Implement balance as prefix-sum

development_notebook/2024-03-17.md

@@ -0,0 +1,35 @@
+# Current State
+
+See [[2024-03-06]] for previous log.
+
+Deployed to production at [negligentoctopus.pythonanywhere.com](negligentoctopus.pythonanywhere.com).
+
+Project has been fully configured from cookiecutter-django using MySQL.
+
+Core models are being defined and added to the django-admin interface to be tested.
+
+## Update
+
+Account and transactions are implemented with balance as prefix-sum.
+
+# Today
+
+Define automatic balance tracking in account.
+
+Prefix-sum: This requires a strict ordering. When adding, deleting or changing the amount: Just add it according to the ordering, then update balance on all transactions that follow. The problem here is that we'll change many transactions, so having such a big lock is not a good ideia, and without having a lock we might access a transaction before it is updated.
+    - Strict Ordering: is implemented by standard on django model Meta.order\_by
+
+## Work Log
+__InProgress__
+
+__ToDo__
+* Implement changeable to amt
+* Implement changeable to timestamp
+* Implement initial balance to accounts - change balance on transation to be relative and set a balance property | requires change to update\_after and prev to use new field
+
+__Done__
+* Implement balance as prefix-sum.
+* Migrate.
+* Test on admin.
+
+# To Do

development_notebook/tools.md

@@ -2,33 +2,65 @@
 
 ## tmux
 
+prefix: `Ctrl + a` or `Ctrl + b`
+
 ### Session
-tmux list-sessions
-tmux attach-session -t \<session name\>
+tmux ps
+    ? list sessions
+
+tmux at -t \<session name\>
+    ? Enter session
 
 ### Windows
-`Ctrl + b` then \<arrow-key\>
-    ? Change window
+`prefix` then `[hjkl]
+    ? Change window using VIM keys
 
-`Ctrl + b` then `%`
+`prefix` then `%`
     ? Split horizontal
 
-`Ctrl + b` then `"`
+`prefix` then `"`
     ? Split vertical
 
-`Ctrl + b` then `Alt+[Arrow UDLR]`
-`Ctrl + b` then `:resize-pane -[UDLR] N`
+`prefix` then `[HJKL]`
     ? Resize window by `N` to [Up, Down, Left, Right]
 
 ## NVim
 
+`Ctrl + n` or `Ctrl + \<space\>`
+    ? Cycle autocomplete options
+
+`,` then `d`
+    ? Jump to definition
+        - Hint: duplicate window using `:sp` before jump
+
 :sp \<filepath\>
     ? Split vertical
 
 :vsp \<filepath\>
     ? Split horizontal
 
-###  TODO -> Include plugin commands
+### Windows
+`Ctrl + W` then `[hjkl]`
+    ? Move cursor to window
+
+`Ctrl + W` then `[HJKL]`
+    ? Move window
+
+`Ctrl + W` then `[+ -]`
+    ? Resize window vertically
+
+`Ctrl + W` then `[\< \>]`
+    ? Resize window horizontally
+
+`Ctrl + W` then `\_`
+    ? Resize to near full-screen
+
+`Ctrl + W` then `\=`
+    ? Resize to equal parts
+
+### NERDTree
+`:NERDTree`
+
 
 ## Bash
 

negligent_octopus/core/admin.py

@@ -13,10 +13,19 @@ class AccountAdmin(admin.ModelAdmin):
         "is_removed",
         "modified",
     ]  # TODO: Check modified catches transaction changes
+    readonly_fields = ["balance"]
 
 
 @admin.register(Transaction)
 class TransactionAdmin(admin.ModelAdmin):
-    list_display = ["title", "account", "get_account_owner", "amount", "timestamp"]
+    list_display = [
+        "title",
+        "account",
+        "get_account_owner",
+        "amount",
+        "timestamp",
+        "balance",
+    ]
     search_fields = ["account__owner__username", "account__name", "title"]
     list_filter = ["account__owner", "account", "timestamp"]
+    readonly_fields = ["balance"]

negligent_octopus/core/migrations/0002_transaction_account_add_balance.py

@@ -0,0 +1,44 @@
+# Generated by Django 4.2.10 on 2024-03-18 00:12
+
+from django.db import migrations, models
+import django.utils.timezone
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("core", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name="transaction",
+            options={
+                "ordering": ["-timestamp", "-created"],
+                "verbose_name": "Transaction",
+                "verbose_name_plural": "Transactions",
+            },
+        ),
+        migrations.RemoveField(
+            model_name="account",
+            name="balance",
+        ),
+        migrations.AddField(
+            model_name="transaction",
+            name="balance",
+            field=models.FloatField(editable=False, null=True),
+        ),
+        migrations.AddField(
+            model_name="transaction",
+            name="timestamp",
+            field=models.DateTimeField(default=django.utils.timezone.now),
+        ),
+        migrations.AlterUniqueTogether(
+            name="transaction",
+            unique_together={("timestamp", "created")},
+        ),
+        migrations.RemoveField(
+            model_name="transaction",
+            name="date",
+        ),
+    ]

negligent_octopus/core/models.py

@@ -1,9 +1,9 @@
 from django.db import models
 from django.db import transaction as db_transaction
 from django.utils import timezone
+from django.utils.functional import cached_property
 from model_utils.models import SoftDeletableModel
 from model_utils.models import TimeStampedModel
-from model_utils.tracker import FieldTracker
 
 from negligent_octopus.users.models import User
 
@@ -12,9 +12,9 @@ class Account(TimeStampedModel, SoftDeletableModel):
     owner = models.ForeignKey(User, on_delete=models.CASCADE)
     name = models.CharField(max_length=255)
 
-    @property
+    @cached_property
     def balance(self):
-        return self.transaction_set.last().balance
+        return self.transaction_set.first().balance
 
     def __str__(self):
         return str(self.name)
@@ -26,56 +26,57 @@ class Meta(TimeStampedModel.Meta, SoftDeletableModel.Meta):
 
 
 class Transaction(TimeStampedModel):
+    account = models.ForeignKey(Account, on_delete=models.CASCADE)
     amount = models.FloatField()
     timestamp = models.DateTimeField(default=timezone.now)
-    account = models.ForeignKey(Account, on_delete=models.CASCADE)
-    balance = models.FloatField(default=0.0, editable=False)
+    balance = models.FloatField(editable=False, null=True)
     title = models.CharField(max_length=127)
     description = models.TextField(blank=True)
 
-    tracker = FieldTracker(
-        fields=["amount", "timestamp"],
-    )  # We need to consider changes to the timestamp
-    # and how to update balances based on these
-
     def get_account_owner(self):
         return str(self.account.owner)
 
     @db_transaction.atomic
     def save(self, *args, **kwargs):
-        universe = self.account.transaction_set
-
-        last_transaction = (
-            universe.filter(
-                timestamp__lte=self.timestamp,
-            )
-            .order_by("-created")
-            .first()
-        )
-        self.balance = last_transaction.balance + self.amount
+        old_model = self.__class__.objects.get(pk=self.pk)
+        if old_model.timestamp != self.timestamp or old_model.account != self.account:
+            msg = "Cannot change fields 'account' or 'timestamp'."
+            raise ValueError(msg)  # TODO: Change fields account or timestamp
+
+        if old_model.amount != self.amount:
+            msg = "Cannot change field 'amount'."
+            raise ValueError(msg)
+            # TODO: Id what trans is (del, change, create) and calculate for approp amt
+
+        if self.balance is None:
+            self.balance = self.amount
+            last_transaction = self.account.transaction_set.filter(
+                models.Q(timestamp__lte=self.timestamp)
+                & models.Q(created__lt=self.created),
+            ).first()
+            if last_transaction is not None:
+                self.balance += last_transaction.balance
+
+            universe = self.account.transaction_set.filter(
+                models.Q(timestamp__gte=self.timestamp)
+                & models.Q(created__gt=self.created),
+            ).reverse()
+
+            previous = universe.first()
+            for transaction in universe:
+                if transaction == universe.first():
+                    continue
+                transaction.balance = transaction.amount + previous.balance
+                transaction.save()
+                previous = transaction
+
         super().save(*args, **kwargs)
-        last_transaction = self
-
-        to_update = universe.filter(
-            timestamp__gte=self.timestamp,
-        ).exclude(
-            created__lt=self.created,
-        )
-        for transaction in to_update:
-            transaction.balance = last_transaction.balance + transaction.amount
-            transaction.save()
-            last_transaction = transaction
-
-    def delete(self, *args, **kwargs):
-        self.amount = -self.amount
-        self.save()
-        super().delete(*args, **kwargs)
 
     def __str__(self):
-        return self.title
+        return str(self.title)
 
     class Meta(TimeStampedModel.Meta):
         verbose_name = "Transaction"
         verbose_name_plural = "Transactions"
-        ordering = ["timestamp", "-modified"]
+        ordering = ["-timestamp", "-created"]
         unique_together = ["timestamp", "created"]