package unit;

/**
 * Regression test for mybatis-0001: CWE-407 O(n² log n) sort comparator
 * in ResultMappingConstructorResolver.sortConstructorMappings().
 *
 * File: src/main/java/org/apache/ibatis/builder/ResultMappingConstructorResolver.java
 * Lines 270–278
 *
 * The sort comparator calls ArrayList.indexOf(o.getProperty()) for both elements
 * on every comparison.  indexOf() is O(P) (P = constructor parameter count).
 * A comparison sort calls the comparator O(N log N) times, giving O(N * P * log N)
 * total — quadratic in combined size when N ≈ P.
 *
 * Fix: pre-build a Map<String,Integer> before sorting; comparator becomes O(1),
 * reducing total to O(N log N).
 */
public class MyBatisConstructorSortTest {

    // ---- Defective sort (mirrors MyBatis before fix) ----

    static java.util.List<String> defectiveSort(
            java.util.List<String> parameterOrder,
            java.util.List<String> resultMappings) {

        final java.util.List<String> ordered = new java.util.ArrayList<>(parameterOrder);
        java.util.List<String> copy = new java.util.ArrayList<>(resultMappings);
        copy.sort((o1, o2) -> {
            // O(P) each — CWE-407
            int idx1 = ordered.indexOf(o1);
            int idx2 = ordered.indexOf(o2);
            return idx1 - idx2;
        });
        return copy;
    }

    // ---- Fixed sort (mirrors MyBatis after fix) ----

    static java.util.List<String> fixedSort(
            java.util.List<String> parameterOrder,
            java.util.List<String> resultMappings) {

        // Pre-build index map: O(P) once
        final java.util.Map<String, Integer> index = new java.util.HashMap<>();
        int i = 0;
        for (String p : parameterOrder) {
            index.put(p, i++);
        }
        java.util.List<String> copy = new java.util.ArrayList<>(resultMappings);
        copy.sort((o1, o2) -> {
            // O(1) each
            int idx1 = index.getOrDefault(o1, -1);
            int idx2 = index.getOrDefault(o2, -1);
            return idx1 - idx2;
        });
        return copy;
    }

    // ---- Tests ----

    public static void main(String[] args) {
        testCorrectness();
        testPerformance();
        System.out.println("All mybatis CWE-407 unit tests passed.");
    }

    static void testCorrectness() {
        java.util.List<String> params = java.util.Arrays.asList("id", "name", "age", "email");
        // Result mappings come in shuffled order
        java.util.List<String> mappings = java.util.Arrays.asList("age", "id", "email", "name");

        java.util.List<String> defectiveResult = defectiveSort(params, mappings);
        java.util.List<String> fixedResult = fixedSort(params, mappings);

        // Both should produce same canonical parameter order
        assert defectiveResult.equals(params)
            : "Defective: expected " + params + " got " + defectiveResult;
        assert fixedResult.equals(params)
            : "Fixed: expected " + params + " got " + fixedResult;

        System.out.println("  [PASS] constructor sort correctness: " + fixedResult);
    }

    static void testPerformance() {
        final int P = 500;   // constructor parameters
        final int N = 500;   // result mappings (N ≈ P = worst case)
        final int REPS = 50; // repetitions to stabilise timing

        java.util.List<String> params = new java.util.ArrayList<>(P);
        for (int i = 0; i < P; i++) {
            params.add("param_" + i);
        }

        // Shuffle result mappings to force real comparisons
        java.util.List<String> mappings = new java.util.ArrayList<>(params.subList(0, N));
        java.util.Collections.shuffle(mappings, new java.util.Random(42));

        // Defective: O(N * P * log N)
        long t0 = System.nanoTime();
        for (int r = 0; r < REPS; r++) {
            defectiveSort(params, mappings);
        }
        long defectiveNs = (System.nanoTime() - t0) / REPS;

        // Fixed: O(N log N)
        t0 = System.nanoTime();
        for (int r = 0; r < REPS; r++) {
            fixedSort(params, mappings);
        }
        long fixedNs = (System.nanoTime() - t0) / REPS;

        double speedup = (double) defectiveNs / fixedNs;
        System.out.printf("  [PERF] N=P=%d  defective=%.2fms  fixed=%.2fms  speedup=%.1fx%n",
            P,
            defectiveNs / 1_000_000.0,
            fixedNs / 1_000_000.0,
            speedup);

        // Expect meaningful speedup: defective is O(N*P*log N) ≈ O(N² log N),
        // fixed is O(N log N), so speedup should be >> 1 at N=P=500
        assert speedup > 3.0
            : "Expected >3x speedup, got " + speedup + "x — fix may not be effective";
    }
}