// 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 (
	"fmt"
	"reflect"

	"go.chromium.org/luci/common/errors"
	"golang.org/x/net/context"
)

type resolvedRunCallback func(reflect.Value, CursorCB) error

func parseRunCallback(cbIface interface{}) (rcb resolvedRunCallback, isKey bool, mat *multiArgType) {
	badSig := func() {
		panic(fmt.Errorf(
			"cb does not match the required callback signature: `%T` != `func(TYPE, [CursorCB]) [error]`",
			cbIface))
	}

	if cbIface == nil {
		badSig()
	}

	// TODO(riannucci): Profile and determine if any of this is causing a real
	// slowdown. Could potentially cache reflection stuff by cbTyp?
	cbVal := reflect.ValueOf(cbIface)
	cbTyp := cbVal.Type()

	if cbTyp.Kind() != reflect.Func {
		badSig()
	}

	numIn := cbTyp.NumIn()
	if numIn != 1 && numIn != 2 {
		badSig()
	}

	firstArg := cbTyp.In(0)
	if firstArg == typeOfKey {
		isKey = true
	} else {
		mat = mustParseArg(firstArg, false)
		if mat.newElem == nil {
			badSig()
		}
	}

	hasCursorCB := numIn == 2
	if hasCursorCB && cbTyp.In(1) != typeOfCursorCB {
		badSig()
	}

	if cbTyp.NumOut() > 1 {
		badSig()
	} else if cbTyp.NumOut() == 1 && cbTyp.Out(0) != typeOfError {
		badSig()
	}
	hasErr := cbTyp.NumOut() == 1

	// Resolve to generic function.
	switch {
	case hasErr && hasCursorCB:
		// func(reflect.Value, CursorCB) error
		rcb = func(v reflect.Value, cb CursorCB) error {
			err := cbVal.Call([]reflect.Value{v, reflect.ValueOf(cb)})[0].Interface()
			if err != nil {
				return err.(error)
			}
			return nil
		}

	case hasErr && !hasCursorCB:
		// func(reflect.Value) error
		rcb = func(v reflect.Value, _ CursorCB) error {
			err := cbVal.Call([]reflect.Value{v})[0].Interface()
			if err != nil {
				return err.(error)
			}
			return nil
		}

	case !hasErr && hasCursorCB:
		// func(reflect.Value, CursorCB)
		rcb = func(v reflect.Value, cb CursorCB) error {
			cbVal.Call([]reflect.Value{v, reflect.ValueOf(cb)})
			return nil
		}

	case !hasErr && !hasCursorCB:
		// func(reflect.Value)
		rcb = func(v reflect.Value, _ CursorCB) error {
			cbVal.Call([]reflect.Value{v})
			return nil
		}

	default:
		badSig()
	}

	return
}

// AllocateIDs allows you to allocate IDs from the datastore without putting
// any data.
//
// A partial valid key will be constructed from each entity's kind and parent,
// if present. An allocation will then be performed against the datastore for
// each key, and the partial key will be populated with a unique integer ID.
// The resulting keys will be applied to their objects using PopulateKey. If
// successful, any existing ID will be destroyed.
//
// If the object is supplied that cannot accept an integer key, this method
// will panic.
//
// ent must be one of:
//	- *S where S is a struct
//	- *P where *P is a concrete type implementing PropertyLoadSaver
//	- []S or []*S where S is a struct
//	- []P or []*P where *P is a concrete type implementing PropertyLoadSaver
//	- []I where i is some interface type. Each element of the slice must
//	  be non-nil, and its underlying type must be either *S or *P.
//	- []*Key, to populate a slice of partial-valid keys.
//
// If an error is encountered, the returned error value will depend on the
// input arguments. If one argument is supplied, the result will be the
// encountered error type. If multiple arguments are supplied, the result will
// be a MultiError whose error index corresponds to the argument in which the
// error was encountered.
//
// If an ent argument is a slice, its error type will be a MultiError. Note
// that in the scenario where multiple slices are provided, this will return a
// MultiError containing a nested MultiError for each slice argument.
func AllocateIDs(c context.Context, ent ...interface{}) error {
	if len(ent) == 0 {
		return nil
	}

	mma, err := makeMetaMultiArg(ent, mmaWriteKeys)
	if err != nil {
		panic(err)
	}

	keys, _, et := mma.getKeysPMs(GetKeyContext(c), false)
	if len(keys) == 0 {
		return nil
	}

	var dat DroppedArgTracker
	dat.MarkNilKeys(keys)
	keys, dal := dat.DropKeys(keys)

	// Convert each key to be partial valid, assigning an integer ID of 0.
	// Confirm that each object can be populated with such a key.
	for compressedIdx, key := range keys {
		keys[compressedIdx] = key.Incomplete()
	}

	err = Raw(c).AllocateIDs(keys, func(compressedIdx int, key *Key, err error) {
		idx := dal.OriginalIndex(compressedIdx)

		index := mma.index(idx)

		if err != nil {
			et.trackError(index, err)
			return
		}

		mat, v := mma.get(index)
		if !mat.setKey(v, key) {
			et.trackError(index, MakeErrInvalidKey("failed to export key [%s]", key).Err())
			return
		}
	})
	if err == nil {
		err = et.error()
	}
	return maybeSingleError(err, ent)
}

// KeyForObj extracts a key from src.
//
// It is the same as KeyForObjErr, except that if KeyForObjErr would have
// returned an error, this method panics. It's safe to use if you know that
// src statically meets the metadata constraints described by KeyForObjErr.
func KeyForObj(c context.Context, src interface{}) *Key {
	ret, err := KeyForObjErr(c, src)
	if err != nil {
		panic(err)
	}
	return ret
}

// KeyForObjErr extracts a key from src.
//
// src must be one of:
//   - *S, where S is a struct
//   - a PropertyLoadSaver
//
// It is expected that the struct exposes the following metadata (as retrieved
// by MetaGetter.GetMeta):
//   - "key" (type: Key) - The full datastore key to use. Must not be nil.
//     OR
//   - "id" (type: int64 or string) - The id of the Key to create.
//   - "kind" (optional, type: string) - The kind of the Key to create. If
//     blank or not present, KeyForObjErr will extract the name of the src
//     object's type.
//   - "parent" (optional, type: Key) - The parent key to use.
//
// By default, the metadata will be extracted from the struct and its tagged
// properties. However, if the struct implements MetaGetterSetter it is
// wholly responsible for exporting the required fields. A struct that
// implements GetMeta to make some minor tweaks can evoke the defualt behavior
// by using GetPLS(s).GetMeta.
//
// If a required metadata item is missing or of the wrong type, then this will
// return an error.
func KeyForObjErr(c context.Context, src interface{}) (*Key, error) {
	return newKeyObjErr(GetKeyContext(c), getMGS(src))
}

// MakeKey is a convenience method for manufacturing a *Key. It should only be
// used when elems... is known statically (e.g. in the code) to be correct.
//
// elems is pairs of (string, string|int|int32|int64) pairs, which correspond
// to Kind/id pairs. Example:
//   dstore.MakeKey("Parent", 1, "Child", "id")
//
// Would create the key:
//   <current appID>:<current Namespace>:/Parent,1/Child,id
//
// If elems is not parsable (e.g. wrong length, wrong types, etc.) this method
// will panic.
func MakeKey(c context.Context, elems ...interface{}) *Key {
	kc := GetKeyContext(c)
	return kc.MakeKey(elems...)
}

// NewKey constructs a new key in the current appID/Namespace, using the
// specified parameters.
func NewKey(c context.Context, kind, stringID string, intID int64, parent *Key) *Key {
	kc := GetKeyContext(c)
	return kc.NewKey(kind, stringID, intID, parent)
}

// NewIncompleteKeys allocates count incomplete keys sharing the same kind and
// parent. It is useful as input to AllocateIDs.
func NewIncompleteKeys(c context.Context, count int, kind string, parent *Key) (keys []*Key) {
	kc := GetKeyContext(c)
	if count > 0 {
		keys = make([]*Key, count)
		for i := range keys {
			keys[i] = kc.NewKey(kind, "", 0, parent)
		}
	}
	return
}

// NewKeyToks constructs a new key in the current appID/Namespace, using the
// specified key tokens.
func NewKeyToks(c context.Context, toks []KeyTok) *Key {
	kc := GetKeyContext(c)
	return kc.NewKeyToks(toks)
}

// PopulateKey loads key into obj.
//
// obj is any object that Interface.Get is able to accept.
//
// Upon successful application, this method will return true. If the key could
// not be applied to the object, this method will return false. It will panic if
// obj is an invalid datastore model.
//
// This method will panic if obj is an invalid datastore model. If the key could
// not be applied to the object, nothing will happen.
func PopulateKey(obj interface{}, key *Key) bool {
	return populateKeyMGS(getMGS(obj), key)
}

func populateKeyMGS(mgs MetaGetterSetter, key *Key) bool {
	if mgs.SetMeta("key", key) {
		return true
	}

	lst := key.LastTok()
	mgs.SetMeta("kind", lst.Kind)
	mgs.SetMeta("parent", key.Parent())

	if lst.StringID != "" {
		if !mgs.SetMeta("id", lst.StringID) {
			return false
		}
	} else {
		if !mgs.SetMeta("id", lst.IntID) {
			return false
		}
	}

	return true
}

// RunInTransaction runs f inside of a transaction. See the appengine SDK's
// documentation for full details on the behavior of transactions in the
// datastore.
//
// Note that the behavior of transactions may change depending on what filters
// have been installed. It's possible that we'll end up implementing things
// like nested/buffered transactions as filters.
func RunInTransaction(c context.Context, f func(c context.Context) error, opts *TransactionOptions) error {
	return Raw(c).RunInTransaction(f, opts)
}

// Run executes the given query, and calls `cb` for each successfully
// retrieved item.
//
// By default, datastore applies a short (~5s) timeout to queries. This can be
// increased, usually to around several minutes, by explicitly setting a
// deadline on the supplied Context.
//
// cb is a callback function whose signature is
//   func(obj TYPE[, getCursor CursorCB]) [error]
//
// Where TYPE is one of:
//   - S or *S, where S is a struct
//   - P or *P, where *P is a concrete type implementing PropertyLoadSaver
//   - *Key (implies a keys-only query)
//
// If the error is omitted from the signature, this will run until the query
// returns all its results, or has an error/times out.
//
// If error is in the signature, the query will continue as long as the
// callback returns nil. If it returns `Stop`, the query will stop and Run
// will return nil. Otherwise, the query will stop and Run will return the
// user's error.
//
// Run may also stop on the first datastore error encountered, which can occur
// due to flakiness, timeout, etc. If it encounters such an error, it will
// be returned.
func Run(c context.Context, q *Query, cb interface{}) error {
	rcb, isKey, mat := parseRunCallback(cb)

	if isKey {
		q = q.KeysOnly(true)
	}
	fq, err := q.Finalize()
	if err != nil {
		return err
	}

	raw := Raw(c)

	if isKey {
		err = raw.Run(fq, func(k *Key, _ PropertyMap, gc CursorCB) error {
			return rcb(reflect.ValueOf(k), gc)
		})
	} else {
		err = raw.Run(fq, func(k *Key, pm PropertyMap, gc CursorCB) error {
			itm := mat.newElem()
			if err := mat.setPM(itm, pm); err != nil {
				return err
			}
			mat.setKey(itm, k)
			return rcb(itm, gc)
		})
	}
	return filterStop(err)
}

// Count executes the given query and returns the number of entries which
// match it.
//
// By default, datastore applies a short (~5s) timeout to queries. This can be
// increased, usually to around several minutes, by explicitly setting a
// deadline on the supplied Context.
func Count(c context.Context, q *Query) (int64, error) {
	fq, err := q.Finalize()
	if err != nil {
		return 0, err
	}
	v, err := Raw(c).Count(fq)
	return v, filterStop(err)
}

// DecodeCursor converts a string returned by a Cursor into a Cursor instance.
// It will return an error if the supplied string is not valid, or could not
// be decoded by the implementation.
func DecodeCursor(c context.Context, s string) (Cursor, error) {
	return Raw(c).DecodeCursor(s)
}

// GetAll retrieves all of the Query results into dst.
//
// By default, datastore applies a short (~5s) timeout to queries. This can be
// increased, usually to around several minutes, by explicitly setting a
// deadline on the supplied Context.
//
// dst must be one of:
//   - *[]S or *[]*S, where S is a struct
//   - *[]P or *[]*P, where *P is a concrete type implementing
//     PropertyLoadSaver
//   - *[]*Key implies a keys-only query.
func GetAll(c context.Context, q *Query, dst interface{}) error {
	return getAllRaw(Raw(c), q, dst)
}

func getAllRaw(raw RawInterface, q *Query, dst interface{}) error {
	v := reflect.ValueOf(dst)
	if v.Kind() != reflect.Ptr {
		panic(fmt.Errorf("invalid GetAll dst: must have a ptr-to-slice: %T", dst))
	}
	if !v.IsValid() || v.IsNil() {
		panic(errors.New("invalid GetAll dst: <nil>"))
	}

	if keys, ok := dst.(*[]*Key); ok {
		fq, err := q.KeysOnly(true).Finalize()
		if err != nil {
			return err
		}

		return raw.Run(fq, func(k *Key, _ PropertyMap, _ CursorCB) error {
			*keys = append(*keys, k)
			return nil
		})
	}
	fq, err := q.Finalize()
	if err != nil {
		return err
	}

	slice := v.Elem()
	mat := mustParseMultiArg(slice.Type())
	if mat.newElem == nil {
		panic(fmt.Errorf("invalid GetAll dst (non-concrete element type): %T", dst))
	}

	errs := map[int]error{}
	i := 0
	err = filterStop(raw.Run(fq, func(k *Key, pm PropertyMap, _ CursorCB) error {
		slice.Set(reflect.Append(slice, mat.newElem()))
		itm := slice.Index(i)
		mat.setKey(itm, k)
		err := mat.setPM(itm, pm)
		if err != nil {
			errs[i] = err
		}
		i++
		return nil
	}))
	if err == nil {
		if len(errs) > 0 {
			me := make(errors.MultiError, slice.Len())
			for i, e := range errs {
				me[i] = e
			}
			err = me
		}
	}
	return err
}

// Exists tests if the supplied objects are present in the datastore.
//
// ent must be one of:
//	- *S, where S is a struct
//	- *P, where *P is a concrete type implementing PropertyLoadSaver
//	- []S or []*S, where S is a struct
//	- []P or []*P, where *P is a concrete type implementing PropertyLoadSaver
//	- []I, where I is some interface type. Each element of the slice must
//	  be non-nil, and its underlying type must be either *S or *P.
//	- *Key, to check a specific key from the datastore.
//	- []*Key, to check a slice of keys from the datastore.
//
// If an error is encountered, the returned error value will depend on the
// input arguments. If one argument is supplied, the result will be the
// encountered error type. If multiple arguments are supplied, the result will
// be a MultiError whose error index corresponds to the argument in which the
// error was encountered.
//
// If an ent argument is a slice, its error type will be a MultiError. Note
// that in the scenario, where multiple slices are provided, this will return a
// MultiError containing a nested MultiError for each slice argument.
func Exists(c context.Context, ent ...interface{}) (*ExistsResult, error) {
	if len(ent) == 0 {
		return nil, nil
	}

	mma, err := makeMetaMultiArg(ent, mmaKeysOnly)
	if err != nil {
		panic(err)
	}

	keys, _, et := mma.getKeysPMs(GetKeyContext(c), false)
	if len(keys) == 0 {
		return nil, nil
	}

	var dat DroppedArgTracker
	dat.MarkNilKeys(keys)
	keys, dal := dat.DropKeys(keys)

	bt := newBoolTracker(mma, et)
	err = Raw(c).GetMulti(keys, nil, func(compressedIdx int, _ PropertyMap, err error) {
		idx := dal.OriginalIndex(compressedIdx)
		bt.trackExistsResult(mma.index(idx), err)
	})

	if err == nil {
		err = bt.error()
	}
	return bt.result(), maybeSingleError(err, ent)
}

// Get retrieves objects from the datastore.
//
// Each element in dst must be one of:
//	- *S, where S is a struct
//	- *P, where *P is a concrete type implementing PropertyLoadSaver
//	- []S or []*S, where S is a struct
//	- []P or []*P, where *P is a concrete type implementing PropertyLoadSaver
//	- []I, where I is some interface type. Each element of the slice must
//	  be non-nil, and its underlying type must be either *S or *P.
//
// If an error is encountered, the returned error value will depend on the
// input arguments. If one argument is supplied, the result will be the
// encountered error type. If multiple arguments are supplied, the result will
// be a MultiError whose error index corresponds to the argument in which the
// error was encountered.
//
// If a dst argument is a slice, its error type will be a MultiError. Note
// that in the scenario where multiple slices are provided, this will return a
// MultiError containing a nested MultiError for each slice argument.
//
// If there was an issue retrieving the entity, the input `dst` objects will
// not be affected. This means that you can populate an object for dst with some
// values, do a Get, and on an ErrNoSuchEntity, do a Put (inside a transaction,
// of course :)).
func Get(c context.Context, dst ...interface{}) error {
	if len(dst) == 0 {
		return nil
	}

	mma, err := makeMetaMultiArg(dst, mmaReadWrite)
	if err != nil {
		panic(err)
	}

	keys, pms, et := mma.getKeysPMs(GetKeyContext(c), true)
	if len(keys) == 0 {
		return nil
	}

	var dat DroppedArgTracker
	dat.MarkNilKeysVals(keys, pms)
	keys, pms, dal := dat.DropKeysAndVals(keys, pms)

	meta := NewMultiMetaGetter(pms)
	err = Raw(c).GetMulti(keys, meta, func(compressedIdx int, pm PropertyMap, err error) {
		idx := dal.OriginalIndex(compressedIdx)
		index := mma.index(idx)
		if err != nil {
			et.trackError(index, err)
			return
		}

		mat, v := mma.get(index)
		if err := mat.setPM(v, pm); err != nil {
			et.trackError(index, err)
			return
		}
	})

	if err == nil {
		err = et.error()
	}
	return maybeSingleError(err, dst)
}

// Put writes objects into the datastore.
//
// src must be one of:
//	- *S, where S is a struct
//	- *P, where *P is a concrete type implementing PropertyLoadSaver
//	- []S or []*S, where S is a struct
//	- []P or []*P, where *P is a concrete type implementing PropertyLoadSaver
//	- []I, where I is some interface type. Each element of the slice must
//	  be non-nil, and its underlying type must be either *S or *P.
//
// A *Key will be extracted from src via KeyForObj. If
// extractedKey.IsIncomplete() is true, and the object is put to the datastore
// successfully, then Put will write the resolved (datastore-generated) *Key
// back to src.
//
// NOTE: The datastore only autogenerates *Keys with integer IDs. Only models
// which use a raw `$key` or integer-typed `$id` field are elegible for this.
// A model with a string-typed `$id` field will not accept an integer id'd *Key
// and will cause the Put to fail.
//
// If an error is encountered, the returned error value will depend on the
// input arguments. If one argument is supplied, the result will be the
// encountered error type. If multiple arguments are supplied, the result will
// be a MultiError whose error index corresponds to the argument in which the
// error was encountered.
//
// If a src argument is a slice, its error type will be a MultiError. Note
// that in the scenario where multiple slices are provided, this will return a
// MultiError containing a nested MultiError for each slice argument.
func Put(c context.Context, src ...interface{}) error {
	return putRaw(Raw(c), GetKeyContext(c), src)
}

func putRaw(raw RawInterface, kctx KeyContext, src []interface{}) error {
	if len(src) == 0 {
		return nil
	}

	mma, err := makeMetaMultiArg(src, mmaReadWrite)
	if err != nil {
		panic(err)
	}

	keys, vals, et := mma.getKeysPMs(kctx, false)
	if len(keys) == 0 {
		return nil
	}

	var dat DroppedArgTracker
	dat.MarkNilKeysVals(keys, vals)
	keys, vals, dal := dat.DropKeysAndVals(keys, vals)

	err = raw.PutMulti(keys, vals, func(compressedIdx int, key *Key, err error) {
		idx := dal.OriginalIndex(compressedIdx)
		index := mma.index(idx)

		if err != nil {
			et.trackError(index, err)
			return
		}

		if !key.Equal(keys[compressedIdx]) {
			mat, v := mma.get(index)
			mat.setKey(v, key)
		}
	})
	if err == nil {
		err = et.error()
	}
	return maybeSingleError(err, src)
}

// Delete removes the supplied entities from the datastore.
//
// ent must be one of:
//	- *S, where S is a struct
//	- *P, where *P is a concrete type implementing PropertyLoadSaver
//	- []S or []*S, where S is a struct
//	- []P or []*P, where *P is a concrete type implementing PropertyLoadSaver
//	- []I, where I is some interface type. Each element of the slice must
//	  be non-nil, and its underlying type must be either *S or *P.
//	- *Key, to remove a specific key from the datastore.
//	- []*Key, to remove a slice of keys from the datastore.
//
// If an error is encountered, the returned error value will depend on the
// input arguments. If one argument is supplied, the result will be the
// encountered error type. If multiple arguments are supplied, the result will
// be a MultiError whose error index corresponds to the argument in which the
// error was encountered.
//
// If an ent argument is a slice, its error type will be a MultiError. Note
// that in the scenario where multiple slices are provided, this will return a
// MultiError containing a nested MultiError for each slice argument.
func Delete(c context.Context, ent ...interface{}) error {
	if len(ent) == 0 {
		return nil
	}

	mma, err := makeMetaMultiArg(ent, mmaKeysOnly)
	if err != nil {
		panic(err)
	}

	keys, _, et := mma.getKeysPMs(GetKeyContext(c), false)
	if len(keys) == 0 {
		return nil
	}

	var dat DroppedArgTracker
	dat.MarkNilKeys(keys)
	keys, dal := dat.DropKeys(keys)

	err = Raw(c).DeleteMulti(keys, func(compressedIdx int, err error) {
		idx := dal.OriginalIndex(compressedIdx)

		if err != nil {
			index := mma.index(idx)
			et.trackError(index, err)
		}
	})

	if err == nil {
		err = et.error()
	}
	return maybeSingleError(err, ent)
}

// GetTestable returns the Testable interface for the implementation, or nil if
// there is none.
func GetTestable(c context.Context) Testable {
	return Raw(c).GetTestable()
}

// maybeSingleError normalizes the error experience between single- and
// multi-element API calls.
//
// Single-element API calls will return a single error for that element, while
// multi-element API calls will return a MultiError, one for each element. This
// accepts the slice of elements that is being operated on and determines what
// sort of error to return.
func maybeSingleError(err error, elems []interface{}) error {
	if err == nil {
		return nil
	}
	if len(elems) == 1 {
		return errors.SingleError(err)
	}
	return err
}

func filterStop(err error) error {
	if err == Stop {
		err = nil
	}
	return err
}