No More Sort Prefixes (#3895)

API/Helpers/BookSortTitlePrefixHelper.cs

@@ -0,0 +1,101 @@
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+
+namespace API.Helpers;
+
+/// <summary>
+/// Responsible for parsing book titles "The man on the street" and removing the prefix -> "man on the street".
+/// </summary>
+/// <remarks>This code is performance sensitive</remarks>
+public static class BookSortTitlePrefixHelper
+{
+    private static readonly Dictionary<string, byte> PrefixLookup;
+    private static readonly Dictionary<char, List<string>> PrefixesByFirstChar;
+
+    static BookSortTitlePrefixHelper()
+    {
+        var prefixes = new[]
+        {
+            // English
+            "the", "a", "an",
+            // Spanish
+            "el", "la", "los", "las", "un", "una", "unos", "unas",
+            // French
+            "le", "la", "les", "un", "une", "des",
+            // German
+            "der", "die", "das", "den", "dem", "ein", "eine", "einen", "einer",
+            // Italian
+            "il", "lo", "la", "gli", "le", "un", "uno", "una",
+            // Portuguese
+            "o", "a", "os", "as", "um", "uma", "uns", "umas",
+            // Russian (transliterated common ones)
+            "в", "на", "с", "к", "от", "для",
+        };
+
+        // Build lookup structures
+        PrefixLookup = new Dictionary<string, byte>(prefixes.Length, StringComparer.OrdinalIgnoreCase);
+        PrefixesByFirstChar = new Dictionary<char, List<string>>();
+
+        foreach (var prefix in prefixes)
+        {
+            PrefixLookup[prefix] = 1;
+
+            var firstChar = char.ToLowerInvariant(prefix[0]);
+            if (!PrefixesByFirstChar.TryGetValue(firstChar, out var list))
+            {
+                list = [];
+                PrefixesByFirstChar[firstChar] = list;
+            }
+            list.Add(prefix);
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static ReadOnlySpan<char> GetSortTitle(ReadOnlySpan<char> title)
+    {
+        if (title.IsEmpty) return title;
+
+        // Fast detection of script type by first character
+        var firstChar = title[0];
+
+        // CJK Unicode ranges - no processing needed for most cases
+        if ((firstChar >= 0x4E00 && firstChar <= 0x9FFF) ||   // CJK Unified
+            (firstChar >= 0x3040 && firstChar <= 0x309F) ||   // Hiragana
+            (firstChar >= 0x30A0 && firstChar <= 0x30FF))     // Katakana
+        {
+            return title;
+        }
+
+        var firstSpaceIndex = title.IndexOf(' ');
+        if (firstSpaceIndex <= 0) return title;
+
+        var potentialPrefix = title.Slice(0, firstSpaceIndex);
+
+        // Fast path: check if first character could match any prefix
+        firstChar = char.ToLowerInvariant(potentialPrefix[0]);
+        if (!PrefixesByFirstChar.ContainsKey(firstChar))
+            return title;
+
+        // Only do the expensive lookup if first character matches
+        if (PrefixLookup.ContainsKey(potentialPrefix.ToString()))
+        {
+            var remainder = title.Slice(firstSpaceIndex + 1);
+            return remainder.IsEmpty ? title : remainder;
+        }
+
+        return title;
+    }
+
+    /// <summary>
+    /// Removes the sort prefix
+    /// </summary>
+    /// <param name="title"></param>
+    /// <returns></returns>
+    public static string GetSortTitle(string title)
+    {
+        var result = GetSortTitle(title.AsSpan());
+
+        return result.ToString();
+    }
+}