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

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

function getCellStyle(count) {
  if (count === 0) return 'bg-surface border-surface-border'
  if (count === 1) return 'bg-gold/25 border-gold/40'
  if (count === 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 => {
        if (!map[d.due_date]) map[d.due_date] = []
        map[d.due_date].push({ deliverable: d, project: p })
      })
    })

    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')
        return { date, key, items: map[key] || [] }
      })
    )

    const all  = projects.flatMap(p => p.deliverables || [])
    const stats = {
      total:       all.length,
      overdue:     all.filter(d => d.status === 'overdue').length,
      in_progress: all.filter(d => d.status === 'in_progress').length,
      completed:   all.filter(d => d.status === 'completed').length,
      upcoming:    all.filter(d => d.status === 'upcoming').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 = 20, GAP = 3

  return (
    <div className="flex flex-col h-full bg-surface overflow-auto p-6">
      {/* Header */}
      <div className="flex items-center justify-between mb-6">
        <div>
          <h2 className="text-gold font-bold text-lg tracking-wide">Workload Heatmap</h2>
          <p className="text-text-muted text-xs mt-0.5">{WEEKS} weeks of deliverable density</p>
        </div>
        <div className="flex items-center gap-2 text-xs text-text-muted">
          <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-4 h-4 rounded-sm border ${c}`} />
          ))}
          <span>More</span>
        </div>
      </div>

      {/* Stat cards */}
      <div className="grid grid-cols-5 gap-3 mb-6">
        {[
          { label: 'Total',       value: stats.total,       color: 'text-text-primary' },
          { label: 'Upcoming',    value: stats.upcoming,    color: 'text-blue-400'     },
          { label: 'In Progress', value: stats.in_progress, color: 'text-amber-400'    },
          { label: 'Completed',   value: stats.completed,   color: 'text-green-400'    },
          { label: 'Overdue',     value: stats.overdue,     color: 'text-red-400'      },
        ].map(({ label, value, color }) => (
          <div key={label} className="bg-surface-elevated border border-surface-border rounded-xl p-4 text-center">
            <p className={`text-2xl font-bold ${color}`}>{value}</p>
            <p className="text-text-muted text-xs mt-1">{label}</p>
          </div>
        ))}
      </div>

      {/* Heatmap grid */}
      <div className="flex gap-3 overflow-x-auto pb-4">
        {/* 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>
          {/* Week columns */}
          <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 }) => (
                  <div key={key}
                    style={{ width: CELL, height: CELL }}
                    className={`rounded-sm border cursor-pointer transition-all hover:scale-125 hover:z-10 relative
                      ${getCellStyle(items.length)}
                      ${isToday(date) ? 'ring-1 ring-white/40' : ''}
                    `}
                    onClick={() => items.length > 0 && openFocus(items[0].project.id, items[0].deliverable.id)}
                    onMouseEnter={(e) => setTooltip({ x: e.clientX, y: e.clientY, date, items })}
                    onMouseLeave={() => setTooltip(null)}
                  />
                ))}
              </div>
            ))}
          </div>
        </div>
      </div>

      {/* 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-[200px] max-w-[280px]"
          style={{ left: Math.min(tooltip.x + 14, window.innerWidth - 290), 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>
          {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>
  )
}
