namespace Campaign_Tracker.Server.LegacyData.Schema;

/// <summary>
/// Release-gate entry point (Story 1.7 AC #4).
///
/// Invoked from <c>Program.cs</c> when the application is launched with the
/// <c>--check-legacy-schema</c> argument. Builds the host, runs the
/// compatibility check synchronously, prints a structured report, and returns
/// an exit code: <c>0</c> when the schema matches the baseline, non-zero (1)
/// when drift is detected. The CI/CD pipeline blocks releases on the non-zero
/// exit code.
/// </summary>
public static class LegacySchemaReleaseGate
{
    public const string CommandLineFlag = "--check-legacy-schema";
    public const int ExitCodePass = 0;
    public const int ExitCodeFail = 1;

    public static bool ShouldRun(string[] args) =>
        args.Any(a => string.Equals(a, CommandLineFlag, StringComparison.Ordinal));

    public static async Task<int> ExecuteAsync(
        ILegacySchemaCompatibilityCheck check,
        ILegacySchemaCheckHistory history,
        TextWriter output,
        CancellationToken cancellationToken = default)
    {
        var result = await check.RunAsync(cancellationToken).ConfigureAwait(false);
        history.Record(result);
        WriteReport(result, output);
        return result.Passed ? ExitCodePass : ExitCodeFail;
    }

    public static void WriteReport(LegacySchemaCheckResult result, TextWriter output)
    {
        if (result.Passed)
        {
            output.WriteLine(
                $"[legacy-schema-check] PASS — {result.TablesVerified} tables verified at {result.CheckedAt:O}, drift=0.");
            return;
        }

        output.WriteLine(
            $"[legacy-schema-check] FAIL — {result.TablesVerified} tables verified at {result.CheckedAt:O}, drift={result.DriftCount}.");
        foreach (var drift in result.Drifts)
        {
            var location = drift.ColumnName is null
                ? drift.TableName
                : $"{drift.TableName}.{drift.ColumnName}";
            output.WriteLine($"  - [{drift.ChangeType}] {location}: {drift.Detail}");
        }
    }
}