execution

type Evaluator interface {
	// Eval evaluates the expression that this Evaluator represents
	// on the given input data. Note that in order to deal with joins and
	// meta information such as timestamps properly, the input data must have
	// the shape:
	//   {"alias_1": {"col_0": ..., "col_1": ...},
	//    "alias_1:meta:x": (meta datum "x" for alias_1's row),
	//    "alias_2": {"col_0": ..., "col_1": ...},
	//    "alias_2:meta:x": (meta datum "x" for alias_2's row),
	//    ...}
	// and every caller (in particular all execution plans)
	// must ensure that the data has this shape even if there's only one input
	// stream.
	//
	// Eval must NOT modify the input.
	Eval(input data.Value) (data.Value, error)
}

type FlatExpression interface {
	// Repr returns a string representation that can be used to
	// identify this expression (e.g., "stream:col+3") and used as
	// a dictionary key for finding duplicate expressions.
	Repr() string

	// Columns returns a list of rowValues used in this expression.
	Columns() []rowValue

	// Volatility returns the volatility of an expression.
	Volatility() VolatilityType

	// ContainsWildcard returns whether this expression contains
	// a wildcard symbol.
	ContainsWildcard() bool
}

type LogicalPlan struct {
	GroupingStmt        bool
	EmitterType         parser.Emitter
	EmitterLimit        int64
	EmitterSampling     float64
	EmitterSamplingType parser.EmitterSamplingType
	Projections         []aliasedExpression
	parser.WindowedFromAST
	Filter    FlatExpression
	GroupList []FlatExpression
	parser.HavingAST
}

type PhysicalPlan interface {
	// Process must be called whenever a new tuple arrives in
	// the input stream. It will return a list of data.Map
	// items where each of these items is to be emitted as
	// a tuple. It is the caller's task to create those tuples
	// and set appropriate meta information such as timestamps.
	//
	// Process must NOT modify any field of the input tuple when its
	// core.TFShared flag is set. To modify the tuple, create a shallow copy of
	// it. Moreover, when Tuple.Data field is cached in the plan,
	// core.TFSharedData flag of the input tuple must be set and the plan must
	// not modify the Data.
	//
	// NB. Process is not thread-safe, i.e., it must be called in
	// a single-threaded context.
	Process(input *core.Tuple) ([]data.Map, error)
}

type VolatilityType int