using System;
using System.Collections.Generic;
using System.Text;

namespace StellaOps.Provcache;

public sealed partial class VeriKeyBuilder
{
    /// <summary>
    /// Builds the final VeriKey by hashing all components together.
    /// </summary>
    /// <returns>The computed VeriKey in format "sha256:&lt;hex&gt;".</returns>
    /// <exception cref="InvalidOperationException">If required components are missing.</exception>
    public string Build()
    {
        ValidateRequiredComponents();

        var components = new StringBuilder();
        components.Append("v1|");
        components.Append(_sourceHash);
        components.Append('|');
        components.Append(_sbomHash);
        components.Append('|');
        components.Append(_vexHashSetHash);
        components.Append('|');
        components.Append(_mergePolicyHash);
        components.Append('|');
        components.Append(_signerSetHash);
        components.Append('|');
        components.Append(_timeWindow);

        var compositeBytes = Encoding.UTF8.GetBytes(components.ToString());
        return ComputeHash(compositeBytes);
    }

    /// <summary>
    /// Builds a <see cref="VeriKeyComponents"/> record with all individual components.
    /// Useful for debugging and serialization.
    /// </summary>
    /// <returns>A record containing all VeriKey components.</returns>
    public VeriKeyComponents BuildWithComponents()
    {
        ValidateRequiredComponents();

        return new VeriKeyComponents
        {
            VeriKey = Build(),
            SourceHash = _sourceHash!,
            SbomHash = _sbomHash!,
            VexHashSetHash = _vexHashSetHash!,
            MergePolicyHash = _mergePolicyHash!,
            SignerSetHash = _signerSetHash!,
            TimeWindow = _timeWindow!
        };
    }

    /// <summary>
    /// Resets the builder to its initial state.
    /// </summary>
    /// <returns>This builder for fluent chaining.</returns>
    public VeriKeyBuilder Reset()
    {
        _sourceHash = null;
        _sbomHash = null;
        _vexHashSetHash = null;
        _mergePolicyHash = null;
        _signerSetHash = null;
        _timeWindow = null;
        return this;
    }

    private void ValidateRequiredComponents()
    {
        var missing = new List<string>();

        if (string.IsNullOrWhiteSpace(_sourceHash))
            missing.Add("SourceHash");
        if (string.IsNullOrWhiteSpace(_sbomHash))
            missing.Add("SbomHash");
        if (string.IsNullOrWhiteSpace(_vexHashSetHash))
            missing.Add("VexHashSetHash");
        if (string.IsNullOrWhiteSpace(_mergePolicyHash))
            missing.Add("MergePolicyHash");
        if (string.IsNullOrWhiteSpace(_signerSetHash))
            missing.Add("SignerSetHash");
        if (string.IsNullOrWhiteSpace(_timeWindow))
            missing.Add("TimeWindow");

        if (missing.Count > 0)
        {
            throw new InvalidOperationException(
                $"Cannot build VeriKey: missing required components: {string.Join(", ", missing)}. " +
                "Use the With* methods to set all required components before calling Build().");
        }
    }
}