#region Setup
using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using ChartForgeX.Core;
using ChartForgeX.Primitives;
using ChartForgeX.Rendering;
using ChartForgeX.Themes;
using ChartForgeX.Topology;
using ChartForgeX.Typography;
using ChartForgeX.VisualArtifacts;
using ChartForgeX.VisualBlocks;

var mode = VisualThemeMode.Light;
var theme = VisualTheme.Graphite();
var model = TrendLineModelRecipe.Create("confidence", mode);
var context = new VisualRenderContext(
    new VisualLayoutOptions(new VisualSize(800, 440)), theme, mode,
    new VisualFrame("Request volume and its trend", "", showLegend: null, showSurface: false));
var prepared = model.Prepare(context);
File.WriteAllText("visual.svg", prepared.ToSvg());
File.WriteAllBytes("visual.png", prepared.ToPng());
File.WriteAllText("visual.html", prepared.ToArtifact("example", VisualArtifactKind.Chart).ToHtmlPage());
#endregion

/// <summary>Fits the selected native model to retained measurements with a pointwise interval.</summary>
public static class TrendLineModelRecipe {
    /// <summary>Creates observed values and a fitted curve; logarithmic-response intervals describe the conditional median.</summary>
    public static Chart Create(string variant = "polynomial", VisualThemeMode mode = VisualThemeMode.Light) {
        var selection = variant.StartsWith("compact-", StringComparison.Ordinal) ? variant.Substring(8) : variant;
        var model = selection switch {
            "polynomial" => ChartTrendLineModel.Polynomial,
            "logarithmic" => ChartTrendLineModel.Logarithmic,
            "exponential" => ChartTrendLineModel.Exponential,
            "power" => ChartTrendLineModel.Power,
            "confidence" or "prediction" => ChartTrendLineModel.Linear,
            _ => throw new ArgumentOutOfRangeException(nameof(variant))
        };
        var source = Enumerable.Range(1, 12).Select(index => {
            double x = index, residual = index % 3 - 1;
            var value = model switch {
                ChartTrendLineModel.Polynomial => 8 + .4 * x * x - .9 * x + .4 * residual,
                ChartTrendLineModel.Logarithmic => 4 + 5 * Math.Log(x) + .2 * residual,
                ChartTrendLineModel.Exponential => 5 * Math.Exp(.13 * x) * (1 + .04 * residual),
                ChartTrendLineModel.Power => 2 * Math.Pow(x, 1.4) * (1 + .04 * residual),
                _ => 12 + 1.8 * x + .8 * residual
            };
            return new ChartPoint(x, value);
        }).ToArray();
        var observations = ChartSeries.CreateScatter(new ChartSeriesId("measurements"), "Measured observations", source);
        var fit = ChartSeries.CreateTrendLine(new ChartSeriesId("native-fit"), model + " fit", source, null, options => {
            options.Model = model; options.PolynomialDegree = 2;
            options.Interval = selection == "prediction" ? ChartTrendLineIntervalKind.Prediction : ChartTrendLineIntervalKind.Confidence;
            options.ConfidenceLevel = .95;
        });
        return Chart.Create().WithXAxis("Source X").WithYAxis("Observed response").WithLegend(true).WithDataLabels(false)
            .AddSeries(observations).AddSeries(fit);
    }
}