package com.ankurm.expandcontract;

import com.ankurm.expandcontract.customer.CustomerService;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.io.TempDir;
import org.springframework.jdbc.core.simple.JdbcClient;

import java.nio.file.Path;

import static org.assertj.core.api.Assertions.assertThat;

/**
 * A trap this article's own first draft of the V2 migration fell into: adding
 * {@code email_address} is not the whole story of "expand" when the column being
 * retired is {@code NOT NULL}. Stage 4 code never writes "email" - so if "email" is
 * still mandatory when Stage 4 starts, every create fails, in production, the moment
 * that deploy reaches its first replica. The fix is one more line in the SAME
 * migration: {@code ALTER TABLE customers ALTER COLUMN email DROP NOT NULL}. See
 * docs/06-the-not-null-trap.md, and compare
 * {@link com.ankurm.expandcontract.customer.CustomerService#create} - the shipped
 * V2 migration (with the fix) is what every other test in this module runs against.
 */
class NotNullConstraintTrapTest {

    @Test
    void stage4FailsIfTheOldColumnIsStillMandatory(@TempDir Path tmp) throws Exception {
        Path db = tmp.resolve("not-null-trap");
        TestSupport.migrateTo(db, "1");
        JdbcClient jdbc = TestSupport.jdbcClient(db);
        Transcript t = Transcript.start("06-not-null-trap",
                "The NOT NULL trap: expand without relaxing the old column's constraint");

        // The NAIVE version of V2: add the column, backfill, stop there. This is
        // exactly V2 minus its last line.
        jdbc.sql("ALTER TABLE customers ADD COLUMN email_address VARCHAR(320)").update();
        jdbc.sql("UPDATE customers SET email_address = email WHERE email_address IS NULL").update();

        CustomerService stage4 = new CustomerService(jdbc, 4);
        Throwable thrown = null;
        try {
            stage4.create("Too Early", "too.early@example.test");
        } catch (Throwable ex) {
            thrown = ex;
        }
        t.section("Stage 4 create() against the NAIVE migration (no DROP NOT NULL)");
        assertThat(thrown).isNotNull();
        Throwable root = thrown;
        while (root.getCause() != null) {
            root = root.getCause();
        }
        t.line(thrown.getClass().getName() + ": " + thrown.getMessage());
        t.line("root cause: " + root.getClass().getName() + ": " + root.getMessage());
        assertThat(root.getMessage()).contains("NULL not allowed for column \"EMAIL\"");

        t.section("Stage 4 create() against the SHIPPED V2 migration (DROP NOT NULL included)");
        Path fixedDb = tmp.resolve("not-null-fixed");
        TestSupport.migrateTo(fixedDb, "2");
        CustomerService fixedStage4 = new CustomerService(TestSupport.jdbcClient(fixedDb), 4);
        long id = fixedStage4.create("On Time", "on.time@example.test");
        var result = fixedStage4.findById(id).orElseThrow();
        t.line(result.toString());
        assertThat(result.email()).isEqualTo("on.time@example.test");

        t.write();
    }
}