feat: add billing pricing rules

apps/billing/models.py

@@ -6,6 +6,10 @@ from django.db.models import Q
 from apps.users.models import ApiKey
 
 
+def normalize_resolution(value: str | None) -> str:
+    return "" if value is None else str(value).strip().upper()
+
+
 class CallRecord(models.Model):
     class OperationType(models.TextChoices):
         TITLE = "title", "Generate title"
@@ -66,6 +70,90 @@ class CallRecord(models.Model):
         return f"{self.operation_type}:{self.alias or '<default>'} {self.status}"
 
 
+class PricingRule(models.Model):
+    operation_type = models.CharField(max_length=32, choices=CallRecord.OperationType.choices)
+    alias = models.CharField(max_length=64)
+    resolution = models.CharField(
+        max_length=32,
+        blank=True,
+        default="",
+        help_text="Leave blank to apply to every resolution for this alias.",
+    )
+    points_cost = models.BigIntegerField()
+    is_active = models.BooleanField(default=True)
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "pricing_rule"
+        ordering = ("operation_type", "alias", "resolution")
+        constraints = [
+            models.UniqueConstraint(
+                fields=("operation_type", "alias", "resolution"),
+                name="unique_pricing_rule_per_alias_resolution",
+            ),
+            models.CheckConstraint(
+                condition=Q(points_cost__gt=0),
+                name="pricing_rule_points_cost_positive",
+            ),
+        ]
+        indexes = [
+            models.Index(fields=("operation_type", "alias", "is_active")),
+            models.Index(fields=("operation_type", "alias", "resolution", "is_active")),
+        ]
+
+    def __str__(self) -> str:
+        resolution = self.resolution or "*"
+        return f"{self.operation_type}:{self.alias}:{resolution} = {self.points_cost}"
+
+    def clean(self) -> None:
+        super().clean()
+        self.alias = str(self.alias or "").strip()
+        self.resolution = normalize_resolution(self.resolution)
+        if not self.alias:
+            raise ValidationError({"alias": "Alias is required."})
+
+    def save(self, *args, **kwargs) -> None:
+        self.full_clean()
+        super().save(*args, **kwargs)
+
+
+class ExchangeRate(models.Model):
+    currency = models.CharField(max_length=10, default="CNY")
+    points_per_unit = models.DecimalField(max_digits=12, decimal_places=4)
+    is_active = models.BooleanField(default=True)
+    effective_from = models.DateTimeField()
+    note = models.CharField(max_length=255, blank=True)
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "exchange_rate"
+        ordering = ("-effective_from", "-id")
+        constraints = [
+            models.CheckConstraint(
+                condition=Q(points_per_unit__gt=0),
+                name="exchange_rate_points_per_unit_positive",
+            ),
+        ]
+        indexes = [
+            models.Index(fields=("currency", "is_active", "effective_from")),
+        ]
+
+    def __str__(self) -> str:
+        return f"{self.currency} 1 = {self.points_per_unit} points"
+
+    def clean(self) -> None:
+        super().clean()
+        self.currency = str(self.currency or "").strip().upper()
+        if not self.currency:
+            raise ValidationError({"currency": "Currency is required."})
+
+    def save(self, *args, **kwargs) -> None:
+        self.full_clean()
+        super().save(*args, **kwargs)
+
+
 class PointsLedger(models.Model):
     class ChangeType(models.TextChoices):
         RECHARGE = "recharge", "Recharge"