class FileSystem {
    constructor() {
        this._root = {
            personal: {
                steam: {
                    type: "link",
                    link: "https://steamcommunity.com/id/Waflix"
                },
                nukapedia: {
                    type: "link",
                    link: "http://fallout.wikia.com/wiki/User:FDekker"
                }
            },
            projects: {
                minor: {
                    dice: {
                        type: "link",
                        link: "https://fwdekker.com/dice"
                    }
                },
                randomness: {
                    type: "link",
                    link: "https://github.com/FWDekker/intellij-randomness"
                },
                schaapi: {
                    type: "link",
                    link: "http://cafejojo.org/schaapi"
                }
            },
            social: {
                github: {
                    type: "link",
                    link: "https://github.com/FWDekker/"
                },
                stackoverflow: {
                    type: "link",
                    link: "https://stackoverflow.com/u/3307872"
                },
                linkedin: {
                    type: "link",
                    link: "https://www.linkedin.com/in/fwdekker/"
                }
            },
            "resume.pdf": {
                type: "link",
                link: "https://fwdekker.com/resume.pdf"
            }
        };
        this.pwd = "/";


        const visited = [];
        const queue = [this._root];

        this._root["."] = this._root;
        this._root[".."] = this._root;

        while (queue.length !== 0) {
            const next = queue.pop();
            if (visited.indexOf(next) >= 0) {
                continue;
            }

            visited.push(next);
            for (const key in next) {
                if (key === "." || key === ".." || FileSystem.isFile(next[key])) {
                    continue;
                }

                next[key]["."] = next[key];
                next[key][".."] = next;
                queue.push(next[key]);
            }
        }
    }


    _absolutePath(path) {
        if (path.startsWith("/")) {
            return path;
        } else {
            return `${this.pwd}/${path}`;
        }
    }

    _childPath(path) {
        const childPath = this._normalisePath(path).split("/").slice(0, -1).slice(-1).join("/");
        return (childPath === "")
            ? "."
            : childPath;
    }

    _executeForEach(inputs, fun) {
        const outputs = [];

        inputs.forEach(input => {
            const output = fun(input);

            if (output !== "") {
                outputs.push(output);
            }
        });

        return outputs.join("\n");
    }

    _getFile(path) {
        path = this._normalisePath(path);

        let file = this._root;
        path.split("/").forEach(part => {
            if (part === "") {
                return;
            }
            if (file === undefined) {
                return;
            }

            file = file[part];
        });

        return file;
    }

    _normalisePath(path) {
        return FileSystem._sanitisePath(this._absolutePath(path));
    }

    _parentPath(path) {
        const parentPath = this._normalisePath(path).split("/").slice(0, -2).join("/");
        return (parentPath === "")
            ? "/"
            : parentPath;
    }

    static _sanitisePath(path) {
        const selfRegex = /\/\.\//; // Match "./"
        const upRegex = /(\/+)([^./]+)(\/+)(\.\.)(\/+)/; // Match "/directory/../"
        const doubleRegex = /\/{2,}/; // Match "///"

        return `${path}/`
            .replaceAll(selfRegex, "/")
            .replaceAll(upRegex, "/")
            .replaceAll(doubleRegex, "/")
            .toString();
    }


    /**
     * Returns true iff {@code file} represents a directory.
     *
     * @param file {Object} an object from the file system
     * @returns {boolean} true iff {@code file} represents a directory
     */
    static isDirectory(file) {
        return (file !== undefined && typeof file.type !== "string");
    }

    /**
     * Returns true iff {@code file} represents a file.
     *
     * @param file {Object} an object from the file system
     * @returns {boolean} true iff {@code file} represents a file
     */
    static isFile(file) {
        return (file !== undefined && typeof file.type === "string");
    }


    /**
     * Changes the current directory to {@code path}, if it exists.
     *
     * @param path the absolute or relative path to change the current directory to
     * @returns {string} an empty string if the change was successful, or an error message explaining what went wrong
     */
    cd(path) {
        if (path === undefined) {
            return "";
        }

        const file = this._getFile(path);
        if (file === undefined || !FileSystem.isDirectory(file)) {
            return `The directory '${path}' does not exist`;
        }

        this.pwd = this._normalisePath(path);
        this.files = file;

        return "";
    }

    /**
     * Returns the directory at {@code path}, or the current directory if no path is given.
     *
     * @param path {string} the absolute or relative path to the directory to return
     * @returns {Object} the directory at {@code path}, or the current directory if no path is given
     */
    ls(path) {
        path = (path || this.pwd);

        const files = this._getFile(path);
        if (files === undefined) {
            return `The directory '${path}' does not exist`;
        }

        const dirList = [];
        const fileList = [];

        Object.keys(files).sort().forEach(fileName => {
            const file = files[fileName];

            if (FileSystem.isFile(file)) {
                fileList.push(fileToString(fileName, file));
            } else if (FileSystem.isDirectory(file)) {
                dirList.push(`${fileName}/`);
            } else {
                throw `${fileName} is neither a file nor a directory!`;
            }
        });

        return dirList.concat(fileList).join("\n");
    }

    /**
     * Creates an empty directory in the file system.
     *
     * @param path {string} the absolute or relative path to the directory to create
     * @returns {string} an empty string if the removal was successful, or a message explaining what went wrong
     */
    mkdir(path) {
        const parentDirName = this._parentPath(path);
        const childDirName = this._childPath(path);

        const parentDir = this._getFile(parentDirName);
        if (!FileSystem.isDirectory(parentDir)) {
            return `The directory '${parentDirName}' does not exist`;
        }
        if (parentDir[childDirName] !== undefined) {
            return `The directory '${childDirName}' already exists`;
        }

        parentDir[childDirName] = {};
        parentDir[childDirName]["."] = parentDir[childDirName];
        parentDir[childDirName][".."] = parentDir;
        return "";
    }

    mkdirs(paths) {
        return this._executeForEach(paths, this.mkdir.bind(this));
    }

    /**
     * Resets navigation in the file system.
     */
    reset() {
        this.pwd = "/";
        this.files = this._root;
    }

    /**
     * Removes a file from the file system.
     *
     * @param path {string} the absolute or relative path to the file to be removed
     * @param force {boolean} true if no warnings should be given if removal is unsuccessful
     * @returns {string} an empty string if the removal was successful, or a message explaining what went wrong
     */
    rm(path, force) {
        const dirName = this._parentPath(path);
        const fileName = this._childPath(path);

        const dir = this._getFile(dirName);
        if (!FileSystem.isDirectory(dir)) {
            return force
                ? ""
                : `The directory '${dirName}' does not exist`;
        }

        const file = dir[fileName];
        if (!FileSystem.isFile(file)) {
            return force
                ? ""
                : `The file '${fileName}' does not exist`;
        }

        delete dir[fileName];
        return "";
    }

    rms(paths, force) {
        return this._executeForEach(paths, path => {
            this.rm(path, force);
        });
    }

    /**
     * Removes a directory from the file system.
     *
     * @param path {string} the absolute or relative path to the directory to be removed
     * @param force {boolean} true iff the directory should be removed regardless of whether it is empty
     * @returns {string} an empty string if the removal was successful, or a message explaining what went wrong
     */
    rmdir(path, force) {
        force = (force || false);

        if (this._normalisePath(path) === "/") {
            if (!force && Object.keys(this._root).length > 1) {
                return `The directory is not empty.`;
            } else {
                this._root = {};
                this._root["."] = this._root;
                return ``;
            }
        }

        const parentDirName = this._parentPath(path);
        const childDirName = this._childPath(path);

        const parentDir = this._getFile(parentDirName);
        if (!FileSystem.isDirectory(parentDir)) {
            return force
                ? ""
                : `The directory '${parentDirName}' does not exist`;
        }

        const childDir = parentDir[childDirName];
        if (!FileSystem.isDirectory(childDir)) {
            return force
                ? ""
                : `The directory '${childDirName}' does not exist`;
        }
        if (!force && Object.keys(childDir).length > 2) {
            return `The directory is not empty`;
        }

        delete parentDir[childDirName];
        return "";
    }

    rmdirs(paths, force) {
        return this._executeForEach(paths, path => {
            return this.rmdir(path, force);
        });
    }
}


const fileToString = function (fileName, file) {
    switch (file.type) {
        case "link":
            return `<a href="${file.link}">${fileName}</a>`;
        default:
            return fileName;
    }
};