const DEFAULTS = {
    INITIAL_RENDER_COUNT: 80,
    LOAD_COUNT: 20,
    instances: new Map(),
};

exports.filter = (value, list, opts) => {
    /*
        This is used by the main object (see `create`),
        but we split it out to make it a bit easier
        to test.
    */
    if (opts.filter.filterer) {
        return opts.filter.filterer(list, value);
    }

    const predicate = opts.filter.predicate;

    return list.filter(function (item) {
        return predicate(item, value);
    });
};

exports.validate_filter = (opts) => {
    if (!opts.filter) {
        return;
    }
    if (opts.filter.predicate) {
        if (typeof opts.filter.predicate !== 'function') {
            blueslip.error('Filter predicate function is missing.');
            return;
        }
        if (opts.filter.filterer) {
            blueslip.error('Filterer and predicate are mutually exclusive.');
            return;
        }
    } else {
        if (typeof opts.filter.filterer !== 'function') {
            blueslip.error('Filter filterer function is missing.');
            return;
        }
    }
};

// @params
// container: jQuery object to append to.
// list: The list of items to progressively append.
// opts: An object of random preferences.
exports.create = function ($container, list, opts) {
    // this memoizes the results and will return a previously invoked
    // instance
    if (opts.name && DEFAULTS.instances.get(opts.name)) {
        const old_widget = DEFAULTS.instances.get(opts.name);

        old_widget.data(list);
        old_widget.redraw();

        return old_widget;
    }

    const meta = {
        sorting_function: null,
        prop: null,
        sorting_functions: new Map(),
        generic_sorting_functions: new Map(),
        offset: 0,
        list: list,
        filtered_list: list,

    };

    function filter_list(value) {
        meta.filtered_list = exports.filter(value, meta.list, opts);
    }

    if (!opts) {
        return;
    }
    exports.validate_filter(opts);

    const widget = {};

    // Reads the provided list (in the scope directly above)
    // and renders the next block of messages automatically
    // into the specified container.
    widget.render = function (how_many) {
        const load_count = how_many || DEFAULTS.LOAD_COUNT;

        // Stop once the offset reaches the length of the original list.
        if (meta.offset >= meta.filtered_list.length) {
            return;
        }

        const slice = meta.filtered_list.slice(meta.offset, meta.offset + load_count);

        const finish = blueslip.start_timing('list_render ' + opts.name);
        let html = "";
        for (const item of slice) {
            let _item = opts.modifier(item);

            // if valid jQuery selection, attempt to grab all elements within
            // and string them together into a giant outerHTML fragment.
            if (_item.constructor === jQuery) {
                _item = (function ($nodes) {
                    let html = "";
                    $nodes.each(function () {
                        if (this.nodeType === 1) {
                            html += this.outerHTML;
                        }
                    });

                    return html;
                }(_item));
            }

            // if is a valid element, get the outerHTML.
            if (_item instanceof Element) {
                _item = _item.outerHTML;
            }

            // append the HTML or nothing if corrupt (null, undef, etc.).
            html += _item || "";
        }

        finish();

        $container.append($(html));
        meta.offset += load_count;
    };

    // Fills the container with an initial batch of items.
    // Needs to be enough to exceed the max height, so that a
    // scrollable area is created.
    widget.redraw = function () {
        widget.clear();
        widget.render(DEFAULTS.INITIAL_RENDER_COUNT);
    };

    widget.filter = function (map_function) {
        meta.filtered_list = meta.list(map_function);
    };

    // reset the data associated with a list. This is so that instead of
    // initializing a new progressive list render instance, you can just
    // update the data of an existing one.
    widget.data = function (...args) {
        // if no args are provided then just return the existing data.
        // this interface is similar to how many jQuery functions operate,
        // where a call to the method without data returns the existing data.
        if (args.length === 0) {
            return meta.list;
        }
        const [data] = args;

        if (Array.isArray(data)) {
            meta.list = data;
            meta.filtered_list = data;

            if (opts.filter && opts.filter.element) {
                const value = $(opts.filter.element).val().toLocaleLowerCase();
                filter_list(value);
            }

            widget.clear();

            return;
        }

        blueslip.warn("The data object provided to the progressive" +
                          " list render is invalid");
    };

    widget.clear = function () {
        $container.html("");
        meta.offset = 0;
    };

    widget.reverse = function () {
        meta.filtered_list.reverse();
        widget.redraw();
    };

    // the sorting function is either the function or string that calls the
    // function to sort the list by. The prop is used for generic functions
    // that can be called to sort with a particular prop.

    // the `map` will normalize the values with a function you provide to make
    // it easier to sort with.

    // `do_not_display` will signal to not update the DOM, likely because in
    // the next function it will be updated in the DOM.
    widget.sort = function (sorting_function, prop, do_not_display) {
        meta.prop = prop;

        if (typeof sorting_function === "function") {
            meta.sorting_function = sorting_function;
        } else if (typeof sorting_function === "string") {
            if (typeof prop === "string") {
                /* eslint-disable max-len */
                meta.sorting_function = meta.generic_sorting_functions.get(sorting_function)(prop);
            } else {
                meta.sorting_function = meta.sorting_functions.get(sorting_function);
            }
        }

        // we do not want to sort if we are just looking to reverse
        // by calling with no sorting_function
        if (meta.sorting_function) {
            meta.filtered_list = meta.filtered_list.sort(meta.sorting_function);
        }

        if (!do_not_display) {
            // clear and re-initialize the list with the newly filtered subset
            // of items.
            widget.redraw();

            if (opts.filter && opts.filter.onupdate) {
                opts.filter.onupdate();
            }
        }
    };

    // generic sorting functions are ones that will use a specified prop
    // and perform a sort on it with the given sorting function.
    widget.add_generic_sort_function = function (name, sorting_function) {
        meta.generic_sorting_functions.set(name, sorting_function);
    };

    widget.remove_sort = function () {
        meta.sorting_function = false;
    };

    widget.set_up_event_handlers = function () {
        let $nearestScrollingContainer = $container;

        while ($nearestScrollingContainer.length) {
            if ($nearestScrollingContainer.is("body, html")) {
                blueslip.warn("Please wrap progressive scrolling lists in an element with 'max-height' attribute. Error found in:\n" + blueslip.preview_node($container));
                break;
            }

            if ($nearestScrollingContainer.css("max-height") !== "none") {
                break;
            }

            $nearestScrollingContainer = $nearestScrollingContainer.parent();
        }

        // on scroll of the nearest scrolling container, if it hits the bottom
        // of the container then fetch a new block of items and render them.
        $nearestScrollingContainer.scroll(function () {
            if (this.scrollHeight - (this.scrollTop + this.clientHeight) < 10) {
                widget.render();
            }
        });

        if (opts.parent_container) {
            opts.parent_container.on("click", "[data-sort]", exports.handle_sort);
        }

        if (opts.filter && opts.filter.element) {
            opts.filter.element.on(opts.filter.event || "input", function () {
                const value = this.value.toLocaleLowerCase();

                // run the sort algorithm that was used last, which is done
                // by passing `undefined` -- which will make it use the params
                // from the last sort.
                // it will then also not run an update in the DOM (because we
                // pass `true`), because it will update regardless below at
                // `widget.redraw()`.
                widget.sort(undefined, meta.prop, true);
                filter_list(value);

                // clear and re-initialize the list with the newly filtered subset
                // of items.
                widget.redraw();

                if (opts.filter.onupdate) {
                    opts.filter.onupdate();
                }
            });
        }
    };

    // add built-in generic sort functions.
    widget.add_generic_sort_function("alphabetic", function (prop) {
        return function (a, b) {
            // The conversion to uppercase helps make the sorting case insensitive.
            const str1 = a[prop].toUpperCase();
            const str2 = b[prop].toUpperCase();

            if (str1 === str2) {
                return 0;
            } else if (str1 > str2) {
                return 1;
            }

            return -1;
        };
    });

    widget.add_generic_sort_function("numeric", function (prop) {
        return function (a, b) {
            if (parseFloat(a[prop]) > parseFloat(b[prop])) {
                return 1;
            } else if (parseFloat(a[prop]) === parseFloat(b[prop])) {
                return 0;
            }

            return -1;
        };
    });

    widget.set_up_event_handlers();

    if (opts.sort_fields) {
        for (const [name, sorting_function] of Object.entries(opts.sort_fields)) {
            meta.sorting_functions.set(name, sorting_function);
        }
    }

    if (opts.init_sort) {
        widget.sort(...opts.init_sort);
    } else {
        widget.redraw();
    }

    // Save the instance for potential future retrieval if a name is provided.
    if (opts.name) {
        DEFAULTS.instances.set(opts.name, widget);
    }

    return widget;
};

exports.get = function (name) {
    return DEFAULTS.instances.get(name) || false;
};

exports.handle_sort = function () {
    /*
        one would specify sort parameters like this:
            - name => sort alphabetic.
            - age  => sort numeric.

        you MUST specify the `data-list-render` in the `.progressive-table-wrapper`

        <div class="progressive-table-wrapper" data-list-render="some-list">
            <table>
                <thead>
                    <th data-sort="alphabetic" data-sort-prop="name"></th>
                    <th data-sort="numeric" data-sort-prop="age"></th>
                </thead>
                <tbody></tbody>
            </table>
        </div>
        */
    const $this = $(this);
    const sort_type = $this.data("sort");
    const prop_name = $this.data("sort-prop");
    const list_name = $this.closest(".progressive-table-wrapper").data("list-render");

    const list = exports.get(list_name);

    if (!list) {
        blueslip.error("Error. This `.progressive-table-wrapper` has no `data-list-render` attribute.");
        return;
    }

    if ($this.hasClass("active")) {
        if (!$this.hasClass("descend")) {
            $this.addClass("descend");
        } else {
            $this.removeClass("descend");
        }

        list.reverse();
        // Table has already been sorted by this property; do not re-sort.
        return;
    }

    // if `prop_name` is defined, it will trigger the generic codepath,
    // and not if it is undefined.
    list.sort(sort_type, prop_name);

    $this.siblings(".active").removeClass("active");
    $this.addClass("active");
};

window.list_render = exports;