"""商品中心模型：Category / Brand / Unit / Product。

预留点：
- Product.ext_data：自定义属性 JSON（行业差异）
- Product.source_channel：manual/api/web/miniprogram/ai_agent
- Product.is_deleted：软删除
"""

from decimal import Decimal

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


class Category(TenantScopedModel):
    """商品分类（树形结构）。"""

    code = models.CharField(max_length=64, help_text="分类代码")
    name = models.CharField(max_length=128)
    parent = models.ForeignKey(
        "self",
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name="children",
    )
    sort_order = models.IntegerField(default=0)

    class Meta:
        db_table = "catalog_category"
        unique_together = [("tenant", "code")]
        verbose_name_plural = "商品分类"
        ordering = ["sort_order", "code"]

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


class Brand(TenantScopedModel):
    """品牌。"""

    code = models.CharField(max_length=64)
    name = models.CharField(max_length=128)
    logo_url = models.URLField(blank=True, default="")

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

    def __str__(self):
        return self.name


class Unit(TenantScopedModel):
    """计量单位（箱/瓶/件/kg）。"""

    code = models.CharField(max_length=16, help_text="单位代码，如 box/bottle/kg")
    name = models.CharField(max_length=32)
    is_base = models.BooleanField(default=True, help_text="是否基本单位")

    class Meta:
        db_table = "catalog_unit"
        unique_together = [("tenant", "code")]
        verbose_name_plural = "计量单位"

    def __str__(self):
        return self.name


class Product(TenantScopedModel):
    """商品档案。"""

    STATUS_ACTIVE = "active"
    STATUS_INACTIVE = "inactive"
    STATUS_CHOICES = [
        (STATUS_ACTIVE, "启用"),
        (STATUS_INACTIVE, "停用"),
    ]

    code = models.CharField(max_length=64, help_text="商品编码（租户内唯一）")
    name = models.CharField(max_length=255)
    spec = models.CharField(max_length=255, blank=True, default="", help_text="规格")
    barcode = models.CharField(max_length=64, blank=True, default="")

    category = models.ForeignKey(
        Category,
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name="products",
    )
    brand = models.ForeignKey(
        Brand,
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name="products",
    )
    base_unit = models.ForeignKey(
        Unit,
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name="products",
    )

    # 价格字段
    cost_price = models.DecimalField(
        max_digits=18, decimal_places=4, default=0, help_text="参考成本价"
    )
    sale_price = models.DecimalField(
        max_digits=18, decimal_places=4, default=0, help_text="默认销售价"
    )
    min_sale_price = models.DecimalField(
        max_digits=18,
        decimal_places=4,
        default=0,
        help_text="最低售价（0=不限制；低于需审批放行）",
    )

    # 批次/效期（食品、医药等批次管理行业）
    is_batch_managed = models.BooleanField(
        default=False, help_text="是否启用批次管理（出库按近效期优先 FEFO）"
    )
    shelf_life_days = models.IntegerField(
        null=True, blank=True, help_text="保质期天数（用于入库时推算默认到期日）"
    )

    # 税率（批次 D4）：默认 13%（一般纳税人常见档），可按商品覆盖
    tax_rate = models.DecimalField(
        max_digits=6, decimal_places=4, default=Decimal("0.13"),
        help_text="增值税率（0.13 = 13%）；0 = 免税/不启用",
    )

    status = models.CharField(
        max_length=16, choices=STATUS_CHOICES, default=STATUS_ACTIVE
    )

    class Meta:
        db_table = "catalog_product"
        unique_together = [("tenant", "code")]
        verbose_name_plural = "商品档案"
        indexes = [
            models.Index(fields=["tenant", "code"]),
            models.Index(fields=["tenant", "name"]),
            models.Index(fields=["tenant", "barcode"]),
            models.Index(fields=["tenant", "category", "-created_at"]),
        ]
        ordering = ["code"]

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


class UnitConversion(TenantScopedModel):
    """商品多单位换算：1 个该单位 = rate × 基本单位。

    例：商品基本单位"瓶"，换算"箱" rate=24 → 1 箱 = 24 瓶。
    """

    product = models.ForeignKey(
        Product,
        on_delete=models.CASCADE,
        related_name="unit_conversions",
    )
    unit = models.ForeignKey(
        Unit,
        on_delete=models.PROTECT,
        related_name="conversions",
    )
    rate = models.DecimalField(
        max_digits=18, decimal_places=6, help_text="1 个该单位 = rate × 基本单位"
    )

    class Meta:
        db_table = "catalog_unit_conversion"
        unique_together = [("tenant", "product", "unit")]
        verbose_name_plural = "商品单位换算"
        ordering = ["product", "unit"]

    def __str__(self):
        return f"{self.product.code}:{self.unit.code}×{self.rate}"