import React, { useState, useRef, useEffect, useCallback, useMemo } from 'react';
import { Plus } from 'lucide-react';
import { DocumentBlock } from '../../lib/types';
import { OutlinerBlock } from './OutlinerBlock';

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;
  onDeleteBlock: (blockId: string) => void;
  onMoveBlock: (blockId: string, newIndex: number, level?: number) => void;
  onTagClick?: (tag: string) => void;
  onWikiLinkClick?: (pageTitle: string) => void;
  initialFocusedBlockId?: string | null;
}

export const OutlinerTree: React.FC<OutlinerTreeProps> = ({
  docId,
  blocks,
  canEdit,
  levelOffset = 0,
  onZoomBlock,
  onUpdateBlock,
  onUpdateBlocks,
  onCreateBlock,
  onDeleteBlock,
  onMoveBlock,
  onTagClick,
  onWikiLinkClick,
  initialFocusedBlockId,
}) => {
  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 };
      }
    },
    []
  );

  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, _currentContent: 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 =
        currentBlock && currentBlock.type === 'todo' ? 'todo' : 'text';

      const newBlock: DocumentBlock = {
        id: `blk_${Date.now().toString(36)}_${Math.random().toString(36).slice(2, 7)}`,
        documentId: docId,
        type: inheritedType,
        content: '',
        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 handleDeleteBlock = useCallback(
    (blockId: string) => {
      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');
      }
      onDeleteBlock(blockId);
    },
    [blocks, canEdit, focusBlockInput, 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 }) => {
        return (
          <OutlinerBlock
            key={block.id}
            block={block}
            index={index}
            maxAllowedLevel={maxAllowedLevel}
            hasChildren={hasChildren}
            isFocused={focusedBlockId === block.id}
            canEdit={canEdit}
            levelOffset={levelOffset}
            onZoomBlock={onZoomBlock}
            onUpdateBlock={onUpdateBlock}
            onCreateBlockBelow={handleCreateBlockBelow}
            onDeleteBlock={handleDeleteBlock}
            onIndentBlock={handleIndentBlock}
            onNavigateFocus={handleNavigateFocus}
            onTagClick={onTagClick}
            onWikiLinkClick={onWikiLinkClick}
            onDragStartBlock={handleDragStartBlock}
            onDragOverBlock={handleDragOverBlock}
            onDropBlock={handleDropBlock}
            isDragTarget={dragOverIndex === index && draggedIndex !== index}
            isTargeted={highlightedBlockId === block.id}
            registerTextareaRef={registerTextareaRef}
          />
        );
      })}

      {canEdit && (
        <div
          className={`pt-2 pl-2 transition-colors ${
            dragOverIndex === blocks.length ? 'border-t-2 border-accent bg-accent/10 rounded' : ''
          }`}
          onDragOver={(e) => {
            e.preventDefault();
            if (draggedIndex !== null) {
              setDragOverIndex(blocks.length);
            }
          }}
          onDrop={() => handleDropBlock(blocks.length)}
        >
          <button
            type="button"
            onClick={() => {
              const lastBlock = blocks[blocks.length - 1];
              if (lastBlock) {
                handleCreateBlockBelow(lastBlock.id, lastBlock.content);
              } else {
                const firstBlock: DocumentBlock = {
                  id: `blk_${Date.now().toString(36)}_0`,
                  documentId: docId,
                  type: 'text',
                  content: '',
                  level: levelOffset || 0,
                  position: 1000,
                };
                pendingFocusRef.current = { blockId: firstBlock.id, cursor: 'start' };
                onCreateBlock(firstBlock);
              }
            }}
            className="btn-action inline-flex items-center gap-1.5 px-2.5 py-1 text-xs text-muted hover:text-main"
          >
            <Plus className="w-3.5 h-3.5" />
            <span>Neuer Punkt</span>
          </button>
        </div>
      )}
    </div>
  );
};