// Copyright (c) StellaOps. All rights reserved.
// Licensed under BUSL-1.1. See LICENSE in the project root.

using System.Collections.Immutable;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Microsoft.ML.OnnxRuntime;
using Microsoft.ML.OnnxRuntime.Tensors;

namespace StellaOps.BinaryIndex.ML;

/// <summary>
/// ONNX Runtime-based embedding inference engine.
/// </summary>
public sealed class OnnxInferenceEngine : IEmbeddingService, IAsyncDisposable
{
    private readonly InferenceSession? _session;
    private readonly ITokenizer _tokenizer;
    private readonly IEmbeddingIndex? _index;
    private readonly MlOptions _options;
    private readonly ILogger<OnnxInferenceEngine> _logger;
    private readonly TimeProvider _timeProvider;
    private bool _disposed;

    public OnnxInferenceEngine(
        ITokenizer tokenizer,
        IOptions<MlOptions> options,
        ILogger<OnnxInferenceEngine> logger,
        TimeProvider timeProvider,
        IEmbeddingIndex? index = null)
    {
        _tokenizer = tokenizer;
        _options = options.Value;
        _logger = logger;
        _timeProvider = timeProvider;
        _index = index;

        if (!string.IsNullOrEmpty(_options.ModelPath) && File.Exists(_options.ModelPath))
        {
            var sessionOptions = new SessionOptions
            {
                GraphOptimizationLevel = GraphOptimizationLevel.ORT_ENABLE_ALL,
                ExecutionMode = ExecutionMode.ORT_PARALLEL,
                InterOpNumThreads = _options.NumThreads,
                IntraOpNumThreads = _options.NumThreads
            };

            _session = new InferenceSession(_options.ModelPath, sessionOptions);
            _logger.LogInformation(
                "Loaded ONNX model from {Path}",
                _options.ModelPath);
        }
        else
        {
            _logger.LogWarning(
                "No ONNX model found at {Path}, using fallback embedding",
                _options.ModelPath);
        }
    }

    /// <inheritdoc />
    public async Task<FunctionEmbedding> GenerateEmbeddingAsync(
        EmbeddingInput input,
        EmbeddingOptions? options = null,
        CancellationToken ct = default)
    {
        ArgumentNullException.ThrowIfNull(input);
        ct.ThrowIfCancellationRequested();

        options ??= new EmbeddingOptions();

        var text = GetInputText(input);
        var functionId = ComputeFunctionId(text);

        float[] vector;

        if (_session is not null)
        {
            vector = await RunInferenceAsync(text, options, ct);
        }
        else
        {
            // Fallback: generate hash-based pseudo-embedding for testing
            vector = GenerateFallbackEmbedding(text, 768);
        }

        if (options.NormalizeVector)
        {
            NormalizeVector(vector);
        }

        return new FunctionEmbedding(
            functionId,
            ExtractFunctionName(text),
            vector,
            EmbeddingModel.CodeBertBinary,
            input.PreferredInput,
            _timeProvider.GetUtcNow());
    }

    /// <inheritdoc />
    public async Task<ImmutableArray<FunctionEmbedding>> GenerateBatchAsync(
        IEnumerable<EmbeddingInput> inputs,
        EmbeddingOptions? options = null,
        CancellationToken ct = default)
    {
        ArgumentNullException.ThrowIfNull(inputs);

        options ??= new EmbeddingOptions();
        var results = new List<FunctionEmbedding>();

        // Process in batches
        var batch = new List<EmbeddingInput>();
        foreach (var input in inputs)
        {
            ct.ThrowIfCancellationRequested();
            batch.Add(input);

            if (batch.Count >= options.BatchSize)
            {
                var batchResults = await ProcessBatchAsync(batch, options, ct);
                results.AddRange(batchResults);
                batch.Clear();
            }
        }

        // Process remaining
        if (batch.Count > 0)
        {
            var batchResults = await ProcessBatchAsync(batch, options, ct);
            results.AddRange(batchResults);
        }

        return [.. results];
    }

    /// <inheritdoc />
    public decimal ComputeSimilarity(
        FunctionEmbedding a,
        FunctionEmbedding b,
        SimilarityMetric metric = SimilarityMetric.Cosine)
    {
        ArgumentNullException.ThrowIfNull(a);
        ArgumentNullException.ThrowIfNull(b);

        if (a.Vector.Length != b.Vector.Length)
        {
            throw new ArgumentException("Embedding vectors must have same dimension");
        }

        return metric switch
        {
            SimilarityMetric.Cosine => CosineSimilarity(a.Vector, b.Vector),
            SimilarityMetric.Euclidean => EuclideanSimilarity(a.Vector, b.Vector),
            SimilarityMetric.Manhattan => ManhattanSimilarity(a.Vector, b.Vector),
            SimilarityMetric.LearnedMetric => CosineSimilarity(a.Vector, b.Vector), // Fallback
            _ => throw new ArgumentOutOfRangeException(nameof(metric))
        };
    }

    /// <inheritdoc />
    public async Task<ImmutableArray<EmbeddingMatch>> FindSimilarAsync(
        FunctionEmbedding query,
        int topK = 10,
        decimal minSimilarity = 0.7m,
        CancellationToken ct = default)
    {
        ArgumentNullException.ThrowIfNull(query);

        if (_index is null)
        {
            _logger.LogWarning("No embedding index configured, cannot search");
            return [];
        }

        var results = await _index.SearchAsync(query.Vector, topK, ct);

        return results
            .Where(r => r.Similarity >= minSimilarity)
            .Select(r => new EmbeddingMatch(
                r.Embedding.FunctionId,
                r.Embedding.FunctionName,
                r.Similarity,
                null, // Library info would come from metadata
                null))
            .ToImmutableArray();
    }

    private async Task<float[]> RunInferenceAsync(
        string text,
        EmbeddingOptions options,
        CancellationToken ct)
    {
        if (_session is null)
        {
            throw new InvalidOperationException("ONNX session not initialized");
        }

        var (inputIds, attentionMask) = _tokenizer.TokenizeWithMask(text, options.MaxSequenceLength);

        var inputIdsTensor = new DenseTensor<long>(inputIds, [1, inputIds.Length]);
        var attentionMaskTensor = new DenseTensor<long>(attentionMask, [1, attentionMask.Length]);

        var inputs = new List<NamedOnnxValue>
        {
            NamedOnnxValue.CreateFromTensor("input_ids", inputIdsTensor),
            NamedOnnxValue.CreateFromTensor("attention_mask", attentionMaskTensor)
        };

        using var results = await Task.Run(() => _session.Run(inputs), ct);

        var outputTensor = results.First().AsTensor<float>();
        return outputTensor.ToArray();
    }

    private async Task<IEnumerable<FunctionEmbedding>> ProcessBatchAsync(
        List<EmbeddingInput> batch,
        EmbeddingOptions options,
        CancellationToken ct)
    {
        // For now, process sequentially
        // TODO: Implement true batch inference with batched tensors
        var results = new List<FunctionEmbedding>();
        foreach (var input in batch)
        {
            var embedding = await GenerateEmbeddingAsync(input, options, ct);
            results.Add(embedding);
        }
        return results;
    }

    private static string GetInputText(EmbeddingInput input)
    {
        return input.PreferredInput switch
        {
            EmbeddingInputType.DecompiledCode => input.DecompiledCode
                ?? throw new ArgumentException("DecompiledCode required"),
            EmbeddingInputType.SemanticGraph => SerializeGraph(input.SemanticGraph
                ?? throw new ArgumentException("SemanticGraph required")),
            EmbeddingInputType.Instructions => SerializeInstructions(input.InstructionBytes
                ?? throw new ArgumentException("InstructionBytes required")),
            _ => throw new ArgumentOutOfRangeException()
        };
    }

    private static string SerializeGraph(Semantic.KeySemanticsGraph graph)
    {
        // Convert graph to textual representation for tokenization
        var sb = new System.Text.StringBuilder();
        sb.AppendLine($"// Graph: {graph.Nodes.Length} nodes");

        foreach (var node in graph.Nodes)
        {
            sb.AppendLine($"node {node.Id}: {node.Operation}");
        }

        foreach (var edge in graph.Edges)
        {
            sb.AppendLine($"edge {edge.SourceId} -> {edge.TargetId}");
        }

        return sb.ToString();
    }

    private static string SerializeInstructions(byte[] bytes)
    {
        // Convert instruction bytes to hex representation
        return Convert.ToHexString(bytes);
    }

    private static string ComputeFunctionId(string text)
    {
        var hash = System.Security.Cryptography.SHA256.HashData(
            System.Text.Encoding.UTF8.GetBytes(text));
        return Convert.ToHexString(hash)[..16];
    }

    private static string ExtractFunctionName(string text)
    {
        // Try to extract function name from code
        var match = System.Text.RegularExpressions.Regex.Match(
            text,
            @"\b(\w+)\s*\(");
        return match.Success ? match.Groups[1].Value : "unknown";
    }

    private static float[] GenerateFallbackEmbedding(string text, int dimension)
    {
        // Generate a deterministic pseudo-embedding based on text hash
        // This is only for testing when no model is available
        var hash = System.Security.Cryptography.SHA256.HashData(
            System.Text.Encoding.UTF8.GetBytes(text));

        var random = new Random(BitConverter.ToInt32(hash, 0));
        var vector = new float[dimension];

        for (var i = 0; i < dimension; i++)
        {
            vector[i] = (float)(random.NextDouble() * 2 - 1);
        }

        return vector;
    }

    private static void NormalizeVector(float[] vector)
    {
        var norm = 0.0;
        for (var i = 0; i < vector.Length; i++)
        {
            norm += vector[i] * vector[i];
        }

        norm = Math.Sqrt(norm);
        if (norm > 0)
        {
            for (var i = 0; i < vector.Length; i++)
            {
                vector[i] /= (float)norm;
            }
        }
    }

    private static decimal CosineSimilarity(float[] a, float[] b)
    {
        var dotProduct = 0.0;
        var normA = 0.0;
        var normB = 0.0;

        for (var i = 0; i < a.Length; i++)
        {
            dotProduct += a[i] * b[i];
            normA += a[i] * a[i];
            normB += b[i] * b[i];
        }

        if (normA == 0 || normB == 0)
        {
            return 0;
        }

        var similarity = dotProduct / (Math.Sqrt(normA) * Math.Sqrt(normB));
        return (decimal)Math.Clamp(similarity, -1.0, 1.0);
    }

    private static decimal EuclideanSimilarity(float[] a, float[] b)
    {
        var sumSquares = 0.0;
        for (var i = 0; i < a.Length; i++)
        {
            var diff = a[i] - b[i];
            sumSquares += diff * diff;
        }

        var distance = Math.Sqrt(sumSquares);
        // Convert distance to similarity (0 = identical, larger = more different)
        return (decimal)(1.0 / (1.0 + distance));
    }

    private static decimal ManhattanSimilarity(float[] a, float[] b)
    {
        var sum = 0.0;
        for (var i = 0; i < a.Length; i++)
        {
            sum += Math.Abs(a[i] - b[i]);
        }

        // Convert distance to similarity
        return (decimal)(1.0 / (1.0 + sum));
    }

    public async ValueTask DisposeAsync()
    {
        if (!_disposed)
        {
            _session?.Dispose();
            _disposed = true;
        }

        await Task.CompletedTask;
    }
}