feat(plotnine): implement waterfall-basic (#5744)

## Implementation: `waterfall-basic` - python/plotnine

Implements the **python/plotnine** version of `waterfall-basic`.

**File:** `plots/waterfall-basic/implementations/python/plotnine.py`

**Parent Issue:** #777

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/25410836349)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Markus Neusinger <2921697+MarkusNeusinger@users.noreply.github.com>

Author: github-actions[bot]

plots/waterfall-basic/implementations/python/plotnine.py

@@ -1,13 +1,17 @@
-""" pyplots.ai
+""" anyplot.ai
 waterfall-basic: Basic Waterfall Chart
-Library: plotnine 0.15.1 | Python 3.13.11
-Quality: 91/100 | Created: 2025-12-14
+Library: plotnine 0.15.4 | Python 3.13.13
+Quality: 84/100 | Created: 2026-05-06
 """
 
+import os
+
 import pandas as pd
 from plotnine import (
     aes,
     element_blank,
+    element_line,
+    element_rect,
     element_text,
     geom_rect,
     geom_segment,
@@ -21,9 +25,15 @@
 )
 
 
+# Theme tokens
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
+
 # Data - quarterly financial breakdown
-categories = ["Revenue", "Product Costs", "Marketing", "Operations", "R&D", "Admin", "Taxes", "Net Profit"]
-values = [500, -150, -60, -45, -35, -30, -40, 140]
+categories = ["Starting Balance", "Q1 Sales", "Operating Costs", "R&D Investment", "Tax Payment", "Ending Balance"]
+values = [1000, 450, -280, -120, -150, 900]
 
 # Calculate waterfall positions
 df = pd.DataFrame({"category": categories, "value": values})
@@ -35,20 +45,17 @@
 ends = []
 bar_types = []
 
-for i, (_cat, val) in enumerate(zip(categories, values, strict=True)):
+for i, val in enumerate(values):
     if i == 0:
-        # First bar: starts at 0, ends at value
         starts.append(0)
         ends.append(val)
         bar_types.append("total")
         running_total = val
-    elif i == len(categories) - 1:
-        # Last bar: total bar starting from 0
+    elif i == len(values) - 1:
         starts.append(0)
         ends.append(running_total)
         bar_types.append("total")
     else:
-        # Middle bars: changes
         if val >= 0:
             starts.append(running_total)
             ends.append(running_total + val)
@@ -64,52 +71,54 @@
 df["bar_type"] = bar_types
 df["x_pos"] = range(len(categories))
 
-# Create connector line data (from end of one bar to start of next)
+# Create connector lines
 connectors = []
 for i in range(len(df) - 1):
-    if i < len(df) - 2:  # Don't connect to the final total bar
+    if i < len(df) - 2:
         connectors.append(
             {"x_start": df.iloc[i]["x_pos"] + 0.4, "x_end": df.iloc[i + 1]["x_pos"] - 0.4, "y": df.iloc[i]["end"]}
         )
-connector_df = pd.DataFrame(connectors)
+connector_df = pd.DataFrame(connectors) if connectors else pd.DataFrame()
+
+# Colors: green for positive, red for negative, gray for totals
+colors = {"total": INK_SOFT, "positive": "#2ecc71", "negative": "#e74c3c"}
 
-# Add labels for values
-df["label_y"] = df.apply(lambda row: row["end"] + 10 if row["end"] >= row["start"] else row["start"] + 10, axis=1)
-df["label_text"] = df.apply(
-    lambda row: f"+{int(row['value'])}" if row["value"] > 0 and row["bar_type"] != "total" else str(int(row["value"])),
-    axis=1,
+# Create plot
+plot = ggplot() + geom_rect(
+    df, aes(xmin="x_pos - 0.35", xmax="x_pos + 0.35", ymin="start", ymax="end", fill="bar_type")
 )
 
-# Colors: blue for totals, green for positive, red for negative
-colors = {"total": "#306998", "positive": "#2ECC71", "negative": "#E74C3C"}
+if not connector_df.empty:
+    plot = plot + geom_segment(
+        connector_df, aes(x="x_start", xend="x_end", y="y", yend="y"), color=INK_SOFT, size=0.5, alpha=0.5
+    )
 
-# Create plot
 plot = (
-    ggplot()
-    + geom_rect(df, aes(xmin="x_pos - 0.4", xmax="x_pos + 0.4", ymin="start", ymax="end", fill="bar_type"))
-    + geom_segment(
-        connector_df, aes(x="x_start", xend="x_end", y="y", yend="y"), color="#666666", size=0.5, linetype="dashed"
-    )
-    + geom_text(df, aes(x="x_pos", y="label_y", label="label_text"), size=12, color="#333333")
+    plot
+    + geom_text(df, aes(x="x_pos", y="end", label="value"), size=10, color=INK)
     + scale_fill_manual(
-        values=colors, name="Type", labels={"total": "Total", "positive": "Increase", "negative": "Decrease"}
+        values=colors, name="Category", labels={"total": "Total", "positive": "Increase", "negative": "Decrease"}
     )
-    + labs(x="", y="Amount ($K)", title="Quarterly Financials · waterfall-basic · plotnine · pyplots.ai")
+    + scale_x_continuous(breaks=list(range(len(categories))), labels=categories, limits=(-0.6, len(categories) - 0.4))
+    + labs(x="", y="Amount ($1K)", title="Quarterly Financial Summary · waterfall-basic · plotnine · anyplot.ai")
     + theme_minimal()
     + theme(
         figure_size=(16, 9),
-        text=element_text(size=14),
-        axis_title=element_text(size=20),
-        axis_text_x=element_text(size=16, rotation=30, ha="right"),
-        axis_text_y=element_text(size=16),
-        plot_title=element_text(size=24),
-        legend_text=element_text(size=16),
-        legend_position="top",
+        plot_background=element_rect(fill=PAGE_BG, color=PAGE_BG),
+        panel_background=element_rect(fill=PAGE_BG),
+        panel_grid_major=element_line(color=INK_SOFT, size=0.3, alpha=0.1, linewidth=0.8),
         panel_grid_minor=element_blank(),
+        panel_border=element_rect(color=INK_SOFT, fill=None, size=0.5),
+        axis_title=element_text(size=20, color=INK),
+        axis_text_x=element_text(size=16, color=INK_SOFT, angle=45, ha="right"),
+        axis_text_y=element_text(size=16, color=INK_SOFT),
+        axis_line=element_line(color=INK_SOFT, size=0.5),
+        plot_title=element_text(size=24, color=INK, face="medium"),
+        legend_background=element_rect(fill=PAGE_BG, color=INK_SOFT, size=0.5),
+        legend_text=element_text(size=16, color=INK_SOFT),
+        legend_title=element_text(size=16, color=INK),
+        legend_position="top",
     )
 )
 
-# Add x-axis labels
-plot = plot + scale_x_continuous(breaks=list(range(len(categories))), labels=categories)
-
-plot.save("plot.png", dpi=300)
+plot.save(f"plot-{THEME}.png", dpi=300, width=16, height=9)