using Microsoft.Data.Sqlite;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using ZB.MOM.WW.LocalDb;

namespace ZB.MOM.WW.ScadaBridge.Host.Tests;

/// <summary>
/// Arch-review 2026-08-19 P4-6 — <c>PRAGMA auto_vacuum = INCREMENTAL</c> only takes effect on
/// a table-less database, and <c>SqliteLocalDb</c>'s constructor creates LocalDb's own
/// bookkeeping tables before anything else ever gets a connection to the consolidated site
/// file. <see cref="SiteLocalDbSetup.EnsureAutoVacuumOnFreshFile"/> is the fix: it pre-creates
/// a genuinely fresh file with the pragma set BEFORE <c>AddZbLocalDb</c>'s lazy singleton ever
/// constructs <c>SqliteLocalDb</c>.
/// </summary>
/// <remarks>
/// These tests exercise <see cref="SiteLocalDbSetup.EnsureAutoVacuumOnFreshFile"/> directly
/// (it is <c>internal</c>, visible here via <c>InternalsVisibleTo</c>) rather than through the
/// full <see cref="SiteServiceRegistration"/> composition root — the mechanism under test is a
/// pure ordering/pragma concern that does not depend on the rest of the site graph, and
/// <see cref="SiteLocalDbWiringTests"/> already proves the composition root wires
/// <c>SiteLocalDbSetup</c> in at all.
/// </remarks>
public class SiteLocalDbAutoVacuumTests
{
    [Fact]
    public void FreshFile_ReportsIncrementalAutoVacuum()
    {
        // The plan's own acceptance test: a fresh file reports PRAGMA auto_vacuum = 2
        // (INCREMENTAL) after the pre-create step runs.
        var path = TempDbPath();
        try
        {
            var config = ConfigFor(path);

            SiteLocalDbSetup.EnsureAutoVacuumOnFreshFile(config);

            Assert.Equal(2L, ReadAutoVacuum(path));
        }
        finally
        {
            Cleanup(path);
        }
    }

    [Fact]
    public void FreshFile_AutoVacuumSurvives_LocalDbCreatingItsOwnBookkeepingTablesAfterward()
    {
        // The real end-to-end claim: the pre-create step has to run BEFORE AddZbLocalDb ever
        // constructs SqliteLocalDb (which creates LocalDb's own tables first, unconditionally,
        // in its constructor) for the ordering fix to mean anything. This proves the flag
        // baked in by EnsureAutoVacuumOnFreshFile survives that later table creation — the
        // exact sequence SiteServiceRegistration.Configure now runs in production.
        var path = TempDbPath();
        try
        {
            var config = ConfigFor(path);

            SiteLocalDbSetup.EnsureAutoVacuumOnFreshFile(config);

            var services = new ServiceCollection();
            services.AddZbLocalDb(config, db => SiteLocalDbSetup.OnReady(db, config));
            using var provider = services.BuildServiceProvider();
            using var scope = provider.CreateScope();

            // Resolving ILocalDb is what triggers SqliteLocalDb's constructor (LocalDbSchema
            // .EnsureCreated) and then OnReady (SiteEventLogSchema.Apply, etc.) — i.e. every
            // real table this file will ever hold. This config carries no
            // LocalDb:Replication section, so OnReady takes the deregistration branch and
            // db.ReplicatedTables stays empty — check the raw file instead to confirm the
            // table genuinely exists.
            var db = scope.ServiceProvider.GetRequiredService<ILocalDb>();
            Assert.NotNull(db);
            Assert.Contains("site_events", TableNames(path));

            Assert.Equal(2L, ReadAutoVacuum(path));
        }
        finally
        {
            SqliteConnection.ClearAllPools();
            Cleanup(path);
        }
    }

    [Fact]
    public void ExistingFile_IsLeftAlone_AutoVacuumStaysNone()
    {
        // Honesty requirement (plan decision 2): the fix only helps a file that does not exist
        // yet. A file that already has tables — every node on the docker rig today, and any
        // site database created before this fix shipped — is untouched, and stays
        // auto_vacuum = NONE forever short of an offline VACUUM this task deliberately does
        // not attempt.
        var path = TempDbPath();
        try
        {
            // Pre-populate the file exactly like a real (pre-fix) LocalDb file: at least one
            // table exists before EnsureAutoVacuumOnFreshFile ever runs.
            using (var seed = new SqliteConnection(new SqliteConnectionStringBuilder { DataSource = path }.ToString()))
            {
                seed.Open();
                using var cmd = seed.CreateCommand();
                cmd.CommandText = "CREATE TABLE legacy_marker (id INTEGER PRIMARY KEY)";
                cmd.ExecuteNonQuery();
            }

            Assert.Equal(0L, ReadAutoVacuum(path)); // NONE, the SQLite default.

            var config = ConfigFor(path);
            SiteLocalDbSetup.EnsureAutoVacuumOnFreshFile(config);

            // Still NONE — the method must not attempt VACUUM against a populated file.
            Assert.Equal(0L, ReadAutoVacuum(path));
        }
        finally
        {
            SqliteConnection.ClearAllPools();
            Cleanup(path);
        }
    }

    [Fact]
    public void MissingLocalDbPath_DoesNotThrow()
    {
        // AddZbLocalDb's own options validation is the authoritative place a missing path is
        // reported; this pre-create step must defer to it rather than throwing its own,
        // differently-worded error first.
        var config = new ConfigurationBuilder().AddInMemoryCollection(
            new Dictionary<string, string?>()).Build();

        var ex = Record.Exception(() => SiteLocalDbSetup.EnsureAutoVacuumOnFreshFile(config));

        Assert.Null(ex);
    }

    private static string TempDbPath() =>
        Path.Combine(Path.GetTempPath(), $"scadabridge_autovacuum_{Guid.NewGuid():N}.db");

    private static IConfiguration ConfigFor(string path) =>
        new ConfigurationBuilder()
            .AddInMemoryCollection(new Dictionary<string, string?> { ["LocalDb:Path"] = path })
            .Build();

    private static long ReadAutoVacuum(string path)
    {
        using var connection = new SqliteConnection(new SqliteConnectionStringBuilder { DataSource = path }.ToString());
        connection.Open();
        using var cmd = connection.CreateCommand();
        cmd.CommandText = "PRAGMA auto_vacuum";
        return Convert.ToInt64(cmd.ExecuteScalar());
    }

    private static HashSet<string> TableNames(string path)
    {
        using var connection = new SqliteConnection(new SqliteConnectionStringBuilder { DataSource = path }.ToString());
        connection.Open();
        using var cmd = connection.CreateCommand();
        cmd.CommandText = "SELECT name FROM sqlite_master WHERE type = 'table'";
        using var reader = cmd.ExecuteReader();
        var names = new HashSet<string>(StringComparer.Ordinal);
        while (reader.Read()) names.Add(reader.GetString(0));
        return names;
    }

    private static void Cleanup(string path)
    {
        foreach (var suffix in new[] { "", "-wal", "-shm" })
        {
            try { File.Delete(path + suffix); } catch { /* best effort */ }
        }
    }
}