using System;
using Azimuth;

namespace Glass.PerformanceTests
{
    /// <summary>
    /// A text layout implementation under comparison.  Each operation returns a fingerprint of its answer, so a run
    /// shows where engines disagree.
    /// </summary>
    public sealed class Engine
    {
        public readonly string Name;
        public readonly Func<Workload, Vector> MeasureWidth;
        public readonly Func<Workload, Vector> CalculateSize;
        public readonly Func<Workload, Vector> PlaceGlyphs;

        /// <summary>
        /// Ignores the operation and every constraint, so scenarios sharing a font and text are the same work.
        /// </summary>
        public readonly bool ReadsOnlyFontAndText;

        public Engine(string name, Func<Workload, Vector> measureWidth, Func<Workload, Vector> calculateSize,
            Func<Workload, Vector> placeGlyphs, bool readsOnlyFontAndText = false)
        {
            Name = name;
            MeasureWidth = measureWidth;
            CalculateSize = calculateSize;
            PlaceGlyphs = placeGlyphs;
            ReadsOnlyFontAndText = readsOnlyFontAndText;
        }

        /// <summary>
        /// A single stage of layout, run the same way whatever the operation or constraints.
        /// </summary>
        public static Engine ForStage(string name, Func<Workload, Vector> run)
        {
            return new Engine(name, run, run, run, readsOnlyFontAndText: true);
        }

        public Func<Workload, Vector> For(Operation operation)
        {
            switch (operation)
            {
                case Operation.MeasureWidth:
                    return MeasureWidth;
                case Operation.CalculateSize:
                    return CalculateSize;
                case Operation.PlaceGlyphs:
                    return PlaceGlyphs;
                default:
                    throw new ArgumentOutOfRangeException(nameof(operation), operation, null);
            }
        }

        /// <summary>
        /// Whether this engine does the same work on both scenarios, so measuring one measures the other.
        /// </summary>
        public bool DoesSameWork(Scenario first, Scenario second)
        {
            if (ReadsOnlyFontAndText)
            {
                return first.Workload.Font == second.Workload.Font && first.Workload.Text == second.Workload.Text;
            }

            return first == second;
        }
    }
}