# A Mongo collection.
#
# Collections are automatically created on the MongoDB server upon insertion of
# the first document.
# There is no need to create a database manually.
class MongoCollection
	super FinalizableOnce

	# Database that collection belongs to.
	var database: MongoDb

	# Name of this collection.
	var name: String

	private var native: NativeMongoCollection is noinit

	# Loads a collection.
	#
	# Call `MongoDb::collection` instead.
	init do
		native = new NativeMongoCollection(
			database.client.native,
			database.name.to_cstring,
			name.to_cstring)
	end

	# Set the autogenerated last id if the `doc` does not contain one already.
	private fun set_id(doc: JsonObject) do
		var last_id = database.client.last_id
		if last_id != null then
			doc["_id"] = last_id.to_json
			database.client.last_id = null
		end
	end

	# Inserts a new document in the collection.
	#
	# If no _id element is found in document, then a new one be generated locally
	# and added to the document.
	#
	# Returns `false` if an error occured. See `Sys::last_mongoc_error`.
	#
	# ~~~
	# var client = new MongoClient("mongodb://mongo:27017/")
	# var db_suffix = "NIT_TESTING_ID".environ
	# var db_name = "test_{db_suffix}"
	# var db = client.database(db_name)
	# var col = db.collection("test")
	# var doc = new JsonObject
	# doc["foo"] = 10
	# doc["bar"] = "bar"
	# doc["baz"] = new JsonArray
	# assert col.insert(doc)
	# assert doc.has_key("_id")
	# ~~~
	fun insert(doc: JsonObject): Bool do
		var res = native.insert(doc.to_bson.native)
		if res then set_id(doc)
		return res
	end

	# Inserts multiple documents in the collection.
	#
	# See `insert`.
	fun insert_all(docs: Collection[JsonObject]): Bool do
		var res = true
		for doc in docs do res = insert(doc) and res
		return res
	end

	# Saves a new document in the collection.
	#
	# If the document has an `_id` field it will be updated.
	# Otherwise it will be inserted.
	#
	# Returns `false` if an error occured. See `Sys::last_mongoc_error`.
	#
	# ~~~
	# var client = new MongoClient("mongodb://mongo:27017/")
	# var db_suffix = "NIT_TESTING_ID".environ
	# var db_name = "test_{db_suffix}"
	# var db = client.database(db_name)
	# var col = db.collection("test")
	#
	# var doc = new JsonObject
	# doc["foo"] = 10
	# doc["bar"] = "bar"
	# doc["baz"] = new JsonArray
	#
	# assert col.save(doc) # will be inserted
	# assert doc.has_key("_id")
	#
	# var id = doc["_id"]
	# assert col.save(doc) # will be updated
	# assert doc["_id"] == id
	# ~~~
	fun save(doc: JsonObject): Bool do
		var bson = doc.to_bson
		var nat = bson.native
		var res = native.save(nat)
		if res then set_id(doc)
		assert nat != self #FIXME used to avoid GC crashes
		assert bson != self #FIXME used to avoid GC crashes
		return res
	end

	# Removes the first document that matches `selector`.
	#
	# Returns `false` if an error occured. See `Sys::last_mongoc_error`.
	#
	# ~~~
	# var client = new MongoClient("mongodb://mongo:27017/")
	# var db_suffix = "NIT_TESTING_ID".environ
	# var db_name = "test_{db_suffix}"
	# var db = client.database(db_name)
	# var col = db.collection("test")
	# var sel = new JsonObject
	# sel["foo"] = 10
	# assert col.remove(sel)
	# ~~~
	fun remove(selector: JsonObject): Bool do
		return native.remove(selector.to_bson.native)
	end

	# Removes all the document that match `selector`.
	#
	# See `remove`.
	fun remove_all(selector: JsonObject): Bool do
		return native.remove_all(selector.to_bson.native)
	end

	# Updates a document already existing in the collection.
	#
	# No upsert is done, see `save` instead.
	#
	# ~~~
	# var client = new MongoClient("mongodb://mongo:27017/")
	# var db_suffix = "NIT_TESTING_ID".environ
	# var db_name = "test_{db_suffix}"
	# var db = client.database(db_name)
	# var col = db.collection("test")
	# var sel = new JsonObject
	# sel["foo"] = 10
	# var upd = new JsonObject
	# upd["bar"] = "BAR"
	# assert col.update(sel, upd)
	# ~~~
	fun update(selector: JsonObject, update: JsonObject): Bool do
		return native.update(
			selector.to_bson.native,
			update.to_bson.native)
	end

	# Updates all documents matching the `selector`.
	#
	# See `update`.
	fun update_all(selector: JsonObject, update: JsonObject): Bool do
		return native.update_all(
			selector.to_bson.native,
			update.to_bson.native)
	end

	# Counts the document matching `query`.
	#
	# Returns `-1` if an error occured. See `Sys::last_mongoc_error`.
	#
	# ~~~
	# var client = new MongoClient("mongodb://mongo:27017/")
	# var db_suffix = "NIT_TESTING_ID".environ
	# var db_name = "test_{db_suffix}"
	# var db = client.database(db_name)
	# var col = db.collection("test")
	# var query = new JsonObject
	# query["foo"] = 10
	# assert col.count(query) > 0
	# ~~~
	fun count(query: JsonObject): Int do
		return native.count(query.to_bson.native)
	end

	# Finds the first document that matches `query`.
	#
	# Params:
	# * `skip` number of documents to skip
	# * `limit` number of documents to return
	#
	# Returns `null` if an error occured. See `Sys::last_mongoc_error`.
	#
	# ~~~
	# var client = new MongoClient("mongodb://mongo:27017/")
	# var db_suffix = "NIT_TESTING_ID".environ
	# var db_name = "test_{db_suffix}"
	# var db = client.database(db_name)
	# var col = db.collection("test")
	# var query = new JsonObject
	# query["foo"] = 10
	# var doc = col.find(query)
	# assert doc["foo"] == 10
	# ~~~
	fun find(query: JsonObject, skip, limit: nullable Int): nullable JsonObject do
		var q = new NativeBSON.from_json_string(query.to_json.to_cstring)
		var s = skip or else 0
		var l = limit or else 0
		var c = native.find(q, s, l)
		q.destroy
		if c == null then return null
		var cursor = new MongoCursor(c)
		if not cursor.is_ok then
			return null
		end
		var item = cursor.item
		assert cursor != self
		return item
	end

	# Finds all the documents matching the `query`.
	#
	# Params:
	# * `skip` number of documents to skip
	# * `limit` number of documents to return
	#
	# ~~~
	# var client = new MongoClient("mongodb://mongo:27017/")
	# var db_suffix = "NIT_TESTING_ID".environ
	# var db_name = "test_{db_suffix}"
	# var db = client.database(db_name)
	# var col = db.collection("test")
	# var query = new JsonObject
	# query["foo"] = 10
	# assert col.find_all(query).length > 0
	# ~~~
	fun find_all(query: JsonObject, skip, limit: nullable Int): Array[JsonObject] do
		var s = skip or else 0
		var l = limit or else 0
		var res = new Array[JsonObject]
		var c = native.find(query.to_bson.native, s, l)
		if c == null then return res
		var cursor = new MongoCursor(c)
		while cursor.is_ok do
			res.add cursor.item
			cursor.next
		end
		return res
	end

	# Applies an aggregation `pipeline` over the collection.
	#
	# ~~~
	# var client = new MongoClient("mongodb://mongo:27017/")
	# var db_suffix = "NIT_TESTING_ID".environ
	# var db_name = "test_{db_suffix}"
	# var db = client.database(db_name)
	# var col = db.collection("test_aggregate")
	#
	# col.drop
	#
	# col.insert("""{ "cust_id": "A123", "amount": 500, "status": "A"}""".parse_json.as(JsonObject))
	# col.insert("""{ "cust_id": "A123", "amount": 250, "status": "A"}""".parse_json.as(JsonObject))
	# col.insert("""{ "cust_id": "B212", "amount": 200, "status": "A"}""".parse_json.as(JsonObject))
	# col.insert("""{ "cust_id": "A123", "amount": 300, "status": "D"}""".parse_json.as(JsonObject))
	#
	# var res = col.aggregate("""[
	#	{ "$match": { "status": "A" } },
	#	{ "$group": { "_id": "$cust_id", "total": { "$sum": "$amount" } } },
        #       { "$sort" : { "_id": 1 } }
	# ]""".parse_json.as(JsonArray))
	#
        # assert res[0].to_json == """{"_id":"A123","total":750}"""
	# assert res[1].to_json == """{"_id":"B212","total":200}"""
	# ~~~
	fun aggregate(pipeline: JsonArray): Array[JsonObject] do
		var q = new JsonObject
		q["pipeline"] = pipeline
		var res = new Array[JsonObject]
		var c = native.aggregate(q.to_bson.native)
		if c == null then return res
		var cursor = new MongoCursor(c)
		while cursor.is_ok do
			res.add cursor.item
			cursor.next
		end
		return res
	end

	# Retrieves statistics about the collection.
	#
	# Returns `null` if an error occured. See `Sys::last_mongoc_error`.
	#
	# ~~~
	# var client = new MongoClient("mongodb://mongo:27017/")
	# var db_suffix = "NIT_TESTING_ID".environ
	# var db_name = "test_{db_suffix}"
	# var db = client.database(db_name)
	# var col = db.collection("test")
	# assert col.stats["ns"] == "{db_name}.test"
	# ~~~
	fun stats: nullable JsonObject do
		var bson = native.stats
		if bson == null then return null
		return new JsonObject.from_bson(new BSON(bson))
	end

	# Drops `self`, returns false if an error occured.
	fun drop: Bool do return native.drop

	# Moves `self` to another `database`.
	#
	# The database will also be updated internally so it is safe to continue using
	# this collection after the move.
	# Additional operations will occur on moved collection.
	fun move(database: MongoDb): Bool do
		self.database = database
		return native.rename(database.name.to_cstring, name.to_cstring)
	end

	# Renames `self`.
	#
	# The name of the collection will also be updated internally so it is safe
	# to continue using this collection after the rename.
	# Additional operations will occur on renamed collection.
	fun rename(name: String): Bool do
		self.name = name
		return native.rename(database.name.to_cstring, name.to_cstring)
	end

	redef fun finalize_once do native.destroy
end