package unit;

import java.util.*;

/**
 * SdlTest — sdl-0001
 *
 * Proves CWE-407 in SDL3 SDL_gamepad.c:
 *   sdl-0001: SDL_PrivateAddMappingForGUID — tail walk of s_pSupportedGamepads
 *             linked list on every insert → O(M²) for M mappings loaded.
 *             The SDL_GameControllerDB community database has >30 000 entries.
 *
 * Run: javac -d . SdlTest.java && java -ea unit.SdlTest
 */
public class SdlTest {

    // ── sdl-0001: tail walk on singly-linked list ───────────────────────────

    /** SLOW: simulate s_pSupportedGamepads — walk to tail on every insert (O(M²)) */
    static long mappingLoadSlow(int mappingCount) {
        // Linked list node: just an index acting as the mapping
        int[] next = new int[mappingCount + 1]; // next[i] = next node, -1 = none
        Arrays.fill(next, -1);
        int head = -1;
        long ops = 0;

        for (int i = 0; i < mappingCount; i++) {
            // Dedup scan: O(M) walk — SDL_PrivateGetGamepadMappingForGUID
            int cur = head;
            boolean found = false;
            while (cur != -1) {
                ops++;
                if (cur == i) { found = true; break; }
                cur = next[cur];
            }
            if (found) continue;

            // Tail walk to append: O(M) — SDL_PrivateAddMappingForGUID lines 2213-2217
            if (head == -1) {
                head = i;
            } else {
                int prev = head;
                while (next[prev] != -1) {
                    ops++;
                    prev = next[prev];
                }
                next[prev] = i;
            }
        }
        return ops;
    }

    /** FAST: tail pointer + hash-map dedup → O(M) total */
    static long mappingLoadFast(int mappingCount) {
        Set<Integer> seen = new HashSet<>();
        int tail = -1;  // tail pointer — s_pLastSupportedGamepad
        long ops = 0;

        for (int i = 0; i < mappingCount; i++) {
            ops++;  // O(1) hash lookup for dedup
            if (seen.add(i)) {
                // O(1) tail-pointer append
                tail = i;
            }
        }
        return ops;
    }

    static void testSdl0001() {
        System.out.println("=== sdl-0001: gamepad mapping bulk load tail walk ===");

        // Small test — correctness
        int[] sizes = {100, 500, 1000, 5000, 10000};
        for (int M : sizes) {
            long slow = mappingLoadSlow(M);
            long fast = mappingLoadFast(M);
            double ratio = (double) slow / fast;
            System.out.printf("  M=%6d  slow_ops=%12d  fast_ops=%8d  ratio=%.1fx%n",
                    M, slow, fast, ratio);
        }

        // Regression: at M=1000 slow should be >> 2x fast
        long slow1000 = mappingLoadSlow(1000);
        long fast1000 = mappingLoadFast(1000);
        double ratio1000 = (double) slow1000 / fast1000;
        assert ratio1000 > 50.0 :
            "sdl-0001 FAIL: expected slow/fast ratio > 50x at M=1000, got " + ratio1000;
        System.out.println("  [PASS] sdl-0001: ratio=" + String.format("%.1f", ratio1000) + "x at M=1000");

        // Verify O(M²) vs O(M) growth: ratio at M=5000 should be >> ratio at M=1000
        long slow5000 = mappingLoadSlow(5000);
        long fast5000 = mappingLoadFast(5000);
        double ratio5000 = (double) slow5000 / fast5000;
        assert ratio5000 > ratio1000 * 3 :
            "sdl-0001 FAIL: O(M²) growth expected; ratio5000=" + ratio5000 + " ratio1000=" + ratio1000;
        System.out.println("  [PASS] sdl-0001: O(M²) growth confirmed (ratio5000=" +
            String.format("%.1f", ratio5000) + "x > 3×ratio1000=" +
            String.format("%.1f", ratio1000) + "x)");
    }

    public static void main(String[] args) {
        testSdl0001();
        System.out.println("\nAll SDL tests PASS.");
    }
}