//
//  ViewBuilder.swift
//  Adwaita
//
//  Created by david-swift on 05.08.23.
//

import Foundation

/// The ``ViewBuilder`` is a result builder for views.
@resultBuilder
public enum ViewBuilder {

    /// A component used in the ``ArrayBuilder``.
    public enum Component {

        /// A view as a component.
        case element(_: View)
        /// An array of components as a component.
        case components(_: [Self])

    }

    /// Build combined results from statement blocks.
    /// - Parameter components: The components.
    /// - Returns: The components in a component.
    public static func buildBlock(_ elements: Component...) -> Component {
        .components(elements)
    }

    /// Translate an element into a ``ViewBuilder.Component``.
    /// - Parameter element: The element to translate.
    /// - Returns: A component created from the element.
    public static func buildExpression(_ element: View) -> Component {
        .element(element)
    }

    /// Translate an array of elements into a ``ViewBuilder.Component``.
    /// - Parameter elements: The elements to translate.
    /// - Returns: A component created from the element.
    public static func buildExpression(_ elements: [View]) -> Component {
        var components: [Component] = []
        for element in elements {
            components.append(.element(element))
        }
        return .components(components)
    }

    /// Fetch a component.
    /// - Parameter component: A component.
    /// - Returns: The component.
    public static func buildExpression(_ component: Component) -> Component {
        component
    }

    /// Enables support for `if` statements without an `else`.
    /// - Parameter component: An optional component.
    /// - Returns: A nonoptional component.
    public static func buildOptional(_ component: Component?) -> Component {
        .element(
            VStack {
                if let component {
                    buildFinalResult(component)
                } else {
                    []
                }
            }
            .visible(component != nil)
        )
    }

    /// Enables support for `if`-`else` and `switch` statements.
    /// - Parameter component: A component.
    /// - Returns: The component.
    public static func buildEither(first component: Component) -> Component {
        .element(ViewStack(id: true) { _ in buildFinalResult(component) })
    }

    /// Enables support for `if`-`else` and `switch` statements.
    /// - Parameter component: A component.
    /// - Returns: The component.
    public static func buildEither(second component: Component) -> Component {
        .element(ViewStack(id: false) { _ in buildFinalResult(component) })
    }

    /// Convert a component to an array of elements.
    /// - Parameter component: The component to convert.
    /// - Returns: The generated array of elements.
    public static func buildFinalResult(_ component: Component) -> [View] {
        switch component {
        case let .element(element):
            return [element]
        case let .components(components):
            return components.flatMap { buildFinalResult($0) }
        }
    }

}
