObjectItem(body, "answer") : NULL;
  int ok = 0;
  if (cJSON_IsNumber(id) && cJSON_IsNumber(ans)) {
    int answer = (int)ans->valuedouble;
    if (answer >= CST_PERM_DENY && answer <= CST_PERM_ALWAYS_PREFIX) {
      pthread_mutex_lock(&w->mu);
      if (w->perm_active && w->perm_id == (uint64_t)id->valuedouble) {
        w->perm_answer = answer;
        pthread_cond_broadcast(&w->cv);
        ok = 1;
      }
      pthread_mutex_unlock(&w->mu);
    }
  }
  cJSON_Delete(body);
  if (!ok)
    return cst_http_send_err(c, 409, "no such permission request");
  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
                           "{\"ok\":true}");
}

static int h_ask_user(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  const cst_http_req_t *req = cst_http_request(c);
  cJSON *body = req->body_len ? cJSON_Parse(req->body) : NULL;
  const cJSON *id = body ? cJSON_GetObjectItem(body, "id") : NULL;
  const cJSON *text = body ? cJSON_GetObjectItem(body, "text") : NULL;
  const cJSON *dismissed = body ? cJSON_GetObjectItem(body, "dismiss") : NULL;
  int ok = 0;
  if (cJSON_IsNumber(id)) {
    pthread_mutex_lock(&w->mu);
    if (w->ask_active && w->ask_id == (uint64_t)id->valuedouble) {
      snprintf(w->ask_ans, sizeof(w->ask_ans), "%s",
               cJSON_IsString(text) ? text->valuestring : "");
      w->ask_rc = (dismissed && cJSON_IsTrue(dismissed)) ? -1 : 1;
      pthread_cond_broadcast(&w->cv);
      ok = 1;
    }
    pthread_mutex_unlock(&w->mu);
  }
  cJSON_Delete(body);
  if (!ok)
    return cst_http_send_err(c, 409, "no such question");
  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
                           "{\"ok\":true}");
}

static int h_sessions(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  const cst_agent_config_t *cfg = cst_agent_config(w->agent);
  static char ids[200][128];
  int n = cst_agent_store_list(cfg->workspace_root, ids, 200);
  cJSON *root = cJSON_CreateObject();
  if (!root)
    return cst_http_send_err(c, 500, "out of memory");
  char cur[128] = "";
  cst_agent_store_get_current(cfg->workspace_root, cur, sizeof(cur));
  cJSON_AddStringToObject(root, "current", cur);
  cJSON *arr = cJSON_AddArrayToObject(root, "sessions");
  for (int i = 0; arr && i < n; i++) {
    cst_session_info_t in;
    if (cst_agent_store_info(cfg->workspace_root, ids[i], &in) != 0)
      continue;
    cJSON *o = cJSON_CreateObject();
    if (!o)
      continue;
    cJSON_AddStringToObject(o, "id", in.id);
    cJSON_AddStringToObject(o, "title",
                            in.title[0] ? in.title : in.first_user);
    cJSON_AddNumberToObject(o, "messages", in.messages);
    cJSON_AddNumberToObject(o, "mtime", (double)in.mtime);
    cJSON_AddItemToArray(arr, o);
  }
  char *json = cJSON_PrintUnformatted(root);
  cJSON_Delete(root);
  int rc = cst_http_send_json(c, 200, json);
  free(json);
  return rc;
}

static int h_session_new(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  char id[128] = "";
  if (cst_agent_new_session(w->agent, id, sizeof(id)) != 0)
    return cst_http_send_err(c, 500, "cannot start a session");
  wui_emit_str(w, "session", "id", id);
  wui_emit_state(w);
  cJSON *o = cJSON_CreateObject();
  if (!o)
    return cst_http_send_err(c, 500, "out of memory");
  cJSON_AddStringToObject(o, "id", id);
  char *json = cJSON_PrintUnformatted(o);
  cJSON_Delete(o);
  int rc = cst_http_send_json(c, 200, json);
  free(json);
  return rc;
}

/* POST /api/workspace {"path":"/abs/dir"} - re-root the agent. The session
 * store is per directory, so this always lands in a fresh session there. */
static int h_workspace(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  const cst_http_req_t *req = cst_http_request(c);
  cJSON *j = req->body_len ? cJSON_Parse(req->body) : NULL;
  const cJSON *p = j ? cJSON_GetObjectItem(j, "path") : NULL;
  if (!cJSON_IsString(p) || !p->valuestring[0]) {
    cJSON_Delete(j);
    return cst_http_send_err(c, 400, "path is required");
  }
  char err[256] = "";
  int rc = cst_agent_set_workspace(w->agent, p->valuestring, err, sizeof(err));
  cJSON_Delete(j);
  if (rc != 0)
    return cst_http_send_err(c, 400, err[0] ? err : "cannot switch workspace");
  char id[128] = "";
  if (cst_agent_new_session(w->agent, id, sizeof(id)) != 0)
    return cst_http_send_err(c, 500, "cannot start a session there");
  wui_emit_str(w, "session", "id", id);
  wui_emit_state(w);
  cJSON *o = cJSON_CreateObject();
  if (!o)
    return cst_http_send_err(c, 500, "out of memory");
  cJSON_AddStringToObject(o, "id", id);
  char *json = cJSON_PrintUnformatted(o);
  cJSON_Delete(o);
  rc = cst_http_send_json(c, 200, json);
  free(json);
  return rc;
}

static int h_session_switch(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  const cst_http_req_t *req = cst_http_request(c);
  cJSON *j = req->body_len ? cJSON_Parse(req->body) : NULL;
  const cJSON *id = j ? cJSON_GetObjectItem(j, "id") : NULL;
  int rc = -2;
  if (cJSON_IsString(id))
    rc = cst_agent_switch_session(w->agent, id->valuestring);
  cJSON_Delete(j);
  if (rc != 0)
    return cst_http_send_err(c, 404, "no such session");
  wui_emit_state(w);
  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
                           "{\"ok\":true}");
}

static int h_config(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  cst_agent_config_t *cfg = cst_agent_config_mut(w->agent);
  const cst_http_req_t *req = cst_http_request(c);
  cJSON *j = req->body_len ? cJSON_Parse(req->body) : NULL;
  if (!j || !cfg) {
    cJSON_Delete(j);
    return cst_http_send_err(c, 400, "expected a JSON object");
  }
  const cJSON *item;
  if ((item = cJSON_GetObjectItem(j, "model")) && cJSON_IsString(item))
    snprintf(cfg->model, sizeof(cfg->model), "%s", item->valuestring);
  if ((item = cJSON_GetObjectItem(j, "provider")) && cJSON_IsString(item))
    snprintf(cfg->provider, sizeof(cfg->provider), "%s", item->valuestring);
  if ((item = cJSON_GetObjectItem(j, "effort")) && cJSON_IsString(item) &&
      cst_effort_valid(item->valuestring))
    snprintf(cfg->effort, sizeof(cfg->effort), "%s", item->valuestring);
  if ((item = cJSON_GetObjectItem(j, "approval")) && cJSON_IsString(item)) {
    int a = 0;
    if (cst_approval_parse(item->valuestring, &a) == 0) {
      cfg->approval = a;
      cfg->auto_approve = a == CST_APPROVAL_YOLO;
    }
  }
  if ((item = cJSON_GetObjectItem(j, "plan_mode")) && cJSON_IsBool(item)) {
    cfg->plan_mode = cJSON_IsTrue(item) ? 1 : 0;
    cfg->read_only = cfg->plan_mode;
  }
  cJSON_Delete(j);
  wui_emit_state(w);
  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
                           "{\"ok\":true}");
}

static int h_undo(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  char report[2048] = "";
  if (cst_agent_undo(w->agent, report, sizeof(report)) != 0)
    return cst_http_send_err(c, 409, "nothing to undo");
  wui_emit_str(w, "status", "message", report);
  wui_emit_state(w);
  return cst_http_send_str(c, 200, "text/plain; charset=utf-8", report);
}

static int h_compact(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  char err[256] = "";
  if (cst_agent_compact(w->agent, err, sizeof(err)) != 0)
    return cst_http_send_err(c, 500, err);
  wui_emit_state(w);
  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
                           "{\"ok\":true}");
}

static int h_attach_upload(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  const cst_http_req_t *req = cst_http_request(c);
  char name[256] = "pasted.png";
  cst_http_query(req, "name", name, sizeof(name));
  if (req->body_len == 0)
    return cst_http_send_err(c, 400, "empty body");
  char err[256] = "";
  if (cst_agent_attach_bytes(w->agent, name, req->body, req->body_len, err,
                             sizeof(err)) != 0)
    return cst_http_send_err(c, 400, err[0] ? err : "cannot attach the image");
  wui_emit_state(w);
  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
                           "{\"ok\":true}");
}

static int h_attach_clear(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  cst_agent_pending_clear(w->agent);
  wui_emit_state(w);
  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
                           "{\"ok\":true}");
}

static int h_quit(cst_http_conn_t *c, void *ud) {
  wui_t *w = ud;
  w->stopping = 1;
  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
                           "{\"ok\":true}");
}

/* --- auth ---------------------------------------------------------------- */

static int token_matches(const wui_t *w, const char *given) {
  if (!given || !w->token[0])
    return 0;
  size_t a = strlen(given), b = strlen(w->token);
  if (a != b)
    return 0;
  unsigned diff = 0;
  for (size_t i = 0; i < a; i++)
    diff |= (unsigned char)given[i] ^ (unsigned char)w->token[i];
  return diff == 0;
}

static int cookie_token(const char *cookie, char *out, size_t out_sz) {
  const char *p = cookie;
  while (p && *p) {
    while (*p == ' ' || *p == ';')
      p++;
    if (strncmp(p, "cst_token=", 10) == 0) {
      const char *v = p + 10;
      const char *end = strchr(v, ';');
      size_t n = end ? (size_t)(end - v) : strlen(v);
      if (n >= out_sz)
        n = out_sz - 1;
      memcpy(out, v, n);
      out[n] = 0;
      return 0;
    }
    p = strchr(p, ';');
  }
  return -1;
}

/* Host header must name this machine's loopback when no token is required:
 * a DNS-rebinding page would send its own name here. */
static int host_is_loopback(const char *host) {
  if (!host || !host[0])
    return 0;
  while (*host == ' ')
    host++;
  if (strncmp(host, "127.0.0.1", 9) == 0) {
    char next = host[9];
    return next == 0 || next == ':';
  }
  if (strncmp(host, "localhost", 9) == 0) {
    char next = host[9];
    return next == 0 || next == ':';
  }
  if (strncmp(host, "[::1]", 5) == 0) {
    char next = host[5];
    return next == 0 || next == ':';
  }
  return 0;
}

static int wui_auth(const cst_http_req_t *req, void *ud) {
  wui_t *w = ud;
  if (!w->need_auth)
    return host_is_loopback(req->host) ? 0 : -1;
  char buf[128];
  if (req->authorization && strncmp(req->authorization, "Bearer ", 7) == 0 &&
      token_matches(w, req->authorization + 7))
    return 0;
  if (req->cookie && cookie_token(req->cookie, buf, sizeof(buf)) == 0 &&
      token_matches(w, buf))
    return 0;
  if (cst_http_query(req, "token", buf, sizeof(buf)) == 0 &&
      token_matches(w, buf))
    return 0;
  return -1;
}

/* --- startup ------------------------------------------------------------- */

static volatile sig_atomic_t g_webui_stop;

static void webui_on_signal(int sig) {
  (void)sig;
  g_webui_stop = 1;
}

static void wui_make_token(char *out, size_t out_sz) {
  unsigned char raw[16];
  size_t got = 0;
  FILE *fp = fopen("/dev/urandom", "rb");
  if (fp) {
    got = fread(raw, 1, sizeof(raw), fp);
    fclose(fp);
  }
  if (got != sizeof(raw)) {
    unsigned seed = (unsigned)(os_now_ms() * 1000.0) ^ (unsigned)os_getpid();
    for (size_t i = 0; i < sizeof(raw); i++) {
      seed = seed * 1103515245u + 12345u;
      raw[i] = (unsigned char)(seed >> 16);
    }
  }
  static const char hex[] = "0123456789abcdef";
  size_t o = 0;
  for (size_t i = 0; i < sizeof(raw) && o + 2 < out_sz; i++) {
    out[o++] = hex[raw[i] >> 4];
    out[o++] = hex[raw[i] & 15];
  }
  out[o] = 0;
}

static void open_browser(const char *url) {
#if defined(_WIN32)
  char cmd[600];
  snprintf(cmd, sizeof(cmd), "start \"\" \"%s\"", url);
  os_run_shell_c(".", cmd, 0, NULL);
#elif defined(__APPLE__)
  char cmd[600];
  snprintf(cmd, sizeof(cmd), "open '%s'", url);
  os_run_shell_c(".", cmd, 0, NULL);
#else
  char cmd[600];
  /* Termux has no xdg-open; termux-open-url hands the URL to Android. */
  const char *opener =
      getenv("TERMUX_VERSION") ? "termux-open-url" : "xdg-open";
  snprintf(cmd, sizeof(cmd), "%s '%s' >/dev/null 2>&1 &", opener, url);
  os_run_shell_c(".", cmd, 0, NULL);
#endif
  (void)url;
}

int cst_webui_run(cst_agent_t *agent, const cst_webui_opts_t *opts) {
  cst_webui_opts_t def;
  if (!opts) {
    memset(&def, 0, sizeof(def));
    opts = &def;
  }
  wui_t *w = calloc(1, sizeof(*w));
  if (!w)
    return 1;
  pthread_mutex_init(&w->mu, NULL);
  w->agent = agent;
  w->perm_timeout_s = opts->perm_timeout_s;
  w->root = opts->root;
  pthread_cond_init(&w->cv, NULL);
  snprintf(w->host, sizeof(w->host), "%s",
           opts->host && opts->host[0] ? opts->host : "127.0.0.1");
  if (opts->token && opts->token[0]) {
    snprintf(w->token, sizeof(w->token), "%s", opts->token);
    w->need_auth = 1;
  } else if (strcmp(w->host, "127.0.0.1") != 0 &&
             strcmp(w->host, "localhost") != 0 && strcmp(w->host, "::1") != 0) {
    wui_make_token(w->token, sizeof(w->token));
    w->need_auth = 1;
  }

  static cst_http_route_t routes[] = {
      {"GET", "/", h_asset, NULL, 0, 0},
      {"GET", "/api/state", h_state, NULL, 0, 0},
      {"GET", "/api/session", h_session, NULL, 0, 0},
      {"GET", "/api/events", h_events, NULL, 0, 0},
      {"GET", "/api/sessions", h_sessions, NULL, 0, 0},
      {"POST", "/api/sessions/new", h_session_new, NULL, 0, 0},
      {"POST", "/api/sessions/switch", h_session_switch, NULL, 0, 0},
      {"POST", "/api/workspace", h_workspace, NULL, 0, 0},
      {"POST", "/api/turn", h_turn, NULL, 0, 0},
      {"POST", "/api/cancel", h_cancel, NULL, 0, 0},
      {"POST", "/api/permission", h_permission, NULL, 0, 0},
      {"POST", "/api/ask_user", h_ask_user, NULL, 0, 0},
      {"POST", "/api/config", h_config, NULL, 0, 0},
      {"POST", "/api/undo", h_undo, NULL, 0, 0},
      {"POST", "/api/compact", h_compact, NULL, 0, 0},
      {"POST", "/api/attach", h_attach_upload, NULL, 0, 32u * 1024u * 1024u},
      {"DELETE", "/api/attach", h_attach_clear, NULL, 0, 0},
      {"POST", "/api/quit", h_quit, NULL, 0, 0},
      {"GET", "*", h_asset, NULL, 0, 0},
  };
  for (size_t i = 0; i < sizeof(routes) / sizeof(routes[0]); i++) {
    routes[i].ud = w;
    routes[i].auth = w->need_auth || strcmp(routes[i].path, "/") != 0;
  }
  routes[0].auth = 0;  /* the shell page itself sets the cookie */
  routes[sizeof(routes) / sizeof(routes[0]) - 1].auth = w->need_auth;

  cst_http_opts_t ho;
  memset(&ho, 0, sizeof(ho));
  ho.host = w->host;
  ho.port = opts->port;
  ho.max_body = 1024 * 1024;
  ho.max_conn = 32;
  ho.routes = routes;
  ho.nroutes = (int)(sizeof(routes) / sizeof(routes[0]));
  ho.auth = wui_auth;
  ho.auth_ud = w;
  char err[256] = "";
  w->srv = cst_http_start(&ho, err, sizeof(err));
  if (!w->srv) {
    fprintf(stderr, "webui: cannot listen on %s:%d: %s\n", w->host,
            opts->port, err);
    pthread_cond_destroy(&w->cv);
    pthread_mutex_destroy(&w->mu);
    free(w);
    return 1;
  }
  char url[256];
  snprintf(url, sizeof(url), "http://%s:%d/%s", strcmp(w->host, "0.0.0.0") == 0
                                                   ? "127.0.0.1"
                                                   : w->host,
           cst_http_port(w->srv),
           w->need_auth ? "" : "");
  fprintf(stderr, "webui: %s\n", url);
  if (w->need_auth)
    fprintf(stderr, "webui: token %s  (append #token=%s to the URL)\n", w->token,
            w->token);
  fflush(stderr);
  wui_emit_state(w);
  if (opts->open_browser)
    open_browser(url);

  if (opts->prompt && opts->prompt[0]) {
    char err2[256] = "";
    if (wui_start_turn(w, opts->prompt, err2, sizeof(err2)) != 0)
      fprintf(stderr, "webui: %s\n", err2);
  }

  /* Serve until Ctrl+C, /api/quit or a signal. */
  signal(SIGINT, webui_on_signal);
  signal(SIGTERM, webui_on_signal);
  while (!w->stopping && !g_webui_stop) {
    struct timespec ts;
    ts.tv_sec = 0;
    ts.tv_nsec = 200 * 1000 * 1000;
    nanosleep(&ts, NULL);
  }
  fprintf(stderr, "webui: shutting down\n");
  w->stopping = 1;
  cst_http_stop(w->srv);
  cst_http_free(w->srv);
  for (int i = 0; i < WUI_RING; i++)
    free(w->ring[i].frame);
  if (w->md)
    cst_web_md_free(w->md);
  pthread_cond_destroy(&w->cv);
  pthread_mutex_destroy(&w->mu);
  free(w);
  return 0;
}