from django.db import models
from django.contrib.auth.models import User
from django.db.models.signals import post_save, pre_delete
from django.dispatch import receiver
import json


class Article(models.Model):
    STATUS_CHOICES = (
        ("draft", "草稿"),
        ("published", "已发布"),
        ("archived", "归档"),
    )
    title = models.CharField(max_length=200, verbose_name="标题")
    content = models.TextField(verbose_name="正文")
    author = models.ForeignKey(User, on_delete=models.CASCADE, verbose_name="作者")
    status = models.CharField(max_length=20, choices=STATUS_CHOICES, default="draft", verbose_name="状态")
    views = models.PositiveIntegerField(default=0, verbose_name="浏览量")
    created_at = models.DateTimeField(auto_now_add=True, verbose_name="创建时间")
    updated_at = models.DateTimeField(auto_now=True, verbose_name="更新时间")
    is_deleted = models.BooleanField(default=False, verbose_name="是否软删除")  # 加分项软删除

    def __str__(self):
        return self.title

    class Meta:
        verbose_name = "文章"
        verbose_name_plural = "文章"
        ordering = ["-created_at"]


class Attachment(models.Model):
    article = models.ForeignKey(Article, on_delete=models.CASCADE, related_name="attachments", verbose_name="关联文章")
    file = models.FileField(upload_to="attachments/", verbose_name="文件")
    filename = models.CharField(max_length=200, verbose_name="文件名")
    upload_time = models.DateTimeField(auto_now_add=True, verbose_name="上传时间")
    downloads = models.PositiveIntegerField(default=0, verbose_name="下载次数")  # 加分项下载计数

    def __str__(self):
        return self.filename

    class Meta:
        verbose_name = "附件"
        verbose_name_plural = "附件"
        ordering = ["-upload_time"]


class AuditLog(models.Model):
    OP_TYPE_CHOICES = (
        ("create", "创建"),
        ("update", "更新"),
        ("publish", "发布"),
        ("archive", "归档"),
        ("delete", "删除"),
    )
    article = models.ForeignKey(Article, on_delete=models.SET_NULL, null=True, verbose_name="关联文章")
    operator = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, verbose_name="操作人")
    op_type = models.CharField(max_length=20, choices=OP_TYPE_CHOICES, verbose_name="操作类型")
    diff = models.JSONField(default=dict, verbose_name="变更摘要")
    time = models.DateTimeField(auto_now_add=True, verbose_name="操作时间")

    def __str__(self):
        return f"{self.get_op_type_display()} - {self.article}"

    class Meta:
        verbose_name = "审计日志"
        verbose_name_plural = "审计日志"
        ordering = ["-time"]


# ========== Django信号：自动生成审计日志（作业硬性要求！禁止在视图手动创建AuditLog） ==========
@receiver(post_save, sender=Article)
def article_post_save(sender, instance, created,** kwargs):
    if created:
        # 新建文章
        AuditLog.objects.create(
            article=instance,
            operator=instance.author,
            op_type="create",
            diff={"title": instance.title, "status": instance.status}
        )
    else:
        # 更新文章，记录状态变更
        # kwargs里有update_fields，用来拿到改动字段
        diff_data = {}
        if kwargs.get("update_fields") and "status" in kwargs["update_fields"]:
            diff_data["status"] = {"new": instance.status}
            if instance.status == "published":
                op_type = "publish"
            elif instance.status == "archived":
                op_type = "archive"
            else:
                op_type = "update"
        else:
            op_type = "update"
            diff_data["title"] = instance.title
        AuditLog.objects.create(
            article=instance,
            operator=instance.author,
            op_type=op_type,
            diff=diff_data
        )


@receiver(pre_delete, sender=Article)
def article_pre_delete(sender, instance,** kwargs):
    # 删除文章前触发信号
    AuditLog.objects.create(
        article=instance,
        operator=instance.author,
        op_type="delete",
        diff={"title": instance.title}
    )