import { Component } from 'react';
import Box from '@mui/material/Box';
import List from '@mui/material/List';
import Pagination from '@mui/material/Pagination';
import Typography from '@mui/material/Typography';
import { alpha } from '@mui/material/styles';

/**
 * FillSpace — paginates `items`.
 *
 * @component FillSpace
 * @import dashgui/FillSpace
 * @defaultExport
 *
 * @prop {Array} items - Wheel flips pages.
 * @prop {React.ComponentType|Function} renderItem - Row renderer (component or callback).
 * @prop {React.ReactNode} [header] - Rendered below pagination controls and above the list items.
 * @prop {number} [minPageSize=10] - Rows per page.
 * @prop {number} [maxPageSize] - Maximum rows per page.
 * @prop {number} [totalCount] - Total items in unfiltered dataset. When unfiltered count <= pageSize, pagination header is removed entirely. When filtering, the header height is preserved to prevent layout shift.
 * @prop {number} [unfilteredCount] - Alias for totalCount.
 * @prop {(page: number) => void} [onPageChange] - Called on page change.
 * @prop {boolean} [virtualScrollbar=false] - Shows a synchronized scrollbar alongside pagination controls.
 * @prop {boolean} [debug=false] - Dashed outline for layout debugging.
 * @prop {object} [sx] - Extra styles.
 */

/** True for class components (e.g. `renderItem={ArtikelMarke}`). Rendered as element, not called. */
function isRowComponent(renderItem) {
  return (
    typeof renderItem === 'function' &&
    (renderItem.prototype?.isReactComponent || renderItem.isFillRowComponent === true)
  );
}

/** Renders one row: component types become `<Row brand item index />`, callbacks are called. */
function renderRowElement(renderItem, item, index) {
  if (isRowComponent(renderItem)) {
    const Row = renderItem;
    return <Row brand={item} item={item} index={index} />;
  }
  return renderItem(item, index);
}

/**
 * Data-free probe of the row height, rendered hidden. Class components
 * (e.g. `renderItem={ArtikelMarke}`) tolerate empty props
 * (`brand`/`item` undefined) and keep a fixed height (40px thumb /
 * text field), so the probe measures the row without depending on the
 * first data element. Plain callbacks are NOT probed — calling arbitrary
 * user code with `undefined` could throw — they fall back to the first
 * rendered data row.
 */
function renderProbeElement(renderItem) {
  if (!isRowComponent(renderItem)) return null;
  const Row = renderItem;
  return <Row brand={undefined} item={undefined} index={0} disabled />;
}

const MIN_THUMB_HEIGHT = 48;
const RACEWAY_WIDTH = 16;
const RACEWAY_BOTTOM_MARGIN = 8;

class FillSpace extends Component {
  constructor(props) {
    super(props);
    const minSize = Math.max(1, Number(props.minPageSize) || 10);
    const maxSize = Number(props.maxPageSize) > 0 ? Number(props.maxPageSize) : Infinity;
    this.state = {
      unitHeight: 0,
      viewportHeight: null,
      pageSize: Math.min(maxSize, minSize),
      currentPage: 1,
      isDragging: false,
      dragThumbTop: 0,
    };
    this.ref = null;
    this.trackRef = null;
    this.thumbRef = null;
    this.probeRef = null;
    this.wheelAcc = 0;
    this.observer = null;
    this.raf = null;
    this.dragStartY = 0;
    this.dragStartThumbTop = 0;
    const explicitCount = props.unfilteredCount ?? props.totalCount;
    this.maxSeenCount =
      explicitCount != null
        ? Number(explicitCount)
        : Array.isArray(props.items)
          ? props.items.length
          : 0;
  }

  componentDidMount() {
    this._probeMeasure();
    this._viewportMeasure();
    this._observe();
    window.addEventListener('resize', this._onViewportChange);
  }

  componentDidUpdate(prevProps) {
    if (prevProps.renderItem !== this.props.renderItem) {
      this._probeMeasure();
    }
    if (
      prevProps.minPageSize !== this.props.minPageSize ||
      prevProps.maxPageSize !== this.props.maxPageSize
    ) {
      const minSize = Math.max(1, Number(this.props.minPageSize) || 10);
      const maxSize = Number(this.props.maxPageSize) > 0 ? Number(this.props.maxPageSize) : Infinity;
      this.setState({ pageSize: Math.min(maxSize, minSize) });
    }
    if (
      prevProps.aboveRef !== this.props.aboveRef ||
      prevProps.belowRef !== this.props.belowRef ||
      prevProps.containerRef !== this.props.containerRef ||
      prevProps.reserveBottom !== this.props.reserveBottom ||
      prevProps.items !== this.props.items ||
      prevProps.header !== this.props.header
    ) {
      this._observe();
      this._viewportMeasure();
    }
    const explicitCount = this.props.unfilteredCount ?? this.props.totalCount;
    if (explicitCount != null) {
      this.maxSeenCount = Number(explicitCount);
    } else if (Array.isArray(this.props.items)) {
      this.maxSeenCount = Math.max(this.maxSeenCount || 0, this.props.items.length);
    }
    // Clamp current page when the item list shrinks (e.g. brand deleted).
    if (
      Array.isArray(this.props.items) &&
      this.props.items !== prevProps.items
    ) {
      const explicitTotal = this.props.unfilteredCount ?? this.props.totalCount;
      const total =
        explicitTotal != null ? Number(explicitTotal) : this.props.items.length;
      const pageCount = Math.max(
        1,
        Math.ceil(total / Math.max(1, this.state.pageSize)),
      );
      if (this.state.currentPage > pageCount) {
        this.setState({ currentPage: pageCount });
        this.props.onPageChange?.(pageCount, {
          pageCount,
          pageSize: this.state.pageSize,
          total,
        });
      }
    }
  }

  componentWillUnmount() {
    if (this.state.isDragging) {
      document.body.style.userSelect = '';
      document.body.style.cursor = '';
      window.removeEventListener('mousemove', this._onThumbDragMove);
      window.removeEventListener('mouseup', this._onThumbDragEnd);
    }
    window.removeEventListener('resize', this._onViewportChange);
    if (this.raf) {
      cancelAnimationFrame(this.raf);
      this.raf = null;
    }
    if (this.observer) {
      this.observer.disconnect();
      this.observer = null;
    }
  }

  _onThumbMouseDown = (e) => {
    e.preventDefault();
    e.stopPropagation();
    const { totalCount, unfilteredCount, items } = this.props;
    const { viewportHeight, pageSize, currentPage } = this.state;
    const explicitTotal = unfilteredCount ?? totalCount;
    const total = explicitTotal != null ? Number(explicitTotal) : (items?.length || 0);
    const pageCount = Math.max(1, Math.ceil(total / Math.max(1, pageSize)));
    const racewayBottom = Math.max(0, Number(this.props.racewayMarginBottom ?? RACEWAY_BOTTOM_MARGIN) || 0);
    const trackHeight = Math.max(0, (viewportHeight || 0) - racewayBottom);
    const thumbHeight = Math.max(MIN_THUMB_HEIGHT, Math.min(trackHeight, total > 0 ? (pageSize / total) * trackHeight : trackHeight));
    const maxThumbTravel = Math.max(0, trackHeight - thumbHeight);
    const currentThumbTop = pageCount > 1 && maxThumbTravel > 0 ? ((currentPage - 1) / (pageCount - 1)) * maxThumbTravel : 0;

    this.dragStartY = e.clientY;
    this.dragStartThumbTop = currentThumbTop;
    this.setState({ isDragging: true, dragThumbTop: currentThumbTop });
    document.body.style.userSelect = 'none';
    document.body.style.cursor = 'grabbing';
    window.addEventListener('mousemove', this._onThumbDragMove);
    window.addEventListener('mouseup', this._onThumbDragEnd);
  };

  _onThumbDragMove = (e) => {
    if (!this.state.isDragging) return;
    const { totalCount, unfilteredCount, items } = this.props;
    const { viewportHeight, pageSize } = this.state;
    const explicitTotal = unfilteredCount ?? totalCount;
    const total = explicitTotal != null ? Number(explicitTotal) : (items?.length || 0);
    const pageCount = Math.max(1, Math.ceil(total / Math.max(1, pageSize)));
    if (pageCount <= 1) return;

    const racewayBottom = Math.max(0, Number(this.props.racewayMarginBottom ?? RACEWAY_BOTTOM_MARGIN) || 0);
    const trackHeight = Math.max(0, (viewportHeight || 0) - racewayBottom);
    const thumbHeight = Math.max(MIN_THUMB_HEIGHT, Math.min(trackHeight, total > 0 ? (pageSize / total) * trackHeight : trackHeight));
    const maxThumbTravel = Math.max(0, trackHeight - thumbHeight);
    if (maxThumbTravel <= 0) return;

    const deltaY = e.clientY - this.dragStartY;
    const nextThumbTop = Math.max(0, Math.min(maxThumbTravel, this.dragStartThumbTop + deltaY));
    const targetPage = Math.min(pageCount, Math.max(1, Math.round(1 + (nextThumbTop / maxThumbTravel) * (pageCount - 1))));

    this.setState({ dragThumbTop: nextThumbTop });
    if (targetPage !== this.state.currentPage) {
      this._goToPage(targetPage);
    }
  };

  _onThumbDragEnd = () => {
    document.body.style.userSelect = '';
    document.body.style.cursor = '';
    window.removeEventListener('mousemove', this._onThumbDragMove);
    window.removeEventListener('mouseup', this._onThumbDragEnd);
    this.setState({ isDragging: false });
  };

  _handleTrackMouseDown = (e) => {
    if (e.target === this.thumbRef || this.thumbRef?.contains(e.target)) return;
    if (!this.trackRef) return;
    const trackRect = this.trackRef.getBoundingClientRect();
    const clickY = e.clientY - trackRect.top;
    const { viewportHeight, pageSize } = this.state;
    const { items, totalCount, unfilteredCount } = this.props;
    const explicitTotal = unfilteredCount ?? totalCount;
    const total = explicitTotal != null ? Number(explicitTotal) : (items?.length || 0);
    const pageCount = Math.max(1, Math.ceil(total / Math.max(1, pageSize)));
    if (pageCount <= 1) return;

    const racewayBottom = Math.max(0, Number(this.props.racewayMarginBottom ?? RACEWAY_BOTTOM_MARGIN) || 0);
    const trackHeight = Math.max(0, (viewportHeight || 0) - racewayBottom);
    if (trackHeight <= 0) return;
    const thumbHeight = Math.max(MIN_THUMB_HEIGHT, Math.min(trackHeight, total > 0 ? (pageSize / total) * trackHeight : trackHeight));
    const maxThumbTravel = Math.max(0, trackHeight - thumbHeight);
    const targetThumbTop = Math.max(0, Math.min(maxThumbTravel, clickY - thumbHeight / 2));
    const targetPage = maxThumbTravel > 0 ? Math.min(pageCount, Math.max(1, Math.round(1 + (targetThumbTop / maxThumbTravel) * (pageCount - 1)))) : 1;
    this._goToPage(targetPage);
  };

  scrollToTop = () => {
    this._goToPage(1);
  };

  scrollToIndex = (index) => {
    const { pageSize } = this.state;
    if (pageSize > 0) {
      const targetPage = Math.floor(index / pageSize) + 1;
      this._goToPage(targetPage);
    }
  };

  _onViewportChange = () => {
    if (this.raf) return;
    this.raf = requestAnimationFrame(() => {
      this.raf = null;
      this._viewportMeasure();
    });
  };

  _observe() {
    if (this.observer) {
      this.observer.disconnect();
    }
    this.observer = new ResizeObserver(() => this._onViewportChange());
    const { aboveRef, belowRef, containerRef } = this.props;
    const aboveList = Array.isArray(aboveRef) ? aboveRef : [aboveRef];
    const belowList = Array.isArray(belowRef) ? belowRef : [belowRef];
    const containerTarget =
      containerRef && 'current' in containerRef ? containerRef.current : containerRef;
    const targets = [
      ...aboveList.map((r) => (r && 'current' in r ? r.current : r)),
      ...belowList.map((r) => (r && 'current' in r ? r.current : r)),
      containerTarget,
    ];
    for (const el of targets) {
      if (el && el.offsetParent !== null) {
        this.observer.observe(el);
      }
    }
  }

  probeMeasure = () => {
    this._probeMeasure();
  };

  viewportMeasure = () => {
    this._viewportMeasure();
  };

  measure = () => {
    this._probeMeasure();
    this._viewportMeasure();
  };

  /** Only measures the height of the `renderItem` probe. Nothing else. */
  _probeMeasure() {
    const firstRow = this.ref?.querySelector('[data-fill-row]');
    const h = this.probeRef?.offsetHeight || firstRow?.offsetHeight;
    if (h > 0 && h !== this.state.unitHeight) {
      this.setState({ unitHeight: h }, () => this._viewportMeasure());
    }
  }

  /** Viewport height minus above/below refs: free space for the list. */
  _viewportMeasure() {
    if (!this.ref) return;
    const { belowRef, containerRef, reserveBottom = 0, minPageSize } = this.props;
    const rect = this.ref.getBoundingClientRect();
    let belowPx = Number(reserveBottom) || 0;
    const belowList = Array.isArray(belowRef) ? belowRef : [belowRef];
    for (const ref of belowList) {
      const el = ref && 'current' in ref ? ref.current : ref;
      if (el && el.offsetParent !== null) {
        belowPx += el.offsetHeight;
        const mt = parseFloat(window.getComputedStyle(el).marginTop);
        if (Number.isFinite(mt)) belowPx += mt;
      }
    }
    const containerEl =
      containerRef && 'current' in containerRef ? containerRef.current : containerRef;
    let available;
    if (containerEl && typeof containerEl.getBoundingClientRect === 'function') {
      const cRect = containerEl.getBoundingClientRect();
      const paddingBottom = parseFloat(window.getComputedStyle(containerEl).paddingBottom) || 0;
      available = Math.max(0, cRect.bottom - rect.top - belowPx - paddingBottom);
    } else {
      available = Math.max(0, window.innerHeight - rect.top - belowPx);
    }
    const minSize = Math.max(1, Number(minPageSize) || 10);
    const maxSize = Number(this.props.maxPageSize) > 0 ? Number(this.props.maxPageSize) : Infinity;
    const { unitHeight } = this.state;
    const calculated =
      unitHeight > 0 ? Math.max(minSize, Math.floor(available / unitHeight)) : minSize;
    const nextPageSize = Math.min(maxSize, calculated);
    const nextViewportHeight =
      Number.isFinite(maxSize) && unitHeight > 0
        ? Math.min(available, nextPageSize * unitHeight)
        : available;
    if (
      nextViewportHeight !== this.state.viewportHeight ||
      nextPageSize !== this.state.pageSize
    ) {
      this.setState({ viewportHeight: nextViewportHeight, pageSize: nextPageSize });
    }
  }

  _handleWheel = (event) => {
    const { items, totalCount, unfilteredCount } = this.props;
    if (!Array.isArray(items)) return;
    if (this.ref && event.target && !this.ref.contains(event.target)) return;
    const { pageSize, currentPage } = this.state;
    const explicitTotal = unfilteredCount ?? totalCount;
    const total = explicitTotal != null ? Number(explicitTotal) : items.length;
    const pageCount = Math.max(1, Math.ceil(total / Math.max(1, pageSize)));
    const delta = event.deltaY || 0;
    if (pageCount <= 1) return;
    if (delta === 0) return;
    if (Math.sign(delta) !== Math.sign(this.wheelAcc || 0)) this.wheelAcc = 0;
    this.wheelAcc = (this.wheelAcc || 0) + delta;
    const threshold = Math.max(50, 800 / pageCount);
    if (Math.abs(this.wheelAcc) < threshold) return;
    const dir = this.wheelAcc > 0 ? 1 : -1;
    this.wheelAcc = 0;
    const next = dir > 0
      ? Math.min(pageCount, currentPage + 1)
      : Math.max(1, currentPage - 1);
    if (next === currentPage) return;
    this._goToPage(next);
  };

  _goToPage = (page) => {
    const { items, onPageChange, totalCount, unfilteredCount } = this.props;
    const explicitTotal = unfilteredCount ?? totalCount;
    const total =
      explicitTotal != null
        ? Number(explicitTotal)
        : Array.isArray(items)
          ? items.length
          : 0;
    const pageCount = Math.max(1, Math.ceil(total / Math.max(1, this.state.pageSize)));
    const next = Math.min(Math.max(1, Number(page) || 1), pageCount);
    if (next === this.state.currentPage) return;
    this.setState({ currentPage: next });
    onPageChange?.(next, { pageCount, pageSize: this.state.pageSize, total });
  };

  render() {
    const {
      // Discarded legacy layout props (kept here so they don't leak to the DOM).
      aboveRef,
      belowRef,
      containerRef,
      reserveBottom,
      minHeight,
      maxHeight,
      minPageSize,
      maxPageSize,
      totalCount,
      unfilteredCount,
      listRef,
      onPageChange,
      onWheel,
      virtualScrollbar = false,
      racewayMarginBottom,
      racewayRight,
      debug = false,
      items,
      renderItem,
      header,
      sx,
      ...rest
    } = this.props;

    // FillSpace owns current page, wheel-pagination and the pagination header.
    // Caller feeds `items` plus one row element via `renderItem` (component
    // type or callback). `items` may be undefined while data is loading.
    const { pageSize, currentPage, viewportHeight } = this.state;
    const list = Array.isArray(items) ? items : [];
    const explicitTotal = unfilteredCount ?? totalCount;
    const total = explicitTotal != null ? Number(explicitTotal) : list.length;
    const fullTotal = Math.max(this.maxSeenCount || 0, total);
    const needsPaginationContainer = fullTotal > pageSize;
    const showPaginationControls = total > pageSize;
    const pageCount = Math.max(1, Math.ceil(total / Math.max(1, pageSize)));
    const safePage = Math.min(Math.max(1, currentPage), pageCount);
    const offset = (safePage - 1) * pageSize;
    const pageItems = list.slice(offset, offset + pageSize);

    const canScroll =
      virtualScrollbar &&
      total > pageSize &&
      (viewportHeight || 0) > 0;

    const racewayBottom = Math.max(0, Number(racewayMarginBottom ?? RACEWAY_BOTTOM_MARGIN) || 0);
    const racewayRightOffset = racewayRight != null ? racewayRight : 0;

    let thumbHeight = 0;
    let thumbTop = 0;

    if (canScroll) {
      const trackHeight = Math.max(0, (viewportHeight || 0) - racewayBottom);
      thumbHeight = Math.max(MIN_THUMB_HEIGHT, Math.min(trackHeight, total > 0 ? (pageSize / total) * trackHeight : trackHeight));
      const maxThumbTravel = Math.max(0, trackHeight - thumbHeight);
      thumbTop = this.state.isDragging
        ? this.state.dragThumbTop
        : (pageCount > 1 && maxThumbTravel > 0 ? ((safePage - 1) / (pageCount - 1)) * maxThumbTravel : 0);
    }

    // Hidden data-free probe: measures `renderItem` itself (no data).
    const probe = renderProbeElement(renderItem);

    return (
      <>
        {needsPaginationContainer ? (
          <Box
            // Fixed single-line bar: the header height must not depend on the
            // filtered count so the content never shifts when filtering.
            sx={{ mb: 1, height: 44, overflow: 'hidden' }}
          >
            <Box
              aria-hidden={!showPaginationControls || undefined}
              sx={{
                display: 'flex',
                justifyContent: 'space-between',
                alignItems: 'center',
                flexWrap: 'nowrap',
                gap: 1,
                width: '100%',
                height: 44,
                visibility: showPaginationControls ? 'visible' : 'hidden',
                pointerEvents: showPaginationControls ? 'auto' : 'none',
              }}
            >
              <Typography
                variant="body2"
                color="text.secondary"
                noWrap
                sx={{ flexShrink: 1, minWidth: 0, overflow: 'hidden', textOverflow: 'ellipsis' }}
              >
                {total === 0 ? '0' : `${offset + 1}–${Math.min(offset + pageSize, total)}`} von{' '}
                {total}
              </Typography>
              <Pagination
                count={pageCount}
                page={safePage}
                onChange={(_e, page) => this._goToPage(page)}
                color="primary"
                size="large"
                onMouseDown={(e) => e.preventDefault()}
                sx={{
                  flexShrink: 0,
                  maxWidth: '100%',
                  overflowX: 'auto',
                  scrollbarWidth: 'none',
                  '&::-webkit-scrollbar': { display: 'none' },
                  '& .MuiPagination-ul': { flexWrap: 'nowrap' },
                  '& .MuiPaginationItem-root': {
                    minWidth: 44,
                    height: 44,
                    fontSize: '1rem',
                  },
                }}
              />
            </Box>
          </Box>
        ) : null}
        {header}
        <Box
          ref={(el) => {
            this.ref = el;
          }}
          onWheel={(e) => {
            this._handleWheel(e);
            onWheel?.(e);
          }}
          {...rest}
          sx={[
            {
              position: 'relative',
              height: viewportHeight ?? 'auto',
              overflow: 'hidden',
              width: '100%',
              // Keep wheel ticks from scrolling the page behind the list.
              // (No preventDefault needed — React wheel is passive.)
              overscrollBehavior: 'contain',
            },
            debug
              ? (theme) => ({
                  outline: `2px dashed ${theme.palette.primary.main}`,
                })
              : undefined,
            sx,
          ]}
        >
          <Box
            sx={{
              width: '100%',
              pr: canScroll ? `${Math.max(0, RACEWAY_WIDTH + racewayRightOffset + 8)}px` : 0,
              boxSizing: 'border-box',
            }}
          >
            <List ref={listRef} dense disablePadding sx={{ width: '100%' }}>
              {pageItems.map((item, i) => (
                <Box key={item?.id ?? offset + i} data-fill-row sx={{ width: '100%' }}>
                  {renderRowElement(renderItem, item, offset + i)}
                </Box>
              ))}
            </List>
          </Box>
          {probe != null ? (
            <Box
              ref={(el) => {
                this.probeRef = el;
              }}
              aria-hidden
              sx={{
                position: 'absolute',
                left: 0,
                top: 0,
                width: '100%',
                visibility: 'hidden',
                pointerEvents: 'none',
              }}
            >
              <List dense disablePadding sx={{ width: '100%' }}>
                <Box data-fill-row sx={{ width: '100%' }}>
                  {probe}
                </Box>
              </List>
            </Box>
          ) : null}

          {canScroll ? (
            <Box
              ref={(el) => {
                this.trackRef = el;
              }}
              onMouseDown={this._handleTrackMouseDown}
              sx={{
                position: 'absolute',
                top: 0,
                right: racewayRightOffset,
                bottom: `${racewayBottom}px`,
                width: RACEWAY_WIDTH,
                zIndex: 5,
                cursor: 'pointer',
                borderRadius: 8,
                bgcolor: (theme) => alpha(theme.palette.text.primary, 0.04),
                transition: 'background-color 0.15s ease',
                '&:hover': {
                  bgcolor: (theme) => alpha(theme.palette.text.primary, 0.09),
                },
              }}
            >
              <Box
                ref={(el) => {
                  this.thumbRef = el;
                }}
                onMouseDown={this._onThumbMouseDown}
                sx={{
                  position: 'absolute',
                  top: thumbTop,
                  height: thumbHeight,
                  left: 2,
                  right: 2,
                  borderRadius: 6,
                  bgcolor: (theme) =>
                    this.state.isDragging
                      ? alpha(theme.palette.primary.main, 0.7)
                      : alpha(theme.palette.text.primary, 0.3),
                  cursor: this.state.isDragging ? 'grabbing' : 'grab',
                  transition: this.state.isDragging ? 'none' : 'background-color 0.15s ease',
                  '&:hover': {
                    bgcolor: (theme) =>
                      this.state.isDragging
                        ? alpha(theme.palette.primary.main, 0.7)
                        : alpha(theme.palette.text.primary, 0.55),
                  },
                }}
              />
            </Box>
          ) : null}
        </Box>
        {debug ? (
          <Box
            sx={(theme) => ({
              position: 'fixed',
              inset: 0,
              pointerEvents: 'none',
              background: alpha(theme.palette.primary.main, 0.08),
              zIndex: 9999,
            })}
          />
        ) : null}
      </>
    );
  }
}

export default FillSpace;