'use client'

import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
import dynamic from 'next/dynamic'
import type { GridResult, GridCell, WordEntry } from '@/app/(admin)/ai/ocr-pipeline/types'

const KLAUSUR_API = '/klausur-api'

// Lazy-load Fabric.js canvas editor (SSR-incompatible)
const FabricReconstructionCanvas = dynamic(
  () => import('./FabricReconstructionCanvas').then(m => ({ default: m.FabricReconstructionCanvas })),
  { ssr: false, loading: () => <div className="py-8 text-center text-sm text-gray-400">Editor wird geladen...</div> }
)

type EditorMode = 'simple' | 'editor'

interface StepReconstructionProps {
  sessionId: string | null
  onNext: () => void
}

interface EditableCell {
  cellId: string
  text: string
  originalText: string
  bboxPct: { x: number; y: number; w: number; h: number }
  colType: string
  rowIndex: number
  colIndex: number
}

type UndoAction = { cellId: string; oldText: string; newText: string }

export function StepReconstruction({ sessionId, onNext }: StepReconstructionProps) {
  const [status, setStatus] = useState<'loading' | 'ready' | 'saving' | 'saved' | 'error'>('loading')
  const [error, setError] = useState('')
  const [cells, setCells] = useState<EditableCell[]>([])
  const [gridCells, setGridCells] = useState<GridCell[]>([])
  const [editorMode, setEditorMode] = useState<EditorMode>('simple')
  const [editedTexts, setEditedTexts] = useState<Map<string, string>>(new Map())
  const [zoom, setZoom] = useState(100)
  const [imageNaturalH, setImageNaturalH] = useState(0)
  const [showEmptyHighlight, setShowEmptyHighlight] = useState(true)

  // Undo/Redo stacks
  const [undoStack, setUndoStack] = useState<UndoAction[]>([])
  const [redoStack, setRedoStack] = useState<UndoAction[]>([])

  // (allCells removed — cells now contains all cells including empty ones)

  const containerRef = useRef<HTMLDivElement>(null)
  const imageRef = useRef<HTMLImageElement>(null)

  // Load session data on mount
  useEffect(() => {
    if (!sessionId) return
    loadSessionData()
  // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [sessionId])

  // Track image natural height for font scaling
  const handleImageLoad = useCallback(() => {
    if (imageRef.current) {
      setImageNaturalH(imageRef.current.naturalHeight)
    }
  }, [])

  const loadSessionData = async () => {
    if (!sessionId) return
    setStatus('loading')
    try {
      const res = await fetch(`${KLAUSUR_API}/api/v1/ocr-pipeline/sessions/${sessionId}`)
      if (!res.ok) throw new Error(`HTTP ${res.status}`)
      const data = await res.json()

      const wordResult: GridResult | undefined = data.word_result
      if (!wordResult) {
        setError('Keine Worterkennungsdaten gefunden. Bitte zuerst Schritt 5 abschliessen.')
        setStatus('error')
        return
      }

      // Build editable cells from grid cells
      const rawGridCells: GridCell[] = wordResult.cells || []
      setGridCells(rawGridCells)
      const allEditableCells: EditableCell[] = rawGridCells.map(c => ({
        cellId: c.cell_id,
        text: c.text,
        originalText: c.text,
        bboxPct: c.bbox_pct,
        colType: c.col_type,
        rowIndex: c.row_index,
        colIndex: c.col_index,
      }))

      setCells(allEditableCells)
      setEditedTexts(new Map())
      setUndoStack([])
      setRedoStack([])
      setStatus('ready')
    } catch (e: unknown) {
      setError(e instanceof Error ? e.message : String(e))
      setStatus('error')
    }
  }

  const handleTextChange = useCallback((cellId: string, newText: string) => {
    setEditedTexts(prev => {
      const oldText = prev.get(cellId)
      const cell = cells.find(c => c.cellId === cellId)
      const prevText = oldText ?? cell?.text ?? ''

      // Push to undo stack
      setUndoStack(stack => [...stack, { cellId, oldText: prevText, newText }])
      setRedoStack([]) // Clear redo on new edit

      const next = new Map(prev)
      next.set(cellId, newText)
      return next
    })
  }, [cells])

  const undo = useCallback(() => {
    setUndoStack(stack => {
      if (stack.length === 0) return stack
      const action = stack[stack.length - 1]
      const newStack = stack.slice(0, -1)

      setRedoStack(rs => [...rs, action])
      setEditedTexts(prev => {
        const next = new Map(prev)
        next.set(action.cellId, action.oldText)
        return next
      })

      return newStack
    })
  }, [])

  const redo = useCallback(() => {
    setRedoStack(stack => {
      if (stack.length === 0) return stack
      const action = stack[stack.length - 1]
      const newStack = stack.slice(0, -1)

      setUndoStack(us => [...us, action])
      setEditedTexts(prev => {
        const next = new Map(prev)
        next.set(action.cellId, action.newText)
        return next
      })

      return newStack
    })
  }, [])

  const resetCell = useCallback((cellId: string) => {
    const cell = cells.find(c => c.cellId === cellId)
    if (!cell) return
    setEditedTexts(prev => {
      const next = new Map(prev)
      next.delete(cellId)
      return next
    })
  }, [cells])

  // Global keyboard shortcuts for undo/redo
  useEffect(() => {
    const handler = (e: KeyboardEvent) => {
      if ((e.metaKey || e.ctrlKey) && e.key === 'z') {
        e.preventDefault()
        if (e.shiftKey) {
          redo()
        } else {
          undo()
        }
      }
    }
    document.addEventListener('keydown', handler)
    return () => document.removeEventListener('keydown', handler)
  }, [undo, redo])

  const getDisplayText = useCallback((cell: EditableCell): string => {
    return editedTexts.get(cell.cellId) ?? cell.text
  }, [editedTexts])

  const isEdited = useCallback((cell: EditableCell): boolean => {
    const edited = editedTexts.get(cell.cellId)
    return edited !== undefined && edited !== cell.originalText
  }, [editedTexts])

  const changedCount = useMemo(() => {
    let count = 0
    for (const cell of cells) {
      if (isEdited(cell)) count++
    }
    return count
  }, [cells, isEdited])

  // Identify empty required cells (EN or DE columns with no text)
  const emptyCellIds = useMemo(() => {
    const required = new Set(['column_en', 'column_de'])
    const ids = new Set<string>()
    for (const cell of cells) {
      if (required.has(cell.colType) && !cell.text.trim()) {
        ids.add(cell.cellId)
      }
    }
    return ids
  }, [cells])

  // Sort cells for tab navigation: by row, then by column
  const sortedCellIds = useMemo(() => {
    return [...cells]
      .sort((a, b) => a.rowIndex !== b.rowIndex ? a.rowIndex - b.rowIndex : a.colIndex - b.colIndex)
      .map(c => c.cellId)
  }, [cells])

  const handleKeyDown = useCallback((e: React.KeyboardEvent, cellId: string) => {
    if (e.key === 'Tab') {
      e.preventDefault()
      const idx = sortedCellIds.indexOf(cellId)
      const nextIdx = e.shiftKey ? idx - 1 : idx + 1
      if (nextIdx >= 0 && nextIdx < sortedCellIds.length) {
        const nextId = sortedCellIds[nextIdx]
        const el = document.getElementById(`cell-${nextId}`)
        el?.focus()
      }
    }
  }, [sortedCellIds])

  const saveReconstruction = useCallback(async () => {
    if (!sessionId) return
    setStatus('saving')
    try {
      const cellUpdates = Array.from(editedTexts.entries())
        .filter(([cellId, text]) => {
          const cell = cells.find(c => c.cellId === cellId)
          return cell && text !== cell.originalText
        })
        .map(([cellId, text]) => ({ cell_id: cellId, text }))

      if (cellUpdates.length === 0) {
        // Nothing changed, just advance
        setStatus('saved')
        return
      }

      const res = await fetch(`${KLAUSUR_API}/api/v1/ocr-pipeline/sessions/${sessionId}/reconstruction`, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ cells: cellUpdates }),
      })

      if (!res.ok) {
        const data = await res.json().catch(() => ({}))
        throw new Error(data.detail || `HTTP ${res.status}`)
      }

      setStatus('saved')
    } catch (e: unknown) {
      setError(e instanceof Error ? e.message : String(e))
      setStatus('error')
    }
  }, [sessionId, editedTexts, cells])

  // Handler for Fabric.js editor cell changes
  const handleFabricCellsChanged = useCallback((updates: { cell_id: string; text: string }[]) => {
    for (const u of updates) {
      setEditedTexts(prev => {
        const next = new Map(prev)
        next.set(u.cell_id, u.text)
        return next
      })
    }
  }, [])

  const dewarpedUrl = sessionId
    ? `${KLAUSUR_API}/api/v1/ocr-pipeline/sessions/${sessionId}/image/dewarped`
    : ''

  const colTypeColor = (colType: string): string => {
    const colors: Record<string, string> = {
      column_en: 'border-blue-400/40 focus:border-blue-500',
      column_de: 'border-green-400/40 focus:border-green-500',
      column_example: 'border-orange-400/40 focus:border-orange-500',
      column_text: 'border-purple-400/40 focus:border-purple-500',
      page_ref: 'border-cyan-400/40 focus:border-cyan-500',
      column_marker: 'border-gray-400/40 focus:border-gray-500',
    }
    return colors[colType] || 'border-gray-400/40 focus:border-gray-500'
  }

  // Font size based on image natural height (not container) scaled by zoom
  const getFontSize = useCallback((bboxH: number): number => {
    const baseH = imageNaturalH || 800
    const px = (bboxH / 100) * baseH * 0.55
    return Math.max(8, Math.min(18, px * (zoom / 100)))
  }, [imageNaturalH, zoom])

  if (!sessionId) {
    return <div className="text-center py-12 text-gray-400">Bitte zuerst eine Session auswaehlen.</div>
  }

  if (status === 'loading') {
    return (
      <div className="flex items-center gap-3 justify-center py-12">
        <div className="animate-spin rounded-full h-5 w-5 border-b-2 border-teal-500" />
        <span className="text-gray-500">Rekonstruktionsdaten werden geladen...</span>
      </div>
    )
  }

  if (status === 'error') {
    return (
      <div className="flex flex-col items-center justify-center py-12 text-center">
        <div className="text-5xl mb-4">&#x26A0;&#xFE0F;</div>
        <h3 className="text-lg font-medium text-red-600 dark:text-red-400 mb-2">Fehler</h3>
        <p className="text-sm text-gray-500 dark:text-gray-400 max-w-lg mb-4">{error}</p>
        <div className="flex gap-3">
          <button onClick={() => { setError(''); loadSessionData() }}
            className="px-5 py-2 bg-teal-600 text-white rounded-lg hover:bg-teal-700 transition-colors text-sm">
            Erneut versuchen
          </button>
          <button onClick={onNext}
            className="px-5 py-2 bg-gray-200 dark:bg-gray-700 text-gray-700 dark:text-gray-300 rounded-lg hover:bg-gray-300 dark:hover:bg-gray-600 transition-colors text-sm">
            Ueberspringen &rarr;
          </button>
        </div>
      </div>
    )
  }

  if (status === 'saved') {
    return (
      <div className="flex flex-col items-center justify-center py-12 text-center">
        <div className="text-5xl mb-4">&#x2705;</div>
        <h3 className="text-lg font-medium text-gray-700 dark:text-gray-300 mb-2">Rekonstruktion gespeichert</h3>
        <p className="text-sm text-gray-500 dark:text-gray-400 mb-6">
          {changedCount > 0 ? `${changedCount} Zellen wurden aktualisiert.` : 'Keine Aenderungen vorgenommen.'}
        </p>
        <button onClick={onNext}
          className="px-6 py-2.5 bg-teal-600 text-white rounded-lg hover:bg-teal-700 transition-colors font-medium">
          Weiter &rarr;
        </button>
      </div>
    )
  }

  return (
    <div className="space-y-3">
      {/* Toolbar */}
      <div className="flex items-center justify-between bg-white dark:bg-gray-800 rounded-lg border border-gray-200 dark:border-gray-700 px-3 py-2">
        <div className="flex items-center gap-2">
          <h3 className="text-sm font-medium text-gray-700 dark:text-gray-300">
            Schritt 7: Rekonstruktion
          </h3>
          {/* Mode toggle */}
          <div className="flex items-center ml-2 border border-gray-300 dark:border-gray-600 rounded overflow-hidden text-xs">
            <button
              onClick={() => setEditorMode('simple')}
              className={`px-2 py-0.5 transition-colors ${
                editorMode === 'simple'
                  ? 'bg-teal-600 text-white'
                  : 'hover:bg-gray-50 dark:hover:bg-gray-700 text-gray-600 dark:text-gray-400'
              }`}
            >
              Einfach
            </button>
            <button
              onClick={() => setEditorMode('editor')}
              className={`px-2 py-0.5 transition-colors ${
                editorMode === 'editor'
                  ? 'bg-teal-600 text-white'
                  : 'hover:bg-gray-50 dark:hover:bg-gray-700 text-gray-600 dark:text-gray-400'
              }`}
            >
              Editor
            </button>
          </div>
          <span className="text-xs text-gray-400">
            {cells.length} Zellen &middot; {changedCount} geaendert
            {emptyCellIds.size > 0 && showEmptyHighlight && (
              <span className="text-red-400 ml-1">&middot; {emptyCellIds.size} leer</span>
            )}
          </span>
        </div>
        <div className="flex items-center gap-2">
          {/* Undo/Redo */}
          <button
            onClick={undo}
            disabled={undoStack.length === 0}
            className="px-2 py-1 text-xs border border-gray-300 dark:border-gray-600 rounded hover:bg-gray-50 dark:hover:bg-gray-700 disabled:opacity-30"
            title="Rueckgaengig (Ctrl+Z)"
          >
            &#x21A9;
          </button>
          <button
            onClick={redo}
            disabled={redoStack.length === 0}
            className="px-2 py-1 text-xs border border-gray-300 dark:border-gray-600 rounded hover:bg-gray-50 dark:hover:bg-gray-700 disabled:opacity-30"
            title="Wiederholen (Ctrl+Shift+Z)"
          >
            &#x21AA;
          </button>

          <div className="w-px h-5 bg-gray-300 dark:bg-gray-600 mx-1" />

          {/* Empty field toggle */}
          <button
            onClick={() => setShowEmptyHighlight(v => !v)}
            className={`px-2 py-1 text-xs border rounded transition-colors ${
              showEmptyHighlight
                ? 'border-red-300 bg-red-50 text-red-600 dark:border-red-700 dark:bg-red-900/30 dark:text-red-400'
                : 'border-gray-300 dark:border-gray-600 hover:bg-gray-50 dark:hover:bg-gray-700'
            }`}
            title="Leere Pflichtfelder markieren"
          >
            Leer
          </button>

          <div className="w-px h-5 bg-gray-300 dark:bg-gray-600 mx-1" />

          {/* Zoom controls */}
          <button
            onClick={() => setZoom(z => Math.max(50, z - 25))}
            className="px-2 py-1 text-xs border border-gray-300 dark:border-gray-600 rounded hover:bg-gray-50 dark:hover:bg-gray-700"
          >
            &minus;
          </button>
          <span className="text-xs text-gray-500 w-10 text-center">{zoom}%</span>
          <button
            onClick={() => setZoom(z => Math.min(200, z + 25))}
            className="px-2 py-1 text-xs border border-gray-300 dark:border-gray-600 rounded hover:bg-gray-50 dark:hover:bg-gray-700"
          >
            +
          </button>
          <button
            onClick={() => setZoom(100)}
            className="px-2 py-1 text-xs border border-gray-300 dark:border-gray-600 rounded hover:bg-gray-50 dark:hover:bg-gray-700"
          >
            Fit
          </button>

          <div className="w-px h-5 bg-gray-300 dark:bg-gray-600 mx-1" />

          <button
            onClick={saveReconstruction}
            disabled={status === 'saving'}
            className="px-4 py-1.5 text-xs bg-teal-600 text-white rounded-lg hover:bg-teal-700 disabled:opacity-50 transition-colors font-medium"
          >
            {status === 'saving' ? 'Speichert...' : 'Speichern'}
          </button>
        </div>
      </div>

      {/* Reconstruction canvas — Simple or Editor mode */}
      {editorMode === 'editor' && sessionId ? (
        <FabricReconstructionCanvas
          sessionId={sessionId}
          cells={gridCells}
          onCellsChanged={handleFabricCellsChanged}
        />
      ) : (
        <div className="border rounded-lg overflow-auto dark:border-gray-700 bg-gray-100 dark:bg-gray-900" style={{ maxHeight: '75vh' }}>
          <div
            ref={containerRef}
            className="relative inline-block"
            style={{ transform: `scale(${zoom / 100})`, transformOrigin: 'top left' }}
          >
            {/* Background image at reduced opacity */}
            {/* eslint-disable-next-line @next/next/no-img-element */}
            <img
              ref={imageRef}
              src={dewarpedUrl}
              alt="Dewarped"
              className="block"
              style={{ opacity: 0.3 }}
              onLoad={handleImageLoad}
            />

            {/* Empty field markers */}
            {showEmptyHighlight && cells
              .filter(c => emptyCellIds.has(c.cellId))
              .map(cell => (
                <div
                  key={`empty-${cell.cellId}`}
                  className="absolute border-2 border-dashed border-red-400/60 rounded pointer-events-none"
                  style={{
                    left: `${cell.bboxPct.x}%`,
                    top: `${cell.bboxPct.y}%`,
                    width: `${cell.bboxPct.w}%`,
                    height: `${cell.bboxPct.h}%`,
                  }}
                />
              ))}

            {/* Editable text fields at bbox positions */}
            {cells.map((cell) => {
              const displayText = getDisplayText(cell)
              const edited = isEdited(cell)

              return (
                <div key={cell.cellId} className="absolute group" style={{
                  left: `${cell.bboxPct.x}%`,
                  top: `${cell.bboxPct.y}%`,
                  width: `${cell.bboxPct.w}%`,
                  height: `${cell.bboxPct.h}%`,
                }}>
                  <input
                    id={`cell-${cell.cellId}`}
                    type="text"
                    value={displayText}
                    onChange={(e) => handleTextChange(cell.cellId, e.target.value)}
                    onKeyDown={(e) => handleKeyDown(e, cell.cellId)}
                    className={`w-full h-full bg-transparent text-black dark:text-white border px-0.5 outline-none transition-colors ${
                      colTypeColor(cell.colType)
                    } ${edited ? 'border-green-500 bg-green-50/30 dark:bg-green-900/20' : ''}`}
                    style={{
                      fontSize: `${getFontSize(cell.bboxPct.h)}px`,
                      lineHeight: '1',
                    }}
                    title={`${cell.cellId} (${cell.colType})`}
                  />
                  {/* Per-cell reset button (X) — only shown for edited cells on hover */}
                  {edited && (
                    <button
                      onClick={() => resetCell(cell.cellId)}
                      className="absolute -top-1 -right-1 w-4 h-4 bg-red-500 text-white rounded-full text-[9px] leading-none opacity-0 group-hover:opacity-100 transition-opacity flex items-center justify-center"
                      title="Zuruecksetzen"
                    >
                      &times;
                    </button>
                  )}
                </div>
              )
            })}
          </div>
        </div>
      )}

      {/* Bottom action */}
      <div className="flex justify-end">
        <button
          onClick={() => {
            if (changedCount > 0) {
              saveReconstruction()
            } else {
              onNext()
            }
          }}
          className="px-6 py-2.5 bg-teal-600 text-white rounded-lg hover:bg-teal-700 transition-colors font-medium text-sm"
        >
          {changedCount > 0 ? 'Speichern & Weiter \u2192' : 'Weiter \u2192'}
        </button>
      </div>
    </div>
  )
}