ESP32 Web PWM Brightness Slider

#include <Arduino.h>
#include <WiFi.h>
#include <WebServer.h>

WebServer server(80);
const char* AP_PASSWORD = "CHANGE_ME_1234"; // Replace with your own 8-63 character password.
bool httpReady = false;

void redirectHome() {
  server.sendHeader("Location", "/");
  server.send(303, "text/plain", "Open the control page\n");
}
String pageStart(const char* title) {
  String page = "<!doctype html><html lang='en'><head>";
  page += "<meta name='viewport' content='width=device-width,initial-scale=1'>";
  page += "<style>body{font:1.1rem system-ui;max-width:40rem;margin:2rem auto;padding:1rem}button,input{font:inherit;margin:.5rem 0}input[type=range]{width:100%}</style>";
  page += "<title>"; page += title; page += "</title></head><body><h1>";
  page += title; page += "</h1>";
  return page;
}
void sendPage(const String& page) {
  server.sendHeader("Cache-Control", "no-store");
  server.send(200, "text/html; charset=utf-8", page + "</body></html>");
}
bool parseUnsigned(const String& text, uint16_t minimum, uint16_t maximum, uint16_t& value) {
  if (text.length() == 0 || text.length() > 4) return false;
  uint32_t n = 0;
  for (size_t i = 0; i < text.length(); ++i) {
    char c = text[i];
    if (c < '0' || c > '9') return false;
    n = n * 10 + (c - '0');
  }
  if (n < minimum || n > maximum) return false;
  value = uint16_t(n); return true;
}
void startHTTP(const char* name) {
  server.onNotFound([]() { server.send(404, "text/plain", "No such route\n"); });
  if (!WiFi.mode(WIFI_AP) || !WiFi.softAP(name, AP_PASSWORD, 6, false, 1)) {
    Serial.println("AP failed; output stays off. Check board and password length.");
    return;
  }
  server.begin(); httpReady = true;
  Serial.print("Join "); Serial.println(name);
  Serial.print("Open http://"); Serial.println(WiFi.softAPIP());
}

constexpr uint8_t LED_PIN = 25, RESOLUTION = 8;
constexpr uint32_t FREQUENCY_HZ = 5000, COMMAND_LIFETIME_MS = 30000;
bool pwmReady = false;
uint16_t duty = 0;
uint32_t lastCommand = 0;

void stopOnFault() {
  if (pwmReady) { ledcWrite(LED_PIN, 0); ledcDetach(LED_PIN); }
  pwmReady = false; duty = 0;
  pinMode(LED_PIN, OUTPUT); digitalWrite(LED_PIN, LOW);
  Serial.println("PWM failure; reset after diagnosis");
}
bool applyDuty(uint16_t next) {
  if (!pwmReady || !ledcWrite(LED_PIN, next)) { stopOnFault(); return false; }
  duty = next; return true;
}
void showPage() {
  String page = pageStart("ESP32 PWM slider");
  page += String("<p>Last accepted duty: ") + duty + " / 255. Driver: ";
  page += pwmReady ? "ready.</p>" : "fault; check Serial and reset.</p>";
  page += "<form method='post' action='/brightness'><label for='duty'>LED duty 0 to 255</label>";
  page += "<input id='duty' name='duty' type='range' min='0' max='255' step='1' value='";
  page += String(duty) + "'><button type='submit'>Apply brightness</button></form>";
  page += "<p>Moving the slider alone sends nothing. Press Apply; nonzero duty expires after 30 seconds. Refresh to read software state.</p>";
  sendPage(page);
}
void setup() {
  Serial.begin(115200);
  pinMode(LED_PIN, OUTPUT); digitalWrite(LED_PIN, LOW);
  pwmReady = ledcAttach(LED_PIN, FREQUENCY_HZ, RESOLUTION);
  if (!pwmReady || !ledcWrite(LED_PIN, 0)) stopOnFault();
  server.on("/", HTTP_GET, showPage);
  server.on("/brightness", HTTP_POST, []() {
    uint16_t next = 0;
    if (server.args() != 1 || !server.hasArg("duty") ||
        !parseUnsigned(server.arg("duty"), 0, 255, next)) {
      server.send(400, "text/plain", "Exactly one integer duty, 0 through 255, is required\n"); return;
    }
    if (!pwmReady || !applyDuty(next)) {
      server.send(503, "text/plain", "PWM unavailable; diagnose and reset\n"); return;
    }
    lastCommand = millis();
    Serial.printf("Accepted duty %u / 255\n", unsigned(duty));
    redirectHome();
  });
  startHTTP("ESP32-WebPWM");
}
void loop() {
  if (httpReady) server.handleClient();
  if (pwmReady && duty != 0 && millis() - lastCommand >= COMMAND_LIFETIME_MS) {
    if (applyDuty(0)) Serial.println("Command expired: duty 0");
  }
  delay(1);
}