feat(tree): add bindings and api

lib/src/tree.dart

@@ -1,9 +1,9 @@
 import 'dart:ffi';
-import 'package:libgit2dart/src/repository.dart';
-
 import 'bindings/libgit2_bindings.dart';
 import 'bindings/tree.dart' as bindings;
+import 'repository.dart';
 import 'oid.dart';
+import 'enums.dart';
 import 'util.dart';
 
 class Tree {
@@ -17,8 +17,8 @@ class Tree {
   /// [Repository] and [Oid] objects.
   ///
   /// Should be freed with `free()` to release allocated memory.
-  Tree.lookup(Repository repo, Oid id) {
-    _treePointer = bindings.lookup(repo.pointer, id.pointer);
+  Tree.lookup(Repository repo, Oid oid) {
+    _treePointer = bindings.lookup(repo.pointer, oid.pointer);
   }
 
   late final Pointer<git_tree> _treePointer;
@@ -26,8 +26,89 @@ class Tree {
   /// Pointer to memory address for allocated tree object.
   Pointer<git_tree> get pointer => _treePointer;
 
-  /// Releases memory allocated for tree object.
-  void free() {
-    bindings.free(_treePointer);
+  /// Returns a list with tree entries of a tree.
+  List<TreeEntry> get entries {
+    final entryCount = bindings.entryCount(_treePointer);
+    var result = <TreeEntry>[];
+    for (var i = 0; i < entryCount; i++) {
+      result.add(TreeEntry(bindings.getByIndex(_treePointer, i)));
+    }
+
+    return result;
   }
+
+  /// Looksup a tree entry in the tree.
+  ///
+  /// If integer [value] is provided, lookup is done by entry position in the tree.
+  ///
+  /// If string [value] is provided, lookup is done by entry filename.
+  ///
+  /// If provided string [value] is a path to file, lookup is done by path. In that case
+  /// returned object should be freed explicitly.
+  TreeEntry operator [](Object value) {
+    if (value is int) {
+      return TreeEntry(bindings.getByIndex(_treePointer, value));
+    } else if (value is String && value.contains('/')) {
+      return TreeEntry(bindings.getByPath(_treePointer, value));
+    } else if (value is String) {
+      return TreeEntry(bindings.getByName(_treePointer, value));
+    } else {
+      throw ArgumentError.value(
+          '$value should be either index position, filename or path');
+    }
+  }
+
+  /// Releases memory allocated for tree object.
+  void free() => bindings.free(_treePointer);
+}
+
+class TreeEntry {
+  /// Initializes a new instance of [TreeEntry] class.
+  TreeEntry(this._treeEntryPointer);
+
+  /// Pointer to memory address for allocated tree entry object.
+  final Pointer<git_tree_entry> _treeEntryPointer;
+
+  /// Returns the Oid of the object pointed by the entry.
+  Oid get id => Oid(bindings.entryId(_treeEntryPointer));
+
+  /// Returns the filename of a tree entry.
+  String get name => bindings.entryName(_treeEntryPointer);
+
+  /// Returns the UNIX file attributes of a tree entry.
+  GitFilemode get filemode {
+    return intToGitFilemode(bindings.entryFilemode(_treeEntryPointer));
+  }
+
+  @override
+  bool operator ==(other) {
+    return (other is TreeEntry) &&
+        (bindings.compare(_treeEntryPointer, other._treeEntryPointer) == 0);
+  }
+
+  bool operator <(other) {
+    return (other is TreeEntry) &&
+        (bindings.compare(_treeEntryPointer, other._treeEntryPointer) == -1);
+  }
+
+  bool operator <=(other) {
+    return (other is TreeEntry) &&
+        (bindings.compare(_treeEntryPointer, other._treeEntryPointer) == -1);
+  }
+
+  bool operator >(other) {
+    return (other is TreeEntry) &&
+        (bindings.compare(_treeEntryPointer, other._treeEntryPointer) == 1);
+  }
+
+  bool operator >=(other) {
+    return (other is TreeEntry) &&
+        (bindings.compare(_treeEntryPointer, other._treeEntryPointer) == 1);
+  }
+
+  @override
+  int get hashCode => _treeEntryPointer.address.hashCode;
+
+  /// Releases memory allocated for tree entry object.
+  void free() => bindings.entryFree(_treeEntryPointer);
 }