/*
 * 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/SkPathOpsCubic.h"
#include "tests/Test.h"

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

static void testCubicRootsReal(skiatest::Reporter* reporter, std::string name,
                               double A, double B, double C, double D,
                               SkSpan<const double> expectedRoots) {
    skiatest::ReporterContext subtest(reporter, name);
    // Validate test case
    REPORTER_ASSERT(reporter, expectedRoots.size() <= 3,
                    "Invalid test case, up to 3 roots allowed");

    for (size_t i = 0; i < expectedRoots.size(); i++) {
        double x = expectedRoots[i];
        // A*x^3 + B*x^2 + C*x + D should equal 0
        double y = A * x * x * x + B * x * x + C * x + D;
        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[3] = {0, 0, 0};
    int rootCount = SkDCubic::RootsReal(A, B, C, D, 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(CubicRootsReal_ActualCubics, reporter) {
    // All answers are given with 16 significant digits (max for a double) or as an integer
    // when the answer is exact.
    testCubicRootsReal(reporter, "one root 1x^3 + 2x^2 + 3x + 4",
                       1, 2, 3, 4,
                       {-1.650629191439388});
                      //-1.650629191439388218880801 from Wolfram Alpha

    // (3x-5)(6x-10)(x+4) = 18x^3 + 12x^2 - 190x + 200
    testCubicRootsReal(reporter, "touches y axis 18x^3 + 12x^2 - 190x + 200",
                       18, 12, -190, 200,
                       {-4.,
                         1.666666666666667, // 5/3
                       });

    testCubicRootsReal(reporter, "three roots 10x^3 - 20x^2 - 30x + 40",
                       10, -20, -30, 40,
                       {-1.561552812808830,
                      //-1.561552812808830274910705 from Wolfram Alpha
                         1.,
                         2.561552812808830,
                      // 2.561552812808830274910705 from Wolfram Alpha
                       });

    testCubicRootsReal(reporter, "three roots -10x^3 + 200x^2 + 300x - 400",
                       -10, 200, 300, -400,
                       {-2.179884793243323,
                      //-2.179884793243323422232630 from Wolfram Alpha
                         0.8607083693981839,
                      // 0.8607083693981838897123320 from Wolfram Alpha
                        21.31917642384514,
                      //21.31917642384513953252030 from Wolfram Alpha
                       });

    testCubicRootsReal(reporter, "one root -x^3 + 0x^2 + 5x - 7",
                       -1, 0, 5, -7,
                       {-2.747346540307211,
                      //-2.747346540307210849971436 from Wolfram Alpha
                       });

    testCubicRootsReal(reporter, "one root 2x^3 - 3x^2 + 0x + 3",
                       2, -3, 0, 3,
                       {-0.806443932358772,
                      //-0.8064439323587723772036250 from Wolfram Alpha
                       });

    testCubicRootsReal(reporter, "one root x^3 + 0x^2 + 0x - 9",
                       1, 0, 0, -9,
                       {2.080083823051904,
                      //2.0800838230519041145300568 from Wolfram Alpha
                       });

    testCubicRootsReal(reporter, "three roots 2x^3 - 3x^2 - 4x + 0",
                       2, -3, -4, 0,
                       {-0.8507810593582122,
                      //-0.8507810593582121716220544 from Wolfram Alpha
                        0.,
                        2.350781059358212
                      //2.350781059358212171622054 from Wolfram Alpha
                       });
}

DEF_TEST(CubicRootsReal_Quadratics, reporter) {
    testCubicRootsReal(reporter, "two roots -2x^2 + 3x + 4",
                       0, -2, 3, 4,
                       {-0.8507810593582122,
                      //-0.8507810593582121716220544 from Wolfram Alpha
                         2.350781059358212,
                      // 2.350781059358212171622054 from Wolfram Alpha
                       });

    testCubicRootsReal(reporter, "touches y axis -x^2 + 3x + 4",
                       0, -2, 3, 4,
                       {-0.8507810593582122,
                      //-0.8507810593582121716220544 from Wolfram Alpha
                         2.350781059358212,
                      // 2.350781059358212171622054 from Wolfram Alpha
                       });

    testCubicRootsReal(reporter, "no roots x^2 + 2x + 7",
                       0, 1, 2, 7,
                       {});
}

DEF_TEST(CubicRootsReal_Linear, reporter) {
    testCubicRootsReal(reporter, "positive slope 3x + 4",
                       0, 0, 3, 4,
                       {-1.333333333333333});

    testCubicRootsReal(reporter, "negative slope -2x - 8",
                       0, 0, -2, -8,
                       {-4.});
}

DEF_TEST(CubicRootsReal_Constant, reporter) {
    testCubicRootsReal(reporter, "No intersections y = 4",
                       0, 0, 0, 4,
                       {});

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

static void testCubicValidT(skiatest::Reporter* reporter, std::string name,
                            double A, double B, double C, double D,
                            SkSpan<const double> expectedRoots) {
    skiatest::ReporterContext subtest(reporter, name);
    // Validate test case
    REPORTER_ASSERT(reporter, expectedRoots.size() <= 3,
                    "Invalid test case, up to 3 roots allowed");

    for (size_t i = 0; i < expectedRoots.size(); i++) {
        double x = expectedRoots[i];
        REPORTER_ASSERT(reporter, x >= 0 && x <= 1,
                        "Invalid test case root %zu. Roots must be in [0, 1]", i);

        // A*x^3 + B*x^2 + C*x + D should equal 0
        double y = A * x * x * x + B * x * x + C * x + D;
        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[3] = {0, 0, 0};
    int rootCount = SkDCubic::RootsValidT(A, B, C, D, 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(CubicRootsValidT, reporter) {
    // All answers are given with 16 significant digits (max for a double) or as an integer
    // when the answer is exact.
    testCubicValidT(reporter, "three roots 24x^3 - 46x^2 + 29x - 6",
                    24, -46, 29, -6,
                    {0.5,
                     0.6666666666666667,
                     0.75});

    testCubicValidT(reporter, "one root = 1 10x^3 - 20x^2 - 30x + 40",
                    10, -20, -30, 40,
                    {1.});

    testCubicValidT(reporter, "one root = 0 2x^3 - 3x^2 - 4x + 0",
                    2, -3, -4, 0,
                    {0.});

    testCubicValidT(reporter, "two roots -2x^3 - 3x^2 + 4x + 0",
                    -2, -3, 4, 0,
                    { 0.,
                      0.8507810593582122,
                   // 0.8507810593582121716220544 from Wolfram Alpha
                    });
}

DEF_TEST(CubicRootsValidT_ClampToZeroAndOne, reporter) {
    // (x + 0.00001)(x - 1.00005), but the answers will be 0 and 1
    double A = 0.;
    double B = 1.;
    double C = -1.00004;
    double D = -0.0000100005;
    double roots[3] = {0, 0, 0};
    int rootCount = SkDCubic::RootsValidT(A, B, C, D, roots);

    REPORTER_ASSERT(reporter, rootCount == 2);
    std::sort(std::begin(roots), std::begin(roots) + rootCount);
    REPORTER_ASSERT(reporter, sk_double_nearly_zero(roots[0]), "%.16f != 0", roots[0]);
    REPORTER_ASSERT(reporter, sk_doubles_nearly_equal_ulps(roots[1], 1), "%.16f != 1", roots[1]);
}