from sqlalchemy.orm import Session
from sqlalchemy import select
from app.models.UserModel import User

class CodeGeneratorService:
    @staticmethod
    def generate_next_code(db: Session, entity_type: str, prefix: str) -> str:
        # Resolve table and column mappings
        if entity_type == "User":
            model_class = User
            column_attr = User.employee_code
        else:
            raise ValueError(f"Unsupported entity type for code generation: {entity_type}")

        # Query highest code using write-lock to prevent race conditions
        stmt = (
            select(column_attr)
            .where(column_attr.like(f"{prefix}%"))
            .order_by(column_attr.desc())
            .limit(1)
            .with_for_update()
        )
        
        result = db.execute(stmt)
        last_code = result.scalar_one_or_none()

        prefix_len = len(prefix)
        if last_code and last_code[prefix_len:].isdigit():
            last_number = int(last_code[prefix_len:])
            new_number = last_number + 1
        else:
            new_number = 1

        # Zero-pad suffix to 4 digits (e.g. TEC0001)
        return f"{prefix}{new_number:04d}"

code_generator_service = CodeGeneratorService()