// Copyright 2017 Google LLC
//
// 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 firestore

import (
	"errors"
	"fmt"
	"io"
	"reflect"
	"sort"

	"golang.org/x/net/context"
	"google.golang.org/api/iterator"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"

	vkit "cloud.google.com/go/firestore/apiv1beta1"
	pb "google.golang.org/genproto/googleapis/firestore/v1beta1"
)

var errNilDocRef = errors.New("firestore: nil DocumentRef")

// A DocumentRef is a reference to a Firestore document.
type DocumentRef struct {
	// The CollectionRef that this document is a part of. Never nil.
	Parent *CollectionRef

	// The full resource path of the document: "projects/P/databases/D/documents..."
	Path string

	// The ID of the document: the last component of the resource path.
	ID string
}

func newDocRef(parent *CollectionRef, id string) *DocumentRef {
	return &DocumentRef{
		Parent: parent,
		ID:     id,
		Path:   parent.Path + "/" + id,
	}
}

// Collection returns a reference to sub-collection of this document.
func (d *DocumentRef) Collection(id string) *CollectionRef {
	return newCollRefWithParent(d.Parent.c, d, id)
}

// Get retrieves the document. If the document does not exist, Get return a NotFound error, which
// can be checked with
//    grpc.Code(err) == codes.NotFound
// In that case, Get returns a non-nil DocumentSnapshot whose Exists method return false and whose
// ReadTime is the time of the failed read operation.
func (d *DocumentRef) Get(ctx context.Context) (*DocumentSnapshot, error) {
	if err := checkTransaction(ctx); err != nil {
		return nil, err
	}
	if d == nil {
		return nil, errNilDocRef
	}
	docsnaps, err := d.Parent.c.getAll(ctx, []*DocumentRef{d}, nil)
	if err != nil {
		return nil, err
	}
	ds := docsnaps[0]
	if !ds.Exists() {
		return ds, status.Errorf(codes.NotFound, "%q not found", d.Path)
	}
	return ds, nil
}

// Create creates the document with the given data.
// It returns an error if a document with the same ID already exists.
//
// The data argument can be a map with string keys, a struct, or a pointer to a
// struct. The map keys or exported struct fields become the fields of the firestore
// document.
// The values of data are converted to Firestore values as follows:
//
//   - bool converts to Bool.
//   - string converts to String.
//   - int, int8, int16, int32 and int64 convert to Integer.
//   - uint8, uint16 and uint32 convert to Integer. uint64 is disallowed,
//     because it can represent values that cannot be represented in an int64, which
//     is the underlying type of a Integer.
//   - float32 and float64 convert to Double.
//   - []byte converts to Bytes.
//   - time.Time and *ts.Timestamp convert to Timestamp. ts is the package
//     "github.com/golang/protobuf/ptypes/timestamp".
//   - *latlng.LatLng converts to GeoPoint. latlng is the package
//     "google.golang.org/genproto/googleapis/type/latlng". You should always use
//     a pointer to a LatLng.
//   - Slices convert to Array.
//   - Maps and structs convert to Map.
//   - nils of any type convert to Null.
//
// Pointers and interface{} are also permitted, and their elements processed
// recursively.
//
// Struct fields can have tags like those used by the encoding/json package. Tags
// begin with "firestore:" and are followed by "-", meaning "ignore this field," or
// an alternative name for the field. Following the name, these comma-separated
// options may be provided:
//
//   - omitempty: Do not encode this field if it is empty. A value is empty
//     if it is a zero value, or an array, slice or map of length zero.
//   - serverTimestamp: The field must be of type time.Time. When writing, if
//     the field has the zero value, the server will populate the stored document with
//     the time that the request is processed.
func (d *DocumentRef) Create(ctx context.Context, data interface{}) (*WriteResult, error) {
	ws, err := d.newCreateWrites(data)
	if err != nil {
		return nil, err
	}
	return d.Parent.c.commit1(ctx, ws)
}

func (d *DocumentRef) newCreateWrites(data interface{}) ([]*pb.Write, error) {
	if d == nil {
		return nil, errNilDocRef
	}
	doc, serverTimestampPaths, err := toProtoDocument(data)
	if err != nil {
		return nil, err
	}
	doc.Name = d.Path
	pc, err := exists(false).preconditionProto()
	if err != nil {
		return nil, err
	}
	return d.newUpdateWithTransform(doc, nil, pc, serverTimestampPaths, false), nil
}

// Set creates or overwrites the document with the given data. See DocumentRef.Create
// for the acceptable values of data. Without options, Set overwrites the document
// completely. Specify one of the Merge options to preserve an existing document's
// fields.
func (d *DocumentRef) Set(ctx context.Context, data interface{}, opts ...SetOption) (*WriteResult, error) {
	ws, err := d.newSetWrites(data, opts)
	if err != nil {
		return nil, err
	}
	return d.Parent.c.commit1(ctx, ws)
}

func (d *DocumentRef) newSetWrites(data interface{}, opts []SetOption) ([]*pb.Write, error) {
	if d == nil {
		return nil, errNilDocRef
	}
	if data == nil {
		return nil, errors.New("firestore: nil document contents")
	}
	if len(opts) == 0 { // Set without merge
		doc, serverTimestampPaths, err := toProtoDocument(data)
		if err != nil {
			return nil, err
		}
		doc.Name = d.Path
		return d.newUpdateWithTransform(doc, nil, nil, serverTimestampPaths, true), nil
	}
	// Set with merge.
	// This is just like Update, except for the existence precondition.
	// So we turn data into a list of (FieldPath, interface{}) pairs (fpv's), as we do
	// for Update.
	fieldPaths, allPaths, err := processSetOptions(opts)
	if err != nil {
		return nil, err
	}
	var fpvs []fpv
	v := reflect.ValueOf(data)
	if allPaths {
		// Set with MergeAll. Collect all the leaves of the map.
		if v.Kind() != reflect.Map {
			return nil, errors.New("firestore: MergeAll can only be specified with map data")
		}
		if v.Len() == 0 {
			// Special case: MergeAll with an empty map.
			return d.newUpdateWithTransform(&pb.Document{Name: d.Path}, []FieldPath{}, nil, nil, true), nil
		}
		fpvsFromData(v, nil, &fpvs)
	} else {
		// Set with merge paths.  Collect only the values at the given paths.
		for _, fp := range fieldPaths {
			val, err := getAtPath(v, fp)
			if err != nil {
				return nil, err
			}
			fpvs = append(fpvs, fpv{fp, val})
		}
	}
	return d.fpvsToWrites(fpvs, nil)
}

// fpvsFromData converts v into a list of (FieldPath, value) pairs.
func fpvsFromData(v reflect.Value, prefix FieldPath, fpvs *[]fpv) {
	switch v.Kind() {
	case reflect.Map:
		for _, k := range v.MapKeys() {
			fpvsFromData(v.MapIndex(k), prefix.with(k.String()), fpvs)
		}
	case reflect.Interface:
		fpvsFromData(v.Elem(), prefix, fpvs)

	default:
		var val interface{}
		if v.IsValid() {
			val = v.Interface()
		}
		*fpvs = append(*fpvs, fpv{prefix, val})
	}
}

// removePathsIf creates a new slice of FieldPaths that contains
// exactly those elements of fps for which pred returns false.
func removePathsIf(fps []FieldPath, pred func(FieldPath) bool) []FieldPath {
	// Return fps if it's empty to preserve the distinction betweeen nil and zero-length.
	if len(fps) == 0 {
		return fps
	}
	var result []FieldPath
	for _, fp := range fps {
		if !pred(fp) {
			result = append(result, fp)
		}
	}
	return result
}

// Delete deletes the document. If the document doesn't exist, it does nothing
// and returns no error.
func (d *DocumentRef) Delete(ctx context.Context, preconds ...Precondition) (*WriteResult, error) {
	ws, err := d.newDeleteWrites(preconds)
	if err != nil {
		return nil, err
	}
	return d.Parent.c.commit1(ctx, ws)
}

func (d *DocumentRef) newDeleteWrites(preconds []Precondition) ([]*pb.Write, error) {
	if d == nil {
		return nil, errNilDocRef
	}
	pc, err := processPreconditionsForDelete(preconds)
	if err != nil {
		return nil, err
	}
	return []*pb.Write{{
		Operation:       &pb.Write_Delete{d.Path},
		CurrentDocument: pc,
	}}, nil
}

func (d *DocumentRef) newUpdatePathWrites(updates []Update, preconds []Precondition) ([]*pb.Write, error) {
	if len(updates) == 0 {
		return nil, errors.New("firestore: no paths to update")
	}
	var fpvs []fpv
	for _, u := range updates {
		v, err := u.process()
		if err != nil {
			return nil, err
		}
		fpvs = append(fpvs, v)
	}
	pc, err := processPreconditionsForUpdate(preconds)
	if err != nil {
		return nil, err
	}
	return d.fpvsToWrites(fpvs, pc)
}

func (d *DocumentRef) fpvsToWrites(fpvs []fpv, pc *pb.Precondition) ([]*pb.Write, error) {
	// Make sure there are no duplications or prefixes among the field paths.
	var fps []FieldPath
	for _, fpv := range fpvs {
		fps = append(fps, fpv.fieldPath)
	}
	if err := checkNoDupOrPrefix(fps); err != nil {
		return nil, err
	}

	// Process each fpv.
	var updatePaths, transformPaths []FieldPath
	doc := &pb.Document{
		Name:   d.Path,
		Fields: map[string]*pb.Value{},
	}
	for _, fpv := range fpvs {
		switch fpv.value {
		case Delete:
			// Send the field path without a corresponding value.
			updatePaths = append(updatePaths, fpv.fieldPath)

		case ServerTimestamp:
			// Use the path in a transform operation.
			transformPaths = append(transformPaths, fpv.fieldPath)

		default:
			updatePaths = append(updatePaths, fpv.fieldPath)
			// Convert the value to a proto and put it into the document.
			v := reflect.ValueOf(fpv.value)
			pv, sawServerTimestamp, err := toProtoValue(v)
			if err != nil {
				return nil, err
			}
			setAtPath(doc.Fields, fpv.fieldPath, pv)
			// Also accumulate any serverTimestamp values within the value.
			if sawServerTimestamp {
				stps, err := extractTransformPaths(v, nil)
				if err != nil {
					return nil, err
				}
				for _, p := range stps {
					transformPaths = append(transformPaths, fpv.fieldPath.concat(p))
				}
			}
		}
	}
	return d.newUpdateWithTransform(doc, updatePaths, pc, transformPaths, false), nil
}

var requestTimeTransform = &pb.DocumentTransform_FieldTransform_SetToServerValue{
	pb.DocumentTransform_FieldTransform_REQUEST_TIME,
}

// newUpdateWithTransform constructs operations for a commit. Most generally, it
// returns an update operation followed by a transform.
//
// If there are no serverTimestampPaths, the transform is omitted.
//
// If doc.Fields is empty, there are no updatePaths, and there is no precondition,
// the update is omitted, unless updateOnEmpty is true.
func (d *DocumentRef) newUpdateWithTransform(doc *pb.Document, updatePaths []FieldPath, pc *pb.Precondition, serverTimestampPaths []FieldPath, updateOnEmpty bool) []*pb.Write {
	// Remove server timestamp fields from updatePaths. Those fields were removed
	// from the document by toProtoDocument, so they should not be in the update
	// mask.
	// Note: this is technically O(n^2), but it is unlikely that there is
	// more than one server timestamp path.
	updatePaths = removePathsIf(updatePaths, func(fp FieldPath) bool {
		return fp.in(serverTimestampPaths)
	})
	var ws []*pb.Write
	if updateOnEmpty || len(doc.Fields) > 0 ||
		len(updatePaths) > 0 || (pc != nil && len(serverTimestampPaths) == 0) {
		var mask *pb.DocumentMask
		if updatePaths != nil {
			sfps := toServiceFieldPaths(updatePaths)
			sort.Strings(sfps) // TODO(jba): make tests pass without this
			mask = &pb.DocumentMask{FieldPaths: sfps}
		}
		w := &pb.Write{
			Operation:       &pb.Write_Update{doc},
			UpdateMask:      mask,
			CurrentDocument: pc,
		}
		ws = append(ws, w)
		pc = nil // If the precondition is in the write, we don't need it in the transform.
	}
	if len(serverTimestampPaths) > 0 || pc != nil {
		ws = append(ws, d.newTransform(serverTimestampPaths, pc))
	}
	return ws
}

func (d *DocumentRef) newTransform(serverTimestampFieldPaths []FieldPath, pc *pb.Precondition) *pb.Write {
	sort.Sort(byPath(serverTimestampFieldPaths)) // TODO(jba): make tests pass without this
	var fts []*pb.DocumentTransform_FieldTransform
	for _, p := range serverTimestampFieldPaths {
		fts = append(fts, &pb.DocumentTransform_FieldTransform{
			FieldPath:     p.toServiceFieldPath(),
			TransformType: requestTimeTransform,
		})
	}
	return &pb.Write{
		Operation: &pb.Write_Transform{
			&pb.DocumentTransform{
				Document:        d.Path,
				FieldTransforms: fts,
				// TODO(jba): should the transform have the same preconditions as the write?
			},
		},
		CurrentDocument: pc,
	}
}

type sentinel int

const (
	// Delete is used as a value in a call to Update or Set with merge to indicate
	// that the corresponding key should be deleted.
	Delete sentinel = iota

	// ServerTimestamp is used as a value in a call to Update to indicate that the
	// key's value should be set to the time at which the server processed
	// the request.
	ServerTimestamp
)

func (s sentinel) String() string {
	switch s {
	case Delete:
		return "Delete"
	case ServerTimestamp:
		return "ServerTimestamp"
	default:
		return "<?sentinel?>"
	}
}

func isStructOrStructPtr(x interface{}) bool {
	v := reflect.ValueOf(x)
	if v.Kind() == reflect.Struct {
		return true
	}
	if v.Kind() == reflect.Ptr && v.Elem().Kind() == reflect.Struct {
		return true
	}
	return false
}

// An Update describes an update to a value referred to by a path.
// An Update should have either a non-empty Path or a non-empty FieldPath,
// but not both.
//
// See DocumentRef.Create for acceptable values.
// To delete a field, specify firestore.Delete as the value.
type Update struct {
	Path      string // Will be split on dots, and must not contain any of "Ëœ*/[]".
	FieldPath FieldPath
	Value     interface{}
}

// An fpv is a pair of validated FieldPath and value.
type fpv struct {
	fieldPath FieldPath
	value     interface{}
}

func (u *Update) process() (fpv, error) {
	if (u.Path != "") == (u.FieldPath != nil) {
		return fpv{}, fmt.Errorf("firestore: update %+v should have exactly one of Path or FieldPath", u)
	}
	fp := u.FieldPath
	var err error
	if fp == nil {
		fp, err = parseDotSeparatedString(u.Path)
		if err != nil {
			return fpv{}, err
		}
	}
	if err := fp.validate(); err != nil {
		return fpv{}, err
	}
	return fpv{fp, u.Value}, nil
}

// Update updates the document. The values at the given
// field paths are replaced, but other fields of the stored document are untouched.
func (d *DocumentRef) Update(ctx context.Context, updates []Update, preconds ...Precondition) (*WriteResult, error) {
	ws, err := d.newUpdatePathWrites(updates, preconds)
	if err != nil {
		return nil, err
	}
	return d.Parent.c.commit1(ctx, ws)
}

// Collections returns an interator over the immediate sub-collections of the document.
func (d *DocumentRef) Collections(ctx context.Context) *CollectionIterator {
	client := d.Parent.c
	it := &CollectionIterator{
		err:    checkTransaction(ctx),
		client: client,
		parent: d,
		it: client.c.ListCollectionIds(
			withResourceHeader(ctx, client.path()),
			&pb.ListCollectionIdsRequest{Parent: d.Path}),
	}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.items) },
		func() interface{} { b := it.items; it.items = nil; return b })
	return it
}

// CollectionIterator is an iterator over sub-collections of a document.
type CollectionIterator struct {
	client   *Client
	parent   *DocumentRef
	it       *vkit.StringIterator
	pageInfo *iterator.PageInfo
	nextFunc func() error
	items    []*CollectionRef
	err      error
}

// PageInfo supports pagination. See the google.golang.org/api/iterator package for details.
func (it *CollectionIterator) PageInfo() *iterator.PageInfo { return it.pageInfo }

// Next returns the next result. Its second return value is iterator.Done if there
// are no more results. Once Next returns Done, all subsequent calls will return
// Done.
func (it *CollectionIterator) Next() (*CollectionRef, error) {
	if err := it.nextFunc(); err != nil {
		return nil, err
	}
	item := it.items[0]
	it.items = it.items[1:]
	return item, nil
}

func (it *CollectionIterator) fetch(pageSize int, pageToken string) (string, error) {
	if it.err != nil {
		return "", it.err
	}
	return iterFetch(pageSize, pageToken, it.it.PageInfo(), func() error {
		id, err := it.it.Next()
		if err != nil {
			return err
		}
		var cr *CollectionRef
		if it.parent == nil {
			cr = newTopLevelCollRef(it.client, it.client.path(), id)
		} else {
			cr = newCollRefWithParent(it.client, it.parent, id)
		}
		it.items = append(it.items, cr)
		return nil
	})
}

// GetAll returns all the collections remaining from the iterator.
func (it *CollectionIterator) GetAll() ([]*CollectionRef, error) {
	var crs []*CollectionRef
	for {
		cr, err := it.Next()
		if err == iterator.Done {
			break
		}
		if err != nil {
			return nil, err
		}
		crs = append(crs, cr)
	}
	return crs, nil
}

// Common fetch code for iterators that are backed by vkit iterators.
// TODO(jba): dedup with same function in logging/logadmin.
func iterFetch(pageSize int, pageToken string, pi *iterator.PageInfo, next func() error) (string, error) {
	pi.MaxSize = pageSize
	pi.Token = pageToken
	// Get one item, which will fill the buffer.
	if err := next(); err != nil {
		return "", err
	}
	// Collect the rest of the buffer.
	for pi.Remaining() > 0 {
		if err := next(); err != nil {
			return "", err
		}
	}
	return pi.Token, nil
}

// Snapshots returns an iterator over snapshots of the document. Each time the document
// changes or is added or deleted, a new snapshot will be generated.
func (d *DocumentRef) Snapshots(ctx context.Context) *DocumentSnapshotIterator {
	return &DocumentSnapshotIterator{
		docref: d,
		ws:     newWatchStreamForDocument(ctx, d),
	}
}

// DocumentSnapshotIterator is an iterator over snapshots of a document.
// Call Next on the iterator to get a snapshot of the document each time it changes.
// Call Stop on the iterator when done.
//
// For an example, see DocumentRef.Snapshots.
type DocumentSnapshotIterator struct {
	docref *DocumentRef
	ws     *watchStream
}

// Next blocks until the document changes, then returns the DocumentSnapshot for
// the current state of the document. If the document has been deleted, Next
// returns a DocumentSnapshot whose Exists method returns false.
//
// Next never returns iterator.Done unless it is called after Stop.
func (it *DocumentSnapshotIterator) Next() (*DocumentSnapshot, error) {
	btree, _, readTime, err := it.ws.nextSnapshot()
	if err != nil {
		if err == io.EOF {
			err = iterator.Done
		}
		// watchStream's error is sticky, so SnapshotIterator does not need to remember it.
		return nil, err
	}
	if btree.Len() == 0 { // document deleted
		return &DocumentSnapshot{Ref: it.docref, ReadTime: readTime}, nil
	}
	snap, _ := btree.At(0)
	return snap.(*DocumentSnapshot), nil
}

// Stop stops receiving snapshots.
// You should always call Stop when you are done with an iterator, to free up resources.
// It is not safe to call Stop concurrently with Next.
func (it *DocumentSnapshotIterator) Stop() {
	it.ws.stop()
}
