[R] sort

[Val]

HI All,
I have a sample of data frame
DF1<-read.table(text="name ddate
  A  2019-10-28
  A  2018-01-25
  A  2020-01-12
  A  2017-10-20
  B  2020-11-20
  B  2019-10-20
  B  2017-05-20
  B  2020-01-20
  c  2009-10-01  ",header=TRUE)

1. I want sort by name and ddate on decreasing order and the output
should like as follow
   A  2020-01-12
   A  2019-01-12
   A  2018-01-25
   A  2017-10-20
   B  2020-11-21
  B  2020-11-01
  B  2019-10-20
  B  2017-05-20
  c  2009-10-01

2.  Take the top two rows by group( names) and the out put should like
   A  2020-01-12
   A  2019-01-12
   B  2020-11-21
   B  2020-11-01
    c  2009-10-01

3.  Within each group (name) get the date difference  between the
first and second rows dates. If a group has only one row then the
difference should be 0

The final out put is
Name diff
   A  365
    B  20
    C  0

Here is my attempt and have an issue at the sorting
DF1$DTime <- as.POSIXct(DF1$ddate , format = "%Y-%m-%d")
DF2 <- DF1[order(DF1$name, ((as.Date(DF1$DTime, decreasing = TRUE)))), ]

not working
Any help?

Thank you