// Copyright (c) 2020 Cesanta Software Limited
// All rights reserved

#include "mjson.h"  // JSON parsing and printing
#include "mongoose.h"

// This is a configuration structure we're going to show on a dashboard
static struct config {
  int value1;
  char *value2;
} s_config = {123, NULL};

// Stringifies the config. A caller must free() it.
static char *stringify_config(struct config *cfg) {
  char *s = NULL;
  mjson_printf(mjson_print_dynamic_buf, &s, "{%Q:%d,%Q:%Q}", "value1",
               cfg->value1, "value2", cfg->value2);
  return s;
}

// Update config structure. Return true if changed, false otherwise
static bool update_config(struct mg_http_message *hm, struct config *cfg) {
  bool changed = false;
  char buf[256];
  double dv;
  if (mjson_get_number(hm->body.ptr, hm->body.len, "$.value1", &dv)) {
    s_config.value1 = dv;
    changed = true;
  }
  if (mjson_get_string(hm->body.ptr, hm->body.len, "$.value2", buf,
                       sizeof(buf)) > 0) {
    free(s_config.value2);
    s_config.value2 = strdup(buf);
    changed = true;
  }
  return changed;
}

// Notify all config watchers about the config change
static void notify_config_change(struct mg_mgr *mgr) {
  struct mg_connection *c;
  char *s = stringify_config(&s_config);
  for (c = mgr->conns; c != NULL; c = c->next) {
    if (c->label[0] == 'W') mg_http_printf_chunk(c, "%s\n", s);
  }
  free(s);
}

// HTTP request handler function. It implements the following endpoints:
//   /api/config/get - returns current config
//   /api/config/set - updates current config
//   /api/config/watch - does not return. Sends config as it changes in
//   chunks all other URI - serves web_root/ directory
static void cb(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
  if (ev == MG_EV_HTTP_MSG) {
    struct mg_http_message *hm = (struct mg_http_message *) ev_data;
    if (mg_http_match_uri(hm, "/api/config/get")) {
      char *s = stringify_config(&s_config);
      mg_printf(c, "HTTP/1.1 200 OK\r\nContent-Length: %d\r\n\r\n%s\n",
                (int) strlen(s) + 1, s);
      free(s);
    } else if (mg_http_match_uri(hm, "/api/config/set")) {
      if (update_config(hm, &s_config)) notify_config_change(fn_data);
      mg_printf(c, "HTTP/1.1 200 OK\r\nContent-Length: 0\r\n\r\n");
    } else if (mg_http_match_uri(hm, "/api/config/watch")) {
      c->label[0] = 'W';  // Mark ourselves as a config watcher
      mg_printf(c, "HTTP/1.1 200 OK\r\nTransfer-Encoding: chunked\r\n\r\n");
    } else {
      struct mg_http_serve_opts opts = {.root_dir = "web_root"};
      mg_http_serve_dir(c, ev_data, &opts);
    }
  }
}

int main(void) {
  struct mg_mgr mgr;
  mg_mgr_init(&mgr);
  mg_http_listen(&mgr, "http://localhost:8000", cb, &mgr);
  for (;;) mg_mgr_poll(&mgr, 1000);
  mg_mgr_free(&mgr);
  return 0;
}