using System.Data.Common;
using FrameworkBLL.Connection;

namespace FrameworkBLL.Engine
{
    // ConflictPolicy values mirror TDSYNCJOB.CONFLICTPOLICY tinyint:
    //   0 = Overwrite  — DELETE target rows WHERE PK IN (chunk PKs), then INSERT all
    //   1 = Skip       — INSERT only if PK absent in target
    //   2 = LastWriteWins — write only if source.ModifiedOn > target.ModifiedOn; insert if absent
    public enum ConflictPolicy : byte { Overwrite = 0, Skip = 1, LastWriteWins = 2 }

    public interface ISyncEngine
    {
        // Streams source rows in configurable-sized pages — never loads the full table.
        // selectSql must already contain ORDER BY and OFFSET/FETCH NEXT @ChunkSize parameters.
        IAsyncEnumerable<IEnumerable<IDictionary<string, object?>>> StreamPagedAsync(
            DbConnection conn, string selectSql, int chunkSize, IDictionary<string, object?> baseParams,
            CancellationToken ct);

        // Applies one chunk to the target using the specified conflict resolution strategy.
        // Returns number of rows written (inserted + updated).
        // srcDbType is required for TypeNormalizer; tgtDbType drives identifier quoting.
        Task<int> ApplyChunkToTargetAsync(
            DbConnection targetConn,
            string schemaName,
            string tableName,
            IEnumerable<IDictionary<string, object?>> chunk,
            string pkColumn,
            ConflictPolicy policy,
            string? modifiedDateColumn,
            DatabaseType srcDbType,
            DatabaseType tgtDbType,
            CancellationToken ct);

        // Detects deletes via CDC for SQL Server or ISDELETED propagation for other engines.
        // tgtDbType drives identifier quoting on the target DELETE statement.
        Task<int> ApplyDeletesAsync(
            DbConnection sourceConn,
            DbConnection targetConn,
            string schemaName,
            string tableName,
            string pkColumn,
            DateTime sinceUtc,
            DatabaseType sourceDbType,
            DatabaseType tgtDbType,
            CancellationToken ct);
    }

    // DatabaseType mirrors MDBTYPE.DBTYPEID
    public enum DatabaseType : int { SqlServer = 1, PostgreSQL = 2, MySQL = 3, Oracle = 4 }
}