db-subclass-to-dto/tests/BeforeAfter.Tests/ExtractMethod/DataFlowClassificationTests.cs

using ExtractMethod.Tooling;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace BeforeAfter.Tests.ExtractMethod;

/// <summary>
/// Tests for yak em 02: the data-flow classifier (buckets: params / returns /
/// locals) over the checked-in Demo.cs fixture. Line anchors are the exact
/// fixture lines pinned by em 01 (see Demo.cs header comment):
///   ScoreReads body 56..58,  Summarize body 68..76 (for-loop 69..72),
///   Heaviest body 87..93.
/// </summary>
public class DataFlowClassificationTests
{
    // ---------------------------------------------------------------------
    // in-param bucket (ScoreReads, full body 56..58).
    // ReadInside = {_seed→field, seed, score, bonus}; the classifier must
    // report the reads that are locals/params — seed/score/bonus — as in-
    // params, and must NOT leak `this` (the implicit this-read behind the
    // _seed field access; filtered via IParameterSymbol.IsThis) into params,
    // nor the _seed field itself (decision #6 keeps fields for em 03).
    // WrittenInside = {seed, score}; no tail, trailing return is an expression
    // (score + bonus) which v1 cannot name -> no returns, both written vars
    // are scratch locals.
    // ---------------------------------------------------------------------
    [Fact]
    public void ScoreReads_full_body_reads_report_three_in_params_and_no_returns()
    {
        var suggestion = ResolveAndClassify(56, 58);

        Assert.Equal(new[] { "bonus", "score", "seed" }, suggestion.Params.Select(p => p.Name));
        // None is reassigned inside (declaration initializers are not write-backs) -> no ref.
        Assert.All(suggestion.Params, p => Assert.False(p.ByRef));
        Assert.Empty(suggestion.Returns);
        // v1 reports the read locals ALSO as scratch locals (decision #6 over-
        // reports local reads); em 03 dedupes them into the signature.
        Assert.Equal(new[] { "score", "seed" }, suggestion.Locals);
    }

    // ---------------------------------------------------------------------
    // multi-statement range case (Summarize 68..72: LocalDeclarationStatement
    // + ForStatement): the resolution, the selection data flow AND the tail
    // data flow all go through the two-argument overload with Succeeded=true
    // (the synth-block trick from parent decision #3 is the DEAD path — see
    // Test for it below). Buckets: total written inside + read at line 74 in
    // the tail -> return; for-var i never read after -> local.
    // ---------------------------------------------------------------------
    [Fact]
    public void Summarize_multi_statement_range_flows_via_two_argument_overload_and_buckets_total_return_i_local()
    {
        var (tree, compilation) = DemoFixture.Load();
        var model = compilation.GetSemanticModel(tree);
        var report = SelectionResolver.Resolve(tree, 68, 72);
        Assert.True(report.Succeeded, report.Error);

        var selectionFlow = DataFlowClassifier.AnalyzeSelectionFlow(model, report);
        Assert.True(selectionFlow.Succeeded, "two-argument AnalyzeDataFlow must succeed on a multi-statement selection");

        var tailFlow = DataFlowClassifier.AnalyzeTailFlow(model, report);
        Assert.NotNull(tailFlow);
        Assert.True(tailFlow.Succeeded, "two-argument AnalyzeDataFlow must succeed on the (multi-statement) tail region");

        var suggestion = DataFlowClassifier.Classify(model, report);
        Assert.Equal(new[] { "total" }, suggestion.Returns.Select(r => r.Name));
        Assert.Equal(new[] { "int" }, suggestion.Returns.Select(r => r.Type));
        Assert.Equal(new[] { "i" }, suggestion.Locals);

        // limit is read in the for-header (68..72) — a plain by-value in-param.
        var limit = Assert.Single(suggestion.Params.Where(p => p.Name == "limit"));
        Assert.False(limit.ByRef);
    }

    // ---------------------------------------------------------------------
    // return + ref-param buckets (Summarize, full body 68..76).
    // Returns: the tail is empty, so the tail-flow rule yields nothing; the
    // selection ends with `return message;` -> message is the trailing-return
    // candidate (parent spec). Locals: everything else written inside:
    // {i, scaled, total}.
    // Params (all ReadInside locals/params): the differential ref check —
    // total is REASSIGNED inside (total += i at line 71) -> ByRef; scaled and
    // limit are never reassigned (declaration write only) -> plain in-params.
    // ---------------------------------------------------------------------
    [Fact]
    public void Summarize_full_body_returns_trailing_message_and_flags_reassigned_total_as_ref()
    {
        var suggestion = ResolveAndClassify(68, 76);

        Assert.Equal(new[] { "message" }, suggestion.Returns.Select(r => r.Name));
        Assert.Equal(new[] { "i", "scaled", "total" }, suggestion.Locals);

        var total = Assert.Single(suggestion.Params.Where(p => p.Name == "total"));
        Assert.True(total.ByRef, "total is reassigned inside (total += i) -> the extraction owes a write-back");

        var scaled = Assert.Single(suggestion.Params.Where(p => p.Name == "scaled"));
        Assert.False(scaled.ByRef, "scaled is only declared inside, never reassigned");

        var limit = Assert.Single(suggestion.Params.Where(p => p.Name == "limit"));
        Assert.False(limit.ByRef);
    }

    // ---------------------------------------------------------------------
    // return + extract-first isolation (Heaviest, full body 87..93).
    // Returns: `return best;` is the last statement -> best (trailing-return
    // rule again). Written inside but never read after: i -> local.
    // Params: reads are best/count/i/widgets; best and i are reassigned
    // inside -> ref. Nothing extract-first (widgets[i] indexer, Bigger
    // invocation — em 03 territory) may leak into any bucket: the params list
    // is exactly the four variable reads.
    // ---------------------------------------------------------------------
    [Fact]
    public void Heaviest_full_body_returns_best_locals_i_and_leaks_no_extract_first_names()
    {
        var suggestion = ResolveAndClassify(87, 93);

        Assert.Equal(new[] { "best" }, suggestion.Returns.Select(r => r.Name));
        Assert.Equal(new[] { "i" }, suggestion.Locals);
        Assert.Equal(new[] { "best", "count", "i", "widgets" }, suggestion.Params.Select(p => p.Name));
        Assert.Equal(new[] { true, false, true, false }, suggestion.Params.Select(p => p.ByRef));
    }

    // ---------------------------------------------------------------------
    // single-statement fallback (ScoreReads, line 58 alone: `return ...;`).
    // The one-argument AnalyzeDataFlow overload is the live path for a single
    // statement. The trailing return is `score + bonus` — an expression, not
    // a simple name — so v1 reports no return candidate (composite return
    // expressions are extract-first shape for em 03) and no locals.
    // ---------------------------------------------------------------------
    [Fact]
    public void Single_statement_selection_uses_one_argument_overload_and_composite_trailing_return_is_not_nameable()
    {
        var (tree, compilation) = DemoFixture.Load();
        var model = compilation.GetSemanticModel(tree);
        var report = SelectionResolver.Resolve(tree, 58, 58);
        Assert.True(report.Succeeded, report.Error);

        Assert.True(DataFlowClassifier.AnalyzeSelectionFlow(model, report).Succeeded);

        var suggestion = DataFlowClassifier.Classify(model, report);
        Assert.Equal(new[] { "bonus", "score" }, suggestion.Params.Select(p => p.Name));
        Assert.All(suggestion.Params, p => Assert.False(p.ByRef));
        Assert.Empty(suggestion.Returns);
        Assert.Empty(suggestion.Locals);
    }

    // ---------------------------------------------------------------------
    // DEAD PATH (parent decision #3, pinned so the choice is self-explanatory
    // to future readers): a synthetic BlockSyntax re-parents tree nodes that
    // are not in the tree, and AnalyzeDataFlow refuses with
    // ArgumentException("statements not within tree"). That is why the live
    // path uses the two-argument overload (both endpoints are real tree
    // nodes) — which also keeps symbol identity across selection and tail
    // analyses, the prerequisite for the written-inside ∩ read-after
    // intersection of the return bucket.
    // ---------------------------------------------------------------------
    [Fact]
    public void Synthetic_block_data_flow_throws_not_within_tree_so_the_two_argument_overload_stays_live()
    {
        var (tree, compilation) = DemoFixture.Load();
        var model = compilation.GetSemanticModel(tree);

        var summarize = tree.GetRoot().DescendantNodes()
            .OfType<MethodDeclarationSyntax>()
            .Single(m => m.Identifier.ValueText == "Summarize");
        var statements = summarize.Body!.Statements;

        // Same node instances, new (synthetic) parent — this is the shape
        // parent decision #3 proposed for multi-statement ranges and tails.
        var syntheticBlock = SyntaxFactory.Block(statements[2], statements[3], statements[4]);

        var ex = Assert.Throws<ArgumentException>(() => model.AnalyzeDataFlow(syntheticBlock));
        Assert.Contains("not within tree", ex.Message, StringComparison.Ordinal);
    }

    private static ExtractionSuggestion ResolveAndClassify(int startLine, int endLine)
    {
        var (tree, compilation) = DemoFixture.Load();
        var model = compilation.GetSemanticModel(tree);

        var report = SelectionResolver.Resolve(tree, startLine, endLine);
        Assert.True(report.Succeeded, report.Error);

        return DataFlowClassifier.Classify(model, report);
    }
}