1 files changed, 162 insertions, 0 deletions
diff --git a/internal/llm/openai.go b/internal/llm/openai.go
new file mode 100644
index 0000000..860c80e
--- /dev/null
+++ b/internal/llm/openai.go
@@ -0,0 +1,162 @@
+package llm
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"time"
+)
+
+// openAIClient implements Client against OpenAI's Chat Completions API.
+type openAIClient struct {
+	httpClient   *http.Client
+	apiKey       string
+	baseURL      string
+	defaultModel string
+	logger       *log.Logger
+}
+
+func newOpenAIFromEnv(apiKey string, logger *log.Logger) Client {
+	base := os.Getenv("OPENAI_BASE_URL")
+	if base == "" {
+		base = "https://api.openai.com/v1"
+	}
+	model := os.Getenv("OPENAI_MODEL")
+	if model == "" {
+		model = "gpt-4o-mini"
+	}
+	return &openAIClient{
+		httpClient:   &http.Client{Timeout: 30 * time.Second},
+		apiKey:       apiKey,
+		baseURL:      base,
+		defaultModel: model,
+		logger:       logger,
+	}
+}
+
+type oaChatRequest struct {
+	Model       string      `json:"model"`
+	Messages    []oaMessage `json:"messages"`
+	Temperature *float64    `json:"temperature,omitempty"`
+	MaxTokens   *int        `json:"max_tokens,omitempty"`
+	Stop        []string    `json:"stop,omitempty"`
+}
+
+type oaMessage struct {
+	Role    string `json:"role"`
+	Content string `json:"content"`
+}
+
+type oaChatResponse struct {
+	Choices []struct {
+		Index   int `json:"index"`
+		Message struct {
+			Role    string `json:"role"`
+			Content string `json:"content"`
+		} `json:"message"`
+		FinishReason string `json:"finish_reason"`
+	} `json:"choices"`
+	Error *struct {
+		Message string `json:"message"`
+		Type    string `json:"type"`
+		Param   any    `json:"param"`
+		Code    any    `json:"code"`
+	} `json:"error,omitempty"`
+}
+
+func (c *openAIClient) Chat(ctx context.Context, messages []Message, opts ...RequestOption) (string, error) {
+	if c.apiKey == "" {
+		return nilStringErr("missing OpenAI API key")
+	}
+	o := Options{Model: c.defaultModel}
+	for _, opt := range opts {
+		opt(&o)
+	}
+	if o.Model == "" {
+		o.Model = c.defaultModel
+	}
+	start := time.Now()
+	c.logf("chat start model=%s temp=%.2f max_tokens=%d stop=%d messages=%d", o.Model, o.Temperature, o.MaxTokens, len(o.Stop), len(messages))
+	for i, m := range messages {
+		c.logf("msg[%d] role=%s size=%d preview=%q", i, m.Role, len(m.Content), trimPreview(m.Content, 200))
+	}
+	req := oaChatRequest{Model: o.Model}
+	req.Messages = make([]oaMessage, len(messages))
+	for i, m := range messages {
+		req.Messages[i] = oaMessage{Role: m.Role, Content: m.Content}
+	}
+	if o.Temperature != 0 {
+		req.Temperature = &o.Temperature
+	}
+	if o.MaxTokens > 0 {
+		req.MaxTokens = &o.MaxTokens
+	}
+	if len(o.Stop) > 0 {
+		req.Stop = o.Stop
+	}
+
+	body, err := json.Marshal(req)
+	if err != nil {
+		c.logf("marshal error: %v", err)
+		return "", err
+	}
+	endpoint := c.baseURL + "/chat/completions"
+	c.logf("POST %s", endpoint)
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(body))
+	if err != nil {
+		c.logf("new request error: %v", err)
+		return "", err
+	}
+	httpReq.Header.Set("Content-Type", "application/json")
+	httpReq.Header.Set("Authorization", "Bearer "+c.apiKey)
+
+	resp, err := c.httpClient.Do(httpReq)
+	if err != nil {
+		c.logf("http error after %s: %v", time.Since(start), err)
+		return "", err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		var apiErr oaChatResponse
+		_ = json.NewDecoder(resp.Body).Decode(&apiErr)
+		if apiErr.Error != nil && apiErr.Error.Message != "" {
+			c.logf("api error status=%d type=%s msg=%s duration=%s", resp.StatusCode, apiErr.Error.Type, apiErr.Error.Message, time.Since(start))
+			return "", fmt.Errorf("openai error: %s (status %d)", apiErr.Error.Message, resp.StatusCode)
+		}
+		c.logf("http non-2xx status=%d duration=%s", resp.StatusCode, time.Since(start))
+		return "", fmt.Errorf("openai http error: status %d", resp.StatusCode)
+	}
+	var out oaChatResponse
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		c.logf("decode error after %s: %v", time.Since(start), err)
+		return "", err
+	}
+	if len(out.Choices) == 0 {
+		c.logf("no choices returned duration=%s", time.Since(start))
+		return "", errors.New("openai: no choices returned")
+	}
+	content := out.Choices[0].Message.Content
+	c.logf("success choice=0 finish=%s size=%d preview=%q duration=%s", out.Choices[0].FinishReason, len(content), trimPreview(content, 200), time.Since(start))
+	return content, nil
+}
+
+// small helper to keep return type consistent
+func nilStringErr(msg string) (string, error) { return "", errors.New(msg) }
+
+func (c *openAIClient) logf(format string, args ...any) {
+	if c.logger != nil {
+		c.logger.Printf("llm/openai "+format, args...)
+	}
+}
+
+func trimPreview(s string, n int) string {
+	if n <= 0 || len(s) <= n {
+		return s
+	}
+	return s[:n] + "…"
+}