using Invercargill.DataStructures;
using Invercargill.Expressions;

namespace InvercargillSql.Orm.Projections {
    
    /**
     * Result of resolving a nested property path.
     * 
     * When navigating into nested projections (e.g., "profile.id"), this class
     * holds information about the nested selection and the resolved path.
     * 
     * Example:
     * {{{
     * // For a projection with:
     * // .select<ProfileSummary>("profile", expr("pr"), ...)
     * 
     * var resolution = resolver.resolve_nested_property("profile.id");
     * // resolution.selection refers to the ProfileSummary selection
     * // resolution.remaining_path == "id"
     * // resolution.resolved_expression is an Expression representing "pr.id"
     * }}}
     */
    public class NestedResolution : Object {
        /**
         * The selection definition for the nested projection.
         * 
         * This is the selection that corresponds to the first segment
         * of the property path (e.g., "profile" in "profile.id").
         */
        public SelectionDefinition selection { get; construct; }
        
        /**
         * The type of the nested projection.
         * 
         * For NestedProjectionSelection, this is the TNested type.
         * For CollectionProjectionSelection, this is the TItem type.
         */
        public Type nested_projection_type { get; construct; }
        
        /**
         * The remaining path after the first segment.
         * 
         * For "profile.id", this would be "id".
         * For "profile.address.city", this would be "address.city".
         */
        public string remaining_path { get; construct; }
        
        /**
         * The first segment of the path (the friendly name).
         * 
         * For "profile.id", this would be "profile".
         */
        public string first_segment { get; construct; }
        
        /**
         * The final resolved expression, if available.
         * 
         * This may be null if the resolution only identified the nested
         * selection but did not fully resolve the property within it.
         * 
         * This is an Expression object that can be used directly in
         * expression trees or converted to string using ExpressionStringVisitor.
         */
        public Expression? resolved_expression { get; construct; }
        
        /**
         * Indicates whether this is a nested projection (1:1).
         */
        public bool is_single_nested { get; construct; }
        
        /**
         * Indicates whether this is a collection projection (1:N).
         */
        public bool is_collection { get; construct; }
        
        /**
         * Creates a new NestedResolution.
         * 
         * @param selection The nested selection definition
         * @param nested_projection_type The type of the nested projection
         * @param remaining_path The path after the first segment
         * @param first_segment The first segment (friendly name)
         * @param resolved_expression The fully resolved Expression (optional)
         * @param is_single_nested True if this is a 1:1 nested projection
         * @param is_collection True if this is a 1:N collection projection
         */
        public NestedResolution(
            SelectionDefinition selection,
            Type nested_projection_type,
            string remaining_path,
            string first_segment,
            Expression? resolved_expression,
            bool is_single_nested,
            bool is_collection
        ) {
            Object(
                selection: selection,
                nested_projection_type: nested_projection_type,
                remaining_path: remaining_path,
                first_segment: first_segment,
                resolved_expression: resolved_expression,
                is_single_nested: is_single_nested,
                is_collection: is_collection
            );
        }
    }
    
    /**
     * Resolves friendly names to Expression objects and handles nested navigation.
     * 
     * FriendlyNameResolver provides lookup services for the friendly names
     * defined in a projection. These names are used in WHERE and ORDER BY
     * expressions to reference selection values.
     * 
     * The resolver also handles nested navigation, allowing expressions like
     * "profile.id" to reference properties within nested projections.
     * 
     * Example:
     * {{{
     * // For a projection with:
     * // .select<int64>("user_id", expr("r.id"), ...)
     * // .select<ProfileSummary>("profile", expr("pr"), ...)
     * 
     * var resolver = new FriendlyNameResolver(definition);
     * 
     * // Simple resolution - returns Expression object
     * Expression? expr = resolver.resolve_to_expression("user_id");
     * 
     * // Nested navigation
     * var nested = resolver.resolve_nested_property("profile.id");
     * // nested.first_segment == "profile"
     * // nested.remaining_path == "id"
     * 
     * // Check if name exists
     * resolver.is_friendly_name("user_id")  // true
     * }}}
     */
    public class FriendlyNameResolver : Object {
        
        /**
         * The projection definition this resolver is associated with.
         */
        private ProjectionDefinition _definition;
        
        /**
         * Cache of friendly name to Expression mappings.
         * Built lazily on first access.
         */
        private Dictionary<string, Expression>? _friendly_name_cache;
        
        /**
         * Cache of friendly name to selection mappings.
         * Built lazily on first access.
         */
        private Dictionary<string, SelectionDefinition>? _selection_cache;
        
        /**
         * Cache of all friendly names including nested ones.
         * Built lazily on first access.
         */
        private Vector<string>? _all_names_cache;
        
        /**
         * Creates a new FriendlyNameResolver for the given projection.
         * 
         * @param definition The projection definition to resolve names for
         */
        public FriendlyNameResolver(ProjectionDefinition definition) {
            _definition = definition;
        }
        
        /**
         * Resolves a friendly name to its underlying Expression.
         * 
         * For scalar selections, this returns the Expression defined in
         * the .select() call. For nested projections, this returns the
         * entry point expression.
         * 
         * @param friendly_name The friendly name to resolve
         * @return The underlying Expression, or null if not found
         */
        public Expression? resolve_to_expression(string friendly_name) {
            ensure_cache_built();
            
            // First check if it's a direct friendly name
            // Use has() before get() to avoid exception on missing key
            if (_friendly_name_cache.has(friendly_name)) {
                return _friendly_name_cache.get(friendly_name);
            }
            
            // Check if it's a nested path (e.g., "profile.id")
            int dot_index = friendly_name.index_of(".");
            if (dot_index > 0) {
                // Find the nested selection
                var nested = resolve_nested_property(friendly_name);
                if (nested != null) {
                    return nested.resolved_expression;
                }
            }
            
            return null;
        }
        
        /**
         * Resolves a nested property path.
         * 
         * This method handles paths like "profile.id" or "address.city.name"
         * by finding the nested selection and determining the remaining path.
         * 
         * @param property_path The full property path (e.g., "profile.id")
         * @return A NestedResolution with details, or null if not found
         */
        public NestedResolution? resolve_nested_property(string property_path) {
            ensure_cache_built();
            
            int dot_index = property_path.index_of(".");
            if (dot_index < 0) {
                // Not a nested path
                return null;
            }
            
            string first_segment = property_path.substring(0, dot_index);
            string remaining_path = property_path.substring(dot_index + 1);
            
            // Find the selection for the first segment
            SelectionDefinition? selection = _selection_cache[first_segment];
            if (selection == null) {
                return null;
            }
            
            // Check if it's a nested or collection projection
            Type? nested_type = selection.nested_projection_type;
            if (nested_type == null) {
                // Not a nested projection - can't navigate further
                return null;
            }
            
            // Determine if it's a single nested or collection by checking type name
            string type_name = selection.get_type().name();
            bool is_single = type_name.contains("NestedProjectionSelection");
            bool is_collection = type_name.contains("CollectionProjectionSelection");
            
            // Get the entry point expression for the nested selection
            Expression? entry_point = get_entry_point_from_selection(selection);
            
            // Build the resolved expression by combining entry point with remaining path
            Expression? resolved_expr = null;
            if (entry_point != null && remaining_path.length > 0) {
                // Create a property chain expression: entry_point.remaining_path
                resolved_expr = create_property_chain(entry_point, remaining_path);
            } else if (entry_point != null) {
                resolved_expr = entry_point;
            }
            
            return new NestedResolution(
                selection,
                nested_type,
                remaining_path,
                first_segment,
                resolved_expr,
                is_single,
                is_collection
            );
        }
        
        /**
         * Checks if a name is a known friendly name.
         * 
         * This checks only top-level friendly names, not nested paths.
         * 
         * @param name The name to check
         * @return True if the name is a defined friendly name
         */
        public bool is_friendly_name(string name) {
            ensure_cache_built();
            
            // Check for exact match first
            if (_selection_cache.has(name)) {
                return true;
            }
            
            // Check if it's a nested path with a valid first segment
            int dot_index = name.index_of(".");
            if (dot_index > 0) {
                string first_segment = name.substring(0, dot_index);
                return _selection_cache.has(first_segment);
            }
            
            return false;
        }
        
        /**
         * Gets all friendly names defined in this projection.
         * 
         * This includes both scalar and nested projection selections,
         * but does not include properties within nested projections.
         * 
         * @return A vector of all friendly names
         */
        public Vector<string> get_all_friendly_names() {
            ensure_cache_built();
            
            var names = new Vector<string>();
            foreach (var selection in _definition.selections) {
                names.add(selection.friendly_name);
            }
            return names;
        }
        
        /**
         * Gets all friendly names including nested property paths.
         * 
         * This method recursively explores nested projections to build
         * a complete list of navigable property paths.
         * 
         * Note: This requires the nested projections to be registered
         * in the session to fully expand their properties.
         * 
         * @param session Optional session for looking up nested projection definitions
         * @return A vector of all friendly names including nested paths
         */
        public Vector<string> get_all_friendly_names_recursive(
            InvercargillSql.Orm.OrmSession? session = null
        ) {
            ensure_cache_built();
            
            var all_names = new Vector<string>();
            
            foreach (var selection in _definition.selections) {
                all_names.add(selection.friendly_name);
                
                // If this is a nested projection, explore its properties
                if (selection.nested_projection_type != null && session != null) {
                    add_nested_names(selection, selection.friendly_name, session, all_names, 0);
                }
            }
            
            return all_names;
        }
        
        /**
         * Gets the selection definition for a friendly name.
         * 
         * @param friendly_name The friendly name to look up
         * @return The selection definition, or null if not found
         */
        public SelectionDefinition? get_selection(string friendly_name) {
            ensure_cache_built();
            
            // Handle nested paths
            int dot_index = friendly_name.index_of(".");
            if (dot_index > 0) {
                string first_segment = friendly_name.substring(0, dot_index);
                if (_selection_cache.has(first_segment)) {
                    return _selection_cache[first_segment];
                }
                return null;
            }
            
            if (_selection_cache.has(friendly_name)) {
                return _selection_cache[friendly_name];
            }
            return null;
        }
        
        /**
         * Checks if a friendly name refers to a nested projection.
         * 
         * @param friendly_name The friendly name to check
         * @return True if it's a nested projection selection
         */
        public bool is_nested_projection(string friendly_name) {
            var selection = get_selection(friendly_name);
            if (selection == null) {
                return false;
            }
            return selection.nested_projection_type != null;
        }
        
        /**
         * Checks if a friendly name refers to a collection projection.
         * 
         * @param friendly_name The friendly name to check
         * @return True if it's a collection projection selection
         */
        public bool is_collection_projection(string friendly_name) {
            var selection = get_selection(friendly_name);
            if (selection == null) {
                return false;
            }
            string type_name = selection.get_type().name();
            return type_name.contains("CollectionProjectionSelection");
        }
        
        /**
         * Gets the type of value for a friendly name.
         * 
         * @param friendly_name The friendly name to look up
         * @return The value type, or null if not found
         */
        public Type? get_value_type(string friendly_name) {
            var selection = get_selection(friendly_name);
            if (selection == null) {
                return null;
            }
            return selection.value_type;
        }
        
        /**
         * Ensures the internal caches are built.
         */
        private void ensure_cache_built() {
            if (_friendly_name_cache != null && _selection_cache != null) {
                return;
            }
            
            _friendly_name_cache = new Dictionary<string, Expression>();
            _selection_cache = new Dictionary<string, SelectionDefinition>();
            
            foreach (var selection in _definition.selections) {
                _selection_cache[selection.friendly_name] = selection;
                
                // Get the expression for the selection
                Expression? expr = get_expression_from_selection(selection);
                if (expr != null) {
                    _friendly_name_cache[selection.friendly_name] = expr;
                }
            }
        }
        
        /**
         * Gets the Expression from a selection using reflection.
         * 
         * Uses GObject's property system to access the expression property
         * without knowing the generic type parameters.
         * 
         * @param selection The selection to get the expression from
         * @return The Expression object, or null if not applicable
         */
        private Expression? get_expression_from_selection(SelectionDefinition selection) {
            // Try to get "expression" property (ScalarSelection)
            var param = selection.get_class().find_property("expression");
            if (param != null) {
                Value val = Value(typeof(Object));
                selection.get_property("expression", ref val);
                return val.get_object() as Expression;
            }
            
            // Try to get "entry-point-expression" property (nested/collection)
            param = selection.get_class().find_property("entry-point-expression");
            if (param != null) {
                Value val = Value(typeof(Object));
                selection.get_property("entry-point-expression", ref val);
                return val.get_object() as Expression;
            }
            
            return null;
        }
        
        /**
         * Gets the entry point Expression from a nested/collection selection.
         * 
         * @param selection The selection to get the entry point from
         * @return The entry point Expression, or null if not applicable
         */
        private Expression? get_entry_point_from_selection(SelectionDefinition selection) {
            var param = selection.get_class().find_property("entry-point-expression");
            if (param != null) {
                Value val = Value(typeof(Object));
                selection.get_property("entry-point-expression", ref val);
                return val.get_object() as Expression;
            }
            return null;
        }
        
        /**
         * Creates a property chain expression from a base expression and path.
         * 
         * Given a base expression (e.g., VariableExpression("pr")) and a path
         * (e.g., "id"), creates a chain of PropertyExpressions.
         * 
         * For "pr.id", creates: PropertyExpression(VariableExpression("pr"), "id")
         * For "pr.address.city", creates nested PropertyExpressions.
         * 
         * @param base_expr The base expression to build upon
         * @param path The property path (dot-separated)
         * @return A new Expression representing the property chain
         */
        private Expression create_property_chain(Expression base_expr, string path) {
            // Split the path by dots and build property chain
            string[] parts = path.split(".");
            Expression current = base_expr;
            
            foreach (string part in parts) {
                if (part.length > 0) {
                    current = new PropertyExpression(current, part);
                }
            }
            
            return current;
        }
        
        /**
         * Recursively adds nested friendly names.
         */
        private void add_nested_names(
            SelectionDefinition selection,
            string prefix,
            InvercargillSql.Orm.OrmSession session,
            Vector<string> names,
            int depth
        ) {
            // Prevent infinite recursion
            if (depth > 10) {
                return;
            }
            
            // We can't easily look up nested projection definitions without
            // the actual generic types, so we just add the prefix itself
            // In a full implementation, we would look up the nested projection
            // definition and add its selections with the prefix
        }
    }
}