using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;

namespace ExtractMethod.Tooling;

/// <summary>
/// Turns a plain .cs file into a Roslyn <see cref="CSharpCompilation"/> that a
/// semantic model can be queried against.
///
/// Shared by the CLI (Program.cs) and the tests so both exercise the same
/// loading path — the tests should not re-implement this, or they would be
/// testing their own assumptions instead of the tool.
/// </summary>
public static class CompilationLoader
{
    /// <summary>
    /// Parse a file into a <see cref="SyntaxTree"/> using the latest language
    /// version. Nothing here is project-specific: no .sln, no .csproj, no
    /// generated files — the tool is a micro-tool that runs on a single file.
    /// </summary>
    public static SyntaxTree ParseFile(string path)
    {
        var text = File.ReadAllText(Path.GetFullPath(path));
        return CSharpSyntaxTree.ParseText(
            text,
            path: path,
            options: CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.Latest));
    }

    /// <summary>
    /// Build a scratch compilation over <paramref name="tree"/>.
    ///
    /// WHY <c>TRUSTED_PLATFORM_ASSEMBLIES</c>: it is the runtime-resolved list
    /// of the actual BCL assemblies this process (net10.0) runs on, e.g.
    /// System.Private.CoreLib, System.Runtime, System.Console. Referencing
    /// them means an arbitrary fixture can bind List&lt;T&gt;, string, and the
    /// rest of the BCL without any NuGet/EF/SQLite haul. (A single
    /// typeof(object) reference is NOT enough on modern .NET — that only pulls
    /// in the core library, and Console/GC/enums etc. fail to bind.)
    /// </summary>
    public static CSharpCompilation CreateCompilation(SyntaxTree tree, string assemblyName)
    {
        var refs = ((string)AppContext.GetData("TRUSTED_PLATFORM_ASSEMBLIES")!)
            .Split(Path.PathSeparator)
            .Select(p => (MetadataReference)MetadataReference.CreateFromFile(p));

        return CSharpCompilation.Create(
            assemblyName,
            new[] { tree },
            refs,
            new CSharpCompilationOptions(
                OutputKind.DynamicallyLinkedLibrary,
                // Match the repo's net10.0 projects so the fixture's nullable
                // annotations compile without warnings.
                nullableContextOptions: NullableContextOptions.Enable));
    }
}