using ItWorx.KnowledgeHub.Application.Knowledge.UseCases;
using ItWorx.KnowledgeHub.Domain.Decisions;

namespace ItWorx.KnowledgeHub.Application.Decisions.UseCases;

public sealed record DecisionDetailResult(
    DecisionRecord Decision,
    PageDetailResult Page,
    string ETag,
    DecisionRecord? Supersedes,
    DecisionRecord? SupersededBy);

/// <summary>Assembles one ADR's full lineage view: its own lifecycle metadata, the
/// linked page's rendered content, and — resolved by one extra lookup each, never a
/// duplicated copy — the decision it supersedes and/or is superseded by
/// (docs/16-runbooks-and-adrs.md: "Links are bidirectional").</summary>
public sealed class GetDecisionUseCase(IDecisionRepository decisions, GetPageUseCase getPage)
{
    public async Task<DecisionDetailResult?> ExecuteAsync(Guid decisionId, CancellationToken cancellationToken)
    {
        var decision = await decisions.FindAsync(decisionId, cancellationToken);
        if (decision is null)
        {
            return null;
        }

        var page = await getPage.ExecuteAsync(decision.PageId, cancellationToken);
        if (page is null)
        {
            return null;
        }

        var etag = await decisions.GetETagAsync(decisionId, cancellationToken) ?? string.Empty;
        var supersedes = decision.SupersedesDecisionId is { } supersedesId
            ? await decisions.FindAsync(supersedesId, cancellationToken)
            : null;
        var supersededBy = decision.SupersededByDecisionId is { } supersededById
            ? await decisions.FindAsync(supersededById, cancellationToken)
            : null;

        return new DecisionDetailResult(decision, page, etag, supersedes, supersededBy);
    }
}