// Licensed under BUSL-1.1. Copyright (C) 2024-2026 StellaOps Contributors.

using System.Collections.Immutable;
using StellaOps.VexLens.Models;
using StellaOps.VexLens.Proof;

namespace StellaOps.VexLens.Propagation;

/// <summary>
/// Default implementation of the propagation rule engine.
/// </summary>
public sealed class PropagationRuleEngine : IPropagationRuleEngine
{
    private readonly ImmutableArray<PropagationRule> _rules;

    /// <summary>
    /// Creates a new PropagationRuleEngine with default rules.
    /// </summary>
    public PropagationRuleEngine() : this(GetDefaultRules())
    {
    }

    /// <summary>
    /// Creates a new PropagationRuleEngine with specified rules.
    /// </summary>
    public PropagationRuleEngine(IEnumerable<PropagationRule> rules)
    {
        _rules = rules.OrderBy(r => r.Priority).ToImmutableArray();
    }

    /// <inheritdoc />
    public PropagationResult Propagate(
        ComponentVerdict componentVerdict,
        IDependencyGraph graph,
        PropagationPolicy policy)
    {
        ArgumentNullException.ThrowIfNull(componentVerdict);
        ArgumentNullException.ThrowIfNull(graph);
        ArgumentNullException.ThrowIfNull(policy);

        var ruleResults = new List<PropagationRuleResult>();
        var analyzedPaths = new List<DependencyPath>();
        VexStatus? inheritedStatus = null;
        var overrideApplied = false;
        string? overrideReason = null;
        var anyTriggered = false;

        // Analyze dependency paths
        var paths = graph.GetPathsTo(componentVerdict.ComponentKey);
        foreach (var path in paths)
        {
            // Skip excluded scopes
            if (policy.ExcludedScopes.Contains(path.Scope))
            {
                continue;
            }

            // Skip if beyond max depth
            if (path.Depth > policy.MaxTransitiveDepth)
            {
                continue;
            }

            analyzedPaths.Add(path);
        }

        // Evaluate rules in priority order
        foreach (var rule in _rules)
        {
            var result = rule.Evaluate(componentVerdict, graph, policy);
            ruleResults.Add(result);

            if (result.Triggered)
            {
                anyTriggered = true;

                // First triggered rule with an effect wins
                if (inheritedStatus is null && !string.IsNullOrEmpty(result.Effect))
                {
                    // Parse effect to determine inherited status
                    if (result.Effect.Contains("affected", StringComparison.OrdinalIgnoreCase))
                    {
                        inheritedStatus = VexStatus.Affected;
                    }
                    else if (result.Effect.Contains("not_affected", StringComparison.OrdinalIgnoreCase))
                    {
                        inheritedStatus = VexStatus.NotAffected;
                    }
                    else if (result.Effect.Contains("fixed", StringComparison.OrdinalIgnoreCase))
                    {
                        inheritedStatus = VexStatus.Fixed;
                    }
                }

                // Check for override
                if (result.Effect?.Contains("override", StringComparison.OrdinalIgnoreCase) == true)
                {
                    overrideApplied = true;
                    overrideReason = result.Effect;
                }
            }
        }

        return new PropagationResult(
            anyTriggered,
            ruleResults.ToImmutableArray(),
            analyzedPaths.ToImmutableArray(),
            inheritedStatus,
            overrideApplied,
            overrideReason);
    }

    /// <inheritdoc />
    public IReadOnlyList<PropagationRule> GetRules() => _rules;

    /// <summary>
    /// Gets the default set of propagation rules.
    /// </summary>
    public static IEnumerable<PropagationRule> GetDefaultRules()
    {
        yield return new DirectDependencyAffectedRule();
        yield return new TransitiveDependencyRule();
        yield return new DependencyFixedRule();
        yield return new DependencyNotAffectedRule();
    }
}

/// <summary>
/// Rule: If direct dependency is affected, product inherits affected unless overridden.
/// </summary>
public sealed class DirectDependencyAffectedRule : PropagationRule
{
    public override string RuleId => "direct-dependency-affected";
    public override string Description => "If direct dependency is affected, product inherits affected unless product-level override";
    public override int Priority => 10;

    public override PropagationRuleResult Evaluate(
        ComponentVerdict verdict,
        IDependencyGraph graph,
        PropagationPolicy policy)
    {
        if (!policy.InheritAffectedFromDirectDependency)
        {
            return new PropagationRuleResult(RuleId, Description, false, null, []);
        }

        // Check if any direct dependency is affected
        var directDeps = graph.GetDirectDependencies(verdict.ComponentKey).ToList();
        var affectedComponents = new List<string>();

        foreach (var dep in directDeps)
        {
            if (dep.PathType == DependencyPathType.DirectDependency)
            {
                // In a real implementation, we would look up the verdict for the dependency
                // For now, we track the dependency for potential impact
                affectedComponents.Add(dep.To);
            }
        }

        // This rule triggers when the component's own verdict is affected and it has direct dependencies
        var triggered = verdict.Status == VexStatus.Affected && affectedComponents.Count > 0;

        return new PropagationRuleResult(
            RuleId,
            Description,
            triggered,
            triggered ? "Product inherits affected status from direct dependency" : null,
            affectedComponents.ToImmutableArray());
    }
}

/// <summary>
/// Rule: If transitive dependency is affected, flag for review but don't auto-inherit.
/// </summary>
public sealed class TransitiveDependencyRule : PropagationRule
{
    public override string RuleId => "transitive-dependency-affected";
    public override string Description => "If transitive dependency is affected, flag for review but don't auto-inherit";
    public override int Priority => 20;

    public override PropagationRuleResult Evaluate(
        ComponentVerdict verdict,
        IDependencyGraph graph,
        PropagationPolicy policy)
    {
        if (!policy.EnableTransitivePropagation)
        {
            return new PropagationRuleResult(RuleId, Description, false, null, []);
        }

        var paths = graph.GetPathsTo(verdict.ComponentKey).ToList();
        var transitivePaths = paths
            .Where(p => p.PathType == DependencyPathType.TransitiveDependency)
            .Where(p => p.Depth <= policy.MaxTransitiveDepth)
            .ToList();

        var triggered = verdict.Status == VexStatus.Affected && transitivePaths.Count > 0;
        var affectedComponents = transitivePaths.Select(p => p.Root).Distinct().ToImmutableArray();

        return new PropagationRuleResult(
            RuleId,
            Description,
            triggered,
            triggered ? "Transitive dependency is affected - flagged for review" : null,
            affectedComponents);
    }
}

/// <summary>
/// Rule: If dependency was affected but is now fixed, allow product NotAffected if vulnerable code was removed.
/// </summary>
public sealed class DependencyFixedRule : PropagationRule
{
    public override string RuleId => "dependency-fixed";
    public override string Description => "If dependency was affected but is now fixed, allow product NotAffected if vulnerable code was removed";
    public override int Priority => 30;

    public override PropagationRuleResult Evaluate(
        ComponentVerdict verdict,
        IDependencyGraph graph,
        PropagationPolicy policy)
    {
        // This rule triggers when a dependency is now fixed
        var triggered = verdict.Status == VexStatus.Fixed;

        return new PropagationRuleResult(
            RuleId,
            Description,
            triggered,
            triggered ? "Dependency is fixed - product may be not_affected with override" : null,
            []);
    }
}

/// <summary>
/// Rule: If dependency is not_affected, product may inherit if dependency is leaf.
/// </summary>
public sealed class DependencyNotAffectedRule : PropagationRule
{
    public override string RuleId => "dependency-not-affected";
    public override string Description => "If dependency is not_affected, product may inherit if dependency is leaf";
    public override int Priority => 40;

    public override PropagationRuleResult Evaluate(
        ComponentVerdict verdict,
        IDependencyGraph graph,
        PropagationPolicy policy)
    {
        if (!policy.InheritNotAffectedFromLeafDependency)
        {
            return new PropagationRuleResult(RuleId, Description, false, null, []);
        }

        var isLeaf = graph.IsLeaf(verdict.ComponentKey);
        var triggered = verdict.Status == VexStatus.NotAffected && isLeaf;

        return new PropagationRuleResult(
            RuleId,
            Description,
            triggered,
            triggered ? "Leaf dependency is not_affected - dependents may inherit" : null,
            []);
    }
}