"""会话历史：数据库保存完整对话，每次请求按 token 预算只带最近的完整轮次

裁剪在服务层组装请求时做一次，意图判断、问答和 screen agent 看到的是同一段历史
"""

from langchain_core.messages import (
    AIMessage,
    BaseMessage,
    HumanMessage,
    trim_messages,
)
from langchain_core.messages.utils import count_tokens_approximately

from app.schemas.base import JsonObject


def history_messages(history: list[JsonObject]) -> list[BaseMessage]:
    """每轮转成一条用户消息和一条助手消息，按时间从早到晚排列"""
    messages: list[BaseMessage] = []
    for turn in history:
        messages.append(HumanMessage(content=turn["user"]))
        messages.append(AIMessage(content=turn["assistant"]))
    return messages


def trim_history(history: list[JsonObject], max_tokens: int) -> list[JsonObject]:
    """从最近一轮往前保留，总量不超过 max_tokens；只保留完整的轮次，不从一段回复中间截断

    单独一轮就超过预算时这一轮也不保留
    """
    kept = trim_messages(
        history_messages(history),
        max_tokens=max_tokens,
        token_counter=count_tokens_approximately,
        strategy="last",
        # 从用户消息开始，助手回复放不下时连同它的用户消息一起去掉
        start_on="human",
    )
    return history[len(history) - len(kept) // 2 :]