using System.Linq;

using Markdig.Helpers;
using Markdig.Parsers;
using Markdig.Syntax.Inlines;

namespace MfGames.Markdown.Extensions;

public class WikiLinkInlineParser : InlineParser
{
    private readonly WikiLinkOptions options;

    public WikiLinkInlineParser(WikiLinkOptions options)
    {
        this.options = options;
        this.OpeningCharacters = new[] { '[' };
    }

    /// <inheritdoc />
    public override bool Match(
        InlineProcessor processor,
        ref StringSlice slice)
    {
        // We are looking for the `[[` opening for the tag and that the first
        // one isn't escaped.
        if (IsNotDelimiter(slice, '['))
        {
            return false;
        }

        // We need to loop over the entire link, including the `[[` and `]]`
        // while keeping track since we'll swallow additional characters beyond
        // the link.
        int linkStart = slice.Start;
        int linkEnd = slice.Start;

        slice.Start += 2;

        // Our content starts after the double '[['.
        int contentStart = slice.Start;

        // We need to find the end of the link (the `]]`).
        while (IsNotDelimiter(slice, ']'))
        {
            slice.NextChar();
            linkEnd = slice.Start;
        }

        // Pull out the components before we adjust for the ']]' for the end.
        int contentEnd = linkEnd;

        // Finish skipping over the `]]`.
        slice.NextChar();
        slice.NextChar();

        // Format the label and the URL.
        string content = slice.Text.Substring(
            contentStart,
            contentEnd - contentStart);
        string[] contentParts = content.Split('|', 2);
        string label = contentParts.Last();
        string url = this.options.GetUrl(contentParts.First());

        // Add in any trailing components. This merges the `'s` from
        // `[[Dale]]'s` into the label.
        while (this.options.IsTrailingLink(slice.CurrentChar))
        {
            label += slice.CurrentChar;
            slice.NextChar();
            linkEnd++;
        }

        // Create the link that we're replacing.
        WikiLink link = new()
        {
            Span =
            {
                Start = processor.GetSourcePosition(
                    linkStart,
                    out int line,
                    out int column),
            },
            Line = line,
            Column = column,
            Url = url,
            IsClosed = true,
        };

        link.AppendChild(
            new LiteralInline()
            {
                Line = line,
                Column = column,
                Content = new StringSlice(label),
                IsClosed = true,
            });

        // Replace the inline and then indicate we have a match.
        processor.Inline = link;

        return true;
    }

    private static bool IsNotDelimiter(
        StringSlice slice,
        char delimiter)
    {
        return slice.CurrentChar != delimiter
            || slice.PeekChar() != delimiter
            || slice.PeekCharExtra(-1) == '\\';
    }
}