import { useState, useRef, useCallback } from 'react'
import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
import { usePOSStore } from '@/stores/pos.store'
import { productSearchOptions, posMutations, posKeys, type Transaction, type Product } from '@/api/pos'
import { Input } from '@/components/ui/input'
import { Button } from '@/components/ui/button'
import { Dialog, DialogContent, DialogHeader, DialogTitle } from '@/components/ui/dialog'
import { Label } from '@/components/ui/label'
import { Skeleton } from '@/components/ui/skeleton'
import { Search, ScanBarcode, Wrench, PenLine } from 'lucide-react'
import { toast } from 'sonner'

interface POSItemPanelProps {
  transaction: Transaction | null
}

export function POSItemPanel({ transaction: _transaction }: POSItemPanelProps) {
  const queryClient = useQueryClient()
  const { currentTransactionId, setTransaction, locationId, accountId } = usePOSStore()
  const [search, setSearch] = useState('')
  const [customOpen, setCustomOpen] = useState(false)
  const [customDesc, setCustomDesc] = useState('')
  const [customPrice, setCustomPrice] = useState('')
  const [customQty, setCustomQty] = useState('1')
  const searchRef = useRef<HTMLInputElement>(null)

  // Debounced product search
  const { data: productsData, isLoading: searchLoading } = useQuery({
    ...productSearchOptions(search),
    enabled: search.length >= 1,
  })
  const products = productsData?.data ?? []

  // Add line item mutation
  const addItemMutation = useMutation({
    mutationFn: async (product: Product) => {
      let txnId = currentTransactionId
      // Auto-create transaction if none exists
      if (!txnId) {
        const txn = await posMutations.createTransaction({
          transactionType: 'sale',
          locationId: locationId ?? undefined,
          accountId: accountId ?? undefined,
        })
        txnId = txn.id
        setTransaction(txnId)
      }
      return posMutations.addLineItem(txnId, {
        productId: product.id,
        description: product.name,
        qty: 1,
        unitPrice: parseFloat(product.price ?? '0'),
      })
    },
    onSuccess: () => {
      const txnId = usePOSStore.getState().currentTransactionId
      queryClient.invalidateQueries({ queryKey: posKeys.transaction(txnId ?? '') })
    },
    onError: (err) => toast.error(err.message),
  })

  // Custom item mutation
  const addCustomMutation = useMutation({
    mutationFn: async () => {
      let txnId = currentTransactionId
      if (!txnId) {
        const txn = await posMutations.createTransaction({
          transactionType: 'sale',
          locationId: locationId ?? undefined,
          accountId: accountId ?? undefined,
        })
        txnId = txn.id
        setTransaction(txnId)
      }
      return posMutations.addLineItem(txnId, {
        description: customDesc,
        qty: parseInt(customQty) || 1,
        unitPrice: parseFloat(customPrice) || 0,
      })
    },
    onSuccess: () => {
      const txnId = usePOSStore.getState().currentTransactionId
      queryClient.invalidateQueries({ queryKey: posKeys.transaction(txnId ?? '') })
      setCustomOpen(false)
      setCustomDesc('')
      setCustomPrice('')
      setCustomQty('1')
    },
    onError: (err) => toast.error(err.message),
  })

  // UPC scan
  const scanMutation = useMutation({
    mutationFn: async (upc: string) => {
      const product = await posMutations.lookupUpc(upc)
      let txnId = currentTransactionId
      if (!txnId) {
        const txn = await posMutations.createTransaction({
          transactionType: 'sale',
          locationId: locationId ?? undefined,
          accountId: accountId ?? undefined,
        })
        txnId = txn.id
        setTransaction(txnId)
      }
      return posMutations.addLineItem(txnId, {
        productId: product.id,
        description: product.name,
        qty: 1,
        unitPrice: parseFloat(product.price ?? '0'),
      })
    },
    onSuccess: () => {
      queryClient.invalidateQueries({ queryKey: posKeys.transaction(currentTransactionId ?? '') })
      setSearch('')
      toast.success('Item scanned')
    },
    onError: (err) => toast.error(err.message),
  })

  const handleSearchKeyDown = useCallback((e: React.KeyboardEvent<HTMLInputElement>) => {
    // Barcode scanners typically send Enter after the code
    if (e.key === 'Enter' && search.length >= 6) {
      // Looks like a UPC — try scanning
      scanMutation.mutate(search)
    }
  }, [search, scanMutation])

  return (
    <div className="flex flex-col h-full">
      {/* Search bar */}
      <div className="p-3 border-b border-border">
        <div className="relative">
          <Search className="absolute left-3 top-1/2 -translate-y-1/2 h-4 w-4 text-muted-foreground" />
          <Input
            ref={searchRef}
            value={search}
            onChange={(e) => setSearch(e.target.value)}
            onKeyDown={handleSearchKeyDown}
            placeholder="Search products or scan barcode..."
            className="pl-10 h-11 text-base"
            autoFocus
          />
        </div>
      </div>

      {/* Product grid */}
      <div className="flex-1 overflow-y-auto p-3">
        {searchLoading ? (
          <div className="grid grid-cols-3 gap-3">
            {Array.from({ length: 6 }).map((_, i) => (
              <Skeleton key={i} className="h-24 rounded-lg" />
            ))}
          </div>
        ) : products.length > 0 ? (
          <div className="grid grid-cols-3 gap-3">
            {products.map((product) => (
              <button
                key={product.id}
                onClick={() => addItemMutation.mutate(product)}
                disabled={addItemMutation.isPending}
                className="flex flex-col items-start p-3 rounded-lg border border-border bg-card hover:bg-accent active:bg-accent/80 transition-colors text-left min-h-[80px]"
              >
                <span className="font-medium text-sm line-clamp-2">{product.name}</span>
                <div className="mt-auto flex items-center justify-between w-full pt-1">
                  <span className="text-base font-semibold">${parseFloat(product.price ?? '0').toFixed(2)}</span>
                  {product.sku && <span className="text-xs text-muted-foreground">{product.sku}</span>}
                </div>
                {product.isSerialized ? (
                  <span className="text-[10px] text-muted-foreground">Serialized</span>
                ) : product.qtyOnHand !== null ? (
                  <span className="text-[10px] text-muted-foreground">{product.qtyOnHand} in stock</span>
                ) : null}
              </button>
            ))}
          </div>
        ) : search.length >= 1 ? (
          <div className="flex items-center justify-center h-32 text-muted-foreground text-sm">
            No products found for "{search}"
          </div>
        ) : (
          <div className="flex items-center justify-center h-32 text-muted-foreground text-sm">
            Search for products to add to the sale
          </div>
        )}
      </div>

      {/* Quick action buttons */}
      <div className="p-3 border-t border-border flex gap-2">
        <Button
          variant="outline"
          className="flex-1 h-11 text-sm gap-2"
          onClick={() => searchRef.current?.focus()}
        >
          <ScanBarcode className="h-4 w-4" />
          Scan
        </Button>
        <Button
          variant="outline"
          className="flex-1 h-11 text-sm gap-2"
          disabled
        >
          <Wrench className="h-4 w-4" />
          Repairs
        </Button>
        <Button
          variant="outline"
          className="flex-1 h-11 text-sm gap-2"
          onClick={() => setCustomOpen(true)}
        >
          <PenLine className="h-4 w-4" />
          Custom
        </Button>
      </div>

      {/* Custom item dialog */}
      <Dialog open={customOpen} onOpenChange={setCustomOpen}>
        <DialogContent>
          <DialogHeader>
            <DialogTitle>Add Custom Item</DialogTitle>
          </DialogHeader>
          <form
            onSubmit={(e) => { e.preventDefault(); addCustomMutation.mutate() }}
            className="space-y-4"
          >
            <div className="space-y-2">
              <Label>Description *</Label>
              <Input
                value={customDesc}
                onChange={(e) => setCustomDesc(e.target.value)}
                placeholder="Item description"
                required
                className="h-11"
              />
            </div>
            <div className="grid grid-cols-2 gap-4">
              <div className="space-y-2">
                <Label>Price *</Label>
                <Input
                  type="number"
                  step="0.01"
                  min="0"
                  value={customPrice}
                  onChange={(e) => setCustomPrice(e.target.value)}
                  placeholder="0.00"
                  required
                  className="h-11"
                />
              </div>
              <div className="space-y-2">
                <Label>Qty</Label>
                <Input
                  type="number"
                  min="1"
                  value={customQty}
                  onChange={(e) => setCustomQty(e.target.value)}
                  className="h-11"
                />
              </div>
            </div>
            <Button type="submit" className="w-full h-11" disabled={addCustomMutation.isPending}>
              {addCustomMutation.isPending ? 'Adding...' : 'Add Item'}
            </Button>
          </form>
        </DialogContent>
      </Dialog>
    </div>
  )
}