using Microsoft.CodeAnalysis;

namespace ExtractMethod.Tooling;

/// <summary>Everything the extract-method report is built from: the resolved
/// selection, the raw classification buckets (em 02), the extract-first
/// candidates (em 03), the promoted signature line (em 03) and the v1
/// limitation notes. One record so the CLI and the tests compose EXACTLY the
/// same thing — the report cannot drift between them.</summary>
public sealed record ExtractionReport(
    SelectionReport Selection,
    ExtractionSuggestion Suggestion,
    IReadOnlyList<ExtractFirstEntry> ExtractFirst,
    SignatureSuggestion Signature,
    IReadOnlyList<string> Notes);

/// <summary>
/// Composes the full extraction suggestion for a resolved selection: the em 02
/// data-flow buckets, the em 03 extract-first scan, the promoted signature and
/// the limitation notes. Throws the same clean exceptions as
/// <see cref="DataFlowClassifier.Classify"/> when analysis cannot bind.
/// </summary>
public static class ExtractionReporter
{
    public static ExtractionReport Compose(SemanticModel model, SelectionReport selection)
    {
        var suggestion = DataFlowClassifier.Classify(model, selection);
        var extractFirst = ExtractFirstScanner.Scan(model, selection);
        var signature = SignatureBuilder.Build(model, selection, suggestion);
        return new ExtractionReport(selection, suggestion, extractFirst, signature, BuildNotes(model, selection));
    }

    /// <summary>
    /// The v1 limitation notes (parent decision #5 and the em 02 contract):
    /// each note is printed only when its limitation actually applies to the
    /// selection, so a clean selection gets a clean report.
    /// </summary>
    private static IReadOnlyList<string> BuildNotes(SemanticModel model, SelectionReport selection)
    {
        var notes = new List<string>();

        if (ExtractFirstScanner.HasNonVariableAssignmentLeftSide(model, selection))
        {
            notes.Add(
                "reads-only scan (decision 5): assignment left-hand sides are skipped, " +
                "so writes to fields/indexers/properties are invisible to this report");
        }

        if (DataFlowClassifier.CompositeTrailingReturn(selection) is { } trailing)
        {
            notes.Add(
                $"the selection ends with a composite return expression ({trailing.Expression!.ToFullString().Trim()}) — " +
                "extract it into a local first to make the return value nameable");
        }

        return notes;
    }
}