import { useMemo, useState } from 'react'
import { format, startOfWeek, addDays, addWeeks, isToday } from 'date-fns'
import useProjectStore from '../../store/useProjectStore'
import HeatmapDayPanel from './HeatmapDayPanel'

const WEEKS   = 20
const DAY_INIT = ['M','T','W','T','F','S','S']
const CELL    = 16
const CELL_LG = 40
const GAP     = 2
const GAP_LG  = 4

const STATUS_KEYS  = ['upcoming','in_progress','completed','overdue']
const STATUS_LABEL = { upcoming: 'Upcoming', in_progress: 'In Progress', completed: 'Completed', overdue: 'Overdue' }
const STATUS_COLOR = { upcoming: 'text-blue-400', in_progress: 'text-amber-400', completed: 'text-green-400', overdue: 'text-red-400' }

const STATUS_CELL_COLORS = {
  upcoming:    ['bg-blue-400/20 border-blue-400/30',  'bg-blue-400/55 border-blue-400/70',  'bg-blue-400 border-blue-400 shadow-[0_0_4px_rgba(96,165,250,0.6)]'],
  in_progress: ['bg-amber-400/20 border-amber-400/30','bg-amber-400/55 border-amber-400/70','bg-amber-400 border-amber-400 shadow-[0_0_4px_rgba(251,191,36,0.6)]'],
  completed:   ['bg-green-400/20 border-green-400/30','bg-green-400/55 border-green-400/70','bg-green-400 border-green-400 shadow-[0_0_4px_rgba(74,222,128,0.6)]'],
  overdue:     ['bg-red-400/20 border-red-400/30',    'bg-red-400/55 border-red-400/70',    'bg-red-400 border-red-400 shadow-[0_0_4px_rgba(248,113,113,0.6)]'],
}

const STATUS_HOVER_RING = {
  upcoming:    'hover:ring-1 hover:ring-blue-300/80',
  in_progress: 'hover:ring-1 hover:ring-amber-300/80',
  completed:   'hover:ring-1 hover:ring-green-300/80',
  overdue:     'hover:ring-1 hover:ring-red-400/90',
}

const STATUS_PRIORITY = { overdue: 4, in_progress: 3, upcoming: 2, completed: 1 }

function getCellClass(count, statusKey) {
  if (count === 0) return 'bg-surface border-surface-border'
  const c = STATUS_CELL_COLORS[statusKey] || STATUS_CELL_COLORS.upcoming
  if (count === 1) return c[0]
  if (count === 2) return c[1]
  return c[2]
}

function getDominantStatus(statusCounts) {
  let dominant = null, maxCount = 0, maxPriority = 0
  for (const [sk, count] of Object.entries(statusCounts)) {
    if (count === 0) continue
    if (count > maxCount || (count === maxCount && (STATUS_PRIORITY[sk] || 0) > maxPriority)) {
      dominant = sk; maxCount = count; maxPriority = STATUS_PRIORITY[sk] || 0
    }
  }
  return { dominant, total: Object.values(statusCounts).reduce((a, b) => a + b, 0) }
}

// 4-cell density legend strip
function DensityLegend({ statusKey }) {
  const c = STATUS_CELL_COLORS[statusKey]
  return (
    <div className="flex items-center gap-1 text-[9px] text-text-muted/35 select-none">
      <span>Less</span>
      <div className="w-2 h-2 rounded-sm border bg-surface border-surface-border" />
      <div className={`w-2 h-2 rounded-sm border ${c[0]}`} />
      <div className={`w-2 h-2 rounded-sm border ${c[1]}`} />
      <div className={`w-2 h-2 rounded-sm border ${c[2]}`} />
      <span>More</span>
    </div>
  )
}

export default function WorkloadHeatmap() {
  const projects = useProjectStore(s => s.projects)
  const [tooltip,     setTooltip]     = useState(null)
  const [selectedDay, setSelectedDay] = useState(null) // Date | null
  const [weekOffset,  setWeekOffset]  = useState(0)    // shifts window in weeks

  const { weeks, stats } = useMemo(() => {
    const start = startOfWeek(addWeeks(new Date(), -10 + weekOffset), { weekStartsOn: 1 })
    const map   = {}

    projects.forEach(p => {
      ;(p.deliverables || []).forEach(d => {
        const key = d.due_date
        if (!map[key]) map[key] = { items: [], statusCounts: { upcoming: 0, in_progress: 0, completed: 0, overdue: 0 } }
        map[key].items.push({ deliverable: d, project: p })
        const s = d.status || 'upcoming'
        if (map[key].statusCounts[s] !== undefined) map[key].statusCounts[s]++
      })
    })

    const grid = Array.from({ length: WEEKS }, (_, wi) =>
      Array.from({ length: 7 }, (_, di) => {
        const date  = addDays(start, wi * 7 + di)
        const key   = format(date, 'yyyy-MM-dd')
        const entry = map[key] || { items: [], statusCounts: { upcoming: 0, in_progress: 0, completed: 0, overdue: 0 } }
        return { date, key, ...entry }
      })
    )

    const all = projects.flatMap(p => p.deliverables || [])
    const stats = {
      total:       all.length,
      upcoming:    all.filter(d => d.status === 'upcoming').length,
      in_progress: all.filter(d => d.status === 'in_progress').length,
      completed:   all.filter(d => d.status === 'completed').length,
      overdue:     all.filter(d => d.status === 'overdue').length,
    }
    return { weeks: grid, stats }
  }, [projects, weekOffset])

  const windowStart = weeks[0]?.[0]?.date
  const windowEnd   = weeks[WEEKS - 1]?.[6]?.date
  const windowLabel = windowStart && windowEnd
    ? `${format(windowStart, 'MMM d')} \u2013 ${format(windowEnd, 'MMM d, yyyy')}`
    : ''

  const monthLabels = useMemo(() => {
    const labels = []; let last = -1
    weeks.forEach((week, wi) => {
      const m = week[0].date.getMonth()
      if (m !== last) { labels.push({ wi, label: format(week[0].date, 'MMM') }); last = m }
    })
    return labels
  }, [weeks])

  const monthLabelsBig = useMemo(() => {
    const labels = []; let last = -1
    weeks.forEach((week, wi) => {
      const m = week[0].date.getMonth()
      if (m !== last) { labels.push({ wi, label: format(week[0].date, 'MMM') }); last = m }
    })
    return labels
  }, [weeks])

  return (
    <div className="flex flex-col h-full bg-surface overflow-auto">

      {/* Header */}
      <div className="flex items-center justify-between pl-24 pr-8 pt-6 pb-3">
        <div>
          <h2 className="text-gold font-bold text-lg tracking-wide">Workload Heatmap</h2>
          <p className="text-text-muted text-xs mt-0.5">20 weeks of deliverable density by status</p>
        </div>

        {/* Window navigation */}
        <div className="flex items-center gap-2">
          <button
            onClick={() => setWeekOffset(o => o - 4)}
            className="text-xs px-2.5 py-1.5 rounded-lg border border-surface-border bg-surface-elevated text-text-muted hover:text-gold hover:border-gold/40 transition-all"
            title="Shift window back 4 weeks"
          >\u2190 4 wks</button>

          <button
            onClick={() => setWeekOffset(0)}
            className={`text-xs px-2.5 py-1.5 rounded-lg border transition-all font-medium ${
              weekOffset === 0
                ? 'border-gold/50 text-gold bg-gold/10'
                : 'border-surface-border bg-surface-elevated text-text-muted hover:text-gold hover:border-gold/40'
            }`}
            title="Center window on today"
          >Today</button>

          <button
            onClick={() => setWeekOffset(o => o + 4)}
            className="text-xs px-2.5 py-1.5 rounded-lg border border-surface-border bg-surface-elevated text-text-muted hover:text-gold hover:border-gold/40 transition-all"
            title="Shift window forward 4 weeks"
          >4 wks \u2192</button>

          <span className="text-[10px] text-text-muted/40 font-mono ml-1 hidden xl:block">{windowLabel}</span>
        </div>
      </div>

      {/* Stat cards + per-status heatmaps */}
      <div className="grid grid-cols-4 gap-4 px-8 pb-4">
        {STATUS_KEYS.map((statusKey) => (
          <div key={statusKey} className="flex flex-col gap-3">

            {/* Stat card */}
            <div className="bg-surface-elevated border border-surface-border rounded-xl p-4 text-center">
              <p className={`text-2xl font-bold ${STATUS_COLOR[statusKey]}`}>{stats[statusKey]}</p>
              <p className="text-text-muted text-xs mt-1">{STATUS_LABEL[statusKey]}</p>
            </div>

            {/* Mini heatmap */}
            <div className="bg-surface-elevated/40 border border-surface-border rounded-xl p-3 flex-1 min-h-[160px] flex flex-col gap-2">
              <div className="flex justify-end">
                <DensityLegend statusKey={statusKey} />
              </div>
              <div className="flex items-center justify-center flex-1">
                <div className="flex gap-2 overflow-x-auto pb-1 justify-center">
                  {/* Day initials */}
                  <div className="flex flex-col flex-shrink-0 pt-6" style={{ gap: GAP }}>
                    {DAY_INIT.map((d, i) => (
                      <div key={i} style={{ height: CELL }} className="flex items-center text-[9px] text-text-muted/50 font-mono w-3">{d}</div>
                    ))}
                  </div>
                  {/* Grid */}
                  <div className="flex flex-col flex-shrink-0">
                    <div className="relative h-4 mb-1">
                      {monthLabels.map(({ wi, label }) => (
                        <span key={label+wi} className="absolute text-[9px] text-text-muted/60 font-medium" style={{ left: wi * (CELL + GAP) }}>{label}</span>
                      ))}
                    </div>
                    <div className="flex" style={{ gap: GAP }}>
                      {weeks.map((week, wi) => (
                        <div key={wi} className="flex flex-col flex-shrink-0" style={{ gap: GAP }}>
                          {week.map(({ date, key, items, statusCounts }) => {
                            const count = (statusCounts || {})[statusKey] || 0
                            return (
                              <div
                                key={key + statusKey}
                                style={{ width: CELL, height: CELL }}
                                className={`rounded-sm border cursor-pointer transition-transform duration-100 hover:scale-125 hover:z-10
                                  ${getCellClass(count, statusKey)}
                                  ${isToday(date) ? 'ring-1 ring-white/60' : ''}
                                  ${count > 0 ? STATUS_HOVER_RING[statusKey] : ''}
                                `}
                                onClick={() => setSelectedDay(date)}
                                onMouseEnter={(e) => {
                                  const filtered = (items || []).filter(({ deliverable }) => deliverable.status === statusKey)
                                  if (!filtered.length) return
                                  setTooltip({ x: e.clientX, y: e.clientY, date, statusKey, items: filtered })
                                }}
                                onMouseLeave={() => setTooltip(null)}
                              />
                            )
                          })}
                        </div>
                      ))}
                    </div>
                  </div>
                </div>
              </div>
            </div>
          </div>
        ))}
      </div>

      {/* Combined All Tasks heatmap */}
      <div className="px-8 pb-8">
        <div className="bg-surface-elevated/40 border border-surface-border rounded-xl p-5">
          <div className="flex items-center justify-between mb-4">
            <div className="flex items-baseline gap-2">
              <h3 className="text-xs font-semibold tracking-widest uppercase text-text-muted/70">All Tasks</h3>
              <span className="text-text-muted/60 text-[10px] font-mono">{stats.total} tasks</span>
            </div>
            <div className="flex items-center gap-4 text-[9px] text-text-muted/60">
              {STATUS_KEYS.map(sk => (
                <div key={sk} className="flex items-center gap-1.5">
                  <div className={`w-2.5 h-2.5 rounded-sm border ${STATUS_CELL_COLORS[sk][2].split(' ').slice(0,2).join(' ')}`} />
                  <span className={STATUS_COLOR[sk]}>{STATUS_LABEL[sk]}</span>
                </div>
              ))}
              <span className="ml-1 text-text-muted/40">\u00b7 color = highest priority</span>
            </div>
          </div>

          <div className="flex gap-3 overflow-x-auto pb-2 justify-center">
            <div className="flex flex-col flex-shrink-0 pt-6" style={{ gap: GAP }}>
              {DAY_INIT.map((d, i) => (
                <div key={i} style={{ height: CELL_LG }} className="flex items-center text-[11px] text-text-muted/50 font-mono w-4">{d}</div>
              ))}
            </div>
            <div className="flex flex-col flex-shrink-0">
              <div className="relative h-5 mb-1">
                {monthLabelsBig.map(({ wi, label }) => (
                  <span key={label+wi} className="absolute text-[10px] text-text-muted/60 font-medium" style={{ left: wi * (CELL_LG + GAP_LG) }}>{label}</span>
                ))}
              </div>
              <div className="flex" style={{ gap: GAP_LG }}>
                {weeks.map((week, wi) => (
                  <div key={wi} className="flex flex-col flex-shrink-0" style={{ gap: GAP_LG }}>
                    {week.map(({ date, key, items, statusCounts }) => {
                      const { dominant, total } = getDominantStatus(statusCounts || {})
                      return (
                        <div
                          key={key + 'combined'}
                          style={{ width: CELL_LG, height: CELL_LG }}
                          className={`rounded-sm border cursor-pointer transition-transform duration-100 hover:scale-125 hover:z-10
                            ${dominant ? getCellClass(total, dominant) : 'bg-surface border-surface-border'}
                            ${isToday(date) ? 'ring-1 ring-white/60' : ''}
                            ${dominant ? STATUS_HOVER_RING[dominant] : ''}
                          `}
                          onClick={() => setSelectedDay(date)}
                          onMouseEnter={(e) => {
                            if (!items?.length) return
                            setTooltip({ x: e.clientX, y: e.clientY, date, statusKey: dominant, items, combined: true, statusCounts })
                          }}
                          onMouseLeave={() => setTooltip(null)}
                        />
                      )
                    })}
                  </div>
                ))}
              </div>
            </div>
          </div>
        </div>
      </div>

      {/* Hover tooltip */}
      {tooltip && (
        <div
          className="fixed z-[200] pointer-events-none bg-surface-elevated border border-surface-border rounded-xl shadow-2xl px-3.5 py-3 min-w-[220px] max-w-[320px]"
          style={{ left: Math.min(tooltip.x + 14, window.innerWidth - 330), top: Math.max(tooltip.y - 100, 8) }}
        >
          <p className={`text-xs font-bold mb-1.5 ${isToday(tooltip.date) ? 'text-gold' : 'text-text-primary'}`}>
            {isToday(tooltip.date) ? 'Today \u2014 ' : ''}{format(tooltip.date, 'EEE, MMM d, yyyy')}
          </p>
          {tooltip.combined && tooltip.statusCounts ? (
            <div className="space-y-1 mb-2">
              {STATUS_KEYS.filter(sk => (tooltip.statusCounts[sk] || 0) > 0).map(sk => (
                <div key={sk} className="flex items-center justify-between gap-3">
                  <span className={`text-[10px] ${STATUS_COLOR[sk]}`}>{STATUS_LABEL[sk]}</span>
                  <span className="text-[10px] text-text-muted/60 font-mono">{tooltip.statusCounts[sk]}</span>
                </div>
              ))}
            </div>
          ) : (
            <p className={`text-[10px] mb-1.5 ${tooltip.statusKey ? STATUS_COLOR[tooltip.statusKey] : 'text-text-muted/60'}`}>
              {tooltip.statusKey ? STATUS_LABEL[tooltip.statusKey] : ''} \u00b7 {tooltip.items.length} task{tooltip.items.length !== 1 ? 's' : ''}
            </p>
          )}
          <div className="space-y-1.5">
            {(tooltip.items || []).slice(0, 5).map(({ deliverable, project }) => (
              <div key={deliverable.id} className="flex items-start gap-1.5">
                <div className="w-1.5 h-1.5 rounded-full mt-1 flex-shrink-0" style={{ backgroundColor: project.color }} />
                <div className="min-w-0 flex-1">
                  <p className="text-[11px] text-text-primary truncate">{deliverable.title}</p>
                  <p className="text-[10px] text-text-muted/60">{project.name}</p>
                </div>
              </div>
            ))}
            {(tooltip.items || []).length > 5 && (
              <p className="text-[10px] text-text-muted/50 pl-3">+{tooltip.items.length - 5} more</p>
            )}
          </div>
          <p className="text-[9px] text-text-muted/25 mt-2 pt-1.5 border-t border-surface-border/50">Click to open day detail</p>
        </div>
      )}

      {/* Day detail panel */}
      {selectedDay && (
        <HeatmapDayPanel
          date={selectedDay}
          onClose={() => setSelectedDay(null)}
        />
      )}
    </div>
  )
}