Koreader progress sync interface (#3025)

Co-authored-by: Joe Milazzo <josephmajora@gmail.com>

API/Helpers/KoreaderHelper.cs

@@ -0,0 +1,107 @@
+using API.DTOs.Koreader;
+using API.DTOs.Progress;
+using API.Services;
+using System;
+using System.IO;
+using System.Linq;
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.RegularExpressions;
+
+namespace API.Helpers;
+
+public static class KoreaderHelper
+{
+    /// <summary>
+    /// Hashes the document according to a custom Koreader hashing algorithm.
+    /// Look at the util.partialMD5 method in the attached link.
+    /// </summary>
+    /// <remarks>The hashing algorithm is relatively quick as it only hashes ~10,000 bytes for the biggest of files.</remarks>
+    /// <see href="https://github.com/koreader/koreader/blob/master/frontend/util.lua#L1040"/>
+    /// <param name="filePath">The path to the file to hash</param>
+    public static string HashContents(string filePath)
+    {
+        if (string.IsNullOrEmpty(filePath))
+        {
+            return null;
+        }
+
+        using var file = File.OpenRead(filePath);
+
+        var step = 1024;
+        var size = 1024;
+        MD5 md5 = MD5.Create();
+        byte[] buffer = new byte[size];
+
+        for (var i = -1; i < 10; i++)
+        {
+            file.Position = step << 2 * i;
+            var bytesRead = file.Read(buffer, 0, size);
+            if (bytesRead > 0)
+            {
+                md5.TransformBlock(buffer, 0, bytesRead, buffer, 0);
+            }
+            else
+            {
+                break;
+            }
+        }
+
+        file.Close();
+        md5.TransformFinalBlock(new byte[0], 0, 0);
+
+        return BitConverter.ToString(md5.Hash).Replace("-", string.Empty).ToUpper();
+
+    }
+
+    /// <summary>
+    /// Koreader can identitfy documents based on contents or title.
+    /// For now we only support by contents.
+    /// </summary>
+    public static string HashTitle(string filePath)
+    {
+        var fileName = Path.GetFileName(filePath);
+        var fileNameBytes = Encoding.ASCII.GetBytes(fileName);
+        var bytes = MD5.HashData(fileNameBytes);
+
+        return BitConverter.ToString(bytes).Replace("-", string.Empty);
+    }
+
+    public static void UpdateProgressDto(string koreaderPosition, ProgressDto progress)
+    {
+        var path = koreaderPosition.Split('/');
+        if (path.Length < 6)
+        {
+            return;
+        }
+        var docNumber = path[2].Replace("DocFragment[", string.Empty).Replace("]", string.Empty);
+        progress.PageNum = Int32.Parse(docNumber) - 1;
+        var lastTag = path[5].ToUpper();
+        if (lastTag == "A")
+        {
+            progress.BookScrollId = null;
+        }
+        else
+        {
+            // The format that Kavita accpets as a progress string. It tells Kavita where Koreader last left off.
+            progress.BookScrollId = $"//html[1]/BODY/APP-ROOT[1]/DIV[1]/DIV[1]/DIV[1]/APP-BOOK-READER[1]/DIV[1]/DIV[2]/DIV[1]/DIV[1]/DIV[1]/{lastTag}";
+        }
+    }
+
+
+    public static string GetKoreaderPosition(ProgressDto progressDto)
+    {
+        string lastTag;
+        var koreaderPageNumber = progressDto.PageNum + 1;
+        if (string.IsNullOrEmpty(progressDto.BookScrollId))
+        {
+            lastTag = "a";
+        }
+        else
+        {
+            lastTag = progressDto.BookScrollId.Split('/').Last().ToLower();
+        }
+        // The format that Koreader accepts as a progress string. It tells Koreader where Kavita last left off.
+        return $"/body/DocFragment[{koreaderPageNumber}]/body/div/{lastTag}";
+    }
+}