import Foundation

final class PostListPageGenerator {

    let source: PostListPageGeneratorSource

    init(source: PostListPageGeneratorSource) {
        self.source = source
    }

    private var language: ContentLanguage {
        source.language
    }

    private var mainContentMaximumWidth: Int {
        source.content.settings.posts.contentWidth
    }

    private func pageUrl(in language: ContentLanguage, pageNumber: Int) -> String {
        "\(source.pageUrlPrefix(for: language))/\(pageNumber)"
    }

    func createPages(for posts: [Post]) {
        // Sort by newest first, filter drafts
        let posts = posts
            .filter { !$0.isDraft }
            .sorted(ascending: false) { $0.startDate }

        let totalCount = posts.count
        guard totalCount > 0 else {
            // Create one empty page
            createPostFeedPage(1, pageCount: 1, posts: [])
            return
        }
        let postsPerPage = source.postsPerPage

        let numberOfPages = (totalCount + postsPerPage - 1) / postsPerPage // Round up
        for pageIndex in 1...numberOfPages {
            let startIndex = (pageIndex - 1) * postsPerPage
            let endIndex = min(pageIndex * postsPerPage, totalCount)
            let postsOnPage = posts[startIndex..<endIndex]
            createPostFeedPage(pageIndex, pageCount: numberOfPages, posts: postsOnPage)
        }
    }

    private func makePostData(post: Post) -> FeedEntryData {
        let localized: LocalizedPost = post.localized(in: language)

        let linkUrl = post.linkedPage.map {
            FeedEntryData.Link(
                url: $0.absoluteUrl(in: language),
                text: localized.pageLinkText ?? post.content.settings.posts.localized(in: language).defaultPageLinkText)
        }

        // Use the tags of the page if one is linked
        let tags: [FeedEntryData.Tag] = post.usedTags().filter { $0.isVisible }.map { tag in
                .init(name: tag.localized(in: language).name,
                      url: tag.absoluteUrl(in: language))
        }

        let images = localized.images.map { image in
            image.imageSet(width: mainContentMaximumWidth, height: mainContentMaximumWidth, language: language)
        }
        images.forEach(source.results.require)

        return FeedEntryData(
            entryId: post.id,
            title: localized.title,
            textAboveTitle: post.dateText(in: language),
            link: linkUrl,
            tags: tags,
            text: localized.text.components(separatedBy: "\n\n"),
            images: images)
        #warning("Treat post text as markdown")
    }

    private func createPostFeedPage(_ pageIndex: Int, pageCount: Int, posts: ArraySlice<Post>) {
        let posts: [FeedEntryData] = posts.map(makePostData)

        let feedPageGenerator = FeedPageGenerator(content: source.content, results: source.results)

        // Includes leading slash
        let languageButtonUrl = pageUrl(in: language.next, pageNumber: pageIndex)

        let fileContent = feedPageGenerator.generatePage(
            language: language,
            posts: posts,
            title: source.pageTitle,
            description: source.pageDescription,
            showTitle: source.showTitle,
            pageNumber: pageIndex,
            totalPages: pageCount,
            languageButtonUrl: languageButtonUrl,
            linkPrefix: source.pageUrlPrefix(for: language))
        // Includes leading slash
        let filePath = pageUrl(in: language, pageNumber: pageIndex) + ".html"
        guard save(fileContent, to: filePath) else {
            source.results.unsavedOutput(filePath, source: .feed)
            return
        }
    }

    private func save(_ content: String, to relativePath: String) -> Bool {
        source.content.storage.write(content, to: relativePath)
    }
}