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// Unit tests for error handling mechanisms in StinkyTofu
// Tests Expected<T> and STINKY_UNREACHABLE() functionality

#include <gtest/gtest.h>

#include <chrono>
#include <memory>
#include <string>
#include <vector>

#include "stinkytofu/support/ErrorHandling.hpp"

using namespace stinkytofu;

// ============================================================================
// Expected<T> - Basic Tests
// ============================================================================

class ExpectedTest : public ::testing::Test {
   protected:
    void SetUp() override {}
};

// Test successful Expected creation with primitive types
TEST_F(ExpectedTest, SuccessWithInt) {
    Expected<int> result(42);

    EXPECT_TRUE(result.hasValue());
    EXPECT_FALSE(result.hasError());
    EXPECT_TRUE(static_cast<bool>(result));
    EXPECT_EQ(*result, 42);
}

// Test successful Expected creation with pointer types
TEST_F(ExpectedTest, SuccessWithPointer) {
    int value = 123;
    Expected<int*> result(&value);

    EXPECT_TRUE(result.hasValue());
    EXPECT_FALSE(result.hasError());
    EXPECT_EQ(*result, &value);
    EXPECT_EQ(**result, 123);
}

// Test successful Expected creation with std::string
TEST_F(ExpectedTest, SuccessWithString) {
    Expected<std::string> result("hello world");

    EXPECT_TRUE(result.hasValue());
    EXPECT_FALSE(result.hasError());
    EXPECT_EQ(*result, "hello world");
}

// Test successful Expected creation with std::vector
TEST_F(ExpectedTest, SuccessWithVector) {
    std::vector<int> vec = {1, 2, 3, 4, 5};
    Expected<std::vector<int>> result(vec);

    EXPECT_TRUE(result.hasValue());
    EXPECT_FALSE(result.hasError());
    EXPECT_EQ(result->size(), 5);
    EXPECT_EQ((*result)[2], 3);
}

// Test error Expected creation
TEST_F(ExpectedTest, ErrorCreation) {
    Expected<int> result = Expected<int>::Error("Something went wrong");

    EXPECT_FALSE(result.hasValue());
    EXPECT_TRUE(result.hasError());
    EXPECT_FALSE(static_cast<bool>(result));
    EXPECT_EQ(result.getError(), "Something went wrong");
}

// Test error Expected with detailed message
TEST_F(ExpectedTest, ErrorWithDetailedMessage) {
    std::string archName = "gfx900";
    Expected<void*> result = Expected<void*>::Error("Instruction s_mul_lo_u32 not supported on " +
                                                    archName + " (requires gfx1250+)");

    EXPECT_TRUE(result.hasError());
    EXPECT_TRUE(result.getError().find("gfx900") != std::string::npos);
    EXPECT_TRUE(result.getError().find("gfx1250") != std::string::npos);
}

// ============================================================================
// Expected<T> - Move Semantics Tests
// ============================================================================

TEST_F(ExpectedTest, MoveConstructorSuccess) {
    Expected<std::string> original("test string");
    Expected<std::string> moved(std::move(original));

    EXPECT_TRUE(moved.hasValue());
    EXPECT_EQ(*moved, "test string");
}

TEST_F(ExpectedTest, MoveConstructorError) {
    Expected<int> original = Expected<int>::Error("error message");
    Expected<int> moved(std::move(original));

    EXPECT_TRUE(moved.hasError());
    EXPECT_EQ(moved.getError(), "error message");
}

TEST_F(ExpectedTest, MoveAssignmentSuccess) {
    Expected<int> original(999);
    Expected<int> assigned(0);
    assigned = std::move(original);

    EXPECT_TRUE(assigned.hasValue());
    EXPECT_EQ(*assigned, 999);
}

TEST_F(ExpectedTest, MoveAssignmentError) {
    Expected<int> original = Expected<int>::Error("test error");
    Expected<int> assigned(0);
    assigned = std::move(original);

    EXPECT_TRUE(assigned.hasError());
    EXPECT_EQ(assigned.getError(), "test error");
}

// ============================================================================
// Expected<T> - Access Operators Tests
// ============================================================================

TEST_F(ExpectedTest, DereferenceOperator) {
    Expected<int> result(42);
    EXPECT_EQ(*result, 42);

    // Test mutability through dereference
    *result = 100;
    EXPECT_EQ(*result, 100);
}

TEST_F(ExpectedTest, ArrowOperator) {
    struct TestStruct {
        int value;
        std::string name;
    };

    TestStruct obj{42, "test"};
    Expected<TestStruct> result(obj);

    EXPECT_EQ(result->value, 42);
    EXPECT_EQ(result->name, "test");

    // Test mutability through arrow operator
    result->value = 100;
    EXPECT_EQ(result->value, 100);
}

TEST_F(ExpectedTest, RValueDereference) {
    auto makeExpected = []() -> Expected<std::string> { return std::string("temporary"); };

    std::string value = *makeExpected();
    EXPECT_EQ(value, "temporary");
}

// ============================================================================
// Expected<T> - Pattern Matching / Error Handling Tests
// ============================================================================

// Helper function that returns Expected<int>
static Expected<int> divideOrError(int numerator, int denominator) {
    if (denominator == 0) {
        return Expected<int>::Error("Division by zero");
    }
    return numerator / denominator;
}

TEST_F(ExpectedTest, PatternMatchingSuccess) {
    auto result = divideOrError(10, 2);

    if (result) {
        EXPECT_EQ(*result, 5);
    } else {
        FAIL() << "Expected success but got error: " << result.getError();
    }
}

TEST_F(ExpectedTest, PatternMatchingError) {
    auto result = divideOrError(10, 0);

    if (result) {
        FAIL() << "Expected error but got success: " << *result;
    } else {
        EXPECT_EQ(result.getError(), "Division by zero");
    }
}

// ============================================================================
// Expected<T> - Complex Type Tests
// ============================================================================

struct ComplexType {
    std::vector<int> data;
    std::unique_ptr<int> ptr;
    std::string name;

    ComplexType(std::vector<int> d, int val, std::string n)
        : data(std::move(d)), ptr(std::make_unique<int>(val)), name(std::move(n)) {}

    // Move-only type
    ComplexType(ComplexType&&) noexcept = default;
    ComplexType& operator=(ComplexType&&) noexcept = default;
    ComplexType(const ComplexType&) = delete;
    ComplexType& operator=(const ComplexType&) = delete;
};

TEST_F(ExpectedTest, MoveOnlyType) {
    ComplexType obj({1, 2, 3}, 42, "test");
    Expected<ComplexType> result(std::move(obj));

    EXPECT_TRUE(result.hasValue());
    EXPECT_EQ(result->data.size(), 3);
    EXPECT_EQ(*result->ptr, 42);
    EXPECT_EQ(result->name, "test");
}

TEST_F(ExpectedTest, UniquePointer) {
    auto ptr = std::make_unique<int>(999);
    Expected<std::unique_ptr<int>> result(std::move(ptr));

    EXPECT_TRUE(result.hasValue());
    EXPECT_EQ(**result, 999);
}

// ============================================================================
// Expected<T> - Real-World Use Cases
// ============================================================================

// Simulate architecture check function
static Expected<void*> createInstructionForArch(const std::string& arch,
                                                const std::string& instruction) {
    if (arch == "gfx900" && instruction == "s_mul_lo_u32") {
        return Expected<void*>::Error("s_mul_lo_u32 not supported on gfx900 (requires gfx1250+)");
    }
    if (arch == "gfx1250") {
        return static_cast<void*>(nullptr);  // Placeholder
    }
    return Expected<void*>::Error("Unknown architecture: " + arch);
}

TEST_F(ExpectedTest, ArchitectureLimitation) {
    auto result1 = createInstructionForArch("gfx900", "s_mul_lo_u32");
    EXPECT_TRUE(result1.hasError());
    EXPECT_TRUE(result1.getError().find("gfx1250") != std::string::npos);

    auto result2 = createInstructionForArch("gfx1250", "s_mul_lo_u32");
    EXPECT_TRUE(result2.hasValue());
}

TEST_F(ExpectedTest, ChainedErrorPropagation) {
    // Simulate function that depends on another Expected-returning function
    auto processInstruction = [](const std::string& arch) -> Expected<int> {
        auto inst = createInstructionForArch(arch, "s_mul_lo_u32");
        if (!inst) {
            return Expected<int>::Error("Failed to create instruction: " + inst.getError());
        }
        return 42;  // Success
    };

    auto result1 = processInstruction("gfx900");
    EXPECT_TRUE(result1.hasError());
    EXPECT_TRUE(result1.getError().find("Failed to create instruction") != std::string::npos);

    auto result2 = processInstruction("gfx1250");
    EXPECT_TRUE(result2.hasValue());
    EXPECT_EQ(*result2, 42);
}

// ============================================================================
// Expected<T> - Edge Cases
// ============================================================================

TEST_F(ExpectedTest, EmptyString) {
    Expected<std::string> result("");
    EXPECT_TRUE(result.hasValue());
    EXPECT_EQ(result->size(), 0);
}

TEST_F(ExpectedTest, EmptyErrorMessage) {
    Expected<int> result = Expected<int>::Error("");
    EXPECT_TRUE(result.hasError());
    EXPECT_EQ(result.getError(), "");
}

TEST_F(ExpectedTest, LargeErrorMessage) {
    std::string longMsg(10000, 'x');
    Expected<int> result = Expected<int>::Error(longMsg);
    EXPECT_TRUE(result.hasError());
    EXPECT_EQ(result.getError().size(), 10000);
}

TEST_F(ExpectedTest, NullPointer) {
    Expected<int*> result(nullptr);
    EXPECT_TRUE(result.hasValue());
    EXPECT_EQ(*result, nullptr);
}

// ============================================================================
// STINKY_UNREACHABLE() Tests
// ============================================================================
// Note: STINKY_UNREACHABLE() aborts the process, so we can't directly test it
// in unit tests. Instead, we test that the code compiles and that we can
// use it in dead code paths.

class UnreachableTest : public ::testing::Test {
   protected:
    void SetUp() override {}
};

// Test that STINKY_UNREACHABLE compiles and can be used in conditional branches
TEST_F(UnreachableTest, CompilationTest) {
    auto testFunction = [](int value) -> int {
        if (value == 0) {
            return 0;
        } else if (value == 1) {
            return 1;
        } else {
            // This branch should never execute in this test
            if (value == 2) {
                return 2;
            }
            // If we somehow get here with value != 2, it's a bug
            // STINKY_UNREACHABLE("Unexpected value");
            // Note: Can't actually execute this in test, just verify compilation
            return -1;  // Placeholder for test
        }
    };

    EXPECT_EQ(testFunction(0), 0);
    EXPECT_EQ(testFunction(1), 1);
    EXPECT_EQ(testFunction(2), 2);
}

// Test pattern: validation followed by unreachable
TEST_F(UnreachableTest, ValidationPattern) {
    auto createWithValidation = [](bool isValid) -> Expected<int> {
        if (!isValid) {
            return Expected<int>::Error("Validation failed");
        }

        // After validation, some operation that should never fail
        int* ptr = new int(42);
        if (!ptr) {
            // This should never happen on modern systems
            // STINKY_UNREACHABLE("Failed to allocate memory after validation");
            // Can't execute in test, but pattern is correct
        }

        int value = *ptr;
        delete ptr;
        return value;
    };

    auto result1 = createWithValidation(true);
    EXPECT_TRUE(result1.hasValue());

    auto result2 = createWithValidation(false);
    EXPECT_TRUE(result2.hasError());
}

// ============================================================================
// Integration Tests - Expected + assert pattern
// ============================================================================

TEST_F(ExpectedTest, AssertPlusExpectedPattern) {
    // Simulate function with precondition checks and recoverable errors
    auto processData = [](int* data, size_t size, bool supportedArch) -> Expected<int> {
        // Debug-time precondition check
        assert(data != nullptr && "Data pointer must not be null");
        assert(size > 0 && "Size must be positive");

        // Recoverable error (architecture limitation)
        if (!supportedArch) {
            return Expected<int>::Error("Operation not supported on this architecture");
        }

        // Success
        int sum = 0;
        for (size_t i = 0; i < size; i++) {
            sum += data[i];
        }
        return sum;
    };

    int testData[] = {1, 2, 3, 4, 5};
    auto result1 = processData(testData, 5, true);
    EXPECT_TRUE(result1.hasValue());
    EXPECT_EQ(*result1, 15);

    auto result2 = processData(testData, 5, false);
    EXPECT_TRUE(result2.hasError());
    EXPECT_TRUE(result2.getError().find("not supported") != std::string::npos);
}

// ============================================================================
// Performance Tests (Sanity Check)
// ============================================================================

TEST_F(ExpectedTest, PerformanceSanity) {
    // Test that Expected doesn't have crazy overhead for simple types
    const int iterations = 10000;

    auto start = std::chrono::high_resolution_clock::now();

    for (int i = 0; i < iterations; i++) {
        Expected<int> result(i);
        if (result) {
            volatile int x = *result;  // Prevent optimization
            (void)x;
        }
    }

    auto end = std::chrono::high_resolution_clock::now();
    auto duration = std::chrono::duration_cast<std::chrono::microseconds>(end - start).count();

    // This should complete in well under 1ms for 10k iterations
    EXPECT_LT(duration, 10000) << "Expected<T> has unreasonable overhead";
}

// ============================================================================
// Documentation Examples Tests
// ============================================================================

// Verify examples from ErrorHandling.hpp actually work
TEST_F(ExpectedTest, DocumentationExample1) {
    auto createInstruction = [](bool arch_supports) -> Expected<int*> {
        if (!arch_supports) {
            return Expected<int*>::Error("Not supported");
        }
        static int inst = 42;
        return &inst;
    };

    // Usage from documentation
    auto result = createInstruction(false);
    if (!result) {
        EXPECT_EQ(result.getError(), "Not supported");
    } else {
        FAIL() << "Should have failed";
    }
}

TEST_F(ExpectedTest, DocumentationExample2) {
    struct StinkyRegister {
        bool isValid() const {
            return true;
        }
    };

    auto createInst = [](StinkyRegister dst) -> Expected<int*> {
        assert(dst.isValid() && "Invalid destination register");
        static int inst = 42;
        return &inst;
    };

    StinkyRegister reg;
    auto result = createInst(reg);
    EXPECT_TRUE(result.hasValue());
}