package storage

import "context"

// The relation and search reads of the room store: threads, edits,
// reactions and references (an event's content.m.relates_to), and the
// full-text index /search is answered from.
//
// Both are projections of the event JSON that the roomserver works out and
// hands over with the event, the same as its type and state key: the store
// still never parses an event. They live in a file of their own because
// they are the Phase 10 additions to the room store, and because neither is
// about a room's state or its stream order — they are about which events
// point at which, and which events say what.

// Relation types the server aggregates. Every rel_type is recorded and can
// be listed through /relations; these are the ones whose summaries go into
// an event's unsigned.m.relations.
const (
	RelThread    = "m.thread"
	RelReplace   = "m.replace"
	RelReference = "m.reference"
	RelAnnotate  = "m.annotation"
)

// RelationsRequest is one page of the events relating to some parents.
//
// The bounds are a TimelineRequest's: Low exclusive, High inclusive, zero
// unbounded at either end, positions possibly negative inside backfilled
// history.
type RelationsRequest struct {
	RoomID string

	// ParentIDs are the events whose children are read. It is one event
	// for a plain /relations call and the event plus its descendants for a
	// recursive one.
	ParentIDs []string

	// RelType and EventType narrow the children, when set.
	RelType   string
	EventType string

	Low       int64
	High      int64
	Direction TimelineDirection

	// Limit caps the rows returned, and is required.
	Limit int
}

// RelationAggregate is what one parent's children of one relation type
// come to, from one sender.
//
// It is per sender because two of the summaries need it: an edit only
// counts when it comes from the original's sender, and a thread reports
// whether the user asking took part. Summing over senders is then the
// roomserver's job.
type RelationAggregate struct {
	ParentID string
	RelType  string
	Sender   string

	// Count is how many children there are.
	Count int

	// LatestEventID is the newest of them, by stream order.
	LatestEventID string

	// LatestOrdering is its position.
	LatestOrdering int64
}

// ThreadsRequest is one page of a room's threads, newest activity first.
type ThreadsRequest struct {
	RoomID string

	// ParticipatedBy, when set, keeps only the threads that user started
	// or replied in.
	ParticipatedBy string

	// Before is an exclusive bound on a thread's latest activity: the page
	// after one whose last thread was last active at Before. Zero is the
	// first page.
	Before int64

	// High bounds what counts as activity, inclusive, for a user whose
	// view of the room ends at their leave. Zero is unbounded.
	High int64

	// Limit caps the threads returned, and is required.
	Limit int
}

// Thread is one thread of a room.
type Thread struct {
	RootID string

	// LatestOrdering is the position of the newest event in the thread,
	// which is what the listing is ordered and paged by.
	LatestOrdering int64
}

// SearchOrder is how /search orders its results.
type SearchOrder string

// The two orders the Client-Server API defines.
const (
	SearchByRank   SearchOrder = "rank"
	SearchByRecent SearchOrder = "recent"
)

// SearchRange is the part of one room a user may search: the window of its
// stream their membership and the room's history visibility allow. The
// bounds are a TimelineRequest's.
type SearchRange struct {
	RoomID string
	Low    int64
	High   int64
}

// SearchRequest is one page of a full-text search.
type SearchRequest struct {
	// Term is what the user typed. The store turns it into its engine's
	// query syntax; a term with no searchable words matches nothing.
	Term string

	// Rooms are where to look, each bounded to what the user may see.
	Rooms []SearchRange

	// Keys narrows which fields match: "content.body", "content.name",
	// "content.topic". Empty means all three.
	Keys []string

	// Filter narrows by type and sender, as a timeline filter does.
	Filter TimelineFilter

	Order SearchOrder

	// Offset skips results, for paging a ranked search. A search by
	// recency pages by Before instead, which stays put as events arrive.
	Offset int

	// Before is an exclusive upper bound on the stream position, for
	// paging a search by recency. Zero is the first page.
	Before int64

	// Limit caps the results returned, and is required.
	Limit int
}

// SearchResult is one event a search found.
type SearchResult struct {
	Event StoredEvent

	// Rank is the engine's relevance score, higher is better. It is only
	// comparable within one search.
	Rank float64
}

// RelationStore is the part of the room store about relations and search.
// It is embedded in RoomStore; it is a separate interface only so that the
// two halves can be read apart.
type RelationStore interface {
	// Relations reads one page of the children of the given parents, in
	// stream order in the direction asked for.
	Relations(ctx context.Context, req RelationsRequest) ([]StoredEvent, error)

	// ChildEventIDs lists the direct children of the given parents,
	// narrowed by relation and event type when those are set. It is how a
	// recursive /relations walks down a level at a time.
	ChildEventIDs(ctx context.Context, roomID string, parentIDs []string, relType, eventType string) ([]string, error)

	// RelationAggregates summarises the thread, edit and reference
	// children of the given parents, up to and including high (zero for
	// no bound).
	RelationAggregates(ctx context.Context, roomID string, parentIDs []string, high int64) ([]RelationAggregate, error)

	// RelationEventIDs lists the children of one relation type of the
	// given parents, oldest first, at most limit of them: the chunk of an
	// m.reference summary.
	RelationEventIDs(ctx context.Context, roomID string, parentIDs []string, relType string, high int64, limit int) (map[string][]string, error)

	// Threads reads one page of a room's threads.
	Threads(ctx context.Context, req ThreadsRequest) ([]Thread, error)

	// Search reads one page of a full-text search and the total number of
	// matches.
	Search(ctx context.Context, req SearchRequest) ([]SearchResult, int, error)
}