main.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"strings"

	"github.com/anthropics/anthropic-sdk-go"
	"github.com/anthropics/anthropic-sdk-go/option"
)

// ReviewComment represents a single structured comment from Claude's code review.
type ReviewComment struct {
	File     string `json:"file"`
	Line     int    `json:"line,omitempty"`
	Severity string `json:"severity"` // "critical", "warning", "suggestion", "praise"
	Comment  string `json:"comment"`
}

// ReviewResult is the structured output Claude returns for a PR review.
type ReviewResult struct {
	Summary  string          `json:"summary"`
	Comments []ReviewComment `json:"comments"`
	Approved bool            `json:"approved"`
}

// sampleDiff simulates a GitHub PR diff — in a real app this comes from the GitHub API.
var sampleDiff = `
diff --git a/handlers/user.go b/handlers/user.go
index abc123..def456 100644
--- a/handlers/user.go
+++ b/handlers/user.go
@@ -15,6 +15,20 @@ func GetUser(w http.ResponseWriter, r *http.Request) {
+func CreateUser(w http.ResponseWriter, r *http.Request) {
+    var user User
+    json.NewDecoder(r.Body).Decode(&user)
+    password := r.FormValue("password")
+    db.Exec("INSERT INTO users VALUES ('" + user.Name + "', '" + password + "')")
+    w.WriteHeader(201)
+}
`

func main() {
	client := anthropic.NewClient(option.WithAPIKey(os.Getenv("ANTHROPIC_API_KEY")))
	ctx := context.Background()

	fmt.Println("Reviewing PR diff...")
	result, err := reviewPR(ctx, client, sampleDiff)
	if err != nil {
		fmt.Fprintf(os.Stderr, "review error: %v\n", err)
		os.Exit(1)
	}

	printReview(result)
}

func reviewPR(ctx context.Context, client *anthropic.Client, diff string) (*ReviewResult, error) {
	// Use structured output — Claude returns valid JSON matching ReviewResult
	resp, err := client.Messages.New(ctx, anthropic.MessageNewParams{
		Model:     anthropic.ModelClaudeOpus4_7,
		MaxTokens: 2048,
		System: []anthropic.TextBlockParam{
			anthropic.NewTextBlockParam(`You are an expert Go code reviewer. Analyse the provided git diff and return a JSON object matching exactly this schema:
{
  "summary": "one paragraph overview of the changes",
  "comments": [
    {"file": "path/to/file.go", "line": 42, "severity": "critical|warning|suggestion|praise", "comment": "specific actionable feedback"}
  ],
  "approved": true|false
}
Return ONLY the JSON object — no markdown, no explanation.`),
		},
		Messages: []anthropic.MessageParam{
			anthropic.NewUserMessage(anthropic.NewTextBlock("Review this PR diff:\n\n" + diff)),
		},
	})
	if err != nil {
		return nil, err
	}

	// Extract the text response
	var sb strings.Builder
	for _, block := range resp.Content {
		switch b := block.AsAny().(type) {
		case anthropic.TextBlock:
			sb.WriteString(b.Text)
		}
	}

	var result ReviewResult
	if err := json.Unmarshal([]byte(sb.String()), &result); err != nil {
		return nil, fmt.Errorf("failed to parse review JSON: %w\nRaw response: %s", err, sb.String())
	}

	return &result, nil
}

func printReview(r *ReviewResult) {
	status := "✅ APPROVED"
	if !r.Approved {
		status = "❌ CHANGES REQUESTED"
	}

	fmt.Printf("\n%s\n\nSummary: %s\n\n", status, r.Summary)

	for _, c := range r.Comments {
		icon := map[string]string{
			"critical":   "🚨",
			"warning":    "⚠️",
			"suggestion": "💡",
			"praise":     "✨",
		}[c.Severity]

		location := c.File
		if c.Line > 0 {
			location = fmt.Sprintf("%s:%d", c.File, c.Line)
		}

		fmt.Printf("%s [%s] %s\n   %s\n\n", icon, strings.ToUpper(c.Severity), location, c.Comment)
	}
}