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

using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using System.Text.RegularExpressions;
using StellaOps.Symbols.Core.Models;

namespace StellaOps.BinaryIndex.DeltaSig;

/// <summary>
/// Builder for deterministic hybrid diff artifacts.
/// </summary>
public interface IHybridDiffComposer
{
    /// <summary>
    /// Generates semantic edits from source file pairs.
    /// </summary>
    SemanticEditScript GenerateSemanticEditScript(IReadOnlyList<SourceFileDiff>? sourceDiffs);

    /// <summary>
    /// Builds a canonical symbol map from a symbol manifest.
    /// </summary>
    SymbolMap BuildSymbolMap(SymbolManifest manifest, string? binaryDigest = null);

    /// <summary>
    /// Builds a deterministic fallback map from signature symbols when debug data is unavailable.
    /// </summary>
    SymbolMap BuildFallbackSymbolMap(DeltaSignature signature, BinaryReference binary, string role);

    /// <summary>
    /// Builds symbol patch plan by linking edits and symbol-level deltas.
    /// </summary>
    SymbolPatchPlan BuildSymbolPatchPlan(
        SemanticEditScript editScript,
        SymbolMap oldSymbolMap,
        SymbolMap newSymbolMap,
        IReadOnlyList<Attestation.FunctionDelta> deltas);

    /// <summary>
    /// Builds normalized patch manifest from function deltas.
    /// </summary>
    PatchManifest BuildPatchManifest(
        string buildId,
        string normalizationRecipeId,
        IReadOnlyList<Attestation.FunctionDelta> deltas);

    /// <summary>
    /// Composes all hybrid diff artifacts into one evidence object.
    /// </summary>
    HybridDiffEvidence Compose(
        IReadOnlyList<SourceFileDiff>? sourceDiffs,
        SymbolMap oldSymbolMap,
        SymbolMap newSymbolMap,
        IReadOnlyList<Attestation.FunctionDelta> deltas,
        string normalizationRecipeId);

    /// <summary>
    /// Computes deterministic digest of a serializable value.
    /// </summary>
    string ComputeDigest<T>(T value);
}

/// <summary>
/// Deterministic implementation of hybrid diff composition.
/// </summary>
public sealed class HybridDiffComposer : IHybridDiffComposer
{
    private static readonly JsonSerializerOptions DigestJsonOptions = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        WriteIndented = false
    };

    private static readonly HashSet<string> ControlKeywords =
    [
        "if",
        "for",
        "while",
        "switch",
        "catch",
        "return",
        "sizeof"
    ];

    private static readonly Regex FunctionAnchorRegex = new(
        @"(?<name>[A-Za-z_][A-Za-z0-9_:\.]*)\s*\(",
        RegexOptions.Compiled | RegexOptions.CultureInvariant);

    /// <inheritdoc />
    public SemanticEditScript GenerateSemanticEditScript(IReadOnlyList<SourceFileDiff>? sourceDiffs)
    {
        var diffs = (sourceDiffs ?? Array.Empty<SourceFileDiff>())
            .OrderBy(d => NormalizePath(d.Path), StringComparer.Ordinal)
            .ToList();

        var edits = new List<SemanticEdit>();
        var treeMaterial = new StringBuilder();

        foreach (var diff in diffs)
        {
            var normalizedPath = NormalizePath(diff.Path);
            var before = diff.BeforeContent ?? string.Empty;
            var after = diff.AfterContent ?? string.Empty;
            var beforeDigest = ComputeDigest(before);
            var afterDigest = ComputeDigest(after);

            treeMaterial
                .Append(normalizedPath)
                .Append('|')
                .Append(beforeDigest)
                .Append('|')
                .Append(afterDigest)
                .Append('\n');

            if (string.Equals(beforeDigest, afterDigest, StringComparison.Ordinal))
            {
                continue;
            }

            var beforeSymbols = ExtractSymbolBlocks(before);
            var afterSymbols = ExtractSymbolBlocks(after);

            if (beforeSymbols.Count == 0 && afterSymbols.Count == 0)
            {
                edits.Add(CreateFileEdit(normalizedPath, beforeDigest, afterDigest));
                continue;
            }

            foreach (var symbol in beforeSymbols.Keys.Except(afterSymbols.Keys, StringComparer.Ordinal).OrderBy(v => v, StringComparer.Ordinal))
            {
                var pre = beforeSymbols[symbol];
                edits.Add(CreateSymbolEdit(
                    normalizedPath,
                    symbol,
                    "remove",
                    pre.Hash,
                    null,
                    new SourceSpan { StartLine = pre.StartLine, EndLine = pre.EndLine },
                    null));
            }

            foreach (var symbol in afterSymbols.Keys.Except(beforeSymbols.Keys, StringComparer.Ordinal).OrderBy(v => v, StringComparer.Ordinal))
            {
                var post = afterSymbols[symbol];
                edits.Add(CreateSymbolEdit(
                    normalizedPath,
                    symbol,
                    "add",
                    null,
                    post.Hash,
                    null,
                    new SourceSpan { StartLine = post.StartLine, EndLine = post.EndLine }));
            }

            foreach (var symbol in beforeSymbols.Keys.Intersect(afterSymbols.Keys, StringComparer.Ordinal).OrderBy(v => v, StringComparer.Ordinal))
            {
                var pre = beforeSymbols[symbol];
                var post = afterSymbols[symbol];
                if (!string.Equals(pre.Hash, post.Hash, StringComparison.Ordinal))
                {
                    edits.Add(CreateSymbolEdit(
                        normalizedPath,
                        symbol,
                        "update",
                        pre.Hash,
                        post.Hash,
                        new SourceSpan { StartLine = pre.StartLine, EndLine = pre.EndLine },
                        new SourceSpan { StartLine = post.StartLine, EndLine = post.EndLine }));
                }
            }
        }

        var orderedEdits = edits
            .OrderBy(e => e.NodePath, StringComparer.Ordinal)
            .ThenBy(e => e.EditType, StringComparer.Ordinal)
            .ToList();

        return new SemanticEditScript
        {
            SourceTreeDigest = ComputeDigest(treeMaterial.ToString()),
            Edits = orderedEdits
        };
    }

    /// <inheritdoc />
    public SymbolMap BuildSymbolMap(SymbolManifest manifest, string? binaryDigest = null)
    {
        ArgumentNullException.ThrowIfNull(manifest);

        var sourcePathByCompiled = (manifest.SourceMappings ?? Array.Empty<SourceMapping>())
            .GroupBy(m => m.CompiledPath, StringComparer.Ordinal)
            .ToDictionary(g => g.Key, g => g.First().SourcePath, StringComparer.Ordinal);

        var symbols = manifest.Symbols
            .OrderBy(s => s.Address)
            .ThenBy(s => s.MangledName, StringComparer.Ordinal)
            .Select(s =>
            {
                var size = s.Size == 0 ? 1UL : s.Size;
                var mappedPath = ResolveSourcePath(s.SourceFile, sourcePathByCompiled);
                var ranges = mappedPath is null || s.SourceLine is null
                    ? null
                    : new[]
                    {
                        new SourceRange
                        {
                            File = NormalizePath(mappedPath),
                            LineStart = s.SourceLine.Value,
                            LineEnd = s.SourceLine.Value
                        }
                    };

                return new SymbolMapEntry
                {
                    Name = string.IsNullOrWhiteSpace(s.DemangledName) ? s.MangledName : s.DemangledName,
                    Kind = MapSymbolKind(s.Type),
                    AddressStart = s.Address,
                    AddressEnd = s.Address + size - 1UL,
                    Section = ".text",
                    SourceRanges = ranges
                };
            })
            .ToList();

        return new SymbolMap
        {
            BuildId = manifest.DebugId,
            BinaryDigest = binaryDigest,
            AddressSource = "manifest",
            Symbols = symbols
        };
    }

    /// <inheritdoc />
    public SymbolMap BuildFallbackSymbolMap(DeltaSignature signature, BinaryReference binary, string role)
    {
        ArgumentNullException.ThrowIfNull(signature);
        ArgumentNullException.ThrowIfNull(binary);

        var sha = GetDigestString(binary.Digest);
        var buildId = string.IsNullOrWhiteSpace(sha)
            ? $"{role}-fallback"
            : $"{role}:{sha[..Math.Min(16, sha.Length)]}";

        ulong nextAddress = string.Equals(role, "old", StringComparison.OrdinalIgnoreCase)
            ? 0x100000UL
            : 0x200000UL;

        var symbols = new List<SymbolMapEntry>();
        foreach (var symbol in signature.Symbols.OrderBy(s => s.Name, StringComparer.Ordinal))
        {
            var size = symbol.SizeBytes <= 0 ? 1UL : (ulong)symbol.SizeBytes;
            var start = nextAddress;
            var end = start + size - 1UL;

            symbols.Add(new SymbolMapEntry
            {
                Name = symbol.Name,
                Kind = "function",
                AddressStart = start,
                AddressEnd = end,
                Section = symbol.Scope,
                SourceRanges = null
            });

            var aligned = ((size + 15UL) / 16UL) * 16UL;
            nextAddress += aligned;
        }

        return new SymbolMap
        {
            BuildId = buildId,
            BinaryDigest = string.IsNullOrWhiteSpace(sha) ? null : $"sha256:{sha}",
            AddressSource = "synthetic-signature",
            Symbols = symbols
        };
    }

    /// <inheritdoc />
    public SymbolPatchPlan BuildSymbolPatchPlan(
        SemanticEditScript editScript,
        SymbolMap oldSymbolMap,
        SymbolMap newSymbolMap,
        IReadOnlyList<Attestation.FunctionDelta> deltas)
    {
        ArgumentNullException.ThrowIfNull(editScript);
        ArgumentNullException.ThrowIfNull(oldSymbolMap);
        ArgumentNullException.ThrowIfNull(newSymbolMap);
        ArgumentNullException.ThrowIfNull(deltas);

        var editsDigest = ComputeDigest(editScript);
        var oldMapDigest = ComputeDigest(oldSymbolMap);
        var newMapDigest = ComputeDigest(newSymbolMap);

        var changes = deltas
            .OrderBy(d => d.FunctionId, StringComparer.Ordinal)
            .Select(delta =>
            {
                var anchors = editScript.Edits
                    .Where(e => IsAnchorMatch(e.Anchor, delta.FunctionId))
                    .Select(e => e.Anchor)
                    .Distinct(StringComparer.Ordinal)
                    .OrderBy(v => v, StringComparer.Ordinal)
                    .ToList();

                if (anchors.Count == 0)
                {
                    anchors.Add(delta.FunctionId);
                }

                return new SymbolPatchChange
                {
                    Symbol = delta.FunctionId,
                    ChangeType = delta.ChangeType,
                    AstAnchors = anchors,
                    PreHash = delta.OldHash,
                    PostHash = delta.NewHash,
                    DeltaRef = "sha256:" + ComputeDigest($"{delta.FunctionId}|{delta.OldHash}|{delta.NewHash}|{delta.OldSize}|{delta.NewSize}")
                };
            })
            .ToList();

        return new SymbolPatchPlan
        {
            BuildIdBefore = oldSymbolMap.BuildId,
            BuildIdAfter = newSymbolMap.BuildId,
            EditsDigest = editsDigest,
            SymbolMapDigestBefore = oldMapDigest,
            SymbolMapDigestAfter = newMapDigest,
            Changes = changes
        };
    }

    /// <inheritdoc />
    public PatchManifest BuildPatchManifest(
        string buildId,
        string normalizationRecipeId,
        IReadOnlyList<Attestation.FunctionDelta> deltas)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(buildId);
        ArgumentException.ThrowIfNullOrWhiteSpace(normalizationRecipeId);
        ArgumentNullException.ThrowIfNull(deltas);

        var patches = deltas
            .OrderBy(d => d.FunctionId, StringComparer.Ordinal)
            .Select(delta =>
            {
                var start = delta.Address < 0 ? 0UL : (ulong)delta.Address;
                var rangeSize = delta.NewSize > 0 ? delta.NewSize : delta.OldSize;
                var end = rangeSize > 0
                    ? start + (ulong)rangeSize - 1UL
                    : start;

                return new SymbolPatchArtifact
                {
                    Symbol = delta.FunctionId,
                    AddressRange = $"0x{start:x}-0x{end:x}",
                    DeltaDigest = "sha256:" + ComputeDigest($"{delta.FunctionId}|{delta.OldHash}|{delta.NewHash}|{delta.OldSize}|{delta.NewSize}|{delta.DiffLen}"),
                    Pre = new PatchSizeHash
                    {
                        Size = delta.OldSize,
                        Hash = string.IsNullOrWhiteSpace(delta.OldHash) ? "sha256:0" : delta.OldHash!
                    },
                    Post = new PatchSizeHash
                    {
                        Size = delta.NewSize,
                        Hash = string.IsNullOrWhiteSpace(delta.NewHash) ? "sha256:0" : delta.NewHash!
                    }
                };
            })
            .ToList();

        return new PatchManifest
        {
            BuildId = buildId,
            NormalizationRecipeId = normalizationRecipeId,
            Patches = patches
        };
    }

    /// <inheritdoc />
    public HybridDiffEvidence Compose(
        IReadOnlyList<SourceFileDiff>? sourceDiffs,
        SymbolMap oldSymbolMap,
        SymbolMap newSymbolMap,
        IReadOnlyList<Attestation.FunctionDelta> deltas,
        string normalizationRecipeId)
    {
        var script = GenerateSemanticEditScript(sourceDiffs);
        var patchPlan = BuildSymbolPatchPlan(script, oldSymbolMap, newSymbolMap, deltas);
        var patchManifest = BuildPatchManifest(newSymbolMap.BuildId, normalizationRecipeId, deltas);

        var scriptDigest = ComputeDigest(script);
        var oldMapDigest = ComputeDigest(oldSymbolMap);
        var newMapDigest = ComputeDigest(newSymbolMap);
        var patchPlanDigest = ComputeDigest(patchPlan);
        var patchManifestDigest = ComputeDigest(patchManifest);

        return new HybridDiffEvidence
        {
            SemanticEditScript = script,
            OldSymbolMap = oldSymbolMap,
            NewSymbolMap = newSymbolMap,
            SymbolPatchPlan = patchPlan,
            PatchManifest = patchManifest,
            SemanticEditScriptDigest = scriptDigest,
            OldSymbolMapDigest = oldMapDigest,
            NewSymbolMapDigest = newMapDigest,
            SymbolPatchPlanDigest = patchPlanDigest,
            PatchManifestDigest = patchManifestDigest
        };
    }

    /// <inheritdoc />
    public string ComputeDigest<T>(T value)
    {
        var json = value is string s
            ? s
            : JsonSerializer.Serialize(value, DigestJsonOptions);

        var bytes = Encoding.UTF8.GetBytes(json);
        Span<byte> hash = stackalloc byte[SHA256.HashSizeInBytes];
        SHA256.HashData(bytes, hash);
        return Convert.ToHexString(hash).ToLowerInvariant();
    }

    private static string? ResolveSourcePath(string? sourceFile, IReadOnlyDictionary<string, string> sourcePathByCompiled)
    {
        if (string.IsNullOrWhiteSpace(sourceFile))
        {
            return null;
        }

        return sourcePathByCompiled.TryGetValue(sourceFile, out var mapped)
            ? mapped
            : sourceFile;
    }

    private static string MapSymbolKind(SymbolType type)
    {
        return type switch
        {
            SymbolType.Function => "function",
            SymbolType.Object or SymbolType.Variable or SymbolType.TlsData => "object",
            SymbolType.Section => "section",
            _ => "function"
        };
    }

    private static string GetDigestString(IReadOnlyDictionary<string, string> digest)
    {
        if (digest.TryGetValue("sha256", out var sha))
        {
            return sha;
        }

        return digest.Values.FirstOrDefault() ?? string.Empty;
    }

    private static string NormalizePath(string path)
    {
        return path.Replace('\\', '/').Trim();
    }

    private static SemanticEdit CreateFileEdit(string path, string beforeDigest, string afterDigest)
    {
        var type = string.IsNullOrWhiteSpace(beforeDigest) || beforeDigest == ComputeEmptyDigest()
            ? "add"
            : string.IsNullOrWhiteSpace(afterDigest) || afterDigest == ComputeEmptyDigest()
                ? "remove"
                : "update";

        var nodePath = $"{path}::file";
        var stableId = ComputeStableId(path, nodePath, type, beforeDigest, afterDigest);
        return new SemanticEdit
        {
            StableId = stableId,
            EditType = type,
            NodeKind = "file",
            NodePath = nodePath,
            Anchor = path,
            PreDigest = beforeDigest,
            PostDigest = afterDigest
        };
    }

    private static SemanticEdit CreateSymbolEdit(
        string path,
        string symbol,
        string type,
        string? preDigest,
        string? postDigest,
        SourceSpan? preSpan,
        SourceSpan? postSpan)
    {
        var nodePath = $"{path}::{symbol}";
        var stableId = ComputeStableId(path, nodePath, type, preDigest, postDigest);

        return new SemanticEdit
        {
            StableId = stableId,
            EditType = type,
            NodeKind = "method",
            NodePath = nodePath,
            Anchor = symbol,
            PreSpan = preSpan,
            PostSpan = postSpan,
            PreDigest = preDigest,
            PostDigest = postDigest
        };
    }

    private static string ComputeStableId(string path, string nodePath, string type, string? preDigest, string? postDigest)
    {
        var material = $"{path}|{nodePath}|{type}|{preDigest}|{postDigest}";
        var bytes = Encoding.UTF8.GetBytes(material);
        Span<byte> hash = stackalloc byte[SHA256.HashSizeInBytes];
        SHA256.HashData(bytes, hash);
        return Convert.ToHexString(hash).ToLowerInvariant();
    }

    private static Dictionary<string, SymbolBlock> ExtractSymbolBlocks(string content)
    {
        var lines = content.Split('\n');
        var blocks = new Dictionary<string, SymbolBlock>(StringComparer.Ordinal);

        for (var i = 0; i < lines.Length; i++)
        {
            var line = lines[i];
            var match = FunctionAnchorRegex.Match(line);
            if (!match.Success)
            {
                continue;
            }

            var name = match.Groups["name"].Value;
            if (ControlKeywords.Contains(name))
            {
                continue;
            }

            var startLine = i + 1;
            var endLine = startLine;

            var depth = CountChar(line, '{') - CountChar(line, '}');
            var foundOpening = line.Contains('{', StringComparison.Ordinal);

            var j = i;
            while (foundOpening && depth > 0 && j + 1 < lines.Length)
            {
                j++;
                var candidate = lines[j];
                depth += CountChar(candidate, '{');
                depth -= CountChar(candidate, '}');
            }

            if (foundOpening)
            {
                endLine = j + 1;
                i = j;
            }

            var sliceStart = startLine - 1;
            var sliceLength = endLine - startLine + 1;
            var blockContent = string.Join("\n", lines.Skip(sliceStart).Take(sliceLength));
            var blockHash = ComputeBlockHash(blockContent);

            blocks[name] = new SymbolBlock(name, blockHash, startLine, endLine);
        }

        return blocks;
    }

    private static int CountChar(string value, char token)
    {
        var count = 0;
        foreach (var c in value)
        {
            if (c == token)
            {
                count++;
            }
        }

        return count;
    }

    private static string ComputeBlockHash(string content)
    {
        var bytes = Encoding.UTF8.GetBytes(content);
        Span<byte> hash = stackalloc byte[SHA256.HashSizeInBytes];
        SHA256.HashData(bytes, hash);
        return Convert.ToHexString(hash).ToLowerInvariant();
    }

    private static bool IsAnchorMatch(string anchor, string functionId)
    {
        if (string.Equals(anchor, functionId, StringComparison.Ordinal))
        {
            return true;
        }

        return anchor.EndsWith($".{functionId}", StringComparison.Ordinal) ||
               anchor.EndsWith($"::{functionId}", StringComparison.Ordinal) ||
               anchor.Contains(functionId, StringComparison.Ordinal);
    }

    private static string ComputeEmptyDigest()
    {
        Span<byte> hash = stackalloc byte[SHA256.HashSizeInBytes];
        SHA256.HashData(Array.Empty<byte>(), hash);
        return Convert.ToHexString(hash).ToLowerInvariant();
    }

    private sealed record SymbolBlock(string Name, string Hash, int StartLine, int EndLine);
}