import { useState, useRef, useEffect, useCallback } from 'react'
import { ChevronDown, Code, X } from 'lucide-react'

export interface AvailableField {
  path: string
  type: string
  nodeName: string
  nodeId: string
  displayName?: string
  isDirectUpstream?: boolean  // true if this is an immediate predecessor node
}

interface ExpressionInputProps {
  value: string
  onChange: (value: string) => void
  placeholder?: string
  availableFields?: AvailableField[]
  multiline?: boolean
  // Set for fields that hold source code, which want a monospace face and room
  // to work in whatever their current contents happen to look like.
  codeMode?: boolean
  className?: string
}

type ContentKind = 'plain' | 'json' | 'broken-json' | 'markdown'

// What someone typed into a field says what it is. A prompt, a JSON body and a
// note are all "string" to the schema, so the shape of the text is the only
// signal available - and it is a reliable one.
function detectContentKind(value: string): ContentKind {
  const text = value.trim()
  if (!text) return 'plain'

  const looksStructured = /^[[{]/.test(text) && /[\]}]$/.test(text)
  if (looksStructured) {
    try {
      JSON.parse(text)
      return 'json'
    } catch {
      return 'broken-json'
    }
  }

  // Two or more markdown constructs, so a lone hyphen or a URL in prose does
  // not get called markdown.
  const markers = [
    /^#{1,6}\s+\S/m,        // heading
    /^\s*[-*+]\s+\S/m,      // bullet list
    /^\s*\d+\.\s+\S/m,     // numbered list
    /\*\*[^*\n]+\*\*/,      // bold
    /\[[^\]\n]+\]\([^)\n]+\)/, // link
    /^>\s+\S/m,            // quote
    /```/,                  // fenced code
  ].filter((pattern) => pattern.test(text)).length

  return markers >= 2 ? 'markdown' : 'plain'
}

const KIND_LABELS: Record<ContentKind, { label: string; className: string } | null> = {
  plain: null,
  json: {
    label: 'JSON',
    className: 'bg-blue-100 dark:bg-blue-900/30 text-blue-700 dark:text-blue-300',
  },
  'broken-json': {
    label: 'JSON with a syntax error',
    className: 'bg-amber-100 dark:bg-amber-900/30 text-amber-800 dark:text-amber-300',
  },
  markdown: {
    label: 'Markdown',
    className: 'bg-violet-100 dark:bg-violet-900/30 text-violet-700 dark:text-violet-300',
  },
}

const TYPE_COLORS: Record<string, string> = {
  string: 'bg-green-100 dark:bg-green-900/30 text-green-800 dark:text-green-300',
  number: 'bg-blue-100 dark:bg-blue-900/30 text-blue-800 dark:text-blue-300',
  boolean: 'bg-purple-100 dark:bg-purple-900/30 text-purple-800 dark:text-purple-300',
  object: 'bg-orange-100 dark:bg-orange-900/30 text-orange-800 dark:text-orange-300',
  array: 'bg-pink-100 dark:bg-pink-900/30 text-pink-800 dark:text-pink-300',
  any: 'bg-gray-100 dark:bg-gray-800 text-gray-800 dark:text-gray-300',
}

export function ExpressionInput({
  value,
  onChange,
  placeholder,
  availableFields = [],
  multiline = false,
  codeMode = false,
  className = '',
}: ExpressionInputProps) {
  const [showAutocomplete, setShowAutocomplete] = useState(false)
  const [autocompletePosition, setAutocompletePosition] = useState({ top: 0, left: 0 })
  const [filterText, setFilterText] = useState('')
  const [selectedIndex, setSelectedIndex] = useState(0)
  const [cursorPosition, setCursorPosition] = useState(0)
  const inputRef = useRef<HTMLTextAreaElement | HTMLInputElement>(null)
  const autocompleteRef = useRef<HTMLDivElement>(null)

  // Check if cursor is inside an expression {{ }}
  const isInsideExpression = useCallback((text: string, position: number): { inside: boolean; start: number; filter: string } => {
    const beforeCursor = text.slice(0, position)
    const lastOpenBrace = beforeCursor.lastIndexOf('{{')
    const lastCloseBrace = beforeCursor.lastIndexOf('}}')

    if (lastOpenBrace > lastCloseBrace) {
      const filter = beforeCursor.slice(lastOpenBrace + 2).trim()
      return { inside: true, start: lastOpenBrace + 2, filter }
    }
    return { inside: false, start: 0, filter: '' }
  }, [])

  // Filter fields based on input
  const filteredFields = availableFields.filter((field) => {
    const searchText = filterText.toLowerCase()
    return (
      field.path.toLowerCase().includes(searchText) ||
      field.nodeName.toLowerCase().includes(searchText) ||
      (field.displayName?.toLowerCase().includes(searchText) ?? false)
    )
  })

  // Handle input change
  const handleChange = (e: React.ChangeEvent<HTMLTextAreaElement | HTMLInputElement>) => {
    const newValue = e.target.value
    const newPosition = e.target.selectionStart || 0
    onChange(newValue)
    setCursorPosition(newPosition)

    const { inside, filter } = isInsideExpression(newValue, newPosition)
    if (inside) {
      setFilterText(filter)
      setShowAutocomplete(true)
      setSelectedIndex(0)

      // Calculate autocomplete position
      if (inputRef.current) {
        const rect = inputRef.current.getBoundingClientRect()
        setAutocompletePosition({
          top: rect.height + 4,
          left: 0,
        })
      }
    } else {
      setShowAutocomplete(false)
    }
  }

  // Handle cursor position changes
  const handleSelect = (e: React.SyntheticEvent<HTMLTextAreaElement | HTMLInputElement>) => {
    const target = e.target as HTMLTextAreaElement | HTMLInputElement
    const newPosition = target.selectionStart || 0
    setCursorPosition(newPosition)

    const { inside, filter } = isInsideExpression(value, newPosition)
    if (inside && availableFields.length > 0) {
      setFilterText(filter)
      setShowAutocomplete(true)
    } else {
      setShowAutocomplete(false)
    }
  }

  // Insert selected field
  const insertField = useCallback((field: AvailableField) => {
    const { inside, start } = isInsideExpression(value, cursorPosition)
    if (!inside) return

    // Build the expression based on whether this is a direct upstream node
    // Direct upstream: raw path (no $node accessor)
    // Non-direct upstream: full expression with node accessor
    const expression = field.isDirectUpstream
      ? field.path
      : `$node["${field.nodeName}"].${field.path}`

    // Find the end of current filter text
    const beforeFilter = value.slice(0, start)
    const afterCursor = value.slice(cursorPosition)

    // Check if there's a closing }}
    const closingBrace = afterCursor.indexOf('}}')
    const afterExpression = closingBrace >= 0 ? afterCursor.slice(closingBrace) : '}}'

    const newValue = beforeFilter + expression + afterExpression
    onChange(newValue)
    setShowAutocomplete(false)

    // Focus back on input
    setTimeout(() => {
      if (inputRef.current) {
        inputRef.current.focus()
        const newPosition = beforeFilter.length + expression.length
        inputRef.current.setSelectionRange(newPosition, newPosition)
      }
    }, 0)
  }, [value, cursorPosition, isInsideExpression, onChange])

  // Keyboard navigation
  const handleKeyDown = (e: React.KeyboardEvent) => {
    if (!showAutocomplete) return

    switch (e.key) {
      case 'ArrowDown':
        e.preventDefault()
        setSelectedIndex((prev) => Math.min(prev + 1, filteredFields.length - 1))
        break
      case 'ArrowUp':
        e.preventDefault()
        setSelectedIndex((prev) => Math.max(prev - 1, 0))
        break
      case 'Enter':
        if (filteredFields[selectedIndex]) {
          e.preventDefault()
          insertField(filteredFields[selectedIndex])
        }
        break
      case 'Escape':
        e.preventDefault()
        setShowAutocomplete(false)
        break
      case 'Tab':
        if (filteredFields[selectedIndex]) {
          e.preventDefault()
          insertField(filteredFields[selectedIndex])
        }
        break
    }
  }

  // Close autocomplete when clicking outside
  useEffect(() => {
    const handleClickOutside = (e: MouseEvent) => {
      if (
        autocompleteRef.current &&
        !autocompleteRef.current.contains(e.target as Node) &&
        inputRef.current &&
        !inputRef.current.contains(e.target as Node)
      ) {
        setShowAutocomplete(false)
      }
    }

    document.addEventListener('mousedown', handleClickOutside)
    return () => document.removeEventListener('mousedown', handleClickOutside)
  }, [])

  // Insert expression template
  const insertExpressionTemplate = () => {
    const template = '{{  }}'
    const newValue = value + template
    onChange(newValue)

    setTimeout(() => {
      if (inputRef.current) {
        inputRef.current.focus()
        const position = value.length + 3 // Position cursor between {{ and }}
        inputRef.current.setSelectionRange(position, position)
        setCursorPosition(position)
        setShowAutocomplete(true)
        setFilterText('')
      }
    }, 0)
  }

  const kind = detectContentKind(value || '')
  const kindLabel = KIND_LABELS[kind]
  const isCode = codeMode || kind === 'json' || kind === 'broken-json'

  // The field is always a textarea so it can grow with what is typed into it
  // without swapping the element under the cursor, which would lose focus and
  // the caret mid-sentence.
  useEffect(() => {
    const el = inputRef.current as HTMLTextAreaElement | null
    if (!el) return
    el.style.height = 'auto'
    const minHeight = codeMode ? 200 : multiline ? 80 : 38
    el.style.height = Math.min(Math.max(el.scrollHeight, minHeight), 420) + 'px'
  }, [value, multiline, codeMode])

  const formatJson = () => {
    try {
      onChange(JSON.stringify(JSON.parse(value), null, 2))
    } catch {
      // Only offered when the value parses, so there is nothing to report here.
    }
  }

  return (
    <div className={`relative ${className}`}>
      <div className="flex items-stretch">
        <div className="relative flex-1">
          <textarea
            ref={inputRef as any}
            value={value}
            onChange={handleChange}
            onSelect={handleSelect}
            onKeyDown={handleKeyDown}
            placeholder={placeholder || 'Enter value or use {{ }} for expressions'}
            className={`w-full px-3 py-2 pr-10 border border-gray-200 dark:border-slate-600 rounded-l-lg text-sm bg-white dark:bg-slate-900 text-gray-900 dark:text-gray-100 focus:ring-2 focus:ring-primary-500 focus:border-primary-500 resize-y overflow-hidden ${
              isCode ? 'font-mono text-xs' : ''
            }`}
            rows={1}
          />

          {/* Clear button */}
          {value && (
            <button
              onClick={() => onChange('')}
              className="absolute right-2 top-2 p-1 text-gray-400 dark:text-gray-500 hover:text-gray-600 dark:hover:text-gray-400"
              title="Clear"
            >
              <X className="w-4 h-4" />
            </button>
          )}
        </div>

        {/* Expression helper button */}
        <button
          onClick={insertExpressionTemplate}
          className="px-3 border border-l-0 border-gray-200 dark:border-slate-600 rounded-r-lg bg-gray-50 dark:bg-slate-800 hover:bg-gray-100 dark:hover:bg-slate-700 text-gray-600 dark:text-gray-400 flex items-center gap-1"
          title="Insert expression {{ }}"
        >
          <Code className="w-4 h-4" />
          <ChevronDown className="w-3 h-3" />
        </button>
      </div>

      {/* Autocomplete dropdown */}
      {showAutocomplete && filteredFields.length > 0 && (
        <div
          ref={autocompleteRef}
          className="absolute z-50 w-full bg-white dark:bg-slate-800 border border-gray-200 dark:border-slate-700 rounded-lg shadow-lg mt-1 max-h-60 overflow-auto"
          style={{
            top: autocompletePosition.top,
            left: autocompletePosition.left,
          }}
        >
          <div className="p-2 text-xs text-gray-500 dark:text-gray-400 border-b border-gray-200 dark:border-slate-700 bg-gray-50 dark:bg-slate-900">
            Available Fields {filterText && `(filtered: "${filterText}")`}
          </div>
          {filteredFields.map((field, index) => (
            <button
              key={`${field.nodeId}-${field.path}`}
              onClick={() => insertField(field)}
              className={`w-full px-3 py-2 text-left flex items-center gap-2 hover:bg-gray-50 dark:hover:bg-slate-700 ${
                index === selectedIndex ? 'bg-primary-50 dark:bg-primary-900/20' : ''
              }`}
            >
              <span
                className={`px-1.5 py-0.5 rounded text-[10px] font-medium ${
                  TYPE_COLORS[field.type] || TYPE_COLORS.any
                }`}
              >
                {field.type}
              </span>
              <div className="flex-1 min-w-0">
                <div className="text-sm font-medium text-gray-900 dark:text-gray-100 truncate">
                  {field.displayName || field.path}
                </div>
                <div className="text-xs text-gray-500 dark:text-gray-400 truncate">
                  {field.nodeName} &rarr; {field.path}
                </div>
              </div>
            </button>
          ))}
        </div>
      )}

      {/* What the field currently holds, and the one action that content wants */}
      {kindLabel && (
        <div className="flex items-center gap-2 mt-1 text-xs">
          <span className={`px-1.5 py-0.5 rounded font-medium ${kindLabel.className}`}>
            {kindLabel.label}
          </span>
          {kind === 'json' && (
            <button
              onClick={formatJson}
              className="text-primary-600 dark:text-primary-400 hover:underline"
              title="Re-indent this JSON"
            >
              Format
            </button>
          )}
          {kind === 'broken-json' && (
            <span className="text-gray-500 dark:text-gray-400">
              Starts and ends like JSON but does not parse - check quotes and commas
            </span>
          )}
          {kind === 'markdown' && (
            <span className="text-gray-500 dark:text-gray-400">
              <code className="bg-gray-100 dark:bg-slate-700 px-1 rounded">**bold**</code>{' '}
              <code className="bg-gray-100 dark:bg-slate-700 px-1 rounded">- list</code>{' '}
              <code className="bg-gray-100 dark:bg-slate-700 px-1 rounded"># heading</code>{' '}
              <code className="bg-gray-100 dark:bg-slate-700 px-1 rounded">[text](url)</code>
            </span>
          )}
        </div>
      )}

      {/* Expression syntax help */}
      {showAutocomplete && filteredFields.length === 0 && (
        <div
          ref={autocompleteRef}
          className="absolute z-50 w-full bg-white dark:bg-slate-800 border border-gray-200 dark:border-slate-700 rounded-lg shadow-lg mt-1 p-3"
          style={{
            top: autocompletePosition.top,
            left: autocompletePosition.left,
          }}
        >
          <div className="text-xs text-gray-600 dark:text-gray-400">
            <div className="font-medium mb-2">Expression Syntax:</div>
            <ul className="space-y-1 text-gray-500 dark:text-gray-400">
              <li><code className="bg-gray-100 dark:bg-slate-700 px-1 rounded">data.field</code> - Access input data</li>
              <li><code className="bg-gray-100 dark:bg-slate-700 px-1 rounded">$node["Name"].field</code> - Access node output</li>
              <li><code className="bg-gray-100 dark:bg-slate-700 px-1 rounded">$trigger.timestamp</code> - Trigger data</li>
            </ul>
          </div>
        </div>
      )}
    </div>
  )
}