def style(style_type, content, title=None, summary=None):
    """Android/Amazon style builder.

    :keyword style_type: String. Must be one of "big_text", "big_picture",
        or "inbox".
    :keyword content: String or array of strings. Content of the style object.
        If style_type is set to "inbox", this will be an array of strings.
        Otherwise, it will be a single string.
    :keyword title: Optional string. Override the notification.
    :keyword summary: Optional string. Override the summary of the
        notification.

    """
    mapping = {"big_text": "big_text", "big_picture": "big_picture", "inbox": "lines"}
    if style_type not in mapping.keys():
        raise ValueError(
            "style_type must be one of {}.".format(", ".join(mapping.keys()))
        )
    payload = {
        "type": style_type,
        mapping[style_type]: content,
        "title": title,
        "summary": summary,
    }
    return {key: val for key, val in iter(payload.items()) if val is not None}