import { useState, useRef, useEffect, useCallback, useMemo } from 'react'
import { format, differenceInDays, startOfDay, addDays, isBefore, isAfter } from 'date-fns'
import { Calendar, Rows3, Rows4 } from 'lucide-react'

const STATUS_COLORS = {
  todo: 'bg-gray-500',
  in_progress: 'bg-blue-500',
  done: 'bg-emerald-500',
  planning: 'bg-amber-500',
  active: 'bg-blue-500',
  paused: 'bg-orange-500',
  completed: 'bg-emerald-500',
  cancelled: 'bg-red-400',
  draft: 'bg-gray-400',
  in_review: 'bg-yellow-500',
  approved: 'bg-indigo-500',
  scheduled: 'bg-purple-500',
  published: 'bg-emerald-500',
  planned: 'bg-amber-400',
  // tracks
  organic_social: 'bg-green-500',
  paid_social: 'bg-blue-500',
  paid_search: 'bg-amber-500',
  seo_content: 'bg-purple-500',
  production: 'bg-red-500',
}

const PRIORITY_BORDER = {
  urgent: 'ring-2 ring-red-400',
  high: 'ring-2 ring-orange-300',
  medium: '',
  low: '',
}

const ZOOM_LEVELS = [
  { key: 'day', label: 'Day', pxPerDay: 48 },
  { key: 'week', label: 'Week', pxPerDay: 20 },
]

function getInitials(name) {
  if (!name) return '?'
  return name.split(' ').map(w => w[0]).join('').toUpperCase().slice(0, 2)
}

export default function InteractiveTimeline({ items = [], mapItem, onDateChange, onItemClick, readOnly = false }) {
  const containerRef = useRef(null)
  const didDragRef = useRef(false)
  const optimisticRef = useRef({}) // { [itemId]: { startDate, endDate } } — keeps bar in place until fresh data arrives
  const [zoomIdx, setZoomIdx] = useState(0)
  const [barMode, setBarMode] = useState('expanded') // 'compact' | 'expanded'
  const [tooltip, setTooltip] = useState(null)
  const [dragState, setDragState] = useState(null) // { itemId, mode: 'move'|'resize-left'|'resize-right', startX, origStart, origEnd }
  const dragStateRef = useRef(null)

  const pxPerDay = ZOOM_LEVELS[zoomIdx].pxPerDay
  const today = useMemo(() => startOfDay(new Date()), [])

  // Clear optimistic overrides when fresh data arrives
  useEffect(() => {
    optimisticRef.current = {}
  }, [items])

  // Map items
  const mapped = useMemo(() => {
    return items.map(raw => {
      const m = mapItem(raw)
      const opt = optimisticRef.current[m.id]
      return {
        ...m,
        _raw: raw,
        startDate: opt?.startDate || (m.startDate ? startOfDay(new Date(m.startDate)) : null),
        endDate: opt?.endDate || (m.endDate ? startOfDay(new Date(m.endDate)) : null),
      }
    })
  }, [items, mapItem])

  // Compute time range
  const { earliest, latest, totalDays, days } = useMemo(() => {
    let earliest = addDays(today, -7)
    let latest = addDays(today, 28)

    mapped.forEach(item => {
      const s = item.startDate || today
      const e = item.endDate || addDays(s, 3)
      if (isBefore(s, earliest)) earliest = addDays(s, -3)
      if (isAfter(e, latest)) latest = addDays(e, 7)
    })

    const totalDays = differenceInDays(latest, earliest) + 1
    const days = []
    for (let i = 0; i < totalDays; i++) {
      days.push(addDays(earliest, i))
    }
    return { earliest, latest, totalDays, days }
  }, [mapped, today])

  // Auto-scroll to today on mount
  useEffect(() => {
    if (containerRef.current) {
      const todayOffset = differenceInDays(today, earliest) * pxPerDay
      containerRef.current.scrollLeft = Math.max(0, todayOffset - 200)
    }
  }, [earliest, pxPerDay, today])

  // Drag handlers
  const handleMouseDown = useCallback((e, item, mode) => {
    if (readOnly || !onDateChange) return
    e.preventDefault()
    e.stopPropagation()
    didDragRef.current = false
    const initial = {
      itemId: item.id,
      mode,
      startX: e.clientX,
      origStart: item.startDate || today,
      origEnd: item.endDate || addDays(item.startDate || today, 3),
    }
    dragStateRef.current = initial
    setDragState(initial)
  }, [readOnly, onDateChange, today])

  useEffect(() => {
    if (!dragState) return

    const handleMouseMove = (e) => {
      const cur = dragStateRef.current
      if (!cur) return
      const dx = e.clientX - cur.startX
      const dayDelta = Math.round(dx / pxPerDay)
      if (dayDelta === 0) return

      didDragRef.current = true
      const newState = { ...cur }

      if (cur.mode === 'move') {
        newState.currentStart = addDays(cur.origStart, dayDelta)
        newState.currentEnd = addDays(cur.origEnd, dayDelta)
      } else if (cur.mode === 'resize-left') {
        const newStart = addDays(cur.origStart, dayDelta)
        if (isBefore(newStart, cur.origEnd)) {
          newState.currentStart = newStart
          newState.currentEnd = cur.origEnd
        }
      } else if (cur.mode === 'resize-right') {
        const newEnd = addDays(cur.origEnd, dayDelta)
        if (isAfter(newEnd, cur.origStart)) {
          newState.currentStart = cur.origStart
          newState.currentEnd = newEnd
        }
      }
      dragStateRef.current = newState
      setDragState(newState)
    }

    const handleMouseUp = () => {
      const prev = dragStateRef.current
      dragStateRef.current = null
      setDragState(null)
      if (prev && (prev.currentStart || prev.currentEnd) && onDateChange) {
        const startDate = prev.currentStart || prev.origStart
        const endDate = prev.currentEnd || prev.origEnd
        // Keep bar in place visually until fresh data arrives
        optimisticRef.current[prev.itemId] = { startDate, endDate }
        onDateChange(prev.itemId, {
          startDate: format(startDate, 'yyyy-MM-dd'),
          endDate: format(endDate, 'yyyy-MM-dd'),
        })
      }
    }

    document.addEventListener('mousemove', handleMouseMove)
    document.addEventListener('mouseup', handleMouseUp)
    return () => {
      document.removeEventListener('mousemove', handleMouseMove)
      document.removeEventListener('mouseup', handleMouseUp)
    }
  }, [dragState?.itemId, pxPerDay, onDateChange])

  const getBarPosition = useCallback((item) => {
    let start, end

    // If this item is being dragged, use the drag state
    if (dragState && dragState.itemId === item.id && (dragState.currentStart || dragState.currentEnd)) {
      start = dragState.currentStart || item.startDate || today
      end = dragState.currentEnd || item.endDate || addDays(start, 3)
    } else {
      // Check optimistic position (keeps bar in place after drop, before API data refreshes)
      const opt = optimisticRef.current[item.id]
      start = opt?.startDate || item.startDate || today
      end = opt?.endDate || item.endDate || addDays(start, 3)
    }

    // Ensure end is after start
    if (!isAfter(end, start)) end = addDays(start, 1)

    const left = differenceInDays(start, earliest) * pxPerDay
    const width = Math.max(pxPerDay, (differenceInDays(end, start) + 1) * pxPerDay)
    return { left, width }
  }, [earliest, pxPerDay, today, dragState])

  const scrollToToday = () => {
    if (containerRef.current) {
      const todayOffset = differenceInDays(today, earliest) * pxPerDay
      containerRef.current.scrollTo({ left: Math.max(0, todayOffset - 200), behavior: 'smooth' })
    }
  }

  const isExpanded = barMode === 'expanded'
  const rowHeight = isExpanded ? 100 : 52
  const barHeight = isExpanded ? 84 : 36
  const headerHeight = 48
  const labelWidth = isExpanded ? 280 : 220
  const todayOffset = differenceInDays(today, earliest) * pxPerDay

  if (items.length === 0) {
    return (
      <div className="bg-white rounded-xl border border-border py-16 text-center">
        <Calendar className="w-12 h-12 text-text-tertiary mx-auto mb-3" />
        <p className="text-text-secondary font-medium">No items to display</p>
        <p className="text-sm text-text-tertiary mt-1">Add items with dates to see the timeline</p>
      </div>
    )
  }

  return (
    <div className="bg-white rounded-xl border border-border overflow-hidden">
      {/* Toolbar */}
      <div className="flex items-center justify-between px-4 py-2 border-b border-border bg-surface-secondary">
        <div className="flex items-center gap-2">
          {ZOOM_LEVELS.map((z, i) => (
            <button
              key={z.key}
              onClick={() => setZoomIdx(i)}
              className={`px-3 py-1 text-xs font-medium rounded-md transition-colors ${
                zoomIdx === i
                  ? 'bg-brand-primary text-white shadow-sm'
                  : 'text-text-tertiary hover:text-text-primary hover:bg-surface-tertiary'
              }`}
            >
              {z.label}
            </button>
          ))}
        </div>
        <div className="flex items-center gap-2">
          <button
            onClick={() => setBarMode(m => m === 'compact' ? 'expanded' : 'compact')}
            className="flex items-center gap-1.5 px-3 py-1 text-xs font-medium text-text-secondary hover:text-text-primary hover:bg-surface-tertiary rounded-md transition-colors"
            title={isExpanded ? 'Compact bars' : 'Expanded bars'}
          >
            {isExpanded ? <Rows4 className="w-3.5 h-3.5" /> : <Rows3 className="w-3.5 h-3.5" />}
            {isExpanded ? 'Compact' : 'Expand'}
          </button>
          <button
            onClick={scrollToToday}
            className="flex items-center gap-1.5 px-3 py-1 text-xs font-medium text-brand-primary hover:bg-brand-primary/10 rounded-md transition-colors"
          >
            <Calendar className="w-3.5 h-3.5" />
            Today
          </button>
        </div>
      </div>

      {/* Timeline */}
      <div ref={containerRef} className="overflow-x-auto relative" style={{ cursor: dragState ? 'grabbing' : undefined }}>
        <div style={{ minWidth: `${labelWidth + totalDays * pxPerDay}px` }}>
          {/* Day header */}
          <div className="flex sticky top-0 z-20 bg-white border-b border-border" style={{ height: headerHeight }}>
            <div className="shrink-0 border-r border-border bg-surface-secondary flex items-center px-4 sticky left-0 z-30" style={{ width: labelWidth }}>
              <span className="text-xs font-semibold text-text-tertiary uppercase tracking-wider">Item</span>
            </div>
            <div className="flex relative">
              {days.map((day, i) => {
                const isToday = differenceInDays(day, today) === 0
                const isWeekend = day.getDay() === 0 || day.getDay() === 6
                const isMonthStart = day.getDate() === 1
                return (
                  <div
                    key={i}
                    style={{ width: pxPerDay, minWidth: pxPerDay }}
                    className={`flex flex-col items-center justify-center border-r border-border-light text-[10px] leading-tight ${
                      isToday ? 'bg-red-50 font-bold text-red-600' :
                      isWeekend ? 'bg-surface-tertiary/40 text-text-tertiary' :
                      'text-text-tertiary'
                    } ${isMonthStart ? 'border-l-2 border-l-text-tertiary/30' : ''}`}
                  >
                    {pxPerDay >= 30 && <div>{format(day, 'd')}</div>}
                    {pxPerDay >= 40 && <div className="text-[8px] uppercase">{format(day, 'EEE')}</div>}
                    {pxPerDay < 30 && day.getDate() % 7 === 1 && <div>{format(day, 'd')}</div>}
                  </div>
                )
              })}
            </div>
          </div>

          {/* Rows */}
          {mapped.map((item, idx) => {
            const { left, width } = getBarPosition(item)
            const statusColor = STATUS_COLORS[item.status] || STATUS_COLORS[item.type] || 'bg-gray-400'
            const priorityRing = PRIORITY_BORDER[item.priority] || ''
            const isDragging = dragState?.itemId === item.id

            return (
              <div
                key={item.id}
                className={`flex border-b border-border-light group/row hover:bg-surface-secondary/50 ${isDragging ? 'bg-blue-50/30' : ''}`}
                style={{ height: rowHeight }}
              >
                {/* Label column */}
                <div
                  className={`shrink-0 border-r border-border flex ${isExpanded ? 'flex-col justify-center gap-1' : 'items-center gap-2'} px-3 overflow-hidden sticky left-0 z-10 bg-white group-hover/row:bg-surface-secondary/50`}
                  style={{ width: labelWidth }}
                >
                  {isExpanded ? (
                    <>
                      <div className="flex items-center gap-2">
                        {item.thumbnailUrl ? (
                          <div className="w-8 h-8 rounded overflow-hidden shrink-0">
                            <img src={item.thumbnailUrl} alt="" className="w-full h-full object-cover" />
                          </div>
                        ) : item.assigneeName ? (
                          <div className="w-6 h-6 rounded-full bg-brand-primary/10 text-brand-primary flex items-center justify-center text-[9px] font-bold shrink-0">
                            {getInitials(item.assigneeName)}
                          </div>
                        ) : null}
                        <span className="text-sm font-semibold text-text-primary truncate">{item.label}</span>
                      </div>
                      {item.description && (
                        <p className="text-[11px] text-text-tertiary line-clamp-2 leading-tight">{item.description}</p>
                      )}
                      {item.tags && item.tags.length > 0 && (
                        <div className="flex items-center gap-1 flex-wrap">
                          {item.tags.slice(0, 4).map((tag, i) => (
                            <span key={i} className="text-[9px] px-1.5 py-0.5 rounded bg-surface-tertiary text-text-secondary font-medium">{tag}</span>
                          ))}
                        </div>
                      )}
                    </>
                  ) : (
                    <>
                      {item.thumbnailUrl ? (
                        <div className="w-6 h-6 rounded overflow-hidden shrink-0">
                          <img src={item.thumbnailUrl} alt="" className="w-full h-full object-cover" />
                        </div>
                      ) : item.assigneeName ? (
                        <div className="w-6 h-6 rounded-full bg-brand-primary/10 text-brand-primary flex items-center justify-center text-[9px] font-bold shrink-0">
                          {getInitials(item.assigneeName)}
                        </div>
                      ) : null}
                      <span className="text-xs font-medium text-text-primary truncate">{item.label}</span>
                    </>
                  )}
                </div>

                {/* Bar area */}
                <div className="relative flex-1" style={{ height: rowHeight }}>
                  {/* Today line */}
                  {todayOffset >= 0 && (
                    <div
                      className="absolute top-0 bottom-0 w-0.5 bg-red-400 z-10"
                      style={{ left: `${todayOffset + pxPerDay / 2}px` }}
                    >
                      {idx === 0 && (
                        <div className="absolute -top-0 left-1 text-[8px] font-bold text-red-500 bg-red-50 px-1 rounded whitespace-nowrap">
                          Today
                        </div>
                      )}
                    </div>
                  )}

                  {/* The bar */}
                  <div
                    className={`absolute rounded-lg ${statusColor} ${priorityRing} shadow-sm transition-shadow hover:shadow-md select-none overflow-hidden group ${
                      !readOnly && onDateChange ? 'cursor-grab active:cursor-grabbing' : 'cursor-pointer'
                    } ${isDragging ? 'opacity-80 shadow-lg' : ''}`}
                    style={{
                      left: `${left}px`,
                      width: `${width}px`,
                      height: `${barHeight}px`,
                      top: isExpanded ? '8px' : '8px',
                    }}
                    onMouseDown={(e) => handleMouseDown(e, item, 'move')}
                    onClick={(e) => {
                      if (didDragRef.current) {
                        didDragRef.current = false
                        return
                      }
                      if (onItemClick) {
                        onItemClick(item._raw)
                      }
                    }}
                    onMouseEnter={(e) => {
                      if (!dragState) {
                        const rect = e.currentTarget.getBoundingClientRect()
                        setTooltip({
                          item,
                          x: rect.left + rect.width / 2,
                          y: rect.top - 8,
                        })
                      }
                    }}
                    onMouseLeave={() => setTooltip(null)}
                  >
                    {/* Left resize handle */}
                    {!readOnly && onDateChange && (
                      <div
                        className="absolute left-0 top-0 bottom-0 w-2 cursor-col-resize hover:bg-white/30 z-10"
                        onMouseDown={(e) => handleMouseDown(e, item, 'resize-left')}
                      />
                    )}

                    {/* Bar content */}
                    {isExpanded ? (
                      <div className="flex flex-col gap-0.5 px-3 py-1.5 flex-1 min-w-0 h-full">
                        <div className="flex items-center gap-1.5">
                          {item.assigneeName && width > 60 && (
                            <span className="text-[9px] font-bold text-white/80 bg-white/20 w-5 h-5 rounded-full flex items-center justify-center shrink-0">
                              {getInitials(item.assigneeName)}
                            </span>
                          )}
                          {width > 80 && (
                            <span className="text-xs font-semibold text-white truncate">
                              {item.label}
                            </span>
                          )}
                          {width > 120 && item.status && (
                            <span className="text-[9px] text-white/70 bg-white/15 px-1.5 py-0.5 rounded ml-auto shrink-0">
                              {item.status.replace(/_/g, ' ')}
                            </span>
                          )}
                        </div>
                        {width > 100 && item.description && (
                          <p className="text-[10px] text-white/60 line-clamp-2 leading-tight">
                            {item.description}
                          </p>
                        )}
                        {width > 80 && (
                          <div className="flex items-center gap-1.5 mt-auto">
                            {item.tags && item.tags.slice(0, 3).map((tag, i) => (
                              <span key={i} className="text-[8px] px-1 py-0.5 rounded bg-white/15 text-white/70 font-medium">{tag}</span>
                            ))}
                            {width > 140 && item.startDate && item.endDate && (
                              <span className="text-[8px] text-white/50 ml-auto">
                                {format(item.startDate, 'MMM d')} – {format(item.endDate, 'MMM d')}
                              </span>
                            )}
                          </div>
                        )}
                      </div>
                    ) : (
                      <div className="flex items-center gap-1.5 px-3 flex-1 min-w-0 h-full">
                        {item.assigneeName && width > 60 && (
                          <span className="text-[9px] font-bold text-white/80 bg-white/20 w-5 h-5 rounded-full flex items-center justify-center shrink-0">
                            {getInitials(item.assigneeName)}
                          </span>
                        )}
                        {width > 80 && (
                          <span className="text-xs font-medium text-white truncate">
                            {item.label}
                          </span>
                        )}
                      </div>
                    )}

                    {/* Right resize handle */}
                    {!readOnly && onDateChange && (
                      <div
                        className="absolute right-0 top-0 bottom-0 w-2 cursor-col-resize hover:bg-white/30 z-10"
                        onMouseDown={(e) => handleMouseDown(e, item, 'resize-right')}
                      />
                    )}
                  </div>
                </div>
              </div>
            )
          })}
        </div>
      </div>

      {/* Tooltip */}
      {tooltip && !dragState && (
        <div
          className="fixed z-50 pointer-events-none"
          style={{
            left: tooltip.x,
            top: tooltip.y,
            transform: 'translate(-50%, -100%)',
          }}
        >
          <div className="bg-gray-900 text-white text-xs rounded-lg px-3 py-2 shadow-lg max-w-xs">
            <div className="font-semibold mb-1">{tooltip.item.label}</div>
            <div className="text-gray-300 space-y-0.5">
              {tooltip.item.startDate && (
                <div>Start: {format(tooltip.item.startDate, 'MMM d, yyyy')}</div>
              )}
              {tooltip.item.endDate && (
                <div>End: {format(tooltip.item.endDate, 'MMM d, yyyy')}</div>
              )}
              {tooltip.item.assigneeName && (
                <div>Assignee: {tooltip.item.assigneeName}</div>
              )}
              {tooltip.item.status && (
                <div>Status: {tooltip.item.status.replace(/_/g, ' ')}</div>
              )}
            </div>
            {!readOnly && onDateChange && (
              <div className="text-gray-400 mt-1 text-[10px] italic">
                Drag to move · Drag edges to resize
              </div>
            )}
          </div>
        </div>
      )}
    </div>
  )
}
