import UIKit
import Foundation

protocol RDEPUBTextContentViewDelegate: AnyObject {
    func textContentView(_ contentView: RDEPUBTextContentView, didChangeSelection selection: RDEPUBSelection?)
    func textContentView(_ contentView: RDEPUBTextContentView, didRequestSelectionAction action: RDEPUBAnnotationMenuAction)
}

final class RDEPUBSelectableTextView: UITextView {
    var onSelectionAction: ((RDEPUBAnnotationMenuAction) -> Void)?

    override func canPerformAction(_ action: Selector, withSender sender: Any?) -> Bool {
        switch action {
        case #selector(rd_copy(_:)),
             #selector(rd_highlight(_:)),
             #selector(rd_annotate(_:)):
            return selectedRange.location != NSNotFound && selectedRange.length > 0
        default:
            return false
        }
    }

    @objc func rd_copy(_ sender: Any?) {
        onSelectionAction?(.copy)
    }

    @objc func rd_highlight(_ sender: Any?) {
        onSelectionAction?(.highlight)
    }

    @objc func rd_annotate(_ sender: Any?) {
        onSelectionAction?(.annotate)
    }
}

final class RDEPUBTextContentView: UIView {
    private var contentInsets: UIEdgeInsets = .zero
    private var currentPage: RDEPUBTextPage?
    private var highlightedRanges: [RDEPUBHighlight] = []
    weak var delegate: RDEPUBTextContentViewDelegate?

    private let textView: RDEPUBSelectableTextView = {
        let view = RDEPUBSelectableTextView()
        view.isEditable = false
        view.isScrollEnabled = false
        view.isSelectable = true
        view.backgroundColor = .clear
        view.textContainerInset = .zero
        view.textContainer.lineFragmentPadding = 0
        return view
    }()

    private let pageNumberLabel: UILabel = {
        let label = UILabel()
        label.font = UIFont.systemFont(ofSize: 13)
        return label
    }()

    override init(frame: CGRect) {
        super.init(frame: frame)
        addSubview(textView)
        addSubview(pageNumberLabel)
        textView.delegate = self
        textView.onSelectionAction = { [weak self] action in
            guard let self else { return }
            self.delegate?.textContentView(self, didRequestSelectionAction: action)
        }
        UIMenuController.shared.menuItems = [
            UIMenuItem(title: "拷贝", action: #selector(RDEPUBSelectableTextView.rd_copy(_:))),
            UIMenuItem(title: "高亮", action: #selector(RDEPUBSelectableTextView.rd_highlight(_:))),
            UIMenuItem(title: "批注", action: #selector(RDEPUBSelectableTextView.rd_annotate(_:)))
        ]
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func layoutSubviews() {
        super.layoutSubviews()

        textView.frame = bounds.inset(by: contentInsets)

        let labelSize = pageNumberLabel.sizeThatFits(CGSize(width: bounds.width, height: 20))
        pageNumberLabel.frame = CGRect(
            x: bounds.width - labelSize.width - 24,
            y: bounds.height - labelSize.height - 20,
            width: labelSize.width,
            height: labelSize.height
        )
    }

    func configure(
        page: RDEPUBTextPage,
        pageNumber: Int,
        totalPages: Int,
        configuration: RDEPUBReaderConfiguration,
        highlights: [RDEPUBHighlight] = [],
        searchState: RDEPUBSearchState? = nil
    ) {
        currentPage = page
        highlightedRanges = highlights
        contentInsets = configuration.reflowableContentInsets
        backgroundColor = configuration.theme.contentBackgroundColor
        pageNumberLabel.textColor = configuration.theme.contentTextColor
        pageNumberLabel.text = "\(pageNumber) / \(totalPages)"

        let displayContent = NSMutableAttributedString(attributedString: page.content)
        let fullRange = NSRange(location: 0, length: displayContent.length)
        displayContent.addAttribute(
            .foregroundColor,
            value: configuration.theme.contentTextColor,
            range: fullRange
        )
        applyHighlights(to: displayContent, page: page)
        applySearchHighlights(to: displayContent, page: page, searchState: searchState)
        textView.tintColor = configuration.theme.toolControlTextColor
        textView.attributedText = displayContent
        textView.selectedRange = NSRange(location: 0, length: 0)
        delegate?.textContentView(self, didChangeSelection: nil)
        setNeedsLayout()
    }

    func clearSelection() {
        textView.selectedRange = NSRange(location: 0, length: 0)
        delegate?.textContentView(self, didChangeSelection: nil)
    }

    private func applyHighlights(to content: NSMutableAttributedString, page: RDEPUBTextPage) {
        let pageRange = absoluteOffsetRange(for: page)
        let pageStart = pageRange.lowerBound
        let pageEndExclusive = pageRange.upperBound

        for highlight in highlightedRanges where highlight.location.href == page.href {
            guard let range = RDEPUBTextOffsetRangeInfo.decode(from: highlight.rangeInfo)?.nsRange else { continue }
            let overlapStart = max(range.location, pageStart)
            let overlapEnd = min(range.location + range.length, pageEndExclusive)
            guard overlapStart < overlapEnd else { continue }

            let relativeRange = NSRange(
                location: overlapStart - pageStart,
                length: overlapEnd - overlapStart
            )
            switch highlight.style {
            case .highlight:
                content.addAttribute(
                    .backgroundColor,
                    value: UIColor(hexString: highlight.color, alpha: 0.45) ?? UIColor(red: 248 / 255, green: 225 / 255, blue: 108 / 255, alpha: 0.45),
                    range: relativeRange
                )
            case .underline:
                content.addAttribute(.underlineStyle, value: NSUnderlineStyle.single.rawValue, range: relativeRange)
                if let color = UIColor(hexString: highlight.color, alpha: 1) {
                    content.addAttribute(.underlineColor, value: color, range: relativeRange)
                }
            }
        }
    }

    private func applySearchHighlights(
        to content: NSMutableAttributedString,
        page: RDEPUBTextPage,
        searchState: RDEPUBSearchState?
    ) {
        guard let searchState else { return }

        let normalColor = UIColor(red: 248 / 255, green: 225 / 255, blue: 108 / 255, alpha: 0.55)
        let activeColor = UIColor(red: 255 / 255, green: 159 / 255, blue: 67 / 255, alpha: 0.75)
        let pageRange = absoluteOffsetRange(for: page)
        let pageStart = pageRange.lowerBound
        let pageEndExclusive = pageRange.upperBound

        for match in searchState.matches where match.href == page.href {
            guard let matchStart = match.rangeLocation else { continue }
            let matchEnd = matchStart + match.rangeLength
            let overlapStart = max(matchStart, pageStart)
            let overlapEnd = min(matchEnd, pageEndExclusive)
            guard overlapStart < overlapEnd else { continue }

            let relativeRange = NSRange(location: Int(overlapStart - pageStart), length: Int(overlapEnd - overlapStart))
            let color = match == searchState.currentMatch ? activeColor : normalColor
            content.addAttribute(.backgroundColor, value: color, range: relativeRange)
        }
    }

    private func absoluteOffsetRange(for page: RDEPUBTextPage) -> Range<Int> {
        let lowerBound = page.pageStartOffset
        let upperBound = page.pageEndOffset + 1
        return lowerBound..<max(upperBound, lowerBound)
    }

}

extension RDEPUBTextContentView: UITextViewDelegate {
    func textViewDidChangeSelection(_ textView: UITextView) {
        guard let page = currentPage else {
            delegate?.textContentView(self, didChangeSelection: nil)
            return
        }

        let selectedRange = textView.selectedRange
        guard selectedRange.location != NSNotFound,
              selectedRange.length > 0,
              let attributedText = textView.attributedText else {
            delegate?.textContentView(self, didChangeSelection: nil)
            return
        }

        let source = attributedText.string as NSString
        let selectedText = source.substring(with: selectedRange).trimmingCharacters(in: .whitespacesAndNewlines)
        guard !selectedText.isEmpty else {
            delegate?.textContentView(self, didChangeSelection: nil)
            return
        }

        let globalStart = page.pageStartOffset + selectedRange.location
        let globalEnd = globalStart + selectedRange.length
        let totalLength = max(page.content.length - 1, 1)
        let selection = RDEPUBSelection(
            location: RDEPUBLocation(
                href: page.href,
                progression: Double(selectedRange.location) / Double(totalLength),
                lastProgression: Double(max(selectedRange.location + selectedRange.length - 1, 0)) / Double(totalLength),
                fragment: nil
            ),
            text: selectedText,
            rangeInfo: RDEPUBTextOffsetRangeInfo(href: page.href, start: globalStart, end: globalEnd).jsonString()
        )
        delegate?.textContentView(self, didChangeSelection: selection)
    }
}

private extension UIColor {
    convenience init?(hexString: String, alpha: CGFloat) {
        var value = hexString.trimmingCharacters(in: .whitespacesAndNewlines)
        value = value.replacingOccurrences(of: "#", with: "")
        guard value.count == 6, let hex = Int(value, radix: 16) else { return nil }
        self.init(
            red: CGFloat((hex >> 16) & 0xFF) / 255,
            green: CGFloat((hex >> 8) & 0xFF) / 255,
            blue: CGFloat(hex & 0xFF) / 255,
            alpha: alpha
        )
    }
}