using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using StellaOps.Scanner.Reachability;

namespace StellaOps.Reachability.FixtureTests.PatchOracle;

/// <summary>
/// Compares a RichGraph against a patch-oracle definition.
/// Reports missing expected elements and present forbidden elements.
/// </summary>
public sealed class PatchOracleComparer
{
    private readonly PatchOracleDefinition _oracle;
    private readonly double _defaultMinConfidence;

    public PatchOracleComparer(PatchOracleDefinition oracle)
    {
        _oracle = oracle ?? throw new ArgumentNullException(nameof(oracle));
        _defaultMinConfidence = oracle.MinConfidence;
    }

    /// <summary>
    /// Compares the graph against the oracle and returns a result.
    /// </summary>
    public PatchOracleResult Compare(RichGraph graph)
    {
        ArgumentNullException.ThrowIfNull(graph);

        var violations = new List<PatchOracleViolation>();

        // Check expected functions
        foreach (var expected in _oracle.ExpectedFunctions.Where(f => f.Required))
        {
            if (!HasMatchingNode(graph, expected))
            {
                violations.Add(new PatchOracleViolation(
                    ViolationType.MissingFunction,
                    expected.SymbolId,
                    null,
                    expected.Reason ?? $"Expected function '{expected.SymbolId}' not found in graph"));
            }
        }

        // Check expected edges
        foreach (var expected in _oracle.ExpectedEdges.Where(e => e.Required))
        {
            var minConf = expected.MinConfidence ?? _defaultMinConfidence;
            if (!HasMatchingEdge(graph, expected, minConf))
            {
                violations.Add(new PatchOracleViolation(
                    ViolationType.MissingEdge,
                    expected.From,
                    expected.To,
                    expected.Reason ?? $"Expected edge '{expected.From}' -> '{expected.To}' not found in graph"));
            }
        }

        // Check expected roots
        foreach (var expected in _oracle.ExpectedRoots.Where(r => r.Required))
        {
            if (!HasMatchingRoot(graph, expected))
            {
                violations.Add(new PatchOracleViolation(
                    ViolationType.MissingRoot,
                    expected.Id,
                    null,
                    expected.Reason ?? $"Expected root '{expected.Id}' not found in graph"));
            }
        }

        // Check forbidden functions
        foreach (var forbidden in _oracle.ForbiddenFunctions)
        {
            if (HasMatchingNode(graph, forbidden))
            {
                violations.Add(new PatchOracleViolation(
                    ViolationType.ForbiddenFunctionPresent,
                    forbidden.SymbolId,
                    null,
                    forbidden.Reason ?? $"Forbidden function '{forbidden.SymbolId}' is present in graph"));
            }
        }

        // Check forbidden edges
        foreach (var forbidden in _oracle.ForbiddenEdges)
        {
            if (HasMatchingEdge(graph, forbidden, 0.0))
            {
                violations.Add(new PatchOracleViolation(
                    ViolationType.ForbiddenEdgePresent,
                    forbidden.From,
                    forbidden.To,
                    forbidden.Reason ?? $"Forbidden edge '{forbidden.From}' -> '{forbidden.To}' is present in graph"));
            }
        }

        // Strict mode: check for unexpected elements
        if (_oracle.StrictMode)
        {
            var unexpectedNodes = FindUnexpectedNodes(graph);
            foreach (var node in unexpectedNodes)
            {
                violations.Add(new PatchOracleViolation(
                    ViolationType.UnexpectedFunction,
                    node.Id,
                    null,
                    $"Strict mode: unexpected function '{node.Id}' found in graph"));
            }

            var unexpectedEdges = FindUnexpectedEdges(graph);
            foreach (var edge in unexpectedEdges)
            {
                violations.Add(new PatchOracleViolation(
                    ViolationType.UnexpectedEdge,
                    edge.From,
                    edge.To,
                    $"Strict mode: unexpected edge '{edge.From}' -> '{edge.To}' found in graph"));
            }
        }

        return new PatchOracleResult(
            OracleId: _oracle.Id,
            CaseRef: _oracle.CaseRef,
            Variant: _oracle.Variant,
            Success: violations.Count == 0,
            Violations: violations,
            Summary: GenerateSummary(graph, violations));
    }

    private bool HasMatchingNode(RichGraph graph, ExpectedFunction expected)
    {
        foreach (var node in graph.Nodes)
        {
            if (!MatchesPattern(node.Id, expected.SymbolId) &&
                !MatchesPattern(node.SymbolId, expected.SymbolId))
            {
                continue;
            }

            if (!string.IsNullOrEmpty(expected.Lang) &&
                !string.Equals(node.Lang, expected.Lang, StringComparison.OrdinalIgnoreCase))
            {
                continue;
            }

            if (!string.IsNullOrEmpty(expected.Kind) &&
                !string.Equals(node.Kind, expected.Kind, StringComparison.OrdinalIgnoreCase))
            {
                continue;
            }

            if (!string.IsNullOrEmpty(expected.PurlPattern) &&
                !MatchesPattern(node.Purl ?? string.Empty, expected.PurlPattern))
            {
                continue;
            }

            return true;
        }

        return false;
    }

    private bool HasMatchingEdge(RichGraph graph, ExpectedEdge expected, double minConfidence)
    {
        foreach (var edge in graph.Edges)
        {
            if (!MatchesPattern(edge.From, expected.From))
            {
                continue;
            }

            if (!MatchesPattern(edge.To, expected.To))
            {
                continue;
            }

            if (!string.IsNullOrEmpty(expected.Kind) &&
                !string.Equals(edge.Kind, expected.Kind, StringComparison.OrdinalIgnoreCase))
            {
                continue;
            }

            if (edge.Confidence < minConfidence)
            {
                continue;
            }

            return true;
        }

        return false;
    }

    private bool HasMatchingRoot(RichGraph graph, ExpectedRoot expected)
    {
        foreach (var root in graph.Roots)
        {
            if (!MatchesPattern(root.Id, expected.Id))
            {
                continue;
            }

            if (!string.IsNullOrEmpty(expected.Phase) &&
                !string.Equals(root.Phase, expected.Phase, StringComparison.OrdinalIgnoreCase))
            {
                continue;
            }

            return true;
        }

        return false;
    }

    private IEnumerable<RichGraphNode> FindUnexpectedNodes(RichGraph graph)
    {
        var allExpected = _oracle.ExpectedFunctions
            .Select(f => f.SymbolId)
            .ToHashSet(StringComparer.Ordinal);

        foreach (var node in graph.Nodes)
        {
            var isExpected = allExpected.Any(pattern => MatchesPattern(node.Id, pattern) || MatchesPattern(node.SymbolId, pattern));
            if (!isExpected)
            {
                yield return node;
            }
        }
    }

    private IEnumerable<RichGraphEdge> FindUnexpectedEdges(RichGraph graph)
    {
        foreach (var edge in graph.Edges)
        {
            var isExpected = _oracle.ExpectedEdges.Any(e =>
                MatchesPattern(edge.From, e.From) && MatchesPattern(edge.To, e.To));
            if (!isExpected)
            {
                yield return edge;
            }
        }
    }

    /// <summary>
    /// Matches a value against a pattern supporting '*' wildcards.
    /// </summary>
    private static bool MatchesPattern(string value, string pattern)
    {
        if (string.IsNullOrEmpty(pattern))
        {
            return true;
        }

        if (string.IsNullOrEmpty(value))
        {
            return false;
        }

        // Exact match
        if (!pattern.Contains('*'))
        {
            return string.Equals(value, pattern, StringComparison.Ordinal);
        }

        // Convert wildcard pattern to regex
        var regexPattern = "^" + Regex.Escape(pattern).Replace("\\*", ".*") + "$";
        return Regex.IsMatch(value, regexPattern, RegexOptions.None, TimeSpan.FromMilliseconds(100));
    }

    private static PatchOracleSummary GenerateSummary(RichGraph graph, List<PatchOracleViolation> violations)
    {
        return new PatchOracleSummary(
            TotalNodes: graph.Nodes.Count,
            TotalEdges: graph.Edges.Count,
            TotalRoots: graph.Roots.Count,
            MissingFunctions: violations.Count(v => v.Type == ViolationType.MissingFunction),
            MissingEdges: violations.Count(v => v.Type == ViolationType.MissingEdge),
            MissingRoots: violations.Count(v => v.Type == ViolationType.MissingRoot),
            ForbiddenFunctionsPresent: violations.Count(v => v.Type == ViolationType.ForbiddenFunctionPresent),
            ForbiddenEdgesPresent: violations.Count(v => v.Type == ViolationType.ForbiddenEdgePresent),
            UnexpectedFunctions: violations.Count(v => v.Type == ViolationType.UnexpectedFunction),
            UnexpectedEdges: violations.Count(v => v.Type == ViolationType.UnexpectedEdge));
    }
}

/// <summary>
/// Result of comparing a graph against a patch-oracle.
/// </summary>
public sealed record PatchOracleResult(
    string OracleId,
    string CaseRef,
    string Variant,
    bool Success,
    IReadOnlyList<PatchOracleViolation> Violations,
    PatchOracleSummary Summary)
{
    /// <summary>
    /// Generates a human-readable report.
    /// </summary>
    public string ToReport()
    {
        var lines = new List<string>
        {
            $"Patch-Oracle Validation Report",
            $"==============================",
            $"Oracle: {OracleId}",
            $"Case: {CaseRef} ({Variant})",
            $"Status: {(Success ? "PASS" : "FAIL")}",
            string.Empty,
            $"Graph Statistics:",
            $"  Nodes: {Summary.TotalNodes}",
            $"  Edges: {Summary.TotalEdges}",
            $"  Roots: {Summary.TotalRoots}",
            string.Empty
        };

        if (Violations.Count > 0)
        {
            lines.Add($"Violations ({Violations.Count}):");
            foreach (var v in Violations)
            {
                var target = v.To is not null ? $" -> {v.To}" : string.Empty;
                lines.Add($"  [{v.Type}] {v.From}{target}");
                lines.Add($"    Reason: {v.Message}");
            }
        }
        else
        {
            lines.Add("No violations found.");
        }

        return string.Join(Environment.NewLine, lines);
    }
}

/// <summary>
/// A single violation found during oracle comparison.
/// </summary>
public sealed record PatchOracleViolation(
    ViolationType Type,
    string From,
    string? To,
    string Message);

/// <summary>
/// Type of oracle violation.
/// </summary>
public enum ViolationType
{
    MissingFunction,
    MissingEdge,
    MissingRoot,
    ForbiddenFunctionPresent,
    ForbiddenEdgePresent,
    UnexpectedFunction,
    UnexpectedEdge
}

/// <summary>
/// Summary statistics for oracle comparison.
/// </summary>
public sealed record PatchOracleSummary(
    int TotalNodes,
    int TotalEdges,
    int TotalRoots,
    int MissingFunctions,
    int MissingEdges,
    int MissingRoots,
    int ForbiddenFunctionsPresent,
    int ForbiddenEdgesPresent,
    int UnexpectedFunctions,
    int UnexpectedEdges);