import Elementary

/// The page links under a card grid; renders nothing for a single page.
struct Pagination: HTML {

    // MARK: Properties

    /// The page shown, counted from one.
    let current: Int

    /// The path of a given page.
    let path: @Sendable (Int) -> String

    /// The number of pages.
    let total: Int

    // MARK: Initializers

    /// Creates the page links.
    /// - Parameters:
    ///   - current: the page shown, counted from one.
    ///   - total: the number of pages.
    ///   - path: the path of a given page.
    init(
        current: Int,
        total: Int,
        path: @escaping @Sendable (Int) -> String
    ) {
        self.current = current
        self.path = path
        self.total = total
    }

    // MARK: Computed

    var body: some HTML {
        if total > 1 {
            nav(
                .class("pagination"),
                .custom(
                    name: "aria-label",
                    value: "Pagination"
                )
            ) {
                for page in 1...total {
                    if page == current {
                        a(
                            .class("pagination__page"),
                            .href(path(page)),
                            .custom(
                                name: "aria-current",
                                value: "page"
                            )
                        ) {
                            "\(page)"
                        }
                    } else {
                        a(
                            .class("pagination__page"),
                            .href(path(page))
                        ) {
                            "\(page)"
                        }
                    }
                }
                if current < total {
                    a(
                        .class("pagination__next"),
                        .href(path(current + 1))
                    ) {
                        "Next"
                    }
                }
            }
        }
    }

}

// MARK: - Extensions

extension Pagination {

    // MARK: Methods

    /// Cuts the items of one page out of a list, clamping the page to the list's range.
    /// - Parameters:
    ///   - items: the whole list.
    ///   - page: the page asked for, counted from one.
    ///   - size: the number of items on a page.
    /// - Returns: the page's items, the page actually shown, and the number of pages.
    static func slice<Item>(
        _ items: [Item],
        page: Int,
        size: Int
    ) -> (items: [Item], current: Int, total: Int) {
        let total = max((items.count + size - 1) / size, 1)
        let current = min(max(page, 1), total)

        return (
            Array(items.dropFirst((current - 1) * size).prefix(size)),
            current,
            total
        )
    }

}