Add an OAuth GitHub api

This just models the basic API that we need for GitJournal. The API
isn't great and could use improvement.

Also, yes, I know I'm committing the secret key, but I don't see any
other way of managing this. GitHub doesn't allow the implicit oauth flow
or dynamic clients registration or anything. So there isn't really any
other way.

lib/apis/github.dart

@@ -0,0 +1,156 @@
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:http/http.dart' as http;
+import 'package:flutter/services.dart';
+
+import 'package:url_launcher/url_launcher.dart';
+
+const _clientID = "aa3072cbfb02b1db14ed";
+const _clientSecret = "010d303ea99f82330f2b228977cef9ddbf7af2cd";
+const _platform = const MethodChannel('gitjournal.io/git');
+
+Future<String> getAccessCode(String authCode) async {
+  var url =
+      "https://github.com/login/oauth/access_token?client_id=${_clientID}&client_secret=${_clientSecret}&code=${authCode}";
+
+  var response = await http.post(url);
+  if (response.statusCode != 200) {
+    print("Github getAccessCode: Invalid response " +
+        response.statusCode.toString() +
+        ": " +
+        response.body);
+    return null;
+  }
+  print("GithubResponse: " + response.body);
+
+  var map = Uri.splitQueryString(response.body);
+  return map["access_token"];
+}
+
+void initGitHub(Function callback) {
+  Future _handleMessages(MethodCall call) async {
+    if (call.method != "onURL") {
+      print("GitHub Unknown Call: " + call.method);
+      return;
+    }
+
+    print("GitHub: Called onUrl with " + call.arguments.toString());
+
+    var url = call.arguments["URL"];
+    var uri = Uri.parse(url);
+    var authCode = uri.queryParameters['code'];
+    if (authCode == null) {
+      print("GitHub: Missing auth code. Now what?");
+      callback();
+    }
+
+    var acesssCode = await getAccessCode(authCode);
+    callback(acesssCode);
+  }
+
+  _platform.setMethodCallHandler(_handleMessages);
+  print("GitHub: Installed Handler");
+}
+
+Future launchOAuthScreen() async {
+  // FIXME: Add some 'state' over here!
+
+  var url = "https://github.com/login/oauth/authorize?client_id=" +
+      _clientID +
+      "&scope=repo";
+  return launch(url);
+}
+
+class Repo {
+  String fullName;
+
+  Repo({this.fullName});
+  factory Repo.fromJson(Map<String, dynamic> parsedJson) {
+    return new Repo(fullName: parsedJson['full_name']);
+  }
+
+  @override
+  String toString() {
+    return 'Repo{fulleName: $fullName}';
+  }
+}
+
+Future<List<Repo>> listRepos(String accessCode) async {
+  var url =
+      "https://api.github.com/user/repos?page=1&per_page=100&access_token=${accessCode}";
+
+  var response = await http.get(url);
+  if (response.statusCode != 200) {
+    print("Github listRepos: Invalid response " +
+        response.statusCode.toString() +
+        ": " +
+        response.body);
+    return null;
+  }
+
+  List<dynamic> list = jsonDecode(response.body);
+  List<Repo> repos = new List<Repo>();
+  list.forEach((dynamic d) {
+    var map = Map<String, dynamic>.from(d);
+    var repo = Repo.fromJson(map);
+    repos.add(repo);
+  });
+
+  // FIXME: Sort these based on some criteria
+  return repos;
+}
+
+Future createRepo(String accessCode, String name) async {
+  var url = "https://api.github.com/user/repos?access_token=${accessCode}";
+  Map<String, dynamic> data = {
+    'name': name,
+    'private': true,
+  };
+
+  var headers = {
+    HttpHeaders.contentTypeHeader: "application/json",
+  };
+
+  var response =
+      await http.post(url, headers: headers, body: json.encode(data));
+  if (response.statusCode != 201) {
+    print("Github createRepo: Invalid response " +
+        response.statusCode.toString() +
+        ": " +
+        response.body);
+    return null;
+  }
+
+  print("GitHub createRepo: " + response.body);
+  return json.decode(response.body);
+}
+
+Future addDeployKey(String accessCode, String sshPublicKey, String repo) async {
+  var url =
+      "https://api.github.com/repos/$repo/keys?access_token=${accessCode}";
+
+  Map<String, dynamic> data = {
+    'title': "GitJournal",
+    'key': sshPublicKey,
+    'read_only': false,
+  };
+
+  var headers = {
+    HttpHeaders.contentTypeHeader: "application/json",
+  };
+
+  var response =
+      await http.post(url, headers: headers, body: json.encode(data));
+  if (response.statusCode != 201) {
+    print("Github addDeployKey: Invalid response " +
+        response.statusCode.toString() +
+        ": " +
+        response.body);
+    return null;
+  }
+
+  print("GitHub addDeployKey: " + response.body);
+  return json.decode(response.body);
+}