package openai

import (
	"bytes"
	"encoding/json"
	"fmt"
	"strings"
	"sync"
	"time"

	"iop/packages/go/streamgate"
)

// openAITunnelCodecState keeps caller-facing provider frames outside semantic
// evidence while the Core holds parsed endpoint events. It is reset before each
// recovery attempt, which is safe because path switches are allowed only before
// any response bytes are committed.
type openAITunnelCodecState struct {
	mu            sync.Mutex
	endpoint      string
	releases      [][]byte
	terminal      []byte
	termSet       bool
	errorResponse *openAITunnelErrorResponse
}

type openAITunnelErrorResponse struct {
	status  int
	headers map[string]string
	body    []byte
}

func (s *openAITunnelCodecState) reset() {
	if s == nil {
		return
	}
	s.mu.Lock()
	s.releases = nil
	s.terminal = nil
	s.termSet = false
	s.errorResponse = nil
	s.mu.Unlock()
}

func (s *openAITunnelCodecState) bindEndpoint(endpoint string) bool {
	if s == nil {
		return false
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.endpoint == "" {
		s.endpoint = endpoint
	}
	return s.endpoint == endpoint
}

func (s *openAITunnelCodecState) endpointIsChat() bool {
	if s == nil {
		return false
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.endpoint == openAIRebuildEndpointChat
}

func (s *openAITunnelCodecState) stageErrorResponseStart(status int, headers map[string]string) {
	if s == nil {
		return
	}
	s.mu.Lock()
	s.errorResponse = &openAITunnelErrorResponse{
		status:  status,
		headers: cloneStringMap(headers),
	}
	s.mu.Unlock()
}

func (s *openAITunnelCodecState) appendErrorResponseWire(payload []byte) {
	if s == nil || len(payload) == 0 {
		return
	}
	s.mu.Lock()
	if s.errorResponse != nil {
		s.errorResponse.body = append(s.errorResponse.body, payload...)
	}
	s.mu.Unlock()
}

func (s *openAITunnelCodecState) popErrorResponse() (openAITunnelErrorResponse, bool) {
	if s == nil {
		return openAITunnelErrorResponse{}, false
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.errorResponse == nil {
		return openAITunnelErrorResponse{}, false
	}
	response := openAITunnelErrorResponse{
		status:  s.errorResponse.status,
		headers: cloneStringMap(s.errorResponse.headers),
		body:    append([]byte(nil), s.errorResponse.body...),
	}
	s.errorResponse = nil
	return response, true
}

func cloneStringMap(src map[string]string) map[string]string {
	if len(src) == 0 {
		return nil
	}
	dst := make(map[string]string, len(src))
	for key, value := range src {
		dst[key] = value
	}
	return dst
}

func (s *openAITunnelCodecState) pushRelease(payload []byte) {
	if s == nil {
		return
	}
	s.mu.Lock()
	s.releases = append(s.releases, append([]byte(nil), payload...))
	s.mu.Unlock()
}

func (s *openAITunnelCodecState) popRelease() ([]byte, bool) {
	if s == nil {
		return nil, false
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if len(s.releases) == 0 {
		return nil, false
	}
	payload := s.releases[0]
	s.releases = s.releases[1:]
	return append([]byte(nil), payload...), true
}

func (s *openAITunnelCodecState) setTerminal(payload []byte) {
	if s == nil {
		return
	}
	s.mu.Lock()
	s.terminal = append([]byte(nil), payload...)
	s.termSet = true
	s.mu.Unlock()
}

func (s *openAITunnelCodecState) popTerminal() ([]byte, bool) {
	if s == nil {
		return nil, false
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if !s.termSet {
		return nil, false
	}
	payload := append([]byte(nil), s.terminal...)
	s.terminal = nil
	s.termSet = false
	return payload, true
}

// openAITunnelEndpointCodec parses Chat Completions or Responses SSE frames
// into semantic Core events while retaining each original frame for lossless
// downstream release.
type openAITunnelEndpointCodec struct {
	endpoint      string
	state         *openAITunnelCodecState
	pending       []byte
	stagedWire    []byte
	chatTools     map[int]openAITunnelToolIdentity
	responseTools map[string]openAITunnelToolIdentity
	terminal      bool
}

type openAITunnelToolIdentity struct {
	id   string
	name string
}

func newOpenAITunnelEndpointCodec(endpoint string, state *openAITunnelCodecState) *openAITunnelEndpointCodec {
	if state == nil || (endpoint != openAIRebuildEndpointChat && endpoint != openAIRebuildEndpointResponses) {
		return nil
	}
	if !state.bindEndpoint(endpoint) {
		return nil
	}
	return &openAITunnelEndpointCodec{
		endpoint:      endpoint,
		state:         state,
		chatTools:     make(map[int]openAITunnelToolIdentity),
		responseTools: make(map[string]openAITunnelToolIdentity),
	}
}

func (c *openAITunnelEndpointCodec) decode(body []byte, flush bool) ([]streamgate.NormalizedEvent, error) {
	if c == nil || c.terminal {
		return nil, nil
	}
	c.pending = append(c.pending, body...)
	var out []streamgate.NormalizedEvent
	for {
		frame, rest, ok := takeOpenAISSEFrame(c.pending)
		if !ok {
			break
		}
		c.pending = rest
		events, err := c.decodeFrame(frame)
		if err != nil {
			return nil, err
		}
		out = append(out, events...)
		if c.terminal {
			c.pending = nil
			return out, nil
		}
	}
	if flush && len(c.pending) > 0 {
		frame := append([]byte(nil), c.pending...)
		c.pending = nil
		events, err := c.decodeFrame(frame)
		if err != nil {
			return nil, err
		}
		out = append(out, events...)
	}
	return out, nil
}

func takeOpenAISSEFrame(buf []byte) (frame, rest []byte, ok bool) {
	lf := bytes.Index(buf, []byte("\n\n"))
	crlf := bytes.Index(buf, []byte("\r\n\r\n"))
	end := -1
	sepLen := 0
	if lf >= 0 {
		end, sepLen = lf, 2
	}
	if crlf >= 0 && (end < 0 || crlf < end) {
		end, sepLen = crlf, 4
	}
	if end < 0 {
		return nil, buf, false
	}
	frame = append([]byte(nil), buf[:end+sepLen]...)
	rest = append([]byte(nil), buf[end+sepLen:]...)
	return frame, rest, true
}

func openAISSEData(frame []byte) string {
	normalized := strings.ReplaceAll(string(frame), "\r\n", "\n")
	var lines []string
	for _, line := range strings.Split(normalized, "\n") {
		if !strings.HasPrefix(line, "data:") {
			continue
		}
		lines = append(lines, strings.TrimSpace(strings.TrimPrefix(line, "data:")))
	}
	return strings.Join(lines, "\n")
}

func (c *openAITunnelEndpointCodec) decodeFrame(frame []byte) ([]streamgate.NormalizedEvent, error) {
	data := openAISSEData(frame)
	if data == "" && json.Valid(bytes.TrimSpace(frame)) {
		data = string(bytes.TrimSpace(frame))
	}
	if strings.TrimSpace(data) == "[DONE]" {
		return c.finishTerminal(frame, false)
	}

	var events []streamgate.NormalizedEvent
	var err error
	if c.endpoint == openAIRebuildEndpointResponses {
		events, err = c.decodeResponsesTunnelFrame(data)
	} else {
		events, err = c.decodeChatTunnelFrame(data)
	}
	if err == nil {
		// Continue below.
	} else {
		return nil, err
	}

	releaseAttached := false
	for _, event := range events {
		switch event.Kind() {
		case streamgate.EventKindTextDelta, streamgate.EventKindReasoningDelta, streamgate.EventKindToolCallFragment:
			if releaseAttached == false {
				payload := append(append([]byte(nil), c.stagedWire...), frame...)
				c.stagedWire = nil
				c.state.pushRelease(payload)
				releaseAttached = true
			} else {
				c.state.pushRelease(nil)
			}
		case streamgate.EventKindProviderError:
			if releaseAttached {
				return c.finishTerminal(nil, true)
			}
			return c.finishTerminal(frame, true)
		}
	}
	if releaseAttached == false {
		// Provider opening/metadata and protocol-level finish frames are wire-only:
		// retain them until the next semantic release or transport terminal rather
		// than manufacturing text evidence from their JSON payload.
		c.stagedWire = append(c.stagedWire, frame...)
	}
	return events, nil
}

// finishTransport turns the physical END boundary into the only terminal when
// no [DONE] marker already did so. A non-2xx response is a provider-error
// lifecycle event even if its body was opaque JSON and therefore wire-only.
func (c *openAITunnelEndpointCodec) finishTransport(body []byte, providerError bool) ([]streamgate.NormalizedEvent, error) {
	if c == nil || c.terminal {
		return nil, nil
	}
	events, err := c.decode(body, true)
	if err == nil && c.terminal == false {
		terminal, terminalErr := c.finishTerminal(nil, providerError)
		if terminalErr != nil {
			return nil, terminalErr
		}
		return append(events, terminal...), nil
	}
	return events, err
}

func (c *openAITunnelEndpointCodec) finishTerminal(frame []byte, providerError bool) ([]streamgate.NormalizedEvent, error) {
	if c.terminal {
		return nil, nil
	}
	payload := append(append([]byte(nil), c.stagedWire...), frame...)
	c.stagedWire = nil
	c.state.setTerminal(payload)
	c.terminal = true
	if providerError {
		ev, err := newOpenAIProviderErrorEvent(streamGateErrorTunnelFailed)
		return []streamgate.NormalizedEvent{ev}, err
	}
	ev, err := streamgate.NewTerminalEvent(streamGateChannelDefault, time.Now())
	return []streamgate.NormalizedEvent{ev}, err
}

func (c *openAITunnelEndpointCodec) decodeChatTunnelFrame(data string) ([]streamgate.NormalizedEvent, error) {
	if strings.TrimSpace(data) == "" {
		return nil, nil
	}
	var payload struct {
		Choices []struct {
			Delta struct {
				Content          string `json:"content"`
				Reasoning        string `json:"reasoning"`
				ReasoningContent string `json:"reasoning_content"`
				ToolCalls        []struct {
					Index    int    `json:"index"`
					ID       string `json:"id"`
					Function struct {
						Name      string `json:"name"`
						Arguments string `json:"arguments"`
					} `json:"function"`
				} `json:"tool_calls"`
			} `json:"delta"`
			Message struct {
				Content          string `json:"content"`
				ReasoningContent string `json:"reasoning_content"`
			} `json:"message"`
			FinishReason *string `json:"finish_reason"`
		} `json:"choices"`
	}
	if err := json.Unmarshal([]byte(data), &payload); err != nil {
		return nil, nil
	}
	var events []streamgate.NormalizedEvent
	for _, choice := range payload.Choices {
		content := choice.Delta.Content
		if content == "" {
			content = choice.Message.Content
		}
		if content != "" {
			ev, err := streamgate.NewTextDeltaEvent(streamGateChannelDefault, content, time.Now())
			if err != nil {
				return nil, err
			}
			events = append(events, ev)
		}
		reasoning := choice.Delta.ReasoningContent
		if reasoning == "" {
			reasoning = choice.Delta.Reasoning
		}
		if reasoning == "" {
			reasoning = choice.Message.ReasoningContent
		}
		if reasoning != "" {
			ev, err := streamgate.NewReasoningDeltaEvent(streamGateChannelDefault, reasoning, time.Now())
			if err != nil {
				return nil, err
			}
			events = append(events, ev)
		}
		for _, tool := range choice.Delta.ToolCalls {
			identity := c.chatTools[tool.Index]
			if tool.ID != "" {
				identity.id = tool.ID
			}
			if tool.Function.Name != "" {
				identity.name = tool.Function.Name
			}
			c.chatTools[tool.Index] = identity
			if tool.Function.Arguments == "" {
				continue
			}
			id := identity.id
			if id == "" {
				id = fmt.Sprintf("tool-%d", tool.Index)
			}
			name := identity.name
			if name == "" {
				name = "function"
			}
			ev, err := streamgate.NewToolCallFragmentEvent(streamGateChannelDefault, id, name, tool.Function.Arguments, time.Now())
			if err != nil {
				return nil, err
			}
			events = append(events, ev)
		}
		// finish_reason is endpoint protocol state, not the transport terminal.
		// Its frame remains in the release queue until [DONE] or END closes once.
	}
	return events, nil
}

func (c *openAITunnelEndpointCodec) rememberResponseTool(identity openAITunnelToolIdentity, keys ...string) {
	if identity.id == "" && identity.name == "" {
		return
	}
	for _, key := range keys {
		if key == "" {
			continue
		}
		current := c.responseTools[key]
		if identity.id != "" {
			current.id = identity.id
		}
		if identity.name != "" {
			current.name = identity.name
		}
		c.responseTools[key] = current
	}
}

func (c *openAITunnelEndpointCodec) responseTool(keys ...string) openAITunnelToolIdentity {
	var identity openAITunnelToolIdentity
	for _, key := range keys {
		candidate := c.responseTools[key]
		if identity.id == "" {
			identity.id = candidate.id
		}
		if identity.name == "" {
			identity.name = candidate.name
		}
	}
	return identity
}

func (c *openAITunnelEndpointCodec) decodeResponsesTunnelFrame(data string) ([]streamgate.NormalizedEvent, error) {
	if strings.TrimSpace(data) == "" {
		return nil, nil
	}
	var payload struct {
		Type       string `json:"type"`
		Delta      string `json:"delta"`
		ItemID     string `json:"item_id"`
		CallID     string `json:"call_id"`
		Name       string `json:"name"`
		OutputIdx  int    `json:"output_index"`
		OutputText string `json:"output_text"`
		Item       struct {
			ID     string `json:"id"`
			CallID string `json:"call_id"`
			Name   string `json:"name"`
		} `json:"item"`
		Output []struct {
			Type      string `json:"type"`
			ID        string `json:"id"`
			CallID    string `json:"call_id"`
			Name      string `json:"name"`
			Arguments string `json:"arguments"`
			Content   []struct {
				Type string `json:"type"`
				Text string `json:"text"`
			} `json:"content"`
		} `json:"output"`
	}
	if err := json.Unmarshal([]byte(data), &payload); err != nil {
		return nil, nil
	}
	outputKey := fmt.Sprintf("output-%d", payload.OutputIdx)
	c.rememberResponseTool(openAITunnelToolIdentity{id: payload.CallID, name: payload.Name}, payload.CallID, payload.ItemID, outputKey)
	c.rememberResponseTool(openAITunnelToolIdentity{id: payload.Item.CallID, name: payload.Item.Name}, payload.Item.CallID, payload.Item.ID, outputKey)
	if payload.Type == "" && (payload.OutputText != "" || len(payload.Output) > 0) {
		var events []streamgate.NormalizedEvent
		text := payload.OutputText
		if text == "" {
			for _, item := range payload.Output {
				for _, content := range item.Content {
					if content.Type == "output_text" {
						text += content.Text
					}
				}
			}
		}
		if text != "" {
			event, eventErr := streamgate.NewTextDeltaEvent(streamGateChannelDefault, text, time.Now())
			if eventErr != nil {
				return nil, eventErr
			}
			events = append(events, event)
		}
		for i, item := range payload.Output {
			key := fmt.Sprintf("output-%d", i)
			c.rememberResponseTool(openAITunnelToolIdentity{id: item.CallID, name: item.Name}, item.CallID, item.ID, key)
			if item.Type != "function_call" || item.Arguments == "" {
				continue
			}
			identity := c.responseTool(item.CallID, item.ID, key)
			id := identity.id
			if id == "" {
				id = fmt.Sprintf("call-%d", i)
			}
			name := identity.name
			if name == "" {
				name = "function"
			}
			event, eventErr := streamgate.NewToolCallFragmentEvent(streamGateChannelDefault, id, name, item.Arguments, time.Now())
			if eventErr != nil {
				return nil, eventErr
			}
			events = append(events, event)
		}
		return events, nil
	}
	switch payload.Type {
	case "response.output_text.delta":
		if payload.Delta == "" {
			return nil, nil
		}
		ev, err := streamgate.NewTextDeltaEvent(streamGateChannelDefault, payload.Delta, time.Now())
		return []streamgate.NormalizedEvent{ev}, err
	case "response.reasoning_text.delta", "response.reasoning_summary_text.delta":
		if payload.Delta == "" {
			return nil, nil
		}
		ev, err := streamgate.NewReasoningDeltaEvent(streamGateChannelDefault, payload.Delta, time.Now())
		return []streamgate.NormalizedEvent{ev}, err
	case "response.function_call_arguments.delta":
		if payload.Delta == "" {
			return nil, nil
		}
		identity := c.responseTool(payload.CallID, payload.ItemID, outputKey)
		id := identity.id
		if id == "" {
			id = fmt.Sprintf("call-%d", payload.OutputIdx)
		}
		name := identity.name
		if name == "" {
			name = "function"
		}
		ev, err := streamgate.NewToolCallFragmentEvent(streamGateChannelDefault, id, name, payload.Delta, time.Now())
		return []streamgate.NormalizedEvent{ev}, err
	case "response.completed", "response.incomplete":
		return nil, nil
	case "response.failed", "error":
		ev, err := newOpenAIProviderErrorEvent(streamGateErrorTunnelFailed)
		return []streamgate.NormalizedEvent{ev}, err
	default:
		return nil, nil
	}
}