package llm

import (
	"context"
	"fmt"
	"io"

	"gitea.stevedudenhoeffer.com/steve/go-llm/v2/provider"
)

// StreamEventType identifies the kind of stream event.
type StreamEventType = provider.StreamEventType

const (
	StreamEventText      = provider.StreamEventText
	StreamEventToolStart = provider.StreamEventToolStart
	StreamEventToolDelta = provider.StreamEventToolDelta
	StreamEventToolEnd   = provider.StreamEventToolEnd
	StreamEventDone      = provider.StreamEventDone
	StreamEventError     = provider.StreamEventError
)

// StreamEvent represents a single event in a streaming response.
type StreamEvent struct {
	Type StreamEventType

	// Text is set for StreamEventText — the text delta.
	Text string

	// ToolCall is set for StreamEventToolStart/ToolDelta/ToolEnd.
	ToolCall *ToolCall

	// ToolIndex identifies which tool call is being updated.
	ToolIndex int

	// Error is set for StreamEventError.
	Error error

	// Response is set for StreamEventDone — the complete, aggregated response.
	Response *Response
}

// StreamReader reads streaming events from an LLM response.
// Must be closed when done.
type StreamReader struct {
	events <-chan StreamEvent
	cancel context.CancelFunc
	done   bool
}

func newStreamReader(ctx context.Context, p provider.Provider, req provider.Request) (*StreamReader, error) {
	ctx, cancel := context.WithCancel(ctx)
	providerEvents := make(chan provider.StreamEvent, 32)

	publicEvents := make(chan StreamEvent, 32)

	go func() {
		defer close(publicEvents)
		for pev := range providerEvents {
			ev := convertStreamEvent(pev)
			select {
			case publicEvents <- ev:
			case <-ctx.Done():
				return
			}
		}
	}()

	go func() {
		defer close(providerEvents)
		if err := p.Stream(ctx, req, providerEvents); err != nil {
			select {
			case providerEvents <- provider.StreamEvent{Type: provider.StreamEventError, Error: err}:
			default:
			}
		}
	}()

	return &StreamReader{
		events: publicEvents,
		cancel: cancel,
	}, nil
}

func convertStreamEvent(pev provider.StreamEvent) StreamEvent {
	ev := StreamEvent{
		Type:      pev.Type,
		Text:      pev.Text,
		ToolIndex: pev.ToolIndex,
	}
	if pev.Error != nil {
		ev.Error = pev.Error
	}
	if pev.ToolCall != nil {
		tc := ToolCall{
			ID:        pev.ToolCall.ID,
			Name:      pev.ToolCall.Name,
			Arguments: pev.ToolCall.Arguments,
		}
		ev.ToolCall = &tc
	}
	if pev.Response != nil {
		resp := convertProviderResponse(*pev.Response)
		ev.Response = &resp
	}
	return ev
}

// Next returns the next event from the stream.
// Returns io.EOF when the stream is complete.
func (sr *StreamReader) Next() (StreamEvent, error) {
	if sr.done {
		return StreamEvent{}, io.EOF
	}
	ev, ok := <-sr.events
	if !ok {
		sr.done = true
		return StreamEvent{}, io.EOF
	}
	if ev.Type == StreamEventError {
		return ev, ev.Error
	}
	if ev.Type == StreamEventDone {
		sr.done = true
	}
	return ev, nil
}

// Close closes the stream reader and releases resources.
func (sr *StreamReader) Close() error {
	sr.cancel()
	return nil
}

// Collect reads all events and returns the final aggregated Response.
func (sr *StreamReader) Collect() (Response, error) {
	var lastResp *Response
	for {
		ev, err := sr.Next()
		if err == io.EOF {
			break
		}
		if err != nil {
			return Response{}, err
		}
		if ev.Type == StreamEventDone && ev.Response != nil {
			lastResp = ev.Response
		}
	}
	if lastResp == nil {
		return Response{}, fmt.Errorf("stream completed without final response")
	}
	return *lastResp, nil
}

// Text is a convenience that collects the stream and returns just the text.
func (sr *StreamReader) Text() (string, error) {
	resp, err := sr.Collect()
	if err != nil {
		return "", err
	}
	return resp.Text, nil
}