// 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 nosql

import (
	"v.io/v23/security/access"
)

// BatchOptions configures a batch.
// TODO(sadovsky): Add more options, e.g. to configure isolation, timeouts,
// whether to track the read set and/or write set, etc.
// TODO(sadovsky): Maybe add a DefaultBatchOptions() function that initializes
// BatchOptions with our desired defaults. Clients would be encouraged to
// initialize their BatchOptions object using that function and then modify it
// to their liking.
type BatchOptions struct {
	// Arbitrary string, typically used to describe the intent behind a batch.
	// Hints are surfaced to clients during conflict resolution.
	// TODO(sadovsky): Use "any" here?
	Hint string

	// ReadOnly specifies whether the batch should allow writes.
	// If ReadOnly is set to true, Abort() should be used to release any resources
	// associated with this batch (though it is not strictly required), and
	// Commit() will always fail.
	ReadOnly bool
}

// PrefixPermissions represents a pair of (prefix, perms).
type PrefixPermissions struct {
	Prefix string
	Perms  access.Permissions
}

// KeyValue is a key-value pair.
type KeyValue struct {
	Key   string
	Value []byte
}

// SyncGroupSpec contains the specification for a SyncGroup.
type SyncGroupSpec struct {
	// Human readable description.
	Description string

	// Permissions for the SyncGroup.
	Perms access.Permissions

	// SyncGroup prefixes (relative to the database).  Prefixes
	// must take the form "<tableName>/<rowKeyPrefix>" where
	// tableName is non-empty.
	Prefixes []string

	// Mount tables at which to advertise this SyncGroup. These
	// are the mount tables used for rendezvous in addition to the
	// one in the neighborhood. Typically, we will have only one
	// entry.  However, an array allows mount tables to be changed
	// over time.
	//
	// TODO(hpucha): Figure out a convention for
	// advertising SyncGroups in the mount table.
	MountTables []string

	// Option to change the privacy of the SyncGroup. Configures
	// whether blobs in a SyncGroup can be served to clients
	// holding blobrefs obtained from other SyncGroups.
	IsPrivate bool
}

// SyncGroupMemberInfo contains per-member metadata.
type SyncGroupMemberInfo struct {
	SyncPriority byte
}

// ResolverType defines the possible conflict resolution policies.
// A Conflict is defined as presence of two independent sets of updates
// originating from the same version of an object. Syncbase
// uses version vectors to determine sequence of changes to a given row. Hence
// if device A updates a row with key "foo" from version V3 to V4, then syncs
// with device B which further updates the same row from version V4 to V5 and
// then V5 is synced back to device A, device A will see V5 as a forward
// progression of "foo" and not a conflict with V3 of "foo". But in the
// meantime if device A had already updated "foo" again from version V4 to
// version V6 then there is a conflict between V5 and V6 with V4 being the
// common ancestor.
type ResolverType enum {
	// LastWins is a policy which resolves a conflict between two writes by
	// choosing the version which has the greatest timestamp.
	// For example, if device A created V6 at time T1 and device B created V5 at
	// time T2 where timestamp T2 > T1, then V5 will be accepted as the
	// resolution of the conflict.
	// Syncbase maintains an internal clock for creating write timestamps. This
	// clock is kept up to date via regular synchronization with NTP and with
	// other syncbases. As long as the syncbase has access to an NTP server
	// directly or indirectly via another syncbase, the internal clock will
	// track NTP time and correct any skews suffered by the local system clock.
	LastWins

	// AppResolves is a policy which allows an App to handle resolution of a
	// conflict on its own. In order to receive the conflicts, the app needs to
	// register a conflict resolution stream using
	// Database.StartConflictResolver().
	AppResolves

	// Defer is a policy that allows an instance of an App to outsource its
	// conflict resolution to some other instance, typically a more capable
	// instance (in terms of resources, knowledge or permissions) such as a
	// cloud or admin instance.
	Defer
}

// SchemaMetadata maintains metadata related to the schema of a given database.
// There is one SchemaMetadata per database.
type SchemaMetadata struct {
	// Non negative Schema version number. Should be increased with every schema change
	// (e.g. adding fields to structs) that cannot be handled by previous
	// versions of the app.
	Version int32
	Policy  CrPolicy
}

// For a given row with a conflict, all rules are matched against the row.
// If no rules match the row, we default to "LastWins". If multiple
// rules match the row, ties are broken as follows:
//  1. If one match has a longer prefix than the other, take that one.
//  2. Else, if only one match specifies a type, take that one.
//  3. Else, the two matches are identical; take the last one in the Rules array.
type CrPolicy struct {
	Rules []CrRule
}

// CrRule provides a filter and the type of resolution to perform for a row
// under conflict that passes the filter.
type CrRule struct {
	// TableName is the name of the table that this rule applies to.
	TableName	string

	// KeyPrefix represents the set of keys within the given table for which
	// this policy applies. TableName must not be empty if this field is set.
	KeyPrefix	string

	// Type includes the full package path for the value type for which this
	// policy applies.
	Type 		string

	// Policy for resolving conflict.
	Resolver 	ResolverType
}

// BlobRef is a reference to a blob.
type BlobRef string

const (
	NullBlobRef = BlobRef("")
)

// BlobFetchState represents the state transitions of a blob fetch.
type BlobFetchState enum {
	Pending // Fetch request is queued.
	Locating // Blob discovery is in progress to find a source for the blob.
	Fetching // Blob transfer is in progress.
	Done // Blob is locally cached.
}

// BlobFetchStatus describes the progress of an asynchronous blob fetch.
type BlobFetchStatus struct {
	State BlobFetchState // State of the blob fetch request.
	Received int64 // Total number of bytes received.
	Total int64 // Blob size.
}

// StoreChange is the new value for a watched entity.
// TODO(rogulenko): Consider adding the Shell state.
type StoreChange struct {
	// Value is the new value for the row if the Change state equals to Exists,
	// otherwise the Value is nil.
	Value []byte

	// FromSync indicates whether the change came from sync. If FromSync is
	// false, then the change originated from the local device.
	FromSync bool
}