Initial import of the CBDDC codebase with docs and tests. Add a .NET-focused gitignore to keep generated artifacts out of source control.

src/ZB.MOM.WW.CBDDC.Core/OplogEntry.cs

@@ -0,0 +1,107 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+using System.Text.Json;
+
+namespace ZB.MOM.WW.CBDDC.Core;
+
+public enum OperationType
+{
+    Put,
+    Delete
+}
+
+public static class OplogEntryExtensions
+{
+    /// <summary>
+    /// Computes a deterministic hash for the specified oplog entry.
+    /// </summary>
+    /// <param name="entry">The oplog entry to hash.</param>
+    /// <returns>The lowercase hexadecimal SHA-256 hash of the entry.</returns>
+    public static string ComputeHash(this OplogEntry entry)
+    {
+        using var sha256 = System.Security.Cryptography.SHA256.Create();
+        var sb = new System.Text.StringBuilder();
+
+        sb.Append(entry.Collection);
+        sb.Append('|');
+        sb.Append(entry.Key);
+        sb.Append('|');
+        // Ensure stable string representation for Enum (integer value)
+        sb.Append(((int)entry.Operation).ToString(System.Globalization.CultureInfo.InvariantCulture));
+        sb.Append('|');
+        // Payload excluded from hash to avoid serialization non-determinism
+        // sb.Append(entry.Payload...); 
+        sb.Append('|');
+        // Timestamp.ToString() is now Invariant
+        sb.Append(entry.Timestamp.ToString());
+        sb.Append('|');
+        sb.Append(entry.PreviousHash);
+
+        var bytes = System.Text.Encoding.UTF8.GetBytes(sb.ToString());
+        var hashBytes = sha256.ComputeHash(bytes);
+
+        // Convert to hex string
+        return BitConverter.ToString(hashBytes).Replace("-", "").ToLowerInvariant();
+    }
+}
+
+public class OplogEntry
+{
+    /// <summary>
+    /// Gets the collection name associated with this entry.
+    /// </summary>
+    public string Collection { get; }
+    /// <summary>
+    /// Gets the document key associated with this entry.
+    /// </summary>
+    public string Key { get; }
+    /// <summary>
+    /// Gets the operation represented by this entry.
+    /// </summary>
+    public OperationType Operation { get; }
+    /// <summary>
+    /// Gets the serialized payload for the operation.
+    /// </summary>
+    public JsonElement? Payload { get; }
+    /// <summary>
+    /// Gets the logical timestamp for this entry.
+    /// </summary>
+    public HlcTimestamp Timestamp { get; }
+    /// <summary>
+    /// Gets the hash of this entry.
+    /// </summary>
+    public string Hash { get; }
+    /// <summary>
+    /// Gets the hash of the previous entry in the chain.
+    /// </summary>
+    public string PreviousHash { get; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="OplogEntry"/> class.
+    /// </summary>
+    /// <param name="collection">The collection name.</param>
+    /// <param name="key">The document key.</param>
+    /// <param name="operation">The operation type.</param>
+    /// <param name="payload">The serialized payload.</param>
+    /// <param name="timestamp">The logical timestamp.</param>
+    /// <param name="previousHash">The previous entry hash.</param>
+    /// <param name="hash">The current entry hash. If null, it is computed.</param>
+    public OplogEntry(string collection, string key, OperationType operation, JsonElement? payload, HlcTimestamp timestamp, string previousHash, string? hash = null)
+    {
+        Collection = collection;
+        Key = key;
+        Operation = operation;
+        Payload = payload;
+        Timestamp = timestamp;
+        PreviousHash = previousHash ?? string.Empty;
+        Hash = hash ?? this.ComputeHash();
+    }
+
+    /// <summary>
+    /// Verifies if the stored Hash matches the content.
+    /// </summary>
+    public bool IsValid()
+    {
+        return Hash == this.ComputeHash();
+    }
+}