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

const WEEKS = 20
const DAY_INIT = ['M','T','W','T','F','S','S']

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',
}

function getCellClass(baseDensity, statusCounts) {
  const total = Object.values(statusCounts).reduce((a, b) => a + b, 0)
  if (total === 0) return 'bg-surface border-surface-border'
  if (baseDensity === 1) return 'bg-gold/25 border-gold/40'
  if (baseDensity === 2) return 'bg-gold/55 border-gold/70'
  return 'bg-gold border-gold shadow-gold'
}

export default function WorkloadHeatmap() {
  const projects  = useProjectStore(s => s.projects)
  const openFocus = useFocusStore(s => s.openFocus)
  const [tooltip, setTooltip] = useState(null)

  const { weeks, stats } = useMemo(() => {
    const start = startOfWeek(addWeeks(new Date(), -10), { 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])

  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 CELL = 16
  const GAP  = 2

  return (
    <div className="flex flex-col h-full bg-surface overflow-auto">
      {/* Header */}
      <div className="flex items-center justify-between px-8 pt-6 pb-4">
        <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>
        <div className="flex items-center gap-3 text-[10px] text-text-muted">
          <span className="uppercase tracking-[0.18em] text-text-muted/60">FABDASH</span>
        </div>
      </div>

      {/* Status heatmaps */}
      <div className="flex flex-col gap-6 px-8 pb-8">
        {STATUS_KEYS.map((statusKey) => (
          <div key={statusKey} className="bg-surface-elevated/40 border border-surface-border rounded-xl p-4">
            <div className="flex items-center justify-between mb-3">
              <div className="flex items-baseline gap-2">
                <h3 className="text-xs font-semibold tracking-widest uppercase text-text-muted/70">
                  {STATUS_LABEL[statusKey]}
                </h3>
                <span className={`${STATUS_COLOR[statusKey]} text-[10px] font-mono`}>
                  {stats[statusKey]} tasks
                </span>
              </div>
              <div className="flex items-center gap-2 text-[9px] text-text-muted/60">
                <span>Less</span>
                {['bg-surface border-surface-border','bg-gold/25 border-gold/40','bg-gold/55 border-gold/70','bg-gold border-gold'].map((c,i) => (
                  <div key={i} className={`w-3 h-3 rounded-sm border ${c}`} />
                ))}
                <span>More</span>
              </div>
            </div>

            <div className="flex gap-3 overflow-x-auto pb-2">
              {/* Day labels */}
              <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-[10px] text-text-muted/50 font-mono w-4">
                    {d}
                  </div>
                ))}
              </div>

              {/* Grid */}
              <div className="flex flex-col flex-shrink-0">
                {/* Month labels */}
                <div className="relative h-5 mb-1">
                  {monthLabels.map(({ wi, label }) => (
                    <span
                      key={label+wi}
                      className="absolute text-[10px] 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 countForStatus = (statusCounts || {})[statusKey] || 0
                        const baseDensity    = countForStatus
                        return (
                          <div
                            key={key + statusKey}
                            style={{ width: CELL, height: CELL }}
                            className={`rounded-sm border cursor-pointer transition-all hover:scale-125 hover:z-10 relative
                              ${getCellClass(baseDensity, statusCounts || {})}
                              ${isToday(date) ? 'ring-1 ring-white/40' : ''}
                            `}
                            onClick={() => {
                              if (!items || !items.length) return
                              const match = items.find(({ deliverable }) => deliverable.status === statusKey) || items[0]
                              if (match) openFocus(match.project.id, match.deliverable.id)
                            }}
                            onMouseEnter={(e) => {
                              const filtered = (items || []).filter(({ deliverable }) => deliverable.status === statusKey)
                              const showItems = filtered.length ? filtered : items || []
                              setTooltip({
                                x: e.clientX,
                                y: e.clientY,
                                date,
                                statusKey,
                                items: showItems,
                              })
                            }}
                            onMouseLeave={() => setTooltip(null)}
                          />
                        )
                      })}
                    </div>
                  ))}
                </div>
              </div>
            </div>
          </div>
        ))}

        {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 — ' : ''}{format(tooltip.date, 'EEE, MMM d, yyyy')}
            </p>
            <p className="text-[10px] text-text-muted/60 mb-1.5">
              {STATUS_LABEL[tooltip.statusKey]} · {tooltip.items.length} task{tooltip.items.length !== 1 ? 's' : ''}
            </p>
            {tooltip.items.length === 0 ? (
              <p className="text-text-muted/50 text-xs">No deliverables</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>
            )}
          </div>
        )}
      </div>
    </div>
  )
}
