(* === DECLARATION === *)
FUNCTION_BLOCK fb_boiler
VAR_INPUT
    // Control Commands
    ha_on: BOOL;              // Home Assistant ON command
    ha_off: BOOL;             // Home Assistant OFF command
    schedule_on: BOOL;        // Scheduled ON
    schedule_off: BOOL;       // Scheduled OFF
    
    // Safety
    emergency_stop: BOOL;     // Emergency stop input
    
    // Configuration
    max_on_time: TIME := T#8H; // Maximum ON time (default 8 hours)
END_VAR
VAR_OUTPUT
    // Outputs
    relay_control: BOOL;      // Control output to relay
    
    // Status
    state: BOOL;              // Current state
    on_time_seconds: DINT;    // Current ON time in seconds
    remaining_seconds: DINT;  // Remaining time in seconds
    
    // Safety Status
    emergency_active: BOOL;   // Emergency stop active
    time_limit_reached: BOOL; // Time limit was reached
    error_state: BOOL;        // Error flag
    error_code: INT;          // Error code
END_VAR
VAR
    // Internal State
    internal_state: BOOL := FALSE;
    last_state: BOOL := FALSE;
    
    // Edge Detection
    r_trig_ha_on: R_TRIG;
    r_trig_ha_off: R_TRIG;
    r_trig_schedule_on: R_TRIG;
    r_trig_schedule_off: R_TRIG;
    r_trig_emergency: R_TRIG;
    f_trig_emergency: F_TRIG;
    
    // Timers
    on_timer: TON;            // Counts ON time
    
    // Time tracking
    max_on_seconds: DINT;
END_VAR

(* === IMPLEMENTATION === *)
// =====================================================
// fb_boiler - Implementation
// =====================================================
// Priority (highest to lowest):
// 1. Emergency Stop       - Immediate shutdown
// 2. Time Limit Exceeded  - Auto shutdown
// 3. OFF Commands         - Turn off
// 4. ON Commands          - Turn on (if safe)
// =====================================================

// Calculate max time in seconds
max_on_seconds := TIME_TO_DINT(max_on_time) / 1000;

// Edge detection for commands
r_trig_ha_on(CLK := ha_on);
r_trig_ha_off(CLK := ha_off);
r_trig_schedule_on(CLK := schedule_on);
r_trig_schedule_off(CLK := schedule_off);
r_trig_emergency(CLK := emergency_stop);
f_trig_emergency(CLK := emergency_stop);

// =====================================================
// SAFETY CHECKS (highest priority)
// =====================================================

// Priority 1: Emergency Stop
IF emergency_stop THEN
    internal_state := FALSE;
    emergency_active := TRUE;
    error_state := TRUE;
    error_code := 1;  // Emergency stop active
    
// Priority 2: Time Limit Check
ELSIF on_timer.Q THEN
    internal_state := FALSE;
    time_limit_reached := TRUE;
    error_state := TRUE;
    error_code := 2;  // Time limit exceeded

// =====================================================
// CONTROL LOGIC (only when safe)
// =====================================================
ELSE
    // Clear safety flags when emergency released
    IF f_trig_emergency.Q THEN
        emergency_active := FALSE;
        error_state := FALSE;
        error_code := 0;
    END_IF;
    
    // Clear time limit flag when boiler turned off
    IF NOT internal_state THEN
        time_limit_reached := FALSE;
        IF error_code = 2 THEN
            error_state := FALSE;
            error_code := 0;
        END_IF;
    END_IF;
    
    // Priority 3: OFF Commands (HA OFF or Schedule OFF)
    IF r_trig_ha_off.Q OR r_trig_schedule_off.Q THEN
        internal_state := FALSE;
        
    // Priority 4: ON Commands (HA ON or Schedule ON)
    ELSIF (r_trig_ha_on.Q OR r_trig_schedule_on.Q) AND NOT time_limit_reached THEN
        internal_state := TRUE;
    END_IF;
END_IF;

// =====================================================
// TIMER MANAGEMENT
// =====================================================

// ON timer - counts total ON time
on_timer(
    IN := internal_state AND NOT emergency_active,
    PT := max_on_time
);

// Calculate current ON time in seconds
IF internal_state THEN
    on_time_seconds := TIME_TO_DINT(on_timer.ET) / 1000;
    remaining_seconds := max_on_seconds - on_time_seconds;
    IF remaining_seconds < 0 THEN
        remaining_seconds := 0;
    END_IF;
ELSE
    on_time_seconds := 0;
    remaining_seconds := max_on_seconds;
END_IF;

// =====================================================
// OUTPUT ASSIGNMENT
// =====================================================

// Relay control - only ON when state is ON and no emergency
relay_control := internal_state AND NOT emergency_active;

// State output
state := internal_state;