import React, { useState, useRef, useEffect, useCallback, useMemo, forwardRef, useImperativeHandle } from 'react';
import { DocumentBlock, BlockType } from '../../lib/types';
import { OutlinerBlock } from './OutlinerBlock';

export interface OutlinerTreeHandle {
  focusFirstBlock: () => void;
  focusBlock: (blockId: string, cursor?: 'start' | 'end') => void;
}

export interface OutlinerTreeProps {
  docId: string;
  blocks: DocumentBlock[];
  canEdit: boolean;
  levelOffset?: number;
  onZoomBlock?: (blockId: string) => void;
  onUpdateBlock: (updated: DocumentBlock, immediate?: boolean) => void;
  onUpdateBlocks?: (updated: DocumentBlock[]) => void;
  onCreateBlock: (newBlock: DocumentBlock, afterBlockId?: string) => void;
  onInsertBlocks?: (afterBlockId: string, updatedCurrent: DocumentBlock, newBlocks: DocumentBlock[]) => void;
  onDeleteBlock: (blockId: string) => void;
  onMoveBlock: (blockId: string, newIndex: number, level?: number) => void;
  onOpenTask?: (taskId: string) => void;
  onTagClick?: (tag: string) => void;
  onWikiLinkClick?: (pageTitle: string) => void;
  initialFocusedBlockId?: string | null;
}

export const OutlinerTree = forwardRef<OutlinerTreeHandle, OutlinerTreeProps>(({
  docId,
  blocks,
  canEdit,
  levelOffset = 0,
  onZoomBlock,
  onUpdateBlock,
  onUpdateBlocks,
  onCreateBlock,
  onInsertBlocks,
  onDeleteBlock,
  onMoveBlock,
  onOpenTask,
  onTagClick,
  onWikiLinkClick,
  initialFocusedBlockId,
}, ref) => {
  const [focusedBlockId, setFocusedBlockId] = useState<string | null>(null);
  const [highlightedBlockId, setHighlightedBlockId] = useState<string | null>(
    initialFocusedBlockId || null
  );
  const [draggedIndex, setDraggedIndex] = useState<number | null>(null);
  const [dragOverIndex, setDragOverIndex] = useState<number | null>(null);

  const textareaMapRef = useRef<Map<string, HTMLTextAreaElement>>(new Map());
  const pendingFocusRef = useRef<{ blockId: string; cursor: 'start' | 'end' | 'select' } | null>(null);

  const focusBlockInput = useCallback(
    (blockId: string, cursor: 'start' | 'end' | 'select' = 'end') => {
      setFocusedBlockId(blockId);
      const el = textareaMapRef.current.get(blockId);
      if (el) {
        requestAnimationFrame(() => {
          el.focus();
          try {
            if (cursor === 'select') {
              el.select();
            } else {
              const pos = cursor === 'end' ? el.value.length : 0;
              el.setSelectionRange(pos, pos);
            }
          } catch {
            // ignore
          }
          el.scrollIntoView({ behavior: 'smooth', block: 'center' });
        });
      } else {
        pendingFocusRef.current = { blockId, cursor };
      }
    },
    []
  );

  useImperativeHandle(
    ref,
    () => ({
      focusFirstBlock: () => {
        if (blocks.length > 0) {
          focusBlockInput(blocks[0].id, 'end');
        } else {
          const firstBlock: DocumentBlock = {
            id: `blk_${Date.now().toString(36)}_0`,
            documentId: docId,
            type: 'text',
            content: '',
            level: levelOffset || 0,
            position: 1000,
          };
          pendingFocusRef.current = { blockId: firstBlock.id, cursor: 'end' };
          onCreateBlock(firstBlock);
        }
      },
      focusBlock: (blockId: string, cursor: 'start' | 'end' = 'end') => {
        focusBlockInput(blockId, cursor);
      },
    }),
    [blocks, docId, levelOffset, onCreateBlock, focusBlockInput]
  );

  const registerTextareaRef = useCallback((blockId: string, el: HTMLTextAreaElement | null) => {
    if (el) {
      textareaMapRef.current.set(blockId, el);
      if (pendingFocusRef.current && pendingFocusRef.current.blockId === blockId) {
        const target = pendingFocusRef.current;
        pendingFocusRef.current = null;
        requestAnimationFrame(() => {
          setFocusedBlockId(blockId);
          el.focus();
          try {
            if (target.cursor === 'select') {
              el.select();
            } else {
              const pos = target.cursor === 'end' ? el.value.length : 0;
              el.setSelectionRange(pos, pos);
            }
          } catch {
            // ignore
          }
          el.scrollIntoView({ behavior: 'smooth', block: 'center' });
        });
      }
    } else {
      textareaMapRef.current.delete(blockId);
    }
  }, []);

  useEffect(() => {
    if (initialFocusedBlockId) {
      setHighlightedBlockId(initialFocusedBlockId);
      focusBlockInput(initialFocusedBlockId, 'select');
      const timer = setTimeout(() => {
        focusBlockInput(initialFocusedBlockId, 'select');
      }, 70);
      const timer2 = setTimeout(() => {
        focusBlockInput(initialFocusedBlockId, 'select');
      }, 200);
      const fadeTimer = setTimeout(() => {
        setHighlightedBlockId(null);
      }, 2800);
      return () => {
        clearTimeout(timer);
        clearTimeout(timer2);
        clearTimeout(fadeTimer);
      };
    }
  }, [initialFocusedBlockId, blocks.length, focusBlockInput]);

  // Compute visibility based on collapsed ancestor blocks
  const visibleEntries = useMemo(() => {
    const result: {
      block: DocumentBlock;
      index: number;
      hasChildren: boolean;
      maxAllowedLevel: number;
    }[] = [];

    let collapsedAboveLevel: number | null = null;

    for (let i = 0; i < blocks.length; i++) {
      const b = blocks[i];
      const lvl = Math.max(0, b.level || 0);

      if (collapsedAboveLevel !== null) {
        if (lvl > collapsedAboveLevel) {
          continue;
        } else {
          collapsedAboveLevel = null;
        }
      }

      const nextBlock = blocks[i + 1];
      const nextLvl = nextBlock ? Math.max(0, nextBlock.level || 0) : 0;
      const hasChildren = Boolean(nextBlock && nextLvl > lvl);

      const prevBlock = i > 0 ? blocks[i - 1] : null;
      const maxAllowedLevel = prevBlock ? Math.max(0, prevBlock.level || 0) + 1 : (levelOffset || 0);

      result.push({
        block: b,
        index: i,
        hasChildren,
        maxAllowedLevel,
      });

      if (b.collapsed && hasChildren) {
        collapsedAboveLevel = lvl;
      }
    }

    return result;
  }, [blocks, levelOffset]);

  const handleCreateBlockBelow = useCallback(
    (afterBlockId: string, newContent: string = '') => {
      if (!canEdit) return;
      const idx = blocks.findIndex((b) => b.id === afterBlockId);
      const currentBlock = idx >= 0 ? blocks[idx] : null;
      const level = currentBlock ? Math.max(0, currentBlock.level || 0) : 0;
      const inheritedType: BlockType = 'text';

      const newBlock: DocumentBlock = {
        id: `blk_${Date.now().toString(36)}_${Math.random().toString(36).slice(2, 7)}`,
        documentId: docId,
        type: inheritedType,
        content: newContent,
        level,
        checked: false,
        collapsed: false,
        position: ((idx >= 0 ? idx + 2 : blocks.length + 1) * 1000),
      };

      pendingFocusRef.current = { blockId: newBlock.id, cursor: 'start' };
      setFocusedBlockId(newBlock.id);
      onCreateBlock(newBlock, afterBlockId);
    },
    [blocks, canEdit, docId, onCreateBlock]
  );

  const handlePasteMultiLines = useCallback(
    (blockId: string, textBefore: string, textAfter: string, rawLines: string[]) => {
      if (!canEdit || rawLines.length === 0) return;
      const idx = blocks.findIndex((b) => b.id === blockId);
      if (idx === -1) return;

      const currentBlock = blocks[idx];
      const baseLevel = Math.max(0, currentBlock.level || 0);

      // Detect indentation style (2-space vs 4-space tabs)
      let detectedSpaceStep = 2;
      const leadingSpacesList: number[] = [];
      for (const line of rawLines) {
        if (!line.trim()) continue;
        let sp = 0;
        while (sp < line.length && line[sp] === ' ') sp++;
        if (sp > 0) leadingSpacesList.push(sp);
      }
      if (leadingSpacesList.length > 0 && leadingSpacesList.every((s) => s % 4 === 0)) {
        detectedSpaceStep = 4;
      }

      // Parse lines into structured blocks
      interface ParsedPasteItem {
        type: BlockType;
        checked?: boolean;
        content: string;
        indent: number;
      }

      const parsed: ParsedPasteItem[] = [];
      let currentItem: ParsedPasteItem | null = null;
      let inCodeBlock = false;
      let afterHeading = false;

      const pushCurrentItem = () => {
        if (currentItem) {
          currentItem.content = currentItem.content.trimEnd();
          parsed.push(currentItem);
          currentItem = null;
        }
      };

      for (let i = 0; i < rawLines.length; i++) {
        const rawLine = rawLines[i];

        // 1. Inside a fenced code block
        if (inCodeBlock) {
          if (currentItem) {
            currentItem.content += '\n' + rawLine;
          }
          if (rawLine.trim().startsWith('```')) {
            inCodeBlock = false;
          }
          continue;
        }

        // 2. Starts a code fence
        if (rawLine.trim().startsWith('```')) {
          inCodeBlock = true;
          if (afterHeading) {
            afterHeading = false;
            pushCurrentItem();
            currentItem = {
              type: 'text',
              content: rawLine,
              indent: 0,
            };
          } else if (currentItem) {
            currentItem.content += (currentItem.content.endsWith('\n') ? '' : '\n') + rawLine;
          } else {
            currentItem = {
              type: 'text',
              content: rawLine,
              indent: 0,
            };
          }
          continue;
        }

        // Measure leading indent
        let tabs = 0;
        let spaces = 0;
        let charIdx = 0;
        while (charIdx < rawLine.length) {
          if (rawLine[charIdx] === '\t') {
            tabs++;
            charIdx++;
          } else if (rawLine[charIdx] === ' ') {
            spaces++;
            charIdx++;
          } else {
            break;
          }
        }
        const strippedLine = rawLine.slice(charIdx);
        const lineIndent = tabs + Math.floor(spaces / detectedSpaceStep);

        // Blank lines
        if (strippedLine.trim() === '') {
          if (currentItem) {
            currentItem.content += '\n';
          }
          continue;
        }

        // Headings: #, ##, ###
        const h3Match = strippedLine.match(/^###\s+(.*)$/);
        const h2Match = strippedLine.match(/^##\s+(.*)$/);
        const h1Match = strippedLine.match(/^#\s+(.*)$/);
        if (h1Match || h2Match || h3Match) {
          pushCurrentItem();
          afterHeading = true;
          const type: BlockType = h1Match ? 'h1' : h2Match ? 'h2' : 'h3';
          const content = (h1Match || h2Match || h3Match)![1];
          parsed.push({ type, content, indent: lineIndent });
          continue;
        }

        // Dividers: ---, ***, ___
        if (/^(?:---|---|\*\*\*|___)\s*$/.test(strippedLine.trim())) {
          pushCurrentItem();
          afterHeading = false;
          parsed.push({ type: 'divider', content: '---', indent: lineIndent });
          continue;
        }

        // Todo items: - [ ], - [x], * [ ], * [x]
        const todoMatch = strippedLine.match(/^[-*]\s*\[([ xX])\]\s*(.*)$/);
        if (todoMatch) {
          pushCurrentItem();
          afterHeading = false;
          parsed.push({
            type: 'todo',
            checked: todoMatch[1].toLowerCase() === 'x',
            content: todoMatch[2],
            indent: lineIndent,
          });
          continue;
        }

        // Explicit bullet or numbered list: - item, * item, • item, 1. item, 1) item
        const bulletMatch = strippedLine.match(/^[-*•]\s+(.*)$/);
        const numMatch = strippedLine.match(/^\d+[\.\)]\s+(.*)$/);
        if (bulletMatch || numMatch) {
          pushCurrentItem();
          afterHeading = false;
          parsed.push({
            type: 'text',
            content: (bulletMatch ? bulletMatch[1] : numMatch![1]),
            indent: lineIndent,
          });
          continue;
        }

        // Regular text line
        if (afterHeading) {
          // This starts the single bullet point after the heading
          afterHeading = false;
          pushCurrentItem();
          currentItem = {
            type: 'text',
            content: strippedLine,
            indent: lineIndent,
          };
        } else if (currentItem) {
          if (currentItem.content.endsWith('\n')) {
            currentItem.content += strippedLine;
          } else {
            currentItem.content += '\n' + strippedLine;
          }
        } else {
          currentItem = {
            type: 'text',
            content: strippedLine,
            indent: lineIndent,
          };
        }
      }

      pushCurrentItem();

      if (parsed.length === 0) return;

      const line0 = parsed[0];
      const baseIndent = line0.indent;
      const isSingle = parsed.length === 1;
      const line0Content = textBefore + line0.content + (isSingle ? textAfter : '');

      const isCurrentEmpty = (currentBlock.content || '').trim() === '';
      const adoptedType = line0.type !== 'text' ? line0.type : (isCurrentEmpty ? 'text' : currentBlock.type);
      const adoptedChecked = line0.type === 'todo' ? (line0.checked ?? false) : currentBlock.checked;

      const updatedCurrentBlock: DocumentBlock = {
        ...currentBlock,
        content: line0Content,
        type: adoptedType,
        checked: adoptedChecked,
      };

      const newBlocks: DocumentBlock[] = [];
      const nowBase = Date.now().toString(36);

      for (let j = 1; j < parsed.length; j++) {
        const p = parsed[j];
        const isLastLine = j === parsed.length - 1;
        const lineContent = isLastLine ? (p.content + textAfter) : p.content;
        const lineLevel = Math.max(0, baseLevel + (p.indent - baseIndent));

        newBlocks.push({
          id: `blk_${nowBase}_${j}_${Math.random().toString(36).slice(2, 6)}`,
          documentId: docId,
          type: p.type,
          checked: p.checked || false,
          content: lineContent,
          level: lineLevel,
          collapsed: false,
          position: (currentBlock.position || 1000) + j * 10,
        });
      }

      const lastTargetId = newBlocks.length > 0 ? newBlocks[newBlocks.length - 1].id : currentBlock.id;
      const existingEl = textareaMapRef.current.get(lastTargetId);
      if (existingEl) {
        pendingFocusRef.current = null;
        focusBlockInput(lastTargetId, 'end');
      } else {
        pendingFocusRef.current = { blockId: lastTargetId, cursor: 'end' };
      }
      setFocusedBlockId(lastTargetId);

      if (onInsertBlocks) {
        onInsertBlocks(currentBlock.id, updatedCurrentBlock, newBlocks);
      } else {
        onUpdateBlock(updatedCurrentBlock, true);
        for (let k = 0; k < newBlocks.length; k++) {
          const afterId = k === 0 ? currentBlock.id : newBlocks[k - 1].id;
          onCreateBlock(newBlocks[k], afterId);
        }
      }
    },
    [blocks, canEdit, docId, focusBlockInput, onCreateBlock, onInsertBlocks, onUpdateBlock]
  );

  const handleDeleteBlock = useCallback(
    (blockId: string, deleteSubtree = false) => {
      if (!canEdit) return;
      const idx = blocks.findIndex((b) => b.id === blockId);
      if (idx === -1) return;

      // If this is the only block in the document (and not in an isolated zoom subtree), clear instead of deleting
      if (blocks.length <= 1 && !levelOffset) {
        const only = blocks[0];
        onUpdateBlock(
          {
            ...only,
            content: '',
            type: 'text',
            level: 0,
            checked: false,
          },
          true
        );
        return;
      }

      const targetFocusBlock = idx > 0 ? blocks[idx - 1] : blocks[idx + 1];
      if (targetFocusBlock) {
        focusBlockInput(targetFocusBlock.id, 'end');
      }

      if (deleteSubtree) {
        const rootLevel = blocks[idx].level || 0;
        const idsToDelete = [blockId];
        for (let j = idx + 1; j < blocks.length; j++) {
          if ((blocks[j].level || 0) > rootLevel) {
            idsToDelete.push(blocks[j].id);
          } else {
            break;
          }
        }
        for (const id of idsToDelete) {
          onDeleteBlock(id);
        }
      } else {
        onDeleteBlock(blockId);
      }
    },
    [blocks, canEdit, focusBlockInput, levelOffset, onDeleteBlock, onUpdateBlock]
  );

  const handleIndentBlock = useCallback(
    (blockId: string, delta: 1 | -1) => {
      if (!canEdit) return;
      const idx = blocks.findIndex((b) => b.id === blockId);
      if (idx === -1) return;

      const current = blocks[idx];
      const currentLevel = Math.max(0, current.level || 0);
      const prevLevel = idx > 0 ? Math.max(0, blocks[idx - 1].level || 0) : 0;
      const minLevel = levelOffset || 0;
      const maxLevel = idx === 0 ? minLevel : prevLevel + 1;

      const nextLevel =
        delta === 1
          ? Math.min(maxLevel, currentLevel + 1)
          : Math.max(minLevel, currentLevel - 1);

      if (nextLevel === currentLevel) return;

      const actualDelta = nextLevel - currentLevel;

      // Find all contiguous children / descendants:
      // contiguous blocks with level > currentLevel
      let count = 1;
      for (let i = idx + 1; i < blocks.length; i++) {
        if (Math.max(0, blocks[i].level || 0) > currentLevel) {
          count++;
        } else {
          break;
        }
      }

      const updatedBlocks: DocumentBlock[] = [];
      for (let i = idx; i < idx + count; i++) {
        const b = blocks[i];
        const newLvl = Math.max(minLevel, (b.level || 0) + actualDelta);
        updatedBlocks.push({
          ...b,
          level: newLvl,
        });
      }

      if (onUpdateBlocks) {
        onUpdateBlocks(updatedBlocks);
      } else {
        for (const b of updatedBlocks) {
          onUpdateBlock(b, true);
        }
      }
    },
    [blocks, canEdit, levelOffset, onUpdateBlock, onUpdateBlocks]
  );

  const handleNavigateFocus = useCallback(
    (blockId: string, direction: 'up' | 'down') => {
      const visIdx = visibleEntries.findIndex((e) => e.block.id === blockId);
      if (visIdx === -1) return;
      const targetEntry =
        direction === 'up' ? visibleEntries[visIdx - 1] : visibleEntries[visIdx + 1];
      if (targetEntry) {
        focusBlockInput(
          targetEntry.block.id,
          direction === 'up' ? 'end' : 'start'
        );
      }
    },
    [focusBlockInput, visibleEntries]
  );

  const handleDragStartBlock = useCallback((index: number) => {
    setDraggedIndex(index);
  }, []);

  const handleDragOverBlock = useCallback(
    (e: React.DragEvent, index: number) => {
      e.preventDefault();
      if (draggedIndex !== null) {
        const parentLevel = Math.max(0, blocks[draggedIndex]?.level || 0);
        let count = 1;
        for (let i = draggedIndex + 1; i < blocks.length; i++) {
          if (Math.max(0, blocks[i].level || 0) > parentLevel) {
            count++;
          } else {
            break;
          }
        }
        // Do not allow dropping inside its own subtree (self or descendants)
        if (index >= draggedIndex && index < draggedIndex + count) {
          setDragOverIndex(null);
          return;
        }
      }
      setDragOverIndex(index);
    },
    [blocks, draggedIndex]
  );

  const handleDropBlock = useCallback(
    (targetIndex: number) => {
      if (draggedIndex === null || draggedIndex === targetIndex) {
        setDraggedIndex(null);
        setDragOverIndex(null);
        return;
      }
      const parentLevel = Math.max(0, blocks[draggedIndex]?.level || 0);
      let count = 1;
      for (let i = draggedIndex + 1; i < blocks.length; i++) {
        if (Math.max(0, blocks[i].level || 0) > parentLevel) {
          count++;
        } else {
          break;
        }
      }
      if (targetIndex >= draggedIndex && targetIndex < draggedIndex + count) {
        setDraggedIndex(null);
        setDragOverIndex(null);
        return;
      }
      const movingBlock = blocks[draggedIndex];
      if (movingBlock) {
        onMoveBlock(movingBlock.id, targetIndex, movingBlock.level);
      }
      setDraggedIndex(null);
      setDragOverIndex(null);
    },
    [blocks, draggedIndex, onMoveBlock]
  );

  useEffect(() => {
    const clearDrag = () => {
      setDraggedIndex(null);
      setDragOverIndex(null);
    };
    window.addEventListener('dragend', clearDrag);
    return () => window.removeEventListener('dragend', clearDrag);
  }, []);

  return (
    <div className="space-y-0.5">
      {visibleEntries.map(({ block, index, hasChildren, maxAllowedLevel }, entryIdx) => {
        const isLast = entryIdx === visibleEntries.length - 1;
        return (
          <OutlinerBlock
            key={block.id}
            docId={docId}
            block={block}
            index={index}
            isLast={isLast}
            maxAllowedLevel={maxAllowedLevel}
            hasChildren={hasChildren}
            isFocused={focusedBlockId === block.id}
            canEdit={canEdit}
            levelOffset={levelOffset}
            onZoomBlock={onZoomBlock}
            onUpdateBlock={onUpdateBlock}
            onCreateBlockBelow={handleCreateBlockBelow}
            onPasteMultiLines={handlePasteMultiLines}
            onDeleteBlock={handleDeleteBlock}
            onIndentBlock={handleIndentBlock}
            onNavigateFocus={handleNavigateFocus}
            onFocusBlock={setFocusedBlockId}
            onOpenTask={onOpenTask}
            onTagClick={onTagClick}
            onWikiLinkClick={onWikiLinkClick}
            onDragStartBlock={handleDragStartBlock}
            onDragOverBlock={handleDragOverBlock}
            onDropBlock={handleDropBlock}
            isDragTarget={dragOverIndex === index && draggedIndex !== index}
            isTargeted={highlightedBlockId === block.id}
            registerTextareaRef={registerTextareaRef}
          />
        );
      })}

      {canEdit && (
        <div
          className={`min-h-[14rem] pt-2 pl-2 transition-colors cursor-text ${
            dragOverIndex === blocks.length ? 'border-t-2 border-accent bg-accent/10 rounded' : ''
          }`}
          onClick={(e) => {
            if (e.target !== e.currentTarget && (e.target as HTMLElement).closest('button, a, input, textarea, select')) {
              return;
            }
            if (blocks.length === 0) {
              const firstBlock: DocumentBlock = {
                id: `blk_${Date.now().toString(36)}_0`,
                documentId: docId,
                type: 'text',
                content: '',
                level: levelOffset || 0,
                position: 1000,
              };
              pendingFocusRef.current = { blockId: firstBlock.id, cursor: 'start' };
              onCreateBlock(firstBlock);
            } else {
              const lastBlock = blocks[blocks.length - 1];
              if (lastBlock.content && lastBlock.content.trim() !== '') {
                handleCreateBlockBelow(lastBlock.id, '');
              } else {
                focusBlockInput(lastBlock.id, 'end');
              }
            }
          }}
          onDragOver={(e) => {
            e.preventDefault();
            if (draggedIndex !== null) {
              setDragOverIndex(blocks.length);
            }
          }}
          onDrop={() => handleDropBlock(blocks.length)}
        />
      )}
    </div>
  );
});