package conversion

import (
	"bytes"
	"strings"

	"nex/backend/internal/conversion/canonical"
)

// StreamDecoder 流式解码器接口
type StreamDecoder interface {
	ProcessChunk(rawChunk []byte) []canonical.CanonicalStreamEvent
	Flush() []canonical.CanonicalStreamEvent
}

// StreamEncoder 流式编码器接口
type StreamEncoder interface {
	EncodeEvent(event canonical.CanonicalStreamEvent) [][]byte
	Flush() [][]byte
}

// StreamConverter 流式转换器接口
type StreamConverter interface {
	ProcessChunk(rawChunk []byte) [][]byte
	Flush() [][]byte
}

// PassthroughStreamConverter 同协议透传流式转换器
type PassthroughStreamConverter struct{}

// NewPassthroughStreamConverter 创建透传流式转换器
func NewPassthroughStreamConverter() *PassthroughStreamConverter {
	return &PassthroughStreamConverter{}
}

// ProcessChunk 直接传递原始字节
func (c *PassthroughStreamConverter) ProcessChunk(rawChunk []byte) [][]byte {
	return [][]byte{rawChunk}
}

// Flush 无缓冲数据
func (c *PassthroughStreamConverter) Flush() [][]byte {
	return nil
}

// SmartPassthroughStreamConverter 同协议 Smart Passthrough 流式转换器
// 按 SSE frame 改写 data JSON 中的 model 字段
type SmartPassthroughStreamConverter struct {
	adapter       ProtocolAdapter
	modelOverride string
	interfaceType InterfaceType
	buffer        []byte
}

// NewSmartPassthroughStreamConverter 创建 Smart Passthrough 流式转换器
func NewSmartPassthroughStreamConverter(adapter ProtocolAdapter, modelOverride string, interfaceType InterfaceType) *SmartPassthroughStreamConverter {
	return &SmartPassthroughStreamConverter{
		adapter:       adapter,
		modelOverride: modelOverride,
		interfaceType: interfaceType,
	}
}

// ProcessChunk 按 SSE frame 改写 data JSON 中的 model 字段
func (c *SmartPassthroughStreamConverter) ProcessChunk(rawChunk []byte) [][]byte {
	if len(rawChunk) == 0 {
		return nil
	}

	c.buffer = append(c.buffer, rawChunk...)
	frames, rest := splitSSEFrames(c.buffer)
	c.buffer = rest

	result := make([][]byte, 0, len(frames))
	for _, frame := range frames {
		result = append(result, c.rewriteFrame(frame))
	}
	return result
}

func (c *SmartPassthroughStreamConverter) rewriteFrame(frame []byte) []byte {
	payload, ok := sseFrameDataPayload(frame)
	if !ok || strings.TrimSpace(payload) == "[DONE]" {
		return frame
	}

	rewrittenPayload, err := c.adapter.RewriteResponseModelName([]byte(payload), c.modelOverride, c.interfaceType)
	if err != nil {
		return frame
	}

	return rebuildSSEFrameWithData(frame, string(rewrittenPayload))
}

// Flush 输出未形成完整 frame 的剩余数据
func (c *SmartPassthroughStreamConverter) Flush() [][]byte {
	if len(c.buffer) == 0 {
		return nil
	}
	frame := append([]byte(nil), c.buffer...)
	c.buffer = nil
	return [][]byte{c.rewriteFrame(frame)}
}

// CanonicalStreamConverter 跨协议规范流式转换器
type CanonicalStreamConverter struct {
	decoder          StreamDecoder
	encoder          StreamEncoder
	chain            *MiddlewareChain
	ctx              ConversionContext
	clientProtocol   string
	providerProtocol string
	modelOverride    string
}

// NewCanonicalStreamConverter 创建规范流式转换器
func NewCanonicalStreamConverter(decoder StreamDecoder, encoder StreamEncoder) *CanonicalStreamConverter {
	return &CanonicalStreamConverter{
		decoder: decoder,
		encoder: encoder,
	}
}

// NewCanonicalStreamConverterWithMiddleware 创建带中间件的规范流式转换器
func NewCanonicalStreamConverterWithMiddleware(decoder StreamDecoder, encoder StreamEncoder, chain *MiddlewareChain, ctx ConversionContext, clientProtocol, providerProtocol, modelOverride string) *CanonicalStreamConverter {
	return &CanonicalStreamConverter{
		decoder:          decoder,
		encoder:          encoder,
		chain:            chain,
		ctx:              ctx,
		clientProtocol:   clientProtocol,
		providerProtocol: providerProtocol,
		modelOverride:    modelOverride,
	}
}

// ProcessChunk 解码 → 中间件 → modelOverride → 编码管道
func (c *CanonicalStreamConverter) ProcessChunk(rawChunk []byte) [][]byte {
	events := c.decoder.ProcessChunk(rawChunk)
	var result [][]byte
	for i := range events {
		if c.chain != nil {
			processed, err := c.chain.ApplyStreamEvent(&events[i], c.clientProtocol, c.providerProtocol, &c.ctx)
			if err != nil {
				continue
			}
			events[i] = *processed
		}
		c.applyModelOverride(&events[i])
		chunks := c.encoder.EncodeEvent(events[i])
		result = append(result, chunks...)
	}
	return result
}

// Flush 刷新解码器和编码器缓冲区
func (c *CanonicalStreamConverter) Flush() [][]byte {
	events := c.decoder.Flush()
	var result [][]byte
	for i := range events {
		if c.chain != nil {
			processed, err := c.chain.ApplyStreamEvent(&events[i], c.clientProtocol, c.providerProtocol, &c.ctx)
			if err != nil {
				continue
			}
			events[i] = *processed
		}
		c.applyModelOverride(&events[i])
		chunks := c.encoder.EncodeEvent(events[i])
		result = append(result, chunks...)
	}
	encoderChunks := c.encoder.Flush()
	result = append(result, encoderChunks...)
	return result
}

// applyModelOverride 在跨协议场景下覆写流式事件中的 Model 字段
func (c *CanonicalStreamConverter) applyModelOverride(event *canonical.CanonicalStreamEvent) {
	if c.modelOverride != "" && event.Message != nil {
		event.Message.Model = c.modelOverride
	}
}

func splitSSEFrames(data []byte) ([][]byte, []byte) {
	var frames [][]byte
	for len(data) > 0 {
		idx, sepLen := findSSEFrameSeparator(data)
		if idx < 0 {
			break
		}
		end := idx + sepLen
		frames = append(frames, append([]byte(nil), data[:end]...))
		data = data[end:]
	}
	return frames, data
}

func findSSEFrameSeparator(data []byte) (int, int) {
	lf := bytes.Index(data, []byte("\n\n"))
	crlf := bytes.Index(data, []byte("\r\n\r\n"))
	switch {
	case lf < 0 && crlf < 0:
		return -1, 0
	case lf < 0:
		return crlf, 4
	case crlf < 0:
		return lf, 2
	case crlf <= lf:
		return crlf, 4
	default:
		return lf, 2
	}
}

func sseFrameDataPayload(frame []byte) (string, bool) {
	text := strings.TrimRight(string(frame), "\r\n")
	lines := strings.Split(text, "\n")
	var dataLines []string
	for _, line := range lines {
		line = strings.TrimRight(line, "\r")
		if strings.HasPrefix(line, "data:") {
			value := strings.TrimPrefix(line, "data:")
			if strings.HasPrefix(value, " ") {
				value = value[1:]
			}
			dataLines = append(dataLines, value)
		}
	}
	if len(dataLines) == 0 {
		return "", false
	}
	return strings.Join(dataLines, "\n"), true
}

func rebuildSSEFrameWithData(frame []byte, data string) []byte {
	lineEnding, separator := sseLineEnding(frame)
	text := strings.TrimRight(string(frame), "\r\n")
	lines := strings.Split(text, "\n")
	out := make([]string, 0, len(lines)+1)
	dataWritten := false
	for _, line := range lines {
		line = strings.TrimRight(line, "\r")
		if strings.HasPrefix(line, "data:") {
			if !dataWritten {
				for _, dataLine := range strings.Split(data, "\n") {
					out = append(out, "data: "+dataLine)
				}
				dataWritten = true
			}
			continue
		}
		out = append(out, line)
	}
	if !dataWritten {
		out = append(out, "data: "+data)
	}
	return []byte(strings.Join(out, lineEnding) + separator)
}

func sseLineEnding(frame []byte) (string, string) {
	if bytes.Contains(frame, []byte("\r\n")) {
		return "\r\n", "\r\n\r\n"
	}
	return "\n", "\n\n"
}