// RDEPUBResourceResolver.swift
// EPUB 资源解析器
// 封装 RDEPUBParser 的资源查询能力，提供 href 规范化、
// spine 索引查找、位置规范化等高层接口。是 Services 层的核心组件，
// 被 RDEPUBPublication 和 RDEPUBReadingSession 广泛使用。

import Foundation

/// EPUB 资源解析器，负责 URL 转换、href 规范化和位置解析
public final class RDEPUBResourceResolver {
    /// 底层解析器引用
    private let parser: RDEPUBParser

    public init(parser: RDEPUBParser) {
        self.parser = parser
    }

    /// OPF 文件所在目录的 URL
    public var opfDirectoryURL: URL? {
        parser.opfDirectoryURL
    }

    /// 将相对路径转换为本地文件 URL
    public func fileURL(forRelativePath relativePath: String) -> URL? {
        parser.fileURL(forRelativePath: relativePath)
    }

    /// 将相对路径转换为 ss-reader://book/ 协议 URL
    public func resourceURL(forRelativePath relativePath: String) -> URL? {
        parser.resourceURL(forRelativePath: relativePath)
    }

    /// 将 ss-reader://book/ 协议 URL 还原为本地文件 URL
    public func fileURL(forResourceURL resourceURL: URL) -> URL? {
        parser.fileURL(forResourceURL: resourceURL)
    }

    /// 规范化 href：基于 OPF 目录和可选的 spine 索引，将相对路径解析为标准化的 OPF 内路径
    public func normalizedHref(_ href: String, relativeToSpineIndex spineIndex: Int? = nil) -> String? {
        guard let opfDirectoryURL else {
            return href.components(separatedBy: "#").first
        }

        let pathPart = href.components(separatedBy: "#").first ?? href
        if pathPart.isEmpty {
            guard let spineIndex, parser.spine.indices.contains(spineIndex) else {
                return nil
            }
            return parser.spine[spineIndex].href.components(separatedBy: "#").first
        }

        let baseURL: URL
        if let spineIndex, parser.spine.indices.contains(spineIndex) {
            baseURL = opfDirectoryURL
                .appendingPathComponent(parser.spine[spineIndex].href)
                .deletingLastPathComponent()
        } else {
            baseURL = opfDirectoryURL
        }

        guard let resolvedURL = URL(string: pathPart, relativeTo: baseURL)?.standardizedFileURL else {
            return pathPart
        }

        let opfPath = opfDirectoryURL.standardizedFileURL.path + "/"
        let resolvedPath = resolvedURL.path
        if resolvedPath.hasPrefix(opfPath) {
            return String(resolvedPath.dropFirst(opfPath.count))
        }
        return pathPart
    }

    /// 规范化 href：基于另一个 href 作为基准路径
    public func normalizedHref(_ href: String, relativeToHref baseHref: String) -> String? {
        guard let opfDirectoryURL else {
            return href.components(separatedBy: "#").first
        }

        let pathPart = href.components(separatedBy: "#").first ?? href
        let basePath = baseHref.components(separatedBy: "#").first ?? baseHref
        let baseURL = opfDirectoryURL
            .appendingPathComponent(basePath)
            .deletingLastPathComponent()

        guard let resolvedURL = URL(string: pathPart, relativeTo: baseURL)?.standardizedFileURL else {
            return pathPart
        }

        let opfPath = opfDirectoryURL.standardizedFileURL.path + "/"
        if resolvedURL.path.hasPrefix(opfPath) {
            return String(resolvedURL.path.dropFirst(opfPath.count))
        }
        return pathPart
    }

    /// 将相对于另一个 href 的引用转换为本地文件 URL
    public func fileURL(forReference href: String, relativeToHref baseHref: String) -> URL? {
        guard let normalizedHref = normalizedHref(href, relativeToHref: baseHref) else {
            return nil
        }
        return fileURL(forRelativePath: normalizedHref)
    }

    /// 规范化位置对象：解析 href、保留 progression 和 fragment
    public func normalizedLocation(
        _ location: RDEPUBLocation,
        relativeToSpineIndex spineIndex: Int? = nil,
        bookIdentifier: String?
    ) -> RDEPUBLocation? {
        let rawHref = location.href
        let hrefParts = rawHref.split(separator: "#", maxSplits: 1, omittingEmptySubsequences: false)
        let pathPart = hrefParts.first.map(String.init) ?? rawHref
        let fragment = location.fragment ?? (hrefParts.count > 1 ? String(hrefParts[1]) : nil)

        let normalizedTargetHref: String
        if pathPart.isEmpty {
            guard let spineIndex, parser.spine.indices.contains(spineIndex) else {
                return nil
            }
            normalizedTargetHref = parser.spine[spineIndex].href.components(separatedBy: "#").first ?? parser.spine[spineIndex].href
        } else {
            guard let href = normalizedHref(pathPart, relativeToSpineIndex: spineIndex) else {
                return nil
            }
            normalizedTargetHref = href
        }

        return RDEPUBLocation(
            bookIdentifier: bookIdentifier,
            href: normalizedTargetHref,
            progression: location.progression,
            lastProgression: location.lastProgression,
            fragment: fragment,
            rangeAnchor: location.rangeAnchor
        )
    }

    /// 通过规范化 href 查找对应的 spine 索引
    public func spineIndex(forNormalizedHref normalizedHref: String) -> Int? {
        parser.spine.firstIndex { item in
            self.normalizedHref(item.href) == normalizedHref
        }
    }

    /// 通过位置查找对应的 spine 索引
    public func spineIndex(for location: RDEPUBLocation) -> Int? {
        guard let normalizedHref = normalizedHref(location.href) else {
            return nil
        }
        return spineIndex(forNormalizedHref: normalizedHref)
    }

    /// 通过 spine 索引获取 href
    public func href(forSpineIndex spineIndex: Int) -> String? {
        guard parser.spine.indices.contains(spineIndex) else {
            return nil
        }
        return parser.spine[spineIndex].href
    }

    /// 通过 spine 索引获取标题
    public func title(forSpineIndex spineIndex: Int) -> String? {
        guard parser.spine.indices.contains(spineIndex) else {
            return nil
        }
        return parser.spine[spineIndex].title
    }

    /// 通过 href 查询 manifest 项
    public func manifestItem(forHref href: String) -> RDEPUBManifestItem? {
        let targetHref = normalizedHref(href) ?? href.components(separatedBy: "#").first ?? href
        return parser.manifest.values.first {
            normalizedHref($0.href) == targetHref
        }
    }
}