// filters walks the where clause of a select statement and returns a map with all series ids
// matching the where clause and any filter expression that should be applied to each
func (m *Measurement) filters(condition influxql.Expr) (map[uint64]influxql.Expr, error) {
	if condition == nil || influxql.OnlyTimeExpr(condition) {
		seriesIdsToExpr := make(map[uint64]influxql.Expr, len(m.seriesIDs))
		for _, id := range m.seriesIDs {
			seriesIdsToExpr[id] = nil
		}
		return seriesIdsToExpr, nil
	}

	ids, seriesIdsToExpr, err := m.walkWhereForSeriesIds(condition)
	if err != nil {
		return nil, err
	}

	// Ensure every id is in the map and replace literal true expressions with
	// nil so the engine doesn't waste time evaluating them.
	for _, id := range ids {
		if expr, ok := seriesIdsToExpr[id]; !ok {
			seriesIdsToExpr[id] = nil
		} else if b, ok := expr.(*influxql.BooleanLiteral); ok && b.Val {
			seriesIdsToExpr[id] = nil
		}
	}
	return seriesIdsToExpr, nil
}

// Ensure that we see if a where clause has only time limitations
func TestOnlyTimeExpr(t *testing.T) {
	var tests = []struct {
		stmt string
		exp  bool
	}{
		{
			stmt: `SELECT value FROM myseries WHERE value > 1`,
			exp:  false,
		},
		{
			stmt: `SELECT value FROM foo WHERE time >= '2000-01-01T00:00:05Z'`,
			exp:  true,
		},
		{
			stmt: `SELECT value FROM foo WHERE time >= '2000-01-01T00:00:05Z' AND time < '2000-01-01T00:00:05Z'`,
			exp:  true,
		},
		{
			stmt: `SELECT value FROM foo WHERE time >= '2000-01-01T00:00:05Z' AND asdf = 'bar'`,
			exp:  false,
		},
		{
			stmt: `SELECT value FROM foo WHERE asdf = 'jkl' AND (time >= '2000-01-01T00:00:05Z' AND time < '2000-01-01T00:00:05Z')`,
			exp:  false,
		},
	}

	for i, tt := range tests {
		// Parse statement.
		stmt, err := influxql.NewParser(strings.NewReader(tt.stmt)).ParseStatement()
		if err != nil {
			t.Fatalf("invalid statement: %q: %s", tt.stmt, err)
		}
		if influxql.OnlyTimeExpr(stmt.(*influxql.SelectStatement).Condition) != tt.exp {
			t.Fatalf("%d. expected statement to return only time dimension to be %t: %s", i, tt.exp, tt.stmt)
		}
	}
}