From 4d65732b4c1ee34206b4bc26dda8d5ab4259093c Mon Sep 17 00:00:00 2001
From: Natalia Portillo <claunia@claunia.com>
Date: Mon, 1 Sep 2025 04:27:37 +0100
Subject: [PATCH] [ARC] Implement identification and information.

---
 Aaru.Archives/Arc/Info.cs          | 121 +++++++++++++++++++++++++++++
 Aaru.Archives/Arc/Unimplemented.cs |   9 ---
 2 files changed, 121 insertions(+), 9 deletions(-)
 create mode 100644 Aaru.Archives/Arc/Info.cs

diff --git a/Aaru.Archives/Arc/Info.cs b/Aaru.Archives/Arc/Info.cs
new file mode 100644
index 000000000..4eb2788c4
--- /dev/null
+++ b/Aaru.Archives/Arc/Info.cs
@@ -0,0 +1,121 @@
+using System.IO;
+using System.Text;
+using Aaru.CommonTypes.Interfaces;
+using Aaru.Helpers;
+using Aaru.Logging;
+
+namespace Aaru.Archives;
+
+public sealed partial class Arc
+{
+#region IArchive Members
+
+    /// <inheritdoc />
+    public bool Identify(IFilter filter)
+    {
+        if(filter.DataForkLength < Marshal.SizeOf<Header>()) return false;
+
+        Stream stream = filter.GetDataForkStream();
+        stream.Position = 0;
+
+        byte[] hdr = new byte[Marshal.SizeOf<Header>()];
+
+        stream.ReadExactly(hdr, 0, hdr.Length);
+
+        Header header = Marshal.ByteArrayToStructureLittleEndian<Header>(hdr);
+
+        // Not a valid marker
+        if(header.marker != MARKER) return false;
+
+        switch(header.method)
+        {
+            // Not a valid compression method
+            case > 12 and < 20:
+            // Not a valid informational item
+            case > 22 and < 30:
+            // Not a valid control item
+            case > 31:
+                return false;
+        }
+
+        for(int i = 0; i < 11; i++)
+
+            // Not a valid filename character
+        {
+            if(header.filename[i] > 0 && header.filename[i] < 0x20) return false;
+        }
+
+        // If the filename is not 8.3, it's probably not an ARC file, but maybe it is in MVS/UNIX?
+        if(header.filename[11] != 0) return false;
+
+        // Compressed size is larger than file size
+        // Hope for the best
+        return header.compressed < stream.Length;
+    }
+
+    /// <inheritdoc />
+    public void GetInformation(IFilter filter, Encoding encoding, out string information)
+    {
+        information = "";
+
+        if(filter.DataForkLength < Marshal.SizeOf<Header>()) return;
+
+        Stream stream = filter.GetDataForkStream();
+        stream.Position = 0;
+
+        byte[] hdr = new byte[Marshal.SizeOf<Header>()];
+
+        stream.ReadExactly(hdr, 0, hdr.Length);
+
+        Header header = Marshal.ByteArrayToStructureLittleEndian<Header>(hdr);
+
+        AaruLogging.Debug(MODULE_NAME, "[navy]header.marker[/] = [teal]0x{0:X2}[/]", header.marker);
+        AaruLogging.Debug(MODULE_NAME, "[navy]header.method[/] = [teal]{0}[/]",      header.method);
+
+        AaruLogging.Debug(MODULE_NAME,
+                          "[navy]header.filename[/] = [green]\"{0}\"[/]",
+                          StringHandlers.CToString(header.filename));
+
+        AaruLogging.Debug(MODULE_NAME, "[navy]header.compressed[/] = [teal]{0}[/]",   header.compressed);
+        AaruLogging.Debug(MODULE_NAME, "[navy]header.date[/] = [teal]{0}[/]",         header.date);
+        AaruLogging.Debug(MODULE_NAME, "[navy]header.time[/] = [teal]{0}[/]",         header.time);
+        AaruLogging.Debug(MODULE_NAME, "[navy]header.crc[/] = [teal]0x{0:X4}[/]",     header.crc);
+        AaruLogging.Debug(MODULE_NAME, "[navy]header.uncompressed[/] = [teal]{0}[/]", header.uncompressed);
+
+        // Not a valid marker
+        if(header.marker != MARKER) return;
+
+        switch(header.method)
+        {
+            // Not a valid compression method
+            case > 12 and < 20:
+            // Not a valid informational item
+            case > 22 and < 30:
+            // Not a valid control item
+            case > 31:
+                return;
+        }
+
+        for(int i = 0; i < 11; i++)
+
+            // Not a valid filename character
+        {
+            if(header.filename[i] > 0 && header.filename[i] < 0x20) return;
+        }
+
+        // If the filename is not 8.3, it's probably not an ARC file, but maybe it is in MVS/UNIX?
+        if(header.filename[11] != 0) return;
+
+        // Compressed size is larger than file size
+        if(header.compressed >= stream.Length) return;
+
+        // Hope for the best
+
+        var sb = new StringBuilder();
+        sb.AppendLine("[bold][blue]ARC archive[/][/]");
+
+        information = sb.ToString();
+    }
+
+#endregion
+}
\ No newline at end of file
diff --git a/Aaru.Archives/Arc/Unimplemented.cs b/Aaru.Archives/Arc/Unimplemented.cs
index a162c8e0b..72a57f934 100644
--- a/Aaru.Archives/Arc/Unimplemented.cs
+++ b/Aaru.Archives/Arc/Unimplemented.cs
@@ -12,9 +12,6 @@ public sealed partial class Arc
 {
 #region IArchive Members
 
-    /// <inheritdoc />
-    public bool Identify(IFilter filter) => throw new NotImplementedException();
-
     /// <inheritdoc />
     public ErrorNumber Open(IFilter filter, Encoding encoding) => throw new NotImplementedException();
 
@@ -54,11 +51,5 @@ public sealed partial class Arc
     /// <inheritdoc />
     public ErrorNumber GetEntry(int entryNumber, out IFilter filter) => throw new NotImplementedException();
 
-    /// <inheritdoc />
-    public void GetInformation(IFilter filter, Encoding encoding, out string information)
-    {
-        throw new NotImplementedException();
-    }
-
 #endregion
 }
\ No newline at end of file