"""不可行分配的容量说明；容量上界不能替代产品范围和双证引用的联合求解。"""
from decimal import Decimal


def allocation_diagnostics(demands, purchases, transports):
    rows = []
    for kind, permits in [('purchase', purchases), ('transport', transports)]:
        for unit in sorted({s.unit for s in demands}):
            sources = [s for s in demands if s.unit == unit]
            products = {s.product_id for s in sources}
            eligible = [p for p in permits if p.product_ids & products]
            demand = sum((s.quantity for s in sources), Decimal(0))
            foreign = any(p.unit != unit for p in eligible)
            available = sum((p.available for p in eligible if p.unit == unit), Decimal(0))
            gap = max(Decimal(0), demand - available)
            reason = ('存在异单位证件，请逐来源人工填写换算量；不能按证面余额推算可覆盖量'
                      if foreign else '余额不足，请补充该证种额度' if gap else
                      '总余额仅为上界；请核对每个合同产品范围、运输引用关系及人工分配约束')
            rows.append({'certType': kind, 'sourceIds': [s.source_id for s in sources],
                         'unit': unit, 'demand': format(demand, 'f'),
                         'availableUpperBound': None if foreign else format(available, 'f'),
                         'gapLowerBound': None if foreign else format(gap, 'f'), 'reason': reason})
    return rows