using System;
using System.Collections.ObjectModel;
using CommunityToolkit.Mvvm.ComponentModel;
using LiveChartsCore;
using LiveChartsCore.Defaults;
using LiveChartsCore.SkiaSharpView;
using LiveChartsCore.SkiaSharpView.Painting;
using SkiaSharp;

namespace HC_APTBS.ViewModels
{
    /// <summary>
    /// Reusable ViewModel for a single real-time scrolling line chart.
    /// Backed by LiveChartsCore with a fixed-width sample window.
    /// </summary>
    public sealed partial class SingleFlowChartViewModel : ObservableObject
    {
        private const int DefaultMaxSamples = 200;

        private readonly ObservableCollection<double> _values = new();
        private readonly int _maxSamples;

        /// <summary>Chart title label.</summary>
        [ObservableProperty] private string _title = string.Empty;

        /// <summary>Most recent sample value, displayed as a numeric label alongside the chart.</summary>
        [ObservableProperty] private double _currentValue;

        /// <summary>Series array bound to the CartesianChart.</summary>
        public ISeries[] Series { get; }

        /// <summary>X axes for the chart (auto-scrolling, no labels).</summary>
        public Axis[] XAxes { get; }

        /// <summary>Y axes for the chart.</summary>
        public Axis[] YAxes { get; }

        /// <summary>
        /// Tolerance band sections overlaid on the chart.
        /// Updated when <see cref="SetTolerance"/> is called.
        /// </summary>
        [ObservableProperty] private RectangularSection[] _sections = Array.Empty<RectangularSection>();

        /// <summary>
        /// Creates a new chart ViewModel.
        /// </summary>
        /// <param name="title">Display title for the chart.</param>
        /// <param name="lineColor">SKColor for the line series.</param>
        /// <param name="maxSamples">Maximum number of samples before the oldest is dropped.</param>
        public SingleFlowChartViewModel(string title, SKColor lineColor, int maxSamples = DefaultMaxSamples)
        {
            _title = title;
            _maxSamples = maxSamples;

            Series = new ISeries[]
            {
                new LineSeries<double>
                {
                    Values = _values,
                    Fill = null,
                    GeometrySize = 0,
                    Stroke = new SolidColorPaint(lineColor, 2),
                    LineSmoothness = 0,
                    AnimationsSpeed = TimeSpan.Zero
                }
            };

            XAxes = new Axis[]
            {
                new Axis
                {
                    IsVisible = false,
                    AnimationsSpeed = TimeSpan.Zero
                }
            };

            YAxes = new Axis[]
            {
                new Axis
                {
                    AnimationsSpeed = TimeSpan.Zero,
                    MinLimit = 0,
                    SeparatorsPaint = new SolidColorPaint(new SKColor(224, 224, 224), 0.75f)
                }
            };
        }

        /// <summary>
        /// Appends a value to the chart. Drops the oldest value when the window is full.
        /// Must be called on the UI thread.
        /// </summary>
        public void AddValue(double value)
        {
            _values.Add(value);
            CurrentValue = value;
            if (_values.Count > _maxSamples)
                _values.RemoveAt(0);
        }

        /// <summary>
        /// Sets the tolerance band (displayed as a shaded region on the chart).
        /// </summary>
        /// <param name="target">Center value of the tolerance band.</param>
        /// <param name="tolerance">Half-width of the tolerance band.</param>
        public void SetTolerance(double target, double tolerance)
        {
            Sections = new[]
            {
                new RectangularSection
                {
                    Yi = target - tolerance,
                    Yj = target + tolerance,
                    Fill = new SolidColorPaint(SKColors.LimeGreen.WithAlpha(40))
                }
            };
        }

        /// <summary>
        /// Clears all sample data and tolerance bands.
        /// </summary>
        public void Clear()
        {
            _values.Clear();
            Sections = Array.Empty<RectangularSection>();
        }
    }
}