using Astralis;
using Json;

namespace UsmWeb {

    /** Errors raised by a malformed `"usm-web"` configuration section. */
    public errordomain UsmWebError {
        /** The section (or its `installer` object) is structurally invalid */
        INVALID_CONFIGURATION,
    }

    /** How the "Install USM" instructions source the installer script. */
    public enum InstallerSource {
        /** No installer configured; the homepage omits the install block. */
        NONE,
        /** The installer lives at an external URL; instructions link out. */
        URL,
        /** The installer is a local file this app serves at /install-usm.sh. */
        PATH;

        /** The wire/display name used as the homepage's `installer_mode`. */
        public string to_string() {
            switch (this) {
                case InstallerSource.NONE:
                    return "none";
                case InstallerSource.URL:
                    return "url";
                case InstallerSource.PATH:
                    return "path";
                default:
                    assert_not_reached();
            }
        }
    }

    /**
     * The `"usm-web"` section of web-config.json.
     *
     * ```json
     * {
     *   "usm-web": {
     *     "repo": "/repo",
     *     "repositories": ["web-stack", "extra"],
     *     "installer": { "path": "install-usm.sh" },
     *     "base_url": "https://repo.example.com/",
     *     "name": "My repositories"
     *   }
     * }
     * ```
     *
     * `repo` is the parent directory holding the repositories this app
     * serves: each is a subdirectory containing a `.usmr` and a `public/`
     * directory. A relative value resolves against the directory of the
     * config file that declared it. It applies only when neither the
     * `--repo` argument nor `USM_WEB_REPO_DIR` is given (precedence:
     * argument > environment > config > `/repo`).
     *
     * `repositories` optionally names the subdirectories to serve (in that
     * order); when absent (or empty) every subdirectory containing a `.usmr`
     * is discovered by scanning. A single-repository layout with the `.usmr`
     * directly inside `repo` is still served as one repository.
     *
     * `installer` carries exactly one of `url` (an external location the
     * homepage links to) or `path` (a file the app serves itself at
     * {@link InstallerScriptEndpoint}); a relative `path` resolves against
     * the directory of the config file that declared it. `base_url` overrides
     * the request-derived repository base (normalised to a trailing slash)
     * and `name` overrides the overview title.
     */
    public class UsmWebConfig : GLib.Object {

        /** The configured installer source, or {@link InstallerSource.NONE}. */
        public InstallerSource installer { get; private set; default = InstallerSource.NONE; }

        /** The external installer URL (`url` mode), or null. */
        public string? installer_url { get; private set; }

        /** The absolute installer script path (`path` mode), or null. */
        public string? installer_path { get; private set; }

        /** The base-URL override (trailing slash), or null to derive per request. */
        public string? base_url { get; private set; }

        /** The overview-title override, or null for the default heading. */
        public string? display_name { get; private set; }

        /**
         * The parent directory holding the served repositories (each a
         * subdirectory with a `.usmr` and `public/`).
         */
        public string repo_dir { get; private set; default = "/repo"; }

        /**
         * The explicitly listed repository subdirectories under
         * {@link repo_dir}; empty means scan for every subdirectory holding
         * a `.usmr`.
         */
        public string[] repositories { get; private set; default = new string[0]; }

        /**
         * Reads the section from the loaded {@link WebConfig}, re-parsing the
         * contributing files with json-glib so the nested `installer` object
         * and the `repositories` array are readable and a relative
         * `path`/`repo` resolves against the config file that declared it
         * (later files win, mirroring WebConfig layering). {@link repo_dir}
         * wins when given; otherwise the config's `repo` applies, falling
         * back to `/repo`.
         */
        public static UsmWebConfig load(WebConfig config, string? repo_dir = null) throws Error {
            var result = new UsmWebConfig();

            string? declared_path = null;
            string declaring_dir = Environment.get_current_dir();
            string? declared_repo = null;
            string repo_declaring_dir = declaring_dir;
            string[]? declared_repositories = null;
            foreach (var file in config.get_loaded_files()) {
                var section = read_section(file);
                if (section == null) {
                    continue;
                }
                var obj = (!)section;

                result.display_name = read_string_member(obj, "name") ?? result.display_name;

                var base_url = read_string_member(obj, "base_url");
                if (base_url != null) {
                    result.base_url = normalise_base((!)base_url);
                }

                var repo = read_string_member(obj, "repo");
                if (repo != null) {
                    declared_repo = repo;
                    repo_declaring_dir = GLib.Path.get_dirname((!)file);
                }

                var repositories = read_string_array_member(obj, "repositories");
                if (repositories != null) {
                    declared_repositories = repositories;
                }

                result.installer_url = read_string_member(obj, "installer", "url") ?? result.installer_url;
                declared_path = read_string_member(obj, "installer", "path") ?? declared_path;
                if (declared_path != null) {
                    declaring_dir = GLib.Path.get_dirname((!)file);
                }
            }

            if (repo_dir != null) {
                result.repo_dir = (!)repo_dir;
            }
            else if (declared_repo != null) {
                var repo = (!)declared_repo;
                result.repo_dir = GLib.Path.is_absolute(repo)
                    ? repo : GLib.Path.build_filename(repo_declaring_dir, repo);
            }

            if (declared_repositories != null) {
                result.repositories = (!)declared_repositories;
            }

            if (result.installer_url != null && declared_path != null) {
                throw new UsmWebError.INVALID_CONFIGURATION(
                    "usm-web.installer: provide exactly one of \"url\" or \"path\", not both");
            }
            if (result.installer_url != null) {
                result.installer = InstallerSource.URL;
            } else if (declared_path != null) {
                var path = (!)declared_path;
                result.installer_path = GLib.Path.is_absolute(path)
                    ? path : GLib.Path.build_filename(declaring_dir, path);
                result.installer = InstallerSource.PATH;
            }

            return result;
        }

        private static string normalise_base(string base_url) {
            return base_url.has_suffix("/") ? base_url : base_url + "/";
        }

        /** The root object of `path`'s `"usm-web"` member, or null when absent. */
        private static Json.Object? read_section(string path) {
            try {
                var parser = new Parser();
                parser.load_from_file(path);
                var root = parser.get_root().get_object();
                return root.has_member("usm-web") ? root.get_member("usm-web").get_object() : null;
            } catch (Error e) {
                return null;
            }
        }

        private static string? read_string_member(Json.Object obj, string member, string? nested = null) {
            if (!obj.has_member(member)) {
                return null;
            }
            var node = obj.get_member(member);
            if (nested != null) {
                if (node.get_node_type() != NodeType.OBJECT) {
                    return null;
                }
                var inner = node.get_object();
                if (!inner.has_member(nested)) {
                    return null;
                }
                node = inner.get_member(nested);
            }
            return node.get_node_type() == NodeType.VALUE ? node.get_string() : null;
        }

        /** The string values of `member` (when it is a JSON array), or null. */
        private static string[]? read_string_array_member(Json.Object obj, string member) {
            if (!obj.has_member(member)) {
                return null;
            }
            var node = obj.get_member(member);
            if (node.get_node_type() != NodeType.ARRAY) {
                return null;
            }
            var array = node.get_array();
            var values = new string[0];
            for (var i = 0; i < array.get_length(); i++) {
                var element = array.get_element(i);
                if (element.get_node_type() == NodeType.VALUE) {
                    values += element.get_string();
                }
            }
            return values;
        }
    }
}