// SPDX-License-Identifier: LGPL-3.0-only
// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

import std;
import Crafter.Build;
namespace fs = std::filesystem;
using namespace Crafter;

// One shader source can be registered more than once, each entry with its own
// defines and a variant that names its output ("tint.spv", "tint.red.spv").
// Build() compiles the entries in parallel into one directory, which is where
// the feature can go wrong in ways the Shader API alone does not show:
//
//   - both entries must land in the bin dir, with different contents;
//   - an entry added later must still be compiled when the other one's output
//     is already there and up to date;
//   - two entries that would write the same file (defines set, variant
//     forgotten) used to race silently: the file held whichever compile
//     finished last, the build reported success, and Check() called both up
//     to date from then on. That has to be a build error naming the cause.
//
// The fixture's `#if TINT_RED` also pins that a bare define is defined to 1,
// like the compiler's -D: an empty definition would not compile.
namespace {
    std::int32_t Failures = 0;

    void Check(bool cond, std::string_view msg) {
        if (!cond) {
            std::println(std::cerr, "FAIL: {}", msg);
            ++Failures;
        }
    }

    // Shader outputs are compared by mtime against the source, and the test
    // adds an entry between passes, so work on a fresh copy outside the repo.
    fs::path StageFixture() {
        fs::path source = fs::current_path() / "tests" / "ShaderVariantBuild" / "fixture";
        fs::path staged = fs::temp_directory_path() / "crafter-build-shader-variant-build";
        fs::remove_all(staged);
        fs::copy(source, staged, fs::copy_options::recursive);
        return staged;
    }

    Configuration MakeApp(const fs::path& staged) {
        Configuration app;
        app.path = staged;
        app.name = "tinted";
        app.outputName = "tinted";
        app.target = HostTarget();
        app.type = ConfigurationType::Executable;
        std::array<fs::path, 0> ifaces = {};
        std::array<fs::path, 1> impls = { "main" };
        app.GetInterfacesAndImplementations(ifaces, impls);
        return app;
    }

    Shader& AddTint(Configuration& app, const fs::path& staged) {
        return app.shaders.emplace_back(staged / "tint.frag", std::string("main"), ShaderType::Fragment);
    }

    BuildResult BuildOnce(Configuration& app) {
        // A fresh depResults per pass: the map memoizes a Configuration's
        // build for the duration of one pass.
        std::unordered_map<fs::path, std::shared_future<BuildResult>> depResults;
        std::mutex depMutex;
        return Build(app, depResults, depMutex);
    }

    std::string ReadAll(const fs::path& file) {
        std::ifstream stream(file, std::ios::binary);
        return std::string(std::istreambuf_iterator<char>(stream), std::istreambuf_iterator<char>());
    }
}

int main() {
    const fs::path staged = StageFixture();

    // Pass 1: the plain entry alone.
    Configuration app = MakeApp(staged);
    AddTint(app, staged);
    BuildResult first = BuildOnce(app);
    Check(first.result.empty(), std::format("the plain entry builds: {}", first.result));
    const fs::path plainSpv = app.BinDir() / "tint.spv";
    const fs::path redSpv = app.BinDir() / "tint.red.spv";
    Check(fs::exists(plainSpv), "tint.spv is in the bin dir");
    Check(!fs::exists(redSpv), "no variant output before the variant is registered");

    // Pass 2: the variant is added while tint.spv is already up to date. It
    // has its own staleness check and must be compiled, into its own file.
    Shader& red = AddTint(app, staged);
    red.defines = {"TINT_RED"};
    red.variant = "red";
    BuildResult second = BuildOnce(app);
    Check(second.result.empty(), std::format("plain + variant builds: {}", second.result));
    Check(fs::exists(redSpv), "tint.red.spv is in the bin dir");
    const std::string plainBytes = ReadAll(plainSpv);
    const std::string redBytes = ReadAll(redSpv);
    Check(!plainBytes.empty() && !redBytes.empty(), "both outputs have content");
    Check(plainBytes != redBytes, "the variant took the other #if branch");

    // Pass 3: the same define without a variant. Both entries would write
    // tint.spv, so the build has to stop and say so, and must leave the file
    // from pass 2 alone.
    Configuration clash = MakeApp(staged);
    AddTint(clash, staged);
    Shader& unnamed = AddTint(clash, staged);
    unnamed.defines = {"TINT_RED"};
    BuildResult third = BuildOnce(clash);
    Check(!third.result.empty(), "two entries with one output name fail the build");
    Check(third.result.contains("tint.spv") && third.result.contains("variant"), std::format("the error names the file and the fix: {}", third.result));
    Check(ReadAll(plainSpv) == plainBytes, "the existing output is not overwritten by the failed build");

    std::error_code ec;
    fs::remove_all(staged, ec);

    if (Failures > 0) {
        std::println(std::cerr, "{} assertions failed", Failures);
        return 1;
    }
    return 0;
}