Add Spending Heatmap Visualization

expense_tracker/core/repositories.py

@@ -170,6 +170,72 @@ def update_transaction(self, transaction_id: int, data: dict) -> None:
         self.conn.execute(query, values)
         self.conn.commit()
 
+    def get_daily_spending_for_month(self, year: int, month: int) -> dict[int, float]:
+        """
+        Returns a dictionary mapping day-of-month (1-31) to total spending.
+        Only includes expenses (negative amounts).
+        """
+        # Create date range for the month
+        start_date = date(year, month, 1)
+        if month == 12:
+            end_date = date(year + 1, 1, 1)
+        else:
+            end_date = date(year, month + 1, 1)
+
+        rows = self.conn.execute(
+            """
+            SELECT CAST(strftime('%d', date) AS INTEGER) as day,
+                   SUM(ABS(amount)) as total
+            FROM transactions
+            WHERE date >= ? AND date < ?
+              AND amount < 0
+            GROUP BY day
+            """,
+            (start_date.isoformat(), end_date.isoformat()),
+        )
+
+        result: dict[int, float] = {}
+        for row in rows.fetchall():
+            result[row["day"]] = row["total"]
+        return result
+
+    def get_transactions_for_date(self, target_date: date) -> list[Transaction]:
+        """
+        Query transactions matching exact date.
+        Order by amount DESC (largest expenses first).
+        """
+        rows = self.conn.execute(
+            "SELECT * FROM transactions WHERE date = ? ORDER BY amount ASC",
+            (target_date.isoformat(),),
+        )
+        transactions: list[Transaction] = []
+        for row in rows.fetchall():
+            transaction = self._row_to_transaction(row)
+            if transaction:
+                transactions.append(transaction)
+        return transactions
+
+    def get_months_with_expenses(self) -> list[tuple[int, int]]:
+        """
+        Returns a list of (year, month) tuples for all months that have expenses.
+        Only includes months with negative amounts (expenses).
+        Ordered by year and month descending (most recent first).
+        """
+        rows = self.conn.execute(
+            """
+            SELECT DISTINCT
+                CAST(strftime('%Y', date) AS INTEGER) as year,
+                CAST(strftime('%m', date) AS INTEGER) as month
+            FROM transactions
+            WHERE amount < 0
+            ORDER BY year DESC, month DESC
+            """
+        )
+        result: list[tuple[int, int]] = []
+        for row in rows.fetchall():
+            result.append((row["year"], row["month"]))
+        return result
+
 
 class MerchantCategoryRepository:
     """

expense_tracker/gui/main_window.py

@@ -1,7 +1,8 @@
 import tkinter as tk
+from datetime import date
 from tkinter import ttk
 
-from expense_tracker.gui.tabs import TransactionsTab
+from expense_tracker.gui.tabs import TransactionsTab, HeatmapTab
 
 
 class MainWindow(tk.Frame):
@@ -23,8 +24,15 @@ def __init__(self, master, transaction_repo, merchant_repo):
             self.notebook, transaction_repo, merchant_repo, self
         )
 
-        # Add tab to notebook
+        # Create Heatmap tab
+        self.heatmap_tab = HeatmapTab(self.notebook, transaction_repo, self)
+
+        # Add tabs to notebook
         self.notebook.add(self.transactions_tab, text="Transactions")
+        self.notebook.add(self.heatmap_tab, text="Heatmap")
+
+        # Bind tab change event for lazy loading
+        self.notebook.bind("<<NotebookTabChanged>>", self._on_tab_changed)
 
     def _open_dialog(self, dialog_class, *args, **kwargs):
         if self._active_dialog is not None and self._active_dialog.winfo_exists():
@@ -51,3 +59,15 @@ def on_close():
 
         self._active_dialog = None
         self.transactions_tab.refresh()
+
+    def _on_tab_changed(self, event):
+        """Refresh tab content when user switches tabs."""
+        current_tab = self.notebook.select()
+        tab_index = self.notebook.index(current_tab)
+        if tab_index == 1:  # Heatmap tab
+            self.heatmap_tab.refresh()
+
+    def show_transactions_for_date(self, target_date: date):
+        """Switch to Transactions tab with date filter applied."""
+        self.notebook.select(0)  # Switch to Transactions tab (index 0)
+        self.transactions_tab.filter_by_date(target_date)

expense_tracker/gui/tabs/__init__.py

@@ -1,3 +1,4 @@
 from .transactions_tab import TransactionsTab
+from .heatmap_tab import HeatmapTab
 
-__all__ = ["TransactionsTab"]
+__all__ = ["TransactionsTab", "HeatmapTab"]