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sprint-9-10-figure-factory-pattern.-.md

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+# Sprint 9-10 - Figure Factory Pattern for Reusable Charts
+
+**Date**: 2026-01-17
+**Tags**: plotly, dash, design-patterns, python, visualization, reusability, code-organization
+
+---
+
+## Context
+Creating multiple chart types across 5 dashboard tabs, with consistent styling and behavior needed across all visualizations.
+
+## Problem
+Without a standardized approach, each callback would create figures inline with:
+- Duplicated styling code (colors, fonts, backgrounds)
+- Inconsistent hover templates
+- Hard-to-maintain figure creation logic
+- No reuse between tabs
+
+## Solution
+Created a `figures/` module with factory functions:
+
+```
+figures/
+├── __init__.py           # Exports all factories
+├── choropleth.py         # Map visualizations
+├── bar_charts.py         # ranking_bar, stacked_bar, horizontal_bar
+├── scatter.py            # scatter_figure, bubble_chart
+├── radar.py              # radar_figure, comparison_radar
+└── demographics.py       # age_pyramid, donut_chart
+```
+
+Factory pattern benefits:
+1. **Consistent styling** - dark theme applied once
+2. **Type-safe interfaces** - clear parameters for each chart type
+3. **Easy testing** - factories can be unit tested with sample data
+4. **Reusability** - same factory used across multiple tabs
+
+Example factory signature:
+```python
+def create_ranking_bar(
+    data: list[dict],
+    name_column: str,
+    value_column: str,
+    title: str = "",
+    top_n: int = 5,
+    bottom_n: int = 5,
+    top_color: str = "#4CAF50",
+    bottom_color: str = "#F44336",
+) -> go.Figure:
+```
+
+## Prevention
+- **Create factories early** - before implementing callbacks
+- **Design generic interfaces** - factories should work with any data matching the schema
+- **Apply styling in one place** - use constants for colors, fonts
+- **Test factories independently** - with synthetic data before integration