feat(highcharts): implement timeseries-forecast-uncertainty (#3284)

## Implementation: `timeseries-forecast-uncertainty` - highcharts

Implements the **highcharts** version of
`timeseries-forecast-uncertainty`.

**File:**
`plots/timeseries-forecast-uncertainty/implementations/highcharts.py`

**Parent Issue:** #3188

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20797279910)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/timeseries-forecast-uncertainty/implementations/highcharts.py

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+""" pyplots.ai
+timeseries-forecast-uncertainty: Time Series Forecast with Uncertainty Band
+Library: highcharts unknown | Python 3.13.11
+Quality: 93/100 | Created: 2026-01-07
+"""
+
+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 AreaRangeSeries, LineSeries
+from selenium import webdriver
+from selenium.webdriver.chrome.options import Options
+
+
+# Data - Monthly product demand with forecast
+np.random.seed(42)
+
+# Historical data: 36 months (3 years)
+n_historical = 36
+n_forecast = 12
+
+# Create dates
+start_date = datetime(2022, 1, 1)
+historical_dates = [start_date + timedelta(days=30 * i) for i in range(n_historical)]
+forecast_dates = [historical_dates[-1] + timedelta(days=30 * (i + 1)) for i in range(n_forecast)]
+all_dates = historical_dates + forecast_dates
+
+# Generate historical data with trend and seasonality
+trend = np.linspace(100, 150, n_historical)
+seasonality = 20 * np.sin(np.linspace(0, 6 * np.pi, n_historical))
+noise = np.random.normal(0, 8, n_historical)
+historical_values = trend + seasonality + noise
+
+# Generate forecast with increasing uncertainty
+last_value = historical_values[-1]
+forecast_trend = np.linspace(last_value, last_value + 20, n_forecast)
+forecast_seasonality = 20 * np.sin(np.linspace(6 * np.pi, 8 * np.pi, n_forecast))
+forecast_values = forecast_trend + forecast_seasonality
+
+# Confidence intervals widen over time
+time_factor = np.linspace(1, 3, n_forecast)
+ci_80 = 10 * time_factor
+ci_95 = 18 * time_factor
+
+lower_80 = forecast_values - ci_80
+upper_80 = forecast_values + ci_80
+lower_95 = forecast_values - ci_95
+upper_95 = forecast_values + ci_95
+
+# Convert dates to timestamps (milliseconds for Highcharts)
+historical_timestamps = [int(d.timestamp() * 1000) for d in historical_dates]
+forecast_timestamps = [int(d.timestamp() * 1000) for d in forecast_dates]
+forecast_start_ts = forecast_timestamps[0]
+
+# Download Highcharts JS
+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")
+
+# Download Highcharts More for arearange
+highcharts_more_url = "https://code.highcharts.com/highcharts-more.js"
+with urllib.request.urlopen(highcharts_more_url, timeout=30) as response:
+    highcharts_more_js = response.read().decode("utf-8")
+
+# Create chart
+chart = Chart(container="container")
+chart.options = HighchartsOptions()
+
+# Chart configuration
+chart.options.chart = {
+    "type": "line",
+    "width": 4800,
+    "height": 2700,
+    "backgroundColor": "#ffffff",
+    "spacingTop": 60,
+    "spacingBottom": 120,
+    "spacingLeft": 100,
+    "spacingRight": 120,
+}
+
+# Title
+chart.options.title = {
+    "text": "timeseries-forecast-uncertainty \u00b7 highcharts \u00b7 pyplots.ai",
+    "style": {"fontSize": "56px", "fontWeight": "bold"},
+    "margin": 40,
+}
+
+chart.options.subtitle = {
+    "text": "Monthly Product Demand with 80% and 95% Confidence Intervals",
+    "style": {"fontSize": "36px", "color": "#666666"},
+}
+
+# X-axis (datetime)
+chart.options.x_axis = {
+    "type": "datetime",
+    "title": {"text": "Date", "style": {"fontSize": "36px"}, "margin": 25},
+    "labels": {"style": {"fontSize": "28px"}},
+    "dateTimeLabelFormats": {"month": "%b %Y"},
+    "gridLineWidth": 1,
+    "gridLineColor": "rgba(0, 0, 0, 0.1)",
+    "plotLines": [
+        {
+            "value": forecast_start_ts,
+            "color": "#666666",
+            "width": 4,
+            "dashStyle": "Dash",
+            "label": {
+                "text": "Forecast Start",
+                "style": {"fontSize": "28px", "color": "#555555", "fontWeight": "bold"},
+                "rotation": 0,
+                "y": -15,
+            },
+            "zIndex": 5,
+        }
+    ],
+}
+
+# Y-axis
+chart.options.y_axis = {
+    "title": {"text": "Product Demand (Units)", "style": {"fontSize": "36px"}, "margin": 25},
+    "labels": {"style": {"fontSize": "28px"}},
+    "gridLineWidth": 1,
+    "gridLineColor": "rgba(0, 0, 0, 0.1)",
+}
+
+# Legend
+chart.options.legend = {
+    "enabled": True,
+    "itemStyle": {"fontSize": "32px"},
+    "symbolWidth": 50,
+    "symbolHeight": 24,
+    "margin": 30,
+}
+
+# Tooltip
+chart.options.tooltip = {"shared": True, "style": {"fontSize": "28px"}, "xDateFormat": "%B %Y", "valueDecimals": 1}
+
+# Plot options for line width
+chart.options.plot_options = {"line": {"lineWidth": 5, "marker": {"radius": 8}}, "arearange": {"lineWidth": 0}}
+
+# 95% confidence band (lighter, behind 80%)
+ci_95_series = AreaRangeSeries()
+ci_95_series.name = "95% Confidence Interval"
+ci_95_series.data = [
+    {"x": forecast_timestamps[i], "low": float(lower_95[i]), "high": float(upper_95[i])} for i in range(n_forecast)
+]
+ci_95_series.color = "rgba(255, 212, 59, 0.25)"
+ci_95_series.fill_opacity = 0.25
+ci_95_series.line_width = 0
+ci_95_series.marker = {"enabled": False}
+ci_95_series.z_index = 0
+
+# 80% confidence band (darker)
+ci_80_series = AreaRangeSeries()
+ci_80_series.name = "80% Confidence Interval"
+ci_80_series.data = [
+    {"x": forecast_timestamps[i], "low": float(lower_80[i]), "high": float(upper_80[i])} for i in range(n_forecast)
+]
+ci_80_series.color = "rgba(255, 212, 59, 0.45)"
+ci_80_series.fill_opacity = 0.45
+ci_80_series.line_width = 0
+ci_80_series.marker = {"enabled": False}
+ci_80_series.z_index = 1
+
+# Historical data series
+historical_series = LineSeries()
+historical_series.name = "Historical (Actual)"
+historical_series.data = [
+    {"x": historical_timestamps[i], "y": float(historical_values[i])} for i in range(n_historical)
+]
+historical_series.color = "#306998"
+historical_series.line_width = 4
+historical_series.marker = {"enabled": True, "radius": 6, "symbol": "circle"}
+historical_series.z_index = 3
+
+# Forecast series
+forecast_series = LineSeries()
+forecast_series.name = "Forecast"
+forecast_series.data = [{"x": forecast_timestamps[i], "y": float(forecast_values[i])} for i in range(n_forecast)]
+forecast_series.color = "#E67E22"
+forecast_series.line_width = 4
+forecast_series.dash_style = "Dash"
+forecast_series.marker = {"enabled": True, "radius": 6, "symbol": "diamond"}
+forecast_series.z_index = 4
+
+# Add series in order (back to front)
+chart.add_series(ci_95_series)
+chart.add_series(ci_80_series)
+chart.add_series(historical_series)
+chart.add_series(forecast_series)
+
+# Disable credits
+chart.options.credits = {"enabled": False}
+
+# Generate HTML with inline scripts
+html_str = chart.to_js_literal()
+html_content = f"""<!DOCTYPE html>
+<html>
+<head>
+    <meta charset="utf-8">
+    <script>{highcharts_js}</script>
+    <script>{highcharts_more_js}</script>
+</head>
+<body style="margin:0;">
+    <div id="container" style="width: 4800px; height: 2700px;"></div>
+    <script>{html_str}</script>
+</body>
+</html>"""
+
+# Save HTML version for interactive viewing (uses CDN for portability)
+cdn_html = f"""<!DOCTYPE html>
+<html>
+<head>
+    <meta charset="utf-8">
+    <script src="https://code.highcharts.com/highcharts.js"></script>
+    <script src="https://code.highcharts.com/highcharts-more.js"></script>
+</head>
+<body style="margin:0;">
+    <div id="container" style="width: 100%; height: 600px;"></div>
+    <script>{html_str}</script>
+</body>
+</html>"""
+with open("plot.html", "w", encoding="utf-8") as f:
+    f.write(cdn_html)
+
+# Take screenshot with Selenium
+with tempfile.NamedTemporaryFile(mode="w", suffix=".html", delete=False, encoding="utf-8") as f:
+    f.write(html_content)
+    temp_path = f.name
+
+chrome_options = Options()
+chrome_options.add_argument("--headless")
+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")
+
+driver = webdriver.Chrome(options=chrome_options)
+driver.get(f"file://{temp_path}")
+time.sleep(5)
+
+# Screenshot the chart container element for exact dimensions
+container = driver.find_element("id", "container")
+container.screenshot("plot.png")
+driver.quit()
+
+Path(temp_path).unlink()