Implement type-safe error codes for FSA validation using an enum. Update documentation to reflect new error code structure and usage examples, enhancing clarity for frontend integration.

Author: JohnnyWan1123

docs/dev.md

@@ -190,7 +190,22 @@ Errors include a `highlight` field that tells the frontend exactly which FSA ele
 | `accept_state` | `state_id` | Highlight the accept state indicator |
 | `alphabet_symbol` | `symbol` | Highlight a symbol in the alphabet |
 
-## Error Codes
+## Error Codes (Enum)
+
+Error codes are defined as a type-safe enum (`ErrorCode`) in `evaluation_function/schemas/result.py`.
+
+```python
+from evaluation_function.schemas import ErrorCode, ValidationError
+
+# Type-safe error creation
+error = ValidationError(
+    message="State 'q5' does not exist",
+    code=ErrorCode.INVALID_STATE,  # Enum value
+    severity="error"
+)
+```
+
+### Available Error Codes
 
 | Code | Highlight Type | Description |
 |------|----------------|-------------|
@@ -205,6 +220,14 @@ Errors include a `highlight` field that tells the frontend exactly which FSA ele
 | `DUPLICATE_TRANSITION` | transition | Non-deterministic transition |
 | `UNREACHABLE_STATE` | state | State not reachable from initial |
 | `DEAD_STATE` | state | State cannot reach accept state |
+| `WRONG_AUTOMATON_TYPE` | general | Wrong automaton type (NFA when DFA expected) |
+| `NOT_DETERMINISTIC` | general | Has non-deterministic transitions |
+| `NOT_COMPLETE` | general | DFA missing some transitions |
+| `LANGUAGE_MISMATCH` | general | Accepts wrong language |
+| `TEST_CASE_FAILED` | general | Failed specific test case |
+| `EMPTY_STATES` | general | No states defined |
+| `EMPTY_ALPHABET` | general | No alphabet symbols |
+| `EVALUATION_ERROR` | general | Internal evaluation error |
 
 ## Examples
 

evaluation_function/schemas/README.md

@@ -237,7 +237,19 @@ The `highlight` field in `ValidationError` tells the frontend which FSA element
 ```
 **Frontend action:** Highlight alphabet symbol "a" in the alphabet list/panel.
 
-## Error Codes
+## Error Codes (`ErrorCode` Enum)
+
+Error codes are defined as a **type-safe enum** in `result.py`:
+
+```python
+from evaluation_function.schemas import ErrorCode
+
+# Use enum values for type safety
+error_code = ErrorCode.INVALID_STATE  # ✅ Type-safe
+error_code = "INVALID_STATE"          # ❌ No type checking
+```
+
+### Available Error Codes
 
 | Code | Element Type | Description |
 |------|--------------|-------------|
@@ -252,13 +264,27 @@ The `highlight` field in `ValidationError` tells the frontend which FSA element
 | `DUPLICATE_TRANSITION` | transition | Multiple transitions for (state, symbol) |
 | `UNREACHABLE_STATE` | state | State not reachable from initial |
 | `DEAD_STATE` | state | State cannot reach accept state |
-| `WRONG_TYPE` | general | Wrong automaton type (NFA vs DFA) |
-| `LANGUAGE_MISMATCH` | general | Accepts wrong language |
+| `WRONG_AUTOMATON_TYPE` | general | Wrong automaton type (e.g., NFA when DFA expected) |
+| `NOT_DETERMINISTIC` | general | FSA has non-deterministic transitions |
+| `NOT_COMPLETE` | general | DFA missing some transitions |
+| `LANGUAGE_MISMATCH` | general | FSA accepts wrong language |
+| `TEST_CASE_FAILED` | general | Failed specific test case |
+| `EMPTY_STATES` | general | No states defined |
+| `EMPTY_ALPHABET` | general | No alphabet symbols defined |
+| `EVALUATION_ERROR` | general | Internal evaluation error |
 
 ## Usage in Evaluation Function
 
 ```python
-from evaluation_function.schemas import FSA, Answer, Params, Result, ElementHighlight, ValidationError
+from evaluation_function.schemas import (
+    FSA, 
+    Answer, 
+    Params, 
+    Result, 
+    ElementHighlight, 
+    ValidationError,
+    ErrorCode  # Import the enum
+)
 
 # Parse student response
 fsa = FSA(**response_data)
@@ -267,7 +293,7 @@ fsa = FSA(**response_data)
 if invalid_state:
     error = ValidationError(
         message=f"State '{state}' does not exist",
-        code="INVALID_STATE",
+        code=ErrorCode.INVALID_STATE,  # Use enum value
         severity="error",
         highlight=ElementHighlight(
             type="state",

evaluation_function/schemas/__init__.py

@@ -8,7 +8,7 @@
 from .fsa import FSA, Transition
 from .answer import Answer, TestCase
 from .params import Params
-from .result import Result, ValidationError, ElementHighlight, FSAFeedback
+from .result import Result, ValidationError, ElementHighlight, FSAFeedback, ErrorCode
 
 __all__ = [
     # FSA representation
@@ -23,5 +23,6 @@
     "Result",
     "ValidationError",
     "ElementHighlight",
+    "ErrorCode",
     "FSAFeedback",
 ]

evaluation_function/schemas/result.py

@@ -4,10 +4,49 @@
 Extended result schema with structured feedback for UI highlighting.
 """
 
-from typing import List, Optional, Literal, Dict, Any
+from typing import List, Optional, Literal
+from enum import Enum
 from pydantic import BaseModel, Field
 
 
+class ErrorCode(str, Enum):
+    """
+    Standardized error codes for FSA validation.
+    
+    These codes allow the frontend to programmatically handle specific error types.
+    """
+    # Structural errors - invalid elements
+    INVALID_STATE = "INVALID_STATE"
+    INVALID_INITIAL = "INVALID_INITIAL"
+    INVALID_ACCEPT = "INVALID_ACCEPT"
+    INVALID_SYMBOL = "INVALID_SYMBOL"
+    
+    # Transition errors
+    INVALID_TRANSITION_SOURCE = "INVALID_TRANSITION_SOURCE"
+    INVALID_TRANSITION_DEST = "INVALID_TRANSITION_DEST"
+    INVALID_TRANSITION_SYMBOL = "INVALID_TRANSITION_SYMBOL"
+    MISSING_TRANSITION = "MISSING_TRANSITION"
+    DUPLICATE_TRANSITION = "DUPLICATE_TRANSITION"
+    
+    # Reachability errors
+    UNREACHABLE_STATE = "UNREACHABLE_STATE"
+    DEAD_STATE = "DEAD_STATE"
+    
+    # Type errors
+    WRONG_AUTOMATON_TYPE = "WRONG_AUTOMATON_TYPE"
+    NOT_DETERMINISTIC = "NOT_DETERMINISTIC"
+    NOT_COMPLETE = "NOT_COMPLETE"
+    
+    # Language errors
+    LANGUAGE_MISMATCH = "LANGUAGE_MISMATCH"
+    TEST_CASE_FAILED = "TEST_CASE_FAILED"
+    
+    # General errors
+    EMPTY_STATES = "EMPTY_STATES"
+    EMPTY_ALPHABET = "EMPTY_ALPHABET"
+    EVALUATION_ERROR = "EVALUATION_ERROR"
+
+
 class ElementHighlight(BaseModel):
     """
     Specifies which FSA element to highlight in the UI.
@@ -73,9 +112,9 @@ class ValidationError(BaseModel):
     """
     message: str = Field(..., description="Human-readable error message")
 
-    code: str = Field(
+    code: ErrorCode = Field(
         ..., 
-        description="Machine-readable error code (e.g., 'MISSING_TRANSITION', 'INVALID_STATE')"
+        description="Standardized error code from ErrorCode enum"
     )
 
     severity: Literal["error", "warning", "info"] = Field(