using System.Text;
using System.Text.Json;
using Microsoft.CodeAnalysis;

namespace PoyoLang.Translator.SourceGenerator;

[Generator]
public class PoyoLangTranslatorGenerator : IIncrementalGenerator
{
    private const char IndentChar = '\t';

    public void Initialize(IncrementalGeneratorInitializationContext context)
    {
        var texts = context.AdditionalTextsProvider;

        // There will be only one of those but incremental generators work as pipelines
        var dictionaries = texts
            .Where(static text => text.Path.EndsWith("dictionary.json"))
            .Select(static (text, _) => text.GetText());

        var parsedDictionaries = dictionaries
            .Select(static (dictionary, _) =>
                JsonSerializer.Deserialize<Dictionary<string, string>>(dictionary!.ToString())
            );

        var formattedDictionaries = parsedDictionaries
            .Select(static (dictionary, _) =>
            {
                // Reverse dictionary order to have ngrams first
                return dictionary!.OrderBy(p => p.Value).ToDictionary(p => p.Value, p => p.Key);
            });

        var prefixTrees = formattedDictionaries
            .Select(static (formattedDictionary, _) => BuildPrefixTree(formattedDictionary));

        context.RegisterSourceOutput(prefixTrees, static (sourceProductionContext, prefixTree) =>
        {
            sourceProductionContext.AddSource("PoyoLangTranslator.g.cs", GenerateSource(prefixTree));
        });
    }

    private static List<Node> BuildPrefixTree(Dictionary<string, string> dictionary)
    {
        var rootNodes = new List<Node>();

        var firstNodes = dictionary.Where(p => p.Key.Length is 1);

        foreach (var firstNode in firstNodes)
        {
            var letter = firstNode.Key[0];
            var target = firstNode.Value;

            var node = new Node(letter, target);
            rootNodes.Add(node);

            // Add sub-nodes
            ParseNodes(node, letter.ToString());
        }

        return rootNodes;

        void ParseNodes(Node node, string prefix)
        {
            // Find nodes that have previous node as prefixed
            var subNodes = dictionary
                .Where(p => p.Key.StartsWith(prefix) && p.Key.Length == prefix.Length + 1);

            foreach (var subNode in subNodes)
            {
                var letter = subNode.Key[prefix.Length];
                var target = subNode.Value;

                var newPrefix = $"{prefix}{letter}";

                var newNode = new Node(letter, target);
                node.Nodes.Add(newNode);

                // Recursively add sub-nodes
                ParseNodes(newNode, newPrefix);
            }
        }
    }

    private static string GenerateSource(List<Node> rootNodes)
    {
        var source = new StringBuilder();

        // Usings and namespace
        source.Append(
            """
            using System;
            using System.Text;
            
            namespace PoyoLang.Translator;
            
            """
        );

        // Partial class definition
        source.Append(
            """
            public partial class PoyoLangTranslator
            {
            
            """
        );

        // Next letter method definition
        source.Append(
            """
                public void NextLetter(ref ReadOnlySpan<char> text, StringBuilder output)
                {
            """
        );

        // 0 length case and caps
        source.Append(
            """
                    if (text.Length < 1)
                    {
                        return;
                    }
                 
                    var isCaps = char.IsUpper(text[0]);
                    
            """
        );

        GenerateSwitchCases(rootNodes, depth: 0, source: source);

        // Next letter method end
        source.Append(
            """
                    // Punctuation/Unknown characters case
                    text = text[1..];
                    
                    output.Append(text[0]);
                }
            """
        );

        // Partial class end
        source.Append(
            """
            }
            """
        );

        return source.ToString();
    }

    private static void GenerateSwitchCases(List<Node> nodes, int depth, StringBuilder source)
    {
        var indent = Indent(depth * 3);

        // Switch-case start
        source.Append(
            $$"""
                    {{indent}}switch (text[{{depth}}])
                    {{indent}}{
            """
        );

        foreach (var node in nodes)
        {
            var targetLower = node.Target;
            var targetUpper = ToTitleCase(targetLower);

            // Case start
            source.Append(
                $$"""
                          {{indent}}    case '{{node.Letter}}' or '{{char.ToUpper(node.Letter)}}':
                          {{indent}}
                  """
            );

            // Sub nodes handling
            if (node.Nodes.Count > 0)
            {
                source.Append(
                    $$"""
                              {{indent}}        if (text.Length > {{depth + 1}})
                              {{indent}}        {
                      """
                );

                // Sub nodes
                GenerateSwitchCases(node.Nodes, depth + 1, source);

                source.Append(
                    $$"""
                              {{indent}}        }
                      """
                );
            }

            // Current node handling fallback
            source.Append(
                $$"""
                          {{indent}}
                          {{indent}}        text = text[{{depth + 1}}..];
                          {{indent}}
                          {{indent}}        output.Append(isCaps ?  "{{targetUpper}}" : "{{targetLower}}");
                          {{indent}}
                          {{indent}}        return;
                  """
            );
        }

        // Switch-case end
        source.Append(
            $$"""
              
                      {{indent}}}
              """
        );
    }

    private static string ToTitleCase(string text)
    {
        return $"{char.ToUpper(text[0])}{text[1..]}";
    }

    private static string Indent(int depth) => new(IndentChar, depth);
}