/*
 * Copyright 2023 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "include/core/SkSpan.h"
#include "include/core/SkTypes.h"
#include "include/private/SkFloatingPoint.h"
#include "src/pathops/SkPathOpsQuad.h"
#include "tests/Test.h"

#include <algorithm>
#include <cstddef>
#include <iterator>
#include <string>

static void testQuadRootsReal(skiatest::Reporter* reporter, std::string name,
                               double A, double B, double C,
                               SkSpan<const double> expectedRoots) {
    skiatest::ReporterContext subtest(reporter, name);
    // Validate test case
    REPORTER_ASSERT(reporter, expectedRoots.size() <= 2,
                    "Invalid test case, up to 2 roots allowed");

    for (size_t i = 0; i < expectedRoots.size(); i++) {
        double x = expectedRoots[i];
        // A*x^2 + B*x + C should equal 0
        double y = A * x * x + B * x + C;
        REPORTER_ASSERT(reporter, sk_double_nearly_zero(y),
                    "Invalid test case root %zu. %.16f != 0", i, y);

        if (i > 0) {
            REPORTER_ASSERT(reporter, expectedRoots[i-1] <= expectedRoots[i],
                    "Invalid test case root %zu. Roots should be sorted in ascending order", i);
        }
    }


    double roots[2] = {0, 0};
    int rootCount = SkDQuad::RootsReal(A, B, C, roots);
    REPORTER_ASSERT(reporter, expectedRoots.size() == size_t(rootCount),
                    "Wrong number of roots returned %zu != %d", expectedRoots.size(), rootCount);

    // We don't care which order the roots are returned from the algorithm.
    // For determinism, we will sort them (and ensure the provided solutions are also sorted).
    std::sort(std::begin(roots), std::begin(roots) + rootCount);
    for (int i = 0; i < rootCount; i++) {
        if (sk_double_nearly_zero(expectedRoots[i])) {
            REPORTER_ASSERT(reporter, sk_double_nearly_zero(roots[i]),
                            "0 != %.16f at index %d", roots[i], i);
        } else {
            REPORTER_ASSERT(reporter, sk_doubles_nearly_equal_ulps(expectedRoots[i], roots[i], 64),
                            "%.16f != %.16f at index %d", expectedRoots[i], roots[i], i);
        }
    }
}

DEF_TEST(QuadRootsReal_ActualQuadratics, reporter) {
    // All answers are given with 16 significant digits (max for a double) or as an integer
    // when the answer is exact.
    testQuadRootsReal(reporter, "two roots 3x^2 - 20x - 40",
                       3, -20, -40,
                       {-1.610798991397109,
                      //-1.610798991397108632474265 from Wolfram Alpha
                         8.277465658063775,
                      // 8.277465658063775299140932 from Wolfram Alpha
                       });

    // (2x - 4)(x + 17)
    testQuadRootsReal(reporter, "two roots 2x^2 + 30x - 68",
                       2, 30, -68,
                       {-17, 2});

    testQuadRootsReal(reporter, "two roots x^2 - 5",
                       1, 0, -5,
                       {-2.236067977499790,
                      //-2.236067977499789696409174 from Wolfram Alpha
                         2.236067977499790,
                      // 2.236067977499789696409174 from Wolfram Alpha
                       });

    testQuadRootsReal(reporter, "one root x^2 - 2x + 1",
                       1, -2, 1,
                       {1});

    testQuadRootsReal(reporter, "no roots 5x^2 + 6x + 7",
                       5, 6, 7,
                       {});
}

DEF_TEST(QuadRootsReal_Linear, reporter) {
    testQuadRootsReal(reporter, "positive slope 5x + 6",
                       0, 5, 6,
                       {-1.2});

    testQuadRootsReal(reporter, "negative slope -3x - 9",
                       0, -3, -9,
                       {-3.});
}

DEF_TEST(QuadRootsReal_Constant, reporter) {
    testQuadRootsReal(reporter, "No intersections y = -10",
                       0, 0, -10,
                       {});

    testQuadRootsReal(reporter, "Infinite solutions y = 0",
                       0, 0, 0,
                       {0.});
}