using Invercargill.DataStructures;
using Invercargill.Expressions;
using InvercargillSql.Dialects;
using InvercargillSql.Orm;

namespace InvercargillSql.Orm.Projections {
    
    /**
     * Query builder for projection types.
     * 
     * ProjectionQuery<TProjection> provides a fluent interface for building
     * database queries that return projection objects instead of full entities.
     * It supports WHERE clauses, ORDER BY, LIMIT, and OFFSET.
     * 
     * The key difference from EntityQuery<T> is that ProjectionQuery uses the
     * ProjectionSqlBuilder to generate SQL that includes JOINs and aggregates
     * based on the projection definition.
     * 
     * Example usage:
     * {{{
     * var results = session.projection_query<UserOrderStats>()
     *     .where("user_id > 100")
     *     .or_where("order_count >= 5")
     *     .order_by_desc("total_spent")
     *     .limit(10)
     *     .materialise();
     * }}}
     * 
     * Note: This class extends Query<TProjection> and uses the base class
     * for common query operations. The where_expr() method is not supported
     * for projections - use where() with string expressions instead.
     * 
     * @param TProjection The projection result type
     */
    public class ProjectionQuery<TProjection> : Query<TProjection> {
        
        /**
         * The projection definition for building SQL.
         */
        private ProjectionDefinition _query_definition;
        
        /**
         * The SQL builder for this projection.
         */
        private ProjectionSqlBuilder _query_sql_builder;
        
        /**
         * Creates a new ProjectionQuery.
         * 
         * This constructor is internal - use OrmSession.projection_query<T>() 
         * to create queries.
         * 
         * @param session The OrmSession that will execute this query
         * @param definition The projection definition
         * @param sql_builder The SQL builder for this projection
         */
        internal ProjectionQuery(
            OrmSession session, 
            ProjectionDefinition definition,
            ProjectionSqlBuilder sql_builder
        ) {
            base(session);  // Initialize base class with session
            _query_definition = definition;
            _query_sql_builder = sql_builder;
        }
        
        // === Abstract property implementations ===
        
        /**
         * The filter expression for this query.
         * 
         * Returns null for projection queries which use string-based where clauses
         * stored in _where_clauses from the base class.
         */
        internal override Expression? filter {
            get { return null; }
        }
        
        /**
         * The ORDER BY clauses for this query.
         * 
         * Returns the _orderings vector from the base class.
         */
        internal override Vector<OrderByClause> orderings {
            get { return _orderings; }
        }
        
        /**
         * The LIMIT value for this query, or null if not set.
         * 
         * Returns the _limit value from the base class.
         */
        internal override int64? limit_value {
            get { return _limit; }
        }
        
        /**
         * The OFFSET value for this query, or null if not set.
         * 
         * Returns the _offset value from the base class.
         */
        internal override int64? offset_value {
            get { return _offset; }
        }
        
        // === Abstract method implementations ===
        
        /**
         * Adds a WHERE clause using a pre-parsed Expression.
         *
         * This method is not supported for projection queries because they
         * need to translate expressions through the projection definition.
         * Use where() with a string expression instead.
         *
         * Note: This method always throws an error. The base class doesn't declare
         * throws, so we throw without declaration - callers should be aware this
         * method may fail at runtime.
         *
         * @param expression The filter expression
         * @return This query for method chaining (never returns - always throws)
         */
        public override Query<TProjection> where_expr(Expression expression) {
            // Throw without declaration - base class doesn't declare throws
            throw new SqlError.GENERAL_ERROR(
                "ProjectionQuery does not support where_expr(). Use where() with a string expression instead."
            );
        }
        
        /**
         * Materializes results synchronously.
         * 
         * Executes the query and returns all matching projections.
         * 
         * @return An ImmutableLot of TProjection instances
         * @throws SqlError if query execution fails
         */
        public override Invercargill.ImmutableLot<TProjection> materialise() throws SqlError {
            // Build the SQL using the projection SQL builder
            // Uses get_combined_where() from base class
            string? where_expr = get_combined_where();
            
            BuiltQuery built = _query_sql_builder.build_with_split(
                where_expr,
                _orderings,  // Use base class field
                _limit,      // Use base class field
                _offset      // Use base class field
            );
            
            string sql = built.sql;
            
            // Execute through session's connection using _session from base class
            var connection = _session.get_connection();
            var command = connection.create_command(sql);
            var results = command.execute_query();
            
            // Materialize the results using the projection mapper
            var mapper = new ProjectionMapper<TProjection>(_query_definition);
            
            try {
                var vector = mapper.map_all(results);
                return vector.to_immutable_buffer();
            } catch (ProjectionError e) {
                throw new SqlError.GENERAL_ERROR(
                    @"Failed to materialize projection: $(e.message)"
                );
            }
        }
        
        /**
         * Materializes results asynchronously.
         *
         * Executes the query asynchronously and returns all matching projections.
         * Uses the async/yield pattern to properly propagate async behavior.
         *
         * @return An ImmutableLot of TProjection instances
         * @throws SqlError if query execution fails
         */
        public override async Invercargill.ImmutableLot<TProjection> materialise_async() throws SqlError {
            // Build the SQL using the projection SQL builder
            // Uses get_combined_where() from base class
            string? where_expr = get_combined_where();
            
            BuiltQuery built = _query_sql_builder.build_with_split(
                where_expr,
                _orderings,  // Use base class field
                _limit,      // Use base class field
                _offset      // Use base class field
            );
            
            string sql = built.sql;
            
            // Execute through session's connection using _session from base class
            var connection = _session.get_connection();
            var command = connection.create_command(sql);
            
            // Execute asynchronously using yield
            var results = yield command.execute_query_async();
            
            // Materialize the results using the projection mapper
            var mapper = new ProjectionMapper<TProjection>(_query_definition);
            
            try {
                var vector = mapper.map_all(results);
                return vector.to_immutable_buffer();
            } catch (ProjectionError e) {
                throw new SqlError.GENERAL_ERROR(
                    @"Failed to materialize projection: $(e.message)"
                );
            }
        }
        
        /**
         * Gets the SQL for this query.
         * 
         * This method is useful for debugging and logging.
         * 
         * @return The SQL SELECT statement
         */
        public override string to_sql() {
            // Uses get_combined_where() from base class
            string? where_expr = get_combined_where();
            
            BuiltQuery built = _query_sql_builder.build_with_split(
                where_expr,
                _orderings,  // Use base class field
                _limit,      // Use base class field
                _offset      // Use base class field
            );
            
            return built.sql;
        }
        
        // === Internal accessor methods for compatibility ===
        
        /**
         * Gets the projection definition for this query.
         * 
         * @return The ProjectionDefinition
         */
        internal ProjectionDefinition get_definition() {
            return _query_definition;
        }
        
        /**
         * Gets the SQL builder for this query.
         * 
         * @return The ProjectionSqlBuilder
         */
        internal ProjectionSqlBuilder get_sql_builder() {
            return _query_sql_builder;
        }
        
        /**
         * Gets the WHERE clauses for this query.
         * 
         * Returns the _where_clauses vector from the base class.
         * 
         * @return The Vector of WHERE expressions
         */
        internal Vector<string> get_where_clauses() {
            return _where_clauses;
        }
        
        /**
         * Gets the ORDER BY clauses for this query.
         * 
         * Returns the _orderings vector from the base class.
         * 
         * @return The Vector of OrderByClause
         */
        internal Vector<OrderByClause> get_order_by_clauses() {
            return _orderings;
        }
        
        /**
         * Gets the LIMIT value for this query.
         * 
         * Returns the _limit value from the base class.
         * 
         * @return The LIMIT value, or null if not set
         */
        internal int64? get_limit_value() {
            return _limit;
        }
        
        /**
         * Gets the OFFSET value for this query.
         * 
         * Returns the _offset value from the base class.
         * 
         * @return The OFFSET value, or null if not set
         */
        internal int64? get_offset_value() {
            return _offset;
        }
        
        /**
         * Gets whether OR logic is used for WHERE clauses.
         * 
         * Returns the _use_or value from the base class.
         * 
         * @return True if OR logic is used
         */
        internal bool get_use_or() {
            return _use_or;
        }
    }
}