Create backend.py

backend.py

@@ -0,0 +1,64 @@
+from fastapi import FastAPI, HTTPException
+from pydantic import BaseModel, field_validator
+import math
+import re
+
+app = FastAPI()
+
+ALLOWED_FUNCTIONS = {'sin', 'cos', 'tan', 'log', 'ln', 'sqrt', 'abs', 'pow'}
+ALLOWED_CONSTANTS = {'pi', 'e'}
+
+class Expression(BaseModel):
+    expr: str
+
+    @field_validator('expr')
+    @classmethod
+    def validate_expression(cls, v: str) -> str:
+        if not v:
+            raise ValueError("Expression cannot be empty")
+        
+        # Check for invalid characters
+        valid_chars = set('0123456789.+-*/()^ \t\nabcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
+        invalid_chars = set(v) - valid_chars
+        if invalid_chars:
+            raise ValueError(f"Invalid characters found: {', '.join(invalid_chars)}")
+        
+        # Check for invalid function names or constants
+        tokens = re.findall(r'\b[a-zA-Z_]\w*\b', v)
+        invalid_tokens = [token for token in tokens if token not in ALLOWED_FUNCTIONS and token not in ALLOWED_CONSTANTS]
+        if invalid_tokens:
+            raise ValueError(f"Invalid function or constant names: {', '.join(invalid_tokens)}")
+        
+        return v
+
+@app.post("/calculate")
+async def calculate_api(expression: Expression):
+    try:
+        result = evaluate_expression(expression.expr)
+        return {"result": result}
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=f"An unexpected error occurred: {str(e)}")
+
+def evaluate_expression(expr: str) -> float:
+    safe_dict = {
+        'sin': math.sin, 'cos': math.cos, 'tan': math.tan,
+        'log': math.log10, 'ln': math.log, 'sqrt': math.sqrt,
+        'pi': math.pi, 'e': math.e,
+        'abs': abs, 'pow': pow
+    }
+    try:
+        # Replace '^' with '**' for exponentiation
+        expr = expr.replace('^', '**')
+        return eval(expr, {"__builtins__": None}, safe_dict)
+    except ZeroDivisionError:
+        raise ValueError("Division by zero is not allowed")
+    except ValueError as e:
+        raise ValueError(f"Math domain error: {str(e)}")
+    except Exception as e:
+        raise ValueError(f"Invalid expression: {str(e)}")
+
+if __name__ == "__main__":
+    import uvicorn
+    uvicorn.run(app, host="0.0.0.0", port=8000)