joiner

type Cache interface {
	Get(src, col int) (Index, bool)
	GetBySrc(src int) ([]Index, bool)
	Delimiter() string
}

type CacheBuilder interface {
	Build(ctx context.Context) (Cache, error)
}

type Index interface {
	KeyFunc() KeyFunc
	Get(key string) ([]Item, bool)
	Read(item Item) (ScannedItem, error)
	Scan(ctx context.Context) <-chan ScannedItem
	AllItems(ctx context.Context) <-chan Item
}

type IndexLoader interface {
	Load(ctx context.Context, key ...KeyFunc) ([]Index, error)
}

type Item interface {
	Key() string
	Offset() int64
	Size() int
}

type Joiner interface {
	Join(ctx context.Context, key *joinkey.JoinKey) <-chan SelectItemList
}

type KeyFunc func(string) (string, error)

type Location interface {
	Source() int
	Column() int
}

type RelationJoiner interface {
	// FullJoin links records with cross join.
	FullJoin(ctx context.Context, rel *joinkey.Relation) <-chan SelectItemList
	// Join links given rows and the other records.
	// Fallback to FullJoin if rowC is nil.
	Join(ctx context.Context, rel *joinkey.Relation, rowC <-chan SelectItemList) <-chan SelectItemList
}

type ScannedItem interface {
	Line() string
	Item() Item
}

type SelectItem interface {
	Source() int
	Item() Item
}

type SelectItemList map[int]SelectItem

type Selector interface {
	// Select forms selected items into a line depending on the target.
	// items specify the data sources, target is columns to be selected.
	Select(tgt *target.Target, items []SelectItem) (string, error)
}