using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;

namespace F1KeywordsTool
{
    public static class Program
    {
        private async static Task<string> GetUrlContentAsync(string url)
        {
            using var client = new HttpClient();
            using HttpResponseMessage response = await client.GetAsync(url);
            using HttpContent content = response.Content;
            return await content.ReadAsStringAsync();
        }

        private async static Task<string> GetEnumSourceCodeAsync()
        {
            return await GetUrlContentAsync("https://raw.githubusercontent.com/dotnet/roslyn/master/src/Compilers/CSharp/Portable/Errors/ErrorCode.cs");
        }

        private async static Task<IEnumerable<string>> GetAlreadyDocumentedErrorNumbersAsync()
        {
            string content1 = await GetUrlContentAsync("https://github.com/dotnet/docs/tree/master/docs/csharp/misc");
            string content2 = await GetUrlContentAsync("https://github.com/dotnet/docs/tree/master/docs/csharp/language-reference/compiler-messages");
            return Regex.Matches(content1, @"title=""(cs\d{4})\.md""", RegexOptions.IgnoreCase).Select(m => m.Groups[1].Value).Concat(
                Regex.Matches(content2, @"title=""(cs\d{4})\.md""", RegexOptions.IgnoreCase).Select(m => m.Groups[1].Value)
                );
        }

        private async static Task<IEnumerable<string>> GetUndocumentedErrorNumbersAsync()
        {
            IEnumerable<string> all = await GetAllRoslynErrorNumbersAsync();
            IEnumerable<string> documented = await GetAlreadyDocumentedErrorNumbersAsync();
            return all.Except(documented, StringComparer.OrdinalIgnoreCase);
        }

        private async static Task<IEnumerable<string>> GetAllRoslynErrorNumbersAsync()
        {
            string sourceCode = await GetEnumSourceCodeAsync();
            SyntaxNode root = await CSharpSyntaxTree.ParseText(sourceCode).GetRootAsync();

            // This line didn't work for some reason.
            //return root.DescendantTokens(token => token.IsKind(SyntaxKind.NumericLiteralToken)).Select(t => $"CS{t.ValueText.PadLeft(4, '0')}");

            return root.DescendantTokens().Where(t => t.IsKind(SyntaxKind.NumericLiteralToken)).Select(t => $"CS{t.ValueText.PadLeft(4, '0')}");
        }

        public static async Task Main()
        {
            IEnumerable<string> undocumented = await GetUndocumentedErrorNumbersAsync();
            await File.WriteAllLinesAsync("Undocumented.txt", undocumented.Select(s => $@"  - ""{s}"""));
        }
    }
}