using Invercargill;
using Invercargill.DataStructures;

namespace Usm.Installer {

    /**
     * Canonical source of the self-contained USM installer script baked into
     * deploy images by default (the compiled form of `installer/` in the usm
     * source tree), hosted at packages.astrologue.nz; override it per deploy
     * with `--installer-url` (whose `file://` form is the sanctioned
     * local-testing path).
     */
    public const string CANONICAL_URL = "https://packages.astrologue.nz/install-usm.sh";
}

/** Default container base image, overridable with `--base`. */
const string DEPLOY_DEFAULT_BASE_IMAGE = "registry.fedoraproject.org/fedora:43";

/** Deploy context directory created inside the packaged project. */
const string DEPLOY_CONTEXT_DIRECTORY = ".usm-deploy";

/** Where the USM installer tree lives inside images (installer TARGET_DIR). */
const string DEPLOY_USM_PREFIX = "/opt/usm";

/** In-image location that file:// repository trees are rewritten to. */
const string DEPLOY_REPO_TREES_PATH = "/usr/share/usm-repos";


/**
 * The system package managers `deploy --spm` can wire into the image, one
 * per shim the installer ships; {@link DeploySpm.NONE} wires none and the
 * image resolves from USM repositories alone.
 */
private enum DeploySpm {
    DNF,
    APT,
    APK,
    EMERGE,
    NONE;

    /**
     * Whether a `--spm` value names a choice, setting {@link parsed} to it
     * (and reporting the valid values) — {@link DeploySpm.NONE} on failure.
     */
    public static bool parse(string value, out DeploySpm parsed) {
        parsed = DeploySpm.NONE;
        switch(value) {
            case "dnf":
                parsed = DeploySpm.DNF;
                return true;
            case "apt":
                parsed = DeploySpm.APT;
                return true;
            case "apk":
                parsed = DeploySpm.APK;
                return true;
            case "emerge":
                parsed = DeploySpm.EMERGE;
                return true;
            case "none":
                parsed = DeploySpm.NONE;
                return true;
            default:
                printerr(@"\"$value\" is not a valid --spm value (expected dnf, apt, apk, emerge or none)\n");
                return false;
        }
    }

    /** The lowercase name completing `usm-spm-` in shim paths. */
    public string shim_name() {
        switch(this) {
            case DeploySpm.DNF:
                return "dnf";
            case DeploySpm.APT:
                return "apt";
            case DeploySpm.APK:
                return "apk";
            case DeploySpm.EMERGE:
                return "emerge";
            default:
                return "none";
        }
    }

    /**
     * The library directory the generated config installs `lib:`
     * resources under: apk targets musl/Alpine and apt targets Debian
     * multiarch, neither of which searches /usr/lib64 (their loaders and
     * pkg-config defaults resolve /usr/lib); the rpm and portage targets
     * follow the lib64 convention.
     */
    public string lib_path() {
        return this == DeploySpm.APK || this == DeploySpm.APT ? "lib" : "lib64";
    }
}


/**
 * `usm deploy <package.usmc|directory> [flags…]` — the package-then-deploy
 * convenience wrapper.
 *
 * A directory is deployed directly by running the manifest deploy verb inside
 * it; a `.usmc` archive is extracted to a temporary directory first, and the
 * finished image artifact is moved back next to the invocation directory.
 * Flags pass through to {@link manifest_deploy} unchanged.
 */
public int deploy_main(string[] args) {
    string? target = null;
    var flags = new Vector<string>();
    for(int i = 2; i < args.length; i++) {
        var argument = args[i];
        if(argument.has_prefix("--")) {
            flags.add(argument);
            if(deploy_option_takes_value(argument.split("=", 2)[0])
                && !argument.contains("=")
                && i + 1 < args.length) {
                flags.add(args[++i]);
            }
            continue;
        }
        if(target != null) {
            printerr(@"Unexpected argument \"$argument\"\n");
            return deploy_usage();
        }
        target = argument;
    }

    if(target == null) {
        return deploy_usage();
    }

    var invocation_dir = Environment.get_current_dir();
    var target_path = Path.is_absolute(target) ? target : Path.build_filename(invocation_dir, target);

    // --repository is given relative to the invocation directory, but the
    // manifest deploy verb runs inside the target project: absolutise before
    // forwarding so both interpretations agree
    var forwarded = new string[] { "usm", "deploy" };
    for(int i = 0; i < flags.length; i++) {
        var flag = flags[i];
        if(flag.has_prefix("--repository=") && !Path.is_absolute(flag.split("=", 2)[1])) {
            forwarded += @"--repository=$(Path.build_filename(invocation_dir, flag.split("=", 2)[1]))";
        }
        else if(flag == "--repository" && i + 1 < flags.length && !Path.is_absolute(flags[i + 1])) {
            forwarded += flag;
            forwarded += Path.build_filename(invocation_dir, flags[++i]);
        }
        else {
            forwarded += flag;
        }
    }

    FileInfo file_info;
    try {
        if(!File.new_for_path(target_path).query_exists()) {
            printerr(@"\"$target\" does not exist\n");
            return 255;
        }
        file_info = File.new_for_path(target_path).query_info("*", FileQueryInfoFlags.NONE);
    }
    catch(Error e) {
        printerr(@"Could not inspect \"$target\": $(e.message)\n");
        return 255;
    }

    if(file_info.get_file_type() == FileType.DIRECTORY) {
        if(!File.new_for_path(Path.build_filename(target_path, "MANIFEST.usm")).query_exists()) {
            printerr(@"\"$target\" contains no MANIFEST.usm file\n");
            return 255;
        }
        Environment.set_current_dir(target_path);
        return manifest_main(forwarded);
    }

    if(!target.has_suffix(".usmc")) {
        printerr("\"$target\" is neither a directory containing MANIFEST.usm nor a .usmc package\n");
        return deploy_usage();
    }

    // Package-then-deploy: extract the archive, deploy from the extracted
    // tree, then bring the artifact back to the invocation directory
    Usm.Manifest archive_manifest;
    var extract_dir = File.new_build_filename("/tmp", @"usm-deploy-$(Uuid.string_random())");
    try {
        archive_manifest = new Usm.Manifest.from_package(target_path);
        extract_dir.make_directory();
        Usm.Util.unarchive(target_path, extract_dir.get_path());
    }
    catch(Error e) {
        printerr(@"Could not extract \"$target\": $(e.message)\n");
        return 243;
    }

    Environment.set_current_dir(extract_dir.get_path());
    var result = manifest_main(forwarded);
    if(result == 0) {
        var artifact = @"$(archive_manifest.name)-$(archive_manifest.version.to_string()).image.tar.xz";
        try {
            var produced = File.new_for_path(Path.build_filename(extract_dir.get_path(), artifact));
            if(produced.query_exists()) {
                produced.move(File.new_for_path(Path.build_filename(invocation_dir, artifact)), FileCopyFlags.OVERWRITE);
                printerr(@"Moved image artifact to \"$invocation_dir/$artifact\"\n");
            }
        }
        catch(Error e) {
            printerr(@"The image was built, but its artifact could not be moved to \"$invocation_dir\": $(e.message)\n");
            printerr(@"It remains at \"$(extract_dir.get_path())/$artifact\"\n");
        }
    }
    printerr(@"Deploy context kept at \"$(extract_dir.get_path())\"\n");
    return result;
}


/**
 * `usm manifest deploy [flags…]` — generate a single-stage container deploy
 * context for the manifest in the current directory, then (unless
 * `--no-build`) build it with podman and save an xz-compressed image
 * archive:
 *
 * - `--exec CMD`: the container command, split on whitespace into the
 *   exec-form ENTRYPOINT. Default: the package's single `bin:` provide
 *   (an error when there are zero or several).
 * - `--base IMAGE`: base image (default {@link DEPLOY_DEFAULT_BASE_IMAGE}).
 * - `--spm dnf|apt|apk|emerge|none`: the system package manager wired into
 *   the image via the matching `usm-spm-<spm>` helper and a per-SPM
 *   bootstrap RUN in the Containerfile. Default `none`: no
 *   `system_package_manager` section and no bootstrap RUN, so the image
 *   resolves everything from USM repositories alone.
 * - `--repository FILE`: use exactly the given `.usmr` files (repeatable)
 *   instead of the machine-configured repositories. `file://` repositories
 *   have their trees copied into the context and their URIs rewritten to the
 *   in-image location.
 * - `--installer-url URL`: override the canonical USM installer source; a
 *   `file://` URL carries the script inside the context.
 * - `--no-build`: stop after generating the context.
 *
 * Only repository public keys ever enter the context or the image.
 */
public int manifest_deploy(string[] args) {
    string? exec_command = null;
    string? base_image = null;
    string? installer_url = null;
    DeploySpm deploy_spm = DeploySpm.NONE;
    bool no_build = false;
    // The top-level --verbose scan strips the flag before this parser runs,
    // so seed from USM_VERBOSE as well
    var verbose_env = Environment.get_variable("USM_VERBOSE");
    bool verbose_deploy = verbose_env != null && verbose_env.length > 0;
    var repository_overrides = new Vector<string>();

    for(int i = 2; i < args.length; i++) {
        var argument = args[i];
        string? inline_value = null;
        if(argument.has_prefix("--") && argument.contains("=")) {
            var assignment = argument.split("=", 2);
            argument = assignment[0];
            inline_value = assignment[1];
        }
        switch(argument) {
            case "--exec":
                exec_command = deploy_option_value(args, ref i, argument, inline_value);
                if(exec_command == null) {
                    return deploy_usage();
                }
                break;
            case "--base":
                base_image = deploy_option_value(args, ref i, argument, inline_value);
                if(base_image == null) {
                    return deploy_usage();
                }
                break;
            case "--repository":
                var repository_file = deploy_option_value(args, ref i, argument, inline_value);
                if(repository_file == null) {
                    return deploy_usage();
                }
                repository_overrides.add(repository_file);
                break;
            case "--spm":
                var spm_value = deploy_option_value(args, ref i, argument, inline_value);
                if(spm_value == null) {
                    return deploy_usage();
                }
                if(!DeploySpm.parse((!)spm_value, out deploy_spm)) {
                    return deploy_usage();
                }
                break;
            case "--installer-url":
                installer_url = deploy_option_value(args, ref i, argument, inline_value);
                if(installer_url == null) {
                    return deploy_usage();
                }
                break;
            case "--no-build":
                no_build = true;
                break;
            case "--verbose":
            case "-v":
                verbose_deploy = true;
                break;
            default:
                printerr(@"Unknown deploy option \"$argument\"\n");
                return deploy_usage();
        }
    }

    if(manifest.is_data_package) {
        printerr("Data packages cannot be deployed: they define no build or install machinery for the in-container install.\n");
        return 246;
    }
    if(manifest.executables == null || manifest.executables.build == null) {
        printerr(@"Package \"$(manifest.name)\" defines no build executable, which the in-container \"usm install\" requires.\n");
        return 245;
    }

    var entrypoint = deploy_entrypoint(exec_command);
    if(entrypoint.length == 0) {
        return 244;
    }

    var project_dir = Environment.get_current_dir();
    var context_dir = Path.build_filename(project_dir, DEPLOY_CONTEXT_DIRECTORY);
    var version_string = manifest.version.to_string();

    printerr(@"Generating deploy context in \"$context_dir\"...\n");
    // A stale context or artifact from an earlier run must never leak into
    // the package this deploy is about to create
    if(File.new_for_path(context_dir).query_exists()) {
        try {
            Usm.Util.delete_tree(context_dir);
        }
        catch(Error e) {
            printerr(@"Could not remove the stale deploy context: $(e.message)\n");
            return 243;
        }
    }
    foreach(var stale in new string[] { @"$(manifest.name)-$version_string.image.tar", @"$(manifest.name)-$version_string.image.tar.xz" }) {
        var stale_file = File.new_for_path(Path.build_filename(project_dir, stale));
        if(stale_file.query_exists()) {
            try {
                stale_file.delete();
            }
            catch(Error e) {
                printerr(@"Could not remove the stale artifact \"$stale\": $(e.message)\n");
                return 243;
            }
        }
    }
    DirUtils.create_with_parents(context_dir, 0755);
    DirUtils.create_with_parents(Path.build_filename(context_dir, "repos"), 0755);
    DirUtils.create_with_parents(Path.build_filename(context_dir, "repo-trees"), 0755);
    DirUtils.create_with_parents(Path.build_filename(context_dir, "package"), 0755);

    printerr("Packaging the project (usm manifest package)...\n");
    try {
        var package_proc = new Subprocess.newv(new string[] { "/proc/self/exe", "manifest", "package" }, SubprocessFlags.INHERIT_FDS);
        package_proc.wait_check();
        var produced = Path.build_filename(project_dir, "..", @"$(manifest.name)-$version_string.usmc");
        File.new_for_path(produced).move(File.new_build_filename(context_dir, "package", "package.usmc"), FileCopyFlags.OVERWRITE);
    }
    catch(Error e) {
        printerr(@"Failed to package the project: $(e.message)\n");
        return 242;
    }

    bool file_trees_provisioned = false;
    var provisioned = deploy_provision_repositories(repository_overrides, context_dir, project_dir, out file_trees_provisioned);
    if(provisioned != 0) {
        return provisioned;
    }

    var effective_installer_url = installer_url ?? Usm.Installer.CANONICAL_URL;
    var bundled_installer = false;
    if(effective_installer_url.has_prefix("file://")) {
        // A file:// installer URL can only usefully refer to the container's
        // own filesystem, so the script is carried inside the context
        var installer_path = deploy_file_uri_path(effective_installer_url);
        if(installer_path == null || !File.new_for_path(installer_path).query_exists()) {
            printerr(@"--installer-url \"$effective_installer_url\" does not point at an installer script on this machine\n");
            return 241;
        }
        try {
            var local_dir = Path.build_filename(context_dir, "installer-local");
            DirUtils.create_with_parents(local_dir, 0755);
            File.new_for_path(installer_path).copy(File.new_build_filename(local_dir, "install-usm.sh"), FileCopyFlags.OVERWRITE);
        }
        catch(Error e) {
            printerr(@"Could not carry the installer script into the context: $(e.message)\n");
            return 241;
        }
        effective_installer_url = "file:///usm-installer-local/install-usm.sh";
        bundled_installer = true;
    }

    try {
        deploy_write_container_config(context_dir, deploy_spm);

        var containerfile = deploy_containerfile(
            base_image ?? DEPLOY_DEFAULT_BASE_IMAGE,
            effective_installer_url,
            bundled_installer,
            manifest.name,
            version_string,
            entrypoint,
            file_trees_provisioned,
            verbose_deploy,
            deploy_spm);
        FileUtils.set_data(Path.build_filename(context_dir, "Containerfile"), containerfile.data);
    }
    catch(Error e) {
        printerr(@"Could not write the deploy context: $(e.message)\n");
        return 240;
    }

    var tag = @"$(deploy_tag_chunk(manifest.name)):$(deploy_tag_chunk(version_string))";
    if(no_build) {
        printerr(@"Deploy context generated in \"$context_dir\" (--no-build); build it with:\n  podman build -t $tag \"$context_dir\"\n");
        return 0;
    }

    printerr(@"Building image \"$tag\" with podman...\n");
    try {
        var build_proc = new Subprocess.newv(new string[] { "podman", "build", "-t", tag, context_dir }, SubprocessFlags.INHERIT_FDS);
        build_proc.wait_check();
    }
    catch(Error e) {
        printerr(@"Image build failed: $(e.message)\n");
        return 239;
    }

    var artifact_base = @"$(manifest.name)-$version_string.image.tar";
    printerr(@"Saving image to \"$artifact_base.xz\"...\n");
    try {
        var save_proc = new Subprocess.newv(new string[] { "podman", "save", "-o", artifact_base, tag }, SubprocessFlags.INHERIT_FDS);
        save_proc.wait_check();
        var compress_proc = new Subprocess.newv(new string[] { "xz", "-T0", artifact_base }, SubprocessFlags.INHERIT_FDS);
        compress_proc.wait_check();
    }
    catch(Error e) {
        printerr(@"Saving the image failed: $(e.message)\n");
        return 238;
    }

    printerr(@"Built image \"$tag\"; artifact \"$artifact_base.xz\".\n");
    printerr(@"Load and run it with:\n  podman load -i \"$artifact_base.xz\"\n  podman run --rm $tag\n");
    return 0;
}


private int deploy_usage() {
    printerr("USAGE:\n\tusm deploy <package.usmc|directory> [--exec CMD] [--base IMAGE] [--spm dnf|apt|apk|emerge|none] [--repository FILE]... [--no-build] [--installer-url URL] [--verbose]\n");
    return 255;
}


/** Whether a deploy option consumes the following argument as its value. */
private bool deploy_option_takes_value(string option) {
    return option == "--exec" || option == "--base" || option == "--spm" || option == "--repository" || option == "--installer-url";
}


/**
 * The value of a valued option, either the `--option=value` inline form or
 * the next argument; prints the option name and returns null when no value
 * follows.
 */
private string? deploy_option_value(string[] args, ref int index, string option, string? inline_value) {
    if(inline_value != null) {
        return inline_value;
    }
    if(index + 1 >= args.length) {
        printerr(@"Expected a value after \"$option\"\n");
        return null;
    }
    return args[++index];
}


/**
 * The exec-form entrypoint words: `--exec`'s command split on whitespace, or
 * by default the package's single `bin:` provide as an absolute /usr/bin
 * path. Returns an empty array (after reporting why) when `--exec` is given
 * without words or the default is ambiguous.
 */
private string[] deploy_entrypoint(string? exec_command) {
    if(exec_command != null) {
        var words = new Vector<string>();
        foreach(var word in exec_command.split(" ")) {
            if(word.length > 0) {
                words.add(word);
            }
        }
        if(words.length == 0) {
            printerr(@"--exec \"$(exec_command)\" contains no command\n");
            return new string[0];
        }
        return words.to_array();
    }

    var binaries = new Vector<string>();
    foreach(var provide in manifest.provides) {
        if(provide.key.resource_type == Usm.ResourceType.BINARY) {
            binaries.add(provide.key.resource);
        }
    }
    if(binaries.length != 1) {
        printerr(@"Cannot pick a default entrypoint: expected exactly one \"bin:\" provide in \"$(manifest.name)\", found $(binaries.length)");
        foreach(var binary in binaries) {
            printerr(@"\n  bin:$binary");
        }
        printerr("\nPass --exec to choose the container command explicitly.\n");
        return new string[0];
    }
    return new string[] { Path.build_filename("/", "usr", "bin", binaries.first_or_default()) };
}


/**
 * Fills the context's `repos/` and `repo-trees/` directories from either the
 * explicit {@link overrides} (exactly those `.usmr` files) or, by default,
 * the machine-configured repositories (`<config dir>/repos.d`, honouring
 * USM_CONFIGDIR like every other usm command).
 *
 * Every `.usmr` is copied with its embedded public key; a `file://` URI
 * additionally has its repository tree copied into `repo-trees/<name>/` and
 * the copied descriptor's URI rewritten to the in-image location so the
 * container resolves it without the host. Private signing key material is
 * never copied. Sets {@link file_trees_provisioned} when at least one tree
 * was carried in.
 */
private int deploy_provision_repositories(Vector<string> overrides, string context_dir, string project_dir, out bool file_trees_provisioned) {
    file_trees_provisioned = false;

    var selected = new Vector<string>();
    if(overrides.length > 0) {
        foreach(var path in overrides) {
            selected.add(Path.is_absolute(path) ? path : Path.build_filename(project_dir, path));
        }
    }
    else {
        var repos_dir = Path.build_filename(paths.usm_config_dir, "repos.d");
        if(File.new_for_path(repos_dir).query_exists()) {
            try {
                foreach(var file in Iterate.directory(repos_dir)) {
                    if(file.has_suffix(".usmr")) {
                        selected.add(Path.build_filename(repos_dir, file));
                    }
                }
            }
            catch(Error e) {
                printerr(@"Could not list \"$repos_dir\": $(e.message)\n");
                return 241;
            }
        }
        else {
            printerr(@"No configured repositories found in \"$repos_dir\"; the image will resolve dependencies from the system package manager alone. Pass --repository to provision USM repositories into the image.\n");
        }
    }

    foreach(var repository_file in selected) {
        Usm.Repository repository;
        try {
            repository = new Usm.Repository.from_file(repository_file);
        }
        catch(Error e) {
            printerr(@"\"$repository_file\" is not a valid repository file: $(e.message)\n");
            return 241;
        }

        var basename = Path.get_basename(repository_file);
        var stem = basename.has_suffix(".usmr") ? basename.substring(0, basename.length - ".usmr".length) : basename;
        var copied_descriptor = Path.build_filename(context_dir, "repos", basename);

        try {
            File.new_for_path(repository_file).copy(File.new_for_path(copied_descriptor), FileCopyFlags.OVERWRITE);

            if(repository.url != null && repository.url.has_prefix("file://")) {
                var tree = deploy_file_uri_path((!)repository.url);
                if(tree == null) {
                    printerr(@"\"$repository_file\" has an unreadable file:// URI\n");
                    return 241;
                }
                if(!File.new_for_path(tree).query_exists()) {
                    printerr(@"The repository tree \"$tree\" referenced by \"$repository_file\" does not exist\n");
                    return 241;
                }

                var destination = Path.build_filename(context_dir, "repo-trees", stem);
                DirUtils.create_with_parents(destination, 0755);
                deploy_copy_repository_tree(tree, destination);

                var element = new InvercargillJson.JsonElement.from_file(copied_descriptor);
                element.as<InvercargillJson.JsonObject>().set_native("url", @"file://$(DEPLOY_REPO_TREES_PATH)/$stem");
                element.write_to_file(copied_descriptor);
                printerr(@"Provisioned repository \"$stem\": tree copied from \"$tree\", URI rewritten to file://$(DEPLOY_REPO_TREES_PATH)/$stem\n");
                file_trees_provisioned = true;
            }
            else {
                printerr(@"Provisioned repository \"$stem\" from \"$repository_file\" (URI \"$(repository.url ?? "none")\")\n");
            }
        }
        catch(Error e) {
            printerr(@"Could not provision repository \"$repository_file\": $(e.message)\n");
            return 241;
        }
    }

    return 0;
}


/**
 * The local path a `file://` URI points at, or null when it cannot be
 * determined (GLib handles the percent-decoding).
 */
private string? deploy_file_uri_path(string uri) {
    try {
        return Filename.from_uri(uri, null);
    }
    catch(Error e) {
        return null;
    }
}


/**
 * Recursively copies a repository tree into the context, refusing to carry
 * anything that looks like signing key material: only public artefacts (the
 * signed listing, packages, public keys) may ever enter a deploy context.
 */
private void deploy_copy_repository_tree(string source, string destination) throws Error {
    var source_dir = File.new_for_path(source);
    var destination_dir = File.new_for_path(destination);
    if(!destination_dir.query_exists()) {
        destination_dir.make_directory();
    }

    var enumerator = source_dir.enumerate_children("*", FileQueryInfoFlags.NOFOLLOW_SYMLINKS);
    while(true) {
        var info = enumerator.next_file();
        if(info == null) {
            break;
        }
        var name = info.get_name();
        if(info.get_file_type() == FileType.DIRECTORY) {
            if(name == "keys" || name == ".git") {
                continue;
            }
            deploy_copy_repository_tree(Path.build_filename(source, name), Path.build_filename(destination, name));
        }
        else if(!name.has_prefix("private-key")) {
            source_dir.get_child(name).copy(destination_dir.get_child(name), FileCopyFlags.OVERWRITE);
        }
    }
}


/**
 * Writes the minimal in-image `usm.config`: managed state under /var/usm
 * and, unless {@link spm} is {@link DeploySpm.NONE}, the system package
 * manager wired to the matching helper the installer ships so in-container
 * resolution asks the SPM before USM repositories. Hand-authored on
 * purpose — the generated image must stay independent of this machine's
 * configuration.
 */
private void deploy_write_container_config(string context_dir, DeploySpm spm) throws Error {
    var spm_section = "";
    if(spm != DeploySpm.NONE) {
        var helper = @"$(DEPLOY_USM_PREFIX)/bin/usm-spm-$(spm.shim_name())";
        spm_section = @",
    \"system_package_manager\": {
        \"query\": [\"$helper\", \"query\"],
        \"install\": [\"$helper\", \"install\"]
    }";
    }
    var config = @"{
    \"is_managed\": true,
    \"managed\": {
        \"state_path\": \"/var/usm\"
    },
    \"paths\": {
        \"lib\": \"$(spm.lib_path())\"
    }$spm_section
}
";
    FileUtils.set_data(Path.build_filename(context_dir, "usm.config"), config.data);
}


/**
 * Renders the single-stage Containerfile: ARG-before-FROM base image, USM
 * installed from the installer URL, the minimal configuration, repository
 * descriptors (plus rewritten `file://` trees), the package pre-seeded into
 * the USM cache and installed in-container, and the exec-form ENTRYPOINT.
 * A {@link spm} other than {@link DeploySpm.NONE} contributes the SPM's
 * bootstrap RUN (emerge needs none — the stage3 base carries portage).
 */
private string deploy_containerfile(string base_image, string installer_url, bool bundled_installer,
        string package_name, string version_string, string[] entrypoint, bool file_trees_provisioned,
        bool verbose_deploy, DeploySpm spm) {
    var builder = new StringBuilder();
    builder.append("# Generated by `usm manifest deploy` — regenerate rather than edit\n\n");
    builder.append_printf("ARG BASE_IMAGE=%s\n", base_image);
    builder.append("FROM ${BASE_IMAGE}\n\n");
    builder.append("# Override at build time with --build-arg USM_INSTALLER_URL=...\n");
    builder.append_printf("ARG USM_INSTALLER_URL=%s\n\n", installer_url);
    if(bundled_installer) {
        builder.append("COPY installer-local/install-usm.sh /usm-installer-local/install-usm.sh\n\n");
    }
    switch(spm) {
        case DeploySpm.DNF:
            builder.append("# DNF4 python bindings for the usm SPM helper (python3 is absent from the base image)\n");
            builder.append("RUN dnf install -y python3-dnf && dnf clean all\n\n");
            break;
        case DeploySpm.APT:
            builder.append("# curl (absent from the debian base) fetches the installer; python3-apt bindings plus the apt-file contents index serve the usm SPM helper\n");
            builder.append("RUN apt-get update && apt-get install -y curl python3 python3-apt apt-file && apt-file update && apt-get clean\n\n");
            break;
        case DeploySpm.APK:
            builder.append("# The shell SPM helper needs nothing beyond busybox; bash serves the package's manage: scripts and curl (absent from the alpine base) fetches the installer\n");
            builder.append("RUN apk add --no-cache bash curl\n\n");
            break;
        case DeploySpm.EMERGE:
        case DeploySpm.NONE:
            break;
    }
    builder.append("# Install USM. The installer is downloaded to a real file first because it\n");
    builder.append("# extracts its payload relative to $0, so `curl ... | sh` cannot work.\n");
    builder.append("RUN curl -fsSL \"${USM_INSTALLER_URL}\" -o /tmp/install-usm.sh \\\n");
    builder.append(" && bash /tmp/install-usm.sh -y \\\n");
    builder.append(" && rm -f /tmp/install-usm.sh\n\n");
    builder.append("COPY usm.config /etc/usm/usm.config\n\n");
    builder.append("COPY repos/ /etc/usm/repos.d/\n");
    if(file_trees_provisioned) {
        builder.append("COPY repo-trees/ /usr/share/usm-repos/\n");
    }
    builder.append("\n");
    builder.append_printf("COPY package/package.usmc /var/usm/packages/%s-%s/package.usmc\n", package_name, version_string);
    builder.append_printf("RUN mkdir -p /var/usm/lists /var/usm/installed && usm install %s%s\n\n", package_name, verbose_deploy ? " --verbose" : "");
    builder.append_printf("ENTRYPOINT %s\n", deploy_entrypoint_json(entrypoint));
    return builder.str;
}


/** The exec-form JSON array for the generated ENTRYPOINT. */
private string deploy_entrypoint_json(string[] entrypoint) {
    var words = new Vector<string>();
    foreach(var word in entrypoint) {
        words.add("\"" + word.replace("\\", "\\\\").replace("\"", "\\\"") + "\"");
    }
    return @"[$(words.to_string(w => w, ", "))]";
}


/**
 * A podman-safe tag chunk: tag syntax only allows `[A-Za-z0-9_.-]`, so
 * anything else (usm release suffixes like `+` in versions, for instance)
 * maps to a dash. Artifact filenames keep the unsanitised form.
 */
private string deploy_tag_chunk(string chunk) {
    var builder = new StringBuilder();
    for(int index = 0; index < chunk.length; index++) {
        var character = chunk[index];
        var valid = (character >= 'a' && character <= 'z')
            || (character >= 'A' && character <= 'Z')
            || (character >= '0' && character <= '9')
            || character == '_' || character == '.' || character == '-';
        builder.append_unichar(valid ? character : '-');
    }
    return builder.str;
}