feat(llm): Mistral SDK backend

go.mod

@@ -17,4 +17,5 @@ require (
 	modernc.org/mathutil v1.7.1 // indirect
 	modernc.org/memory v1.11.0 // indirect
 	modernc.org/sqlite v1.48.0 // indirect
+	somegit.dev/vikingowl/mistral-go-sdk v1.2.0 // indirect
 )

go.sum

@@ -31,3 +31,5 @@ modernc.org/memory v1.11.0 h1:o4QC8aMQzmcwCK3t3Ux/ZHmwFPzE6hf2Y5LbkRs+hbI=
 modernc.org/memory v1.11.0/go.mod h1:/JP4VbVC+K5sU2wZi9bHoq2MAkCnrt2r98UGeSK7Mjw=
 modernc.org/sqlite v1.48.0 h1:ElZyLop3Q2mHYk5IFPPXADejZrlHu7APbpB0sF78bq4=
 modernc.org/sqlite v1.48.0/go.mod h1:hWjRO6Tj/5Ik8ieqxQybiEOUXy0NJFNp2tpvVpKlvig=
+somegit.dev/vikingowl/mistral-go-sdk v1.2.0 h1:9NEGCKzw1Bu2c8LaSEKNlpj08iMsU0fkDFJO6W1Zh+Y=
+somegit.dev/vikingowl/mistral-go-sdk v1.2.0/go.mod h1:pN7nQdOIYYEMRdwye5cSfymtwhZJHd+caK6J69Z4XMY=

internal/llm/mistral.go

@@ -0,0 +1,98 @@
+package llm
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"strings"
+
+	mistral "somegit.dev/vikingowl/mistral-go-sdk"
+	"somegit.dev/vikingowl/mistral-go-sdk/chat"
+
+	"somegit.dev/vikingowl/reddit-reader/internal/domain"
+)
+
+// MistralClient wraps the Mistral AI SDK and implements the Summarizer interface.
+type MistralClient struct {
+	client *mistral.Client
+	model  string
+}
+
+// MistralOption configures a MistralClient.
+type MistralOption func(*mistralOpts)
+
+type mistralOpts struct {
+	baseURL string
+}
+
+// WithMistralBaseURL overrides the Mistral API base URL (useful for tests).
+func WithMistralBaseURL(url string) MistralOption {
+	return func(o *mistralOpts) { o.baseURL = url }
+}
+
+// NewMistralClient creates a MistralClient using the given API key and model.
+func NewMistralClient(apiKey, model string, opts ...MistralOption) *MistralClient {
+	var mo mistralOpts
+	for _, o := range opts {
+		o(&mo)
+	}
+
+	var clientOpts []mistral.Option
+	if mo.baseURL != "" {
+		clientOpts = append(clientOpts, mistral.WithBaseURL(mo.baseURL))
+	}
+
+	return &MistralClient{
+		client: mistral.NewClient(apiKey, clientOpts...),
+		model:  model,
+	}
+}
+
+// Score returns a relevance score in [0.0, 1.0] for the given post against the user's interests.
+func (m *MistralClient) Score(ctx context.Context, post domain.Post, interests domain.Interests) (float64, error) {
+	systemPrompt := buildScorePrompt(interests)
+	userPrompt := fmt.Sprintf("Title: %s\n\nContent: %s", post.Title, truncate(post.SelfText, 500))
+
+	resp, err := m.client.ChatComplete(ctx, &chat.CompletionRequest{
+		Model: m.model,
+		Messages: []chat.Message{
+			&chat.SystemMessage{Content: chat.TextContent(systemPrompt)},
+			&chat.UserMessage{Content: chat.TextContent(userPrompt)},
+		},
+	})
+	if err != nil {
+		return 0, fmt.Errorf("mistral score: %w", err)
+	}
+	if len(resp.Choices) == 0 {
+		return 0, fmt.Errorf("mistral score: no choices")
+	}
+
+	text := strings.TrimSpace(resp.Choices[0].Message.Content.String())
+	score, err := strconv.ParseFloat(text, 64)
+	if err != nil {
+		return 0, fmt.Errorf("mistral parse score %q: %w", text, err)
+	}
+	return score, nil
+}
+
+// Summarize produces a 5-bullet summary of the given post.
+func (m *MistralClient) Summarize(ctx context.Context, post domain.Post) (string, error) {
+	systemPrompt := "You are a concise summarizer. Given a Reddit post, produce exactly 5 bullet points summarizing the key information. Each bullet starts with '- '. No other text."
+	userPrompt := fmt.Sprintf("Title: %s\n\nContent: %s", post.Title, post.SelfText)
+
+	resp, err := m.client.ChatComplete(ctx, &chat.CompletionRequest{
+		Model: m.model,
+		Messages: []chat.Message{
+			&chat.SystemMessage{Content: chat.TextContent(systemPrompt)},
+			&chat.UserMessage{Content: chat.TextContent(userPrompt)},
+		},
+	})
+	if err != nil {
+		return "", fmt.Errorf("mistral summarize: %w", err)
+	}
+	if len(resp.Choices) == 0 {
+		return "", fmt.Errorf("mistral summarize: no choices")
+	}
+
+	return strings.TrimSpace(resp.Choices[0].Message.Content.String()), nil
+}

internal/llm/mistral_test.go

@@ -0,0 +1,57 @@
+package llm_test
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"somegit.dev/vikingowl/reddit-reader/internal/domain"
+	"somegit.dev/vikingowl/reddit-reader/internal/llm"
+)
+
+func TestMistralScore(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]any{
+			"id": "test", "object": "chat.completion", "model": "mistral-small-latest", "created": 1234567890,
+			"choices": []map[string]any{
+				{"index": 0, "finish_reason": "stop", "message": map[string]any{"role": "assistant", "content": "0.72"}},
+			},
+			"usage": map[string]any{"prompt_tokens": 10, "completion_tokens": 5, "total_tokens": 15},
+		})
+	}))
+	defer srv.Close()
+
+	client := llm.NewMistralClient("test-key", "mistral-small-latest", llm.WithMistralBaseURL(srv.URL))
+	score, err := client.Score(context.Background(), domain.Post{Title: "Test"}, domain.Interests{Description: "Go"})
+	if err != nil {
+		t.Fatalf("Score: %v", err)
+	}
+	if score != 0.72 {
+		t.Errorf("score = %f, want 0.72", score)
+	}
+}
+
+func TestMistralSummarize(t *testing.T) {
+	want := "- bullet one\n- bullet two\n- bullet three\n- bullet four\n- bullet five"
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]any{
+			"id": "test", "object": "chat.completion", "model": "mistral-small-latest", "created": 1234567890,
+			"choices": []map[string]any{
+				{"index": 0, "finish_reason": "stop", "message": map[string]any{"role": "assistant", "content": want}},
+			},
+			"usage": map[string]any{"prompt_tokens": 10, "completion_tokens": 5, "total_tokens": 15},
+		})
+	}))
+	defer srv.Close()
+
+	client := llm.NewMistralClient("test-key", "mistral-small-latest", llm.WithMistralBaseURL(srv.URL))
+	got, err := client.Summarize(context.Background(), domain.Post{Title: "Test", SelfText: "content"})
+	if err != nil {
+		t.Fatalf("Summarize: %v", err)
+	}
+	if got != want {
+		t.Errorf("summary = %q, want %q", got, want)
+	}
+}