// Package claude provides HTTP handlers for Claude API code-related functionality.
// This package implements Claude-compatible streaming chat completions with sophisticated
// client rotation and quota management systems to ensure high availability and optimal
// resource utilization across multiple backend clients. It handles request translation
// between Claude API format and the underlying Gemini backend, providing seamless
// API compatibility while maintaining robust error handling and connection management.
package claude

import (
	"bufio"
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"time"

	"github.com/gin-gonic/gin"
	. "github.com/router-for-me/CLIProxyAPI/v6/internal/constant"
	"github.com/router-for-me/CLIProxyAPI/v6/internal/interfaces"
	"github.com/router-for-me/CLIProxyAPI/v6/internal/registry"
	"github.com/router-for-me/CLIProxyAPI/v6/sdk/api/handlers"
	"github.com/tidwall/gjson"
)

// ClaudeCodeAPIHandler contains the handlers for Claude API endpoints.
// It holds a pool of clients to interact with the backend service.
type ClaudeCodeAPIHandler struct {
	*handlers.BaseAPIHandler
}

// NewClaudeCodeAPIHandler creates a new Claude API handlers instance.
// It takes an BaseAPIHandler instance as input and returns a ClaudeCodeAPIHandler.
//
// Parameters:
//   - apiHandlers: The base API handler instance.
//
// Returns:
//   - *ClaudeCodeAPIHandler: A new Claude code API handler instance.
func NewClaudeCodeAPIHandler(apiHandlers *handlers.BaseAPIHandler) *ClaudeCodeAPIHandler {
	return &ClaudeCodeAPIHandler{
		BaseAPIHandler: apiHandlers,
	}
}

// HandlerType returns the identifier for this handler implementation.
func (h *ClaudeCodeAPIHandler) HandlerType() string {
	return Claude
}

// Models returns a list of models supported by this handler.
func (h *ClaudeCodeAPIHandler) Models() []map[string]any {
	// Get dynamic models from the global registry
	modelRegistry := registry.GetGlobalRegistry()
	return modelRegistry.GetAvailableModels("claude")
}

// ClaudeMessages handles Claude-compatible streaming chat completions.
// This function implements a sophisticated client rotation and quota management system
// to ensure high availability and optimal resource utilization across multiple backend clients.
//
// Parameters:
//   - c: The Gin context for the request.
func (h *ClaudeCodeAPIHandler) ClaudeMessages(c *gin.Context) {
	// Extract raw JSON data from the incoming request
	rawJSON, err := c.GetRawData()
	// If data retrieval fails, return a 400 Bad Request error.
	if err != nil {
		c.JSON(http.StatusBadRequest, handlers.ErrorResponse{
			Error: handlers.ErrorDetail{
				Message: fmt.Sprintf("Invalid request: %v", err),
				Type:    "invalid_request_error",
			},
		})
		return
	}

	// Check if the client requested a streaming response.
	streamResult := gjson.GetBytes(rawJSON, "stream")
	if !streamResult.Exists() || streamResult.Type == gjson.False {
		h.handleNonStreamingResponse(c, rawJSON)
	} else {
		h.handleStreamingResponse(c, rawJSON)
	}
}

// ClaudeMessages handles Claude-compatible streaming chat completions.
// This function implements a sophisticated client rotation and quota management system
// to ensure high availability and optimal resource utilization across multiple backend clients.
//
// Parameters:
//   - c: The Gin context for the request.
func (h *ClaudeCodeAPIHandler) ClaudeCountTokens(c *gin.Context) {
	// Extract raw JSON data from the incoming request
	rawJSON, err := c.GetRawData()
	// If data retrieval fails, return a 400 Bad Request error.
	if err != nil {
		c.JSON(http.StatusBadRequest, handlers.ErrorResponse{
			Error: handlers.ErrorDetail{
				Message: fmt.Sprintf("Invalid request: %v", err),
				Type:    "invalid_request_error",
			},
		})
		return
	}

	c.Header("Content-Type", "application/json")

	alt := h.GetAlt(c)
	cliCtx, cliCancel := h.GetContextWithCancel(h, c, context.Background())

	modelName := gjson.GetBytes(rawJSON, "model").String()

	resp, errMsg := h.ExecuteCountWithAuthManager(cliCtx, h.HandlerType(), modelName, rawJSON, alt)
	if errMsg != nil {
		h.WriteErrorResponse(c, errMsg)
		cliCancel(errMsg.Error)
		return
	}
	_, _ = c.Writer.Write(resp)
	cliCancel()
}

// ClaudeModels handles the Claude models listing endpoint.
// It returns a JSON response containing available Claude models and their specifications.
//
// Parameters:
//   - c: The Gin context for the request.
func (h *ClaudeCodeAPIHandler) ClaudeModels(c *gin.Context) {
	c.JSON(http.StatusOK, gin.H{
		"data": h.Models(),
	})
}

// handleNonStreamingResponse handles non-streaming content generation requests for Claude models.
// This function processes the request synchronously and returns the complete generated
// response in a single API call. It supports various generation parameters and
// response formats.
//
// Parameters:
//   - c: The Gin context for the request
//   - modelName: The name of the Gemini model to use for content generation
//   - rawJSON: The raw JSON request body containing generation parameters and content
func (h *ClaudeCodeAPIHandler) handleNonStreamingResponse(c *gin.Context, rawJSON []byte) {
	c.Header("Content-Type", "application/json")
	alt := h.GetAlt(c)
	cliCtx, cliCancel := h.GetContextWithCancel(h, c, context.Background())

	modelName := gjson.GetBytes(rawJSON, "model").String()

	resp, errMsg := h.ExecuteWithAuthManager(cliCtx, h.HandlerType(), modelName, rawJSON, alt)
	if errMsg != nil {
		h.WriteErrorResponse(c, errMsg)
		cliCancel(errMsg.Error)
		return
	}
	_, _ = c.Writer.Write(resp)
	cliCancel()
}

// handleStreamingResponse streams Claude-compatible responses backed by Gemini.
// It sets up SSE, selects a backend client with rotation/quota logic,
// forwards chunks, and translates them to Claude CLI format.
//
// Parameters:
//   - c: The Gin context for the request.
//   - rawJSON: The raw JSON request body.
func (h *ClaudeCodeAPIHandler) handleStreamingResponse(c *gin.Context, rawJSON []byte) {
	// Set up Server-Sent Events (SSE) headers for streaming response
	// These headers are essential for maintaining a persistent connection
	// and enabling real-time streaming of chat completions
	c.Header("Content-Type", "text/event-stream")
	c.Header("Cache-Control", "no-cache")
	c.Header("Connection", "keep-alive")
	c.Header("Access-Control-Allow-Origin", "*")

	// Get the http.Flusher interface to manually flush the response.
	// This is crucial for streaming as it allows immediate sending of data chunks
	flusher, ok := c.Writer.(http.Flusher)
	if !ok {
		c.JSON(http.StatusInternalServerError, handlers.ErrorResponse{
			Error: handlers.ErrorDetail{
				Message: "Streaming not supported",
				Type:    "server_error",
			},
		})
		return
	}

	modelName := gjson.GetBytes(rawJSON, "model").String()

	// Create a cancellable context for the backend client request
	// This allows proper cleanup and cancellation of ongoing requests
	cliCtx, cliCancel := h.GetContextWithCancel(h, c, context.Background())

	dataChan, errChan := h.ExecuteStreamWithAuthManager(cliCtx, h.HandlerType(), modelName, rawJSON, "")
	h.forwardClaudeStream(c, flusher, func(err error) { cliCancel(err) }, dataChan, errChan)
	return
}

func (h *ClaudeCodeAPIHandler) forwardClaudeStream(c *gin.Context, flusher http.Flusher, cancel func(error), data <-chan []byte, errs <-chan *interfaces.ErrorMessage) {
	// v6.1: Intelligent Buffered Streamer strategy
	// Enhanced buffering with larger buffer size (16KB) and longer flush interval (120ms).
	// Smart flush only when buffer is sufficiently filled (≥50%), dramatically reducing
	// flush frequency from ~12.5Hz to ~5-8Hz while maintaining low latency.
	writer := bufio.NewWriterSize(c.Writer, 16*1024) // 4KB → 16KB
	ticker := time.NewTicker(120 * time.Millisecond) // 80ms → 120ms
	defer ticker.Stop()

	var chunkIdx int

	for {
		select {
		case <-c.Request.Context().Done():
			// Context cancelled, flush any remaining data before exit
			_ = writer.Flush()
			cancel(c.Request.Context().Err())
			return

		case <-ticker.C:
			// Smart flush: only flush when buffer has sufficient data (≥50% full)
			// This reduces flush frequency while ensuring data flows naturally
			buffered := writer.Buffered()
			if buffered >= 8*1024 { // At least 8KB (50% of 16KB buffer)
				if err := writer.Flush(); err != nil {
					// Error flushing, cancel and return
					cancel(err)
					return
				}
				flusher.Flush() // Also flush the underlying http.ResponseWriter
			}

		case chunk, ok := <-data:
			if !ok {
				// Stream ended, flush remaining data
				_ = writer.Flush()
				cancel(nil)
				return
			}

			// Forward the complete SSE event block directly (already formatted by the translator).
			// The translator returns a complete SSE-compliant event block, including event:, data:, and separators.
			// The handler just needs to forward it without reassembly.
			if len(chunk) > 0 {
				_, _ = writer.Write(chunk)
			}
			chunkIdx++

		case errMsg, ok := <-errs:
			if !ok {
				continue
			}
			if errMsg != nil {
				// An error occurred: emit as a proper SSE error event
				errorBytes, _ := json.Marshal(h.toClaudeError(errMsg))
				_, _ = writer.WriteString("event: error\n")
				_, _ = writer.WriteString("data: ")
				_, _ = writer.Write(errorBytes)
				_, _ = writer.WriteString("\n\n")
				_ = writer.Flush()
			}
			var execErr error
			if errMsg != nil {
				execErr = errMsg.Error
			}
			cancel(execErr)
			return
		}
	}
}

type claudeErrorDetail struct {
	Type    string `json:"type"`
	Message string `json:"message"`
}

type claudeErrorResponse struct {
	Type  string            `json:"type"`
	Error claudeErrorDetail `json:"error"`
}

func (h *ClaudeCodeAPIHandler) toClaudeError(msg *interfaces.ErrorMessage) claudeErrorResponse {
	return claudeErrorResponse{
		Type: "error",
		Error: claudeErrorDetail{
			Type:    "api_error",
			Message: msg.Error.Error(),
		},
	}
}