/*-------------------------------------------------------------------------
 *
 * dependency.c
 *	  Functions to reason about distributed objects and their dependencies
 *
 * Copyright (c) Citus Data, Inc.
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "distributed/pg_version_constants.h"

#include "access/genam.h"
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/skey.h"
#include "access/sysattr.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/pg_class.h"
#include "catalog/pg_depend.h"
#include "catalog/pg_proc_d.h"
#include "catalog/pg_rewrite.h"
#include "catalog/pg_rewrite_d.h"
#include "catalog/pg_shdepend.h"
#include "catalog/pg_type.h"
#if PG_VERSION_NUM >= PG_VERSION_13
#include "common/hashfn.h"
#endif
#include "distributed/commands.h"
#include "distributed/commands/utility_hook.h"
#include "distributed/listutils.h"
#include "distributed/metadata/dependency.h"
#include "distributed/metadata/distobject.h"
#include "distributed/metadata_cache.h"
#include "distributed/version_compat.h"
#include "miscadmin.h"
#include "utils/fmgroids.h"
#include "utils/hsearch.h"
#include "utils/lsyscache.h"

/*
 * ObjectAddressCollector keeps track of collected ObjectAddresses. This can be used
 * together with RecurseObjectDependencies.
 *
 * We keep three different datastructures for the following reasons
 *  - A List ordered by insert/collect order
 *  - A Set to quickly O(1) check if an ObjectAddress has already been collected
 *  - A set to check which objects are already visited
 */
typedef struct ObjectAddressCollector
{
	List *dependencyList;
	HTAB *dependencySet;

	HTAB *visitedObjects;
} ObjectAddressCollector;

/*
 * DependencyMode distinguishes the data stored in DependencyDefinition. For details see
 * DependencyDefinition's inline comments in the data union.
 */
typedef enum DependencyMode
{
	DependencyObjectAddress,
	DependencyPgDepend,
	DependencyPgShDepend
} DependencyMode;

typedef struct DependencyDefinition
{
	/* describe how the dependency data is stored in the data field */
	DependencyMode mode;

	/*
	 * Dependencies can be found in different ways and therefore stored differently on the
	 * definition.
	 */
	union
	{
		/*
		 * pg_depend is used for dependencies found in the database local pg_depend table.
		 * The entry is copied while scanning the table. The record can be inspected
		 * during the chasing algorithm to follow dependencies of different classes, or
		 * based on dependency type.
		 */
		FormData_pg_depend pg_depend;

		/*
		 * pg_shdepend is used for dependencies found in the global pg_shdepend table.
		 * The entry is copied while scanning the table. The record can be inspected
		 * during the chasing algorithm to follow dependencies of different classes, or
		 * based on dependency type.
		 */
		FormData_pg_shdepend pg_shdepend;

		/*
		 * address is used for dependencies that are artificially added during the
		 * chasing. Since they are added by citus code we assume the dependency needs to
		 * be chased anyway, ofcourse it will only actually be chased if the object is a
		 * suppported object by citus
		 */
		ObjectAddress address;
	} data;
} DependencyDefinition;

/*
 * ViewDependencyNode represents a view (or possibly a table) in a dependency graph of
 * views.
 */
typedef struct ViewDependencyNode
{
	Oid id;
	int remainingDependencyCount;
	List *dependingNodes;
}ViewDependencyNode;


static List * GetRelationTriggerFunctionDepencyList(Oid relationId);
static DependencyDefinition * CreateObjectAddressDependencyDef(Oid classId, Oid objectId);
static ObjectAddress DependencyDefinitionObjectAddress(DependencyDefinition *definition);

/* forward declarations for functions to interact with the ObjectAddressCollector */
static void InitObjectAddressCollector(ObjectAddressCollector *collector);
static void CollectObjectAddress(ObjectAddressCollector *collector,
								 const ObjectAddress *address);
static bool IsObjectAddressCollected(ObjectAddress findAddress,
									 ObjectAddressCollector *collector);
static void MarkObjectVisited(ObjectAddressCollector *collector,
							  ObjectAddress target);
static bool TargetObjectVisited(ObjectAddressCollector *collector,
								ObjectAddress target);

typedef List *(*expandFn)(ObjectAddressCollector *collector, ObjectAddress target);
typedef bool (*followFn)(ObjectAddressCollector *collector,
						 DependencyDefinition *definition);
typedef void (*applyFn)(ObjectAddressCollector *collector,
						DependencyDefinition *definition);

/* forward declaration of functions that recurse pg_depend */
static void RecurseObjectDependencies(ObjectAddress target, expandFn expand,
									  followFn follow, applyFn apply,
									  ObjectAddressCollector *collector);
static List * DependencyDefinitionFromPgDepend(ObjectAddress target);
static List * DependencyDefinitionFromPgShDepend(ObjectAddress target);
static bool FollowAllSupportedDependencies(ObjectAddressCollector *collector,
										   DependencyDefinition *definition);
static bool FollowNewSupportedDependencies(ObjectAddressCollector *collector,
										   DependencyDefinition *definition);
static void ApplyAddToDependencyList(ObjectAddressCollector *collector,
									 DependencyDefinition *definition);
static List * ExpandCitusSupportedTypes(ObjectAddressCollector *collector,
										ObjectAddress target);
static ViewDependencyNode * BuildViewDependencyGraph(Oid relationId, HTAB *nodeMap);
static Oid GetDependingView(Form_pg_depend pg_depend);


/*
 * GetUniqueDependenciesList takes a list of object addresses and returns a new list
 * of ObjectAddesses whose elements are unique.
 */
List *
GetUniqueDependenciesList(List *objectAddressesList)
{
	ObjectAddressCollector objectAddressCollector = { 0 };
	InitObjectAddressCollector(&objectAddressCollector);

	ObjectAddress *objectAddress = NULL;
	foreach_ptr(objectAddress, objectAddressesList)
	{
		if (IsObjectAddressCollected(*objectAddress, &objectAddressCollector))
		{
			/* skip objects that are already collected */
			continue;
		}

		CollectObjectAddress(&objectAddressCollector, objectAddress);
	}

	return objectAddressCollector.dependencyList;
}


/*
 * GetDependenciesForObject returns a list of ObjectAddesses to be created in order
 * before the target object could safely be created on a worker. Some of the object might
 * already be created on a worker. It should be created in an idempotent way.
 */
List *
GetDependenciesForObject(const ObjectAddress *target)
{
	ObjectAddressCollector collector = { 0 };
	InitObjectAddressCollector(&collector);

	RecurseObjectDependencies(*target,
							  &ExpandCitusSupportedTypes,
							  &FollowNewSupportedDependencies,
							  &ApplyAddToDependencyList,
							  &collector);

	return collector.dependencyList;
}


/*
 * OrderObjectAddressListInDependencyOrder given a list of ObjectAddresses return a new
 * list of the same ObjectAddresses ordered on dependency order where dependencies
 * precedes the corresponding object in the list.
 *
 * The algortihm traveses pg_depend in a depth first order starting at the first object in
 * the provided list. By traversing depth first it will put the first dependency at the
 * head of the list with dependencies depending on them later.
 *
 * If the object is already in the list it is skipped for traversal. This happens when an
 * object was already added to the target list before it occurred in the input list.
 */
List *
OrderObjectAddressListInDependencyOrder(List *objectAddressList)
{
	ObjectAddressCollector collector = { 0 };
	InitObjectAddressCollector(&collector);

	ObjectAddress *objectAddress = NULL;
	foreach_ptr(objectAddress, objectAddressList)
	{
		if (IsObjectAddressCollected(*objectAddress, &collector))
		{
			/* skip objects that are already ordered */
			continue;
		}

		RecurseObjectDependencies(*objectAddress,
								  &ExpandCitusSupportedTypes,
								  &FollowAllSupportedDependencies,
								  &ApplyAddToDependencyList,
								  &collector);

		CollectObjectAddress(&collector, objectAddress);
	}

	return collector.dependencyList;
}


/*
 * RecurseObjectDependencies recursively visits all dependencies of an object. It sources
 * the dependencies from pg_depend and pg_shdepend while 'expanding' the list via an
 * optional `expand` function.
 *
 * Starting from the target ObjectAddress. For every dependency found the `follow`
 * function will be called. When `follow` returns true it will recursively visit the
 * dependencies for that object.
 *
 * Visiting will happen in depth first order, which is useful to create or sorted lists of
 * dependencies to create.
 *
 * For all dependencies that should be visited the apply function will be called. This
 * function is designed to be the mutating function for the context being passed. Although
 * nothing prevents the follow function to also mutate the context.
 *
 *  - follow will be called on the way down, so the invocation order is top to bottom of
 *    the dependency tree
 *  - apply is called on the way back, so the invocation order is bottom to top. Apply is
 *    not called for entries for which follow has returned false.
 */
static void
RecurseObjectDependencies(ObjectAddress target, expandFn expand, followFn follow,
						  applyFn apply, ObjectAddressCollector *collector)
{
	if (TargetObjectVisited(collector, target))
	{
		/* prevent infinite loops due to circular dependencies */
		return;
	}

	MarkObjectVisited(collector, target);

	/* lookup both pg_depend and pg_shdepend for dependencies */
	List *pgDependDefinitions = DependencyDefinitionFromPgDepend(target);
	List *pgShDependDefinitions = DependencyDefinitionFromPgShDepend(target);
	List *dependenyDefinitionList = list_concat(pgDependDefinitions,
												pgShDependDefinitions);

	/* concat expanded entries if applicable */
	if (expand != NULL)
	{
		List *expandedEntries = expand(collector, target);
		dependenyDefinitionList = list_concat(dependenyDefinitionList, expandedEntries);
	}

	/* iterate all entries and recurse depth first */
	DependencyDefinition *dependencyDefinition = NULL;
	foreach_ptr(dependencyDefinition, dependenyDefinitionList)
	{
		if (follow == NULL || !follow(collector, dependencyDefinition))
		{
			/* skip all pg_depend entries the user didn't want to follow */
			continue;
		}

		/*
		 * recurse depth first, this makes sure we call apply for the deepest dependency
		 * first.
		 */
		ObjectAddress address = DependencyDefinitionObjectAddress(dependencyDefinition);
		RecurseObjectDependencies(address, expand, follow, apply, collector);

		/* now apply changes for current entry */
		if (apply != NULL)
		{
			apply(collector, dependencyDefinition);
		}
	}
}


/*
 * DependencyDefinitionFromPgDepend loads all pg_depend records describing the
 * dependencies of target.
 */
static List *
DependencyDefinitionFromPgDepend(ObjectAddress target)
{
	ScanKeyData key[2];
	HeapTuple depTup = NULL;
	List *dependenyDefinitionList = NIL;

	/*
	 * iterate the actual pg_depend catalog
	 */
	Relation depRel = table_open(DependRelationId, AccessShareLock);

	/* scan pg_depend for classid = $1 AND objid = $2 using pg_depend_depender_index */
	ScanKeyInit(&key[0], Anum_pg_depend_classid, BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(target.classId));
	ScanKeyInit(&key[1], Anum_pg_depend_objid, BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(target.objectId));
	SysScanDesc depScan = systable_beginscan(depRel, DependDependerIndexId, true, NULL, 2,
											 key);

	while (HeapTupleIsValid(depTup = systable_getnext(depScan)))
	{
		Form_pg_depend pg_depend = (Form_pg_depend) GETSTRUCT(depTup);
		DependencyDefinition *dependency = palloc0(sizeof(DependencyDefinition));

		/* keep track of all pg_depend records as dependency definitions */
		dependency->mode = DependencyPgDepend;
		dependency->data.pg_depend = *pg_depend;
		dependenyDefinitionList = lappend(dependenyDefinitionList, dependency);
	}

	systable_endscan(depScan);
	relation_close(depRel, AccessShareLock);

	return dependenyDefinitionList;
}


/*
 * DependencyDefinitionFromPgDepend loads all pg_shdepend records describing the
 * dependencies of target.
 */
static List *
DependencyDefinitionFromPgShDepend(ObjectAddress target)
{
	ScanKeyData key[3];
	HeapTuple depTup = NULL;
	List *dependenyDefinitionList = NIL;

	/*
	 * iterate the actual pg_shdepend catalog
	 */
	Relation shdepRel = table_open(SharedDependRelationId, AccessShareLock);

	/*
	 * Scan pg_shdepend for dbid = $1 AND classid = $2 AND objid = $3 using
	 * pg_shdepend_depender_index
	 */
	ScanKeyInit(&key[0], Anum_pg_shdepend_dbid, BTEqualStrategyNumber, F_OIDEQ,
				MyDatabaseId);
	ScanKeyInit(&key[1], Anum_pg_shdepend_classid, BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(target.classId));
	ScanKeyInit(&key[2], Anum_pg_shdepend_objid, BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(target.objectId));
	SysScanDesc shdepScan = systable_beginscan(shdepRel, SharedDependDependerIndexId,
											   true, NULL, 3, key);

	while (HeapTupleIsValid(depTup = systable_getnext(shdepScan)))
	{
		Form_pg_shdepend pg_shdepend = (Form_pg_shdepend) GETSTRUCT(depTup);
		DependencyDefinition *dependency = palloc0(sizeof(DependencyDefinition));

		/* keep track of all pg_shdepend records as dependency definitions */
		dependency->mode = DependencyPgShDepend;
		dependency->data.pg_shdepend = *pg_shdepend;
		dependenyDefinitionList = lappend(dependenyDefinitionList, dependency);
	}

	systable_endscan(shdepScan);
	relation_close(shdepRel, AccessShareLock);

	return dependenyDefinitionList;
}


/*
 * InitObjectAddressCollector takes a pointer to an already allocated (possibly stack)
 * ObjectAddressCollector struct. It makes sure this struct is ready to be used for object
 * collection.
 *
 * If an already initialized collector is passed the collector will be cleared from its
 * contents to be reused.
 */
static void
InitObjectAddressCollector(ObjectAddressCollector *collector)
{
	HASHCTL info;

	memset(&info, 0, sizeof(info));
	info.keysize = sizeof(ObjectAddress);
	info.entrysize = sizeof(ObjectAddress);
	info.hcxt = CurrentMemoryContext;
	int hashFlags = (HASH_ELEM | HASH_CONTEXT | HASH_BLOBS);

	collector->dependencySet = hash_create("dependency set", 128, &info, hashFlags);
	collector->dependencyList = NULL;

	collector->visitedObjects = hash_create("visited object set", 128, &info, hashFlags);
}


/*
 * TargetObjectVisited returns true if the input target has been visited while
 * traversing pg_depend.
 */
static bool
TargetObjectVisited(ObjectAddressCollector *collector, ObjectAddress target)
{
	bool found = false;

	/* find in set */
	hash_search(collector->visitedObjects, &target, HASH_FIND, &found);

	return found;
}


/*
 * MarkObjectVisited marks the object as visited during the traversal of
 * pg_depend.
 */
static void
MarkObjectVisited(ObjectAddressCollector *collector, ObjectAddress target)
{
	bool found = false;

	/* add to set */
	ObjectAddress *address = (ObjectAddress *) hash_search(collector->visitedObjects,
														   &target,
														   HASH_ENTER, &found);

	if (!found)
	{
		/* copy object address in */
		*address = target;
	}
}


/*
 * CollectObjectAddress adds an ObjectAddress to the collector.
 */
static void
CollectObjectAddress(ObjectAddressCollector *collector, const ObjectAddress *collect)
{
	bool found = false;

	/* add to set */
	ObjectAddress *address = (ObjectAddress *) hash_search(collector->dependencySet,
														   collect,
														   HASH_ENTER, &found);

	if (!found)
	{
		/* copy object address in */
		*address = *collect;
	}

	/* add to list*/
	collector->dependencyList = lappend(collector->dependencyList, address);
}


/*
 * IsObjectAddressCollected is a helper function that can check if an ObjectAddress is
 * already in a (unsorted) list of ObjectAddresses
 */
static bool
IsObjectAddressCollected(ObjectAddress findAddress,
						 ObjectAddressCollector *collector)
{
	bool found = false;

	/* add to set */
	hash_search(collector->dependencySet, &findAddress, HASH_FIND, &found);

	return found;
}


/*
 * SupportedDependencyByCitus returns whether citus has support to distribute the object
 * addressed.
 */
bool
SupportedDependencyByCitus(const ObjectAddress *address)
{
	if (!EnableDependencyCreation)
	{
		/*
		 * If the user has disabled object propagation we need to fall back to the legacy
		 * behaviour in which we only support schema creation
		 */
		switch (getObjectClass(address))
		{
			case OCLASS_SCHEMA:
			{
				return true;
			}

			default:
			{
				return false;
			}
		}

		/* should be unreachable */
		Assert(false);
	}

	/*
	 * looking at the type of a object to see if we know how to create the object on the
	 * workers.
	 */
	switch (getObjectClass(address))
	{
#if PG_VERSION_NUM >= 120000
		case OCLASS_AM:
		{
			/*
			 * Only support access methods if they came from extensions
			 * During the dependency resolution it will cascade into the extension and
			 * distributed that one instead of the Access Method. Now access methods can
			 * be configured on tables on the workers.
			 */
			return IsObjectAddressOwnedByExtension(address, NULL);
		}
#endif

		case OCLASS_COLLATION:
		case OCLASS_SCHEMA:
		{
			return true;
		}

		case OCLASS_PROC:
		{
			return true;
		}

		case OCLASS_ROLE:
		{
			/*
			 * Community only supports the extension owner as a distributed object to
			 * propagate alter statements for this user
			 */
			if (address->objectId == CitusExtensionOwner())
			{
				return true;
			}

			return false;
		}

		case OCLASS_EXTENSION:
		{
			return true;
		}

		case OCLASS_TYPE:
		{
			switch (get_typtype(address->objectId))
			{
				case TYPTYPE_ENUM:
				case TYPTYPE_COMPOSITE:
				{
					return true;
				}

				case TYPTYPE_BASE:
				{
					/*
					 * array types should be followed but not created, as they get created
					 * by the original type.
					 */
					return type_is_array(address->objectId);
				}

				default:
				{
					/* type not supported */
					return false;
				}
			}

			/*
			 * should be unreachable, break here is to make sure the function has a path
			 * without return, instead of falling through to the next block */
			break;
		}

		case OCLASS_CLASS:
		{
			/*
			 * composite types have a reference to a relation of composite type, we need
			 * to follow those to get the dependencies of type fields.
			 */
			if (get_rel_relkind(address->objectId) == RELKIND_COMPOSITE_TYPE)
			{
				return true;
			}

			return false;
		}

		default:
		{
			/* unsupported type */
			return false;
		}
	}
}


/*
 * IsTableOwnedByExtension returns whether the table with the given relation ID is
 * owned by an extension.
 */
bool
IsTableOwnedByExtension(Oid relationId)
{
	ObjectAddress tableAddress = { 0 };
	ObjectAddressSet(tableAddress, RelationRelationId, relationId);

	return IsObjectAddressOwnedByExtension(&tableAddress, NULL);
}


/*
 * IsObjectAddressOwnedByExtension returns whether or not the object is owned by an
 * extension. It is assumed that an object having a dependency on an extension is created
 * by that extension and therefore owned by that extension.
 *
 * If extensionAddress is not set to a NULL pointer the function will write the extension
 * address this function depends on into this location.
 */
bool
IsObjectAddressOwnedByExtension(const ObjectAddress *target,
								ObjectAddress *extensionAddress)
{
	ScanKeyData key[2];
	HeapTuple depTup = NULL;
	bool result = false;

	Relation depRel = table_open(DependRelationId, AccessShareLock);

	/* scan pg_depend for classid = $1 AND objid = $2 using pg_depend_depender_index */
	ScanKeyInit(&key[0], Anum_pg_depend_classid, BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(target->classId));
	ScanKeyInit(&key[1], Anum_pg_depend_objid, BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(target->objectId));
	SysScanDesc depScan = systable_beginscan(depRel, DependDependerIndexId, true, NULL, 2,
											 key);

	while (HeapTupleIsValid(depTup = systable_getnext(depScan)))
	{
		Form_pg_depend pg_depend = (Form_pg_depend) GETSTRUCT(depTup);
		if (pg_depend->deptype == DEPENDENCY_EXTENSION)
		{
			result = true;
			if (extensionAddress != NULL)
			{
				ObjectAddressSubSet(*extensionAddress, pg_depend->refclassid,
									pg_depend->refobjid, pg_depend->refobjsubid);
			}
			break;
		}
	}

	systable_endscan(depScan);
	table_close(depRel, AccessShareLock);

	return result;
}


/*
 * FollowNewSupportedDependencies applies filters on pg_depend entries to follow all
 * objects which should be distributed before the root object can safely be created.
 */
static bool
FollowNewSupportedDependencies(ObjectAddressCollector *collector,
							   DependencyDefinition *definition)
{
	if (definition->mode == DependencyPgDepend)
	{
		/*
		 *  For dependencies found in pg_depend:
		 *
		 *  Follow only normal and extension dependencies. The latter is used to reach the
		 *  extensions, the objects that directly depend on the extension are eliminated
		 *  during the "apply" phase.
		 *
		 *  Other dependencies are internal dependencies and managed by postgres.
		 */
		if (definition->data.pg_depend.deptype != DEPENDENCY_NORMAL &&
			definition->data.pg_depend.deptype != DEPENDENCY_EXTENSION)
		{
			return false;
		}
	}

	/* rest of the tests are to see if we want to follow the actual dependency */
	ObjectAddress address = DependencyDefinitionObjectAddress(definition);

	/*
	 * If the object is already in our dependency list we do not have to follow any
	 * further
	 */
	if (IsObjectAddressCollected(address, collector))
	{
		return false;
	}

	/*
	 * If the object is already distributed it is not a `new` object that needs to be
	 * distributed before we create a dependant object
	 */
	if (IsObjectDistributed(&address))
	{
		return false;
	}

	/*
	 * We can only distribute dependencies that citus knows how to distribute.
	 *
	 * But we don't want to bail out if the object is owned by extension, because
	 * Citus can create the extension.
	 */
	if (!SupportedDependencyByCitus(&address) &&
		!IsObjectAddressOwnedByExtension(&address, NULL))
	{
		return false;
	}

	if (CitusExtensionObject(&address))
	{
		/* following citus extension could complicate role management */
		return false;
	}

	return true;
}


/*
 * FollowAllSupportedDependencies applies filters on pg_depend entries to follow the
 * dependency tree of objects in depth first order. We will visit all supported objects.
 * This is used to sort a list of dependencies in dependency order.
 */
static bool
FollowAllSupportedDependencies(ObjectAddressCollector *collector,
							   DependencyDefinition *definition)
{
	if (definition->mode == DependencyPgDepend)
	{
		/*
		 *  For dependencies found in pg_depend:
		 *
		 *  Follow only normal and extension dependencies. The latter is used to reach the
		 *  extensions, the objects that directly depend on the extension are eliminated
		 *  during the "apply" phase.
		 *
		 *  Other dependencies are internal dependencies and managed by postgres.
		 */
		if (definition->data.pg_depend.deptype != DEPENDENCY_NORMAL &&
			definition->data.pg_depend.deptype != DEPENDENCY_EXTENSION)
		{
			return false;
		}
	}

	/* rest of the tests are to see if we want to follow the actual dependency */
	ObjectAddress address = DependencyDefinitionObjectAddress(definition);

	/*
	 * If the object is already in our dependency list we do not have to follow any
	 * further
	 */
	if (IsObjectAddressCollected(address, collector))
	{
		return false;
	}

	/*
	 * We can only distribute dependencies that citus knows how to distribute.
	 *
	 * But we don't want to bail out if the object is owned by extension, because
	 * Citus can create the extension.
	 */
	if (!SupportedDependencyByCitus(&address) &&
		!IsObjectAddressOwnedByExtension(&address, NULL))
	{
		return false;
	}

	if (CitusExtensionObject(&address))
	{
		/* following citus extension could complicate role management */
		return false;
	}

	return true;
}


/*
 * ApplyAddToDependencyList is an apply function for RecurseObjectDependencies that will collect
 * all the ObjectAddresses for pg_depend entries to the context. The context here is
 * assumed to be a (ObjectAddressCollector *) to the location where all ObjectAddresses
 * will be collected.
 */
static void
ApplyAddToDependencyList(ObjectAddressCollector *collector,
						 DependencyDefinition *definition)
{
	ObjectAddress address = DependencyDefinitionObjectAddress(definition);

	/*
	 * Objects owned by an extension are assumed to be created on the workers by creating
	 * the extension in the cluster, we we don't want explicitly create them.
	 *
	 * Since we do need to capture the extension as a dependency we are following the
	 * object instead of breaking the traversal there.
	 */
	if (IsObjectAddressOwnedByExtension(&address, NULL))
	{
		return;
	}

	CollectObjectAddress(collector, &address);
}


/*
 * ExpandCitusSupportedTypes base on supported types by citus we might want to expand
 * the list of objects to visit in pg_depend.
 *
 * An example where we want to expand is for types. Their dependencies are not captured
 * with an entry in pg_depend from their object address, but by the object address of the
 * relation describing the type.
 */
static List *
ExpandCitusSupportedTypes(ObjectAddressCollector *collector, ObjectAddress target)
{
	List *result = NIL;

	switch (target.classId)
	{
		case TypeRelationId:
		{
			/*
			 * types depending on other types are not captured in pg_depend, instead they
			 * are described with their dependencies by the relation that describes the
			 * composite type.
			 */
			if (get_typtype(target.objectId) == TYPTYPE_COMPOSITE)
			{
				Oid typeRelationId = get_typ_typrelid(target.objectId);
				DependencyDefinition *dependency =
					CreateObjectAddressDependencyDef(RelationRelationId, typeRelationId);
				result = lappend(result, dependency);
			}

			/*
			 * array types don't have a normal dependency on their element type, instead
			 * their dependency is an internal one. We can't follow interal dependencies
			 * as that would cause a cyclic dependency on others, instead we expand here
			 * to follow the dependency on the element type.
			 */
			if (type_is_array(target.objectId))
			{
				Oid typeId = get_element_type(target.objectId);
				DependencyDefinition *dependency =
					CreateObjectAddressDependencyDef(TypeRelationId, typeId);
				result = lappend(result, dependency);
			}

			break;
		}

		case RelationRelationId:
		{
			/*
			 * Triggers both depend to the relations and to the functions they
			 * execute. Also, pg_depend records dependencies from triggers to the
			 * functions but not from relations to their triggers. Given above two,
			 * we directly expand depencies for the relations to trigger functions.
			 * That way, we won't attempt to create the trigger as a dependency of
			 * the relation, which would fail as the relation itself is not created
			 * yet when ensuring dependencies.
			 */
			Oid relationId = target.objectId;
			List *triggerFunctionDepencyList =
				GetRelationTriggerFunctionDepencyList(relationId);
			result = list_concat(result, triggerFunctionDepencyList);
		}

		default:
		{
			/* no expansion for unsupported types */
			break;
		}
	}
	return result;
}


/*
 * GetRelationTriggerFunctionDepencyList returns a list of DependencyDefinition
 * objects for the functions that triggers of the relation with relationId depends.
 */
static List *
GetRelationTriggerFunctionDepencyList(Oid relationId)
{
	List *dependencyList = NIL;

	List *triggerIdList = GetExplicitTriggerIdList(relationId);
	Oid triggerId = InvalidOid;
	foreach_oid(triggerId, triggerIdList)
	{
		Oid functionId = GetTriggerFunctionId(triggerId);
		DependencyDefinition *dependency =
			CreateObjectAddressDependencyDef(ProcedureRelationId, functionId);
		dependencyList = lappend(dependencyList, dependency);
	}

	return dependencyList;
}


/*
 * CreateObjectAddressDependencyDef returns DependencyDefinition object that
 * stores the ObjectAddress for the database object identified by classId and
 * objectId.
 */
static DependencyDefinition *
CreateObjectAddressDependencyDef(Oid classId, Oid objectId)
{
	DependencyDefinition *dependency = palloc0(sizeof(DependencyDefinition));
	dependency->mode = DependencyObjectAddress;
	ObjectAddressSet(dependency->data.address, classId, objectId);
	return dependency;
}


/*
 * DependencyDefinitionObjectAddress returns the object address of the dependency defined
 * by the dependency definition, irregardless what the source of the definition is
 */
static ObjectAddress
DependencyDefinitionObjectAddress(DependencyDefinition *definition)
{
	switch (definition->mode)
	{
		case DependencyObjectAddress:
		{
			return definition->data.address;
		}

		case DependencyPgDepend:
		{
			ObjectAddress address = { 0 };
			ObjectAddressSet(address,
							 definition->data.pg_depend.refclassid,
							 definition->data.pg_depend.refobjid);
			return address;
		}

		case DependencyPgShDepend:
		{
			ObjectAddress address = { 0 };
			ObjectAddressSet(address,
							 definition->data.pg_shdepend.refclassid,
							 definition->data.pg_shdepend.refobjid);
			return address;
		}
	}

	ereport(ERROR, (errmsg("unsupported dependency definition mode")));
}


/*
 * BuildViewDependencyGraph gets a relation (or a view) and builds a dependency graph for the
 * depending views.
 */
static ViewDependencyNode *
BuildViewDependencyGraph(Oid relationId, HTAB *nodeMap)
{
	bool found = false;
	ViewDependencyNode *node = (ViewDependencyNode *) hash_search(nodeMap, &relationId,
																  HASH_ENTER, &found);

	if (found)
	{
		return node;
	}

	node->id = relationId;
	node->remainingDependencyCount = 0;
	node->dependingNodes = NIL;

	ObjectAddress target = { 0 };
	ObjectAddressSet(target, RelationRelationId, relationId);

	ScanKeyData key[2];
	HeapTuple depTup = NULL;

	/*
	 * iterate the actual pg_depend catalog
	 */
	Relation depRel = table_open(DependRelationId, AccessShareLock);

	ScanKeyInit(&key[0], Anum_pg_depend_refclassid, BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(target.classId));
	ScanKeyInit(&key[1], Anum_pg_depend_refobjid, BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(target.objectId));
	SysScanDesc depScan = systable_beginscan(depRel, DependReferenceIndexId,
											 true, NULL, 2, key);

	while (HeapTupleIsValid(depTup = systable_getnext(depScan)))
	{
		Form_pg_depend pg_depend = (Form_pg_depend) GETSTRUCT(depTup);

		Oid dependingView = GetDependingView(pg_depend);
		if (dependingView != InvalidOid)
		{
			ViewDependencyNode *dependingNode = BuildViewDependencyGraph(dependingView,
																		 nodeMap);

			node->dependingNodes = lappend(node->dependingNodes, dependingNode);
			dependingNode->remainingDependencyCount++;
		}
	}

	systable_endscan(depScan);
	relation_close(depRel, AccessShareLock);

	return node;
}


/*
 * GetDependingViews takes a relation id, finds the views that depend on the relation
 * and returns list of the oids of those views. It recurses on the pg_depend table to
 * find the views that recursively depend on the table.
 *
 * The returned views will have the correct order for creating them, from the point of
 * dependencies between.
 */
List *
GetDependingViews(Oid relationId)
{
	HASHCTL info;
	memset(&info, 0, sizeof(info));
	info.keysize = sizeof(Oid);
	info.entrysize = sizeof(ViewDependencyNode);
	info.hash = oid_hash;
	uint32 hashFlags = (HASH_ELEM | HASH_FUNCTION);
	HTAB *nodeMap = hash_create("view dependency map (oid)", 32, &info, hashFlags);

	ViewDependencyNode *tableNode = BuildViewDependencyGraph(relationId, nodeMap);

	List *dependingViews = NIL;
	List *nodeQueue = list_make1(tableNode);
	ViewDependencyNode *node = NULL;
	foreach_ptr_append(node, nodeQueue)
	{
		ViewDependencyNode *dependingNode = NULL;
		foreach_ptr(dependingNode, node->dependingNodes)
		{
			dependingNode->remainingDependencyCount--;
			if (dependingNode->remainingDependencyCount == 0)
			{
				nodeQueue = lappend(nodeQueue, dependingNode);
				dependingViews = lappend_oid(dependingViews, dependingNode->id);
			}
		}
	}
	return dependingViews;
}


/*
 * GetDependingView gets a row of pg_depend and returns the oid of the view that is depended.
 * If the depended object is not a rewrite object, the object to rewrite is not a view or it
 * is the same view with the depending one InvalidOid is returned.
 */
Oid
GetDependingView(Form_pg_depend pg_depend)
{
	if (pg_depend->classid != RewriteRelationId)
	{
		return InvalidOid;
	}

	Relation rewriteRel = table_open(RewriteRelationId, AccessShareLock);
	ScanKeyData rkey[1];

#if PG_VERSION_NUM >= PG_VERSION_12
	ScanKeyInit(&rkey[0],
				Anum_pg_rewrite_oid,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(pg_depend->objid));
#else
	ScanKeyInit(&rkey[0],
				ObjectIdAttributeNumber,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(pg_depend->objid));
#endif

	SysScanDesc rscan = systable_beginscan(rewriteRel, RewriteOidIndexId,
										   true, NULL, 1, rkey);

	HeapTuple rewriteTup = systable_getnext(rscan);
	Form_pg_rewrite pg_rewrite = (Form_pg_rewrite) GETSTRUCT(rewriteTup);

	bool isView = get_rel_relkind(pg_rewrite->ev_class) == RELKIND_VIEW;
	bool isDifferentThanRef = pg_rewrite->ev_class != pg_depend->refobjid;

	systable_endscan(rscan);
	relation_close(rewriteRel, AccessShareLock);

	if (isView && isDifferentThanRef)
	{
		return pg_rewrite->ev_class;
	}
	return InvalidOid;
}