class MiniProgramStreaming:
    streaming_mode = "block"
    preview_stream_throttle_ms = 160
    preview_min_initial_chars = 18

    block_streaming_enabled = True
    block_streaming_break = "text_end"
    block_streaming_chunk_min_chars = 200
    block_streaming_chunk_max_chars = 1200
    block_streaming_chunk_break_preference = "paragraph"
    block_streaming_coalesce_defaults = {
        "min_chars": 80,
        "max_chars": 400,
        "idle_ms": 500,
    }

    finish_mark = "[↓]"

    def create_draft_stream_session(self, target_id: str) -> object:
        return {"target_id": target_id, "mode": "block"}

    def create_block_chunker(self) -> object:
        return {
            "mode": "length",
            "min_chars": self.block_streaming_chunk_min_chars,
            "max_chars": self.block_streaming_chunk_max_chars,
        }

    def should_stream(self, estimated_length: int) -> bool:
        return estimated_length > self.block_streaming_chunk_min_chars

    def build_chunk(self, text: str, is_final: bool) -> str:
        if is_final:
            return text
        return f"{text}\n{self.finish_mark}"