/*
 * ATtiny85 Fan Controller
 * 
 * Target: ATtiny85 @ 8MHz
 * 
 * Schematic:
 *              ATtiny85
 *             +---v---+
 *       RST  1|       |8  VCC
 *     (NC)   2|       |7  PB2 (POT - Target Temp)
 *     (NC)   3|       |6  PB1 (PWM - Fan Ctrl)
 *       GND  4|       |5  PB0 (DS18B20 Data)
 *             +-------+
 */
#include <Arduino.h>
#include <OneWire.h>
#include <DallasTemperature.h>

// --- Pin Definitions ---
// PB1 (MISO/DO/OC1A) - PWM Output
// PB2 (ADC1/SCK/USCK/SCL) - Potentiometer Input
// PB0 (MOSI/DI/SDA) - DS18B20 Data Line
#define PIN_PWM  1 // PB1
#define PIN_POT  A1 // PB2 is Analog Input 1
#define PIN_ONE_WIRE 0 // PB0

// --- Constants ---
#define PWM_TOP 159 // For 25kHz with Prescaler 2 (8MHz / 2 / (159+1) = 25kHz)

// --- Globals ---
OneWire oneWire(PIN_ONE_WIRE);
DallasTemperature sensors(&oneWire);

// Temperature Curve
// We will define a simple curve:
// Below MIN_TEMP -> Min Duty
// Above MAX_TEMP -> Max Duty
// In between -> Linear
const float MIN_TEMP = 25.0; // Start ramping up here
const float MAX_TEMP = 50.0; // Full speed here
const uint8_t MIN_DUTY = 32; // ~20% duty cycle (32/159) - Fan start
const uint8_t MAX_DUTY = 159; // 100% duty cycle
const float CONTROL_BAND = 10.0; // 10 degrees band, in this band around target temp the fan speed is linearly interpolated

// Potentiometer Mapping Constants
const int POT_MIN_TEMP = 20; // 0 on ADC maps to this temp
const int POT_MAX_TEMP = 60; // 1023 on ADC maps to this temp

void setupPWM() {
    // Configure Timer1 for PWM on PB1 (OC1A)
    // We want ~25kHz. 
    // System Clock = 8MHz.
    // Timer1 is 8-bit.
    // Prescaler = 2 -> Timer Clock = 4MHz.
    // OCR1C (Top) = 159 -> Freq = 4MHz / 160 = 25kHz.
    
    // Clear Timer on Compare Match (CTC) mode is not exactly what we want for PWM
    // typically. We want Pulse Width Modulator A Enable (PWM1A).
    
    // TCCR1: 
    // CTC1 = 0
    // PWM1A = 1 (Enable PWM A)
    // COM1A1:0 = 10 (Clear OC1A on Compare Match, Set on 0x00) -> Non-Inverted PWM
    // CS13:10 = 0010 (Prescaler = 2)
    
    TCCR1 = 0;
    TCCR1 |= (1 << PWM1A) | (1 << COM1A1) | (1 << CS11);
    
    // OCR1C sets the TOP value (Frequency)
    OCR1C = PWM_TOP;
    
    // Initial Duty Cycle 0
    OCR1A = 0;
    
    // Set PB1 as Output
    pinMode(PIN_PWM, OUTPUT);
}

void setup() {
    setupPWM();
    
    // Initialize Sensors
    sensors.begin();
    
    // Initialize Potentiometer Pin
    pinMode(PIN_POT, INPUT); // Not strictly necessary for AnalogRead but good practice
}

void loop() {
    
    // the Pot maps to a target temperature range
    int potValue = analogRead(PIN_POT);
    float targetTemp = map(potValue, 0, 1023, POT_MIN_TEMP, POT_MAX_TEMP);
    
    // Read Current Temp
    sensors.requestTemperatures(); 
    float currentTemp = sensors.getTempCByIndex(0);
    
    // Handle error reading
    if (currentTemp == DEVICE_DISCONNECTED_C) {
        // Safe fail: Full speed
        OCR1A = MAX_DUTY;
        delay(1000);
        return;
    }
    
    // If current < target -> Min Speed (or Off)
    // If current > target + band -> Max Speed
    // Linear in betwen
    
    int newDuty = 0;
    
    if (currentTemp < targetTemp) {
        newDuty = MIN_DUTY; // Keep it running at min speed or 0? 
        // Let's say Min Speed to keep airflow.
    } else if (currentTemp >= targetTemp + CONTROL_BAND) {
        newDuty = MAX_DUTY;
    } else {
        // Interpolate
        // Fraction = (Temp - Target) / Band
        float fraction = (currentTemp - targetTemp) / CONTROL_BAND;
        newDuty = MIN_DUTY + (int)(fraction * (MAX_DUTY - MIN_DUTY));
    }
    
    // Constrain safely
    if (newDuty > MAX_DUTY) newDuty = MAX_DUTY;
    if (newDuty < 0) newDuty = 0; // Should not happen with unsigned logic but...
    
    // Write PWM
    OCR1A = newDuty;
    
    delay(500); // 2Hz update rate
}