import Foundation

/**
 The metadata for all site elements.
 */
struct GenericMetadata {

    /**
     The name of the metadata file contained in the folder of each site element.
     */
    static let metadataFileName = "metadata.json"

    /**
     A custom id to uniquely identify the element on the site.

     The id is used for short-hand links to pages, in the form of `![page](page_id)`
     for thumbnail previews or `[text](page:page_id)` for simple links.

     If no custom id is set, then the name of the element folder is used.
     */
    let customId: String?

    /**
     The author of the content.

     If no author is set, then the author from the parent element is used.
     */
    let author: String?

    /**
     The title used in the top bar of the website, next to the logo.

     This title can be HTML content, and only the root level value is used.
     */
    let topBarTitle: String?

    /**
     The (start) date of the element.

     The date is printed on content pages and may also used for sorting elements,
     depending on the `useManualSorting` property of the parent.
     */
    let date: String?

    /**
     The end date of the element.

     This property can be used to specify a date range for a content page.
     */
    let endDate: String?

    /**
     The deployment state of the page.

     - Note: This property defaults to ``PageState.standard`
     */
    let state: String?

    /**
     The sort index of the page for manual sorting.

     - Note: This property is only used (and must be set) if `useManualSorting` option of the parent is set.
     */
    let sortIndex: Int?

    /**
     All files which may occur in content but is stored externally.

     Missing files which would otherwise produce a warning are ignored when included here.
     - Note: This property defaults to an empty set.
     */
    let externalFiles: Set<String>?

    /**
     Specifies additional files which should be copied to the destination when generating the content.
     - Note: This property defaults to an empty set.
     */
    let requiredFiles: Set<String>?

    /**
     Additional images required by the element.

     These images are specified as: `source_name destination_name width (height)`.
     */
    let images: Set<String>?

    /**
     The path to the thumbnail file.

     This property is optional, and defaults to ``Element.defaultThumbnailName``.
     Note: The generator first looks for localized versions of the thumbnail by appending `-[lang]` to the file name,
     e.g. `customThumb-en.jpg`. If no file is found, then the specified file is tried.
     */
    let thumbnailPath: String?

    /**
     The style of thumbnail to use when generating overviews.

     - Note: This property is only relevant for sections.
     - Note: This property is inherited from the parent if not specified.
     */
    let thumbnailStyle: String?

    /**
     Sort the child elements by their `sortIndex` property when generating overviews, instead of using the `date`.

     - Note: This property is only relevant for sections.
     - Note: This property defaults to `false`
     */
    let useManualSorting: Bool?

    /**
     The number of items to show when generating overviews of this element.
     - Note: This property is only relevant for sections.
     - Note: This property is inherited from the parent if not specified.
     */
    let overviewItemCount: Int?

    /**
     Indicate the header type to be generated automatically.

     If this option is set to `none`, then custom header code should be present in the page source files
     - Note: If not specified, this property defaults to `left`.
     - Note: Overview pages are always using `center`.
     */
    let headerType: String?

    /**
     The localized metadata for each language.
     */
    let languages: [LocalizedMetadata]?
}

extension GenericMetadata: Codable {

    private static var knownKeyList: [CodingKeys] {
        [
            .customId,
            .author,
            .topBarTitle,
            .date,
            .endDate,
            .state,
            .sortIndex,
            .externalFiles,
            .requiredFiles,
            .images,
            .thumbnailPath,
            .thumbnailStyle,
            .useManualSorting,
            .overviewItemCount,
            .headerType,
            .languages,
        ]
    }

    static var knownKeys: Set<String> {
        Set(knownKeyList.map { $0.stringValue })
    }
}

extension GenericMetadata {

    /**
     Decode metadata in a folder.

     - Parameter data: The binary data of the metadata file.
     - Parameter source: The path to the metadata file, relative to the source root
     - Note: The decoding routine also checks for unknown properties, and writes them to the output.
     - Note: Uses global objects
     */
    init?(source: String, log: MetadataInfoLogger) {
        guard let data = log.readPotentialMetadata(atPath: source, source: source) else {
            return nil
        }

        let decoder = JSONDecoder()
        
        let knownKeys = GenericMetadata.knownKeys
        let knownLocalizedKeys = LocalizedMetadata.knownKeys
        decoder.keyDecodingStrategy = .custom { keys in
            let key = keys.last!
            // Only one key means we are decoding the generic metadata
            guard keys.count > 1 else {
                if !knownKeys.contains(key.stringValue) {
                    log.unknown(property: key.stringValue, source: source)
                }
                return key
            }
            // Two levels means we're decoding the localized metadata
            if !knownLocalizedKeys.contains(key.stringValue) {
                log.unknown(property: key.stringValue, source: source)
            }
            return key
        }
        do {
            self = try decoder.decode(from: data)
        } catch {
            log.failedToDecodeMetadata(source: source, error: error)
            return nil
        }
    }
}

extension GenericMetadata {

    static var full: GenericMetadata {
        .init(
            customId: "",
            author: "",
            topBarTitle: "",
            date: "",
            endDate: "",
            state: "",
            sortIndex: 1,
            externalFiles: [],
            requiredFiles: [],
            images: [],
            thumbnailPath: "",
            thumbnailStyle: "",
            useManualSorting: false,
            overviewItemCount: 6,
            headerType: "left",
            languages: [.full])
    }
}