Created Tengo (markdown)

Tengo.md

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+# Tengo
+
+Tengo can be used fo advanced scripting in matterbridge, you can modify incoming and outgoing messages.
+
+You can also use it to modify the `{TENGO}` parameter in the `RemoteNickFormat`.
+
+```
+[tengo]
+InMessage="yourscript.tengo"
+OutMessage="yourotherscript.tengo"
+RemoteNickFormat="remotenickformat.tengo"
+```
+
+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
+
+FIXME: Document support for [dropping messages](https://github.com/42wim/matterbridge/pull/1272).
+
+## InMessage
+
+InMessage 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"
+}
+```
+
+`InMessage="example.tengo"`
+
+## OutMessage
+
+OutMessage allows you to specify the location of the script that will be invoked on each message being sent to a bridge and can be used to modify the Username and the Text of that message.
+
+The script will have the following global variables: \
+read-only: \
+`inAccount`, `inProtocol`, `inChannel`, `inGateway`, `inEvent` \
+`outAccount`, `outProtocol`, `outChannel`, `outGateway`, `outEvent` \
+
+read-write: \
+`msgText`, `msgUsername`
+
+The script is reloaded on every message, so you can modify the script on the fly.
+
+The default script in <https://github.com/42wim/matterbridge/tree/master/internal/tengo/outmessage.tengo>
+is compiled in and will be executed if no script is specified.
+
+`OutMessage="example.tengo"`
+
+## RemoteNickFormat
+
+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>
+
+`RemoteNickFormat="remotenickformat.tengo"`
+
+## More information
+
+You can find more tengo examples/info here:
+- <https://github.com/42wim/matterbridge/issues?q=is%3Aissue+tengo+label%3Atengo+is%3Aclosed>
+- <https://github.com/42wim/matterbridge/tree/master/internal/tengo>
+- <https://github.com/42wim/matterbridge/tree/master/contrib>
+- <https://github.com/42wim/matterbridge/wiki/settings#tengo>
+
+The tengo documentation can be found here: <https://github.com/d5/tengo/tree/master/docs>