Add tengo support to RemoteNickFormat (#793)

This commit add support for using the result of a tengo script in RemoteNickFormat using {TENGO}
Also adds a new toml table [tengo] with key RemoteNickFormat and value location of the script.
This also moves the TengoModifyMessage from [general] to Message in [tengo]

Documentation:

RemoteNickFormat allows you to specify the location of a tengo (https://github.com/d5/tengo/) script.
The script will have the following global variables:
to modify: result
to read: channel, bridge, gateway, protocol, nick

The result will be set in {TENGO} in the RemoteNickFormat key of every bridge where {TENGO} is specified
The script is reloaded on every message, so you can modify the script on the fly.
Example script can be found in https://github.com/42wim/matterbridge/tree/master/contrib/remotenickformat.tengo

[tengo]
RemoteNickFormat="remotenickformat.tengo"

4 files changed, 98 insertions, 0 deletions

diff --git a/bridge/config/config.go b/bridge/config/config.go
index 230ddb9e..29261d58 100644
--- a/bridge/config/config.go
+++ b/bridge/config/config.go
@@ -166,6 +166,11 @@ type Gateway struct {
 	InOut  []Bridge
 }
 
+type Tengo struct {
+	Message          string
+	RemoteNickFormat string
+}
+
 type SameChannelGateway struct {
 	Name     string
 	Enable   bool
@@ -190,6 +195,7 @@ type BridgeValues struct {
 	WhatsApp           map[string]Protocol // TODO is this struct used? Search for "SlackLegacy" for example didn't return any results
 	Zulip              map[string]Protocol
 	General            Protocol
+	Tengo              Tengo
 	Gateway            []Gateway
 	SameChannelGateway []SameChannelGateway
 }
diff --git a/contrib/remotenickformat.tengo b/contrib/remotenickformat.tengo
new file mode 100644
index 00000000..2ca856eb
--- /dev/null
+++ b/contrib/remotenickformat.tengo
@@ -0,0 +1,9 @@
+/*
+This script will return the current time in kitchen format if the protocol (of the remote bridge) isn't irc
+See https://github.com/d5/tengo/blob/master/docs/stdlib-times.md
+This result can be used in {TENGO} in RemoteNickFormat
+*/
+times := import("times")
+if protocol != "irc" {
+   result=times.time_format(times.now(),times.format_kitchen)
+}
diff --git a/gateway/gateway.go b/gateway/gateway.go
index e76e1d59..d46f75d6 100644
--- a/gateway/gateway.go
+++ b/gateway/gateway.go
@@ -331,6 +331,11 @@ func (gw *Gateway) modifyUsername(msg *config.Message, dest *bridge.Bridge) stri
 	nick = strings.Replace(nick, "{LABEL}", br.GetString("Label"), -1)
 	nick = strings.Replace(nick, "{NICK}", msg.Username, -1)
 	nick = strings.Replace(nick, "{CHANNEL}", msg.Channel, -1)
+	tengoNick, err := gw.modifyUsernameTengo(msg, br)
+	if err != nil {
+		gw.logger.Errorf("modifyUsernameTengo error: %s", err)
+	}
+	nick = strings.Replace(nick, "{TENGO}", tengoNick, -1) //nolint:gocritic
 	return nick
 }
 
@@ -347,6 +352,9 @@ func (gw *Gateway) modifyMessage(msg *config.Message) {
 	if err := modifyMessageTengo(gw.BridgeValues().General.TengoModifyMessage, msg); err != nil {
 		gw.logger.Errorf("TengoModifyMessage failed: %s", err)
 	}
+	if err := modifyMessageTengo(gw.BridgeValues().Tengo.Message, msg); err != nil {
+		gw.logger.Errorf("Tengo.Message failed: %s", err)
+	}
 
 	// replace :emoji: to unicode
 	msg.Text = emojilib.Replace(msg.Text)
@@ -503,3 +511,36 @@ func modifyMessageTengo(filename string, msg *config.Message) error {
 	msg.Username = c.Get("msgUsername").String()
 	return nil
 }
+
+func (gw *Gateway) modifyUsernameTengo(msg *config.Message, br *bridge.Bridge) (string, error) {
+	filename := gw.BridgeValues().Tengo.RemoteNickFormat
+	if filename == "" {
+		return "", nil
+	}
+	res, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return "", err
+	}
+	s := script.New(res)
+	s.SetImports(stdlib.GetModuleMap(stdlib.AllModuleNames()...))
+	_ = s.Add("result", "")
+	_ = s.Add("msgText", msg.Text)
+	_ = s.Add("msgUsername", msg.Username)
+	_ = s.Add("nick", msg.Username)
+	_ = s.Add("msgAccount", msg.Account)
+	_ = s.Add("msgChannel", msg.Channel)
+	_ = s.Add("channel", msg.Channel)
+	_ = s.Add("msgProtocol", msg.Protocol)
+	_ = s.Add("remoteAccount", br.Account)
+	_ = s.Add("protocol", br.Protocol)
+	_ = s.Add("bridge", br.Name)
+	_ = s.Add("gateway", gw.Name)
+	c, err := s.Compile()
+	if err != nil {
+		return "", err
+	}
+	if err := c.Run(); err != nil {
+		return "", err
+	}
+	return c.Get("result").String(), nil
+}
diff --git a/matterbridge.toml.sample b/matterbridge.toml.sample
index 3b4dc407..6856a837 100644
--- a/matterbridge.toml.sample
+++ b/matterbridge.toml.sample
@@ -1480,6 +1480,7 @@ RemoteNickFormat="{NICK}"
 #The string "{PROTOCOL}" (case sensitive) will be replaced by the protocol used by the bridge
 #The string "{GATEWAY}" (case sensitive) will be replaced by the origin gateway name that is replicating the message.
 #The string "{CHANNEL}" (case sensitive) will be replaced by the origin channel name used by the bridge
+#The string "{TENGO}" (case sensitive) will be replaced by the output of the RemoteNickFormat script under [tengo]
 #OPTIONAL (default empty)
 RemoteNickFormat="[{PROTOCOL}] <{NICK}> "
 
@@ -1553,6 +1554,47 @@ IgnoreFailureOnStart=false
 TengoModifyMessage="example.tengo"
 
 ###################################################################
+#Tengo configuration
+###################################################################
+#More information about tengo on: https://github.com/d5/tengo/blob/master/docs/tutorial.md and
+#https://github.com/d5/tengo/blob/master/docs/stdlib.md
+
+[tengo]
+#Message allows you to specify the location of a tengo (https://github.com/d5/tengo/) script.
+#This script will receive every incoming message and can be used to modify the Username and the Text of that message.
+#The script will have the following global variables:
+#to modify: msgUsername and msgText
+#to read: msgChannel and msgAccount
+#
+#The script is reloaded on every message, so you can modify the script on the fly.
+#
+#Example script can be found in https://github.com/42wim/matterbridge/tree/master/gateway/bench.tengo
+#and https://github.com/42wim/matterbridge/tree/master/contrib/example.tengo
+#
+#The example below will check if the text contains blah and if so, it'll replace the text and the username of that message.
+#text := import("text")
+#if text.re_match("blah",msgText) {
+#    msgText="replaced by this"
+#    msgUsername="fakeuser"
+#}
+#OPTIONAL (default empty)
+Message="example.tengo"
+
+#RemoteNickFormat allows you to specify the location of a tengo (https://github.com/d5/tengo/) script.
+#The script will have the following global variables:
+#to modify: result
+#to read: channel, bridge, gateway, protocol, nick
+#
+#The result will be set in {TENGO} in the RemoteNickFormat key of every bridge where {TENGO} is specified
+#
+#The script is reloaded on every message, so you can modify the script on the fly.
+#
+#Example script can be found in https://github.com/42wim/matterbridge/tree/master/contrib/remotenickformat.tengo
+#
+#OPTIONAL (default empty)
+RemoteNickFormat="remotenickformat.tengo"
+
+###################################################################
 #Gateway configuration
 ###################################################################