import AppKit

final class DocumentTreeController: NSTreeController {
	override init(content: Any?) {
		super.init(content: content)
		leafKeyPath = "leaf"
		childrenKeyPath = "children"
	}
	
	required init?(coder: NSCoder) {
		fatalError("init(coder:) has not been implemented")
	}

	static let headingAttributes: [NSAttributedString.Key: Any] = {
		let paragraphStyle = NSMutableParagraphStyle()
		paragraphStyle.headerLevel = 1
		paragraphStyle.paragraphSpacing = 10

		return [
			.foregroundColor: NSColor.textColor,
			.font: NSFont.systemFont(ofSize: 15, weight: .bold),
			.paragraphStyle: paragraphStyle,
		]
	}()

	func dividerAttributedString(blockID: UUID) -> NSAttributedString {
		let dividerString = NSMutableAttributedString()
		dividerString.append(NSAttributedString(string: "\n", attributes: [.newlineBeforeDivider: ()]))
		dividerString.append(NSAttributedString(attachment: DividerTextAttachment()))
		dividerString.append(NSAttributedString(string: "\n", attributes: [.newlineAfterDivider: ()]))

		var attributes = CodeTextView.typingAttributes
		attributes[.dividerBlockID] = blockID

		let dividerRange = NSRange(location: 0, length: dividerString.length)
		dividerString.addAttributes(attributes, range: dividerRange)

		return dividerString
	}

	var visibleDocumentNodes: [DocumentNode] {
		var accumulator = DocumentNodeAccumulator()

		let selectedObjects = selectedObjects
		for object in selectedObjects {
			guard let item = object as? DocumentNode else { continue }
			accumulator.visit(item)
		}

		return accumulator.items
	}
	
	var firstVisibleDocumentNode: DocumentNode? {
		var firstNode: DocumentNode? = nil
		for object in selectedObjects {
			if let node = object as? DocumentNode {
				firstNode = node
				break
			}
		}
		return firstNode
	}
	
	var visibleBlockRanges: [UUID: NSRange] {
		guard let firstBlockID = firstVisibleDocumentNode?.id else { return [:] }
		return attributedString.blockRanges(firstBlockID: firstBlockID)
	}
	
	func firstTreeNode(where predicate: (NSTreeNode) throws -> Bool) rethrows -> NSTreeNode? {
		var workList: [NSTreeNode] = [arrangedObjects]
		while let node = workList.popLast() {
			if try predicate(node) {
				return node
			} else if let children = node.children {
				workList.append(contentsOf: children)
			}
		}
		
		return nil
	}

	@objc dynamic var attributedString: NSAttributedString {
		get {
			let out = NSMutableAttributedString()

			let items = visibleDocumentNodes

			for (index, item) in items.enumerated() {
				if index != items.startIndex {
					out.append(dividerAttributedString(blockID: item.id))
				}

				if item.displaysSectionHeading {
					out.append(NSAttributedString(string: item.title))
					out.append(NSAttributedString(string: "\n"))
				}

				out.append(NSAttributedString(string: item.content))
			}

			applyAttributes(out)

			return out
		}

		set {
			guard let firstItem = selectedObjects.first as? DocumentNode else { return }
			let blockRanges = newValue.blockRanges(firstBlockID: firstItem.id)

			for selectedObject in selectedObjects {
				guard let item = selectedObject as? DocumentNode else { continue }
				item.update(from: NSString(string: newValue.string), blockRanges: blockRanges)
			}
		}
	}
	
	func range(for targetID: UUID, in attributedString: NSAttributedString) -> NSRange? {
		guard let firstBlockID = firstVisibleDocumentNode?.id else { return nil }
		var foundRange: NSRange? = nil
		attributedString.enumerateBlockRanges(in: NSRange(location: 0, length: attributedString.length)) { blockIDOrNil, blockRange, shouldStop in
			let blockID = blockIDOrNil ?? firstBlockID
			if blockID == targetID {
				foundRange = blockRange
				shouldStop = false
			}
		}
		
		return foundRange
	}
	
	func titleRange(for targetID: UUID, in attributedString: NSAttributedString) -> (String, NSRange, NSRange)? {
		guard let blockRange = range(for: targetID, in: attributedString) else { return nil }
		
		let string = NSString(string: attributedString.string)
		var title: String? = nil
		var titleRange: NSRange? = nil
		var titleEnclosingRange: NSRange? = nil
		
		string.enumerateSubstrings(in: blockRange, options: .byParagraphs) { paragraph, paragraphRange, enclosingRange, shouldStop in
			title = paragraph
			titleRange = paragraphRange
			titleEnclosingRange = enclosingRange
			shouldStop.pointee = true
		}
		
		guard let title, let titleRange, let titleEnclosingRange else { return nil }
		return (title, titleRange, titleEnclosingRange)
	}
	
	func applyAttributes(_ string: NSMutableAttributedString) {
		let items = visibleDocumentNodes

		guard let firstItem = items.first else { return }

		string.enumerateBlockRanges(in: NSRange(location: 0, length: string.length)) { blockIDOrNil, blockRange, _ in
			let blockID = blockIDOrNil ?? firstItem.id
			guard let block = items.first(where: { $0.id == blockID }) else { return }
			if block.displaysSectionHeading {
				var currentParagraph = 0
				string.mutableString.enumerateSubstrings(in: blockRange, options: .byParagraphs) { substring, substringRange, enclosingRange, shouldStop in
					let attributes = currentParagraph == 0 ? Self.headingAttributes : CodeTextView.typingAttributes
					string.setAttributes(attributes, range: enclosingRange)
					currentParagraph += 1
				}
			} else {
				string.setAttributes(CodeTextView.typingAttributes, range: blockRange)
			}
		}
	}
	
	func indexPathForDocumentNodeInsertion() -> IndexPath? {
		func isDocumentNode(_ node: NSTreeNode) -> Bool {
			node.representedObject is DocumentNode
		}

		let targetTreeNode =
			selectedNodes.last(where: isDocumentNode)
			?? arrangedObjects.first(where: isDocumentNode)

		guard let targetTreeNode else { return nil }
		// If the target tree node is a leaf node, we should insert directly after it. If it is a branch node, we should insert at the end of its children.
		var targetIndexPath = targetTreeNode.indexPath
		if targetTreeNode.isLeaf {
			targetIndexPath[targetIndexPath.count - 1] += 1
		} else {
			// I believe that targetTreeNode must not be nil because targetTreeNode.isLeaf == false.
			targetIndexPath.append(IndexPath(index: targetTreeNode.children!.count))
		}

		return targetIndexPath
	}
}