feat: add Perplexity AI provider support with token limits and streaming

## CHANGES

- feat: Add `MaxTokens` field to `ChatOptions` struct for response control
- feat: Integrate Perplexity client into core plugin registry initialization
- build: Add perplexity-go/v2 dependency to enable API interactions
- feat: Implement stream handling in Perpexlty client using sync.WaitGroup
- fix: Correct parameter types for penalty options in API requests
## LINKS

<https://github.com/sgaunet/perlexipty-go> - Client library used

plugins/ai/perplexity/perplexity.go

@@ -0,0 +1,222 @@
+package perplexity
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"sync" // Added sync package
+
+	"github.com/danielmiessler/fabric/common"
+	"github.com/danielmiessler/fabric/plugins"
+	perplexity "github.com/sgaunet/perplexity-go/v2"
+
+	goopenai "github.com/sashabaranov/go-openai"
+)
+
+const (
+	providerName = "Perplexity"
+)
+
+var models = []string{
+	"r1-1776", "sonar", "sonar-pro", "sonar-reasoning", "sonar-reasoning-pro",
+}
+
+type Client struct {
+	*plugins.PluginBase
+	APIKey *plugins.SetupQuestion
+	client *perplexity.Client
+}
+
+func NewClient() *Client {
+	c := &Client{}
+	c.PluginBase = &plugins.PluginBase{
+		Name:            providerName,
+		EnvNamePrefix:   plugins.BuildEnvVariablePrefix(providerName),
+		ConfigureCustom: c.Configure, // Assign the Configure method
+	}
+	c.APIKey = c.AddSetupQuestion("API_KEY", true)
+	return c
+}
+
+func (c *Client) Configure() error {
+	// The PluginBase.Configure() is called by the framework if needed.
+	// We only need to handle specific logic for this plugin.
+	if c.APIKey.Value == "" {
+		// Attempt to get from environment variable if not set by user during setup
+		envKey := c.EnvNamePrefix + "API_KEY"
+		apiKeyFromEnv := os.Getenv(envKey)
+		if apiKeyFromEnv != "" {
+			c.APIKey.Value = apiKeyFromEnv
+		} else {
+			return fmt.Errorf("%s API key not configured. Please set the %s environment variable or run 'fabric --setup %s'", providerName, envKey, providerName)
+		}
+	}
+	c.client = perplexity.NewClient(c.APIKey.Value)
+	return nil
+}
+
+func (c *Client) ListModels() ([]string, error) {
+	// Perplexity API does not have a ListModels endpoint.
+	// We return a predefined list.
+	return models, nil
+}
+
+func (c *Client) Send(ctx context.Context, msgs []*goopenai.ChatCompletionMessage, opts *common.ChatOptions) (string, error) {
+	if c.client == nil {
+		if err := c.Configure(); err != nil {
+			return "", fmt.Errorf("failed to configure Perplexity client: %w", err)
+		}
+	}
+
+	var perplexityMessages []perplexity.Message
+	for _, msg := range msgs {
+		perplexityMessages = append(perplexityMessages, perplexity.Message{
+			Role:    msg.Role,
+			Content: msg.Content,
+		})
+	}
+
+	requestOptions := []perplexity.CompletionRequestOption{
+		perplexity.WithModel(opts.Model),
+		perplexity.WithMessages(perplexityMessages),
+	}
+	if opts.MaxTokens > 0 {
+		requestOptions = append(requestOptions, perplexity.WithMaxTokens(opts.MaxTokens))
+	}
+	if opts.Temperature > 0 { // Perplexity default is 1.0, only set if user specifies
+		requestOptions = append(requestOptions, perplexity.WithTemperature(opts.Temperature))
+	}
+	if opts.TopP > 0 { // Perplexity default is not specified, typically 1.0
+		requestOptions = append(requestOptions, perplexity.WithTopP(opts.TopP))
+	}
+	if opts.PresencePenalty != 0 {
+		// Corrected: Pass float64 directly
+		requestOptions = append(requestOptions, perplexity.WithPresencePenalty(opts.PresencePenalty))
+	}
+	if opts.FrequencyPenalty != 0 {
+		// Corrected: Pass float64 directly
+		requestOptions = append(requestOptions, perplexity.WithFrequencyPenalty(opts.FrequencyPenalty))
+	}
+
+	request := perplexity.NewCompletionRequest(requestOptions...)
+
+	// Corrected: Use SendCompletionRequest method from perplexity-go library
+	resp, err := c.client.SendCompletionRequest(request) // Pass request directly
+	if err != nil {
+		return "", fmt.Errorf("perplexity API request failed: %w", err) // Corrected capitalization
+	}
+
+	return resp.GetLastContent(), nil
+}
+
+func (c *Client) SendStream(msgs []*goopenai.ChatCompletionMessage, opts *common.ChatOptions, channel chan string) error {
+	if c.client == nil {
+		if err := c.Configure(); err != nil {
+			close(channel) // Ensure channel is closed on error
+			return fmt.Errorf("failed to configure Perplexity client: %w", err)
+		}
+	}
+
+	var perplexityMessages []perplexity.Message
+	for _, msg := range msgs {
+		perplexityMessages = append(perplexityMessages, perplexity.Message{
+			Role:    msg.Role,
+			Content: msg.Content,
+		})
+	}
+
+	requestOptions := []perplexity.CompletionRequestOption{
+		perplexity.WithModel(opts.Model),
+		perplexity.WithMessages(perplexityMessages),
+		perplexity.WithStream(true), // Enable streaming
+	}
+
+	if opts.MaxTokens > 0 {
+		requestOptions = append(requestOptions, perplexity.WithMaxTokens(opts.MaxTokens))
+	}
+	if opts.Temperature > 0 {
+		requestOptions = append(requestOptions, perplexity.WithTemperature(opts.Temperature))
+	}
+	if opts.TopP > 0 {
+		requestOptions = append(requestOptions, perplexity.WithTopP(opts.TopP))
+	}
+	if opts.PresencePenalty != 0 {
+		// Corrected: Pass float64 directly
+		requestOptions = append(requestOptions, perplexity.WithPresencePenalty(opts.PresencePenalty))
+	}
+	if opts.FrequencyPenalty != 0 {
+		// Corrected: Pass float64 directly
+		requestOptions = append(requestOptions, perplexity.WithFrequencyPenalty(opts.FrequencyPenalty))
+	}
+
+	request := perplexity.NewCompletionRequest(requestOptions...)
+
+	responseChan := make(chan perplexity.CompletionResponse)
+	var wg sync.WaitGroup // Use sync.WaitGroup
+	wg.Add(1)
+
+	go func() {
+		err := c.client.SendSSEHTTPRequest(&wg, request, responseChan)
+		if err != nil {
+			// Log error, can't send to string channel directly.
+			// Consider a mechanism to propagate this error if needed.
+			fmt.Fprintf(os.Stderr, "perplexity streaming error: %v\\n", err) // Corrected capitalization
+			// If the error occurs during stream setup, the channel might not have been closed by the receiver loop.
+			// However, closing it here might cause a panic if the receiver loop also tries to close it.
+			// close(channel) // Caution: Uncommenting this may cause panic, as channel is closed in the receiver goroutine.
+		}
+	}()
+
+	go func() {
+		defer close(channel) // Ensure the output channel is closed when this goroutine finishes
+		for resp := range responseChan {
+			if len(resp.Choices) > 0 {
+				content := ""
+				// Corrected: Check Delta.Content and Message.Content directly for non-emptiness
+				// as Delta and Message are structs, not pointers, in perplexity.Choice
+				if resp.Choices[0].Delta.Content != "" {
+					content = resp.Choices[0].Delta.Content
+				} else if resp.Choices[0].Message.Content != "" {
+					content = resp.Choices[0].Message.Content
+				}
+				if content != "" {
+					channel <- content
+				}
+			}
+		}
+	}()
+
+	return nil
+}
+
+func (c *Client) NeedsRawMode(modelName string) bool {
+	return true
+}
+
+// Setup is called by the fabric CLI framework to guide the user through configuration.
+func (c *Client) Setup() error {
+	return c.PluginBase.Setup()
+}
+
+// GetName returns the name of the plugin.
+func (c *Client) GetName() string {
+	return c.PluginBase.Name
+}
+
+// GetEnvNamePrefix returns the environment variable prefix for the plugin.
+// Corrected: Receiver name
+func (c *Client) GetEnvNamePrefix() string {
+	return c.PluginBase.EnvNamePrefix
+}
+
+// AddSetupQuestion adds a setup question to the plugin.
+// This is a helper method, usually called from NewClient.
+func (c *Client) AddSetupQuestion(text string, isSensitive bool) *plugins.SetupQuestion {
+	return c.PluginBase.AddSetupQuestion(text, isSensitive)
+}
+
+// GetSetupQuestions returns the setup questions for the plugin.
+// Corrected: Return the slice of setup questions from PluginBase
+func (c *Client) GetSetupQuestions() []*plugins.SetupQuestion {
+	return c.PluginBase.SetupQuestions
+}