import json
from fastapi import HTTPException


def validate_message_format(messages):
    """
    Validate the format of messages.
    """
    try:
        json.dumps(messages)
    except TypeError:
        raise HTTPException(
            status_code=400,
            detail="Invalid message format - messages must be valid JSON",
        )

    for msg in messages:
        if "role" not in msg or "content" not in msg:
            raise HTTPException(
                status_code=400,
                detail="Messages must contain 'role' and 'content' fields",
            )
        if (
            not isinstance(msg["role"], str)
            or msg["role"] not in ["user", "assistant", "system"]
            or msg["content"] is None
            or not isinstance(msg["content"], (str, list))
        ):
            raise HTTPException(
                status_code=400,
                detail="Invalid role or content - role must be 'user', 'assistant', or 'system', and content must be a string or list",
            )