From 79d6d80f6a346b8b4297f1a67a6b39c6a965daf1 Mon Sep 17 00:00:00 2001
From: Daniel Worrall <Daniel.Worrall@hotmail.co.uk>
Date: Tue, 12 Jun 2018 01:20:48 +0100
Subject: Add IRC

---
 shard.yml                  |  2 ++
 spec/irc_spec.cr           | 11 ++++++++
 src/twitch/irc.cr          | 65 ++++++++++++++++++++++++++++++++++++++++++++++
 src/twitch/rate_limiter.cr | 39 ++++++++++++++++++++++++++++
 4 files changed, 117 insertions(+)
 create mode 100644 spec/irc_spec.cr
 create mode 100644 src/twitch/irc.cr
 create mode 100644 src/twitch/rate_limiter.cr

diff --git a/shard.yml b/shard.yml
index 1a9881f..27d4133 100644
--- a/shard.yml
+++ b/shard.yml
@@ -14,3 +14,5 @@ dependencies:
   fast_irc:
     github: rx14/fast_irc.cr
     version: 0.3.0
+  rate_limiter:
+    github: z64/rate_limiter
diff --git a/spec/irc_spec.cr b/spec/irc_spec.cr
new file mode 100644
index 0000000..0053024
--- /dev/null
+++ b/spec/irc_spec.cr
@@ -0,0 +1,11 @@
+require "./spec_helper"
+
+describe "PING" do
+  it "responds with PONG" do
+    response = String.build do |io|
+      client = Twitch::IRC.new(io, "foo", "bar")
+      client.dispatch FastIRC::Message.new("PING", nil)
+    end
+    response.should eq FastIRC::Message.new("PONG", ["tmi.twitch.tv"]).to_s
+  end
+end
diff --git a/src/twitch/irc.cr b/src/twitch/irc.cr
new file mode 100644
index 0000000..f5fccfc
--- /dev/null
+++ b/src/twitch/irc.cr
@@ -0,0 +1,65 @@
+require "socket"
+require "fast_irc"
+require "./rate_limiter"
+
+class Twitch::IRC
+  private getter socket : IO
+  private getter limiter : RateLimiter(String)
+
+  def self.new(nick, token)
+    new(TCPSocket.new("irc.chat.twitch.tv", 6667), nick, token)
+  end
+
+  def initialize(@socket : IO, @nick : String, @token : String)
+    @limiter = RateLimiter(String).new
+    limiter.bucket(:join, 50_u32, 15.seconds)
+  end
+
+  def run(channels)
+    authenticate
+    spawn join_channels(channels)
+    @connected = true
+    FastIRC.parse(socket) do |message|
+      spawn dispatch(message)
+    end
+  end
+
+  def on_message(&@on_message : FastIRC::Message ->)
+  end
+
+  def join_channel(channel)
+    return unless @connected
+    wait = limiter.rate_limited?(:join, "")
+    sleep(wait) if wait.is_a?(Time::Span)
+    raw_write("JOIN", ["##{channel}"])
+  end
+
+  def dispatch(message)
+    puts message.inspect
+    case message.command
+    when "PING"
+      pong
+    when "PRIVMSG"
+      @on_message.try &.call(message)
+    end
+  end
+
+  private def authenticate
+    raw_write("PASS", [@token])
+    raw_write("NICK", [@nick])
+  end
+
+  private def join_channels(channels)
+    channels.each do |channel|
+      join_channel(channel)
+    end
+  end
+
+  private def pong
+    raw_write("PONG", ["tmi.twitch.tv"])
+  end
+
+  private def raw_write(command, params, prefix = nil, tags = nil)
+    FastIRC::Message.new(command, params, prefix: prefix, tags: tags).to_s(socket)
+  end
+end
diff --git a/src/twitch/rate_limiter.cr b/src/twitch/rate_limiter.cr
new file mode 100644
index 0000000..929dbc0
--- /dev/null
+++ b/src/twitch/rate_limiter.cr
@@ -0,0 +1,39 @@
+require "rate_limiter"
+
+class RateLimiter(T)
+  class Bucket(K)
+    def initialize(@limit : UInt32, @time_span : Time::Span,
+                   @delay : Time::Span = 0.seconds)
+      @bucket = {} of K => Deque(Time)
+    end
+
+    def rate_limited?(key : K, rate_limit_time = Time.now)
+      queue = @bucket[key]?
+
+      unless queue
+        @bucket[key] = Deque(Time).new(1, rate_limit_time)
+        return false
+      end
+
+      first_time = queue[0]
+      last_time = queue[-1]
+
+      if @limit && (queue.size + 1) > @limit
+        return (first_time + @time_span) - rate_limit_time if (first_time + @time_span) > rate_limit_time
+
+        clean_queue(queue, rate_limit_time - @time_span)
+      end
+
+      return (last_time + @delay) - rate_limit_time if @delay && (last_time + @delay) > rate_limit_time
+
+      queue.push(rate_limit_time)
+      false
+    end
+
+    def clean_queue(queue, rate_limit_time = Time.now)
+      while queue[0] < rate_limit_time
+        queue.shift
+      end
+    end
+  end
+end
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