Shell Programming and Scripting

Which is the best command(s) to arrange data of a file?

This is my example input file:

Tom ------
apples: 5
oranges: 7
pears: 10
apples: 2
oranges: 8
Jack ------
apples: 3
pears: 10
Lucy ------
oranges: 1
pears: 8
peaches: 9
Tom ------
peaches: 1
Jack ------
oranges:3

Output file:

Tom -----
apples: 5, 2
oranges: 7, 8
pears: 10
peaches: 1
Jack -----
apples: 3
oranges: 3
pears: 10
peaches:
Lucy -----
apples: 8
oranges: 1
pears:
peaches: 9

Actually I don't know how can I write in a line of a file at the end of the line... like APPEND option of files.

I'm trying to implement the whole program by awk...

Thanks a lot!!!