import Foundation

extension RDEPUBParser {

    func buildSpine(from packageDocument: OPFPackageDocument, opfURL: URL) throws -> [RDEPUBSpineItem] {
        let opfDirectoryURL = opfURL.deletingLastPathComponent()
        let publicationLayout = packageDocument.metadata.layout

        let spineItems = try packageDocument.spineReferences.map { reference in
            guard let manifestItem = packageDocument.manifestByID[reference.idref] else {
                throw RDEPUBParserError.missingManifestItem(idref: reference.idref)
            }

            let normalizedHref = normalize(href: manifestItem.href, relativeTo: opfDirectoryURL)
            let title = manifestItem.title?.trimmingCharacters(in: .whitespacesAndNewlines)
            let fallbackTitle = normalizedHref
                .split(separator: "/")
                .last
                .map(String.init)
                .map { $0.replacingOccurrences(of: ".xhtml", with: "") }
                .map { $0.replacingOccurrences(of: ".html", with: "") }
                .flatMap { $0.isEmpty ? nil : $0 }
                ?? reference.idref

            let effectiveLayout: RDEPUBLayout?
            if reference.properties.contains("rendition:layout-pre-paginated") || manifestItem.properties.contains("rendition:layout-pre-paginated") {
                effectiveLayout = .fixed
            } else if reference.properties.contains("rendition:layout-reflowable") || manifestItem.properties.contains("rendition:layout-reflowable") {
                effectiveLayout = .reflowable
            } else {
                effectiveLayout = publicationLayout == .fixed ? .fixed : nil
            }

            return RDEPUBSpineItem(
                idref: reference.idref,
                href: normalizedHref,
                mediaType: manifestItem.mediaType,
                title: title?.isEmpty == false ? title! : fallbackTitle,
                linear: reference.linear,
                properties: reference.properties,
                pageSpread: reference.pageSpread,
                layout: effectiveLayout
            )
        }

        guard !spineItems.isEmpty else {
            throw RDEPUBParserError.emptySpine
        }

        return spineItems
    }
}

struct OPFPackageDocument {
    var metadata: RDEPUBMetadata
    var manifest: [RDEPUBManifestItem]
    var manifestByID: [String: RDEPUBManifestItem]
    var spineReferences: [OPFSpineReference]

    var ncxItem: RDEPUBManifestItem?

    var navigationItem: RDEPUBManifestItem?
}

struct OPFSpineReference {

    var idref: String

    var linear: Bool

    var properties: [String]

    var pageSpread: RDEPUBPageSpread?
}

final class OPFPackageParserDelegate: NSObject, XMLParserDelegate {

    private var metadata = RDEPUBMetadata()

    private var manifestItems: [RDEPUBManifestItem] = []

    private var spineReferences: [OPFSpineReference] = []

    private let xmlContext = XMLParserContext()

    private var uniqueIdentifierID: String?

    private var currentIdentifierElementID: String?

    private var currentMetaProperty: String?

    private var identifierByID: [String: String] = [:]

    private var manifestTitleByID: [String: String] = [:]

    private var currentMetaRefinesID: String?

    private var ncxID: String?

    func packageDocument() -> OPFPackageDocument {
        if metadata.identifier == nil, let fallbackIdentifier = identifierByID.values.first {
            metadata.identifier = fallbackIdentifier
        }
        metadata.title = metadata.title.trimmingCharacters(in: .whitespacesAndNewlines)
        metadata.author = metadata.author?.trimmingCharacters(in: .whitespacesAndNewlines)
        metadata.language = metadata.language?.trimmingCharacters(in: .whitespacesAndNewlines)

        let manifest = manifestItems.map { item in
            var updatedItem = item
            updatedItem.title = manifestTitleByID[item.id]
            return updatedItem
        }
        // 部分历史 EPUB 的 OPF manifest 含重复 id。`uniqueKeysWithValues` 会在
        // 此处触发运行时断言，导致整本书无法打开；spine 按 OPF 顺序解析，故保留
        // 第一个声明即可维持其原始引用语义。
        let manifestByID = manifest.reduce(into: [String: RDEPUBManifestItem]()) { result, item in
            guard !item.id.isEmpty, result[item.id] == nil else { return }
            result[item.id] = item
        }

        return OPFPackageDocument(
            metadata: metadata,
            manifest: manifest,
            manifestByID: manifestByID,
            spineReferences: spineReferences,
            ncxItem: manifest.first(where: { $0.id == ncxID || $0.isNCX }),
            navigationItem: manifest.first(where: { $0.isNavigationDocument })
        )
    }

    func parser(
        _ parser: XMLParser,
        didStartElement elementName: String,
        namespaceURI: String?,
        qualifiedName qName: String?,
        attributes attributeDict: [String: String] = [:]
    ) {
        let name = xmlContext.startElement(named: qName ?? elementName)

        switch name {
        case "package":
            metadata.version = attributeDict["version"]
            uniqueIdentifierID = attributeDict["unique-identifier"]
        case "identifier":
            if currentSection == .metadata {
                currentIdentifierElementID = attributeDict["id"]
            }
        case "item":
            guard currentSection == .manifest,
                  let id = attributeDict["id"],
                  let href = attributeDict["href"],
                  let mediaType = attributeDict["media-type"] else {
                return
            }
            manifestItems.append(
                RDEPUBManifestItem(
                    id: id,
                    href: href,
                    mediaType: mediaType,
                    properties: XMLName.tokenize(attributeDict["properties"]),
                    fallback: attributeDict["fallback"],
                    mediaOverlay: attributeDict["media-overlay"]
                )
            )
        case "itemref":
            guard currentSection == .spine, let idref = attributeDict["idref"] else {
                return
            }
            spineReferences.append(
                OPFSpineReference(
                    idref: idref,
                    linear: (attributeDict["linear"]?.lowercased() ?? "yes") != "no",
                    properties: XMLName.tokenize(attributeDict["properties"]),
                    pageSpread: pageSpread(from: attributeDict)
                )
            )
        case "meta":
            currentMetaProperty = attributeDict["property"] ?? attributeDict["name"]
            currentMetaRefinesID = attributeDict["refines"].flatMap(XMLName.refinedID(from:))
            if let property = currentMetaProperty?.lowercased(),
               property == "rendition:layout",
               let value = attributeDict["content"] {
                metadata.layout = layout(from: value)
            }
            if let property = currentMetaProperty?.lowercased(),
               property == "rendition:spread" {
                metadata.spread = attributeDict["content"]
            }
            if let property = currentMetaProperty?.lowercased(),
               property == "rendition:orientation",
               let value = attributeDict["content"] {
                metadata.orientation = orientation(from: value)
            }
            if let property = currentMetaProperty?.lowercased(),
               property == "title",
               let refinesID = currentMetaRefinesID,
               let value = attributeDict["content"],
               !value.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
                manifestTitleByID[refinesID] = value.trimmingCharacters(in: .whitespacesAndNewlines)
            }
        default:
            break
        }

        if name == "spine" {
            if let direction = attributeDict["page-progression-direction"]?.lowercased() {
                metadata.readingProgression = direction == "ltr" ? .ltr : (direction == "rtl" ? .rtl : .auto)
            }
            ncxID = attributeDict["toc"]
        }
    }

    func parser(_ parser: XMLParser, foundCharacters string: String) {
        xmlContext.appendCharacters(string)
    }

    func parser(
        _ parser: XMLParser,
        didEndElement elementName: String,
        namespaceURI: String?,
        qualifiedName qName: String?
    ) {
        let name = XMLName.localName(from: qName ?? elementName)
        let text = xmlContext.trimmedCharacters

        switch (currentSection, name) {
        case (.metadata, "identifier"):
            if let identifierID = currentIdentifierElementID, !text.isEmpty {
                identifierByID[identifierID] = text
                if identifierID == uniqueIdentifierID {
                    metadata.identifier = text
                }
            } else if metadata.identifier == nil, !text.isEmpty {
                metadata.identifier = text
            }
            currentIdentifierElementID = nil
        case (.metadata, "title"):
            if metadata.title.isEmpty, !text.isEmpty {
                metadata.title = text
            }
        case (.metadata, "creator"):
            if metadata.author == nil, !text.isEmpty {
                metadata.author = text
            }
        case (.metadata, "language"):
            if metadata.language == nil, !text.isEmpty {
                metadata.language = text
            }
        case (.metadata, "meta"):
            applyMetaValue(text)
            currentMetaProperty = nil
            currentMetaRefinesID = nil
        default:
            break
        }

        xmlContext.endElement()
    }

    private var currentSection: XMLSection {
        if xmlContext.containsElement(named: "manifest") {
            return .manifest
        }
        if xmlContext.containsElement(named: "spine") {
            return .spine
        }
        if xmlContext.containsElement(named: "metadata") {
            return .metadata
        }
        return .other
    }

    private func applyMetaValue(_ value: String) {
        let normalizedValue = value.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !normalizedValue.isEmpty, let property = currentMetaProperty?.lowercased() else {
            return
        }

        switch property {
        case "rendition:layout":
            metadata.layout = layout(from: normalizedValue)
        case "rendition:spread":
            metadata.spread = normalizedValue
        case "rendition:orientation":
            metadata.orientation = orientation(from: normalizedValue)
        case "dcterms:identifier", "identifier":
            if metadata.identifier == nil {
                metadata.identifier = normalizedValue
            }
        case "title":
            if let refinesID = currentMetaRefinesID {
                manifestTitleByID[refinesID] = normalizedValue
            }
        default:
            break
        }
    }

    private func pageSpread(from attributes: [String: String]) -> RDEPUBPageSpread? {
        if let properties = attributes["properties"]?.lowercased() {
            if properties.contains("page-spread-left") {
                return .left
            }
            if properties.contains("page-spread-right") {
                return .right
            }
            if properties.contains("page-spread-center") {
                return .center
            }
        }

        if let legacySpread = attributes["page-spread"]?.lowercased() {
            switch legacySpread {
            case "left":
                return .left
            case "right":
                return .right
            case "center":
                return .center
            default:
                return nil
            }
        }

        return nil
    }

    private func layout(from rawValue: String) -> RDEPUBLayout {
        rawValue.lowercased().contains("pre-paginated") ? .fixed : .reflowable
    }

    private func orientation(from rawValue: String) -> RDEPUBOrientation? {
        switch rawValue.lowercased().trimmingCharacters(in: .whitespacesAndNewlines) {
        case "portrait":
            return .portrait
        case "landscape":
            return .landscape
        case "auto":
            return .auto
        default:
            return nil
        }
    }
}

enum XMLSection {
    case metadata
    case manifest
    case spine
    case other
}

enum XMLName {

    static func localName(from rawName: String) -> String {
        rawName.split(separator: ":").last.map(String.init) ?? rawName
    }

    static func tokenize(_ rawValue: String?) -> [String] {
        guard let rawValue else { return [] }
        return rawValue
            .split(whereSeparator: { $0 == " " || $0 == "\n" || $0 == "\t" || $0 == "\r" })
            .map(String.init)
    }

    static func refinedID(from rawValue: String) -> String? {
        let trimmed = rawValue.trimmingCharacters(in: .whitespacesAndNewlines)
        guard trimmed.hasPrefix("#") else {
            return nil
        }
        return String(trimmed.dropFirst())
    }
}

final class XMLParserContext {

    private var elementStack: [String] = []

    private var currentCharacters = ""

    var trimmedCharacters: String {
        currentCharacters.trimmingCharacters(in: .whitespacesAndNewlines)
    }

    func startElement(named rawName: String) -> String {
        let name = XMLName.localName(from: rawName)
        elementStack.append(name)
        currentCharacters = ""
        return name
    }

    func appendCharacters(_ string: String) {
        currentCharacters += string
    }

    func endElement() {
        if !elementStack.isEmpty {
            _ = elementStack.removeLast()
        }
        currentCharacters = ""
    }

    func containsElement(named name: String) -> Bool {
        elementStack.contains(name)
    }
}