// Animancer // https://kybernetik.com.au/animancer // Copyright 2018-2024 Kybernetik //
// Inspector Gadgets // https://kybernetik.com.au/animancer // Copyright 2017-2024 Kybernetik //

#if UNITY_EDITOR && UNITY_IMGUI

using Animancer.Editor;
using System;
using System.Collections.Generic;
using System.Globalization;
using UnityEditor;

namespace Animancer.Units.Editor
//namespace InspectorGadgets.Editor
{
    /// <summary>[Editor-Only]
    /// A system for formatting floats as strings that fit into a limited area and storing the results so they can be
    /// reused to minimise the need for garbage collection, particularly for string construction.
    /// </summary>
    /// 
    /// <remarks>
    /// This system only affects the display value. Once you select a field, it shows its actual value.
    /// <para></para>
    /// <strong>Example:</strong>
    /// With <c>"x"</c> as the suffix:
    /// <list type="bullet">
    /// <item><c>1.111111</c> could instead show <c>1.111~x</c>.</item>
    /// <item><c>0.00001234567</c> would normally show <c>1.234567e-05</c>, but with this it instead shows <c>0~x</c>
    /// because very small values generally aren't useful.</item>
    /// <item><c>99999999</c> shows <c>1e+08x</c> because very large values are already approximations and trying to
    /// format them correctly would be very difficult.</item>
    /// </list>
    /// </remarks>
    /// 
    /// https://kybernetik.com.au/animancer/api/Animancer.Units.Editor/CompactUnitConversionCache
    /// https://kybernetik.com.au/inspector-gadgets/api/InspectorGadgets.Editor/CompactUnitConversionCache
    /// 
    public class CompactUnitConversionCache
    {
        /************************************************************************************************************************/

        /// <summary>Should the fields show approximations if the value is too long for the GUI?</summary>
        public static bool ShowApproximations
            => AnimancerSettingsGroup<AnimationTimeAttributeSettings>.Instance.showApproximations;
        //  => PropertyDrawers.TransformPropertyDrawer.ShowApproximations;

        /************************************************************************************************************************/

        /// <summary>The suffix added to the end of each value.</summary>
        public readonly string Suffix;

        /// <summary>The <see cref="Suffix"/> with a <c>~</c> before it to indicate an approximation.</summary>
        public readonly string ApproximateSuffix;

        /// <summary>The value <c>0</c> with the <see cref="Suffix"/>.</summary>
        public readonly string ConvertedZero;

        /// <summary>The value <c>0</c> with the <see cref="ApproximateSuffix"/>.</summary>
        public readonly string ConvertedSmallPositive;

        /// <summary>The value <c>-0</c> with the <see cref="ApproximateSuffix"/>.</summary>
        public readonly string ConvertedSmallNegative;

        /// <summary>The pixel width of the <see cref="Suffix"/> when drawn by <see cref="EditorStyles.numberField"/>.</summary>
        public float _SuffixWidth;

        /// <summary>The caches for each character count.</summary>
        /// <remarks><c>this[x]</c> is a cache that outputs strings with <c>x</c> characters.</remarks>
        private readonly List<ConversionCache<float, string>>
            Caches = new();

        /************************************************************************************************************************/

        /// <summary>Strings mapped to the width they would require for a <see cref="EditorStyles.numberField"/>.</summary>
        private static ConversionCache<string, float> _WidthCache;

        /// <summary>Padding around the text in a <see cref="EditorStyles.numberField"/>.</summary>
        public static float _FieldPadding;

        /// <summary>The pixel width of the <c>~</c> character when drawn by <see cref="EditorStyles.numberField"/>.</summary>
        public static float _ApproximateSymbolWidth;

        /// <summary>The character(s) used to separate decimal values in the current OS language.</summary>
        public static string _DecimalSeparator;

        /// <summary>Values smaller than this become <c>0~</c> or <c>-0~</c>.</summary>
        public const float
            SmallExponentialThreshold = 0.0001f;

        /// <summary>Values larger than this can't be approximated.</summary>
        public const float
            LargeExponentialThreshold = 9999999f;

        /************************************************************************************************************************/

        /// <summary>Creates a new <see cref="CompactUnitConversionCache"/>.</summary>
        public CompactUnitConversionCache(string suffix)
        {
            Suffix = suffix;
            ApproximateSuffix = "~" + Suffix;
            ConvertedZero = "0" + Suffix;
            ConvertedSmallPositive = "0" + ApproximateSuffix;
            ConvertedSmallNegative = "-0" + ApproximateSuffix;
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Returns a cached string representing the `value` trimmed to fit within the `width` (if necessary) and with
        /// the <see cref="Suffix"/> added on the end.
        /// </summary>
        public string Convert(float value, float width)
        {
            if (value == 0)
                return ConvertedZero;

            if (!ShowApproximations)
                return GetCache(0).Convert(value);

            if (value < SmallExponentialThreshold &&
                value > -SmallExponentialThreshold)
                return value > 0 ? ConvertedSmallPositive : ConvertedSmallNegative;

            var index = CalculateCacheIndex(value, width);
            return GetCache(index).Convert(value);
        }

        /************************************************************************************************************************/

        /// <summary>Calculate the index of the cache to use for the given parameters.</summary>
        private int CalculateCacheIndex(float value, float width)
        {
            //if (value > LargeExponentialThreshold ||
            //    value < -LargeExponentialThreshold)
            //    return 0;

            var valueString = value.ToStringCached();

            // It the approximated string wouldn't be shorter than the original, don't approximate.
            if (valueString.Length < 2 + ApproximateSuffix.Length)
                return 0;

            if (_SuffixWidth == 0)
            {
                if (_WidthCache == null)
                {
                    _WidthCache = ConversionCache.CreateWidthCache(EditorStyles.numberField);
                    _FieldPadding = EditorStyles.numberField.padding.horizontal;
                    _ApproximateSymbolWidth = _WidthCache.Convert("~") - _FieldPadding;
                }

                if (!string.IsNullOrWhiteSpace(Suffix))
                    _SuffixWidth = _WidthCache.Convert(Suffix);
            }

            // If the field is wide enough to fit the full value, don't approximate.
            width -= _FieldPadding + _ApproximateSymbolWidth * 0.75f;
            var valueWidth = _WidthCache.Convert(valueString) + _SuffixWidth;
            if (valueWidth <= width)
                return 0;

            // If the number of allowed characters would include the full value, don't approximate.
            var suffixedLength = valueString.Length + Suffix.Length;
            var allowedCharacters = (int)(suffixedLength * width / valueWidth);
            if (allowedCharacters + 2 >= suffixedLength)
                return 0;

            return allowedCharacters;
        }

        /************************************************************************************************************************/

        /// <summary>Creates and returns a cache for the specified `characterCount`.</summary>
        private ConversionCache<float, string> GetCache(int characterCount)
        {
            while (Caches.Count <= characterCount)
                Caches.Add(null);

            var cache = Caches[characterCount];
            if (cache == null)
            {
                if (characterCount == 0)
                {
                    cache = new((value) =>
                    {
                        return value.ToStringCached() + Suffix;
                    });
                }
                else
                {
                    cache = new((value) =>
                    {
                        var valueString = value.ToStringCached();

                        if (value > LargeExponentialThreshold ||
                            value < -LargeExponentialThreshold)
                            goto IsExponential;

                        _DecimalSeparator ??= CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator;

                        var decimalIndex = valueString.IndexOf(_DecimalSeparator);
                        if (decimalIndex < 0 || decimalIndex > characterCount)
                            goto IsExponential;

                        // Not exponential.
                        return valueString[..characterCount] + ApproximateSuffix;

                        IsExponential:
                        var digits = Math.Max(0, characterCount - ApproximateSuffix.Length - 1);
                        var format = GetExponentialFormat(digits);
                        valueString = value.ToString(format);
                        TrimExponential(ref valueString);
                        return valueString + Suffix;
                    });
                }

                Caches[characterCount] = cache;
            }

            return cache;
        }

        /************************************************************************************************************************/

        private static List<string> _ExponentialFormats;

        /// <summary>Returns a format string to include the specified number of `digits` in an exponential number.</summary>
        public static string GetExponentialFormat(int digits)
        {
            _ExponentialFormats ??= new();

            while (_ExponentialFormats.Count <= digits)
                _ExponentialFormats.Add("g" + _ExponentialFormats.Count);

            return _ExponentialFormats[digits];
        }

        /************************************************************************************************************************/

        private static void TrimExponential(ref string valueString)
        {
            var length = valueString.Length;
            if (length <= 4 ||
                valueString[length - 4] != 'e' ||
                valueString[length - 2] != '0')
                return;

            valueString =
                valueString[..(length - 2)] +
                valueString[length - 1];
        }

        /************************************************************************************************************************/
    }
}

#endif