import Foundation
import Ink

struct PageGenerator {

    private let factory: LocalizedSiteTemplate

    init(factory: LocalizedSiteTemplate) {
        self.factory = factory
    }

    func generate(page: Element, language: String, previousPage: Element?, nextPage: Element?) {
        guard !page.isExternalPage else {
            return
        }
        let path = page.fullPageUrl(for: language)
        let inputContentPath = page.path + "/\(language).md"
        let metadata = page.localized(for: language)
        let nextLanguage = page.nextLanguage(for: language)
        let (pageContent, pageIncludesCode, pageIsEmpty) = makeContent(
            page: page, metadata: metadata, language: language, path: inputContentPath)

        var content = [PageTemplate.Key : String]()
        content[.head] = factory.pageHead.generate(page: page, language: language, includesCode: pageIncludesCode)
        let sectionUrl = page.sectionUrl(for: language)
        content[.topBar] = factory.topBar.generate(sectionUrl: sectionUrl, languageButton: nextLanguage, page: page)
        content[.contentClass] = "content"

        content[.header] = makeHeader(page: page, metadata: metadata, language: language)
        content[.content] = pageContent
        content[.previousPageLinkText] = previousText(for: previousPage, language: language)
        content[.previousPageUrl] = navLink(from: page, to: previousPage, language: language)
        content[.nextPageLinkText] = nextText(for: nextPage, language: language)
        content[.nextPageUrl] = navLink(from: page, to: nextPage, language: language)
        content[.footer] = page.customFooterContent()

        if pageIncludesCode {
            let highlightCode = factory.factory.html.codeHighlightFooter()
            content[.footer] = (content[.footer].unwrapped { $0 + "\n" } ?? "") + highlightCode
        }

        let url = files.urlInOutputFolder(path)
        if page.state == .draft {
            files.isDraft(path: page.path)
        } else if pageIsEmpty, page.state != .hidden {
            files.isEmpty(page: path)
        }
        guard factory.page.generate(content, to: url) else {
            return
        }
        files.generated(page: path)
    }

    private func navLink(from element: Element, to destination: Element?, language: String) -> String? {
        guard let fullPath = destination?.fullPageUrl(for: language) else {
            return nil
        }
        return element.relativePathToOtherSiteElement(file: fullPath)
    }

    private func previousText(for element: Element?, language: String) -> String? {
        guard let text = element?.localized(for: language).navigationTextAsPreviousPage else {
            return nil
        }
        return factory.factory.html.makePrevText(text)
    }

    private func nextText(for element: Element?, language: String) -> String? {
        guard let text = element?.localized(for: language).navigationTextAsNextPage else {
            return nil
        }
        return factory.factory.html.makeNextText(text)
    }

    private func makeContent(page: Element, metadata: Element.LocalizedMetadata, language: String, path: String) -> (content: String, includesCode: Bool, isEmpty: Bool) {
        let create = configuration.createMdFilesIfMissing
        if let raw = files.contentOfOptionalFile(atPath: path, source: page.path, createEmptyFileIfMissing: create)?
            .trimmed.nonEmpty {
            let (content, includesCode) = PageContentGenerator(factory: factory.factory)
                .generate(page: page, language: language, content: raw)
            return (content, includesCode, false)
        } else {
            let (content, includesCode) = PageContentGenerator(factory: factory.factory)
                .generate(page: page, language: language, content: metadata.placeholderText)
            let placeholder = factory.factory.makePlaceholder(title: metadata.placeholderTitle, text: content)
            return (placeholder, includesCode, true)
        }
    }

    private func makeHeader(page: Element, metadata: Element.LocalizedMetadata, language: String) -> String? {
        let content = factory.makeHeaderContent(page: page, metadata: metadata, language: language)
        switch page.headerType {
        case .none:
            return nil
        case .left:
            return factory.factory.leftHeader.generate(content)
        case .center:
            return factory.factory.centeredHeader.generate(content)
        }
    }

}