// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.

using System.Collections.Generic;
using System.Collections.Immutable;
using Microsoft.VisualStudio.Text.Adornments;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.Editor.Implementation.IntelliSense
{
    internal static class Helpers
    {
        internal static IEnumerable<object> BuildClassifiedTextElements(ImmutableArray<TaggedText> taggedTexts)
        {
            // This method produces a sequence of zero or more paragraphs
            var paragraphs = new List<object>();

            // Each paragraph is constructed from one or more lines
            var currentParagraph = new List<ClassifiedTextElement>();

            // Each line is constructed from one or more inline elements
            var currentRuns = new List<ClassifiedTextRun>();

            foreach (var part in taggedTexts)
            {
                if (part.Tag == TextTags.LineBreak)
                {
                    if (currentRuns.Count > 0)
                    {
                        // This line break means the end of a line within a paragraph.
                        currentParagraph.Add(new ClassifiedTextElement(currentRuns));
                        currentRuns.Clear();
                    }
                    else
                    {
                        // This line break means the end of a paragraph. Empty paragraphs are ignored, but could appear
                        // in the input to this method:
                        //
                        // * Empty <para> elements
                        // * Explicit line breaks at the start of a comment
                        // * Multiple line breaks between paragraphs
                        if (currentParagraph.Count > 0)
                        {
                            // The current paragraph is not empty, so add it to the result collection
                            paragraphs.Add(CreateParagraphFromLines(currentParagraph));
                            currentParagraph.Clear();
                        }
                        else
                        {
                            // The current paragraph is empty, so we simply ignore it.
                        }
                    }
                }
                else
                {
                    // This is tagged text getting added to the current line we are building.
                    currentRuns.Add(new ClassifiedTextRun(part.Tag.ToClassificationTypeName(), part.Text));
                }
            }

            if (currentRuns.Count > 0)
            {
                // Add the final line to the final paragraph.
                currentParagraph.Add(new ClassifiedTextElement(currentRuns));
            }

            if (currentParagraph.Count > 0)
            {
                // Add the final paragraph to the result.
                paragraphs.Add(CreateParagraphFromLines(currentParagraph));
            }

            return paragraphs;
        }

        internal static object CreateParagraphFromLines(IReadOnlyList<ClassifiedTextElement> lines)
        {
            Contract.ThrowIfFalse(lines.Count > 0);

            if (lines.Count == 1)
            {
                // The paragraph contains only one line, so it doesn't need to be added to a container. Avoiding the
                // wrapping container here also avoids a wrapping element in the WPF elements used for rendering,
                // improving efficiency.
                return lines[0];
            }
            else
            {
                // The lines of a multi-line paragraph are stacked to produce the full paragraph.
                return new ContainerElement(ContainerElementStyle.Stacked, lines);
            }
        }
    }
}