"""套餐与订阅模型（批次 C1）。

设计要点：
- `Plan.limits` 是**唯一事实来源**：官网价格表、配额校验、升级引导弹窗都读它，
  一处定义两处使用（计划要求）。
- `Subscription` 每租户一条：free/basic/pro，含试用期与账期。
- 试用到期由 Dramatiq cron 每日扫描 → 降级 free（见 tasks.py）。
"""

from __future__ import annotations

from datetime import timedelta

from django.db import models
from django.utils import timezone

from apps.core.base_models import TenantScopedModel


# 预置套餐（定价依据：卡在金蝶 698 与用友 1500 之间偏上，凭"带总账 + AI 风控"打差异）
DEFAULT_PLANS = [
    {
        "code": "free",
        "name": "免费版",
        "price_monthly": 0,
        "sort_order": 0,
        "description": "30 天全功能试用，适合先跑通流程",
        "limits": {
            "users": 1,
            "products": 100,
            "bills_monthly": 50,
            "ai_parse_order": 10,
            "ai_ask": 20,
            "batch_managed": True,
            "finance_ledger": True,
            "print_templates": 2,
            "storefront": False,
        },
    },
    {
        "code": "basic",
        "name": "基础版",
        "price_monthly": 998,
        "sort_order": 1,
        "description": "单店经销商：进销存 + 应收应付 + 打印",
        "limits": {
            "users": 5,
            "products": 3000,
            "bills_monthly": 2000,
            "ai_parse_order": 200,
            "ai_ask": 500,
            "batch_managed": True,
            "finance_ledger": True,
            "print_templates": 20,
            "storefront": False,
        },
    },
    {
        "code": "pro",
        "name": "专业版",
        "price_monthly": 4800,
        "sort_order": 2,
        "description": "多仓多业务员：总账 + 批次效期 + AI 风控 + 订货商城",
        "limits": {
            "users": 50,
            "products": 100000,
            "bills_monthly": 0,          # 0 = 不限
            "ai_parse_order": 2000,
            "ai_ask": 5000,
            "batch_managed": True,
            "finance_ledger": True,
            "print_templates": 0,        # 0 = 不限
            "storefront": True,
        },
    },
]


class Plan(models.Model):
    """套餐定义（全局，非租户级）。"""

    code = models.CharField(max_length=32, unique=True)
    name = models.CharField(max_length=64)
    price_monthly = models.DecimalField(max_digits=10, decimal_places=2, default=0,
                                        help_text="月费（元）；0 = 免费")
    limits = models.JSONField(default=dict, help_text="配额与功能开关（唯一事实来源）")
    description = models.CharField(max_length=255, blank=True, default="")
    sort_order = models.IntegerField(default=0)
    is_active = models.BooleanField(default=True)

    class Meta:
        db_table = "billing_plan"
        verbose_name_plural = "套餐"
        ordering = ["sort_order", "code"]

    def __str__(self):
        return f"{self.name}（¥{self.price_monthly}/月）"


class Subscription(TenantScopedModel):
    """租户订阅（每租户一条）。"""

    STATUS_TRIAL = "trial"
    STATUS_ACTIVE = "active"
    STATUS_EXPIRED = "expired"
    STATUS_CHOICES = [
        (STATUS_TRIAL, "试用中"),
        (STATUS_ACTIVE, "已订阅"),
        (STATUS_EXPIRED, "已过期"),
    ]

    plan = models.ForeignKey(Plan, on_delete=models.PROTECT, related_name="subscriptions")
    status = models.CharField(max_length=16, choices=STATUS_CHOICES, default=STATUS_TRIAL)
    trial_ends_at = models.DateTimeField(null=True, blank=True)
    period_start = models.DateField(null=True, blank=True)
    period_end = models.DateField(null=True, blank=True)
    remark = models.TextField(blank=True, default="")

    class Meta:
        db_table = "billing_subscription"
        verbose_name_plural = "订阅"
        ordering = ["-created_at"]

    def __str__(self):
        return f"{self.tenant_id}:{self.plan.code}/{self.status}"

    @property
    def is_trial_expired(self) -> bool:
        return bool(
            self.status == self.STATUS_TRIAL
            and self.trial_ends_at
            and timezone.now() > self.trial_ends_at
        )

    def effective_limits(self) -> dict:
        """当前生效配额：试用过期或已过期 → 回落 free 套餐限制。"""
        if self.status == self.STATUS_EXPIRED or self.is_trial_expired:
            free = Plan.objects.filter(code="free", is_active=True).first()
            return dict(free.limits) if free else {}
        return dict(self.plan.limits or {})


def seed_plans() -> int:
    """幂等写入预置套餐。返回新建数量。"""
    created = 0
    for spec in DEFAULT_PLANS:
        _, was_created = Plan.objects.update_or_create(
            code=spec["code"],
            defaults={
                "name": spec["name"],
                "price_monthly": spec["price_monthly"],
                "limits": spec["limits"],
                "description": spec["description"],
                "sort_order": spec["sort_order"],
                "is_active": True,
            },
        )
        created += 1 if was_created else 0
    return created


def subscribe(
    tenant,
    *,
    plan_code: str = "free",
    status: str = Subscription.STATUS_TRIAL,
    trial_days: int = 30,
) -> Subscription:
    """为新租户开通订阅（幂等：已存在则原样返回）。"""
    existing = Subscription.objects.filter(tenant=tenant).first()
    if existing is not None:
        return existing

    plan = Plan.objects.filter(code=plan_code, is_active=True).first()
    if plan is None:
        seed_plans()
        plan = Plan.objects.filter(code=plan_code, is_active=True).first()

    now = timezone.now()
    return Subscription.objects.create(
        tenant=tenant,
        plan=plan,
        status=status,
        trial_ends_at=(now + timedelta(days=trial_days)) if status == Subscription.STATUS_TRIAL else None,
        period_start=now.date(),
        period_end=(now + timedelta(days=trial_days)).date(),
    )


def get_subscription(tenant) -> Subscription:
    """取订阅，没有则自动开通 free 试用（保证任何租户都有配额可查）。"""
    sub = Subscription.objects.filter(tenant=tenant).select_related("plan").first()
    if sub is None:
        sub = subscribe(tenant)
    return sub


def upgrade(tenant, plan_code: str, *, months: int = 1) -> Subscription:
    """升级/续订套餐（真实支付接入后，由支付回调调用）。"""
    sub = get_subscription(tenant)
    plan = Plan.objects.filter(code=plan_code, is_active=True).first()
    if plan is None:
        raise ValueError(f"plan {plan_code} not found")

    today = timezone.now().date()
    base = sub.period_end if (sub.period_end and sub.period_end > today) else today
    sub.plan = plan
    sub.status = Subscription.STATUS_ACTIVE
    sub.period_start = today
    sub.period_end = base + timedelta(days=30 * months)
    sub.trial_ends_at = None
    sub.save(update_fields=["plan", "status", "period_start", "period_end",
                            "trial_ends_at", "updated_at"])
    return sub