ReadViewSDK/Sources/RDEpubReaderView/EPUBCore/Models/RDEPUBPaginationModels.swift

import Foundation

public enum RDEPUBTextPageBreakReason: String, Codable, Equatable {

    case chapterEnd

    case frameLimit

    case blockBoundary

    case attachmentBoundary

    case semanticBoundary
}

public enum RDEPUBTextAttachmentKind: String, Codable, Equatable {

    case image

    case generic

    case footnote
}

public struct RDEPUBTextPageMetadata: Codable, Equatable {

    public var breakReason: RDEPUBTextPageBreakReason

    public var blockRange: NSRange?

    public var attachmentRanges: [NSRange]

    public var attachmentKinds: [RDEPUBTextAttachmentKind]

    public var blockKinds: [RDEPUBTextBlockKind]

    public var semanticHints: [RDEPUBTextSemanticHint]

    public var attachmentPlacements: [RDEPUBTextAttachmentPlacement]

    public var trailingFragmentID: String?

    public var diagnostics: [String]

    public init(
        breakReason: RDEPUBTextPageBreakReason,
        blockRange: NSRange? = nil,
        attachmentRanges: [NSRange] = [],
        attachmentKinds: [RDEPUBTextAttachmentKind] = [],
        blockKinds: [RDEPUBTextBlockKind] = [],
        semanticHints: [RDEPUBTextSemanticHint] = [],
        attachmentPlacements: [RDEPUBTextAttachmentPlacement] = [],
        trailingFragmentID: String? = nil,
        diagnostics: [String] = []
    ) {
        self.breakReason = breakReason
        self.blockRange = blockRange
        self.attachmentRanges = attachmentRanges
        self.attachmentKinds = attachmentKinds
        self.blockKinds = blockKinds
        self.semanticHints = semanticHints
        self.attachmentPlacements = attachmentPlacements
        self.trailingFragmentID = trailingFragmentID
        self.diagnostics = diagnostics
    }
}

public struct EPUBChapterInfo: Codable, Equatable {

    public var spineIndex: Int

    public var title: String

    public var pageCount: Int

    public init(spineIndex: Int, title: String, pageCount: Int) {
        self.spineIndex = spineIndex
        self.title = title
        self.pageCount = pageCount
    }
}

public struct EPUBPage: Codable, Equatable {

    public var spineIndex: Int

    public var chapterIndex: Int

    public var pageIndexInChapter: Int

    public var totalPagesInChapter: Int

    public var chapterTitle: String

    public var fixedSpread: EPUBFixedSpread?

    public init(
        spineIndex: Int,
        chapterIndex: Int,
        pageIndexInChapter: Int,
        totalPagesInChapter: Int,
        chapterTitle: String,
        fixedSpread: EPUBFixedSpread?
    ) {
        self.spineIndex = spineIndex
        self.chapterIndex = chapterIndex
        self.pageIndexInChapter = pageIndexInChapter
        self.totalPagesInChapter = totalPagesInChapter
        self.chapterTitle = chapterTitle
        self.fixedSpread = fixedSpread
    }
}

public struct EPUBFixedSpreadResource: Codable, Equatable {

    public var spineIndex: Int

    public var href: String

    public var title: String

    public var pageSpread: RDEPUBPageSpread?

    public init(spineIndex: Int, href: String, title: String, pageSpread: RDEPUBPageSpread? = nil) {
        self.spineIndex = spineIndex
        self.href = href
        self.title = title
        self.pageSpread = pageSpread
    }
}

public struct EPUBFixedSpread: Codable, Equatable {

    public var resources: [EPUBFixedSpreadResource]

    public init(resources: [EPUBFixedSpreadResource]) {
        self.resources = resources
    }

    public var primaryResource: EPUBFixedSpreadResource {
        resources.first ?? EPUBFixedSpreadResource(spineIndex: 0, href: "", title: "")
    }

    public func contains(normalizedHref: String, normalizer: (String) -> String?) -> Bool {
        resources.contains { resource in
            normalizer(resource.href) == normalizedHref
        }
    }

    public static func makeSpreads(spine: [RDEPUBSpineItem], spreadEnabled: Bool) -> [EPUBFixedSpread] {
        let resources = spine.enumerated().map { index, item in
            EPUBFixedSpreadResource(
                spineIndex: index,
                href: item.href,
                title: item.title,
                pageSpread: item.pageSpread
            )
        }

        guard spreadEnabled, resources.count > 1 else {
            return resources.map { EPUBFixedSpread(resources: [$0]) }
        }

        var spreads: [EPUBFixedSpread] = []
        var cursor = 0

        while cursor < resources.count {
            let current = resources[cursor]

            guard cursor + 1 < resources.count else {
                spreads.append(EPUBFixedSpread(resources: [current]))
                break
            }

            let next = resources[cursor + 1]
            if shouldPair(current: current, next: next) {
                spreads.append(EPUBFixedSpread(resources: [current, next]))
                cursor += 2
            } else {
                spreads.append(EPUBFixedSpread(resources: [current]))
                cursor += 1
            }
        }

        return spreads
    }

    public static func makeSpreads(parser: RDEPUBParser, spreadEnabled: Bool) -> [EPUBFixedSpread] {
        makeSpreads(spine: parser.spine, spreadEnabled: spreadEnabled)
    }

    private static func shouldPair(current: EPUBFixedSpreadResource, next: EPUBFixedSpreadResource) -> Bool {
        if current.pageSpread == .center || next.pageSpread == .center {
            return false
        }

        switch (current.pageSpread, next.pageSpread) {
        case (.left, .right), (.right, .left):
            return true
        case (.left, .left), (.right, .right):
            return false
        default:
            return true
        }
    }
}