using Microsoft.Iris.Asm.Models;
using Sprache;
using System;
using System.Globalization;
using System.Linq;
using System.Text;

namespace Microsoft.Iris.Asm;

partial class Lexer
{
    private static IResult<IDirective> ParseDirective(IInput input)
    {
        input = ConsumeWhitespace(input);
        var line = input.Line;
        var column = input.Column;

        var directiveBeginResult = Parse.Char('.')(input);
        input = directiveBeginResult.Remainder;
        if (!directiveBeginResult.WasSuccessful)
            return Result.Failure<IDirective>(input, "Invalid directive", ["Expected '.', followed by an identifier"]);

        var directiveIdResult = WordText(input);
        input = directiveIdResult.Remainder;
        if (!directiveIdResult.WasSuccessful)
            return Result.Failure<IDirective>(input, "Invalid directive", ["Expected a valid directive name"]);

        IDirective directive;
        switch (directiveIdResult.Value.ToUpperInvariant())
        {
            case "DATATABLE":
                if (StatementEnd(input).WasSuccessful)
                    return Result.Failure<IDirective>(input, "Invalid data table import", ["Expected a URI"]);

                var dataTableUriResult = Uri.Token()(input);
                input = dataTableUriResult.Remainder;
                if (!dataTableUriResult.WasSuccessful)
                    return dataTableUriResult.ForType<IDirective>();

                directive = new SharedDataTableDirective(dataTableUriResult.Value)
                {
                    Line = line,
                    Column = column,
                };
                break;

            case "IMPORT":
                return ParseImportAsDirective(input);

            case "SECTION":
                if (StatementEnd(input).WasSuccessful)
                    return Result.Failure<IDirective>(input, "Invalid section directive", ["Expected a section name"]);

                var sectionNameResult = Parse.Letter.AtLeastOnce().Token().Text()(input);
                input = sectionNameResult.Remainder;
                if (!sectionNameResult.WasSuccessful)
                    return Result.Failure<IDirective>(input, "Invalid section name", ["Expected a section name containing only letters"]);

                directive = new SectionDirective(sectionNameResult.Value)
                {
                    Line = line,
                    Column = column,
                };
                break;

            case "CONSTANT":
                if (StatementEnd(input).WasSuccessful)
                    return Result.Failure<IDirective>(input, "Invalid constant directive", ["Expected a constant declaration"]);

                var constNameResult = Identifier.Token()(input);
                input = constNameResult.Remainder;
                if (!constNameResult.WasSuccessful)
                    return constNameResult.ForType<IDirective>();

                input = Parse.Char('=').Token()(input).Remainder;

                var typeNameResult = QualifiedTypeName.Token()(input);
                input = typeNameResult.Remainder;
                if (!typeNameResult.WasSuccessful)
                    return typeNameResult.ForType<IDirective>();

                Markup.MarkupConstantPersistMode? persistMode = null;
                string content = "";

                var encodingMarkerResult = Parse.Char('.')(input);
                input = encodingMarkerResult.Remainder;
                if (!encodingMarkerResult.WasSuccessful)
                {
                    // Support defining constants from string literals

                    // Skip the opening brace
                    input = input.Advance();
                    if (input.Current != '"')
                        return Result.Failure<IDirective>(input, "Invalid constant", ["Expected a string literal."]);

                    input = input.Advance();

                    StringBuilder literalBuilder = new();
                    char c;
                    while (true)
                    {
                        c = input.Current;
                        if (c == '\\')
                        {
                            // https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/lexical-structure#unicode-character-escape-sequences
                            input = input.Advance();
                            c = input.Current switch
                            {
                                '0' => '\0',
                                'b' => '\b',
                                'n' => '\n',
                                'r' => '\r',
                                't' => '\t',
                                _ => input.Current
                            };
                        }

                        input = input.Advance();

                        if (c == '"')
                            break;

                        literalBuilder.Append(c);
                    }

                    if (input.Current != ')')
                        return Result.Failure<IDirective>(input, "Invalid constant", ["Missing closed brace."]);

                    input = input.Advance();

                    persistMode = Markup.MarkupConstantPersistMode.FromString;
                    content = literalBuilder.ToString();
                }
                else
                {
                    var persistModeResult = Parse.CharExcept('(').AtLeastOnce().Text().Token()(input);
                    input = persistModeResult.Remainder;
                    if (!persistModeResult.WasSuccessful)
                        return persistModeResult.ForType<IDirective>("No constant persist mode was specified");

                    persistMode = persistModeResult.Value.ToLowerInvariant() switch
                    {
                        "bin" => Markup.MarkupConstantPersistMode.Binary,
                        "str" => Markup.MarkupConstantPersistMode.FromString,
                        "can" => Markup.MarkupConstantPersistMode.Canonical,
                        _ => null
                    };

                    var openBracketResult = Parse.Char('(').Token()(input);
                    input = openBracketResult.Remainder;
                    if (!openBracketResult.WasSuccessful)
                        return Result.Failure<IDirective>(input, "Invalid constant directive", ["Expected '('"]);

                    var contentResult = Parse.AnyChar.Until(StatementEnd).Text().Token()(input);
                    input = contentResult.Remainder;
                    if (!contentResult.WasSuccessful)
                        return contentResult.ForType<IDirective>();

                    content = contentResult.Value;
                    if (content.Length <= 1 || content[^1] != ')')
                        return Result.Failure<IDirective>(input, "Invalid constant directive", ["Expected ')'"]);
                    content = content[..^1];
                }

                var constantName = constNameResult.Value;
                var typeName = typeNameResult.Value;

                if (persistMode == Markup.MarkupConstantPersistMode.FromString)
                {
                    directive = new StringEncodedConstantDirective(constantName, typeName, content)
                    {
                        Line = line,
                        Column = column,
                    };
                }
                else if (persistMode == Markup.MarkupConstantPersistMode.Canonical)
                {
                    directive = new CanonicalInstanceConstantDirective(constantName, typeName, content)
                    {
                        Line = line,
                        Column = column,
                    };
                }
                else if (persistMode == Markup.MarkupConstantPersistMode.Binary)
                {
                    byte[] constantBytes;
                    var byteParts = content.Split(',');
                    if (byteParts.Length == 1)
                    {
                        var constantStr = byteParts[0].Trim();
                        if (constantStr.StartsWith("0x"))
                        {
                            constantStr = constantStr[2..];
                        }

                        if (constantStr.Length == 2)
                        {
                            constantBytes = [byte.Parse(constantStr, NumberStyles.HexNumber)];
                        }
                        else if (constantStr.Length == 4)
                        {
                            constantBytes = BitConverter.GetBytes(
                                ushort.Parse(constantStr, NumberStyles.HexNumber));
                        }
                        else if (constantStr.Length == 8)
                        {
                            constantBytes = BitConverter.GetBytes(
                                uint.Parse(constantStr, NumberStyles.HexNumber));
                        }
                        else
                        {
                            return Result.Failure<IDirective>(input, "Invalid constant directive", [$"Expected a 1-, 2-, or 4-digit hex number, or a list of bytes"]);
                        }
                    }
                    else
                    {
                        constantBytes = byteParts
                            .Select(s => byte.Parse(s.Trim().TrimStart('0', 'x'), NumberStyles.HexNumber))
                            .ToArray();
                    }

                    directive = new BinaryEncodedConstantDirective(constantName, typeName, constantBytes)
                    {
                        Line = line,
                        Column = column,
                    };
                }
                else
                {
                    return Result.Failure<IDirective>(input, "Invalid constant directive", [$"Invalid persist mode"]);
                }
                break;

            case "EXPORT":
                if (StatementEnd(input).WasSuccessful)
                    return Result.Failure<IDirective>(input, "Invalid export directive", ["Expected export information"]);

                var labelPrefixResult = Identifier.Token()(input);
                input = labelPrefixResult.Remainder;
                if (!labelPrefixResult.WasSuccessful)
                    return labelPrefixResult.ForType<IDirective>();

                var listenerCountResult = WholeNumber.Token()(input);
                input = listenerCountResult.Remainder;
                if (!listenerCountResult.WasSuccessful)
                    return Result.Failure<IDirective>(input, "Invalid export directive", ["Expected listener count"]);

                if (!uint.TryParse(listenerCountResult.Value, out var listenerCount))
                    return Result.Failure<IDirective>(input, "Invalid export directive", ["Expected export listener count to be an unsigned integer"]);

                var baseTypeNameResult = AlphanumericText.Token()(input);
                input = baseTypeNameResult.Remainder;
                if (!baseTypeNameResult.WasSuccessful)
                    return Result.Failure<IDirective>(input, "Invalid export directive", ["Expected base type name"]);

                var labelPrefix = labelPrefixResult.Value;
                var baseTypeName = baseTypeNameResult.Value;
                directive = new ExportDirective(labelPrefix, listenerCount, baseTypeName)
                {
                    Line = line,
                    Column = column,
                };
                break;

            default:
                return Result.Failure<IDirective>(input, $"Unknown import type '{directiveIdResult.Value}'", ["Expected 'export', 'import', or 'section'"]);
        }

        return Result.Success(directive, input);
    }
}