using System;
using StardewModdingAPI.Toolkit.Utilities;
using StardewModdingAPI.Utilities.AssetPathUtilities;
using StardewValley;
using ToolkitPathUtilities = StardewModdingAPI.Toolkit.Utilities.PathUtilities;

namespace StardewModdingAPI.Framework.Content
{
    /// <summary>An asset name that can be loaded through the content pipeline.</summary>
    internal class AssetName : IAssetName
    {
        /*********
        ** Fields
        *********/
        /// <summary>A lowercase version of <see cref="Name"/> used for consistent hash codes and equality checks.</summary>
        private readonly string ComparableName;


        /*********
        ** Accessors
        *********/
        /// <inheritdoc />
        public string Name { get; }

        /// <inheritdoc />
        public string BaseName { get; }

        /// <inheritdoc />
        public string? LocaleCode { get; }

        /// <inheritdoc />
        public LocalizedContentManager.LanguageCode? LanguageCode { get; }


        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        /// <param name="baseName">The base asset name without the locale code.</param>
        /// <param name="localeCode">The locale code specified in the <see cref="Name"/>, if it's a valid code recognized by the game content.</param>
        /// <param name="languageCode">The language code matching the <see cref="LocaleCode"/>, if applicable.</param>
        public AssetName(string baseName, string? localeCode, LocalizedContentManager.LanguageCode? languageCode)
        {
            // validate
            if (string.IsNullOrWhiteSpace(baseName))
                throw new ArgumentException("The asset name can't be null or empty.", nameof(baseName));
            if (string.IsNullOrWhiteSpace(localeCode))
                localeCode = null;

            // set base values
            this.BaseName = PathUtilities.NormalizeAssetName(baseName);
            this.LocaleCode = localeCode;
            this.LanguageCode = languageCode;

            // set derived values
            this.Name = localeCode != null
                ? string.Concat(this.BaseName, '.', this.LocaleCode)
                : this.BaseName;
            this.ComparableName = this.Name.ToLowerInvariant();
        }

        /// <summary>Parse a raw asset name into an instance.</summary>
        /// <param name="rawName">The raw asset name to parse.</param>
        /// <param name="parseLocale">Get the language code for a given locale, if it's valid.</param>
        /// <exception cref="ArgumentException">The <paramref name="rawName"/> is null or empty.</exception>
        public static AssetName Parse(string rawName, Func<string, LocalizedContentManager.LanguageCode?> parseLocale)
        {
            if (string.IsNullOrWhiteSpace(rawName))
                throw new ArgumentException("The asset name can't be null or empty.", nameof(rawName));

            string baseName = rawName;
            string? localeCode = null;
            LocalizedContentManager.LanguageCode? languageCode = null;

            int lastPeriodIndex = rawName.LastIndexOf('.');
            if (lastPeriodIndex > 0 && rawName.Length > lastPeriodIndex + 1)
            {
                string possibleLocaleCode = rawName[(lastPeriodIndex + 1)..];
                LocalizedContentManager.LanguageCode? possibleLanguageCode = parseLocale(possibleLocaleCode);

                if (possibleLanguageCode != null)
                {
                    baseName = rawName[..lastPeriodIndex];
                    localeCode = possibleLocaleCode;
                    languageCode = possibleLanguageCode;
                }
            }

            return new AssetName(baseName, localeCode, languageCode);
        }

        /// <inheritdoc />
        public bool IsEquivalentTo(string? assetName, bool useBaseName = false)
        {
            // empty asset key is never equivalent
            if (string.IsNullOrWhiteSpace(assetName))
                return false;

            AssetNamePartEnumerator curParts = new(useBaseName ? this.BaseName : this.Name);
            AssetNamePartEnumerator otherParts = new(assetName.AsSpan().Trim());

            while (true)
            {
                bool curHasMore = curParts.MoveNext();
                bool otherHasMore = otherParts.MoveNext();

                // mismatch: lengths differ
                if (otherHasMore != curHasMore)
                    return false;

                // match: both reached the end without a mismatch
                if (!curHasMore)
                    return true;

                // mismatch: current segment is different
                if (!curParts.Current.Equals(otherParts.Current, StringComparison.OrdinalIgnoreCase))
                    return false;
            }
        }

        /// <inheritdoc />
        public bool IsEquivalentTo(IAssetName? assetName, bool useBaseName = false)
        {
            if (useBaseName)
                return this.BaseName.Equals(assetName?.BaseName, StringComparison.OrdinalIgnoreCase);

            if (assetName is AssetName impl)
                return this.ComparableName == impl.ComparableName;

            return this.Name.Equals(assetName?.Name, StringComparison.OrdinalIgnoreCase);
        }

        /// <inheritdoc />
        public bool StartsWith(string? prefix, bool allowPartialWord = true, bool allowSubfolder = true)
        {
            // asset keys never start with null
            if (prefix is null)
                return false;

            // get initial values
            ReadOnlySpan<char> trimmedPrefix = prefix.AsSpan().Trim();
            if (trimmedPrefix.Length == 0)
                return true;
            ReadOnlySpan<char> pathSeparators = new(ToolkitPathUtilities.PossiblePathSeparators); // just to simplify calling other span APIs

            // asset keys can't have a leading slash, but AssetPathYielder will trim them
            if (pathSeparators.Contains(trimmedPrefix[0]))
                return false;

            // compare segments
            AssetNamePartEnumerator curParts = new(this.Name);
            AssetNamePartEnumerator prefixParts = new(trimmedPrefix);
            while (true)
            {
                bool curHasMore = curParts.MoveNext();
                bool prefixHasMore = prefixParts.MoveNext();

                // reached end for one side
                if (prefixHasMore != curHasMore)
                {
                    // mismatch: prefix is longer
                    if (prefixHasMore)
                        return false;

                    // match: every segment in the prefix matched and subfolders are allowed (e.g. prefix 'Data/Events' with target 'Data/Events/Beach')
                    if (allowSubfolder)
                        return true;

                    // Special case: the prefix ends with a path separator, but subfolders aren't allowed. This case
                    // matches if there's no further path separator in the asset name *after* the current separator.
                    // For example, the prefix 'A/B/' matches 'A/B/C' but not 'A/B/C/D'.
                    return pathSeparators.Contains(trimmedPrefix[^1]) && curParts.Remainder.Length == 0;
                }

                // previous segments matched exactly and both reached the end
                // match if prefix doesn't end with '/' (which should only match subfolders)
                if (!prefixHasMore)
                    return !pathSeparators.Contains(trimmedPrefix[^1]);

                // compare segment
                if (curParts.Current.Length == prefixParts.Current.Length)
                {
                    // mismatch: segments aren't equivalent
                    if (!curParts.Current.Equals(prefixParts.Current, StringComparison.OrdinalIgnoreCase))
                        return false;
                }
                else
                {
                    // mismatch: prefix has more beyond this, and this segment isn't an exact match
                    if (prefixParts.Remainder.Length != 0)
                        return false;

                    // mismatch: cur segment doesn't start with prefix
                    if (!curParts.Current.StartsWith(prefixParts.Current, StringComparison.OrdinalIgnoreCase))
                        return false;

                    // mismatch: something like "Maps/" would need an exact match
                    if (pathSeparators.Contains(trimmedPrefix[^1]))
                        return false;

                    // mismatch: partial word match not allowed, and the first or last letter of the suffix isn't a word separator
                    if (!allowPartialWord && char.IsLetterOrDigit(prefixParts.Current[^1]) && char.IsLetterOrDigit(curParts.Current[prefixParts.Current.Length]))
                        return false;

                    // possible match
                    return allowSubfolder || (pathSeparators.Contains(trimmedPrefix[^1]) ? curParts.Remainder.IndexOfAny(ToolkitPathUtilities.PossiblePathSeparators) < 0 : curParts.Remainder.Length == 0);
                }
            }
        }

        /// <inheritdoc />
        public bool IsDirectlyUnderPath(string? assetFolder)
        {
            if (assetFolder is null)
                return false;

            return this.StartsWith(assetFolder + ToolkitPathUtilities.PreferredPathSeparator, allowPartialWord: false, allowSubfolder: false);
        }

        /// <inheritdoc />
        IAssetName IAssetName.GetBaseAssetName()
        {
            return this.LocaleCode == null
                ? this
                : new AssetName(this.BaseName, null, null);
        }

        /// <inheritdoc />
        public bool Equals(IAssetName? other)
        {
            return other switch
            {
                null => false,
                AssetName otherImpl => this.ComparableName == otherImpl.ComparableName,
                _ => StringComparer.OrdinalIgnoreCase.Equals(this.Name, other.Name)
            };
        }

        /// <inheritdoc />
        public override int GetHashCode()
        {
            return this.ComparableName.GetHashCode();
        }

        /// <inheritdoc />
        public override string ToString()
        {
            return this.Name;
        }
    }
}