Wishing you a happy birthday; Wishing you a merry Christmas; Wishing you well; To use *Wish you a happy weekend you need to add I to make the sentence grammatical. i.e. I wish you a happy weekend. A notable exception to this is the common postcard sign off Wish you were here where it is idiomatic to leave out the I. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.