using System.Text.RegularExpressions;
using Microsoft.Data.SqlClient;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Migrations;

namespace ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Tests.Migrations;

/// <summary>
/// SQL Server tests for the deploy artifact itself: the <c>dotnet ef migrations script
/// --idempotent</c> output that upgrades a central configuration database (ScadaBridge#126).
/// </summary>
/// <remarks>
/// EF puts each migration of an idempotent script in ONE batch behind per-statement
/// <c>IF NOT EXISTS (… __EFMigrationsHistory …)</c> guards, and SQL Server compiles the whole
/// batch before any guard runs. A raw-SQL statement that references a column added earlier in
/// the same migration therefore fails with Msg 207 even though the guard would have let the
/// ADD COLUMN run first — <c>database update</c> / <c>Migrate()</c> never see it because they
/// send one command at a time. The tests in this class migrate the fixture database down and
/// back up, so they own their fixture and leave the database fully migrated.
/// </remarks>
public sealed class IdempotentMigrationScriptTests : IClassFixture<MsSqlMigrationFixture>
{
    // The last migration deployed everywhere before the 2026-11 central-pair migration window
    // (migration 57). The idempotent script from here to head is what DEV/QA/prod run.
    private const string BaselineMigration = "20260914173147_AddSiteArtifactRevision";

    private static readonly Regex BatchSeparator = new(@"^\s*GO\s*$", RegexOptions.Multiline | RegexOptions.IgnoreCase);

    private readonly MsSqlMigrationFixture _fixture;

    /// <summary>Creates the test class with its own migrated SQL Server database.</summary>
    /// <param name="fixture">The per-class migration fixture.</param>
    public IdempotentMigrationScriptTests(MsSqlMigrationFixture fixture) => _fixture = fixture;

    /// <summary>
    /// From the migration-57 baseline the generated idempotent script runs batch by batch
    /// without an error, applies every pending migration, and a second run is a no-op.
    /// </summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [SkippableFact]
    public async Task IdempotentScript_FromBaseline_RunsClean_AndReRunsAsANoOp()
    {
        Skip.IfNot(_fixture.Available, _fixture.SkipReason);

        await using var ctx = CreateContext();
        var migrator = ctx.GetService<IMigrator>();
        var all = ctx.Database.GetMigrations().ToList();
        var script = migrator.GenerateScript(
            fromMigration: BaselineMigration,
            options: MigrationsSqlGenerationOptions.Idempotent);

        try
        {
            await migrator.MigrateAsync(BaselineMigration);
            Assert.Equal(all.IndexOf(BaselineMigration) + 1, (await ReadHistoryAsync()).Count);

            await RunScriptAsync(script);
            Assert.Equal(all, await ReadHistoryAsync());
            Assert.Equal(2, await CountChainIndexesAsync());

            // Second run against the fully-migrated database: every guard is false.
            await RunScriptAsync(script);
            Assert.Equal(all, await ReadHistoryAsync());
        }
        finally
        {
            // Leave the fixture database fully migrated whatever happened above.
            await migrator.MigrateAsync();
        }
    }

    private ScadaBridgeDbContext CreateContext()
        => new(new DbContextOptionsBuilder<ScadaBridgeDbContext>()
            .UseSqlServer(_fixture.ConnectionString, sql => sql.CommandTimeout(600)).Options);

    private async Task RunScriptAsync(string script)
    {
        await using var conn = new SqlConnection(_fixture.ConnectionString);
        await conn.OpenAsync();
        foreach (var batch in BatchSeparator.Split(script))
        {
            if (string.IsNullOrWhiteSpace(batch))
            {
                continue;
            }

            await using var cmd = conn.CreateCommand();
            cmd.CommandTimeout = 600;
            cmd.CommandText = batch;
            await cmd.ExecuteNonQueryAsync();
        }
    }

    private async Task<List<string>> ReadHistoryAsync()
    {
        await using var conn = new SqlConnection(_fixture.ConnectionString);
        await conn.OpenAsync();
        await using var cmd = conn.CreateCommand();
        cmd.CommandText = "SELECT MigrationId FROM __EFMigrationsHistory ORDER BY MigrationId";
        var ids = new List<string>();
        await using var reader = await cmd.ExecuteReaderAsync();
        while (await reader.ReadAsync())
        {
            ids.Add(reader.GetString(0));
        }

        return ids;
    }

    private async Task<int> CountChainIndexesAsync()
    {
        await using var conn = new SqlConnection(_fixture.ConnectionString);
        await conn.OpenAsync();
        await using var cmd = conn.CreateCommand();
        cmd.CommandText = """
            SELECT COUNT(*) FROM sys.indexes
            WHERE object_id = OBJECT_ID('dbo.AuditLog')
              AND name IN ('IX_AuditLog_Unchained', 'IX_AuditLog_ChainSeq')
            """;
        return (int)(await cmd.ExecuteScalarAsync())!;
    }
}