chore: add pre callbacks

examples/pipeline/callbacks/main.go

@@ -31,26 +31,24 @@ func main() {
 		},
 	)
 
-	cbTranslate := pipeline.PipelineCallback(func(output types.M) (types.M, error) {
-		iterator++
-		return output, nil
+	translatePreCallback := pipeline.PipelineCallback(func(input types.M) (types.M, error) {
+		input["language"] = languages[iterator]
+		input["sentence"] = sentence
+		return input, nil
 	})
 
-	cbExpand := pipeline.PipelineCallback(func(output types.M) (types.M, error) {
-
+	expandPostCallback := pipeline.PipelineCallback(func(output types.M) (types.M, error) {
+		iterator++
 		if iterator >= len(languages) {
 			pipeline.SetNextTubeExit(output)
 		} else {
 			pipeline.SetNextTube(output, 0)
-			output["language"] = languages[iterator]
-			output["sentence"] = sentence
 		}
-
 		return output, nil
 	})
 
-	pipeLine := pipeline.New(translate, expand).WithCallbacks(cbTranslate, cbExpand)
+	pipeLine := pipeline.New(translate, expand).WithPreCallbacks(translatePreCallback, nil).WithPostCallbacks(nil, expandPostCallback)
 
-	pipeLine.Run(context.Background(), types.M{"sentence": sentence, "language": languages[iterator]})
+	pipeLine.Run(context.Background(), nil)
 
 }

pipeline/pipeline.go

@@ -31,44 +31,73 @@ type Pipe interface {
 	Run(ctx context.Context, input types.M) (types.M, error)
 }
 
-type PipelineCallback func(input types.M) (types.M, error)
+type PipelineCallback func(values types.M) (types.M, error)
 
 type pipeline struct {
-	pipes     []Pipe
-	callbacks []PipelineCallback
+	pipes         map[int]Pipe
+	preCallbacks  map[int]PipelineCallback
+	postCallbacks map[int]PipelineCallback
 }
 
 func New(pipes ...Pipe) *pipeline {
+
+	pipesMap := make(map[int]Pipe)
+	for i, pipe := range pipes {
+		pipesMap[i] = pipe
+	}
+
 	return &pipeline{
-		pipes: pipes,
+		pipes: pipesMap,
 	}
 }
 
-func (p *pipeline) WithCallbacks(callbacks ...PipelineCallback) pipeline {
-	p.callbacks = callbacks
-	return *p
+func (p *pipeline) WithPreCallbacks(callbacks ...PipelineCallback) *pipeline {
+
+	p.preCallbacks = make(map[int]PipelineCallback)
+	for i, callback := range callbacks {
+		p.preCallbacks[i] = callback
+	}
+
+	return p
+}
+
+func (p *pipeline) WithPostCallbacks(callbacks ...PipelineCallback) *pipeline {
+
+	p.postCallbacks = make(map[int]PipelineCallback)
+	for i, callback := range callbacks {
+		p.postCallbacks[i] = callback
+	}
+
+	return p
 }
 
 // Run chains the steps of the pipeline and returns the output of the last step.
 func (p pipeline) Run(ctx context.Context, input types.M) (types.M, error) {
 	var err error
-	var output types.M
-	currentTube := -1
+	currentTube := 0
+
+	if input == nil {
+		input = types.M{}
+	}
+
+	output := input
 
 	for {
 
-		if currentTube == -1 {
-			currentTube = 0
-			output = input
+		if p.thereIsAValidPreCallbackForTube(currentTube) {
+			output, err = p.preCallbacks[currentTube](output)
+			if err != nil {
+				return nil, err
+			}
 		}
 
 		output, err = p.pipes[currentTube].Run(ctx, output)
 		if err != nil {
 			return nil, err
 		}
 
-		if p.thereIsAValidCallbackForTube(currentTube) {
-			output, err = p.callbacks[currentTube](output)
+		if p.thereIsAValidPostCallbackForTube(currentTube) {
+			output, err = p.postCallbacks[currentTube](output)
 			if err != nil {
 				return nil, err
 			}
@@ -105,8 +134,14 @@ func SetNextTubeExit(output types.M) types.M {
 	return output
 }
 
-func (p *pipeline) thereIsAValidCallbackForTube(currentTube int) bool {
-	return len(p.callbacks) == len(p.pipes) && p.callbacks[currentTube] != nil
+func (p *pipeline) thereIsAValidPreCallbackForTube(currentTube int) bool {
+	cb, ok := p.preCallbacks[currentTube]
+	return cb != nil && ok
+}
+
+func (p *pipeline) thereIsAValidPostCallbackForTube(currentTube int) bool {
+	cb, ok := p.postCallbacks[currentTube]
+	return cb != nil && ok
 }
 
 func (p *pipeline) getNextTube(output types.M) *int {