"""LLM 上下文准备。

不改 Session 持久化历史,只在发给模型前做低风险压缩。只压旧 tool 消息**内容**,
绝不动 assistant 的 `tool_call.arguments` —— arguments 是模型"该怎么调工具"的范本,
把它改写成 `{"_compacted":...}` 这种"看着像合法调用"的标记会毒化模型:它在长任务里
看到几十次"过去的 run_python/write 长这样",就照葫芦画瓢把 marker 当参数原样吐出来,
executor 拿不到 code/path → 报错空转(2026-06-12 DB 实测 60 个 task 命中 83 次,
其中 61 次是模型仿写 marker;详 PROGRESS)。故 arguments 一律原样保留。
"""
from __future__ import annotations

from copy import deepcopy
from typing import Any, List
import json
import re


def _compact_old_tool_content(content: str, max_chars: int) -> str:
    if len(content) <= max_chars:
        return content
    head = max_chars // 2
    tail = max_chars - head
    omitted = len(content) - head - tail
    return (
        content[:head]
        + f"\n[compacted old tool result, {omitted} chars omitted]\n"
        + content[-tail:]
    )


_LOAD_SKILL_HEADER_RE = re.compile(r"\[skill=([^,\]]+)(?:,\s*dir=([^\]]+))?\]")


def _compact_load_skill_content(content: str) -> str:
    first_line = content.splitlines()[0] if content else ""
    match = _LOAD_SKILL_HEADER_RE.search(first_line)
    if match:
        skill = match.group(1)
        skill_dir = match.group(2) or ""
        suffix = f", dir={skill_dir}" if skill_dir else ""
        return f"[loaded skill: {skill}{suffix}; full SKILL.md omitted from old context]"
    return "[loaded skill; full SKILL.md omitted from old context]"


def _message_chars(msg: dict[str, Any]) -> int:
    try:
        return len(json.dumps(msg, ensure_ascii=False))
    except TypeError:
        return len(str(msg))


def prepare_messages_for_llm(
    messages: List[dict[str, Any]],
    *,
    keep_recent: int = 12,
    old_tool_chars: int = 2_000,
    compact_threshold_chars: int = 0,
) -> List[dict[str, Any]]:
    """返回发给 LLM 的 messages 副本。

    - system 和最近 keep_recent 条消息原样保留。
    - 较旧且过长的 tool content 压缩为头尾摘要。
    - assistant 的 tool_call.arguments 一律原样保留(改写会毒化模型,见模块注释)。
    - role/tool_call_id/name 等协议字段不变。
    """
    prepared, _ = prepare_messages_with_stats(
        messages,
        keep_recent=keep_recent,
        old_tool_chars=old_tool_chars,
        compact_threshold_chars=compact_threshold_chars,
    )
    return prepared


def prepare_messages_with_stats(
    messages: List[dict[str, Any]],
    *,
    keep_recent: int = 12,
    old_tool_chars: int = 2_000,
    compact_threshold_chars: int = 0,
) -> tuple[List[dict[str, Any]], dict[str, int]]:
    """返回发给 LLM 的 messages 副本和压缩统计。

    `compact_threshold_chars`:上下文压力门槛。总体量(原始 chars)未超过它时**完全不压缩**
    —— 短任务不丢旧工具细节,且 prompt 前缀逐轮字节一致、DeepSeek 等前缀缓存全程命中。
    默认 0 = 永远压缩(向后兼容)。caller(loop)按模型 reliable_context 折算传入。
    """
    if keep_recent < 0:
        keep_recent = 0
    original_chars = sum(_message_chars(m) for m in messages)

    # 未到上下文压力门槛 → 原样发,零压缩(缓存全暖 + 不丢信息)。压缩是"放不下"才做的事。
    if original_chars < compact_threshold_chars:
        prepared = [deepcopy(m) for m in messages]
        stats = {
            "original_chars": original_chars,
            "sent_chars": original_chars,
            "saved_chars": 0,
            "compacted_tool_messages": 0,
            "compacted_skill_messages": 0,
            "compaction_skipped": 1,
        }
        return prepared, stats

    recent_start = max(0, len(messages) - keep_recent)
    prepared: List[dict[str, Any]] = []
    compacted_tool_messages = 0
    compacted_skill_messages = 0
    for idx, msg in enumerate(messages):
        new_msg = deepcopy(msg)
        is_recent = idx >= recent_start
        # assistant 的 tool_call.arguments 一律原样保留 —— 压成 marker 会毒化模型(见模块注释)。
        if (
            not is_recent
            and new_msg.get("role") == "tool"
            and isinstance(new_msg.get("content"), str)
        ):
            before = new_msg["content"]
            if new_msg.get("name") == "load_skill":
                new_msg["content"] = _compact_load_skill_content(before)
                compacted_skill_messages += int(new_msg["content"] != before)
            elif new_msg.get("name") == "task_progress":
                new_msg["content"] = "[task_progress updated; UI-only details omitted from context]"
            else:
                new_msg["content"] = _compact_old_tool_content(
                    before,
                    max_chars=max(0, old_tool_chars),
                )
            compacted_tool_messages += int(new_msg["content"] != before)
        prepared.append(new_msg)
    sent_chars = sum(_message_chars(m) for m in prepared)
    stats = {
        "original_chars": original_chars,
        "sent_chars": sent_chars,
        "saved_chars": max(0, original_chars - sent_chars),
        "compacted_tool_messages": compacted_tool_messages,
        "compacted_skill_messages": compacted_skill_messages,
        "compaction_skipped": 0,
    }
    return prepared, stats