main.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"

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

// Person represents a structured person record extracted from unstructured text.
type Person struct {
	Name       string `json:"name"`
	Age        int    `json:"age"`
	Occupation string `json:"occupation"`
	Summary    string `json:"summary"`
}

// MovieReview represents a structured movie review extracted from unstructured text.
type MovieReview struct {
	Title     string   `json:"title"`
	Rating    int      `json:"rating"`
	Sentiment string   `json:"sentiment"`
	Pros      []string `json:"pros"`
	Cons      []string `json:"cons"`
}

const extractionSystemPrompt = "You are a data extraction assistant. Always respond with valid JSON only, no markdown, no explanation. Match the exact schema requested."

func extractText(ctx context.Context, client *anthropic.Client, userPrompt string) (string, error) {
	msg, err := client.Messages.New(ctx, anthropic.MessageNewParams{
		Model:     anthropic.ModelClaudeOpus4_7,
		MaxTokens: 1024,
		System: []anthropic.TextBlockParam{
			{Text: extractionSystemPrompt},
		},
		Messages: []anthropic.MessageParam{
			anthropic.NewUserMessage(anthropic.NewTextBlock(userPrompt)),
		},
	})
	if err != nil {
		return "", fmt.Errorf("API call failed: %w", err)
	}

	for _, block := range msg.Content {
		switch v := block.AsAny().(type) {
		case anthropic.TextBlock:
			return v.Text, nil
		}
	}

	return "", fmt.Errorf("no text block found in response")
}

func extractPerson(ctx context.Context, client *anthropic.Client) error {
	blurb := `Meet Dr. Sarah Chen, a 38-year-old neuroscientist at the Karolinska Institute in Stockholm.
She has spent the last decade mapping the neural correlates of memory consolidation during sleep.
Originally from Vancouver, Canada, Sarah completed her PhD at MIT before moving to Sweden.
Her colleagues describe her as meticulous, collaborative, and endlessly curious about the brain.`

	prompt := fmt.Sprintf(`Extract the person's details from the following text and return a JSON object with these exact fields:
- name (string)
- age (integer)
- occupation (string)
- summary (string, one or two sentences)

Text:
%s`, blurb)

	raw, err := extractText(ctx, client, prompt)
	if err != nil {
		return err
	}

	var person Person
	if err := json.Unmarshal([]byte(raw), &person); err != nil {
		return fmt.Errorf("failed to unmarshal person: %w\nraw response: %s", err, raw)
	}

	fmt.Println("=== Extracted Person ===")
	fmt.Printf("Name:       %s\n", person.Name)
	fmt.Printf("Age:        %d\n", person.Age)
	fmt.Printf("Occupation: %s\n", person.Occupation)
	fmt.Printf("Summary:    %s\n\n", person.Summary)

	return nil
}

func extractMovieReview(ctx context.Context, client *anthropic.Client) error {
	blurb := `I just watched Dune: Part Two and honestly it blew me away. The cinematography is jaw-dropping,
Hans Zimmer's score is hypnotic, and Zendaya finally gets the screen time she deserved. Denis Villeneuve
proves once again that he's one of the best directors working today. My only gripes are that some of the
political subtext felt rushed in the third act, and a couple of minor characters were underwritten.
Still, I'd give it a 9 out of 10 — an absolute must-watch for sci-fi fans.`

	prompt := fmt.Sprintf(`Extract the movie review details from the following text and return a JSON object with these exact fields:
- title (string)
- rating (integer, out of 10)
- sentiment (string: "positive", "negative", or "mixed")
- pros (array of strings)
- cons (array of strings)

Text:
%s`, blurb)

	raw, err := extractText(ctx, client, prompt)
	if err != nil {
		return err
	}

	var review MovieReview
	if err := json.Unmarshal([]byte(raw), &review); err != nil {
		return fmt.Errorf("failed to unmarshal movie review: %w\nraw response: %s", err, raw)
	}

	fmt.Println("=== Extracted Movie Review ===")
	fmt.Printf("Title:     %s\n", review.Title)
	fmt.Printf("Rating:    %d/10\n", review.Rating)
	fmt.Printf("Sentiment: %s\n", review.Sentiment)
	fmt.Println("Pros:")
	for _, pro := range review.Pros {
		fmt.Printf("  + %s\n", pro)
	}
	fmt.Println("Cons:")
	for _, con := range review.Cons {
		fmt.Printf("  - %s\n", con)
	}
	fmt.Println()

	return nil
}

func main() {
	client := anthropic.NewClient()
	ctx := context.Background()

	if err := extractPerson(ctx, client); err != nil {
		log.Fatalf("extractPerson: %v", err)
	}

	if err := extractMovieReview(ctx, client); err != nil {
		log.Fatalf("extractMovieReview: %v", err)
	}
}