Handle message type 7 (member join)

When message type 7 is received from the gateway, transform the content
if the type is 7 to a proper greeting.

Additionally, when the type is 6, provide a proper content notifying that a
user has pinned a message to the channel.

These transformations are not done at REST-level when retrieving messages, and
are instead done in `ChannelId::message` and `ChannelId::messages`.

4 files changed, 69 insertions, 2 deletions

diff --git a/src/client/dispatch.rs b/src/client/dispatch.rs
index cea3ed3..56b5f6e 100644
--- a/src/client/dispatch.rs
+++ b/src/client/dispatch.rs
@@ -108,10 +108,14 @@ pub fn dispatch(event: Event,
 }
 
 fn dispatch_message(context: Context,
-                    message: Message,
+                    mut message: Message,
                     event_store: &Arc<RwLock<EventStore>>) {
     if let Some(handler) = handler!(on_message, event_store) {
-        thread::spawn(move || (handler)(context, message));
+        thread::spawn(move || {
+            message.transform_content();
+
+            (handler)(context, message);
+        });
     }
 }
 
diff --git a/src/constants.rs b/src/constants.rs
index de670c9..5c98527 100644
--- a/src/constants.rs
+++ b/src/constants.rs
@@ -12,6 +12,32 @@ pub const MESSAGE_CODE_LIMIT: u16 = 2000;
 /// [UserAgent]: ../hyper/header/struct.UserAgent.html
 pub const USER_AGENT: &'static str = concat!("DiscordBot (https://github.com/zeyla/serenity, ", env!("CARGO_PKG_VERSION"), ")");
 
+/// List of messages Discord shows on member join.
+pub static JOIN_MESSAGES: &'static [&'static str] = &[
+  "$user just joined the server - glhf!",
+  "$user just joined. Everyone, look busy!",
+  "$user just joined. Can I get a heal?",
+  "$user joined your party.",
+  "$user joined. You must construct additional pylons.",
+  "Ermagherd. $user is here.",
+  "Welcome, $user. Stay awhile and listen.",
+  "Welcome, $user. We were expecting you ( ͡° ͜ʖ ͡°)",
+  "Welcome, $user. We hope you brought pizza.",
+  "Welcome $user. Leave your weapons by the door.",
+  "A wild $user appeared.",
+  "Swoooosh. $user just landed.",
+  "Brace yourselves. $user just joined the server.",
+  "$user just joined. Hide your bananas.",
+  "$user just arrived. Seems OP - please nerf.",
+  "$user just slid into the server.",
+  "A $user has spawned in the server.",
+  "Big $user showed up!",
+  "Where’s $user? In the server!",
+  "$user hopped into the server. Kangaroo!!",
+  "$user just showed up. Hold my beer."
+];
+
+
 #[allow(dead_code)]
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub enum ErrorCode {
diff --git a/src/model/channel/channel_id.rs b/src/model/channel/channel_id.rs
index 66bbbf3..46b00c6 100644
--- a/src/model/channel/channel_id.rs
+++ b/src/model/channel/channel_id.rs
@@ -255,6 +255,11 @@ impl ChannelId {
     #[inline]
     pub fn message<M: Into<MessageId>>(&self, message_id: M) -> Result<Message> {
         rest::get_message(self.0, message_id.into().0)
+            .map(|mut msg| {
+                msg.transform_content();
+
+                msg
+            })
     }
 
     /// Gets messages from the channel.
@@ -279,6 +284,13 @@ impl ChannelId {
         }
 
         rest::get_messages(self.0, &query)
+            .map(|msgs| msgs
+                .into_iter()
+                .map(|mut msg| {
+                    msg.transform_content();
+
+                    msg
+                }).collect::<Vec<Message>>())
     }
 
     /// Pins a [`Message`] to the channel.
diff --git a/src/model/channel/message.rs b/src/model/channel/message.rs
index d360975..593aa48 100644
--- a/src/model/channel/message.rs
+++ b/src/model/channel/message.rs
@@ -1,4 +1,5 @@
 use std::mem;
+use time;
 use ::constants;
 use ::client::rest;
 use ::model::*;
@@ -189,6 +190,28 @@ impl Message {
         }
     }
 
+    #[doc(hidden)]
+    pub fn transform_content(&mut self) {
+        match self.kind {
+            MessageType::PinsAdd => {
+                self.content = format!("{} pinned a message to this channel. See all the pins.", self.author);
+            },
+            MessageType::MemberJoin => {
+                if let Ok(tm) = time::strptime(&self.timestamp, "%Y-%m-%dT%H:%M:%S") {
+                    let sec = tm.to_timespec().sec as usize;
+                    let chosen = constants::JOIN_MESSAGES[sec % constants::JOIN_MESSAGES.len()];
+
+                    self.content = if chosen.contains("$user") {
+                        chosen.replace("$user", &self.author.mention())
+                    } else {
+                        chosen.to_owned()
+                    };
+                }
+            },
+            _ => {},
+        }
+    }
+
     /// Returns message content, but with user and role mentions replaced with
     /// names and everyone/here mentions cancelled.
     #[cfg(feature="cache")]
@@ -550,6 +573,8 @@ enum_number!(
         GroupIconUpdate = 5,
         /// An indicator that a message was pinned by the author.
         PinsAdd = 6,
+        /// An indicator that a member joined the guild.
+        MemberJoin = 7,
     }
 );