# -*- coding: utf-8 -*-
"""新视频在收藏夹中的插入位置计算（纯函数）。"""

from __future__ import annotations

from dataclasses import dataclass
from typing import Mapping, Sequence


@dataclass(frozen=True)
class VideoMeta:
    up_mid: int | None
    pubdate: int


@dataclass(frozen=True)
class InsertionPlan:
    target_position: int
    moves: tuple[tuple[int, int], ...]  # (pred_aid, moved_aid)

    @property
    def needs_head_move(self) -> bool:
        return len(self.moves) == 2


def plan_insertion(
    current_ids: Sequence[int],
    new_aid: int,
    metadata: Mapping[int, VideoMeta],
    new_meta: VideoMeta,
) -> InsertionPlan:
    """按“同 UP 连续、组间按最早投稿倒序”计算插入点。

    ``current_ids`` 可以包含 ``new_aid``（通常在末尾），函数会先排除它。
    """
    ordered = [int(aid) for aid in current_ids if int(aid) != int(new_aid)]
    if not ordered:
        return InsertionPlan(target_position=1, moves=())

    groups: list[dict] = []
    for index, aid in enumerate(ordered):
        meta = metadata.get(aid)
        up_mid = meta.up_mid if meta else None
        if up_mid is not None and groups and groups[-1]["up_mid"] == up_mid:
            groups[-1]["aids"].append(aid)
        else:
            groups.append({"up_mid": up_mid, "aids": [aid], "start": index})

    for group in groups:
        keys = [
            metadata[aid].pubdate
            for aid in group["aids"]
            if aid in metadata and metadata[aid].pubdate > 0
        ]
        group["key"] = min(keys) if keys else 0

    insert_index: int | None = None
    if new_meta.up_mid is not None:
        for group in groups:
            if group["up_mid"] == new_meta.up_mid:
                insert_index = group["start"]
                break
    if insert_index is None:
        for group in groups:
            if group["key"] < new_meta.pubdate:
                insert_index = group["start"]
                break
    if insert_index is None:
        insert_index = len(ordered)

    target_position = insert_index + 1
    if insert_index == 0:
        first = ordered[0]
        return InsertionPlan(
            target_position=1,
            moves=((first, int(new_aid)), (int(new_aid), first)),
        )
    predecessor = ordered[insert_index - 1]
    return InsertionPlan(
        target_position=target_position,
        moves=((predecessor, int(new_aid)),),
    )