import jsonschema

# Schémas simplifiés pour la démo (basés sur la spec OCPP 1.6)
SCHEMAS = {
    "BootNotification": {
        "type": "object",
        "properties": {
            "chargePointVendor": {"type": "string", "maxLength": 20},
            "chargePointModel": {"type": "string", "maxLength": 20}
        },
        "required": ["chargePointVendor", "chargePointModel"]
    },
    "Authorize": {
        "type": "object",
        "properties": {
            "idTag": {"type": "string", "maxLength": 20}
        },
        "required": ["idTag"]
    },
    "StartTransaction": {
        "type": "object",
        "properties": {
            "connectorId": {"type": "integer"},
            "idTag": {"type": "string"},
            "meterStart": {"type": "integer"},
            "timestamp": {"type": "string"}
        },
        "required": ["connectorId", "idTag", "meterStart", "timestamp"]
    }
}

def validate_payload(action, payload):
    if action in SCHEMAS:
        try:
            jsonschema.validate(instance=payload, schema=SCHEMAS[action])
            return None
        except jsonschema.ValidationError as e:
            return e.message
    return None