using System.Text;
using NubLang.Code;
using NubLang.Parsing.Syntax;
using NubLang.Tokenization;

namespace NubLang.Diagnostics;

public class Diagnostic
{
    public class DiagnosticBuilder
    {
        private readonly DiagnosticSeverity _severity;
        private readonly string _message;
        private SourceFileSpan? _fileSpan;
        private string? _help;

        public DiagnosticBuilder(DiagnosticSeverity severity, string message)
        {
            _severity = severity;
            _message = message;
        }

        public DiagnosticBuilder At(SyntaxNode? node)
        {
            if (node != null)
            {
                var first = node.Tokens.FirstOrDefault();
                if (first?.FileSpan != null)
                {
                    var span = SourceSpan.Merge(node.Tokens.Select(x => x.FileSpan?.Span ?? SourceSpan.Zero));
                    At(new SourceFileSpan(first.FileSpan.SourceFile, span));
                }
            }

            return this;
        }

        public DiagnosticBuilder At(Token? token)
        {
            if (token != null)
            {
                At(token.FileSpan);
            }

            return this;
        }

        public DiagnosticBuilder At(SourceFileSpan? fileSpan)
        {
            if (fileSpan != null)
            {
                _fileSpan = fileSpan;
            }

            return this;
        }

        public DiagnosticBuilder WithHelp(string help)
        {
            _help = help;
            return this;
        }

        public Diagnostic Build() => new(_severity, _message, _help, _fileSpan);
    }

    public static DiagnosticBuilder Error(string message) => new(DiagnosticSeverity.Error, message);
    public static DiagnosticBuilder Warning(string message) => new(DiagnosticSeverity.Warning, message);
    public static DiagnosticBuilder Info(string message) => new(DiagnosticSeverity.Info, message);

    public DiagnosticSeverity Severity { get; }
    public string Message { get; }
    public string? Help { get; }
    public SourceFileSpan? FileSpan { get; }

    private Diagnostic(DiagnosticSeverity severity, string message, string? help, SourceFileSpan? fileSpan)
    {
        Severity = severity;
        Message = message;
        Help = help;
        FileSpan = fileSpan;
    }

    public string FormatANSI()
    {
        var sb = new StringBuilder();

        sb.Append(Severity switch
        {
            DiagnosticSeverity.Error => ConsoleColors.Colorize("error", ConsoleColors.Bold + ConsoleColors.Red),
            DiagnosticSeverity.Warning => ConsoleColors.Colorize("warning", ConsoleColors.Bold + ConsoleColors.Yellow),
            DiagnosticSeverity.Info => ConsoleColors.Colorize("info", ConsoleColors.Bold + ConsoleColors.Blue),
            _ => ConsoleColors.Colorize("unknown", ConsoleColors.Bold + ConsoleColors.White)
        });

        if (FileSpan != null)
        {
            sb.Append(ConsoleColors.Colorize($" at {FileSpan.SourceFile.Path}:{FileSpan.Span}", ConsoleColors.Faint));
        }

        sb.Append(": ");
        sb.Append(ConsoleColors.Colorize(Message, ConsoleColors.BrightWhite));

        if (FileSpan != null)
        {
            sb.AppendLine();
            var text = FileSpan.SourceFile.GetText();

            var lines = text.Split('\n');

            var startLine = FileSpan.Span.Start.Line;
            var endLine = FileSpan.Span.End.Line;

            const int CONTEXT_LINES = 3;

            var contextStartLine = Math.Max(1, startLine - CONTEXT_LINES);
            var contextEndLine = Math.Min(lines.Length, endLine + CONTEXT_LINES);

            var numberPadding = contextEndLine.ToString().Length;
            var codePadding = lines.Skip(contextStartLine - 1).Take(contextEndLine - contextStartLine).Max(x => x.Length);

            sb.Append('╭');
            sb.Append(new string('─', numberPadding + 2));
            sb.Append('┬');
            sb.Append(new string('─', codePadding + 2));
            sb.Append('╮');
            sb.AppendLine();

            var tokenizer = new Tokenizer(FileSpan.SourceFile);
            var tokens = tokenizer.Tokenize().ToList();

            for (var i = contextStartLine; i <= contextEndLine; i++)
            {
                var line = lines[i - 1];

                sb.Append("│ ");
                sb.Append(i.ToString().PadRight(numberPadding));
                sb.Append(" │ ");
                sb.Append(ApplySyntaxHighlighting(line.PadRight(codePadding), i, tokens));
                sb.Append(" │");
                sb.AppendLine();

                if (i >= startLine && i <= endLine)
                {
                    var markerStartColumn = 1;
                    var markerEndColumn = line.Length + 1;

                    if (i == startLine)
                    {
                        markerStartColumn = FileSpan.Span.Start.Column;
                    }

                    if (i == endLine)
                    {
                        markerEndColumn = FileSpan.Span.End.Column;
                    }

                    var markerLength = markerEndColumn - markerStartColumn;
                    var marker = new string('^', markerLength);

                    var markerColor = Severity switch
                    {
                        DiagnosticSeverity.Info => ConsoleColors.Blue,
                        DiagnosticSeverity.Warning => ConsoleColors.Yellow,
                        DiagnosticSeverity.Error => ConsoleColors.Red,
                        _ => ConsoleColors.White
                    };

                    sb.Append("│ ");
                    sb.Append(new string(' ', numberPadding));
                    sb.Append(" │ ");
                    sb.Append(new string(' ', markerStartColumn - 1));
                    sb.Append(ConsoleColors.Colorize(marker, markerColor));
                    sb.Append(new string(' ', codePadding - markerEndColumn + 1));
                    sb.Append(" │");
                    sb.AppendLine();
                }
            }

            sb.Append('╰');
            sb.Append(new string('─', numberPadding + 2));
            sb.Append('┴');
            sb.Append(new string('─', codePadding + 2));
            sb.Append('╯');
        }

        if (Help != null)
        {
            sb.AppendLine();
            sb.Append(ConsoleColors.Colorize($"help: {Help}", ConsoleColors.Cyan));
        }

        return sb.ToString();
    }

    private static string ApplySyntaxHighlighting(string line, int lineNumber, List<Token> tokens)
    {
        var sb = new StringBuilder();
        var lineTokens = tokens
            .Where(t => t.FileSpan.Span.Start.Line == lineNumber)
            .OrderBy(t => t.FileSpan.Span.Start.Column)
            .ToList();

        if (lineTokens.Count == 0)
        {
            return line;
        }

        var currentColumn = 1;

        foreach (var token in lineTokens)
        {
            var tokenStart = token.FileSpan.Span.Start.Column;
            var tokenEnd = token.FileSpan.Span.End.Column;

            if (tokenStart > currentColumn)
            {
                var beforeToken = line.Substring(currentColumn - 1, tokenStart - currentColumn);
                sb.Append(beforeToken);
            }

            var tokenLength = tokenEnd - tokenStart;
            if (tokenStart - 1 + tokenLength <= line.Length)
            {
                var tokenText = line.Substring(tokenStart - 1, tokenLength);

                var coloredToken = ColorizeToken(token, tokenText);
                sb.Append(coloredToken);
            }

            currentColumn = tokenEnd;
        }

        if (currentColumn <= line.Length)
        {
            var remaining = line[(currentColumn - 1)..];
            sb.Append(remaining);
        }

        return sb.ToString();
    }

    private static string ColorizeToken(Token token, string tokenText)
    {
        switch (token)
        {
            case IdentifierToken:
            {
                return ConsoleColors.Colorize(tokenText, ConsoleColors.BrightWhite);
            }
            case LiteralToken literal:
            {
                if (literal.Kind == LiteralKind.String)
                {
                    return ConsoleColors.Colorize(tokenText, ConsoleColors.Green);
                }

                return ConsoleColors.Colorize(tokenText, ConsoleColors.Magenta);
            }
            case SymbolToken symbolToken:
            {
                switch (symbolToken.Symbol)
                {
                    case Symbol.Func:
                    case Symbol.Return:
                    case Symbol.If:
                    case Symbol.Else:
                    case Symbol.While:
                    case Symbol.Break:
                    case Symbol.Continue:
                    case Symbol.Struct:
                    case Symbol.Let:
                    case Symbol.Calls:
                    case Symbol.Interface:
                    case Symbol.For:
                    case Symbol.Extern:
                    {
                        return ConsoleColors.Colorize(tokenText, ConsoleColors.Bold + ConsoleColors.Blue);
                    }
                    case Symbol.Assign:
                    case Symbol.Bang:
                    case Symbol.Equal:
                    case Symbol.NotEqual:
                    case Symbol.LessThan:
                    case Symbol.LessThanOrEqual:
                    case Symbol.GreaterThan:
                    case Symbol.GreaterThanOrEqual:
                    case Symbol.Plus:
                    case Symbol.Minus:
                    case Symbol.Star:
                    case Symbol.ForwardSlash:
                    case Symbol.Caret:
                    case Symbol.Ampersand:
                    {
                        return ConsoleColors.Colorize(tokenText, ConsoleColors.Yellow);
                    }
                    case Symbol.Colon:
                    case Symbol.OpenParen:
                    case Symbol.CloseParen:
                    case Symbol.OpenBrace:
                    case Symbol.CloseBrace:
                    case Symbol.OpenBracket:
                    case Symbol.CloseBracket:
                    case Symbol.Comma:
                    case Symbol.Period:
                    case Symbol.Semi:
                    {
                        return ConsoleColors.Colorize(tokenText, ConsoleColors.BrightBlack);
                    }
                }

                break;
            }
        }

        return tokenText;
    }
}

public enum DiagnosticSeverity
{
    Info,
    Warning,
    Error
}