package com.ankurm.jackson3.part0setup;

import com.fasterxml.jackson.annotation.JsonInclude;
import tools.jackson.databind.DeserializationFeature;
import tools.jackson.databind.json.JsonMapper;

import java.time.LocalDate;

/**
 * Post: Jackson 101 — https://ankurm.com/jackson-java-tutorial/
 * Section: "The ObjectMapper Lifecycle — The One Rule That Matters Most"
 *
 * Build the mapper ONCE at startup and share it. In Jackson 3 this is enforced
 * by the API rather than by convention: the built mapper has no setters at all.
 */
public class A02SharedMapperConfiguration {

    public record Invoice(Long invoiceId, String customerName, LocalDate issuedOn, String note) { }

    /**
     * The Jackson 3 equivalent of the classic Spring @Bean ObjectMapper.
     *
     * Three of the four settings people habitually copy from Jackson 2 tutorials
     * are unnecessary or wrong in Jackson 3 — the comments say which and why.
     */
    static JsonMapper buildSharedMapper() {
        return JsonMapper.builder()
                // NOT NEEDED: FAIL_ON_UNKNOWN_PROPERTIES already defaults to false in
                // Jackson 3. Listed here only because it is the single most-copied line
                // from Jackson 2 configuration; deleting it changes nothing.
                .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)

                // NOT NEEDED: java.time support is built into jackson-databind 3.x and
                // dates already serialise as ISO-8601 strings. There is no
                // SerializationFeature.WRITE_DATES_AS_TIMESTAMPS in Jackson 3 — the flag
                // moved to tools.jackson.databind.cfg.DateTimeFeature and is off by
                // default. See beyond/Y03DateTimeDefaults for proof.

                // Skip null fields. Jackson 2's setSerializationInclusion(...) and the
                // builder's serializationInclusion(...) do NOT exist in Jackson 3.
                // The real API is changeDefaultPropertyInclusion.
                .changeDefaultPropertyInclusion(
                        incl -> incl.withValueInclusion(JsonInclude.Include.NON_NULL))
                .build();
    }

    public static void main(String[] args) {
        JsonMapper mapper = buildSharedMapper();

        Invoice invoice = new Invoice(500L, "Alice", LocalDate.of(2026, 4, 9), null);
        System.out.println("configured : " + mapper.writeValueAsString(invoice));

        JsonMapper plain = JsonMapper.builder().build();
        System.out.println("defaults   : " + plain.writeValueAsString(invoice));

        // Proof that the mapper is immutable: ObjectMapper in Jackson 3 exposes no
        // set*() mutators at all, so there is no way to reconfigure a shared instance.
        long setterCount = java.util.Arrays.stream(
                        tools.jackson.databind.ObjectMapper.class.getMethods())
                .filter(m -> m.getName().startsWith("set"))
                .count();
        System.out.println("ObjectMapper set*() methods in Jackson 3: " + setterCount);
    }
}