feat(bokeh): implement sankey-basic (#5602)

## Implementation: `sankey-basic` - python/bokeh

Implements the **python/bokeh** version of `sankey-basic`.

**File:** `plots/sankey-basic/implementations/python/bokeh.py`

**Parent Issue:** #810

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/25156351219)*

---------

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/sankey-basic/implementations/python/bokeh.py

@@ -1,15 +1,32 @@
-""" pyplots.ai
+""" anyplot.ai
 sankey-basic: Basic Sankey Diagram
-Library: bokeh 3.8.1 | Python 3.13.11
-Quality: 91/100 | Created: 2025-12-23
+Library: bokeh 3.9.0 | Python 3.13.13
+Quality: 86/100 | Updated: 2026-04-30
 """
 
+import os
+import sys
+
+
+_script_dir = os.path.dirname(os.path.abspath(__file__))
+sys.path = [p for p in sys.path if os.path.abspath(p or ".") != _script_dir]
+
 import numpy as np
-from bokeh.io import export_png, save
+from bokeh.io import export_png, output_file, save
 from bokeh.models import Label
 from bokeh.plotting import figure
 
 
+# Theme tokens
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+ELEVATED_BG = "#FFFDF6" if THEME == "light" else "#242420"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
+
+# Okabe-Ito palette — first source always #009E73
+OKABE_ITO = ["#009E73", "#D55E00", "#0072B2", "#CC79A7", "#E69F00"]
+
 # Data - Energy flow from sources to sectors (TWh)
 flows = [
     {"source": "Coal", "target": "Industrial", "value": 25},
@@ -34,21 +51,11 @@
     if f["target"] not in targets:
         targets.append(f["target"])
 
-# Color palette for sources (Python Blue first, then colorblind-safe)
-source_colors = {
-    "Coal": "#306998",  # Python Blue
-    "Gas": "#FFD43B",  # Python Yellow
-    "Nuclear": "#9B59B6",  # Purple
-    "Hydro": "#3498DB",  # Light blue
-    "Solar": "#E67E22",  # Orange
-}
-
-# Target colors (darker shades)
-target_colors = {
-    "Industrial": "#2C3E50",  # Dark blue-grey
-    "Commercial": "#1ABC9C",  # Teal
-    "Residential": "#E74C3C",  # Red
-}
+# Source colors: Okabe-Ito in canonical order
+source_colors = {s: OKABE_ITO[i] for i, s in enumerate(sources)}
+
+# Target node colors: slightly muted variants of INK_SOFT family
+target_node_colors = {"Industrial": "#5A6A7A", "Commercial": "#7A6A8A", "Residential": "#6A7A5A"}
 
 # Calculate totals for node sizing
 source_totals = {s: sum(f["value"] for f in flows if f["source"] == s) for s in sources}
@@ -64,37 +71,37 @@
 
 # Calculate node positions for sources (left side)
 source_height_total = sum(source_totals.values())
-scale_factor = (total_height - 2 * padding_y - (len(sources) - 1) * node_gap) / source_height_total
+scale_src = (total_height - 2 * padding_y - (len(sources) - 1) * node_gap) / source_height_total
 
 source_nodes = {}
 current_y = padding_y
 for s in sources:
-    height = source_totals[s] * scale_factor
+    height = source_totals[s] * scale_src
     source_nodes[s] = {"x": left_x, "y": current_y, "height": height, "value": source_totals[s]}
     current_y += height + node_gap
 
 # Calculate node positions for targets (right side)
 target_height_total = sum(target_totals.values())
-scale_factor_t = (total_height - 2 * padding_y - (len(targets) - 1) * node_gap) / target_height_total
+scale_tgt = (total_height - 2 * padding_y - (len(targets) - 1) * node_gap) / target_height_total
 
 target_nodes = {}
 current_y = padding_y
 for t in targets:
-    height = target_totals[t] * scale_factor_t
+    height = target_totals[t] * scale_tgt
     target_nodes[t] = {"x": right_x - node_width, "y": current_y, "height": height, "value": target_totals[t]}
     current_y += height + node_gap
 
 # Track flow offsets for stacking flows at each node
-source_offsets = dict.fromkeys(sources, 0)
-target_offsets = dict.fromkeys(targets, 0)
+source_offsets = dict.fromkeys(sources, 0.0)
+target_offsets = dict.fromkeys(targets, 0.0)
 
-# Create figure (4800 × 2700 px)
+# Plot
 p = figure(
     width=4800,
     height=2700,
-    title="Energy Flow · sankey-basic · bokeh · pyplots.ai",
-    x_range=(-15, 115),
-    y_range=(-5, 105),
+    title="Energy Flow · sankey-basic · bokeh · anyplot.ai",
+    x_range=(-18, 118),
+    y_range=(-5, 108),
     tools="",
     toolbar_location=None,
 )
@@ -105,52 +112,41 @@
     tgt = f["target"]
     value = f["value"]
 
-    # Get node info
     src_node = source_nodes[src]
     tgt_node = target_nodes[tgt]
 
-    # Flow height proportional to value
     src_flow_height = (value / source_totals[src]) * src_node["height"]
     tgt_flow_height = (value / target_totals[tgt]) * tgt_node["height"]
 
-    # Source connection points
     x0 = src_node["x"] + node_width
     y0_bottom = src_node["y"] + source_offsets[src]
     y0_top = y0_bottom + src_flow_height
 
-    # Target connection points
     x1 = tgt_node["x"]
     y1_bottom = tgt_node["y"] + target_offsets[tgt]
     y1_top = y1_bottom + tgt_flow_height
 
-    # Update offsets for stacking
     source_offsets[src] += src_flow_height
     target_offsets[tgt] += tgt_flow_height
 
-    # Create smooth bezier flow path
-    t = np.linspace(0, 1, 50)
+    t = np.linspace(0, 1, 60)
     cx0 = x0 + (x1 - x0) * 0.4
     cx1 = x0 + (x1 - x0) * 0.6
 
-    # Cubic bezier for x positions
     x_path = (1 - t) ** 3 * x0 + 3 * (1 - t) ** 2 * t * cx0 + 3 * (1 - t) * t**2 * cx1 + t**3 * x1
-
-    # Linear interpolation for y positions
     y_bottom = (1 - t) * y0_bottom + t * y1_bottom
     y_top = (1 - t) * y0_top + t * y1_top
 
-    # Create closed polygon
     xs = list(x_path) + list(x_path[::-1])
     ys = list(y_top) + list(y_bottom[::-1])
 
-    # Draw flow with source color and transparency
     p.patch(
         xs,
         ys,
         fill_color=source_colors[src],
-        fill_alpha=0.5,
+        fill_alpha=0.45,
         line_color=source_colors[src],
-        line_alpha=0.7,
+        line_alpha=0.6,
         line_width=1,
     )
 
@@ -163,19 +159,19 @@
         bottom=node["y"],
         top=node["y"] + node["height"],
         fill_color=source_colors[s],
-        fill_alpha=0.9,
-        line_color="white",
+        fill_alpha=0.92,
+        line_color=PAGE_BG,
         line_width=2,
     )
-    # Add label to the left of node
     label = Label(
-        x=node["x"] - 1,
+        x=node["x"] - 1.5,
         y=node["y"] + node["height"] / 2,
         text=f"{s} ({node['value']} TWh)",
         text_font_size="22pt",
         text_align="right",
         text_baseline="middle",
-        text_color="#333333",
+        text_color=INK,
+        text_font="helvetica",
     )
     p.add_layout(label)
 
@@ -187,38 +183,39 @@
         right=node["x"] + node_width,
         bottom=node["y"],
         top=node["y"] + node["height"],
-        fill_color=target_colors[t],
-        fill_alpha=0.9,
-        line_color="white",
+        fill_color=target_node_colors[t],
+        fill_alpha=0.92,
+        line_color=PAGE_BG,
         line_width=2,
     )
-    # Add label to the right of node
     label = Label(
-        x=node["x"] + node_width + 1,
+        x=node["x"] + node_width + 1.5,
         y=node["y"] + node["height"] / 2,
         text=f"{t} ({node['value']} TWh)",
         text_font_size="22pt",
         text_align="left",
         text_baseline="middle",
-        text_color="#333333",
+        text_color=INK,
+        text_font="helvetica",
     )
     p.add_layout(label)
 
-# Styling
+# Style — theme-adaptive chrome
 p.title.text_font_size = "32pt"
+p.title.text_color = INK
 p.title.align = "center"
+p.title.text_font = "helvetica"
 
-# Hide axes for cleaner Sankey look
 p.xaxis.visible = False
 p.yaxis.visible = False
 p.xgrid.visible = False
 p.ygrid.visible = False
 p.outline_line_color = None
 
-# Background
-p.background_fill_color = "#FAFAFA"
-p.border_fill_color = "#FFFFFF"
+p.background_fill_color = PAGE_BG
+p.border_fill_color = PAGE_BG
 
-# Save outputs
-export_png(p, filename="plot.png")
-save(p, filename="plot.html")
+# Save
+export_png(p, filename=f"plot-{THEME}.png")
+output_file(f"plot-{THEME}.html")
+save(p)