import Foundation

public struct RDEPUBCFIResolverResult: Equatable {

    public var href: String?

    public var fileIndex: Int?

    public var chapterOffset: Int?

    public var fragmentID: String?

    public init(href: String? = nil, fileIndex: Int? = nil, chapterOffset: Int? = nil, fragmentID: String? = nil) {
        self.href = href
        self.fileIndex = fileIndex
        self.chapterOffset = chapterOffset
        self.fragmentID = fragmentID
    }
}

public enum RDEPUBCFIResolver {

    public static func resolve(_ cfi: RDEPUBCFI) -> RDEPUBCFIResolverResult {

        // EPUB CFI spec: package path structure is /6/2[spine]/2n[manifest-id]
        // Manifest step is always the 3rd step (index 2) if present, or the last step with an id assertion.
        let manifestStep: RDEPUBCFIStep?
        if cfi.packagePath.steps.count >= 3 {
            manifestStep = cfi.packagePath.steps[2]
        } else {
            manifestStep = cfi.packagePath.steps.last(where: { $0.idAssertion?.rd_nilIfEmpty != nil })
        }
        let href = manifestStep?.idAssertion

        // Spine step is the 2nd step (index 1) in the package path
        let fileIndex: Int?
        if cfi.packagePath.steps.count >= 2 {
            fileIndex = max((cfi.packagePath.steps[1].index / 2) - 1, 0)
        } else {
            fileIndex = nil
        }

        let fragmentID = cfi.contentPath.steps.last(where: { $0.idAssertion?.rd_nilIfEmpty != nil })?.idAssertion
        return RDEPUBCFIResolverResult(
            href: href,
            fileIndex: fileIndex,
            chapterOffset: cfi.characterOffset,
            fragmentID: fragmentID
        )
    }
}