using Sprache;
using System.Collections.Generic;
using System.Linq;

namespace Microsoft.Iris.Asm;

public static class Lexer
{
    public static readonly Parser<string> AlphanumericText = Parse.LetterOrDigit.AtLeastOnce().Text();

    public static readonly Parser<string> Uri = Parse.LetterOrDigit.Or(Parse.Chars(":/!._-")).AtLeastOnce().Text();

    public static readonly Parser<string> StatementEnd = Parse.Char(';').Return(";").Or(Parse.LineTerminator);

    public static readonly Parser<IImport> Import = ParseImport;

    public static readonly Parser<IBodyItem> BodyItem = ParseBodyItem;

    public static readonly Parser<Program> Program =
        from imports in Import.Token().Many()
        from body in BodyItem.Many()
        select new Program(imports, body);

    private static IResult<IBodyItem> ParseBodyItem(IInput input)
    {
        input = ConsumeWhitespace(input);

        var identifierResult = Parse.Letter.AtLeastOnce().Text().Invoke(input);
        if (!identifierResult.WasSuccessful)
            return Result.Failure<Instruction>(input, "Invalid code", System.Array.Empty<string>());

        input = identifierResult.Remainder;
        var identifier = identifierResult.Value;
        IBodyItem bodyItem;

        if (!input.AtEnd && input.Current == ':')
        {
            input = input.Advance();
            bodyItem = new Label(identifier);
            input = StatementEnd(input).Remainder;
        }
        else
        {
            List<Operand> operands = new();
            var endOfInstructionResult = StatementEnd(input);
            input = endOfInstructionResult.Remainder;

            if (!endOfInstructionResult.WasSuccessful)
            {
                input = ConsumeWhitespace(input);

                var operandsResult = Parse.Ref(() => AlphanumericText).DelimitedBy(Parse.Char(',').Token())(input);
                operands.AddRange(operandsResult.Value.Select(s => new Operand(s)));
                input = operandsResult.Remainder;
            }

            bodyItem = new Instruction(identifier, operands);
        }

        return Result.Success(bodyItem, input);
    }

    private static IResult<IImport> ParseImport(IInput input)
    {
        input = ConsumeWhitespace(input);

        var importDirectiveResult = Parse.String(".import-")(input);
        input = importDirectiveResult.Remainder;
        if (!importDirectiveResult.WasSuccessful)
            return Result.Failure<IImport>(input, "Invalid import directive", null);

        var importTypeResult = Parse.Letter.AtLeastOnce().Text()(input);
        input = importTypeResult.Remainder;
        if (!importTypeResult.WasSuccessful)
            return Result.Failure<IImport>(input, "Invalid import type", null);

        IImport import;
        switch (importTypeResult.Value.ToUpperInvariant())
        {
            case "NS":
                var uriResult = Uri.Token()(input);
                input = uriResult.Remainder;
                if (!uriResult.WasSuccessful)
                    return Result.Failure<IImport>(input, "Invalid URI", null);

                input = Parse.String("as").Token()(input).Remainder;

                var nameResult = AlphanumericText(input);
                input = nameResult.Remainder;
                if (!nameResult.WasSuccessful)
                    return Result.Failure<IImport>(input, "Invalid namespace alias", null);

                import = new NamespaceImport(uriResult.Value, nameResult.Value);
                break;

            default:
                return Result.Failure<IImport>(input, $"Unknown import type '{importTypeResult.Value}'", null);
        }

        return Result.Success(import, input);
    }

    private static IInput ConsumeWhitespace(IInput input) => Parse.WhiteSpace.Many()(input).Remainder;
}