feat(highcharts): implement line-annotated-events (#3045)

## Implementation: `line-annotated-events` - highcharts

Implements the **highcharts** version of `line-annotated-events`.

**File:** `plots/line-annotated-events/implementations/highcharts.py`

**Parent Issue:** #2997

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20617493187)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/line-annotated-events/implementations/highcharts.py

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+""" pyplots.ai
+line-annotated-events: Annotated Line Plot with Event Markers
+Library: highcharts unknown | Python 3.13.11
+Quality: 92/100 | Created: 2025-12-31
+"""
+
+import tempfile
+import time
+import urllib.request
+from datetime import datetime, timedelta
+from pathlib import Path
+
+import numpy as np
+from highcharts_core.chart import Chart
+from highcharts_core.options import HighchartsOptions
+from highcharts_core.options.series.area import LineSeries
+from highcharts_core.options.series.scatter import ScatterSeries
+from selenium import webdriver
+from selenium.webdriver.chrome.options import Options
+
+
+# Data - Simulated daily product metrics over 6 months with event annotations
+np.random.seed(42)
+
+# Generate dates for 180 days
+start_date = datetime(2024, 1, 1)
+dates = [start_date + timedelta(days=i) for i in range(180)]
+timestamps = [int(d.timestamp() * 1000) for d in dates]  # Highcharts uses milliseconds
+
+# Generate realistic user growth data with trend and seasonality
+base = 10000
+trend = np.linspace(0, 5000, 180)
+seasonal = 500 * np.sin(np.linspace(0, 4 * np.pi, 180))
+noise = np.random.randn(180) * 300
+values = base + trend + seasonal + noise
+
+# Define significant events to annotate
+events = [
+    (datetime(2024, 1, 15), "Feature A Launch"),
+    (datetime(2024, 2, 20), "Marketing Campaign"),
+    (datetime(2024, 3, 25), "App Redesign"),
+    (datetime(2024, 4, 30), "Partnership Deal"),
+    (datetime(2024, 5, 28), "Mobile Update"),
+]
+event_timestamps = [int(e[0].timestamp() * 1000) for e in events]
+event_labels = [e[1] for e in events]
+
+# Find y-values at event dates for scatter markers
+event_y_values = []
+for evt_date, _ in events:
+    idx = (evt_date - start_date).days
+    if 0 <= idx < len(values):
+        event_y_values.append(round(values[idx]))
+    else:
+        event_y_values.append(None)
+
+# Create chart with container specified
+chart = Chart(container="container")
+chart.options = HighchartsOptions()
+
+# Chart configuration - explicit size for proper rendering
+chart.options.chart = {
+    "type": "line",
+    "width": 4800,
+    "height": 2700,
+    "backgroundColor": "#ffffff",
+    "style": {"fontFamily": "Arial, sans-serif"},
+}
+
+# Title
+chart.options.title = {
+    "text": "line-annotated-events · highcharts · pyplots.ai",
+    "style": {"fontSize": "48px", "fontWeight": "bold", "color": "#333333"},
+}
+
+# Subtitle
+chart.options.subtitle = {
+    "text": "Daily Active Users with Key Milestones",
+    "style": {"fontSize": "32px", "color": "#666666"},
+}
+
+# Build plot lines for events with alternating label positions
+plot_lines = []
+for i, (ts, label) in enumerate(zip(event_timestamps, event_labels, strict=False)):
+    plot_lines.append(
+        {
+            "value": ts,
+            "color": "#FFD43B",
+            "width": 5,
+            "dashStyle": "Dash",
+            "zIndex": 5,
+            "label": {
+                "text": label,
+                "rotation": 0,
+                "style": {"fontSize": "28px", "fontWeight": "bold", "color": "#333333"},
+                "y": 25 if i % 2 == 0 else 70,
+                "x": 12,
+                "align": "left",
+            },
+        }
+    )
+
+# X-axis (datetime)
+chart.options.x_axis = {
+    "type": "datetime",
+    "title": {"text": "Date", "style": {"fontSize": "40px", "color": "#333333"}},
+    "labels": {"style": {"fontSize": "32px", "color": "#333333"}},
+    "dateTimeLabelFormats": {"day": "%e %b", "week": "%e %b", "month": "%b '%y", "year": "%Y"},
+    "plotLines": plot_lines,
+    "lineColor": "#333333",
+    "lineWidth": 2,
+    "tickColor": "#333333",
+    "tickInterval": 30 * 24 * 3600 * 1000,  # Monthly ticks
+}
+
+# Y-axis
+chart.options.y_axis = {
+    "title": {"text": "Daily Active Users", "style": {"fontSize": "40px", "color": "#333333"}},
+    "labels": {"style": {"fontSize": "32px", "color": "#333333"}},
+    "gridLineWidth": 1,
+    "gridLineColor": "#E0E0E0",
+    "gridLineDashStyle": "Dash",
+    "lineColor": "#333333",
+    "lineWidth": 2,
+}
+
+# Legend configuration
+chart.options.legend = {
+    "enabled": True,
+    "itemStyle": {"fontSize": "32px", "color": "#333333"},
+    "align": "center",
+    "verticalAlign": "bottom",
+    "y": 30,
+    "symbolRadius": 6,
+    "symbolWidth": 24,
+}
+
+# Plot options for styling
+chart.options.plot_options = {
+    "line": {"lineWidth": 5, "marker": {"enabled": False}},
+    "scatter": {"marker": {"symbol": "circle", "radius": 16, "lineWidth": 4, "lineColor": "#333333"}},
+}
+
+# Credits
+chart.options.credits = {"enabled": False}
+
+# Add main line series
+line_series = LineSeries()
+line_series.name = "Daily Active Users"
+line_series.data = [[ts, round(val)] for ts, val in zip(timestamps, values, strict=False)]
+line_series.color = "#306998"
+line_series.line_width = 5
+line_series.marker = {"enabled": False}
+
+chart.add_series(line_series)
+
+# Add event marker series (scatter points on the line at event dates)
+event_series = ScatterSeries()
+event_series.name = "Key Events"
+event_series.data = [
+    {"x": ts, "y": yval} for ts, yval in zip(event_timestamps, event_y_values, strict=False) if yval is not None
+]
+event_series.color = "#FFD43B"
+event_series.marker = {"symbol": "circle", "radius": 18, "lineWidth": 4, "lineColor": "#333333", "fillColor": "#FFD43B"}
+event_series.z_index = 10
+
+chart.add_series(event_series)
+
+# Download Highcharts JS for inline embedding
+highcharts_url = "https://code.highcharts.com/highcharts.js"
+with urllib.request.urlopen(highcharts_url, timeout=30) as response:
+    highcharts_js = response.read().decode("utf-8")
+
+# Generate chart JS code
+chart_js = chart.to_js_literal()
+
+# Build HTML with inline scripts - use string concatenation to avoid f-string issues
+# with JavaScript template literals containing braces
+html_parts = [
+    "<!DOCTYPE html>",
+    "<html>",
+    "<head>",
+    '    <meta charset="utf-8">',
+    "    <style>",
+    "        * { margin: 0; padding: 0; }",
+    "        body { background: #ffffff; }",
+    "        #container { width: 4800px; height: 2700px; }",
+    "    </style>",
+    "    <script>",
+    highcharts_js,
+    "    </script>",
+    "</head>",
+    "<body>",
+    '    <div id="container"></div>',
+    "    <script>",
+    chart_js,
+    "    </script>",
+    "</body>",
+    "</html>",
+]
+html_content = "\n".join(html_parts)
+
+# Write temp HTML
+with tempfile.NamedTemporaryFile(mode="w", suffix=".html", delete=False, encoding="utf-8") as f:
+    f.write(html_content)
+    temp_path = f.name
+
+# Save HTML file for interactive version
+with open("plot.html", "w", encoding="utf-8") as f:
+    f.write(html_content)
+
+# Take screenshot with headless Chrome
+chrome_options = Options()
+chrome_options.add_argument("--headless=new")
+chrome_options.add_argument("--no-sandbox")
+chrome_options.add_argument("--disable-dev-shm-usage")
+chrome_options.add_argument("--disable-gpu")
+chrome_options.add_argument("--window-size=5000,3000")
+chrome_options.add_argument("--force-device-scale-factor=1")
+
+driver = webdriver.Chrome(options=chrome_options)
+driver.set_window_size(5000, 3000)
+driver.get(f"file://{temp_path}")
+time.sleep(6)  # Wait for chart to render
+
+# Find the chart container and take screenshot of it
+container = driver.find_element("id", "container")
+container.screenshot("plot.png")
+driver.quit()
+
+# Clean up temp file
+Path(temp_path).unlink()

plots/line-annotated-events/metadata/highcharts.yaml

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+library: highcharts
+specification_id: line-annotated-events
+created: '2025-12-31T11:00:38Z'
+updated: '2025-12-31T11:11:16Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20617493187
+issue: 2997
+python_version: 3.13.11
+library_version: unknown
+preview_url: https://storage.googleapis.com/pyplots-images/plots/line-annotated-events/highcharts/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/line-annotated-events/highcharts/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/line-annotated-events/highcharts/plot.html
+quality_score: 92
+review:
+  strengths:
+  - Excellent implementation of event annotation pattern using plotLines with alternating
+    label positions
+  - Clean colorblind-safe palette with blue line and yellow event markers
+  - Proper use of Highcharts datetime axis with appropriate label formatting
+  - Well-structured code following KISS principles with proper Selenium screenshot
+    workflow
+  - Realistic business scenario with 5 distinct milestones across 180-day period
+  weaknesses:
+  - Legend text could be larger for better visibility at full resolution
+  - Could leverage Highcharts native annotation module for more sophisticated event
+    labels
+  - Event marker scatter points could have tooltips showing event details for better
+    interactivity in HTML output