feat(alerts): detectar orçamento apertado (#142)

src/main/java/com/financebot/alert/domain/TightBudgetAlert.java

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+package com.financebot.alert.domain;
+
+import java.math.BigDecimal;
+
+public record TightBudgetAlert(
+        BigDecimal commitmentPercentage,
+        BigDecimal projectedNet,
+        String explanation
+) {
+}

src/main/java/com/financebot/alert/service/TightBudgetDetector.java

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+package com.financebot.alert.service;
+
+import com.financebot.alert.domain.TightBudgetAlert;
+import com.financebot.analysis.dto.response.FinancialCommitmentResponse;
+import org.springframework.stereotype.Service;
+
+import java.math.BigDecimal;
+
+@Service
+public class TightBudgetDetector {
+
+    private static final BigDecimal ALERT_THRESHOLD = BigDecimal.valueOf(60);
+
+    public TightBudgetAlert detect(FinancialCommitmentResponse analysis) {
+        if (analysis == null) {
+            throw new IllegalArgumentException("Financial analysis is required");
+        }
+        BigDecimal percentage = valueOrZero(analysis.commitmentPercentage());
+        BigDecimal projectedNet = valueOrZero(analysis.projectedNetNextMonth());
+        if (percentage.compareTo(ALERT_THRESHOLD) < 0 && projectedNet.signum() >= 0) {
+            return null;
+        }
+        String reason = projectedNet.signum() < 0
+                ? "a projeção do próximo mês ficou negativa"
+                : "o comprometimento projetado atingiu " + percentage + "%";
+        return new TightBudgetAlert(
+                percentage,
+                projectedNet,
+                "Seu orçamento está apertado: " + reason + "."
+        );
+    }
+
+    private BigDecimal valueOrZero(BigDecimal value) {
+        return value == null ? BigDecimal.ZERO : value;
+    }
+}

src/test/java/com/financebot/alert/service/TightBudgetDetectorTest.java

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+package com.financebot.alert.service;
+
+import com.financebot.analysis.dto.response.FinancialCommitmentResponse;
+import org.junit.jupiter.api.Test;
+
+import java.math.BigDecimal;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class TightBudgetDetectorTest {
+
+    private final TightBudgetDetector detector = new TightBudgetDetector();
+
+    @Test
+    void shouldDetectCommitmentAtSixtyPercent() {
+        var alert = detector.detect(analysis("60", "100"));
+
+        assertThat(alert).isNotNull();
+        assertThat(alert.commitmentPercentage()).isEqualByComparingTo("60");
+        assertThat(alert.explanation()).contains("60");
+    }
+
+    @Test
+    void shouldDetectNegativeProjectedNetEvenBelowPercentageThreshold() {
+        var alert = detector.detect(analysis("20", "-1"));
+
+        assertThat(alert).isNotNull();
+        assertThat(alert.explanation()).contains("negativa");
+    }
+
+    @Test
+    void shouldIgnoreHealthyBudget() {
+        assertThat(detector.detect(analysis("59.99", "100"))).isNull();
+    }
+
+    @Test
+    void shouldRejectNullAnalysis() {
+        assertThatThrownBy(() -> detector.detect(null))
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessage("Financial analysis is required");
+    }
+
+    private FinancialCommitmentResponse analysis(String percentage, String projectedNet) {
+        return new FinancialCommitmentResponse(
+                BigDecimal.ZERO, BigDecimal.ZERO, BigDecimal.ZERO, BigDecimal.ZERO,
+                BigDecimal.ZERO, BigDecimal.ZERO, BigDecimal.ZERO,
+                new BigDecimal(projectedNet), new BigDecimal(percentage), 0L,
+                false, false, false, "LOW", ""
+        );
+    }
+}