Add scripting (tengo) support for every incoming message (#731)

TengoModifyMessage 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"
}

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

1 files changed, 47 insertions, 0 deletions

diff --git a/vendor/github.com/d5/tengo/objects/builtin_function.go b/vendor/github.com/d5/tengo/objects/builtin_function.go
new file mode 100644
index 00000000..1d021617
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtin_function.go
@@ -0,0 +1,47 @@
+package objects
+
+import (
+	"github.com/d5/tengo/compiler/token"
+)
+
+// BuiltinFunction represents a builtin function.
+type BuiltinFunction struct {
+	Name  string
+	Value CallableFunc
+}
+
+// TypeName returns the name of the type.
+func (o *BuiltinFunction) TypeName() string {
+	return "builtin-function:" + o.Name
+}
+
+func (o *BuiltinFunction) String() string {
+	return "<builtin-function>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *BuiltinFunction) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *BuiltinFunction) Copy() Object {
+	return &BuiltinFunction{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *BuiltinFunction) IsFalsy() bool {
+	return false
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *BuiltinFunction) Equals(x Object) bool {
+	return false
+}
+
+// Call executes a builtin function.
+func (o *BuiltinFunction) Call(args ...Object) (Object, error) {
+	return o.Value(args...)
+}