package unit;

/**
 * GoInferTest — CWE-407 unit test for go-0001
 *
 * Models the O(n) slices.Index membership check in tpWalker.isParameterized
 * (src/cmd/compile/internal/types2/infer.go:630) that fires for every TypeParam
 * node during type inference.
 *
 * slow(): simulates tpWalker with slice-based tparams — O(n) scan per lookup.
 * fast(): simulates tpWalker with map-based tparams — O(1) lookup.
 *
 * Both perform QUERIES * TPARAMS membership checks (same logical work).
 * We assert slow() requires >= 5x more comparisons than fast().
 */
public class GoInferTest {

    static final int TPARAMS = 200;   // type parameters in a large generic function
    static final int QUERIES = 500;   // TypeParam nodes visited during walk
    static final int N = 5;           // minimum speedup factor required

    /**
     * Slow path: slice-based tparams lookup (mirrors slices.Index).
     * For each query, scans from index 0 until the target is found.
     * Returns total number of element comparisons performed.
     */
    static long slow() {
        // Build tparams slice (indices 0..TPARAMS-1)
        int[] tparams = new int[TPARAMS];
        for (int i = 0; i < TPARAMS; i++) tparams[i] = i;

        long ops = 0;
        // Simulate QUERIES lookups — target is the last element (worst case)
        for (int q = 0; q < QUERIES; q++) {
            int target = TPARAMS - 1; // worst case: found at end
            for (int i = 0; i < tparams.length; i++) {
                ops++;
                if (tparams[i] == target) break;
            }
        }
        return ops;
    }

    /**
     * Fast path: map-based tparams lookup (mirrors map[*TypeParam]bool).
     * Each query is O(1) hash lookup. We simulate this by tracking
     * exactly 1 "probe" per lookup (hash table amortized cost).
     */
    static long fast() {
        // Build tparams set
        java.util.HashSet<Integer> tparams = new java.util.HashSet<>();
        for (int i = 0; i < TPARAMS; i++) tparams.add(i);

        long ops = 0;
        for (int q = 0; q < QUERIES; q++) {
            int target = TPARAMS - 1;
            // Simulate O(1) hash lookup: count 1 operation per query
            ops++;
            tparams.contains(target);
        }
        return ops;
    }

    public static void main(String[] args) {
        long sOps = slow();
        long fOps = fast();

        System.out.println("slow ops: " + sOps);
        System.out.println("fast ops: " + fOps);
        System.out.println("ratio:    " + sOps + "/" + fOps + " = " + (sOps / fOps) + "x");

        // slow must be >= N times more expensive than fast
        if (sOps < fOps * N) {
            System.out.println("1/1 FAIL — expected slowOps >= " + N + "x fastOps, got ratio=" + (sOps / fOps));
            System.exit(1);
        }
        System.out.println("1/1 PASS");
    }
}