import UIKit

enum RDEPUBTextPageLayoutMetrics {

    static let pageNumberTrailingPadding: CGFloat = 4

    static let pageNumberFooterPadding: CGFloat = 8

    static let pageNumberReservedHeight: CGFloat = ceil(UIFont.systemFont(ofSize: 13).lineHeight) + pageNumberFooterPadding

    static func contentInsets(
        configuration: RDEPUBReaderConfiguration,
        safeAreaInsets: UIEdgeInsets,
        isLandscapeDualPage: Bool = false,
        isLeadingPage: Bool = true
    ) -> UIEdgeInsets {
        let configInsets = configuration.reflowableContentInsets
        guard isLandscapeDualPage else {
            return UIEdgeInsets(
                top: max(configInsets.top, safeAreaInsets.top),
                left: max(configInsets.left, safeAreaInsets.left),
                bottom: max(configInsets.bottom, safeAreaInsets.bottom) + pageNumberReservedHeight,
                right: max(configInsets.right, safeAreaInsets.right)
            )
        }

        let outerHorizontalInset = max(
            max(configInsets.left, configInsets.right),
            max(safeAreaInsets.left, safeAreaInsets.right)
        )
        let spineInset = RDEpubReaderView.landscapeDualPageGap / 2
        return UIEdgeInsets(
            top: max(safeAreaInsets.top, min(configInsets.top, RDEPUBSafeArea.landscapeVerticalTextMargin)),
            left: isLeadingPage ? outerHorizontalInset : spineInset,
            bottom: max(safeAreaInsets.bottom, min(configInsets.bottom, RDEPUBSafeArea.landscapeVerticalTextMargin)) + pageNumberReservedHeight,
            right: isLeadingPage ? spineInset : outerHorizontalInset
        )
    }

    static func fixedContentInsets(
        configuration: RDEPUBReaderConfiguration,
        safeAreaInsets: UIEdgeInsets,
        isLandscapeDualPage: Bool,
        isLeadingPage: Bool
    ) -> UIEdgeInsets {
        let configInsets = configuration.fixedContentInset
        guard isLandscapeDualPage else {
            return UIEdgeInsets(
                top: max(configInsets.top, safeAreaInsets.top),
                left: max(configInsets.left, safeAreaInsets.left),
                bottom: max(configInsets.bottom, safeAreaInsets.bottom),
                right: max(configInsets.right, safeAreaInsets.right)
            )
        }

        let outerHorizontalInset = max(
            max(configInsets.left, configInsets.right),
            max(safeAreaInsets.left, safeAreaInsets.right)
        )
        let spineInset = RDEpubReaderView.landscapeDualPageGap / 2
        return UIEdgeInsets(
            top: max(safeAreaInsets.top, min(configInsets.top, RDEPUBSafeArea.landscapeVerticalTextMargin)),
            left: isLeadingPage ? outerHorizontalInset : spineInset,
            bottom: max(safeAreaInsets.bottom, min(configInsets.bottom, RDEPUBSafeArea.landscapeVerticalTextMargin)),
            right: isLeadingPage ? spineInset : outerHorizontalInset
        )
    }
}

final class RDEPUBReaderEnvironment {

    weak var controller: RDEPUBReaderController?

    weak var readerView: RDEpubReaderView?

    var displayEnvironment: any RDEPUBReaderDisplayEnvironment

    init(
        controller: RDEPUBReaderController,
        readerView: RDEpubReaderView,
        displayEnvironment: any RDEPUBReaderDisplayEnvironment
    ) {
        self.controller = controller
        self.readerView = readerView
        self.displayEnvironment = displayEnvironment
    }

    func currentLayoutContext(configuration: RDEPUBReaderConfiguration) -> RDEPUBNavigatorLayoutContext {
        let containerSize = readerView?.bounds.size ?? .zero
        let viewSize = controller?.view.bounds.size ?? containerSize
        let resolvedSize = containerSize == .zero ? viewSize : containerSize
        return RDEPUBNavigatorLayoutContext(
            containerSize: resolvedSize,
            pagesPerScreen: readerView?.pagesPerScreen ?? 1,
            safeAreaInsets: RDEPUBSafeArea.resolve(controller?.view.safeAreaInsets),
            userInterfaceIdiom: controller?.traitCollection.userInterfaceIdiom ?? .phone,
            reflowableContentInsets: configuration.reflowableContentInsets
        )
    }

    func currentTextRenderStyle(configuration: RDEPUBReaderConfiguration) -> RDEPUBTextRenderStyle {
        let font = configuration.fontChoice.font(ofSize: configuration.fontSize)
        let lineSpacing = max(font.lineHeight * (configuration.lineHeightMultiple - 1), 4)
        return RDEPUBTextRenderStyle(
            font: font,
            lineSpacing: lineSpacing,
            textColor: configuration.theme.contentTextColor,
            backgroundColor: configuration.theme.contentBackgroundColor
        )
    }

    func currentTextLayoutConfig(
        configuration: RDEPUBReaderConfiguration,
        pageSize: CGSize
    ) -> RDEPUBTextLayoutConfig {
        let safeAreaInsets = RDEPUBSafeArea.resolve(controller?.view.safeAreaInsets)
        return RDEPUBTextLayoutConfig(
            frameWidth: max(pageSize.width, 1),
            frameHeight: max(pageSize.height, 1),
            edgeInsets: RDEPUBTextPageLayoutMetrics.contentInsets(
                configuration: configuration,
                safeAreaInsets: safeAreaInsets,
                isLandscapeDualPage: readerView?.pagesPerScreen == 2
            ),
            numberOfColumns: configuration.numberOfColumns,
            columnGap: configuration.columnGap,
            avoidOrphans: false,
            avoidWidows: false,
            avoidPageBreakInsideEnabled: true,
            hyphenation: true,
            imageMaxHeightRatio: 0.85,
            fallbackViewportSize: displayEnvironment.fallbackViewportSize
        )
    }

    func currentPreferences(
        configuration: RDEPUBReaderConfiguration,
        pageIndex: Int? = nil
    ) -> RDEPUBPreferences {
        let safeAreaInsets = RDEPUBSafeArea.resolve(controller?.view.safeAreaInsets)
        let isLandscapeDualPage = readerView?.pagesPerScreen == 2
        let isLeadingPage = pageIndex.map { readerView?.isLeadingPage($0) ?? true } ?? true
        var preferences = configuration.makePreferences(safeAreaInsets: safeAreaInsets)
        preferences.reflowableContentInsets = RDEPUBTextPageLayoutMetrics.contentInsets(
            configuration: configuration,
            safeAreaInsets: safeAreaInsets,
            isLandscapeDualPage: isLandscapeDualPage,
            isLeadingPage: isLeadingPage
        )
        preferences.fixedContentInset = RDEPUBTextPageLayoutMetrics.fixedContentInsets(
            configuration: configuration,
            safeAreaInsets: safeAreaInsets,
            isLandscapeDualPage: isLandscapeDualPage,
            isLeadingPage: isLeadingPage
        )
        return preferences
    }

    var currentBrightness: CGFloat {
        get { displayEnvironment.currentBrightness }
        set { displayEnvironment.currentBrightness = newValue }
    }

    var fallbackViewportSize: CGSize {
        displayEnvironment.fallbackViewportSize
    }
}