import Foundation

typealias LinkedElement = (previous: Element?, element: Element, next: Element?)

struct SiteGenerator {

    let templates: TemplateFactory

    init() throws {
        let templatesFolder = files.urlInContentFolder("templates")
        self.templates = try TemplateFactory(templateFolder: templatesFolder)
    }

    func generate(site: Element) {
        site.languages.forEach {
            generate(site: site, metadata: $0)
        }
    }

    private func generate(site: Element, metadata: Element.LocalizedMetadata) {
        let language = metadata.language
        let template = LocalizedSiteTemplate(
            factory: templates,
            language: language,
            site: site)

        // Generate sections
        let overviewGenerator = OverviewPageGenerator(factory: template)
        let pageGenerator = PageGenerator(factory: template, siteRoot: site)
        
        var elementsToProcess: [LinkedElement] = [(nil, site, nil)]
        while let (previous, element, next) = elementsToProcess.popLast() {
            // Move recursively down to all pages
            elementsToProcess.append(contentsOf: element.linkedElements)

            processAllFiles(for: element)

            if !element.elements.isEmpty {
                overviewGenerator.generate(section: element, language: language)
            } else {
                pageGenerator.generate(
                    page: element,
                    language: language,
                    previousPage: previous,
                    nextPage: next)
            }
        }
    }

    private func processAllFiles(for element: Element) {
        element.requiredFiles.forEach(files.require)
        element.externalFiles.forEach(files.exclude)
        element.images.forEach {
            files.requireSingleImage(
                source: $0.sourcePath,
                destination: $0.destinationPath,
                requiredBy: element.path,
                width: $0.desiredWidth,
                desiredHeight: $0.desiredHeight)
        }
    }
}