// Copyright 2015 The LUCI Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package datastore

import (
	"go.chromium.org/gae/service/info"

	"golang.org/x/net/context"
)

type key int

const (
	rawDatastoreKey key = iota
	rawDatastoreFilterKey
	rawDatastoreBatchKey
)

// RawFactory is the function signature for factory methods compatible with
// SetRawFactory.
type RawFactory func(c context.Context) RawInterface

// RawFilter is the function signature for a RawFilter implementation. It
// gets the current RDS implementation, and returns a new RDS implementation
// backed by the one passed in.
type RawFilter func(context.Context, RawInterface) RawInterface

// rawUnfiltered gets gets the RawInterface implementation from context without
// any of the filters applied.
func rawUnfiltered(c context.Context) RawInterface {
	if f, ok := c.Value(rawDatastoreKey).(RawFactory); ok && f != nil {
		return f(c)
	}
	return nil
}

// rawWithFilters gets the datastore (transactional or not), and applies all of
// the currently installed filters to it.
func rawWithFilters(c context.Context) RawInterface {
	ret := rawUnfiltered(c)
	if ret == nil {
		return nil
	}
	for _, f := range getCurFilters(c) {
		ret = f(c, ret)
	}

	ret = applyBatchFilter(c, ret)
	ret = applyCheckFilter(c, ret)
	return ret
}

// Raw gets the RawInterface implementation from context.
func Raw(c context.Context) RawInterface {
	return rawWithFilters(c)
}

// SetRawFactory sets the function to produce Datastore instances, as returned by
// the Raw method.
func SetRawFactory(c context.Context, rdsf RawFactory) context.Context {
	return context.WithValue(c, rawDatastoreKey, rdsf)
}

// SetRaw sets the current Datastore object in the context. Useful for testing
// with a quick mock. This is just a shorthand SetRawFactory invocation to set
// a factory which always returns the same object.
func SetRaw(c context.Context, rds RawInterface) context.Context {
	return SetRawFactory(c, func(context.Context) RawInterface { return rds })
}

func getCurFilters(c context.Context) []RawFilter {
	curFiltsI := c.Value(rawDatastoreFilterKey)
	if curFiltsI != nil {
		return curFiltsI.([]RawFilter)
	}
	return nil
}

// AddRawFilters adds RawInterface filters to the context.
func AddRawFilters(c context.Context, filts ...RawFilter) context.Context {
	if len(filts) == 0 {
		return c
	}
	cur := getCurFilters(c)
	newFilts := make([]RawFilter, 0, len(cur)+len(filts))
	newFilts = append(newFilts, getCurFilters(c)...)
	newFilts = append(newFilts, filts...)
	return context.WithValue(c, rawDatastoreFilterKey, newFilts)
}

// GetKeyContext returns the KeyContext whose AppID and Namespace match those
// installed in the supplied Context.
func GetKeyContext(c context.Context) KeyContext {
	ri := info.Raw(c)
	return MkKeyContext(ri.FullyQualifiedAppID(), ri.GetNamespace())
}

// WithBatching enables or disables automatic operation batching. Batching is
// enabled by default, and batch sizes are defined by the datastore's
// Constraints.
//
// Datastore has built-in constraints that it applies to some operations:
//
//	- For Get, there is a maximum number of elements that can be processed in a
//	  single RPC (see Constriants.MaxGetSize).
//	- For Put, there is a maximum number of elements that can be processed in a
//	  single RPC (see Constriants.MaxPutSize).
//	- For Delete, there is a maximum number of elements that can be processed in
//	  a single RPC (see Constriants.MaxDeleteSize).
//
// Batching masks these limitations, providing an interface that meets user
// expectations. Behind the scenes, it splits large operations into a series of
// parallel smaller operations that fit within the datastore's constraints.
func WithBatching(c context.Context, enabled bool) context.Context {
	return context.WithValue(c, rawDatastoreBatchKey, enabled)
}

func getBatchingEnabled(c context.Context) bool {
	val, ok := c.Value(rawDatastoreBatchKey).(bool)
	if !ok {
		return true // defaults to true if the user hasn't specified anything.
	}
	return val
}