using System.Linq;

namespace StellaOps.DistroIntel;

public static partial class DistroMappings
{
    /// <summary>
    /// Finds derivatives for a canonical (parent) distro at a specific major release.
    /// Use this to find alternative evidence sources when native OVAL/CSAF is unavailable.
    /// </summary>
    /// <param name="canonicalDistro">The canonical distro identifier (e.g., "rhel").</param>
    /// <param name="majorRelease">The major release version.</param>
    /// <returns>Matching derivative mappings, ordered by confidence (High first).</returns>
    /// <example>
    /// var derivatives = DistroMappings.FindDerivativesFor("rhel", 9);
    /// // Returns: [(rhel, almalinux, 9, High), (rhel, rocky, 9, High), (rhel, oracle, 9, High)]
    /// </example>
    public static IEnumerable<DistroDerivative> FindDerivativesFor(string canonicalDistro, int majorRelease)
    {
        var key = (canonicalDistro.ToLowerInvariant(), majorRelease);
        if (_byCanonicalIndex.TryGetValue(key, out var derivatives))
        {
            return derivatives.OrderByDescending(d => d.Confidence);
        }

        return [];
    }

    /// <summary>
    /// Finds the canonical (parent) distro for a derivative distro.
    /// Use this to map a derivative back to its upstream source.
    /// </summary>
    /// <param name="derivativeDistro">The derivative distro identifier (e.g., "almalinux").</param>
    /// <param name="majorRelease">The major release version.</param>
    /// <returns>The canonical mapping if found, null otherwise.</returns>
    /// <example>
    /// var canonical = DistroMappings.FindCanonicalFor("almalinux", 9);
    /// // Returns: (rhel, almalinux, 9, High)
    /// </example>
    public static DistroDerivative? FindCanonicalFor(string derivativeDistro, int majorRelease)
    {
        var key = (derivativeDistro.ToLowerInvariant(), majorRelease);
        return _byDerivativeIndex.GetValueOrDefault(key);
    }

    /// <summary>
    /// Gets the confidence multiplier for a derivative relationship.
    /// Apply this to the base confidence when using derivative evidence.
    /// </summary>
    /// <param name="confidence">The derivative confidence level.</param>
    /// <returns>Multiplier value (0.95 for High, 0.80 for Medium).</returns>
    public static decimal GetConfidenceMultiplier(DerivativeConfidence confidence)
    {
        return confidence switch
        {
            DerivativeConfidence.High => 0.95m,
            DerivativeConfidence.Medium => 0.80m,
            _ => 0.70m // Unknown - conservative
        };
    }
}