"""记忆上下文组装与检索结果数据结构（纯领域，无 IO）。

``MemoryRetrievalResult`` 持有已加载的 Memory ORM 实例（由 services/memory 检索后传入），
``build_memory_context`` 把它组装成注入上下文的文本。本模块只接收已加载数据、输出结构化对象。
"""

from __future__ import annotations

from datetime import UTC, datetime

from pydantic import BaseModel, ConfigDict

from app.core.time import utc_now
from app.models.memory import Memory


class MemoryRetrievalResult(BaseModel):
    """记忆检索结果（持有已加载的 Memory ORM 实例列表）。"""

    model_config = ConfigDict(arbitrary_types_allowed=True)

    memories: list[Memory]


def _to_aware(dt: datetime | None) -> datetime | None:
    """确保 datetime 有时区信息，naive 视为 UTC。"""
    if dt is None:
        return None
    if dt.tzinfo is None:
        return dt.replace(tzinfo=UTC)
    return dt


def build_memory_context(result: MemoryRetrievalResult, *, max_length: int = 3000) -> str | None:
    """把检索到的记忆组装成注入上下文的文本；无记忆时返回 None。

    按**重要性降序**排列，每条附带重要性标签和相对时间。
    超过 ``max_length`` 字符时截断，避免上下文窗口膨胀。
    """
    if not result.memories:
        return None

    now = utc_now()

    def _mem_sort_key(m: Memory) -> float:
        """排序键：重要性（越高越优先），同时辅助时间衰减。"""
        ca = _to_aware(m.created_at)
        hours_ago = (now - ca).total_seconds() / 3600 if ca else 0
        decay = max(0.5, 1.0 - hours_ago / 720)  # 30 天内缓慢衰减
        return (m.importance or 0.5) * decay

    sorted_mems = sorted(result.memories, key=_mem_sort_key, reverse=True)

    lines: list[str] = []
    total_chars = 0
    for idx, item in enumerate(sorted_mems):
        importance_label = _importance_label(item.importance)
        ca = _to_aware(item.created_at)
        hours_ago = (now - ca).total_seconds() / 3600 if ca else 0
        time_label = _time_ago_str(hours_ago)
        line = f"- 「{item.title}」{time_label} [{importance_label}]\n  {item.content}"
        line_len = len(line) + 1  # +1 for newline
        if total_chars + line_len > max_length:
            remaining = len(sorted_mems) - idx
            if remaining > 0:
                lines.append(f"…以及 {remaining} 条其他记忆（已截断）")
            break
        lines.append(line)
        total_chars += line_len

    return "相关记忆：\n" + "\n".join(lines)


def _importance_label(importance: float) -> str:
    if importance >= 0.8:
        return "★重要"
    if importance >= 0.5:
        return "●一般"
    return "○参考"


def _time_ago_str(hours_ago: float) -> str:
    if hours_ago < 1:
        return "刚刚"
    if hours_ago < 24:
        return f"{int(hours_ago)}小时前"
    days = int(hours_ago / 24)
    if days < 30:
        return f"{days}天前"
    months = int(days / 30)
    return f"{months}个月前"