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

module;
// Supplied on the command line by build.sh and project.cpp (from the
// CRAFTER_BUILD_VERSION environment variable or `git describe`); a build
// that passes nothing is a development build.
#ifndef CRAFTER_BUILD_VERSION
#define CRAFTER_BUILD_VERSION "0.0.0-dev"
#endif
module Crafter.Build:Toolchain_impl;
import std;
import :Toolchain;
import :Platform;
namespace fs = std::filesystem;
using namespace Crafter;

namespace {
    constexpr std::string_view EnvVars[] = {
        "CRAFTER_BUILD_LLVM_DIR",
        "CRAFTER_BUILD_LIBCXX_DIR",
        "CRAFTER_BUILD_LIBCLANG",
        "CRAFTER_BUILD_WASI_SYSROOT",
        "CRAFTER_MINGW_DIR",
    };

    std::string_view Env(const ToolchainInputs& in, std::string_view name) {
        auto it = in.env.find(name);
        return it == in.env.end() ? std::string_view{} : std::string_view(it->second);
    }

    // "Arch Linux clang version 22.1.8" / "clang version 22.1.8" -> "22.1.8".
    std::string ShortVersion(std::string_view versionLine) {
        constexpr std::string_view Marker = "version ";
        std::size_t at = versionLine.find(Marker);
        if (at == std::string_view::npos) return "unknown";
        std::string_view rest = versionLine.substr(at + Marker.size());
        std::size_t end = rest.find_first_of(" \t(");
        return std::string(rest.substr(0, end));
    }

    std::string Trimmed(std::string s) {
        while (!s.empty() && (s.back() == '\n' || s.back() == '\r' || s.back() == ' ')) s.pop_back();
        return s;
    }
}

std::string Toolchain::LibcxxCompileFlags() const {
    if (libcxxDir.empty()) return {};
    return std::format(" -nostdinc++ -isystem {}", (libcxxDir / "include" / "c++" / "v1").string());
}

std::string Toolchain::LibcxxLinkFlags() const {
    // clang searches its per-target runtime directory and the system library
    // paths for -lc++, not <prefix>/lib, so a toolchain outside /usr with the
    // classic layout needs the search path as well as the run-time path.
    fs::path lib;
    if (!libcxxDir.empty()) {
        lib = libcxxDir / "lib";
    } else if (!prefix.empty() && prefix != "/usr") {
        lib = prefix / "lib";
    }
    if (lib.empty()) return {};
    return std::format(" -L{} -Wl,-rpath,{}", lib.string(), lib.string());
}

std::string Toolchain::Key() const {
    std::string identity;
    for (const std::string& part : {clangxx.string(), clangVersion, libcxxDir.string(), stdCppm.string()}) {
        identity += part;
        identity += '\0';
    }
    return std::format("{}-{:08x}", ShortVersion(clangVersion), static_cast<std::uint32_t>(std::hash<std::string>{}(identity)));
}

Toolchain Crafter::ResolveToolchain(const ToolchainInputs& in) {
    Toolchain tc;

    // 1. The compiler: an explicit prefix, else one installed beside
    //    crafter-build, else PATH. An explicit prefix without a clang++ is an
    //    error rather than a fallback, for the same reason CRAFTER_BUILD_LIBCLANG
    //    is exclusive: an override that silently yields to something else
    //    cannot be used to diagnose which compiler is in play.
    if (std::string_view dir = Env(in, "CRAFTER_BUILD_LLVM_DIR"); !dir.empty()) {
        tc.prefix = fs::path(dir);
        if (!fs::exists(tc.prefix / "bin" / "clang++")) {
            tc.error = std::format("clang++ not found at {} (CRAFTER_BUILD_LLVM_DIR)", (tc.prefix / "bin" / "clang++").string());
        }
    } else if (!in.crafterPrefix.empty() && fs::exists(in.crafterPrefix / "bin" / "clang++")) {
        tc.prefix = in.crafterPrefix;
    }
    if (tc.prefix.empty()) {
        tc.clangxx = "clang++";
        tc.clang = "clang";
        tc.llvmAr = "llvm-ar";
    } else {
        tc.clangxx = tc.prefix / "bin" / "clang++";
        tc.clang = tc.prefix / "bin" / "clang";
        tc.llvmAr = tc.prefix / "bin" / "llvm-ar";
        if (tc.prefix != "/usr" && fs::exists(tc.prefix / "include" / "clang-c" / "Index.h")) {
            tc.llvmIncludeDir = tc.prefix / "include";
        }
    }

    // 2. libclang. The override is exclusive and unchecked on purpose: a
    //    broken path must fail loudly when dlopened, not be papered over.
    if (std::string_view pinned = Env(in, "CRAFTER_BUILD_LIBCLANG"); !pinned.empty()) {
        tc.libclang = fs::path(pinned);
    } else if (!tc.prefix.empty() && fs::exists(tc.prefix / "lib" / "libclang.so")) {
        tc.libclang = tc.prefix / "lib" / "libclang.so";
    }

    // 3. libc++ and its std module source. The compiler's own copy lives at
    //    <prefix>/share/libc++/v1 when the prefix carries libc++; the system
    //    copy is the last resort either way. The headers of the same install
    //    say which release the source belongs to.
    fs::path libcxxRoot = "/usr";
    if (std::string_view dir = Env(in, "CRAFTER_BUILD_LIBCXX_DIR"); !dir.empty()) {
        tc.libcxxDir = fs::path(dir);
        libcxxRoot = tc.libcxxDir;
    } else if (!tc.prefix.empty() && fs::exists(tc.prefix / "share" / "libc++" / "v1" / "std.cppm")) {
        libcxxRoot = tc.prefix;
    }
    tc.stdCppm = libcxxRoot / "share" / "libc++" / "v1" / "std.cppm";
    tc.libcxxVersion = LibcxxVersion(libcxxRoot / "include" / "c++" / "v1");
    if (!in.crafterPrefix.empty()) {
        tc.stdModulesDir = in.crafterPrefix / "share" / "crafter-build" / "libc++-modules";
    }

    // 4. Sysroots for the cross targets that have a conventional location.
    if (std::string_view dir = Env(in, "CRAFTER_BUILD_WASI_SYSROOT"); !dir.empty()) {
        tc.wasiSysroot = fs::path(dir);
    } else if (!tc.prefix.empty() && fs::exists(tc.prefix / "share" / "wasi-sysroot")) {
        tc.wasiSysroot = tc.prefix / "share" / "wasi-sysroot";
    } else {
        tc.wasiSysroot = "/usr/share/wasi-sysroot";
    }
    if (std::string_view dir = Env(in, "CRAFTER_MINGW_DIR"); !dir.empty()) {
        tc.mingwSysroot = fs::path(dir);
    } else if (!in.hostRoot.empty() && fs::exists(in.hostRoot / "usr" / "x86_64-w64-mingw32")) {
        // The sandbox has no mingw-w64 of its own, and no mingw gcc on PATH
        // for clang to find one by.
        tc.mingwSysroot = in.hostRoot / "usr";
    }
    return tc;
}

const Toolchain& Crafter::GetToolchain() {
    static const Toolchain Resolved = []() {
        ToolchainInputs in;
        for (std::string_view name : EnvVars) {
            if (const char* value = std::getenv(std::string(name).c_str()); value && *value) {
                in.env.emplace(std::string(name), value);
            }
        }
        // GetCrafterBuildHome throws when no share/crafter-build is found
        // near the executable; a toolchain can still come from PATH then.
        try {
            in.crafterPrefix = GetCrafterBuildHome().parent_path().parent_path();
        } catch (const std::exception&) {}
        if (fs::exists("/.flatpak-info")) in.hostRoot = "/run/host";

        Toolchain tc = ResolveToolchain(in);
        if (!tc.error.empty()) return tc;

        CommandResult triple = RunCommandChecked(std::format("{} -print-target-triple", tc.clangxx.string()));
        if (triple.exitCode != 0) {
            tc.error = std::format("could not run {} (exit {}): {}", tc.clangxx.string(), triple.exitCode, Trimmed(triple.output));
            if (tc.prefix.empty()) tc.error += "; install clang or set CRAFTER_BUILD_LLVM_DIR";
            return tc;
        }
        tc.hostTriple = Trimmed(std::move(triple.output));
        CommandResult version = RunCommandChecked(std::format("{} --version", tc.clangxx.string()));
        if (version.exitCode == 0) {
            std::string first = version.output.substr(0, version.output.find('\n'));
            tc.clangVersion = Trimmed(std::move(first));
        }
        return tc;
    }();
    return Resolved;
}

const Toolchain& Crafter::RequireToolchain() {
    const Toolchain& tc = GetToolchain();
    if (!tc.error.empty()) throw std::runtime_error(tc.error);
    return tc;
}

std::int32_t Crafter::LibcxxVersion(const fs::path& includeDir) {
    // "#  define _LIBCPP_VERSION 230102", the one place libc++ states its
    // release in a form the preprocessor does not have to be run for.
    constexpr std::string_view Marker = "define _LIBCPP_VERSION ";
    std::ifstream config(includeDir / "__config");
    std::string line;
    while (std::getline(config, line)) {
        const std::size_t at = line.find(Marker);
        if (at == std::string::npos) continue;
        const std::string_view digits = std::string_view(line).substr(at + Marker.size());
        std::int32_t version = 0;
        if (std::from_chars(digits.data(), digits.data() + digits.size(), version).ec == std::errc{}) return version;
    }
    return 0;
}

std::string Crafter::LibcxxVersionString(std::int32_t version) {
    return std::format("{}.{}.{}", version / 10000, version / 100 % 100, version % 100);
}

StdModuleSource Crafter::SysrootStdModule(const Toolchain& tc, const fs::path& sysroot) {
    const fs::path own = sysroot / "usr" / "share" / "libc++" / "v1" / "std.cppm";
    if (fs::exists(own)) return {own, {}};

    const fs::path includeDir = sysroot / "usr" / "include" / "c++" / "v1";
    if (!fs::exists(includeDir / "__config")) {
        return {{}, std::format("sysroot {} has no libc++ headers at {}; install its libc++ development package", sysroot.string(), includeDir.string())};
    }
    const std::int32_t wanted = LibcxxVersion(includeDir);
    const bool comparable = wanted != 0 && tc.libcxxVersion != 0;
    // Releases are matched on the major version: a release branch only takes
    // fixes, so 22.1.3 headers and the 22.1.8 module source name the same
    // declarations.
    if (comparable && wanted / 10000 == tc.libcxxVersion / 10000 && fs::exists(tc.stdCppm)) return {tc.stdCppm, {}};
    if (wanted != 0 && !tc.stdModulesDir.empty()) {
        const fs::path shipped = tc.stdModulesDir / std::to_string(wanted / 10000) / "std.cppm";
        if (fs::exists(shipped)) return {shipped, {}};
    }
    // One of the two releases is unknown, so there is nothing to compare:
    // hand over the toolchain's source and let the compile decide, which is
    // what happened for every sysroot before releases were compared.
    if (!comparable && fs::exists(tc.stdCppm)) return {tc.stdCppm, {}};

    const std::string sysrootRelease = wanted != 0 ? LibcxxVersionString(wanted) : std::string("of an unknown release");
    const std::string toolchainSource = !fs::exists(tc.stdCppm)
        ? std::string("the toolchain has no std module source at all")
        : std::format("the toolchain's is for libc++ {}", LibcxxVersionString(tc.libcxxVersion));
    return {{}, std::format("sysroot {} carries libc++ {} without its std module source, and crafter-build has none for that release ({}); install the share/libc++/v1 directory of that libc++ release (std.cppm and std/) as {}", sysroot.string(), sysrootRelease, toolchainSource, own.parent_path().string())};
}

std::string_view Crafter::CrafterBuildVersion() {
    return CRAFTER_BUILD_VERSION;
}