package providers

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"time"

	"github.com/rs/zerolog/log"
)

const (
	anthropicAPIURL     = "https://api.anthropic.com/v1/messages"
	anthropicAPIVersion = "2023-06-01"
	maxRetries          = 3
	initialBackoff      = 2 * time.Second
)

// AnthropicClient implements the Provider interface for Anthropic's Claude API
type AnthropicClient struct {
	apiKey string
	model  string
	client *http.Client
}

// NewAnthropicClient creates a new Anthropic API client
func NewAnthropicClient(apiKey, model string) *AnthropicClient {
	return &AnthropicClient{
		apiKey: apiKey,
		model:  model,
		client: &http.Client{
			// 5 minutes - Opus and other large models can take a very long time
			Timeout: 300 * time.Second,
		},
	}
}

// Name returns the provider name
func (c *AnthropicClient) Name() string {
	return "anthropic"
}

// anthropicRequest is the request body for the Anthropic API
type anthropicRequest struct {
	Model       string             `json:"model"`
	Messages    []anthropicMessage `json:"messages"`
	MaxTokens   int                `json:"max_tokens"`
	System      string             `json:"system,omitempty"`
	Temperature float64            `json:"temperature,omitempty"`
	Tools       []anthropicTool    `json:"tools,omitempty"`
}

type anthropicMessage struct {
	Role    string        `json:"role"`
	Content interface{}   `json:"content"` // Can be string or []anthropicContent
}

// anthropicTool represents a regular function tool
type anthropicTool struct {
	Type        string                 `json:"type,omitempty"`        // "web_search_20250305" for web search, omit for regular tools
	Name        string                 `json:"name"`
	Description string                 `json:"description,omitempty"` // Not used for web search
	InputSchema map[string]interface{} `json:"input_schema,omitempty"` // Not used for web search
	MaxUses     int                    `json:"max_uses,omitempty"`    // For web search: limit searches per request
}

// anthropicResponse is the response from the Anthropic API
type anthropicResponse struct {
	ID           string `json:"id"`
	Type         string `json:"type"`
	Role         string `json:"role"`
	Content      []anthropicContent `json:"content"`
	Model        string `json:"model"`
	StopReason   string `json:"stop_reason"`
	StopSequence string `json:"stop_sequence,omitempty"`
	Usage        anthropicUsage `json:"usage"`
}

type anthropicContent struct {
	Type      string                 `json:"type"`                  // "text", "tool_use", "tool_result", "server_tool_use", "web_search_tool_result"
	Text      string                 `json:"text,omitempty"`
	ID        string                 `json:"id,omitempty"`          // For tool_use
	Name      string                 `json:"name,omitempty"`        // For tool_use
	Input     map[string]interface{} `json:"input,omitempty"`       // For tool_use
	ToolUseID string                 `json:"tool_use_id,omitempty"` // For tool_result
	Content   json.RawMessage        `json:"content,omitempty"`     // Can be string or array (for web_search_tool_result)
	IsError   bool                   `json:"is_error,omitempty"`    // For tool_result
}

type anthropicUsage struct {
	InputTokens  int `json:"input_tokens"`
	OutputTokens int `json:"output_tokens"`
}

type anthropicError struct {
	Type    string `json:"type"`
	Error   anthropicErrorDetail `json:"error"`
}

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

// Chat sends a chat request to the Anthropic API
func (c *AnthropicClient) Chat(ctx context.Context, req ChatRequest) (*ChatResponse, error) {
	// Convert messages to Anthropic format
	messages := make([]anthropicMessage, 0, len(req.Messages))
	for _, m := range req.Messages {
		// Anthropic doesn't use "system" role in messages array
		if m.Role == "system" {
			continue
		}

		// Handle tool results specially
		if m.ToolResult != nil {
			// Tool result message - Content needs to be JSON-encoded string
			contentJSON, _ := json.Marshal(m.ToolResult.Content)
			messages = append(messages, anthropicMessage{
				Role: "user",
				Content: []anthropicContent{
					{
						Type:      "tool_result",
						ToolUseID: m.ToolResult.ToolUseID,
						Content:   contentJSON,
						IsError:   m.ToolResult.IsError,
					},
				},
			})
			continue
		}

		// Handle assistant messages with tool calls
		if m.Role == "assistant" && len(m.ToolCalls) > 0 {
			contentBlocks := make([]anthropicContent, 0)
			if m.Content != "" {
				contentBlocks = append(contentBlocks, anthropicContent{
					Type: "text",
					Text: m.Content,
				})
			}
			for _, tc := range m.ToolCalls {
				contentBlocks = append(contentBlocks, anthropicContent{
					Type:  "tool_use",
					ID:    tc.ID,
					Name:  tc.Name,
					Input: tc.Input,
				})
			}
			messages = append(messages, anthropicMessage{
				Role:    "assistant",
				Content: contentBlocks,
			})
			continue
		}

		// Simple text message
		messages = append(messages, anthropicMessage{
			Role:    m.Role,
			Content: m.Content,
		})
	}

	// Use provided model or fall back to client default
	model := req.Model
	if model == "" {
		model = c.model
	}

	// Set max tokens (Anthropic requires this)
	maxTokens := req.MaxTokens
	if maxTokens == 0 {
		maxTokens = 4096
	}

	anthropicReq := anthropicRequest{
		Model:     model,
		Messages:  messages,
		MaxTokens: maxTokens,
		System:    req.System,
	}

	if req.Temperature > 0 {
		anthropicReq.Temperature = req.Temperature
	}

	// Add tools if provided
	if len(req.Tools) > 0 {
		anthropicReq.Tools = make([]anthropicTool, len(req.Tools))
		for i, t := range req.Tools {
			if t.Type == "web_search_20250305" {
				// Web search tool has a special format
				anthropicReq.Tools[i] = anthropicTool{
					Type:    t.Type,
					Name:    t.Name,
					MaxUses: t.MaxUses,
				}
			} else {
				// Regular function tool
				anthropicReq.Tools[i] = anthropicTool{
					Name:        t.Name,
					Description: t.Description,
					InputSchema: t.InputSchema,
				}
			}
		}
	}

	body, err := json.Marshal(anthropicReq)
	if err != nil {
		return nil, fmt.Errorf("failed to marshal request: %w", err)
	}

	// Retry loop for transient errors (429, 529, 5xx)
	var respBody []byte
	var lastErr error

	for attempt := 0; attempt <= maxRetries; attempt++ {
		if attempt > 0 {
			// Exponential backoff: 2s, 4s, 8s
			backoff := initialBackoff * time.Duration(1<<(attempt-1))
			log.Warn().
				Int("attempt", attempt).
				Dur("backoff", backoff).
				Str("last_error", lastErr.Error()).
				Msg("Retrying Anthropic API request after transient error")

			select {
			case <-ctx.Done():
				return nil, ctx.Err()
			case <-time.After(backoff):
			}
		}

		httpReq, err := http.NewRequestWithContext(ctx, "POST", anthropicAPIURL, bytes.NewReader(body))
		if err != nil {
			return nil, fmt.Errorf("failed to create request: %w", err)
		}

		httpReq.Header.Set("Content-Type", "application/json")
		httpReq.Header.Set("x-api-key", c.apiKey)
		httpReq.Header.Set("anthropic-version", anthropicAPIVersion)

		resp, err := c.client.Do(httpReq)
		if err != nil {
			lastErr = fmt.Errorf("request failed: %w", err)
			continue
		}

		respBody, err = io.ReadAll(resp.Body)
		resp.Body.Close()
		if err != nil {
			lastErr = fmt.Errorf("failed to read response: %w", err)
			continue
		}

		// Check if this is a retryable error
		if resp.StatusCode == 429 || resp.StatusCode == 529 || resp.StatusCode >= 500 {
			var errResp anthropicError
			errMsg := string(respBody)
			if err := json.Unmarshal(respBody, &errResp); err == nil && errResp.Error.Message != "" {
				errMsg = errResp.Error.Message
			}
			lastErr = fmt.Errorf("API error (%d): %s", resp.StatusCode, errMsg)
			continue
		}

		// Non-retryable error
		if resp.StatusCode != http.StatusOK {
			var errResp anthropicError
			if err := json.Unmarshal(respBody, &errResp); err == nil && errResp.Error.Message != "" {
				return nil, fmt.Errorf("API error (%d): %s", resp.StatusCode, errResp.Error.Message)
			}
			return nil, fmt.Errorf("API error (%d): %s", resp.StatusCode, string(respBody))
		}

		// Success - break out of retry loop
		lastErr = nil
		break
	}

	if lastErr != nil {
		return nil, fmt.Errorf("failed after %d retries: %w", maxRetries, lastErr)
	}

	var anthropicResp anthropicResponse
	if err := json.Unmarshal(respBody, &anthropicResp); err != nil {
		return nil, fmt.Errorf("failed to parse response: %w", err)
	}

	// Extract content and tool calls from response
	var textContent string
	var toolCalls []ToolCall
	for _, c := range anthropicResp.Content {
		switch c.Type {
		case "text":
			textContent += c.Text
		case "tool_use":
			// Regular tool use - we need to execute these
			toolCalls = append(toolCalls, ToolCall{
				ID:    c.ID,
				Name:  c.Name,
				Input: c.Input,
			})
		case "server_tool_use":
			// Server-side tool (like web_search) - Anthropic handles these automatically
			// We just log it for debugging, no action needed
			log.Debug().
				Str("tool_name", c.Name).
				Msg("Server tool use detected (handled by Anthropic)")
		case "web_search_tool_result":
			// Results from web search - already incorporated into Claude's response
			log.Debug().Msg("Web search results received")
		}
	}

	return &ChatResponse{
		Content:      textContent,
		Model:        anthropicResp.Model,
		StopReason:   anthropicResp.StopReason,
		ToolCalls:    toolCalls,
		InputTokens:  anthropicResp.Usage.InputTokens,
		OutputTokens: anthropicResp.Usage.OutputTokens,
	}, nil
}

// TestConnection validates the API key by making a minimal request
func (c *AnthropicClient) TestConnection(ctx context.Context) error {
	// Make a minimal request to validate the API key
	_, err := c.Chat(ctx, ChatRequest{
		Messages: []Message{
			{Role: "user", Content: "Hi"},
		},
		MaxTokens: 10, // Minimal tokens to save cost
	})
	return err
}