feat(bokeh): implement gauge-basic (#9534)

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

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

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

**Parent Issue:** #857

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/28476691727)*

---------

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

@@ -1,15 +1,26 @@
 """ anyplot.ai
 gauge-basic: Basic Gauge Chart
-Library: bokeh 3.9.0 | Python 3.14.4
-Quality: 87/100 | Updated: 2026-04-25
+Library: bokeh 3.9.1 | Python 3.13.14
+Quality: 89/100 | Updated: 2026-06-30
 """
 
 import os
+import sys
+import time
+from pathlib import Path
+
+
+# Remove script's own directory from sys.path to prevent self-shadowing
+# (this file is named bokeh.py; without this, `import bokeh` would find itself)
+_here = os.path.dirname(os.path.abspath(__file__))
+sys.path = [p for p in sys.path if os.path.abspath(p or ".") != _here]
 
 import numpy as np
-from bokeh.io import export_png, output_file, save
-from bokeh.models import Label
+from bokeh.io import output_file, save
+from bokeh.models import ColumnDataSource, HoverTool, Label
 from bokeh.plotting import figure
+from selenium import webdriver
+from selenium.webdriver.chrome.options import Options
 
 
 # Theme tokens
@@ -19,12 +30,12 @@
 INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
 INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
 
-# Okabe-Ito zones: low / mid / high (intuitive + colorblind-safe)
-ZONE_LOW = "#AE3030"  # imprint red — bad
-ZONE_MID = "#DDCC77"  # imprint amber — caution
-ZONE_HIGH = "#009E73"  # imprint green — good
+# Imprint zone colors — semantic convention: red=bad, amber=caution, green=good
+ZONE_LOW = "#AE3030"  # Imprint matte red
+ZONE_MID = "#DDCC77"  # Imprint amber
+ZONE_HIGH = "#009E73"  # Imprint brand green
 
-# Data
+# Data — CPU utilization
 value = 72
 min_value = 0
 max_value = 100
@@ -34,8 +45,9 @@
 center_x, center_y = 0.0, 0.0
 outer_radius = 0.95
 inner_radius = 0.62
+arc_mid_radius = (inner_radius + outer_radius) / 2  # label midpoint inside arc
 needle_length = 0.86
-start_angle = np.pi  # left
+start_angle = np.pi  # leftmost position (180°)
 
 # Map data values onto the semi-circle (pi → 0 radians)
 zone_bounds = np.array([min_value] + thresholds + [max_value])
@@ -46,39 +58,86 @@
 
 needle_angle = start_angle - (value - min_value) / (max_value - min_value) * np.pi
 
-# Figure
+# Figure — landscape canvas; toolbar_location=None prevents height bloat in screenshot
+W, H = 3200, 1800
 p = figure(
-    width=4800,
-    height=2700,
-    title="gauge-basic · bokeh · anyplot.ai",
-    x_range=(-1.25, 1.25),
-    y_range=(-0.45, 1.20),
+    width=W,
+    height=H,
+    title="gauge-basic · python · bokeh · anyplot.ai",
+    x_range=(-1.5, 1.5),
+    y_range=(-0.58, 1.32),
     tools="",
     toolbar_location=None,
     background_fill_color=PAGE_BG,
     border_fill_color=PAGE_BG,
     outline_line_color=None,
+    min_border_bottom=80,
+    min_border_left=80,
+    min_border_top=120,
+    min_border_right=80,
 )
 p.axis.visible = False
 p.grid.visible = False
+p.outline_line_color = None
 
-p.title.text_font_size = "44pt"
+p.title.text_font_size = "50pt"
 p.title.text_color = INK
 p.title.align = "center"
 
-# Zone arcs via annular_wedge (cleaner than manual polygons)
+# Zone arcs via annular_wedge — ColumnDataSource enables HoverTool
 zone_colors = [ZONE_LOW, ZONE_MID, ZONE_HIGH]
-for i, color in enumerate(zone_colors):
-    p.annular_wedge(
-        x=center_x,
-        y=center_y,
-        inner_radius=inner_radius,
-        outer_radius=outer_radius,
-        start_angle=zone_angles[i + 1],
-        end_angle=zone_angles[i],
-        fill_color=color,
-        line_color=PAGE_BG,
-        line_width=4,
+zone_names = ["Low", "Caution", "Optimal"]
+zone_ranges = ["0–30", "30–70", "70–100"]
+
+zone_source = ColumnDataSource(
+    data={
+        "x": [center_x, center_x, center_x],
+        "y": [center_y, center_y, center_y],
+        "inner_radius": [inner_radius, inner_radius, inner_radius],
+        "outer_radius": [outer_radius, outer_radius, outer_radius],
+        "start_angle": [float(zone_angles[1]), float(zone_angles[2]), float(zone_angles[3])],
+        "end_angle": [float(zone_angles[0]), float(zone_angles[1]), float(zone_angles[2])],
+        "fill_color": zone_colors,
+        "zone": zone_names,
+        "range": zone_ranges,
+    }
+)
+
+zone_renderer = p.annular_wedge(
+    x="x",
+    y="y",
+    inner_radius="inner_radius",
+    outer_radius="outer_radius",
+    start_angle="start_angle",
+    end_angle="end_angle",
+    fill_color="fill_color",
+    line_color=PAGE_BG,
+    line_width=4,
+    source=zone_source,
+)
+
+p.add_tools(HoverTool(renderers=[zone_renderer], tooltips=[("Zone", "@zone"), ("Range", "@range")]))
+
+# Zone labels inside each arc segment — contrasting fixed colors (zones are theme-invariant)
+# red/green zones get light text; amber zone gets dark text for contrast
+zone_mid_values = [15.0, 50.0, 85.0]
+zone_label_colors = ["#FFFDF6", "#1A1A17", "#FFFDF6"]
+
+for mid_val, label_text, label_color in zip(zone_mid_values, zone_names, zone_label_colors, strict=True):
+    a = start_angle - (mid_val / max_value) * np.pi
+    lx = arc_mid_radius * np.cos(a)
+    ly = arc_mid_radius * np.sin(a)
+    p.add_layout(
+        Label(
+            x=lx,
+            y=ly,
+            text=label_text,
+            text_font_size="22pt",
+            text_color=label_color,
+            text_align="center",
+            text_baseline="middle",
+            angle=float(a - np.pi / 2),  # tangent along arc for natural text flow
+        )
     )
 
 # Tick marks and labels
@@ -94,17 +153,17 @@
 
     p.add_layout(
         Label(
-            x=center_x + (outer_radius + 0.20) * cos_a,
-            y=center_y + (outer_radius + 0.20) * sin_a,
+            x=center_x + (outer_radius + 0.22) * cos_a,
+            y=center_y + (outer_radius + 0.22) * sin_a,
             text=str(tick_val),
-            text_font_size="30pt",
+            text_font_size="31pt",
             text_color=INK_SOFT,
             text_align="center",
             text_baseline="middle",
         )
     )
 
-# Needle (triangle)
+# Needle (triangle pointing to current value)
 needle_tip_x = center_x + needle_length * np.cos(needle_angle)
 needle_tip_y = center_y + needle_length * np.sin(needle_angle)
 half_base = 0.035
@@ -119,23 +178,62 @@
 )
 
 # Center hub
-p.scatter(x=[center_x], y=[center_y], size=70, marker="circle", fill_color=INK, line_color=PAGE_BG, line_width=4)
+p.scatter(x=[center_x], y=[center_y], size=55, marker="circle", fill_color=INK, line_color=PAGE_BG, line_width=4)
 
 # Value display
 p.add_layout(
     Label(
         x=center_x,
-        y=-0.28,
+        y=-0.20,
         text=str(value),
-        text_font_size="84pt",
+        text_font_size="80pt",
         text_color=INK,
         text_align="center",
         text_baseline="middle",
         text_font_style="bold",
     )
 )
 
-# Save
-export_png(p, filename=f"plot-{THEME}.png")
-output_file(f"plot-{THEME}.html")
+# Metric label
+p.add_layout(
+    Label(
+        x=center_x,
+        y=-0.44,
+        text="CPU Utilization (%)",
+        text_font_size="30pt",
+        text_color=INK_SOFT,
+        text_align="center",
+        text_baseline="middle",
+    )
+)
+
+# Save interactive HTML
+html_path = Path(f"plot-{THEME}.html")
+output_file(str(html_path))
 save(p)
+
+# Inject body background CSS to prevent thin border artifact in headless-Chrome screenshot
+html_content = html_path.read_text()
+body_style = f"<style>body{{margin:0;padding:0;background:{PAGE_BG};}}</style>"
+html_content = html_content.replace("</head>", f"{body_style}\n</head>", 1)
+html_path.write_text(html_content)
+
+# Screenshot via headless Chrome — use CDP to set exact viewport to match figure dimensions
+opts = Options()
+for arg in (
+    "--headless=new",
+    "--no-sandbox",
+    "--disable-dev-shm-usage",
+    "--disable-gpu",
+    f"--window-size={W},{H}",
+    "--hide-scrollbars",
+):
+    opts.add_argument(arg)
+driver = webdriver.Chrome(options=opts)
+driver.execute_cdp_cmd(
+    "Emulation.setDeviceMetricsOverride", {"width": W, "height": H, "deviceScaleFactor": 1, "mobile": False}
+)
+driver.get(f"file://{html_path.resolve()}")
+time.sleep(3)
+driver.save_screenshot(f"plot-{THEME}.png")
+driver.quit()