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

// Wires Crafter.Debug into a consumer's build. In the consumer's project.cpp:
//
//     #pragma crafter dependency "https://forgejo.catcrafts.net/Catcrafts/Crafter.Debug.git" project "tooling/project.cpp"
//     import Crafter.Debug.Build;
//     ...
//     Debug::Use(cfg, { .enabled = opts.Has("--debug-api"), .flag = "--debug-api",
//                       .define = "MYAPP_DEBUG_API", .args = depArgs });
//
// crafter-build builds this module for the host and links it into the
// consumer's project.so, the way Crafter.LintRules gets in, so Use runs each
// time crafter-build loads the consumer: for every verb, before anything is
// built. With the consumer's flag on, Use adds the Crafter.Debug library from
// the checkout this module was built from, and writes build/crafter-debug, the
// launcher for the client that library builds. The client is one of the
// library's dependencies, so the build that follows compiles it in the same
// pass as the app, from the same sources.
//
// The launcher is a POSIX sh script, because what it starts has to run where
// it was built. A client built inside the CrafterBuild Flatpak links the libc++
// in that Flatpak's /app/lib against the runtime's glibc, so on the host the
// launcher starts it through `flatpak run`: nothing the Flatpak compiled runs
// on the host itself. The script keeps to what every /bin/sh on Linux shares
// (test, command -v, grep -q, exec "$@"), and every path in it is quoted.
export module Crafter.Debug.Build;
import std;
import Crafter.Build;
namespace fs = std::filesystem;

namespace Crafter::Debug {
    // The checkout this module was built from. crafter-build compiles module
    // sources from absolute paths, and this file is
    // <checkout>/tooling/interfaces/Crafter.Debug.Build.cppm.
    fs::path Checkout() {
        return fs::path(std::source_location::current().file_name()).parent_path().parent_path().parent_path();
    }

    // The value of `key` in `section` of an INI-style file such as
    // /.flatpak-info, or "" when either is missing.
    std::string IniValue(std::string_view text, std::string_view section, std::string_view key) {
        bool inSection = false;
        for (const auto part : std::views::split(text, '\n')) {
            const std::string_view line(std::ranges::data(part), std::ranges::size(part));
            if (line.starts_with('[')) {
                inSection = line.size() == section.size() + 2 && line.substr(1, section.size()) == section && line.back() == ']';
                continue;
            }
            if (inSection && line.size() > key.size() && line.starts_with(key) && line[key.size()] == '=') {
                return std::string(line.substr(key.size() + 1));
            }
        }
        return {};
    }

    // The Flatpak crafter-build runs in, as its /.flatpak-info describes it:
    // the app id and the branch. Both empty when crafter-build runs natively.
    struct Sandbox {
        std::string app;
        std::string branch;
    };

    Sandbox CurrentSandbox() {
        std::ifstream in("/.flatpak-info");
        if (!in) return {};
        const std::string text((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>());
        return { IniValue(text, "Application", "name"), IniValue(text, "Instance", "branch") };
    }

    // A target the debug server can run on: Linux, not the browser.
    bool NativeLinux(std::string_view target) {
        return target.find("-linux-") != std::string_view::npos && !target.starts_with("wasm");
    }

    // The launcher for `client`. Inside the Flatpak that built the client it
    // runs it directly; on the host it starts it in that Flatpak, on the
    // branch that built it, so the client gets the runtime it was linked
    // against; from another app's sandbox it goes through flatpak-spawn.
    // `--die-with-parent` ends the client when whatever started the launcher
    // is killed, a timed-out `wait` or a Monitor-stopped `log --follow`.
    std::string LauncherText(const fs::path& client, const Sandbox& sandbox, std::string_view flag) {
        std::string text = std::format(
            "#!/bin/sh\n"
            "# Written by Crafter.Debug (Debug::Use) each time crafter-build loads this\n"
            "# project with {0}: runs the crafter-debug client that build compiled.\n"
            "client={1}\n"
            "if [ ! -x \"$client\" ]; then\n"
            "    echo \"crafter-debug: the client is not built yet; build with: crafter-build {0}\" >&2\n"
            "    exit 2\n"
            "fi\n",
            flag, ShellQuote(client.string()));
        if (sandbox.app.empty()) {
            text += "exec \"$client\" \"$@\"\n";
            return text;
        }
        const std::string run = std::format("flatpak run --die-with-parent --branch={} --command=\"$client\" {} \"$@\"",
                                            ShellQuote(sandbox.branch), ShellQuote(sandbox.app));
        text += std::format(
            "if grep -qsx {0} /.flatpak-info; then exec \"$client\" \"$@\"; fi\n"
            "if command -v flatpak >/dev/null 2>&1; then exec {1}; fi\n"
            "if command -v flatpak-spawn >/dev/null 2>&1; then exec flatpak-spawn --host {1}; fi\n"
            "echo \"crafter-debug: needs flatpak to start $client\" >&2\n"
            "exit 1\n",
            ShellQuote(std::format("name={}", sandbox.app)), run);
        return text;
    }

    // What build/crafter-debug says before the project has been built with
    // its debug flag.
    std::string StubText(std::string_view flag) {
        return std::format(
            "#!/bin/sh\n"
            "# Written by Crafter.Debug (Debug::Use): this project has no debug build yet.\n"
            "echo \"crafter-debug: no debug build yet; build with: crafter-build {}\" >&2\n"
            "exit 2\n",
            flag);
    }

    // Replaces `file` with `text`, executable, unless it already holds it.
    // Through a temporary name and a rename, so a launcher that is running
    // never reads half a file. A failure is a warning: the build itself does
    // not depend on the launcher.
    void WriteIfChanged(const fs::path& file, const std::string& text) {
        {
            std::ifstream in(file, std::ios::binary);
            if (in && std::string((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>()) == text) return;
        }
        std::error_code ec;
        fs::create_directories(file.parent_path(), ec);
        std::random_device random;
        fs::path temp = file;
        temp += std::format(".{:08x}.tmp", random());
        {
            std::ofstream out(temp, std::ios::binary | std::ios::trunc);
            out << text;
            if (!out) {
                std::println(std::cerr, "Crafter.Debug: could not write {}", temp.string());
                return;
            }
        }
        fs::permissions(temp, fs::perms::owner_all | fs::perms::group_read | fs::perms::group_exec | fs::perms::others_read | fs::perms::others_exec, ec);
        fs::rename(temp, file, ec);
        if (ec) {
            std::println(std::cerr, "Crafter.Debug: could not write {}: {}", file.string(), ec.message());
            fs::remove(temp, ec);
        }
    }
}

export namespace Crafter::Debug {
    struct UseOptions {
        // Whether this build includes Crafter.Debug: the consumer's own flag,
        // such as `opts.Has("--debug-api")`. Crafter.Debug never sees the flag.
        bool enabled = false;
        // That flag as the user types it, for the launcher's messages.
        std::string flag = "--debug-api";
        // The define the consumer's own sources test, such as "MYAPP_DEBUG_API".
        std::string define;
        // The args the consumer hands its other dependencies. A dependency
        // two paths share must get the same list on both, or crafter-build
        // refuses the graph ("module ... built twice").
        std::vector<std::string> args;
    };

    // Adds Crafter.Debug to `cfg` when options.enabled, and writes the
    // launcher; see the comment at the top. `at` defaults to the call site,
    // which is how Use finds the consumer's directory.
    void Use(Configuration& cfg, const UseOptions& options, std::source_location at = std::source_location::current()) {
        const fs::path launcher = fs::path(at.file_name()).parent_path() / "build" / "crafter-debug";
        // Only for the project crafter-build was pointed at: a consumer loaded
        // as someone else's dependency has no agent driving it from its own
        // directory. Asked before LocalProject, which loads another project.
        const bool topLevel = IsTopLevelProject();
        if (!options.enabled || !NativeLinux(cfg.target)) {
            if (topLevel && !fs::exists(launcher)) WriteIfChanged(launcher, StubText(options.flag));
            return;
        }
        Configuration* library = LocalProject({ .projectFile = Checkout() / "project.cpp", .args = options.args });
        cfg.dependencies.push_back(library);
        if (!options.define.empty()) cfg.defines.push_back({ options.define, "" });
        if (!topLevel) return;
        const auto client = std::ranges::find(library->dependencies, std::string_view("crafter.debug-cli"),
                                              [](const Configuration* dependency) { return std::string_view(dependency->name); });
        if (client == library->dependencies.end()) {
            throw std::runtime_error(std::format("Crafter.Debug: {} declares no crafter.debug-cli client", (Checkout() / "project.cpp").string()));
        }
        WriteIfChanged(launcher, LauncherText((*client)->BinDir() / (*client)->outputName, CurrentSandbox(), options.flag));
    }
}