import { approxEqual, memo, notUndefined } from "./utils";

export * from "./utils";

//

type ScrollDirection = "forward" | "backward";

type ScrollAlignment = "start" | "center" | "end" | "auto";

type ScrollBehavior = "auto" | "smooth";

export interface ScrollToOptions {
    align?: ScrollAlignment;
    behavior?: ScrollBehavior;
}

type ScrollToOffsetOptions = ScrollToOptions;

type ScrollToIndexOptions = ScrollToOptions;

export interface Range {
    startIndex: number;
    endIndex: number;
    overscan: number;
    count: number;
}

type Key = number | string;

export interface VirtualItem {
    key: Key;
    id: number | string;
    index: number;
    start: number;
    end: number;
    size: number;
    lane: number;
}

interface Rect {
    width: number;
    height: number;
}

//

export const defaultKeyExtractor = (index: number) => index;

export const defaultRangeExtractor = (range: Range) => {
    const start = Math.max(range.startIndex - range.overscan, 0);
    const end = Math.min(range.endIndex + range.overscan, range.count - 1);

    const arr = [];

    for (let i = start; i <= end; i++) {
        arr.push(i);
    }

    return arr;
};

export const observeElementRect = <T extends Element>(
    instance: Virtualizer<T, any>,
    cb: (rect: Rect) => void,
) => {
    const element = instance.scrollElement;
    if (!element) {
        return;
    }

    const handler = (rect: Rect) => {
        const { width, height } = rect;
        cb({ width: Math.round(width), height: Math.round(height) });
    };

    handler(element.getBoundingClientRect());

    const observer = new ResizeObserver((entries) => {
        const entry = entries[0];
        if (entry?.borderBoxSize) {
            const box = entry.borderBoxSize[0];
            if (box) {
                handler({ width: box.inlineSize, height: box.blockSize });
                return;
            }
        }
        handler(element.getBoundingClientRect());
    });

    observer.observe(element, { box: "border-box" });

    return () => {
        observer.unobserve(element);
    };
};

export const observeWindowRect = (instance: Virtualizer<Window, any>, cb: (rect: Rect) => void) => {
    const element = instance.scrollElement;
    if (!element) {
        return;
    }

    const handler = () => {
        cb({ width: element.innerWidth, height: element.innerHeight });
    };
    handler();

    element.addEventListener("resize", handler, {
        passive: true,
    });

    return () => {
        element.removeEventListener("resize", handler);
    };
};

export const observeElementOffset = <T extends Element>(
    instance: Virtualizer<T, any>,
    cb: (offset: number) => void,
) => {
    const element = instance.scrollElement;
    if (!element) {
        return;
    }

    const handler = () => {
        cb(instance.getElementOffset(instance));
    };
    handler();

    element.addEventListener("scroll", handler, {
        passive: true,
    });

    return () => {
        element.removeEventListener("scroll", handler);
    };
};

export const observeWindowOffset = (
    instance: Virtualizer<Window, any>,
    cb: (offset: number) => void,
) => {
    const element = instance.scrollElement;
    if (!element) {
        return;
    }

    const handler = () => {
        cb(instance.getElementOffset(instance));
    };
    handler();

    element.addEventListener("scroll", handler, {
        passive: true,
    });

    return () => {
        element.removeEventListener("scroll", handler);
    };
};

export const measureElement = <TItemElement extends Element>(
    element: TItemElement,
    entry: ResizeObserverEntry | undefined,
    instance: Virtualizer<any, TItemElement>,
) => {
    if (entry?.borderBoxSize) {
        const box = entry.borderBoxSize[0];
        if (box) {
            const size = Math.round(box[instance.options.horizontal ? "inlineSize" : "blockSize"]);
            return size;
        }
    }
    return Math.round(
        element.getBoundingClientRect()[instance.options.horizontal ? "width" : "height"],
    );
};

export const windowScroll = <T extends Window>(
    offset: number,
    { adjustments = 0, behavior }: { adjustments?: number; behavior?: ScrollBehavior },
    instance: Virtualizer<T, any>,
) => {
    const toOffset = offset + adjustments;

    instance.scrollElement?.scrollTo?.({
        [instance.options.horizontal ? "left" : "top"]: toOffset,
        behavior,
    });
};

export const elementScroll = <T extends Element>(
    offset: number,
    { adjustments = 0, behavior }: { adjustments?: number; behavior?: ScrollBehavior },
    instance: Virtualizer<T, any>,
) => {
    const toOffset = offset + adjustments;

    instance.scrollElement?.scrollTo?.({
        [instance.options.horizontal ? "left" : "top"]: toOffset,
        behavior,
    });
};

export interface VirtualizerOptions<
    TScrollElement extends Element | Window,
    TItemElement extends Element,
> {
    // Required from the user
    count: number;
    getScrollElement: () => TScrollElement | null;
    estimateSize: (index: number) => number;

    // Required from the framework adapter (but can be overridden)
    scrollToFn: (
        offset: number,
        options: { adjustments?: number; behavior?: ScrollBehavior },
        instance: Virtualizer<TScrollElement, TItemElement>,
    ) => void;
    observeElementRect: (
        instance: Virtualizer<TScrollElement, TItemElement>,
        cb: (rect: Rect) => void,
    ) => undefined | (() => void);
    observeElementOffset: (
        instance: Virtualizer<TScrollElement, TItemElement>,
        cb: (offset: number) => void,
    ) => undefined | (() => void);

    // Optional
    debug?: any;
    initialRect?: Rect;
    onChange?: (instance: Virtualizer<TScrollElement, TItemElement>, sync: boolean) => void;
    measureElement?: (
        element: TItemElement,
        entry: ResizeObserverEntry | undefined,
        instance: Virtualizer<TScrollElement, TItemElement>,
    ) => number;
    getElementOffset?: (instance: Virtualizer<TScrollElement, TItemElement>) => number;
    overscan?: number;
    horizontal?: boolean;
    paddingStart?: number;
    paddingEnd?: number;
    scrollPaddingStart?: number;
    scrollPaddingEnd?: number;
    initialOffset?: number;
    getItemKey?: (index: number) => Key;
    rangeExtractor?: (range: Range) => number[];
    scrollMargin?: number;
    scrollingDelay?: number;
    indexAttribute?: string;
    initialMeasurementsCache?: VirtualItem[];
    lanes?: number;
}

export class Virtualizer<TScrollElement extends Element | Window, TItemElement extends Element> {
    // biome-ignore lint/suspicious/noConfusingVoidType: <explanation>
    private unsubs: (void | (() => void))[] = [];
    options!: Required<VirtualizerOptions<TScrollElement, TItemElement>>;
    scrollElement: TScrollElement | null = null;
    isScrolling = false;
    private isScrollingTimeoutId: ReturnType<typeof setTimeout> | null = null;
    private scrollToIndexTimeoutId: ReturnType<typeof setTimeout> | null = null;
    measurementsCache: VirtualItem[] = [];
    private itemSizeCache = new Map<Key, number>();
    private pendingMeasuredCacheIndexes: number[] = [];
    scrollRect: Rect;
    scrollOffset: number;
    scrollDirection: ScrollDirection | null = null;
    private scrollAdjustments = 0;
    measureElementCache = new Map<Key, TItemElement>();
    private observer = (() => {
        let _ro: ResizeObserver | null = null;

        const get = () => {
            if (_ro) {
                return _ro;
            }
            if (typeof ResizeObserver !== "undefined") {
                // biome-ignore lint/suspicious/noAssignInExpressions: <explanation>
                return (_ro = new ResizeObserver((entries) => {
                    entries.forEach((entry) => {
                        this._measureElement(entry.target as TItemElement, entry);
                    });
                }));
            }
            return null;
        };

        return {
            disconnect: () => get()?.disconnect(),
            observe: (target: Element) => get()?.observe(target, { box: "border-box" }),
            unobserve: (target: Element) => get()?.unobserve(target),
        };
    })();
    range: { startIndex: number; endIndex: number } | null = null;

    constructor(opts: VirtualizerOptions<TScrollElement, TItemElement>) {
        this.setOptions(opts);
        this.scrollRect = this.options.initialRect;
        this.scrollOffset = this.options.initialOffset;
        this.measurementsCache = this.options.initialMeasurementsCache;
        this.measurementsCache.forEach((item) => {
            this.itemSizeCache.set(item.key, item.size);
        });

        this.maybeNotify();
        if (this.options.getElementOffset) this.getElementOffset = this.options.getElementOffset;
    }
    getElementOffset(instance: Virtualizer<TScrollElement, TItemElement>) {
        if (instance.scrollElement === null) throw Error(" ScrollElement Void");
        if (instance.scrollElement instanceof Window) {
            return Math.abs(
                instance.scrollElement[instance.options.horizontal ? "scrollX" : "scrollY"],
            );
        }
        // 反向列表的数值是负数，所以需要进行正数操作
        return Math.abs(
            instance.scrollElement[instance.options.horizontal ? "scrollLeft" : "scrollTop"],
        );
    }

    setOptions = (opts: VirtualizerOptions<TScrollElement, TItemElement>) => {
        Object.entries(opts).forEach(([key, value]) => {
            if (typeof value === "undefined") Reflect.deleteProperty(opts, key);
        });
        /** @ts-ignore */
        this.options = {
            debug: false,
            initialOffset: 0,
            overscan: 1,
            paddingStart: 0,
            paddingEnd: 0,
            scrollPaddingStart: 0,
            scrollPaddingEnd: 0,
            horizontal: false,
            getItemKey: defaultKeyExtractor,
            rangeExtractor: defaultRangeExtractor,
            onChange: () => {},
            measureElement,
            initialRect: { width: 0, height: 0 },
            scrollMargin: 0,
            scrollingDelay: 150,
            indexAttribute: "data-index",
            initialMeasurementsCache: [],
            lanes: 1,
            ...opts,
        };
    };

    private notify = (sync: boolean) => {
        this.options.onChange?.(this, sync);
    };

    private maybeNotify = memo(
        () => {
            this.calculateRange();

            return [
                this.isScrolling,
                this.range ? this.range.startIndex : null,
                this.range ? this.range.endIndex : null,
            ];
        },
        (isScrolling) => {
            this.notify(isScrolling);
        },
        {
            key: process.env.NODE_ENV !== "production" && "maybeNotify",
            debug: () => this.options.debug,
            initialDeps: [
                this.isScrolling,
                this.range ? this.range.startIndex : null,
                this.range ? this.range.endIndex : null,
            ] as [boolean, number | null, number | null],
        },
    );

    private cleanup = () => {
        this.unsubs.filter(Boolean).forEach((d) => d!());
        this.unsubs = [];
        this.scrollElement = null;
    };

    _didMount = () => {
        this.measureElementCache.forEach(this.observer.observe);
        return () => {
            this.observer.disconnect();
            this.cleanup();
        };
    };

    _willUpdate = () => {
        const scrollElement = this.options.getScrollElement();

        if (this.scrollElement !== scrollElement) {
            this.cleanup();

            this.scrollElement = scrollElement;

            this._scrollToOffset(this.scrollOffset, {
                adjustments: undefined,
                behavior: undefined,
            });

            this.unsubs.push(
                this.options.observeElementRect(this, (rect) => {
                    this.scrollRect = rect;
                    this.maybeNotify();
                }),
            );

            this.unsubs.push(
                this.options.observeElementOffset(this, (offset) => {
                    this.scrollAdjustments = 0;

                    if (this.scrollOffset === offset) {
                        return;
                    }

                    if (this.isScrollingTimeoutId !== null) {
                        clearTimeout(this.isScrollingTimeoutId);
                        this.isScrollingTimeoutId = null;
                    }

                    this.isScrolling = true;
                    this.scrollDirection = this.scrollOffset < offset ? "forward" : "backward";
                    this.scrollOffset = offset;

                    this.maybeNotify();

                    this.isScrollingTimeoutId = setTimeout(() => {
                        this.isScrollingTimeoutId = null;
                        this.isScrolling = false;
                        this.scrollDirection = null;

                        this.maybeNotify();
                    }, this.options.scrollingDelay);
                }),
            );
        }
    };

    private getSize = () => {
        return this.scrollRect[this.options.horizontal ? "width" : "height"];
    };

    private memoOptions = memo(
        () => [
            this.options.count,
            this.options.paddingStart,
            this.options.scrollMargin,
            this.options.getItemKey,
        ],
        (count, paddingStart, scrollMargin, getItemKey) => {
            this.pendingMeasuredCacheIndexes = [];
            return {
                count,
                paddingStart,
                scrollMargin,
                getItemKey,
            };
        },
        {
            key: false,
        },
    );

    private getFurthestMeasurement = (measurements: VirtualItem[], index: number) => {
        const furthestMeasurementsFound = new Map<number, true>();
        const furthestMeasurements = new Map<number, VirtualItem>();
        for (let m = index - 1; m >= 0; m--) {
            const measurement = measurements[m]!;

            if (furthestMeasurementsFound.has(measurement.lane)) {
                continue;
            }

            const previousFurthestMeasurement = furthestMeasurements.get(measurement.lane);
            if (
                previousFurthestMeasurement == null ||
                measurement.end > previousFurthestMeasurement.end
            ) {
                furthestMeasurements.set(measurement.lane, measurement);
            } else if (measurement.end < previousFurthestMeasurement.end) {
                furthestMeasurementsFound.set(measurement.lane, true);
            }

            if (furthestMeasurementsFound.size === this.options.lanes) {
                break;
            }
        }

        return furthestMeasurements.size === this.options.lanes
            ? Array.from(furthestMeasurements.values()).sort((a, b) => {
                  if (a.end === b.end) {
                      return a.index - b.index;
                  }

                  return a.end - b.end;
              })[0]
            : undefined;
    };

    private getMeasurements = memo(
        () => [this.memoOptions(), this.itemSizeCache],
        ({ count, paddingStart, scrollMargin, getItemKey }, itemSizeCache) => {
            const min =
                this.pendingMeasuredCacheIndexes.length > 0
                    ? Math.min(...this.pendingMeasuredCacheIndexes)
                    : 0;
            this.pendingMeasuredCacheIndexes = [];

            const measurements = this.measurementsCache.slice(0, min);

            for (let i = min; i < count; i++) {
                const key = getItemKey(i);

                const furthestMeasurement =
                    this.options.lanes === 1
                        ? measurements[i - 1]
                        : this.getFurthestMeasurement(measurements, i);

                const start = furthestMeasurement
                    ? furthestMeasurement.end
                    : paddingStart + scrollMargin;

                const measuredSize = itemSizeCache.get(key);
                const size =
                    typeof measuredSize === "number" ? measuredSize : this.options.estimateSize(i);

                const end = start + size;

                const lane = furthestMeasurement
                    ? furthestMeasurement.lane
                    : i % this.options.lanes;

                measurements[i] = {
                    index: i,
                    id: key,
                    start,
                    size,
                    end,
                    key,
                    lane,
                };
            }

            this.measurementsCache = measurements;

            return measurements;
        },
        {
            key: process.env.NODE_ENV !== "production" && "getMeasurements",
            debug: () => this.options.debug,
        },
    );

    calculateRange = memo(
        () => [this.getMeasurements(), this.getSize(), this.scrollOffset],
        (measurements, outerSize, scrollOffset) => {
            // biome-ignore lint/suspicious/noAssignInExpressions: <explanation>
            return (this.range =
                measurements.length > 0 && outerSize > 0
                    ? calculateRange({
                          measurements,
                          outerSize,
                          scrollOffset,
                      })
                    : null);
        },
        {
            key: process.env.NODE_ENV !== "production" && "calculateRange",
            debug: () => this.options.debug,
        },
    );

    private getIndexes = memo(
        () => [
            this.options.rangeExtractor,
            this.calculateRange(),
            this.options.overscan,
            this.options.count,
        ],
        (rangeExtractor, range, overscan, count) => {
            return range === null
                ? []
                : rangeExtractor({
                      ...range,
                      overscan,
                      count,
                  });
        },
        {
            key: process.env.NODE_ENV !== "production" && "getIndexes",
            debug: () => this.options.debug,
        },
    );

    indexFromElement = (node: TItemElement) => {
        const attributeName = this.options.indexAttribute;
        const indexStr = node.getAttribute(attributeName);

        if (!indexStr) {
            console.warn(`Missing attribute name '${attributeName}={index}' on measured element.`);
            return -1;
        }

        return Number.parseInt(indexStr, 10);
    };

    private _measureElement = (node: TItemElement, entry: ResizeObserverEntry | undefined) => {
        const item = this.measurementsCache[this.indexFromElement(node)];

        if (!item || !node.isConnected) {
            this.measureElementCache.forEach((cached, key) => {
                if (cached === node) {
                    this.observer.unobserve(node);
                    this.measureElementCache.delete(key);
                }
            });
            return;
        }

        const prevNode = this.measureElementCache.get(item.key);

        if (prevNode !== node) {
            if (prevNode) {
                this.observer.unobserve(prevNode);
            }
            this.observer.observe(node);
            this.measureElementCache.set(item.key, node);
        }

        const measuredItemSize = this.options.measureElement(node, entry, this);

        this.resizeItem(item, measuredItemSize);
    };

    resizeItem = (item: VirtualItem, size: number) => {
        const itemSize = this.itemSizeCache.get(item.key) ?? item.size;
        const delta = size - itemSize;

        if (delta !== 0) {
            if (item.start < this.scrollOffset + this.scrollAdjustments) {
                if (process.env.NODE_ENV !== "production" && this.options.debug) {
                    console.info("correction", delta);
                }

                this._scrollToOffset(this.scrollOffset, {
                    // biome-ignore lint/suspicious/noAssignInExpressions: <explanation>
                    adjustments: (this.scrollAdjustments += delta),
                    behavior: undefined,
                });
            }

            this.pendingMeasuredCacheIndexes.push(item.index);
            this.itemSizeCache = new Map(this.itemSizeCache.set(item.key, size));

            this.notify(false);
        }
    };

    measureElement = (node: TItemElement | null) => {
        if (!node) {
            return;
        }

        this._measureElement(node, undefined);
    };

    getVirtualItems = memo(
        () => [this.getIndexes(), this.getMeasurements()],
        (indexes, measurements) => {
            const virtualItems: VirtualItem[] = [];

            for (let k = 0, len = indexes.length; k < len; k++) {
                const i = indexes[k]!;
                const measurement = measurements[i]!;

                virtualItems.push(measurement);
            }

            return virtualItems;
        },
        {
            key: process.env.NODE_ENV !== "production" && "getIndexes",
            debug: () => this.options.debug,
        },
    );

    getVirtualItemForOffset = (offset: number) => {
        const measurements = this.getMeasurements();

        return notUndefined(
            measurements[
                findNearestBinarySearch(
                    0,
                    measurements.length - 1,
                    (index: number) => notUndefined(measurements[index]).start,
                    offset,
                )
            ],
        );
    };

    getOffsetForAlignment = (toOffset: number, align: ScrollAlignment) => {
        const size = this.getSize();

        if (align === "auto") {
            if (toOffset <= this.scrollOffset) {
                align = "start";
            } else if (toOffset >= this.scrollOffset + size) {
                align = "end";
            } else {
                align = "start";
            }
        }

        if (align === "start") {
            // toOffset = toOffset;
        } else if (align === "end") {
            toOffset = toOffset - size;
        } else if (align === "center") {
            toOffset = toOffset - size / 2;
        }

        const scrollSizeProp = this.options.horizontal ? "scrollWidth" : "scrollHeight";
        const scrollSize = this.scrollElement
            ? "document" in this.scrollElement
                ? this.scrollElement.document.documentElement[scrollSizeProp]
                : this.scrollElement[scrollSizeProp]
            : 0;

        const maxOffset = scrollSize - this.getSize();

        return Math.max(Math.min(maxOffset, toOffset), 0);
    };

    getOffsetForIndex = (index: number, align: ScrollAlignment = "auto") => {
        index = Math.max(0, Math.min(index, this.options.count - 1));

        const measurement = notUndefined(this.getMeasurements()[index]);

        if (align === "auto") {
            if (
                measurement.end >=
                this.scrollOffset + this.getSize() - this.options.scrollPaddingEnd
            ) {
                align = "end";
            } else if (measurement.start <= this.scrollOffset + this.options.scrollPaddingStart) {
                align = "start";
            } else {
                return [this.scrollOffset, align] as const;
            }
        }

        const toOffset =
            align === "end"
                ? measurement.end + this.options.scrollPaddingEnd
                : measurement.start - this.options.scrollPaddingStart;

        return [this.getOffsetForAlignment(toOffset, align), align] as const;
    };

    private isDynamicMode = () => this.measureElementCache.size > 0;

    private cancelScrollToIndex = () => {
        if (this.scrollToIndexTimeoutId !== null) {
            clearTimeout(this.scrollToIndexTimeoutId);
            this.scrollToIndexTimeoutId = null;
        }
    };

    scrollToOffset = (
        toOffset: number,
        { align = "start", behavior }: ScrollToOffsetOptions = {},
    ) => {
        this.cancelScrollToIndex();

        if (behavior === "smooth" && this.isDynamicMode()) {
            console.warn("The `smooth` scroll behavior is not fully supported with dynamic size.");
        }

        this._scrollToOffset(this.getOffsetForAlignment(toOffset, align), {
            adjustments: undefined,
            behavior,
        });
    };

    scrollToIndex = (
        index: number,
        { align: initialAlign = "auto", behavior }: ScrollToIndexOptions = {},
    ) => {
        index = Math.max(0, Math.min(index, this.options.count - 1));

        this.cancelScrollToIndex();

        if (behavior === "smooth" && this.isDynamicMode()) {
            console.warn("The `smooth` scroll behavior is not fully supported with dynamic size.");
        }

        const [toOffset, align] = this.getOffsetForIndex(index, initialAlign);

        this._scrollToOffset(toOffset, { adjustments: undefined, behavior });

        if (behavior !== "smooth" && this.isDynamicMode()) {
            this.scrollToIndexTimeoutId = setTimeout(() => {
                this.scrollToIndexTimeoutId = null;

                const elementInDOM = this.measureElementCache.has(this.options.getItemKey(index));

                if (elementInDOM) {
                    const [toOffset] = this.getOffsetForIndex(index, align);

                    if (!approxEqual(toOffset, this.scrollOffset)) {
                        this.scrollToIndex(index, { align, behavior });
                    }
                } else {
                    this.scrollToIndex(index, { align, behavior });
                }
            });
        }
    };

    scrollBy = (delta: number, { behavior }: ScrollToOffsetOptions = {}) => {
        this.cancelScrollToIndex();

        if (behavior === "smooth" && this.isDynamicMode()) {
            console.warn("The `smooth` scroll behavior is not fully supported with dynamic size.");
        }

        this._scrollToOffset(this.scrollOffset + delta, {
            adjustments: undefined,
            behavior,
        });
    };

    getTotalSize = () => {
        const measurements = this.getMeasurements();

        let end: number;
        // If there are no measurements, set the end to paddingStart
        if (measurements.length === 0) {
            end = this.options.paddingStart;
        } else {
            // If lanes is 1, use the last measurement's end, otherwise find the maximum end value among all measurements
            end =
                this.options.lanes === 1
                    ? measurements[measurements.length - 1]?.end ?? 0
                    : Math.max(...measurements.slice(-this.options.lanes).map((m) => m.end));
        }

        return end - this.options.scrollMargin + this.options.paddingEnd;
    };

    private _scrollToOffset = (
        offset: number,
        {
            adjustments,
            behavior,
        }: {
            adjustments: number | undefined;
            behavior: ScrollBehavior | undefined;
        },
    ) => {
        this.options.scrollToFn(offset, { behavior, adjustments }, this);
    };

    measure = () => {
        this.itemSizeCache = new Map();
        this.notify(false);
    };
}

const findNearestBinarySearch = (
    low: number,
    high: number,
    getCurrentValue: (i: number) => number,
    value: number,
) => {
    while (low <= high) {
        const middle = ((low + high) / 2) | 0;
        const currentValue = getCurrentValue(middle);

        if (currentValue < value) {
            low = middle + 1;
        } else if (currentValue > value) {
            high = middle - 1;
        } else {
            return middle;
        }
    }

    if (low > 0) {
        return low - 1;
    }
    return 0;
};

function calculateRange({
    measurements,
    outerSize,
    scrollOffset,
}: {
    measurements: VirtualItem[];
    outerSize: number;
    scrollOffset: number;
}) {
    const count = measurements.length - 1;
    const getOffset = (index: number) => measurements[index]!.start;

    const startIndex = findNearestBinarySearch(0, count, getOffset, scrollOffset);
    let endIndex = startIndex;

    while (endIndex < count && measurements[endIndex]!.end < scrollOffset + outerSize) {
        endIndex++;
    }

    return { startIndex, endIndex };
}