"""认识时长、离线档位、自然语言时长表达。

全部纯函数。离线阈值以参数传入（集成层从 ``TimeConfig`` 提供），不在本模块
读取配置，保持零 IO。
"""

from __future__ import annotations

import math
from datetime import datetime

from pydantic import BaseModel, model_validator

_MINUTES_PER_DAY = 1440


class OfflineThresholds(BaseModel):
    """离线档位阈值（分钟）。默认值见辰正设计 §7.1。"""

    active_minutes: float = 60  # < 1h -> active
    short_absence_minutes: float = 720  # 1-12h -> short_absence
    long_absence_minutes: float = 4320  # 12h-3d -> long_absence
    reunion_impact_minutes: float = 4320  # > 3d -> reunion_impact

    @model_validator(mode="after")
    def _check_monotonicity(self) -> OfflineThresholds:
        if not (
            self.active_minutes
            < self.short_absence_minutes
            < self.long_absence_minutes
            <= self.reunion_impact_minutes
        ):
            raise ValueError(
                "OfflineThresholds 必须满足 "
                "active_minutes < short_absence_minutes "
                "< long_absence_minutes <= reunion_impact_minutes"
            )
        return self


class AcquaintanceDuration(BaseModel):
    """认识时长。"""

    total_days: int
    years: int
    months: int
    days: int
    natural_language: str


class OfflineDuration(BaseModel):
    """离线时长与档位。"""

    minutes: float
    band: str  # offline_band 枚举
    reunion_intensity: float  # [0,1]，仅 reunion_impact 档显著


def format_duration_cn(days: int) -> str:
    """把天数格式化为中文自然语言。"""
    if days <= 0:
        return "今天"
    if days < 30:
        return f"{days} 天"
    years = days // 365
    remaining_after_year = days % 365
    months = remaining_after_year // 30
    rest = remaining_after_year % 30
    if years >= 1 and months >= 1 and rest >= 1:
        return f"{years} 年 {months} 个月 {rest} 天（{days} 天）"
    if years >= 1 and months >= 1:
        return f"{years} 年 {months} 个月（{days} 天）"
    if years >= 1:
        return f"{years} 年（{days} 天）"
    return f"{months} 个月 {rest} 天（{days} 天）"


def compute_acquaintance_duration(anchor: datetime, now: datetime) -> AcquaintanceDuration:
    """计算从 anchor 到 now 的认识时长。

    年/月/日按 365 天/年、30 天/月近似拆分（用于自然语言展示，非历法精确）。
    """
    delta = now - anchor
    total_seconds = max(delta.total_seconds(), 0)
    total_days = int(total_seconds // 86400)
    years = total_days // 365
    remaining_after_year = total_days % 365
    months = remaining_after_year // 30
    days = remaining_after_year % 30
    return AcquaintanceDuration(
        total_days=total_days,
        years=years,
        months=months,
        days=days,
        natural_language=format_duration_cn(total_days),
    )


def classify_offline_band(
    last_active: datetime, now: datetime, thresholds: OfflineThresholds
) -> OfflineDuration:
    """按离线时长判定档位与重逢强度。"""
    delta = now - last_active
    minutes = max(delta.total_seconds() / 60.0, 0.0)

    if minutes < thresholds.active_minutes:
        return OfflineDuration(minutes=minutes, band="active", reunion_intensity=0.0)
    if minutes < thresholds.short_absence_minutes:
        return OfflineDuration(minutes=minutes, band="short_absence", reunion_intensity=0.0)
    if minutes < thresholds.long_absence_minutes:
        return OfflineDuration(minutes=minutes, band="long_absence", reunion_intensity=0.0)
    # reunion_impact：超过阈值后强度随离线时长对数增长，钳位 [0.5, 1.0]
    excess = minutes - thresholds.reunion_impact_minutes
    # 1 天以上额外 -> 强度快速上升；用 log 压缩
    intensity = max(0.5, min(1.0, 0.5 + 0.5 * math.log10(max(excess, 1) / _MINUTES_PER_DAY + 1)))
    return OfflineDuration(
        minutes=minutes, band="reunion_impact", reunion_intensity=round(intensity, 3)
    )