// Copyright 2015 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package syncbase defines the wire API for a structured store that supports
// peer-to-peer synchronization.
//
// TODO(sadovsky): Write a detailed package description, or provide a reference
// to the Syncbase documentation.
package syncbase

import (
	"time"

  "v.io/v23/security/access"
  "v.io/v23/services/permissions"
	"v.io/v23/services/watch"
)

// NOTE(sadovsky): Various methods below may end up needing additional options.

// TODO(sadovsky): Move "DevMode" methods elsewhere, so that they are completely
// hidden from clients. Relatedly, configure the server to not even export these
// RPC methods if the --dev flag is not set.

// Service represents a Vanadium Syncbase service.
// Service.Glob operates over Database ids.
type Service interface {
	// DevModeUpdateVClock updates various bits of Syncbase virtual clock and
	// clock daemon state based on the specified options.
	// Requires --dev flag to be set (in addition to Admin check).
	DevModeUpdateVClock(uco DevModeUpdateVClockOpts) error {access.Admin}

	// DevModeGetTime returns the current time per the Syncbase clock.
	// Requires --dev flag to be set (in addition to Admin check).
	DevModeGetTime() (time.Time | error) {access.Admin}

	// SetPermissions and GetPermissions are included from the Object interface.
	permissions.Object
}

// Database represents a set of Collections. Batches, queries, sync, watch, etc.
// all operate at the Database level.
// Database.Glob operates over Collection names.
type Database interface {
	// Create creates this Database.
	// TODO(sadovsky): Specify what happens if perms is nil.
	// Create requires the caller to have Write permission at the Service.
	Create(metadata ?SchemaMetadata, perms access.Permissions) error {access.Write}

	// Destroy destroys this Database, permanently removing all of its data.
	Destroy() error {access.Write}

	// Exists returns true only if this Database exists. Insufficient permissions
	// cause Exists to return false instead of an error.
	// TODO(ivanpi): Exists may fail with an error if higher levels of hierarchy
	// do not exist.
	Exists() (bool | error) {access.Resolve}

	// ListCollections returns a list of all Collection names.
	// This method exists on Database but not on Service because for the latter
	// we can simply use glob, while for the former glob lists only Collections
	// visible in a new snapshot of the Database, ignoring user batches.
	// (Note that the same issue is present in glob on Collection, where Scan can
	// be used instead if batch awareness is required.)
	// Note, the glob client library checks Resolve access on every component
	// along the path (by doing a Dispatcher.Lookup), whereas this doesn't happen
	// for other RPCs.
	// TODO(ivanpi): Resolve should be checked on all RPCs.
	// TODO(sadovsky): Maybe switch to streaming RPC.
	ListCollections(bh BatchHandle) ([]string | error) {access.Read}

	// Exec executes a syncQL query with positional parameters and returns all
	// results as specified by the query's select/delete statement.
	// Concurrency semantics are documented in model.go.
	Exec(bh BatchHandle, query string, params []any) stream<_, []any> error {access.Read}

	// BeginBatch creates a new batch. It returns a batch handle to pass in when
	// calling batch-aware RPCs.
	// Concurrency semantics are documented in model.go.
	// All batch-aware RPCs can also be called outside a batch (with an empty
	// handle), with the exception of Commit and Abort which only make sense on
	// a batch. Note that glob RPCs are not batch-aware.
	// TODO(sadovsky): Maybe make BatchOptions optional. Also, rename it to 'opts'
	// everywhere now that v.io/i/912 is resolved.
	BeginBatch(bo BatchOptions) (BatchHandle | error) {access.Read}

	// Commit persists the pending changes to the database.
	// If the BatchHandle is empty, Commit() will fail with ErrNotBoundToBatch.
	Commit(bh BatchHandle) error {access.Read}

	// Abort notifies the server that any pending changes can be discarded.
	// It is not strictly required, but it may allow the server to release locks
	// or other resources sooner than if it was not called.
	// If the BatchHandle is empty, Abort() will fail with ErrNotBoundToBatch.
	Abort(bh BatchHandle) error {access.Read}

	// PauseSync pauses sync for this database. Incoming sync, as well as
	// outgoing sync of subsequent writes, will be disabled until ResumeSync
	// is called. PauseSync is idempotent.
	PauseSync() error {access.Write}

	// ResumeSync resumes sync for this database. ResumeSync is idempotent.
	ResumeSync() error {access.Write}

	// SetPermissions and GetPermissions are included from the Object interface.
	permissions.Object

	// DatabaseWatcher implements the API to watch for updates in the database.
	DatabaseWatcher

	// SyncgroupManager implements the API for managing syncgroups attached to a
	// Database.
	SyncgroupManager

	// BlobManager implements the API for managing blobs attached to rows in
	// a Database.
	BlobManager

	// SchemaManager implements the API for managing schema metadata attached
	// to a Database.
	SchemaManager

	// ConflictManager implements the API for registering resolvers, receiving
	// conflicts and sending resolutions.
	ConflictManager
}

// Collection represents a collection of Rows.
// Collection.Glob operates over the primary keys of Rows in the Collection.
type Collection interface {
	// Create creates this Collection.
	// If perms is nil, we inherit (copy) the Database perms.
	Create(bh BatchHandle, perms access.Permissions) error {access.Write}

	// Destroy destroys this Collection.
	Destroy(bh BatchHandle) error {access.Write}

	// Exists returns true only if this Collection exists. Insufficient
	// permissions cause Exists to return false instead of an error.
	// TODO(ivanpi): Exists may fail with an error if higher levels of hierarchy
	// do not exist.
	Exists(bh BatchHandle) (bool | error) {access.Resolve}

	// GetPermissions returns the current Permissions for the Collection.
	GetPermissions(bh BatchHandle) (access.Permissions | error) {access.Admin}

	// SetPermissions replaces the current Permissions for the Collection.
	SetPermissions(bh BatchHandle, perms access.Permissions) error {access.Admin}

	// DeleteRange deletes all rows in the given half-open range [start, limit).
	// If limit is "", all rows with keys >= start are included.
	DeleteRange(bh BatchHandle, start, limit []byte) error {access.Write}

	// Scan returns all rows in the given half-open range [start, limit). If limit
	// is "", all rows with keys >= start are included. Concurrency semantics are
	// documented in model.go.
	Scan(bh BatchHandle, start, limit []byte) stream<_, KeyValue> error {access.Read}
}

// Row represents a single row in a Collection.
// All access checks are performed against the Collection ACL.
// NOTE(sadovsky): Currently we send []byte values over the wire for Get, Put,
// and Scan. If there's a way to avoid encoding/decoding on the server side, we
// can use vdl.Value everywhere without sacrificing performance.
type Row interface {
	// Exists returns true only if this Row exists. Insufficient permissions
	// cause Exists to return false instead of an error.
	// Note, Exists on Row requires read permissions, unlike higher levels of
	// hierarchy which require resolve, because Row existence usually carries
	// more information.
	// TODO(ivanpi): Exists may fail with an error if higher levels of hierarchy
	// do not exist.
	Exists(bh BatchHandle) (bool | error) {access.Read}

	// Get returns the value for this Row.
	Get(bh BatchHandle) ([]byte | error) {access.Read}

	// Put writes the given value for this Row.
	Put(bh BatchHandle, value []byte) error {access.Write}

	// Delete deletes this Row.
	Delete(bh BatchHandle) error {access.Write}
}

// SyncgroupManager is the interface for syncgroup operations.
// TODO(hpucha): Add blessings to create/join and add a refresh method.
type SyncgroupManager interface {
	// GetSyncgroupNames returns the global names of all syncgroups attached to
	// this database.
	GetSyncgroupNames() ([]string | error) {access.Read}

	// CreateSyncgroup creates a new syncgroup with the given spec.
	//
	// Requires: Client must have at least Read access on the Database; all
	// Collections specified in prefixes must exist; Client must have at least
	// Read access on each of the Collection ACLs.
	CreateSyncgroup(sgName string, spec SyncgroupSpec, myInfo SyncgroupMemberInfo) error {access.Read}

	// JoinSyncgroup joins the syncgroup.
	//
	// Requires: Client must have at least Read access on the Database and on the
	// syncgroup ACL.
	JoinSyncgroup(sgName string, myInfo SyncgroupMemberInfo) (spec SyncgroupSpec | error) {access.Read}

	// LeaveSyncgroup leaves the syncgroup. Previously synced data will continue
	// to be available.
	//
	// Requires: Client must have at least Read access on the Database.
	LeaveSyncgroup(sgName string) error {access.Read}

	// DestroySyncgroup destroys the syncgroup. Previously synced data will
	// continue to be available to all members.
	//
	// Requires: Client must have at least Read access on the Database, and must
	// have Admin access on the syncgroup ACL.
	DestroySyncgroup(sgName string) error {access.Read}

	// EjectFromSyncgroup ejects a member from the syncgroup. The ejected member
	// will not be able to sync further, but will retain any data it has already
	// synced.
	//
	// Requires: Client must have at least Read access on the Database, and must
	// have Admin access on the syncgroup ACL.
	EjectFromSyncgroup(sgName, member string) error {access.Read}

	// GetSyncgroupSpec gets the syncgroup spec. version allows for atomic
	// read-modify-write of the spec - see comment for SetSyncgroupSpec.
	//
	// Requires: Client must have at least Read access on the Database and on the
	// syncgroup ACL.
	GetSyncgroupSpec(sgName string) (spec SyncgroupSpec, version string | error) {access.Read}

	// SetSyncgroupSpec sets the syncgroup spec. version may be either empty or
	// the value from a previous Get. If not empty, Set will only succeed if the
	// current version matches the specified one.
	//
	// Requires: Client must have at least Read access on the Database, and must
	// have Admin access on the syncgroup ACL.
	SetSyncgroupSpec(sgName string, spec SyncgroupSpec, version string) error {access.Read}

	// GetSyncgroupMembers gets the info objects for members of the syncgroup.
	//
	// Requires: Client must have at least Read access on the Database and on the
	// syncgroup ACL.
	GetSyncgroupMembers(sgName string) (members map[string]SyncgroupMemberInfo | error) {access.Read}

	// TODO(hpucha): Allow clients to tune the behavior of sync.
	// - Suspend/ResumeSync
	// - Get/SetSyncPolicy with policies such as "sync only via wifi", "sync
	//   aggressively", "sync once per day"
}

// SchemaManager implements the API for managing schema metadata attached
// to a Database.
type SchemaManager interface {
	// GetSchemaMetadata retrieves schema metadata for this database.
	//
	// Requires: Client must have at least Read access on the Database.
	GetSchemaMetadata() (SchemaMetadata | error) {access.Read}

	// SetSchemaMetadata stores schema metadata for this database.
	//
	// Requires: Client must have at least Write access on the Database.
	SetSchemaMetadata(metadata SchemaMetadata) error {access.Write}
}

// ConflictManager interface provides all the methods necessary to handle
// conflict resolution for a given database.
type ConflictManager interface {
	// StartConflictResolver registers a resolver for the database that is
	// associated with this ConflictManager and creates a stream to receive
	// conflicts and send resolutions.
	// Batches of ConflictInfos will be sent over with the Continued field
	// within the ConflictInfo representing the batch boundary. Client must
	// respond with a batch of ResolutionInfos in the same fashion.
	// A key is under conflict if two different values were written to it
	// concurrently (in logical time), i.e. neither value is an ancestor of the
	// other in the history graph.
	// A key under conflict can be a part of a batch committed on local or
	// remote or both syncbases. ConflictInfos for all keys in these two batches
	// are grouped together. These keys may themselves be under conflict; the
	// presented batch is a transitive closure of all batches containing keys
	// under conflict.
	// For example, for local batch {key1, key2} and remote batch {key1, key3},
	// the batch sent for conflict resolution will be {key1, key2, key3}.
	// If there was another concurrent batch {key2, key4}, then the batch sent
	// for conflict resolution will be {key1, key2, key3, key4}.
	StartConflictResolver() stream<ResolutionInfo, ConflictInfo> error {access.Write}
}

// BlobManager is the interface for blob operations.
//
// Description of API for resumable blob creation (append-only):
// - Up until commit, a BlobRef may be used with PutBlob, GetBlobSize,
//   DeleteBlob, and CommitBlob. Blob creation may be resumed by obtaining the
//   current blob size via GetBlobSize and appending to the blob via PutBlob.
// - After commit, a blob is immutable, at which point PutBlob and CommitBlob
//   may no longer be used.
// - All other methods (GetBlob, FetchBlob, PinBlob, etc.) may only be used
//   after commit.
type BlobManager interface {
	// CreateBlob returns a BlobRef for a newly created blob.
	CreateBlob() (br BlobRef | error) {access.Write}

	// PutBlob appends the byte stream to the blob.
	PutBlob(br BlobRef) stream<[]byte, _> error {access.Write}

	// CommitBlob marks the blob as immutable.
	CommitBlob(br BlobRef) error {access.Write}

	// GetBlobSize returns the count of bytes written as part of the blob
	// (committed or uncommitted).
	GetBlobSize(br BlobRef) (int64 | error) {access.Read}

	// DeleteBlob locally deletes the blob (committed or uncommitted).
	DeleteBlob(br BlobRef) error {access.Write}

	// GetBlob returns the byte stream from a committed blob starting at offset.
	GetBlob(br BlobRef, offset int64) stream<_, []byte> error {access.Read}

	// FetchBlob initiates fetching a blob if not locally found. priority
	// controls the network priority of the blob. Higher priority blobs are
	// fetched before the lower priority ones. However, an ongoing blob
	// transfer is not interrupted. Status updates are streamed back to the
	// client as fetch is in progress.
	FetchBlob(br BlobRef, priority uint64) stream<_, BlobFetchStatus> error {access.Read}

	// PinBlob locally pins the blob so that it is not evicted.
	PinBlob(br BlobRef) error {access.Write}

	// UnpinBlob locally unpins the blob so that it can be evicted if needed.
	UnpinBlob(br BlobRef) error {access.Write}

	// KeepBlob locally caches the blob with the specified rank. Lower
	// ranked blobs are more eagerly evicted.
	KeepBlob(br BlobRef, rank uint64) error {access.Write}

	// TODO(hpucha): Clarify how to pick priority and rank. Add API for
	// efficient blob cloning. Options include: (1) CloneBlob RPC with an
	// array of mods that specify the offset and len for the new bytes. This
	// might need two len fields to support growing a blob in the middle
	// instead of just replacing byte for byte in the src blob. Or perhaps
	// Offset>=0 to mean "read from old blob at this offset for Length
	// bytes", and Offset<0 to mean "read the next Length Bytes from the
	// PutBlob() stream". (2) We could adopt API similar to the local blob
	// store with BlockOrFile segments, giving a more flexible way to clone
	// blobs. Also provide support for parallel blob upload.
}

// DatabaseWatcher allows a client to watch for updates to the database. For
// each watch request, the client will receive a reliable stream of watch events
// without re-ordering. See watch.GlobWatcher for a detailed explanation of the
// behavior.
// TODO(rogulenko): Currently the only supported watch patterns are
// "<collectionName>/<rowPrefix>*". Consider changing that.
//
// Watching is done by starting a streaming RPC. The RPC takes a ResumeMarker
// argument that points to a particular place in the database event log. If an
// empty ResumeMarker is provided, the WatchStream will begin with a Change
// batch containing the initial state. Otherwise, the WatchStream will contain
// only changes since the provided ResumeMarker.
//
// The result stream consists of a never-ending sequence of Change messages
// (until the call fails or is canceled). Each Change contains the Name field in
// the form "<collectionName>/<rowKey>" and the Value field of the StoreChange
// type. If the client has no access to a row specified in a change, that change
// is excluded from the result stream.
//
// Note: A single Watch Change batch may contain changes from more than one
// batch as originally committed on a remote Syncbase or obtained from conflict
// resolution. However, changes from a single original batch will always appear
// in the same Change batch.
type DatabaseWatcher interface {
	watch.GlobWatcher

	// GetResumeMarker returns the ResumeMarker that points to the current end
	// of the event log. GetResumeMarker() can be called on a batch.
	GetResumeMarker(bh BatchHandle) (watch.ResumeMarker | error) {access.Read}
}

error (
	NotInDevMode() {"en": "not running with --dev=true"}
	InvalidName(name string) {"en": "invalid name: {name}"}
	CorruptDatabase(path string) {"en": "database corrupt, moved to {path}; client must create a new database"}
	UnknownBatch() {"en": "unknown batch, perhaps the server restarted"}
	NotBoundToBatch() {"en": "not bound to batch"}
	ReadOnlyBatch() {"en": "batch is read-only"}
	ConcurrentBatch() {"en": "concurrent batch"}
	BlobNotCommitted() {"en": "blob is not yet committed"}
	SyncgroupJoinFailed() {"en": "syncgroup join failed"}
	BadExecStreamHeader() {"en": "Exec stream header improperly formatted"}
)