using System;
using Microsoft.EntityFrameworkCore.Migrations;

#nullable disable

namespace ScadaLink.ConfigurationDatabase.Migrations
{
    /// <summary>
    /// Adds the <c>ParentExecutionId</c> correlation column to the centralized
    /// <c>AuditLog</c> table (#23). <c>ParentExecutionId</c> carries the
    /// <c>ExecutionId</c> of the execution that spawned this run, letting a
    /// spawned execution point back at its spawner — a sibling to the universal
    /// per-run <c>ExecutionId</c>.
    ///
    /// The change is purely additive:
    /// 1. <c>ParentExecutionId uniqueidentifier NULL</c> is added with no default,
    ///    so the operation is a metadata-only <c>ALTER TABLE … ADD</c> — it does
    ///    NOT rewrite the monthly-partitioned <c>AuditLog</c> table, and
    ///    historical rows stay <c>NULL</c> (no backfill).
    /// 2. <c>IX_AuditLog_ParentExecution</c> is created via raw SQL so it lands on
    ///    the <c>ps_AuditLog_Month(OccurredAtUtc)</c> partition scheme, matching
    ///    every other <c>IX_AuditLog_*</c> index. Keeping it partition-aligned
    ///    preserves the partition-switch purge path (see
    ///    AuditLogRepository.SwitchOutPartitionAsync).
    /// </summary>
    public partial class AddAuditLogParentExecutionId : Migration
    {
        /// <inheritdoc />
        protected override void Up(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.AddColumn<Guid>(
                name: "ParentExecutionId",
                table: "AuditLog",
                type: "uniqueidentifier",
                nullable: true);

            // Raw SQL so the index is created on the partition scheme — EF's
            // CreateIndex cannot express the ON ps_AuditLog_Month(OccurredAtUtc)
            // clause. Mirrors IX_AuditLog_Execution (filtered, aligned).
            migrationBuilder.Sql(@"
CREATE NONCLUSTERED INDEX IX_AuditLog_ParentExecution
ON dbo.AuditLog (ParentExecutionId)
WHERE ParentExecutionId IS NOT NULL
ON ps_AuditLog_Month(OccurredAtUtc);");
        }

        /// <inheritdoc />
        protected override void Down(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.Sql(@"
IF EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_AuditLog_ParentExecution' AND object_id = OBJECT_ID('dbo.AuditLog'))
    DROP INDEX IX_AuditLog_ParentExecution ON dbo.AuditLog;");

            migrationBuilder.DropColumn(
                name: "ParentExecutionId",
                table: "AuditLog");
        }
    }
}