using System;

namespace WasmBox.Pixie.Markup {
    /// <summary>
    /// Describes a diagnostic as issued by typical command-line tools:
    /// a self-contained nugget of information to the user.
    /// </summary>
    public sealed class Diagnostic : MarkupNode {
        /// <summary>
        /// Creates a diagnostic.
        /// </summary>
        /// <param name="origin">
        /// The origin of the diagnostic: the line of code
        /// or application that causes the diagnostic to be
        /// issued.
        /// </param>
        /// <param name="kind">
        /// A single-word description of the kind of diagnostic
        /// to create.
        /// </param>
        /// <param name="themeColor">
        /// The diagnostic's theme color.
        /// </param>
        /// <param name="title">
        /// The contents of the diagnostic's title.
        /// </param>
        /// <param name="message"></param>
        public Diagnostic(
            MarkupNode origin,
            string kind,
            Color themeColor,
            MarkupNode title,
            MarkupNode message) {
            this.Origin = origin;
            this.Kind = kind;
            this.ThemeColor = themeColor;
            this.Title = title;
            this.Message = message;
        }

        /// <summary>
        /// Gets the origin of this diagnostic: the line of code
        /// or application that causes the diagnostic to be
        /// issued.
        /// </summary>
        /// <returns>The origin of the diagnostic.</returns>
        public MarkupNode Origin { get; private set; }

        /// <summary>
        /// Gets a (single-word) description of the kind of diagnostic
        /// this instance is.
        /// </summary>
        /// <returns>The kind of diagnostic.</returns>
        public string Kind { get; private set; }

        /// <summary>
        /// Gets this diagnostic's theme color.
        /// </summary>
        /// <returns>The theme color.</returns>
        public Color ThemeColor { get; private set; }

        /// <summary>
        /// Gets the contents of this diagnostic's title.
        /// </summary>
        /// <returns>The title.</returns>
        public MarkupNode Title { get; private set; }

        /// <summary>
        /// Gets this diagnostic's message.
        /// </summary>
        /// <returns>The message node.</returns>
        public MarkupNode Message { get; private set; }

        /// <inheritdoc/>
        public override MarkupNode Fallback {
            get {
                var titlePart = Text.IsEmpty(Title)
                    ? Title
                    : new Sequence(Title, new Text(": "));

                var header =
                    new Sequence(
                        Origin,
                        new Text(": "),
                        new ColorSpan(
                            new Text(Kind + ": "),
                            ThemeColor),
                        titlePart);

                return new Sequence(
                    new DecorationSpan(header, TextDecoration.Bold),
                    Message);
            }
        }

        /// <inheritdoc/>
        public override MarkupNode Map(Func<MarkupNode, MarkupNode> mapping) {
            var newOrigin = mapping(Origin);
            var newTitle = mapping(Title);
            var newMessage= mapping(Message);

            if (newOrigin == Origin
                && newTitle == Title
                && newMessage == Message) {
                return this;
            }
            else {
                return new Diagnostic(
                    newOrigin,
                    Kind,
                    ThemeColor,
                    newTitle,
                    newMessage);
            }
        }
    }
}