package google

import (
	"context"
	"encoding/json"
	"io"
	"iter"
	"strconv"
	"sync"

	"google.golang.org/genai"

	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
)

// Stream implements llm.Model over the SDK's range-over-func stream
// (iter.Seq2), adapted to majordomo's pull-based Stream via iter.Pull2.
func (m *model) Stream(ctx context.Context, req llm.Request, opts ...llm.Option) (llm.Stream, error) {
	req = req.Apply(opts...)
	if err := m.enforceCapabilities(req); err != nil {
		return nil, err
	}
	client, err := m.provider.genaiClient(ctx)
	if err != nil {
		return nil, err
	}
	system, contents, err := m.buildContents(req)
	if err != nil {
		return nil, err
	}
	cfg, err := m.buildConfig(req, system)
	if err != nil {
		return nil, err
	}

	seq := client.Models.GenerateContentStream(ctx, m.id, contents, cfg)
	next, stop := iter.Pull2(iter.Seq2[*genai.GenerateContentResponse, error](seq))
	return &stream{model: m, next: next, stop: stop}, nil
}

type stream struct {
	model *model
	next  func() (*genai.GenerateContentResponse, error, bool)
	stop  func()

	mu        sync.Mutex
	closeOnce sync.Once
	finished  bool
	pending   []llm.StreamEvent
	text      []byte
	toolCalls []llm.ToolCall
	usage     llm.Usage
	finish    genai.FinishReason
}

func (s *stream) Next() (llm.StreamEvent, error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	for {
		if len(s.pending) > 0 {
			ev := s.pending[0]
			s.pending = s.pending[1:]
			return ev, nil
		}
		if s.finished {
			return llm.StreamEvent{}, io.EOF
		}

		chunk, err, ok := s.next()
		if !ok {
			s.queueFinal()
			continue
		}
		if err != nil {
			return llm.StreamEvent{}, s.model.mapError(err)
		}

		if chunk.UsageMetadata != nil {
			s.usage = llm.Usage{
				InputTokens:  int(chunk.UsageMetadata.PromptTokenCount),
				OutputTokens: int(chunk.UsageMetadata.CandidatesTokenCount + chunk.UsageMetadata.ThoughtsTokenCount),
			}
		}
		if len(chunk.Candidates) == 0 {
			continue
		}
		cand := chunk.Candidates[0]
		if cand.FinishReason != "" {
			s.finish = cand.FinishReason
		}
		if cand.Content == nil {
			continue
		}
		for _, part := range cand.Content.Parts {
			if part == nil {
				continue
			}
			if part.Text != "" && !part.Thought {
				s.text = append(s.text, part.Text...)
				s.pending = append(s.pending, llm.StreamEvent{TextDelta: part.Text})
			}
			// Function calls arrive whole per chunk in the Gemini stream.
			if fc := part.FunctionCall; fc != nil {
				id := fc.ID
				if id == "" {
					id = "call_" + strconv.Itoa(len(s.toolCalls))
				}
				args, err := json.Marshal(fc.Args)
				if err != nil || len(fc.Args) == 0 {
					args = json.RawMessage("{}")
				}
				call := llm.ToolCall{ID: id, Name: fc.Name, Arguments: args}
				s.toolCalls = append(s.toolCalls, call)
				s.pending = append(s.pending, llm.StreamEvent{ToolCall: &call})
			}
		}
	}
}

func (s *stream) queueFinal() {
	resp := &llm.Response{
		Model:        s.model.qualified(),
		Usage:        s.usage,
		FinishReason: mapFinish(s.finish, len(s.toolCalls) > 0),
	}
	if len(s.text) > 0 {
		resp.Parts = append(resp.Parts, llm.Text(string(s.text)))
	}
	if len(s.toolCalls) > 0 {
		resp.ToolCalls = append([]llm.ToolCall(nil), s.toolCalls...)
	}
	s.pending = append(s.pending, llm.StreamEvent{Response: resp})
	s.finished = true
}

func (s *stream) Close() error {
	s.closeOnce.Do(s.stop)
	return nil
}