"""完整财务模型：
第一部分：业务往来（应收、应付、收款、付款、核销明细）
第二部分：总账系统（会计科目、会计期间、记账凭证、凭证分录）

设计原则：
- 新会计准则，借贷记账法
- 业务与财务一体化：销售/采购/收付款过账时，自动或按需生成对应记账凭证
- 辅助核算：支持客户、供应商等辅助维度
- 凭证支持草稿、已过账、已作废状态机管理
"""

from decimal import Decimal
from django.conf import settings
from django.db import models

from apps.core.base_models import TenantScopedModel


# ============================================================
# 第一部分：应收应付与核销（AR / AP）
# ============================================================

class Receivable(TenantScopedModel):
    """应收单（销售/其他应收）。"""

    STATUS_CHOICES = [
        ("open", "未收"),
        ("partial", "部分已收"),
        ("paid", "已结清"),
        ("cancelled", "已取消"),
    ]

    customer = models.ForeignKey(
        "partner.Customer",
        on_delete=models.PROTECT,
        related_name="receivables",
    )
    bill_no = models.CharField(max_length=64, help_text="应收单号（系统生成）")
    source_type = models.CharField(max_length=32, default="sale", help_text="来源：sale/manual/...")
    source_ref = models.CharField(max_length=64, blank=True, default="")
    bill_date = models.DateField()
    due_date = models.DateField(null=True, blank=True)
    total_amount = models.DecimalField(max_digits=18, decimal_places=4, default=0)
    paid_amount = models.DecimalField(max_digits=18, decimal_places=4, default=0)
    status = models.CharField(max_length=16, choices=STATUS_CHOICES, default="open")
    remark = models.TextField(blank=True, default="")

    class Meta:
        db_table = "finance_receivable"
        unique_together = [("tenant", "bill_no")]
        verbose_name_plural = "应收单"
        indexes = [
            models.Index(fields=["tenant", "customer", "status"]),
            models.Index(fields=["tenant", "bill_date"]),
        ]
        ordering = ["-bill_date", "-id"]

    @property
    def balance(self) -> Decimal:
        return self.total_amount - self.paid_amount

    def __str__(self):
        return f"{self.bill_no} ({self.customer.name}) {self.total_amount}"


class Payable(TenantScopedModel):
    """应付单（采购/其他应付）。"""

    STATUS_CHOICES = [
        ("open", "未付"),
        ("partial", "部分已付"),
        ("paid", "已结清"),
        ("cancelled", "已取消"),
    ]

    supplier = models.ForeignKey(
        "partner.Supplier",
        on_delete=models.PROTECT,
        related_name="payables",
    )
    bill_no = models.CharField(max_length=64)
    source_type = models.CharField(max_length=32, default="purchase")
    source_ref = models.CharField(max_length=64, blank=True, default="")
    bill_date = models.DateField()
    due_date = models.DateField(null=True, blank=True)
    total_amount = models.DecimalField(max_digits=18, decimal_places=4, default=0)
    paid_amount = models.DecimalField(max_digits=18, decimal_places=4, default=0)
    status = models.CharField(max_length=16, choices=STATUS_CHOICES, default="open")
    remark = models.TextField(blank=True, default="")

    class Meta:
        db_table = "finance_payable"
        unique_together = [("tenant", "bill_no")]
        verbose_name_plural = "应付单"
        indexes = [
            models.Index(fields=["tenant", "supplier", "status"]),
            models.Index(fields=["tenant", "bill_date"]),
        ]
        ordering = ["-bill_date", "-id"]

    @property
    def balance(self) -> Decimal:
        return self.total_amount - self.paid_amount

    def __str__(self):
        return f"{self.bill_no} ({self.supplier.name}) {self.total_amount}"


class Receipt(TenantScopedModel):
    """收款单。"""

    STATUS_CHOICES = [
        ("draft", "草稿"),
        ("posted", "已过账"),
        ("cancelled", "已取消"),
    ]

    customer = models.ForeignKey(
        "partner.Customer",
        on_delete=models.PROTECT,
        related_name="receipts",
    )
    bill_no = models.CharField(max_length=64)
    bill_date = models.DateField()
    amount = models.DecimalField(max_digits=18, decimal_places=4)
    method = models.CharField(max_length=32, blank=True, default="", help_text="现金/银行/微信/支付宝")
    status = models.CharField(max_length=16, choices=STATUS_CHOICES, default="draft")
    remark = models.TextField(blank=True, default="")

    class Meta:
        db_table = "finance_receipt"
        unique_together = [("tenant", "bill_no")]
        verbose_name_plural = "收款单"
        ordering = ["-bill_date", "-id"]

    def __str__(self):
        return f"{self.bill_no} {self.customer.name} {self.amount}"


class Payment(TenantScopedModel):
    """付款单。"""

    STATUS_CHOICES = [
        ("draft", "草稿"),
        ("posted", "已过账"),
        ("cancelled", "已取消"),
    ]

    supplier = models.ForeignKey(
        "partner.Supplier",
        on_delete=models.PROTECT,
        related_name="payments",
    )
    bill_no = models.CharField(max_length=64)
    bill_date = models.DateField()
    amount = models.DecimalField(max_digits=18, decimal_places=4)
    method = models.CharField(max_length=32, blank=True, default="")
    status = models.CharField(max_length=16, choices=STATUS_CHOICES, default="draft")
    remark = models.TextField(blank=True, default="")

    class Meta:
        db_table = "finance_payment"
        unique_together = [("tenant", "bill_no")]
        verbose_name_plural = "付款单"
        ordering = ["-bill_date", "-id"]

    def __str__(self):
        return f"{self.bill_no} {self.supplier.name} {self.amount}"


class Allocation(TenantScopedModel):
    """核销明细。"""

    KIND_CHOICES = [
        ("receipt", "收款核销"),
        ("payment", "付款核销"),
    ]

    receivable = models.ForeignKey(
        Receivable,
        null=True,
        blank=True,
        on_delete=models.CASCADE,
        related_name="allocations",
    )
    payable = models.ForeignKey(
        Payable,
        null=True,
        blank=True,
        on_delete=models.CASCADE,
        related_name="allocations",
    )
    receipt = models.ForeignKey(
        Receipt,
        null=True,
        blank=True,
        on_delete=models.CASCADE,
        related_name="allocations",
    )
    payment = models.ForeignKey(
        Payment,
        null=True,
        blank=True,
        on_delete=models.CASCADE,
        related_name="allocations",
    )
    kind = models.CharField(max_length=16, choices=KIND_CHOICES)
    amount = models.DecimalField(max_digits=18, decimal_places=4)

    class Meta:
        db_table = "finance_allocation"
        verbose_name_plural = "核销明细"
        indexes = [
            models.Index(fields=["tenant", "receivable"]),
            models.Index(fields=["tenant", "payable"]),
        ]


# ============================================================
# 第二部分：总账系统（科目、期间、凭证、分录）
# ============================================================

class Account(TenantScopedModel):
    """会计科目。

    类别（5 大类）：
    - asset 资产
    - liability 负债
    - equity 所有者权益
    - revenue 收入
    - expense 费用

    余额方向：
    - debit 借方余额（资产/费用）
    - credit 贷方余额（负债/权益/收入）
    """

    CATEGORY_CHOICES = [
        ("asset", "资产"),
        ("liability", "负债"),
        ("equity", "所有者权益"),
        ("revenue", "收入"),
        ("expense", "费用"),
    ]
    BALANCE_TYPE_CHOICES = [
        ("debit", "借方余额"),
        ("credit", "贷方余额"),
    ]

    code = models.CharField(max_length=32, help_text="科目编号（GB/T 标准 4-2-2）")
    name = models.CharField(max_length=64)
    category = models.CharField(max_length=16, choices=CATEGORY_CHOICES)
    balance_type = models.CharField(max_length=8, choices=BALANCE_TYPE_CHOICES)
    parent = models.ForeignKey(
        "self",
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name="children",
    )
    is_active = models.BooleanField(default=True)
    is_system = models.BooleanField(default=False, help_text="系统预置科目（不可删）")
    aux_customer = models.BooleanField(default=False, help_text="是否需要客户辅助核算")
    aux_supplier = models.BooleanField(default=False, help_text="是否需要供应商辅助核算")
    remark = models.CharField(max_length=255, blank=True, default="")

    class Meta:
        db_table = "finance_account"
        unique_together = [("tenant", "code")]
        verbose_name_plural = "会计科目"
        ordering = ["code"]

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


class Period(TenantScopedModel):
    """会计期间（月度）。"""

    STATUS_CHOICES = [
        ("open", "未结"),
        ("closed", "已结账"),
    ]

    # YYYY-MM
    code = models.CharField(max_length=16, help_text="期间代码，如 2026-09")
    start_date = models.DateField()
    end_date = models.DateField()
    status = models.CharField(max_length=16, choices=STATUS_CHOICES, default="open")
    closed_at = models.DateTimeField(null=True, blank=True)
    closed_by = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name="+",
    )

    class Meta:
        db_table = "finance_period"
        unique_together = [("tenant", "code")]
        verbose_name_plural = "会计期间"
        ordering = ["-code"]

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


class Voucher(TenantScopedModel):
    """记账凭证。"""

    STATUS_CHOICES = [
        ("draft", "草稿"),
        ("posted", "已过账"),
        ("cancelled", "已作废"),
    ]

    SOURCE_CHOICES = [
        ("manual", "手工"),
        ("sale", "销售单"),
        ("sale_cost", "销售成本"),
        ("purchase", "采购单"),
        ("receipt", "收款"),
        ("payment", "付款"),
        ("inventory_adjust", "库存调整"),
        ("period_close", "期末结转"),
    ]

    bill_no = models.CharField(max_length=64, help_text="凭证号 V{YYYYMM}{seq:04d}")
    period = models.ForeignKey(
        Period,
        on_delete=models.PROTECT,
        related_name="vouchers",
    )
    source_type = models.CharField(max_length=24, choices=SOURCE_CHOICES, default="manual")
    source_ref = models.CharField(max_length=64, blank=True, default="")
    voucher_date = models.DateField()

    total_debit = models.DecimalField(max_digits=18, decimal_places=4, default=0)
    total_credit = models.DecimalField(max_digits=18, decimal_places=4, default=0)
    status = models.CharField(max_length=16, choices=STATUS_CHOICES, default="draft")

    summary = models.CharField(max_length=255, blank=True, default="", help_text="摘要")
    posted_at = models.DateTimeField(null=True, blank=True)
    posted_by = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name="+",
    )

    class Meta:
        db_table = "finance_voucher"
        unique_together = [("tenant", "bill_no")]
        verbose_name_plural = "记账凭证"
        indexes = [
            models.Index(fields=["tenant", "period", "-voucher_date"]),
            models.Index(fields=["tenant", "source_type", "source_ref"]),
        ]
        ordering = ["-voucher_date", "-id"]

    def __str__(self):
        return f"{self.bill_no} ({self.voucher_date}) 借/贷:{self.total_debit}/{self.total_credit} [{self.status}]"


class VoucherEntry(TenantScopedModel):
    """凭证分录（一条 = 一借或一贷）。"""

    voucher = models.ForeignKey(
        Voucher,
        on_delete=models.CASCADE,
        related_name="entries",
    )
    account = models.ForeignKey(
        Account,
        on_delete=models.PROTECT,
        related_name="voucher_entries",
    )
    # 辅助核算
    customer = models.ForeignKey(
        "partner.Customer",
        null=True,
        blank=True,
        on_delete=models.PROTECT,
        related_name="voucher_entries",
    )
    supplier = models.ForeignKey(
        "partner.Supplier",
        null=True,
        blank=True,
        on_delete=models.PROTECT,
        related_name="voucher_entries",
    )
    summary = models.CharField(max_length=255, blank=True, default="")

    debit = models.DecimalField(max_digits=18, decimal_places=4, default=0, help_text="借方")
    credit = models.DecimalField(max_digits=18, decimal_places=4, default=0, help_text="贷方")

    class Meta:
        db_table = "finance_voucher_entry"
        verbose_name_plural = "凭证分录"
        ordering = ["id"]

    def __str__(self):
        return f"{self.voucher.bill_no} #{self.id} {self.account.code} 借:{self.debit} 贷:{self.credit}"


class StatementShare(TenantScopedModel):
    """对账单公开分享链接（token 化匿名访问）。"""

    customer = models.ForeignKey(
        "partner.Customer", on_delete=models.CASCADE, related_name="statement_shares"
    )
    token = models.UUIDField(unique=True, db_index=True)
    date_from = models.DateField()
    date_to = models.DateField()
    expires_at = models.DateTimeField(null=True, blank=True)
    revoked = models.BooleanField(default=False)

    class Meta:
        db_table = "finance_statement_share"
        verbose_name_plural = "对账单分享"
        ordering = ["-created_at"]

    def __str__(self):
        return f"share:{self.token} {self.customer.code} {self.date_from}~{self.date_to}"