feat: add library setup for linux

lib/src/util.dart

@@ -3,13 +3,73 @@
 import 'dart:ffi';
 import 'dart:io';
 
+import 'package:cli_util/cli_logging.dart' show Ansi, Logger;
+import 'package:ffi/ffi.dart';
 import 'package:libgit2dart/src/bindings/libgit2_bindings.dart';
 
-DynamicLibrary loadLibrary() {
-  if (Platform.isLinux || Platform.isAndroid || Platform.isFuchsia) {
+const tag = 'libs-v1.3.0';
+const libUrl =
+    'https://github.com/SkinnyMind/libgit2dart/releases/download/$tag/';
+const libgit2Version = '1.3.0';
+const libDir = '.dart_tool/libgit2/';
+
+String getLibName(String platform) {
+  var ext = 'so';
+
+  if (Platform.isWindows) {
+    ext = 'dll';
+  } else if (Platform.isMacOS) {
+    ext = 'dylib';
+  } else if (!(Platform.isLinux || Platform.isAndroid)) {
+    throw Exception('Unsupported platform.');
+  }
+
+  return 'libgit2-$libgit2Version.$ext';
+}
+
+/// Checks if [File]/[Link] exists for an [uri].
+bool _doesFileExist(Uri uri) {
+  return File.fromUri(uri).existsSync() || Link.fromUri(uri).existsSync();
+}
+
+String? _resolveLibUri(String name) {
+  var libUri = Directory.current.uri.resolve(name);
+  final dartTool = '.dart_tool/libgit2/${Platform.operatingSystem}';
+
+  // If lib is in Present Working Directory.
+  if (_doesFileExist(libUri)) {
+    return libUri.toFilePath(windows: Platform.isWindows);
+  }
+
+  // If lib is in Present Working Directory's .dart_tool folder.
+  libUri = Directory.current.uri.resolve('$dartTool/$name');
+  if (_doesFileExist(libUri)) {
+    return libUri.toFilePath(windows: Platform.isWindows);
+  }
+
+  return null;
+}
+
+DynamicLibrary loadLibrary(String name) {
+  try {
     return DynamicLibrary.open(
-      '${Directory.current.path}/libgit2/libgit2.so.1.3.0',
+      _resolveLibUri(name) ?? name,
     );
+  } catch (e) {
+    final logger = Logger.standard();
+    final ansi = Ansi(Ansi.terminalSupportsAnsi);
+
+    logger.stderr(
+      '${ansi.red}Failed to open the library. Make sure that required '
+      'library is in place.${ansi.none}',
+    );
+    logger.stdout(
+      'To download the library, please run the following command from the '
+      'root of your project:',
+    );
+    logger.stdout('${ansi.yellow}dart run libgit2dart:setup${ansi.none}');
+    logger.stdout(ansi.none);
+    rethrow;
   }
   // if (Platform.isMacOS) {
   //   return DynamicLibrary.open(
@@ -19,10 +79,26 @@ DynamicLibrary loadLibrary() {
   //   return DynamicLibrary.open(
   //       '${Directory.current.path}/libgit2/libgit2-1.2.0.dll');
   // }
-  throw Exception('Platform not implemented');
 }
 
-final libgit2 = Libgit2(loadLibrary());
+final libgit2 = Libgit2(loadLibrary(getLibName(Platform.operatingSystem)));
+
+String getVersionNumber() {
+  libgit2.git_libgit2_init();
+
+  final major = calloc<Int32>();
+  final minor = calloc<Int32>();
+  final rev = calloc<Int32>();
+  libgit2.git_libgit2_version(major, minor, rev);
+
+  final version = '${major.value}.${minor.value}.${rev.value}';
+
+  calloc.free(major);
+  calloc.free(minor);
+  calloc.free(rev);
+
+  return version;
+}
 
 bool isValidShaHex(String str) {
   final hexRegExp = RegExp(r'^[0-9a-fA-F]+$');