package backend

import "context"

// Noop is a programmable test backend that satisfies the Backend interface
// without making any network calls. By default it returns an empty response
// immediately. Set ChatStreamFunc to override behavior.
type Noop struct {
	name  string
	model string

	// ChatStreamFunc, if non-nil, replaces the default ChatStream behavior.
	// Use this to simulate blocking, errors, or custom responses.
	ChatStreamFunc func(ctx context.Context, messages []Message, tools []Tool, params GenerationParams) (<-chan StreamEvent, error)
}

// NewNoop creates a Noop backend with the given name and model.
func NewNoop(name, model string) *Noop {
	if name == "" {
		name = "noop"
	}
	if model == "" {
		model = "noop"
	}
	return &Noop{name: name, model: model}
}

func (n *Noop) Name() string         { return n.name }
func (n *Noop) DefaultModel() string  { return n.model }
func (n *Noop) Model() string         { return n.model }
func (n *Noop) SetModel(model string) { n.model = model }

func (n *Noop) ContextLength(_ context.Context) int { return 128000 }

func (n *Noop) Models(_ context.Context) []string {
	return []string{n.model}
}

func (n *Noop) ChatStream(ctx context.Context, messages []Message, tools []Tool, params GenerationParams) (<-chan StreamEvent, error) {
	if n.ChatStreamFunc != nil {
		return n.ChatStreamFunc(ctx, messages, tools, params)
	}
	ch := make(chan StreamEvent, 1)
	ch <- StreamEvent{Done: true, StopReason: "end_turn"}
	close(ch)
	return ch, nil
}