using System;
using System.Collections.Generic;

namespace WasmBox.Pixie.Markup {
    /// <summary>
    /// A node that visualizes a diff of a pair of strings.
    /// </summary>
    public sealed class TextDiff : MarkupNode {
		/// <summary>
		/// Creates a text diff node.
		/// </summary>
		/// <param name="diff">
		/// The diff to render.
		/// </param>
		/// <param name="operationColors">
		/// A dictionary that maps diff operations to the color in which
		/// diff elements that use those operations are painted. Diff operations
		/// that do not appear as keys in the dictionary are not rendered, except
		/// for <see cref="DiffOperation.Unchanged"/>, which is rendered
		/// without color if it does not show up as a key.
		/// </param>
		public TextDiff(
            Diff<char> diff,
            IReadOnlyDictionary<DiffOperation, Color> operationColors) {
            this.Diff = diff;
            this.OperationColors = operationColors;
        }

        /// <summary>
        /// Gets the diff to render.
        /// </summary>
        /// <returns>The diff to render.</returns>
        public Diff<char> Diff { get; private set; }

		/// <summary>
		/// Gets a dictionary that maps diff operations to the color in which
		/// diff elements that use those operations are painted. Diff operations
		/// that do not appear as keys in the dictionary are not rendered, except
		/// for <see cref="DiffOperation.Unchanged"/>, which is rendered
		/// without color if it does not show up as a key.
		/// </summary>
		/// <returns>A mapping of diff operations to colors.</returns>
		public IReadOnlyDictionary<DiffOperation, Color> OperationColors { get; private set; }

        /// <inheritdoc/>
        public override MarkupNode Fallback {
            get {
                var nodes = new List<MarkupNode>();
                int elemCount = Diff.Elements.Count;
                for (int i = 0; i < elemCount; i++) {
                    var elem = Diff.Elements[i];
                    Color color;
                    if (OperationColors.TryGetValue(elem.Operation, out color)) {
                        nodes.Add(
                            new ColorSpan(
                                string.Concat( elem.Values),
                                color));
                    }
                    else if (elem.Operation == DiffOperation.Unchanged) {
                        nodes.Add(string.Concat( elem.Values));
                    }
                }
                return new Sequence(nodes);
            }
        }

        /// <inheritdoc/>
        public override MarkupNode Map(Func<MarkupNode, MarkupNode> mapping) {
            return this;
        }

        /// <summary>
        /// Creates a text diff that renders the deletions in a diff.
        /// </summary>
        /// <param name="diff">A diff to render.</param>
        /// <returns>
        /// A text diff node that renders deletions and unchanged diff elements only.
        /// </returns>
        public static TextDiff RenderDeletions(Diff<char> diff) {
            return new TextDiff(
                diff,
                new Dictionary<DiffOperation, Color>() { { DiffOperation.Deletion, Colors.Red }
                });
        }

        /// <summary>
        /// Creates a text diff that renders the insertions in a diff.
        /// </summary>
        /// <param name="diff">A diff to render.</param>
        /// <returns>
        /// A text diff node that renders insertions and unchanged diff elements only.
        /// </returns>
        public static TextDiff RenderInsertions(Diff<char> diff) {
            return new TextDiff(
                diff,
                new Dictionary<DiffOperation, Color>() { { DiffOperation.Insertion, Colors.Green }
                });
        }

        /// <summary>
        /// Creates a text diff that renders the both the deletions
        /// and insertions in a diff.
        /// </summary>
        /// <param name="diff">A diff to render.</param>
        /// <returns>
        /// A text diff node that renders all diff elements.
        /// </returns>
        public static TextDiff RenderAll(Diff<char> diff) {
            return new TextDiff(
                diff,
                new Dictionary<DiffOperation, Color>() { { DiffOperation.Deletion, Colors.Red }, { DiffOperation.Insertion, Colors.Green }
                });
        }
    }
}