/
transform.go
148 lines (130 loc) · 3.28 KB
/
transform.go
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package streams
import (
"context"
"errors"
)
type TransformerState uint8
const (
TransformerPaused TransformerState = iota
TransformerFlowing
TransformerFinished
)
type TransformerFunc[I any, O any] func(ctx context.Context, input I) (output O, err error)
type Transformer[I any, O any] struct {
sourceEvents *SourceEvents[O]
sinkEvents *SinkEvents[I]
fn TransformerFunc[I, O]
state TransformerState
buffer []O
maximum int
}
func NewTransform[I any, O any](fn TransformerFunc[I, O]) *Transformer[I, O] {
return &Transformer[I, O]{
sourceEvents: &SourceEvents[O]{},
sinkEvents: &SinkEvents[I]{},
fn: fn,
maximum: 10,
}
}
// Pump draws from source, transforms, then pushes to target.
//
// Deprecated: Use Connect as it has better test coverage and less specific
func (t *Transformer[I, O]) Pump(ctx context.Context, source Source[I], target Sink[O]) error {
target.SinkEvents().Drained.OnE(func(ctx context.Context, event Sink[O]) error {
return t.Resume(ctx)
})
t.sinkEvents.Drained.OnE(func(ctx context.Context, event Sink[I]) error {
return source.Resume(ctx)
})
t.sourceEvents.Data.OnE(func(ctx context.Context, event O) error {
return target.Write(ctx, event)
})
source.SourceEvents().Data.OnE(func(ctx context.Context, event I) error {
return t.Write(ctx, event)
})
return target.Resume(ctx)
}
func (t *Transformer[I, O]) Resume(ctx context.Context) error {
switch t.state {
case TransformerFinished:
return Done
}
t.state = TransformerFlowing
if err := t.pumpInternal(ctx); err != nil {
return err
}
return t.sinkEvents.Drained.Emit(ctx, t)
}
func (t *Transformer[I, O]) Pause(ctx context.Context) error {
switch t.state {
case TransformerFinished:
return Done
case TransformerFlowing:
t.state = TransformerPaused
}
return nil
}
func (t *Transformer[I, O]) pumpInternal(ctx context.Context) error {
for i, e := range t.buffer {
err := t.sourceEvents.Data.Emit(ctx, e)
if err == nil {
continue
}
//remove pushed elements
if i > 0 { // not first
t.buffer = t.buffer[i-1:]
}
//todo: state cycles?
return err
}
t.buffer = nil
return nil
}
func (t *Transformer[I, O]) Write(ctx context.Context, v I) error {
switch t.state {
case TransformerPaused:
if len(t.buffer) >= t.maximum {
return Full
}
case TransformerFinished:
return Done
}
out, err := t.fn(ctx, v)
if err != nil {
return err
}
switch t.state {
case TransformerPaused:
t.buffer = append(t.buffer, out)
case TransformerFlowing:
if t.buffer != nil {
t.buffer = append(t.buffer, out)
return t.pumpInternal(ctx)
} else {
problem := t.sourceEvents.Data.Emit(ctx, out)
switch problem {
case Full:
t.buffer = append(t.buffer, out)
}
return problem
}
}
return nil
}
func (t *Transformer[I, O]) Finish(ctx context.Context) error {
if t.state == TransformerFinished {
return nil
}
t.state = TransformerFinished
//todo: should only be emitted after it is completed
return t.sinkEvents.Finished.Emit(ctx, t)
}
func (t *Transformer[I, O]) SinkEvents() *SinkEvents[I] {
return t.sinkEvents
}
func (t *Transformer[I, O]) SourceEvents() *SourceEvents[O] {
return t.sourceEvents
}
func (t *Transformer[I, O]) ReadSlice(ctx context.Context, to []O) (int, error) {
return 0, errors.New("todo")
}