nostrdb: add initial swift integration

nostrdb/NdbNote.swift

@@ -0,0 +1,42 @@
+//
+//  NdbNote.swift
+//  damus
+//
+//  Created by William Casarin on 2023-07-21.
+//
+
+import Foundation
+
+struct NdbNote {
+    private var owned: Data?
+    let note: UnsafeMutablePointer<ndb_note>
+
+    init(notePointer: UnsafeMutablePointer<ndb_note>, data: Data?) {
+        self.note = notePointer
+        self.owned = data
+    }
+
+    var id: Data {
+        Data(buffer: UnsafeBufferPointer(start: ndb_note_id(note), count: 32))
+    }
+
+    func tags() -> TagsSequence {
+        return .init(note: note)
+    }
+
+    static func owned_from_json(json: String, bufsize: Int = 2 << 18) -> NdbNote? {
+        var data = Data(capacity: bufsize)
+        guard var json_cstr = json.cString(using: .utf8) else { return nil }
+
+        var note: UnsafeMutablePointer<ndb_note>?
+
+        let len = data.withUnsafeMutableBytes { (bytes: UnsafeMutableRawBufferPointer) -> Int in
+            return Int(ndb_note_from_json(&json_cstr, Int32(json_cstr.count), &note, bytes.baseAddress, Int32(bufsize)))
+        }
+
+        guard let note else { return nil }
+
+        // Create new Data with just the valid bytes
+        let validData = Data(bytes: &note.pointee, count: len)
+        return NdbNote(notePointer: note, data: validData)
+    }}