Invercargill-Sql/src/orm/projections/projection-mapper.vala

using Invercargill.DataStructures;

namespace InvercargillSql.Orm.Projections {
    
    /**
     * Materializes projection results from database rows.
     * 
     * ProjectionMapper takes the results of a projection query (as Properties collections)
     * and materializes them into projection objects. It handles:
     * - Simple scalar properties (int, string, double, etc.)
     * - Nested projection objects (select_one) - limited support
     * - Collection properties (select_many) - placeholder for future implementation
     * 
     * The mapper uses the ProjectionDefinition to determine how to map each column
     * to the corresponding property on the projection type.
     * 
     * Example usage:
     * {{{
     * var mapper = new ProjectionMapper<UserStats>(definition);
     * var results = mapper.map_all(query_results);
     * }}}
     * 
     * @param TProjection The projection result type
     */
    public class ProjectionMapper<TProjection> : Object {
        
        /**
         * The projection definition containing selection mappings.
         */
        private ProjectionDefinition _mapper_definition;
        
        /**
         * Creates a new ProjectionMapper for the given definition.
         * 
         * @param definition The ProjectionDefinition describing how to map results
         */
        public ProjectionMapper(ProjectionDefinition definition) {
            _mapper_definition = definition;
        }
        
        /**
         * Creates a new instance of the projection type.
         *
         * Uses GObject's Object.new() to create instances.
         *
         * @return A new TProjection instance
         * @throws ProjectionError if instance creation fails
         */
        public TProjection create_instance() throws ProjectionError {
            var type = typeof(TProjection);
            
            if (type.is_object()) {
                var obj = Object.new(type);
                // In Vala, we can't use 'as TProjection' directly for generics
                // Instead, we return the object and rely on the type system
                return (TProjection)obj;
            }
            
            throw new ProjectionError.NESTED_RESOLUTION_FAILED(
                @"Failed to create instance of type $(type.name())"
            );
        }
        
        /**
         * Maps a single database row to a projection instance.
         * 
         * This method takes a Properties collection (representing a database row)
         * and creates a new TProjection instance with all properties populated.
         * 
         * @param row The Properties collection from a database query
         * @return A new TProjection instance
         * @throws ProjectionError if mapping fails
         */
        public TProjection map_row(Invercargill.Properties row) throws ProjectionError {
            var instance = create_instance();
            var obj = instance as Object;
            if (obj == null) {
                throw new ProjectionError.NESTED_RESOLUTION_FAILED(
                    "Projection instance is not a GObject"
                );
            }
            
            // Map each selection from the definition
            foreach (var selection in _mapper_definition.selections) {
                map_selection_to_object(obj, selection, row);
            }
            
            return instance;
        }
        
        /**
         * Maps all rows to projection instances.
         * 
         * This method iterates through all rows in the result set and
         * materializes each one as a TProjection instance.
         * 
         * For projections with collections (select_many), this method also
         * performs client-side grouping to consolidate related rows.
         * 
         * @param results An Enumerable of Properties collections
         * @return A Vector of TProjection instances
         * @throws ProjectionError if mapping fails
         */
        public Vector<TProjection> map_all(Invercargill.Enumerable<Invercargill.Properties> results) 
            throws ProjectionError {
            
            var mapped_results = new Vector<TProjection>();
            
            // Check if we have any collection selections that need grouping
            bool needs_grouping = false;
            foreach (var selection in _mapper_definition.selections) {
                if (selection is CollectionProjectionSelection) {
                    needs_grouping = true;
                    break;
                }
            }
            
            if (needs_grouping) {
                // For now, use simple mapping without grouping
                // TODO: Implement proper grouping when needed
                foreach (var row in results) {
                    mapped_results.add(map_row(row));
                }
            } else {
                // Simple case: each row maps to one projection
                foreach (var row in results) {
                    mapped_results.add(map_row(row));
                }
            }
            
            return mapped_results;
        }
        
        /**
         * Maps a selection to a generic Object instance.
         * 
         * This method dispatches to the appropriate handler based on the
         * selection type (ScalarSelection, NestedProjectionSelection, or
         * CollectionProjectionSelection).
         * 
         * @param instance The Object instance to populate
         * @param selection The selection definition
         * @param row The database row data
         * @throws ProjectionError if mapping fails
         */
        private void map_selection_to_object(
            Object instance,
            SelectionDefinition selection,
            Invercargill.Properties row
        ) throws ProjectionError {
            
            // Check if this is a scalar selection (has value_type that's not a projection)
            var nested_type = selection.nested_projection_type;
            
            if (nested_type == null) {
                // Scalar selection
                map_scalar_selection(instance, selection, row);
            } else {
                // Check if it's a collection or nested projection
                // For now, treat all nested types as scalar objects
                map_scalar_selection(instance, selection, row);
            }
        }
        
        /**
         * Maps a scalar selection to a property.
         * 
         * Scalar selections represent simple values like int, string, double, etc.
         * The value is extracted from the row, converted to the appropriate type,
         * and set on the projection instance.
         * 
         * @param instance The Object instance
         * @param selection The selection definition
         * @param row The database row data
         * @throws ProjectionError if mapping fails
         */
        private void map_scalar_selection(
            Object instance,
            SelectionDefinition selection,
            Invercargill.Properties row
        ) throws ProjectionError {
            
            string column_name = selection.friendly_name;
            
            // Try to get the value from the row
            var element = row.get(column_name);
            if (element == null) {
                // Value not present in row - could be null or missing column
                return;
            }
            
            // Get the value from the element
            Value? val = extract_value_from_element(element, selection.value_type);
            if (val == null) {
                return;
            }
            
            // Set the property on the instance
            set_property_on_object(instance, selection.friendly_name, val);
        }
        
        /**
         * Extracts a value from an Element, converting to the target type.
         *
         * Uses the Element's try_get_as<T>() method for type-safe extraction.
         *
         * @param element The Element containing the value
         * @param target_type The target Vala type
         * @return The converted Value, or null if conversion fails
         */
        private Value? extract_value_from_element(
            Invercargill.Element element,
            Type target_type
        ) {
            if (element.is_null()) {
                return null;
            }
            
            Value result = Value(target_type);
            
            // Use try_get_as for type-safe extraction
            if (target_type == typeof(int64)) {
                int64? val = null;
                if (element.try_get_as<int64?>(out val) && val != null) {
                    result.set_int64(val);
                    return result;
                }
            } else if (target_type == typeof(int)) {
                int? val = null;
                if (element.try_get_as<int>(out val) && val != null) {
                    result.set_int(val);
                    return result;
                }
            } else if (target_type == typeof(long)) {
                long? val = null;
                if (element.try_get_as<long>(out val) && val != null) {
                    result.set_long(val);
                    return result;
                }
            } else if (target_type == typeof(double)) {
                double? val = null;
                if (element.try_get_as<double?>(out val) && val != null) {
                    result.set_double(val);
                    return result;
                }
            } else if (target_type == typeof(float)) {
                float? val = null;
                if (element.try_get_as<float?>(out val) && val != null) {
                    result.set_float(val);
                    return result;
                }
            } else if (target_type == typeof(string)) {
                string? val = null;
                if (element.try_get_as<string>(out val) && val != null) {
                    result.set_string(val);
                    return result;
                }
            } else if (target_type == typeof(bool)) {
                bool? val = null;
                if (element.try_get_as<bool>(out val) && val != null) {
                    result.set_boolean(val);
                    return result;
                }
            } else if (target_type == typeof(DateTime)) {
                DateTime? val = null;
                if (element.try_get_as<DateTime>(out val) && val != null) {
                    result.set_boxed(val);
                    return result;
                }
            } else if (target_type == typeof(Invercargill.BinaryData)) {
                Invercargill.BinaryData? val = null;
                if (element.try_get_as<Invercargill.BinaryData>(out val) && val != null) {
                    result.set_object(val as Object);
                    return result;
                }
            } else if (target_type.is_object()) {
                // For other object types, try direct object extraction
                Object? val = null;
                if (element.try_get_as<Object>(out val) && val != null) {
                    result.set_object(val);
                    return result;
                }
            }
            
            // Fallback: could not convert
            return null;
        }
        
        /**
         * Converts a value to the target type.
         *
         * This is a secondary conversion method for when we already have a Value
         * but need it in a different type.
         *
         * @param raw_value The raw value
         * @param target_type The target Vala type
         * @return The converted Value
         */
        private Value convert_value(Value raw_value, Type target_type) {
            Value result = Value(target_type);
            
            if (target_type == typeof(int64)) {
                if (raw_value.type() == typeof(int64)) {
                    result.set_int64(raw_value.get_int64());
                } else if (raw_value.type() == typeof(int)) {
                    result.set_int64((int64)raw_value.get_int());
                } else if (raw_value.type() == typeof(long)) {
                    result.set_int64((int64)raw_value.get_long());
                } else if (raw_value.type() == typeof(string)) {
                    int64 parsed = 0;
                    if (int64.try_parse(raw_value.get_string(), out parsed)) {
                        result.set_int64(parsed);
                    }
                } else {
                    result.set_int64(raw_value.get_int64());
                }
            } else if (target_type == typeof(int)) {
                if (raw_value.type() == typeof(int64)) {
                    result.set_int((int)raw_value.get_int64());
                } else if (raw_value.type() == typeof(int)) {
                    result.set_int(raw_value.get_int());
                } else {
                    result.set_int((int)raw_value.get_int64());
                }
            } else if (target_type == typeof(double)) {
                if (raw_value.type() == typeof(double)) {
                    result.set_double(raw_value.get_double());
                } else if (raw_value.type() == typeof(float)) {
                    result.set_double((double)raw_value.get_float());
                } else if (raw_value.type() == typeof(string)) {
                    double parsed = 0.0;
                    if (double.try_parse(raw_value.get_string(), out parsed)) {
                        result.set_double(parsed);
                    }
                } else {
                    result.set_double(raw_value.get_double());
                }
            } else if (target_type == typeof(float)) {
                if (raw_value.type() == typeof(double)) {
                    result.set_float((float)raw_value.get_double());
                } else if (raw_value.type() == typeof(float)) {
                    result.set_float(raw_value.get_float());
                } else {
                    result.set_float((float)raw_value.get_double());
                }
            } else if (target_type == typeof(string)) {
                if (raw_value.type() == typeof(string)) {
                    result.set_string(raw_value.get_string());
                } else if (raw_value.type() == typeof(int64)) {
                    result.set_string(raw_value.get_int64().to_string());
                } else if (raw_value.type() == typeof(double)) {
                    result.set_string(raw_value.get_double().to_string());
                } else if (raw_value.type() == typeof(bool)) {
                    result.set_string(raw_value.get_boolean() ? "true" : "false");
                }
            } else if (target_type == typeof(bool)) {
                if (raw_value.type() == typeof(int64)) {
                    result.set_boolean(raw_value.get_int64() != 0);
                } else if (raw_value.type() == typeof(int)) {
                    result.set_boolean(raw_value.get_int() != 0);
                } else if (raw_value.type() == typeof(bool)) {
                    result.set_boolean(raw_value.get_boolean());
                } else {
                    result.set_boolean(raw_value.get_boolean());
                }
            } else if (target_type.is_object()) {
                result.set_object(raw_value.get_object());
            } else {
                result = raw_value;
            }
            
            return result;
        }
        
        /**
         * Sets a property value on a generic Object instance.
         * 
         * @param instance The Object instance
         * @param property_name The property name
         * @param value The value to set
         */
        private void set_property_on_object(Object instance, string property_name, Value value) {
            string gobject_name = friendly_name_to_property_name_for_type(
                instance.get_type(), 
                property_name
            );
            
            var obj_class = (ObjectClass)instance.get_type().class_ref();
            var spec = obj_class.find_property(gobject_name);
            
            if (spec != null) {
                Value converted = convert_value(value, spec.value_type);
                instance.set_property(gobject_name, converted);
            }
        }
        
        /**
         * Converts a friendly_name to a GObject property name for a specific type.
         * 
         * @param type The GObject type
         * @param friendly_name The friendly name
         * @return The GObject property name
         */
        private string friendly_name_to_property_name_for_type(Type type, string friendly_name) {
            var obj_class = (ObjectClass)type.class_ref();
            
            // Try as-is
            if (obj_class.find_property(friendly_name) != null) {
                return friendly_name;
            }
            
            // Try kebab-case
            string kebab_case = friendly_name.replace("_", "-");
            if (obj_class.find_property(kebab_case) != null) {
                return kebab_case;
            }
            
            // Try camelCase
            string camel_case = snake_to_camel(friendly_name);
            if (obj_class.find_property(camel_case) != null) {
                return camel_case;
            }
            
            return friendly_name;
        }
        
        /**
         * Converts a snake_case string to camelCase.
         * 
         * @param snake The snake_case string
         * @return The camelCase version
         */
        private string snake_to_camel(string snake) {
            var result = new StringBuilder();
            bool capitalize_next = false;
            
            for (int i = 0; i < snake.length; i++) {
                char c = snake[i];
                
                if (c == '_') {
                    capitalize_next = true;
                } else {
                    if (capitalize_next) {
                        result.append_c(c.toupper());
                        capitalize_next = false;
                    } else {
                        result.append_c(c);
                    }
                }
            }
            
            return result.str;
        }
        
        /**
         * Gets the projection definition.
         * 
         * @return The ProjectionDefinition
         */
        internal ProjectionDefinition definition {
            get { return _mapper_definition; }
            set { _mapper_definition = value; }
        }
    }
}