feat: implement basic Letter model and unit tests

backend/letters/migrations/0001_initial.py

@@ -0,0 +1,46 @@
+# Generated by Django 6.0.4 on 2026-04-10 15:26
+
+import uuid
+
+import django.db.models.deletion
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    initial = True
+
+    dependencies = [
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="Letter",
+            fields=[
+                ("public_id", models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True, serialize=False)),
+                (
+                    "type",
+                    models.CharField(
+                        choices=[("KEPT", "Kept"), ("SENT", "Sent"), ("VAULT", "Vault")], default="KEPT", max_length=10
+                    ),
+                ),
+                (
+                    "status",
+                    models.CharField(
+                        choices=[("DRAFT", "Draft"), ("SEALED", "Sealed"), ("BURNED", "Burned")],
+                        default="DRAFT",
+                        max_length=10,
+                    ),
+                ),
+                ("created_at", models.DateTimeField(auto_now_add=True)),
+                ("updated_at", models.DateTimeField(auto_now=True)),
+                (
+                    "user",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE, related_name="letters", to=settings.AUTH_USER_MODEL
+                    ),
+                ),
+            ],
+        ),
+    ]

backend/letters/models.py

@@ -1 +1,26 @@
-# Create your models here.
+import uuid
+
+from django.conf import settings
+from django.db import models
+
+
+class Letter(models.Model):
+    class Type(models.TextChoices):
+        KEPT = "KEPT", "Kept"
+        SENT = "SENT", "Sent"
+        VAULT = "VAULT", "Vault"
+
+    class Status(models.TextChoices):
+        DRAFT = "DRAFT", "Draft"
+        SEALED = "SEALED", "Sealed"
+        BURNED = "BURNED", "Burned"
+
+    public_id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name="letters")
+    type = models.CharField(max_length=10, choices=Type.choices, default=Type.KEPT)
+    status = models.CharField(max_length=10, choices=Status.choices, default=Status.DRAFT)
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    def __str__(self):
+        return f"{self.type} - {self.status}"

backend/letters/tests.py

@@ -1 +1,24 @@
-# Create your tests here.
+from django.contrib.auth import get_user_model
+from django.test import TestCase
+
+from .models import Letter
+
+User = get_user_model()
+
+
+class LetterModelTest(TestCase):
+    def setUp(self):
+        self.user = User.objects.create_user(email="test@pi-ku.app", password="password1234", full_name="Test User")
+
+    def test_create_letter_basic(self):
+        """create a basic Letter model with required fields"""
+        letter = Letter.objects.create(user=self.user, type="KEPT", status="DRAFT")
+
+        self.assertEqual(letter.user, self.user)
+        self.assertEqual(letter.type, "KEPT")
+        self.assertEqual(letter.status, "DRAFT")
+        self.assertIsNotNone(letter.public_id)
+
+        # Verify timestamps are auto-added
+        self.assertIsNotNone(letter.created_at)
+        self.assertIsNotNone(letter.updated_at)