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assignment03/SYSC3303_A03_W26_Starting_code/README.txt

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+================================================================================
+PELICAN CROSSING STATE MACHINE - README
+================================================================================
+PROJECT OVERVIEW
+================================================================================
+Project: Pelican Pedestrian Crossing Controller - Finite State Machine
+Language: Java 8+
+Design Pattern: Enum + Switch-Based State Machine
+Implementation: PelicanCrossing.java
+Test Harness: PelicanCrossingPublicTest.java
+
+This implementation models a traffic light controller that safely manages the
+intersection between vehicle traffic and pedestrian crossing using a finite
+state machine with event-driven behaviour.
+
+SOURCE FILES
+================================================================================
+Primary Implementation: PelicanCrossing.java - Complete FSM implementation
+Required for Testing: PelicanCrossingPublicTest.java - Provided test harness
+
+DESIGN APPROACH
+================================================================================
+This solution uses the Enum + Switch-Based approach (allowed alternative to
+State Pattern). This design was chosen because:
+    1. Fixed State Set: The crossing has exactly eight states that never change
+    2. Simple Logic: Each state behaviour is straightforward (update timers/signals)
+    3. Performance: Direct switch dispatch is fast and lightweight
+    4. Clarity: Easy to understand the complete flow in one place
+    5. Embedded Fit: Suitable for embedded systems with resource constraints
+The architecture:
+  • Single State variable (the provided State enum)
+  • Constructor initializes automatically
+  • dispatch(Event) routes via switch on current state
+  • Private handler method per state processes events
+  • Each handler directly updates state and signals
+
+COMPILATION & EXECUTION
+================================================================================
+Compile:
+  $ javac PelicanCrossing.java
+  Expected: No errors or warnings
+Run Manual Test:
+  PelicanCrossing fsm = new PelicanCrossing();
+  System.out.println(fsm.getState());       // OPERATIONAL_CARS_GREEN_NO_PED
+  System.out.println(fsm.getCarSignal());   // GREEN
+  System.out.println(fsm.getPedSignal());   // DONT_WALK_ON
+Run Provided Test Harness:
+  $ javac -cp junit-jupiter-api-5.x.x.jar \
+      PelicanCrossing.java PelicanCrossingPublicTest.java
+  $ java -cp junit-platform-console-standalone-1.x.x.jar \
+      org.junit.platform.console.ConsoleLauncher --scan-classpath
+  Expected Results:
+      init_entersOperationalCarsGreenNoPed PASSED
+      pedsWaiting_beforeMinGreen_remembersWaitingButStaysInCarsGreen PASSED
+      pedWaiting_duringMinGreen_thenAutoYellow_whenMinGreenEnds PASSED
+      walkTimesOut_thenFlash PASSED
+      offlineMode_offFromAnyOperationalState_setsSafeAndFlashes PASSED
+
+IMPLEMENTATION DETAILS
+================================================================================
+State Variable: Single State enum (provided in starter code)
+  • Tracks current leaf state
+  • Updated directly by dispatch handlers
+  • Returned by getState() for test harness
+Signal Variables: CarSignal and PedSignal enums
+  • Updated as state enters or transitions
+  • Maintained by dispatch handlers
+  • Accessible via getCarSignal() and getPedSignal()
+Private Timers:
+  • greenTimer: Countdown for minimum green phase
+  • yellowTimer: Countdown for yellow phase
+  • walkTimer: Countdown for pedestrian walk phase
+  • flashCounter: Counter for pedestrian flashing
+Private Flags:
+  • pedsWaiting: Boolean flag for pedestrian button pressed
+Constructor: Calls dispatch(Event.INIT) to initialize FSM
+Dispatch: Routes to handler method based on current state
+Handlers: 8 private methods (one per state), each processing events for that state
+
+STATE MACHINE BEHAVIOR
+================================================================================
+HIGH-LEVEL FLOW:
+  Operational Mode (Normal Operation):
+    ├─ Vehicles Enabled Phase
+    │  ├─ OPERATIONAL_CARS_GREEN_NO_PED: Green for cars, no pedestrians waiting
+    │  ├─ OPERATIONAL_CARS_GREEN_PED_WAIT: Green for cars, pedestrians waiting
+    │  └─ OPERATIONAL_CARS_GREEN_INT: Interruptible green (waiting for ped)
+    ├─ Yellow Transition
+    │  └─ OPERATIONAL_CARS_YELLOW: 2-tick yellow transition
+    └─ Pedestrians Enabled Phase
+       ├─ OPERATIONAL_PEDS_WALK: 3-tick walk phase
+       └─ OPERATIONAL_PEDS_FLASH: 6-tick flashing "Don't Walk"
+  Offline Mode (Safety/Maintenance):
+    ├─ OFFLINE_FLASH_ON: Flashing amber + flashing don't walk
+    └─ OFFLINE_FLASH_OFF: Amber off + pedestrian signal off
+
+TIMING BEHAVIOR
+================================================================================
+Green Phase (Minimum 3 ticks):
+  • Vehicles receive GREEN signal
+  • Pedestrians see DONT_WALK_ON
+  • If pedestrian arrives before timeout, transition to yellow when min-green ends
+  • If no pedestrian, enter interruptible green (stay green indefinitely)
+Yellow Phase (2 ticks):
+  • Vehicles receive YELLOW signal
+  • Pedestrians see DONT_WALK_ON
+Walk Phase (3 ticks):
+  • Pedestrians receive WALK signal
+  • Vehicles receive RED signal
+Pedestrian Flashing (6 ticks):
+  • Pedestrian signal alternates between DONT_WALK_ON and DONT_WALK_OFF
+  • Vehicles receive RED signal
+  • After flashing completes, cycle returns to vehicle green
+Offline Phase:
+  • Car signal alternates between FLASHING_AMBER_ON and FLASHING_AMBER_OFF
+  • Pedestrian signal alternates between DONT_WALK_ON and DONT_WALK_OFF
+  • Each Q_TIMEOUT event toggles the flashing state
+
+SAFETY GUARANTEES
+================================================================================
+Property 1: Vehicles Always Safe
+  ├─ Cars are RED outside vehicle-enabled phases
+  ├─ Cars cannot be GREEN during pedestrian phases
+  └─ Enforced by state machine structure
+Property 2: Pedestrians Always Safe
+  ├─ Pedestrians show DONT_WALK outside pedestrian-enabled phases
+  ├─ Pedestrians cannot be WALK during vehicle green
+  └─ Enforced by state machine structure
+
+EVENTS
+================================================================================
+INIT:
+  • Initialization event
+  • Triggers first entry to OPERATIONAL_CARS_GREEN_NO_PED
+  • Called automatically in constructor
+PEDS_WAITING:
+  • Pedestrian button pressed
+  • Marks pedestrians as waiting
+  • If during min-green, triggers yellow when minimum ends
+  • If during interruptible green, immediately triggers yellow
+Q_TIMEOUT:
+  • Simulated clock tick (one unit of time)
+  • Decrements internal timers
+  • Triggers state transitions when timers expire
+  • No real-time delays or threads used
+OFF:
+  • Enter offline mode from any operational state
+  • Sets safe signals (flashing amber and flashing don't walk)
+  • Enters OFFLINE_FLASH_ON state
+ON:
+  • Exit offline mode from any offline state
+  • Returns to OPERATIONAL_CARS_GREEN_NO_PED
+  • Reinitialize timers and pedestrian flag
+
+SIGNAL OUTPUTS
+================================================================================
+Car Signal (5 possible values):
+  • RED: Vehicles must stop
+  • GREEN: Vehicles may proceed
+  • YELLOW: Vehicles prepare to stop
+  • FLASHING_AMBER_ON: Offline mode (amber on)
+  • FLASHING_AMBER_OFF: Offline mode (amber off)
+Pedestrian Signal (3 possible values):
+  • WALK: Pedestrians may cross
+  • DONT_WALK_ON: Steady don't walk
+  • DONT_WALK_OFF: Flashing don't walk (off phase)