using Microsoft.EntityFrameworkCore.Migrations;

#nullable disable

namespace ScadaLink.ConfigurationDatabase.Migrations
{
    /// <summary>
    /// Bundle C (#23 M1): creates the centralized AuditLog table with monthly
    /// partitioning and the two access-control roles documented in alog.md §4.
    ///
    /// Structure:
    /// 1. Partition function <c>pf_AuditLog_Month</c> (RANGE RIGHT) with 24
    ///    monthly boundaries covering 2026-01-01 through 2027-12-01 UTC.
    /// 2. Partition scheme <c>ps_AuditLog_Month</c> mapping every partition to
    ///    [PRIMARY] (dev/test parity; production may relocate via filegroups).
    /// 3. <c>AuditLog</c> table created via raw SQL so it is created directly
    ///    on the partition scheme. The clustered PK is composite
    ///    {EventId, OccurredAtUtc} — required because partition-aligned PKs
    ///    must include the partition column.
    /// 4. Five reconciliation/query indexes from alog.md §4, plus the
    ///    UX_AuditLog_EventId unique index that preserves single-column
    ///    EventId uniqueness for InsertIfNotExistsAsync (M1-T8). All
    ///    non-clustered indexes are partition-aligned on
    ///    <c>ps_AuditLog_Month(OccurredAtUtc)</c>.
    /// 5. Two database roles:
    ///    - <c>scadalink_audit_writer</c>: INSERT + SELECT on AuditLog, with
    ///      explicit DENY on UPDATE and DELETE so additive role membership
    ///      (e.g. later db_datawriter) cannot accidentally re-enable mutation.
    ///    - <c>scadalink_audit_purger</c>: SELECT on AuditLog and ALTER on
    ///      SCHEMA::dbo so the purger can run ALTER PARTITION FUNCTION SWITCH
    ///      and SWITCH PARTITION when sliding the retention window.
    /// </summary>
    public partial class AddAuditLogTable : Migration
    {
        /// <inheritdoc />
        protected override void Up(MigrationBuilder migrationBuilder)
        {
            // 1) Partition function (monthly boundaries Jan 2026 – Dec 2027 UTC).
            //    RANGE RIGHT — the boundary value belongs to the right-hand partition,
            //    matching the convention used by SQL Server partition-switch tooling.
            migrationBuilder.Sql(@"
CREATE PARTITION FUNCTION pf_AuditLog_Month (datetime2(7))
AS RANGE RIGHT FOR VALUES (
  '2026-01-01T00:00:00', '2026-02-01T00:00:00', '2026-03-01T00:00:00', '2026-04-01T00:00:00',
  '2026-05-01T00:00:00', '2026-06-01T00:00:00', '2026-07-01T00:00:00', '2026-08-01T00:00:00',
  '2026-09-01T00:00:00', '2026-10-01T00:00:00', '2026-11-01T00:00:00', '2026-12-01T00:00:00',
  '2027-01-01T00:00:00', '2027-02-01T00:00:00', '2027-03-01T00:00:00', '2027-04-01T00:00:00',
  '2027-05-01T00:00:00', '2027-06-01T00:00:00', '2027-07-01T00:00:00', '2027-08-01T00:00:00',
  '2027-09-01T00:00:00', '2027-10-01T00:00:00', '2027-11-01T00:00:00', '2027-12-01T00:00:00'
);");

            // 2) Partition scheme mapping every partition to [PRIMARY].
            migrationBuilder.Sql(@"
CREATE PARTITION SCHEME ps_AuditLog_Month
AS PARTITION pf_AuditLog_Month ALL TO ([PRIMARY]);");

            // 3) Create the table directly on the partition scheme. Column shapes
            //    are copied from AuditLogEntityTypeConfiguration so the live schema
            //    matches the EF model exactly. The clustered PK is composite to
            //    satisfy SQL Server's rule that partition-aligned clustered indexes
            //    must include the partition column.
            migrationBuilder.Sql(@"
CREATE TABLE dbo.AuditLog (
    EventId            uniqueidentifier NOT NULL,
    OccurredAtUtc      datetime2(7)     NOT NULL,
    IngestedAtUtc      datetime2(7)     NULL,
    Channel            varchar(32)      NOT NULL,
    Kind               varchar(32)      NOT NULL,
    CorrelationId      uniqueidentifier NULL,
    SourceSiteId       varchar(64)      NULL,
    SourceInstanceId   varchar(128)     NULL,
    SourceScript       varchar(128)     NULL,
    Actor              varchar(128)     NULL,
    Target             varchar(256)     NULL,
    Status             varchar(32)      NOT NULL,
    HttpStatus         int              NULL,
    DurationMs         int              NULL,
    ErrorMessage       nvarchar(1024)   NULL,
    ErrorDetail        nvarchar(max)    NULL,
    RequestSummary     nvarchar(max)    NULL,
    ResponseSummary    nvarchar(max)    NULL,
    PayloadTruncated   bit              NOT NULL,
    Extra              nvarchar(max)    NULL,
    ForwardState       varchar(32)      NULL,
    CONSTRAINT PK_AuditLog PRIMARY KEY CLUSTERED (EventId, OccurredAtUtc)
        ON ps_AuditLog_Month(OccurredAtUtc)
) ON ps_AuditLog_Month(OccurredAtUtc);");

            // 4) Reconciliation/query indexes from alog.md §4. All non-clustered
            //    indexes are partition-aligned on ps_AuditLog_Month(OccurredAtUtc)
            //    so partition-switch operations only touch a single partition. The
            //    filtered indexes carry their NOT NULL predicates as documented.
            migrationBuilder.Sql(@"
CREATE NONCLUSTERED INDEX IX_AuditLog_OccurredAtUtc
ON dbo.AuditLog (OccurredAtUtc DESC)
ON ps_AuditLog_Month(OccurredAtUtc);");

            migrationBuilder.Sql(@"
CREATE NONCLUSTERED INDEX IX_AuditLog_Site_Occurred
ON dbo.AuditLog (SourceSiteId ASC, OccurredAtUtc DESC)
ON ps_AuditLog_Month(OccurredAtUtc);");

            migrationBuilder.Sql(@"
CREATE NONCLUSTERED INDEX IX_AuditLog_CorrelationId
ON dbo.AuditLog (CorrelationId)
WHERE CorrelationId IS NOT NULL
ON ps_AuditLog_Month(OccurredAtUtc);");

            migrationBuilder.Sql(@"
CREATE NONCLUSTERED INDEX IX_AuditLog_Channel_Status_Occurred
ON dbo.AuditLog (Channel ASC, Status ASC, OccurredAtUtc DESC)
ON ps_AuditLog_Month(OccurredAtUtc);");

            migrationBuilder.Sql(@"
CREATE NONCLUSTERED INDEX IX_AuditLog_Target_Occurred
ON dbo.AuditLog (Target ASC, OccurredAtUtc DESC)
WHERE Target IS NOT NULL
ON ps_AuditLog_Month(OccurredAtUtc);");

            // The EventId uniqueness index supports InsertIfNotExistsAsync
            // (M1-T8). It is INTENTIONALLY non-aligned (placed on [PRIMARY]
            // rather than ps_AuditLog_Month).
            //
            // SQL Server's rule for unique partition-aligned indexes is that the
            // partition column must be a SUBSET of the index key. Including
            // OccurredAtUtc in the key would change the uniqueness semantics
            // from "EventId is globally unique" to "(EventId, OccurredAtUtc)
            // is unique", which is the same guarantee the composite PK already
            // provides — it would not give us single-column EventId uniqueness.
            //
            // Trade-off: a non-aligned index disables ALTER TABLE … SWITCH
            // PARTITION on AuditLog. The M1 purge story (M2/M3) uses an
            // explicit rebuild path that drops and re-creates this index
            // around the switch, so the aligned-indexes pattern is preserved
            // for partition switching at purge time.
            migrationBuilder.Sql(@"
CREATE UNIQUE NONCLUSTERED INDEX UX_AuditLog_EventId
ON dbo.AuditLog (EventId)
ON [PRIMARY];");

            // 5) DB roles. Both definitions are idempotent so the migration is
            //    safe to re-apply against a database that already has the role.
            //    The DENY UPDATE / DENY DELETE on the writer role is deliberate —
            //    a future db_datawriter membership cannot quietly re-enable
            //    mutation because DENY outranks GRANT.
            migrationBuilder.Sql(@"
IF DATABASE_PRINCIPAL_ID('scadalink_audit_writer') IS NULL
    EXEC sp_executesql N'CREATE ROLE scadalink_audit_writer';
GRANT INSERT ON dbo.AuditLog TO scadalink_audit_writer;
GRANT SELECT ON dbo.AuditLog TO scadalink_audit_writer;
DENY UPDATE ON dbo.AuditLog TO scadalink_audit_writer;
DENY DELETE ON dbo.AuditLog TO scadalink_audit_writer;");

            migrationBuilder.Sql(@"
IF DATABASE_PRINCIPAL_ID('scadalink_audit_purger') IS NULL
    EXEC sp_executesql N'CREATE ROLE scadalink_audit_purger';
GRANT SELECT ON dbo.AuditLog TO scadalink_audit_purger;
GRANT ALTER ON SCHEMA::dbo TO scadalink_audit_purger;");
        }

        /// <inheritdoc />
        protected override void Down(MigrationBuilder migrationBuilder)
        {
            // Drop in reverse dependency order so each statement's prerequisites
            // still exist when it runs. Each DROP is guarded so a partial Up()
            // (or a re-applied Down()) cannot fail on missing objects.
            migrationBuilder.Sql(@"
IF DATABASE_PRINCIPAL_ID('scadalink_audit_purger') IS NOT NULL
    EXEC sp_executesql N'DROP ROLE scadalink_audit_purger';
IF DATABASE_PRINCIPAL_ID('scadalink_audit_writer') IS NOT NULL
    EXEC sp_executesql N'DROP ROLE scadalink_audit_writer';");

            // Indexes are dropped implicitly when the table goes away, but
            // dropping them explicitly first keeps the Down() statement self-
            // describing and mirrors the Up() shape.
            migrationBuilder.Sql(@"
IF EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'UX_AuditLog_EventId' AND object_id = OBJECT_ID('dbo.AuditLog'))
    DROP INDEX UX_AuditLog_EventId ON dbo.AuditLog;
IF EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_AuditLog_Target_Occurred' AND object_id = OBJECT_ID('dbo.AuditLog'))
    DROP INDEX IX_AuditLog_Target_Occurred ON dbo.AuditLog;
IF EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_AuditLog_Channel_Status_Occurred' AND object_id = OBJECT_ID('dbo.AuditLog'))
    DROP INDEX IX_AuditLog_Channel_Status_Occurred ON dbo.AuditLog;
IF EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_AuditLog_CorrelationId' AND object_id = OBJECT_ID('dbo.AuditLog'))
    DROP INDEX IX_AuditLog_CorrelationId ON dbo.AuditLog;
IF EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_AuditLog_Site_Occurred' AND object_id = OBJECT_ID('dbo.AuditLog'))
    DROP INDEX IX_AuditLog_Site_Occurred ON dbo.AuditLog;
IF EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_AuditLog_OccurredAtUtc' AND object_id = OBJECT_ID('dbo.AuditLog'))
    DROP INDEX IX_AuditLog_OccurredAtUtc ON dbo.AuditLog;");

            migrationBuilder.Sql(@"
IF OBJECT_ID('dbo.AuditLog', 'U') IS NOT NULL
    DROP TABLE dbo.AuditLog;");

            migrationBuilder.Sql(@"
IF EXISTS (SELECT 1 FROM sys.partition_schemes WHERE name = 'ps_AuditLog_Month')
    DROP PARTITION SCHEME ps_AuditLog_Month;
IF EXISTS (SELECT 1 FROM sys.partition_functions WHERE name = 'pf_AuditLog_Month')
    DROP PARTITION FUNCTION pf_AuditLog_Month;");
        }
    }
}