namespace Dashboard
{
    public enum MeasurementUnit
    {
        /// <summary>
        /// The default unit. A size of a single picture element.
        /// </summary>
        Pixel,
        /// <summary>
        /// 1/72th of an inch traditional in graphics design.
        /// </summary>
        Point,
        /// <summary>
        /// The universal length unit for small distances.
        /// </summary>
        Millimeter,
        /// <summary>
        /// An inverse proportional unit with respect to the container size.
        /// </summary>
        Star,
        /// <summary>
        /// A directly proportional unit with respect to the container size.
        /// </summary>
        Percent,
    }

    public record struct AdvancedMetric(MeasurementUnit Unit, float Value)
    {
        public AdvancedMetric Convert(MeasurementUnit target, float dpi, float rel, int stars)
        {
            if (Unit == target)
                return this;

            float pixels = Unit switch {
                MeasurementUnit.Pixel => Value,
                MeasurementUnit.Point => Value * (72f / dpi),
                MeasurementUnit.Millimeter => Value * (28.3464566929f / dpi),
                MeasurementUnit.Star => Value * rel / stars,
                MeasurementUnit.Percent => Value * rel / 100,
                _ => throw new Exception(),
            };

            float value = target switch {
                MeasurementUnit.Pixel => pixels,
                MeasurementUnit.Point => Value * (dpi / 72f),
                // MeasurementUnit.Millimeter =>
            };

            return new AdvancedMetric(target, value);
        }

        public override string ToString()
        {
            return $"{Value} {Unit.ToShortString()}";
        }

        public static bool TryParse(ReadOnlySpan<char> str, out AdvancedMetric metric)
        {
            metric = default;
            return false;
        }

        public static AdvancedMetric Parse(ReadOnlySpan<char> str) =>
            TryParse(str, out AdvancedMetric metric)
                ? metric
                : throw new Exception($"Could not parse the value '{str}'.");
    }

    public static class MeasurementExtensions
    {
        public static bool IsRelative(this MeasurementUnit unit) => unit switch {
            MeasurementUnit.Star or MeasurementUnit.Percent => true,
            _ => false,
        };
        public static bool IsAbsolute(this MeasurementUnit unit) => !IsRelative(unit);

        public static string ToShortString(this MeasurementUnit unit) => unit switch {
            MeasurementUnit.Pixel => "px",
            MeasurementUnit.Point => "pt",
            MeasurementUnit.Millimeter => "mm",
            MeasurementUnit.Star => "*",
            MeasurementUnit.Percent => "%",
            _ => throw new Exception("Unknown unit."),
        };
    }
}