"""Scoped child reconciliation. Callers supply the complete writable scope, never global IDs."""
from datetime import datetime

from fastapi import HTTPException

from app.core.utils import generate_uuid


def validate_child_ids(items, existing, label):
    """Validate the whole collection before a caller mutates any ORM instance."""
    by_id = {row.id: row for row in existing}
    seen = set()
    for item in items or []:
        row_id = (getattr(item, 'id', None) or '').strip()
        if not row_id:
            continue
        if row_id in seen:
            raise HTTPException(422, f'{label} id 重复：{row_id}')
        if row_id not in by_id:
            raise HTTPException(422, f'{label} id 无效、已删除或不属于当前主单：{row_id}')
        seen.add(row_id)
    return by_id, seen


def prepare_keyed_rows(existing, values, key_fields, label):
    """Natural-key relations keep their identities; ambiguous keys must be corrected explicitly."""
    old = {}
    for row in existing:
        key = tuple(getattr(row, field, None) or '' for field in key_fields)
        if key in old:
            raise HTTPException(409, f'{label}存在重复历史记录，请先核对')
        old[key] = row
    seen = set()
    pairs = []
    for value in values:
        key = tuple(value.get(field) or '' for field in key_fields)
        if key in seen:
            raise HTTPException(422, f'{label}不能重复提交')
        seen.add(key)
        row = old.get(key)
        if value.get('id') and (row is None or value['id'] != row.id):
            raise HTTPException(422, f'{label} id 无效或不属于当前主单')
        pairs.append((row, value))
    return pairs, [row for key, row in old.items() if key not in seen]


def apply_keyed_rows(db, model, prepared, *, user_id, dept_id='', order_start=0):
    pairs, removed = prepared
    now = datetime.now()
    result = []
    for idx, (row, value) in enumerate(pairs, start=order_start):
        fields = {key: val for key, val in value.items() if key != 'id'}
        if row is None:
            row = model(id=generate_uuid(), create_by=user_id, create_dept_id=dept_id or '',
                        create_time=now, del_flag=0, **fields)
            db.add(row)
        else:
            for key, val in fields.items():
                setattr(row, key, val)
        row.order_num = idx
        row.update_by = user_id
        row.update_time = now
        result.append(row)
    for row in removed:
        row.del_flag = 1
        row.update_by = user_id
        row.update_time = now
    return result