From 2c94d89f9fa08e9720ad1cf2430fda1de2cfe8e0 Mon Sep 17 00:00:00 2001
From: Marko Budiselic <mbudiselicbuda@gmail.com>
Date: Mon, 5 Dec 2016 10:10:12 +0100
Subject: [PATCH] File System Watcher Implementation

---
 include/utils/file_system_watcher.hpp | 131 ++++++++++++++++++++++++++
 1 file changed, 131 insertions(+)
 create mode 100644 include/utils/file_system_watcher.hpp

diff --git a/include/utils/file_system_watcher.hpp b/include/utils/file_system_watcher.hpp
new file mode 100644
index 000000000..71eb748de
--- /dev/null
+++ b/include/utils/file_system_watcher.hpp
@@ -0,0 +1,131 @@
+#pragma once
+
+#include <vector>
+#include <atomic>
+#include <sys/inotify.h>
+#include <chrono>
+// TODO: remove experimental from here once that becomes possible
+#include <experimental/filesystem>
+
+#include "utils/exceptions/basic_exception.hpp"
+#include "utils/exceptions/not_yet_implemented.hpp"
+
+// TODO: remove experimental from here once it becomes possible
+namespace fs = std::experimental::filesystem;
+
+namespace utils
+{
+
+using ms = std::chrono::milliseconds;
+
+enum class FSEvent : int
+{
+    Created  = 0x1,
+    Modified = 0x2,
+    Deleted  = 0x4
+};
+
+class FSWatcherException : public BasicException
+{
+public:
+    using BasicException::BasicException;
+};
+
+/*
+ * File System Watcher
+ *
+ * parameters:
+ *     * interval
+ */
+class FSWatcher
+{
+    using wd_t = int;
+    using callback_t = std::function<void(fs::path &path, FSEvent event)>;
+    // <path, watch descriptor, callback>
+    using entry_t = std::tuple<fs::path, wd_t, callback_t>;
+
+public:
+    FSWatcher(ms interval = 100ms) : interval_(interval) { init(); }
+    ~FSWatcher() = default;
+
+    // copy and move constructors and assignemnt operators are deleted because
+    // std::atomic can't be copied or moved
+    FSWatcher(const FSWatcher &other) = delete;
+    FSWatcher(FSWatcher &&other)      = delete;
+    FSWatcher &operator=(const FSWatcher &) = delete;
+    FSWatcher &operator=(FSWatcher &&) = delete;
+
+    void init()
+    {
+        inotify_fd_ = inotify_init();
+        if (inotify_fd_ == -1)
+            throw FSWatcherException("Unable to initialize inotify");
+    }
+
+    void watch(const fs::path &path, callback_t callback)
+    {
+        int wd = inotify_add_watch(inotify_fd_, path.c_str(), IN_ALL_EVENTS);
+        if (wd == -1)
+            throw FSWatcherException("Unable to add watch");
+        entries_.emplace_back(std::make_tuple(path, wd, callback));
+    }
+
+    void unwatch(const fs::path &path)
+    {
+        // iterate through all entries and remove specified watch descriptor
+        for (auto &entry : entries_)
+        {
+            // if paths are not equal pass
+            if (std::get<fs::path>(entry) != path)
+                continue;
+            
+            // get watch descriptor and remove it from the watching
+            auto status = inotify_rm_watch(inotify_fd_, std::get<wd_t>(entry));
+            if (status == -1)
+                throw FSWatcherException("Unable to remove watch");
+        }
+    }
+
+    void unwatchAll()
+    {
+        // iterate through all entries and remove all watch descriptors
+        for (auto &entry : entries_)
+        {
+            auto status = inotify_rm_watch(inotify_fd_, std::get<wd_t>(entry));
+            if (status == -1)
+                throw FSWatcherException("Unable to remove watch");
+        }
+    }
+
+    /*
+     * Start watching
+     */
+    void start()
+    {
+        is_running_.store(true);
+
+        // TODO: run on a separate thread
+
+        while (is_running_.load())
+        {
+            // TODO: read
+        }
+
+        throw NotYetImplemented("FSWatch::start");
+    }
+
+    /*
+     * Stop watching
+     */
+    void stop()
+    {
+        is_running_.store(false);
+    }
+
+private:
+    int inotify_fd_;
+    std::atomic<bool> is_running_;
+    ms interval_;
+    std::vector<entry_t> entries_;
+};
+}