// RDEPUBReaderController+TableOfContents.swift
// EPUB 阅读器目录功能
// 提供目录（Table of Contents）相关功能，包括解析当前页面对应的目录项
// 以及将嵌套目录树结构扁平化为线性列表。

import Foundation

/// RDEPUBReaderController 目录扩展
///
/// 本文件提供目录（Table of Contents）相关功能，包括解析当前页面对应的目录项
/// 以及将嵌套目录树结构扁平化为线性列表。

extension RDEPUBReaderController {
    /// 解析当前阅读位置对应的目录项，按页码或 href 匹配
    func resolvedCurrentTableOfContentsItem() -> RDEPUBReaderTableOfContentsItem? {
        let items = flattenedTableOfContents
        guard !items.isEmpty else { return nil }

        let currentPageNumber = max(readerView.currentPage + 1, 1)
        let pageAnchoredMatch = items.last { item in
            guard let pageNumber = item.pageNumber else { return false }
            return pageNumber <= currentPageNumber
        }
        if let pageAnchoredMatch {
            return pageAnchoredMatch
        }

        guard let publication,
              let currentLocation = currentVisibleLocation(),
              let normalizedCurrentHref = publication.resourceResolver.normalizedHref(currentLocation.href) else {
            return nil
        }

        if let textBook,
           let chapterData = textBook.chapterData(
            for: currentLocation,
            resolver: publication.resourceResolver,
            bookIdentifier: currentBookIdentifier
           ),
           let tocItem = chapterData.primaryTableOfContentsItem(
            from: publication.tableOfContents,
            normalizer: { publication.resourceResolver.normalizedHref($0) }
           ) {
            return items.last { $0.href == tocItem.href } ?? items.last {
                guard let normalizedItemHref = publication.resourceResolver.normalizedHref($0.href.components(separatedBy: "#").first ?? $0.href) else {
                    return false
                }
                return normalizedItemHref == normalizedCurrentHref
            }
        }

        return items.last { item in
            guard let normalizedItemHref = publication.resourceResolver.normalizedHref(item.href.components(separatedBy: "#").first ?? item.href) else {
                return false
            }
            return normalizedItemHref == normalizedCurrentHref
        }
    }

    /// 将嵌套目录树递归扁平化为线性列表，并计算每项目标页码
    func flattenedTableOfContentsItems(
        from items: [EPUBTableOfContentsItem],
        depth: Int = 0
    ) -> [RDEPUBReaderTableOfContentsItem] {
        items.flatMap { item in
            let location = RDEPUBLocation(bookIdentifier: currentBookIdentifier, href: item.href, progression: 0)
            let pageNumber: Int?
            if let textBook, let publication,
               let chapterData = textBook.chapterData(for: location, resolver: publication.resourceResolver, bookIdentifier: currentBookIdentifier) {
                let normalizedLocation = publication.resourceResolver.normalizedLocation(
                    location,
                    bookIdentifier: currentBookIdentifier
                ) ?? location
                pageNumber = chapterData.pageNumber(for: normalizedLocation)
                    ?? textBook.pageNumber(
                        for: location,
                        resolver: publication.resourceResolver,
                        bookIdentifier: currentBookIdentifier
                    )
            } else if let readingSession {
                pageNumber = readingSession.pageIndex(for: location, bookIdentifier: currentBookIdentifier).map { $0 + 1 }
            } else {
                pageNumber = nil
            }

            let current = RDEPUBReaderTableOfContentsItem(
                title: item.title,
                href: item.href,
                depth: depth,
                pageNumber: pageNumber
            )
            return [current] + flattenedTableOfContentsItems(from: item.children, depth: depth + 1)
        }
    }
}