import UIKit

struct RDEPUBTextOverlayDecoration {
    enum Kind: String {
        case selection
        case highlight
        case underline
        case search
        case activeSearch
        case locate
    }

    var kind: Kind
    var absoluteRange: NSRange
    var rects: [CGRect]
    var color: UIColor
}

final class RDEPUBSelectionOverlayView: UIView {
    private(set) var page: RDEPUBTextPage?
    private var snapshot: RDEPUBPageLayoutSnapshot?
    private(set) var selectionRange: NSRange?
    private var selectionRects: [CGRect] = []
    private var decorations: [RDEPUBTextOverlayDecoration] = []
    private let selectionVerticalAdjustment: CGFloat = -1

    var selectionColor: UIColor = UIColor(red: 70 / 255, green: 140 / 255, blue: 1, alpha: 0.24) {
        didSet {
            setNeedsDisplay()
        }
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .clear
        isOpaque = false
        isUserInteractionEnabled = false
    }

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

    func configure(page: RDEPUBTextPage, selectionColor: UIColor, snapshot: RDEPUBPageLayoutSnapshot? = nil) {
        self.page = page
        self.snapshot = snapshot
        self.selectionColor = selectionColor
        selectionRange = nil
        decorations = []
        setNeedsDisplay()
    }

    func updateSnapshot(_ snapshot: RDEPUBPageLayoutSnapshot?) {
        self.snapshot = snapshot
    }

    func updateSelection(absoluteRange: NSRange?) {
        selectionRange = absoluteRange
        selectionRects = []
        setNeedsDisplay()
    }

    func updateSelection(absoluteRange: NSRange?, rects: [CGRect]) {
        selectionRange = absoluteRange
        selectionRects = rects
        setNeedsDisplay()
    }

    func applyDecorations(_ decorations: [RDEPUBTextOverlayDecoration]) {
        self.decorations = decorations
        setNeedsDisplay()
    }

    func clearSelection() {
        updateSelection(absoluteRange: nil)
    }

    func absoluteRange(at point: CGPoint) -> NSRange? {
        if let selectionRange,
           selectionRects.contains(where: { $0.insetBy(dx: -4, dy: -4).contains(point) }) {
            return selectionRange
        }

        if let snapshot,
           let attachment = snapshot.attachment(at: point) {
            return attachment.stringRange
        }

        if let snapshot {
            let hitDecorations = snapshot.rects(containing: point, in: resolvedDecorations)
            if let mostSpecific = hitDecorations.min(by: { lhs, rhs in
                lhs.absoluteRange.length < rhs.absoluteRange.length
            }) {
                return mostSpecific.absoluteRange
            }
        }

        for decoration in resolvedDecorations {
            for rect in decoration.rects {
                if rect.insetBy(dx: -4, dy: -4).contains(point) {
                    return decoration.absoluteRange
                }
            }
        }
        return nil
    }

    func decorationSummary() -> String {
        let counts = Dictionary(grouping: resolvedDecorations, by: \.kind).mapValues(\.count)
        let selectionLabel = selectionRange.map(NSStringFromRange) ?? "none"
        let highlightCount = counts[.highlight, default: 0]
        let underlineCount = counts[.underline, default: 0]
        let searchCount = counts[.search, default: 0]
        let activeSearchCount = counts[.activeSearch, default: 0]
        let locateLabel = resolvedDecorations.first(where: { $0.kind == .locate }).map { NSStringFromRange($0.absoluteRange) } ?? "none"
        return [
            "selection \(selectionLabel)",
            "highlight \(highlightCount)",
            "underline \(underlineCount)",
            "search \(searchCount)",
            "activeSearch \(activeSearchCount)",
            "locate \(locateLabel)"
        ].joined(separator: " · ")
    }

    override func draw(_ rect: CGRect) {
        guard let context = UIGraphicsGetCurrentContext() else { return }

        for decoration in resolvedDecorations {
            switch decoration.kind {
            case .underline:
                context.setStrokeColor(decoration.color.cgColor)
                context.setLineWidth(2)
                for underlineRect in decoration.rects {
                    let y = underlineRect.maxY - 1
                    context.move(to: CGPoint(x: underlineRect.minX, y: y))
                    context.addLine(to: CGPoint(x: underlineRect.maxX, y: y))
                    context.strokePath()
                }
            default:
                context.setFillColor(decoration.color.cgColor)
                for selectionRect in decoration.rects {
                    let adjustedRect = selectionRect.offsetBy(dx: 0, dy: selectionVerticalAdjustment)
                    let path = UIBezierPath(roundedRect: adjustedRect.insetBy(dx: -1, dy: -1), cornerRadius: 4)
                    context.addPath(path.cgPath)
                    context.fillPath()
                }
            }
        }
    }

    private var resolvedDecorations: [RDEPUBTextOverlayDecoration] {
        guard page != nil else { return [] }

        var result = decorations.filter { !$0.rects.isEmpty }

        if let selectionRange, !selectionRects.isEmpty {
            result.append(
                RDEPUBTextOverlayDecoration(
                    kind: .selection,
                    absoluteRange: selectionRange,
                    rects: selectionRects,
                    color: selectionColor
                )
            )
        }

        return result
    }
}