"""库存模型：Warehouse / Stock / StockMovement。

设计：
- Warehouse 仓库（在 tenant 下唯一编码）
- Stock 按 (tenant, warehouse, product) 唯一定义当前库存数 / 锁定数
- StockMovement 是每次库存变化的流水（不可变），用于审计与回溯

锁库存语义：
- on_hand: 在手数量（可卖/可用）
- locked: 已锁定（销售订单已确认但未出库）
- available = on_hand - locked
"""

from django.db import models
from apps.core.base_models import TenantScopedModel
from decimal import Decimal


class Warehouse(TenantScopedModel):
    """仓库。"""

    code = models.CharField(max_length=64)
    name = models.CharField(max_length=128)
    location = models.CharField(max_length=255, blank=True, default="")
    is_active = models.BooleanField(default=True)
    is_default = models.BooleanField(default=False, help_text="默认仓库")

    class Meta:
        db_table = "inventory_warehouse"
        unique_together = [("tenant", "code")]
        verbose_name_plural = "仓库"
        ordering = ["code"]

    def __str__(self):
        return f"{self.code} {self.name}"


class Stock(TenantScopedModel):
    """库存账面（每个 (warehouse, product) 一行）。"""

    warehouse = models.ForeignKey(
        Warehouse,
        on_delete=models.PROTECT,
        related_name="stocks",
    )
    product = models.ForeignKey(
        "catalog.Product",
        on_delete=models.PROTECT,
        related_name="stocks",
    )
    on_hand = models.DecimalField(max_digits=18, decimal_places=4, default=0)
    locked = models.DecimalField(max_digits=18, decimal_places=4, default=0)
    avg_cost = models.DecimalField(max_digits=18, decimal_places=4, default=0)

    class Meta:
        db_table = "inventory_stock"
        unique_together = [("tenant", "warehouse", "product")]
        verbose_name_plural = "库存账面"
        indexes = [
            models.Index(fields=["tenant", "warehouse", "product"]),
            models.Index(fields=["tenant", "product"]),
        ]
        ordering = ["warehouse", "product"]

    @property
    def available(self) -> Decimal:
        return self.on_hand - self.locked

    def __str__(self):
        return f"{self.warehouse.code}/{self.product.code} on_hand={self.on_hand} locked={self.locked}"


class StockMovement(TenantScopedModel):
    """库存流水（不可变）。"""

    MOVEMENT_INBOUND = "inbound"     # 入库（采购入库、调拨入库、其他入库）
    MOVEMENT_OUTBOUND = "outbound"   # 出库（销售出库、调拨出库、其他出库）
    MOVEMENT_LOCK = "lock"           # 锁定
    MOVEMENT_UNLOCK = "unlock"       # 释放锁定
    MOVEMENT_ADJUST = "adjust"       # 盘点调整

    MOVEMENT_CHOICES = [
        (MOVEMENT_INBOUND, "入库"),
        (MOVEMENT_OUTBOUND, "出库"),
        (MOVEMENT_LOCK, "锁定"),
        (MOVEMENT_UNLOCK, "释放"),
        (MOVEMENT_ADJUST, "盘点"),
    ]

    SOURCE_CHOICES = [
        ("purchase", "采购入库"),
        ("sale", "销售出库"),
        ("transfer", "调拨"),
        ("adjust", "盘点调整"),
        ("manual", "手工"),
    ]

    warehouse = models.ForeignKey(
        Warehouse, on_delete=models.PROTECT, related_name="movements"
    )
    product = models.ForeignKey(
        "catalog.Product", on_delete=models.PROTECT, related_name="movements"
    )

    movement_type = models.CharField(max_length=16, choices=MOVEMENT_CHOICES)
    source_type = models.CharField(max_length=16, choices=SOURCE_CHOICES, default="manual")
    source_ref = models.CharField(max_length=64, blank=True, default="", help_text="来源单据号")

    quantity = models.DecimalField(max_digits=18, decimal_places=4, help_text="本次变动数量（正数）")
    unit_cost = models.DecimalField(max_digits=18, decimal_places=4, default=0, help_text="单位成本")
    batch_detail = models.JSONField(
        default=list,
        blank=True,
        help_text="批次商品出库时的 FEFO 分摊明细 [{batch_no, quantity, expiry_date}]",
    )

    # 流水是不可变的：不允许 delete / 修改后影响金额
    class Meta:
        db_table = "inventory_movement"
        verbose_name_plural = "库存流水"
        indexes = [
            models.Index(fields=["tenant", "warehouse", "-created_at"]),
            models.Index(fields=["tenant", "product", "-created_at"]),
            models.Index(fields=["source_type", "source_ref"]),
        ]
        ordering = ["-created_at"]

    def __str__(self):
        sign = "+" if self.movement_type in (self.MOVEMENT_INBOUND, self.MOVEMENT_UNLOCK) else "-"
        return f"[{self.created_at}] {self.warehouse.code}/{self.product.code} {sign}{self.quantity}"


class StockBatch(TenantScopedModel):
    """批次库存账（批次管理商品的 (warehouse, product, batch_no) 维度账面）。

    与总账 Stock 并行维护：sum(StockBatch.on_hand) == Stock.on_hand。
    出库按 FEFO（近效期优先）自动分摊。
    """

    warehouse = models.ForeignKey(
        Warehouse, on_delete=models.PROTECT, related_name="batches"
    )
    product = models.ForeignKey(
        "catalog.Product", on_delete=models.PROTECT, related_name="batches"
    )
    batch_no = models.CharField(max_length=64, help_text="批次号")
    production_date = models.DateField(null=True, blank=True, help_text="生产日期")
    expiry_date = models.DateField(null=True, blank=True, help_text="到期日期")
    on_hand = models.DecimalField(max_digits=18, decimal_places=4, default=0)
    locked = models.DecimalField(max_digits=18, decimal_places=4, default=0)
    unit_cost = models.DecimalField(max_digits=18, decimal_places=4, default=0)

    class Meta:
        db_table = "inventory_stock_batch"
        unique_together = [("tenant", "warehouse", "product", "batch_no")]
        verbose_name_plural = "批次库存"
        indexes = [
            models.Index(fields=["tenant", "product", "expiry_date"]),
            models.Index(fields=["tenant", "warehouse", "product"]),
        ]
        ordering = ["expiry_date", "id"]

    @property
    def available(self) -> Decimal:
        return self.on_hand - self.locked

    def __str__(self):
        return f"{self.warehouse.code}/{self.product.code}/{self.batch_no} on_hand={self.on_hand}"