package llm

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"time"
)

// AICoreOpenAIAPIVersion is the API version used for OpenAI models through AI Core.
// Update this when SAP AI Core releases a new stable version.
const AICoreOpenAIAPIVersion = "2024-12-01-preview"

// AICoreConfig holds SAP AI Core authentication and connection settings.
type AICoreConfig struct {
	ClientID      string
	ClientSecret  string
	AuthURL       string
	APIURL        string
	ResourceGroup string
}

// AICoreClient wraps AI Core authentication and deployment discovery.
// Thread-safe for concurrent use after construction.
type AICoreClient struct {
	config AICoreConfig
	http   *http.Client

	mu          sync.RWMutex
	token       string
	tokenExpiry time.Time
	deployments map[string]deployment // model name -> deployment info
}

type deployment struct {
	ID  string
	URL string
}

// NewAICoreClient creates a new AI Core client with the given configuration.
// The client uses a default 5-minute timeout; use WithTimeout to customize.
func NewAICoreClient(cfg AICoreConfig) *AICoreClient {
	return &AICoreClient{
		config:      cfg,
		http:        &http.Client{Timeout: 5 * time.Minute},
		deployments: make(map[string]deployment),
	}
}

// WithTimeout sets the HTTP request timeout for AI Core calls.
// This should be called during construction, before concurrent use.
func (c *AICoreClient) WithTimeout(d time.Duration) *AICoreClient {
	c.http.Timeout = d
	return c
}

// getToken returns a valid OAuth token, refreshing if necessary.
func (c *AICoreClient) getToken(ctx context.Context) (string, error) {
	c.mu.RLock()
	if c.token != "" && time.Now().Add(5*time.Minute).Before(c.tokenExpiry) {
		token := c.token
		c.mu.RUnlock()
		return token, nil
	}
	c.mu.RUnlock()

	c.mu.Lock()
	defer c.mu.Unlock()

	// Double-check after acquiring write lock
	if c.token != "" && time.Now().Add(5*time.Minute).Before(c.tokenExpiry) {
		return c.token, nil
	}

	token, expiry, err := c.fetchToken(ctx)
	if err != nil {
		return "", err
	}
	c.token = token
	c.tokenExpiry = expiry
	return token, nil
}

func (c *AICoreClient) fetchToken(ctx context.Context) (string, time.Time, error) {
	tokenURL := strings.TrimRight(c.config.AuthURL, "/") + "/oauth/token"

	data := url.Values{}
	data.Set("grant_type", "client_credentials")
	data.Set("client_id", c.config.ClientID)
	data.Set("client_secret", c.config.ClientSecret)

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, tokenURL, strings.NewReader(data.Encode()))
	if err != nil {
		return "", time.Time{}, fmt.Errorf("create token request: %w", err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	resp, err := c.http.Do(req)
	if err != nil {
		return "", time.Time{}, fmt.Errorf("token request: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return "", time.Time{}, fmt.Errorf("read token response: %w", err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return "", time.Time{}, fmt.Errorf("token request failed (status %d): %s", resp.StatusCode, string(body))
	}

	var tokenResp struct {
		AccessToken string `json:"access_token"`
		ExpiresIn   int    `json:"expires_in"`
	}
	if err := json.Unmarshal(body, &tokenResp); err != nil {
		return "", time.Time{}, fmt.Errorf("parse token response: %w", err)
	}

	if tokenResp.AccessToken == "" {
		return "", time.Time{}, fmt.Errorf("empty access token in response")
	}

	expiry := time.Now().Add(time.Duration(tokenResp.ExpiresIn) * time.Second)
	return tokenResp.AccessToken, expiry, nil
}

// getDeploymentURL returns the deployment URL for a model, fetching deployments if needed.
func (c *AICoreClient) getDeploymentURL(ctx context.Context, model string) (string, error) {
	c.mu.RLock()
	if d, ok := c.deployments[model]; ok {
		c.mu.RUnlock()
		return d.URL, nil
	}
	c.mu.RUnlock()

	// Fetch token first (before acquiring write lock to avoid deadlock)
	token, err := c.getToken(ctx)
	if err != nil {
		return "", fmt.Errorf("get token for deployments: %w", err)
	}

	c.mu.Lock()
	defer c.mu.Unlock()

	// Double-check after acquiring write lock
	if d, ok := c.deployments[model]; ok {
		return d.URL, nil
	}

	if err := c.fetchDeployments(ctx, token); err != nil {
		return "", err
	}

	if d, ok := c.deployments[model]; ok {
		return d.URL, nil
	}
	return "", fmt.Errorf("no deployment found for model %q", model)
}

func (c *AICoreClient) fetchDeployments(ctx context.Context, token string) error {
	deployURL := strings.TrimRight(c.config.APIURL, "/") + "/v2/lm/deployments"
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, deployURL, nil)
	if err != nil {
		return fmt.Errorf("create deployments request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+token)
	req.Header.Set("AI-Resource-Group", c.config.ResourceGroup)

	resp, err := c.http.Do(req)
	if err != nil {
		return fmt.Errorf("deployments request: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return fmt.Errorf("read deployments response: %w", err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf("deployments request failed (status %d): %s", resp.StatusCode, string(body))
	}

	var deployResp struct {
		Resources []struct {
			ID            string `json:"id"`
			DeploymentURL string `json:"deploymentUrl"`
			Status        string `json:"status"`
			Details       struct {
				Resources struct {
					BackendDetails struct {
						Model struct {
							Name string `json:"name"`
						} `json:"model"`
					} `json:"backend_details"`
				} `json:"resources"`
			} `json:"details"`
		} `json:"resources"`
	}
	if err := json.Unmarshal(body, &deployResp); err != nil {
		return fmt.Errorf("parse deployments response: %w", err)
	}

	for _, r := range deployResp.Resources {
		if r.Status != "RUNNING" {
			continue
		}
		modelName := r.Details.Resources.BackendDetails.Model.Name
		if modelName == "" {
			continue
		}
		c.deployments[modelName] = deployment{
			ID:  r.ID,
			URL: r.DeploymentURL,
		}
	}

	return nil
}

// CompleteAnthropic sends a request to an Anthropic model via AI Core.
func (c *AICoreClient) CompleteAnthropic(ctx context.Context, model string, messages []Message, maxTokens int, temperature float64) (string, error) {
	deployURL, err := c.getDeploymentURL(ctx, model)
	if err != nil {
		return "", err
	}

	token, err := c.getToken(ctx)
	if err != nil {
		return "", err
	}

	// Extract system message
	var system string
	var userMessages []anthropicMsg
	for _, m := range messages {
		if m.Role == "system" {
			system = m.Content
		} else {
			userMessages = append(userMessages, anthropicMsg{
				Role:    m.Role,
				Content: m.Content,
			})
		}
	}

	reqBody := anthropicRequest{
		AnthropicVersion: "2023-06-01",
		// Model omitted - AI Core deployment already specifies model
		MaxTokens: maxTokens,
		System:    system,
		Messages:  userMessages,
	}
	if temperature > 0 {
		reqBody.Temperature = temperature
	}

	data, err := json.Marshal(reqBody)
	if err != nil {
		return "", fmt.Errorf("marshal request: %w", err)
	}

	// AI Core uses /invoke for Anthropic models
	invokeURL := strings.TrimRight(deployURL, "/") + "/invoke"
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, invokeURL, bytes.NewReader(data))
	if err != nil {
		return "", fmt.Errorf("create request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+token)
	req.Header.Set("AI-Resource-Group", c.config.ResourceGroup)
	req.Header.Set("Content-Type", "application/json")

	resp, err := c.http.Do(req)
	if err != nil {
		return "", fmt.Errorf("AI Core request: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return "", fmt.Errorf("read response: %w", err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return "", fmt.Errorf("AI Core API error (status %d): %s", resp.StatusCode, string(body))
	}

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

	if len(anthropicResp.Content) == 0 {
		return "", fmt.Errorf("no content in response")
	}

	var sb strings.Builder
	for _, block := range anthropicResp.Content {
		if block.Type == "text" {
			sb.WriteString(block.Text)
		}
	}
	result := sb.String()
	if result == "" {
		return "", fmt.Errorf("no text content in response")
	}
	return result, nil
}

// CompleteOpenAI sends a request to an OpenAI model via AI Core.
func (c *AICoreClient) CompleteOpenAI(ctx context.Context, model string, messages []Message, temperature float64) (string, error) {
	deployURL, err := c.getDeploymentURL(ctx, model)
	if err != nil {
		return "", err
	}

	token, err := c.getToken(ctx)
	if err != nil {
		return "", err
	}

	reqBody := ChatRequest{
		Model:       model,
		Temperature: temperature,
		Messages:    messages,
	}

	data, err := json.Marshal(reqBody)
	if err != nil {
		return "", fmt.Errorf("marshal request: %w", err)
	}

	// AI Core uses /chat/completions?api-version=<version> for OpenAI models
	chatURL := strings.TrimRight(deployURL, "/") + "/chat/completions?api-version=" + AICoreOpenAIAPIVersion
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, chatURL, bytes.NewReader(data))
	if err != nil {
		return "", fmt.Errorf("create request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+token)
	req.Header.Set("AI-Resource-Group", c.config.ResourceGroup)
	req.Header.Set("Content-Type", "application/json")

	resp, err := c.http.Do(req)
	if err != nil {
		return "", fmt.Errorf("AI Core request: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return "", fmt.Errorf("read response: %w", err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return "", fmt.Errorf("AI Core API error (status %d): %s", resp.StatusCode, string(body))
	}

	var openaiResp ChatResponse
	if err := json.Unmarshal(body, &openaiResp); err != nil {
		return "", fmt.Errorf("parse response: %w", err)
	}

	if len(openaiResp.Choices) == 0 {
		return "", fmt.Errorf("no choices in response")
	}
	return openaiResp.Choices[0].Message.Content, nil
}

// IsAnthropicModel returns true if the model name indicates an Anthropic model.
// SAP AI Core uses "anthropic--" prefix for Anthropic models (e.g., "anthropic--claude-3-5-sonnet").
func IsAnthropicModel(model string) bool {
	return strings.HasPrefix(model, "anthropic--")
}