Change the quotations as if in Microsoft Word

Question

I noticed that in Microsoft Word, single quotations are either ‘ or ’, but not in Notepad. Your task today is: given a string q, convert all the ' characters (only) to ‘ or ’, according to these rules, and then output it:

• If the character before the quote is a space, and after it comes a character, it becomes ‘
• If the character before the quote is a letter, and after it is a space, it becomes ’
• If the character before and after the quote is a letter, it becomes ’
• If the character before and after the quote is a space, it becomes ‘
• If the quote comes at the beginning it will be ‘, if it comes at the end it becomes ’
• If consecutive quotes come one after another, the first 2 become ‘’ and remaining ones become ’

Test Cases

'Hello'= ‘Hello’ (rules 1 and 2)
'=‘              (rule 5)
H'h=H’h          (rule 3)
 ' = ‘           (rule 4)
'' = ‘’          (rule 6)
a'''b=a‘’’b      (overriding by rule 6)

I'm keeping it this because although it is confusing, it is what the output should be, so if I had to make it more clearer, it will come at the expense of understanding it.

You can assume q contains only upper and lowercase letters, spaces, and quotation marks.

This is code-golf, so shortest answer wins!

EDIT: Although in MS Word rule 6 does not override all the other rules, since answers have already been posted that assume this case, I will keep it this way

Answer 1

Retina, 42 bytes

'('+)
‘$.1*’
(^| )'
$1‘
'($|\w)
’$1

Assumes rule 6 takes prio over the other rules.

I have the feeling the first step can be shorter (perhaps with a +^ loop), but couldn't really find anything yet..

Try it online or try it online with </> instead of ‘/’ so it's a bit more distinguishable).

Explanation:

Replace any sequence of two or more quotes with one opening quote and the rest closing quotes:

'('+)
‘$.1*’

Replace a quote at the start of the string, or a quote with a space before it, with the opening quote:

(^| )'
$1‘

Replace a quote at the end of the string, or a quote with a after it, with the closing quote:

'($|\w)
’$1

Answer 2

Retina 0.8.2, 28 bytes

(?<=^| )'|\b'(?=')
‘
'
’

Try it online! Link includes test cases. Explanation:

(?<=^| )'|\b'(?=')
‘

Quotes become "smart open" quotes at the beginning of the string (by rule 5), after a space (by rules 1, 4 and 6), or after a letter and before a quote (by rule 6).

'
’

All other quotes become "smart close" quotes.

I tried coding the reverse logic by handling "smart close" quotes first but the best I could do was 29 bytes:

(?<=')'|\b'(?!')|'$
’
'
‘

Try it online! Link includes test cases. Explanation: Quotes become "smart close" quotes after quotes (by rule 6), after a letter but not before a quote (by rules 2 and 3), or at the end (by rule 5).

Answer 3

sed, 109 bytes

:z;s/'''/''’/g;t z;
s/''/‘’/g
s/ '(.)/ ‘\1/g
s/([a-zA-Z])'([a-zA-Z ])/\1’\2/g
s/^'/‘/g
s/'$/’/g

Try it online!

Answer 4

C (clang), 75 bytes

x,o;f(*s){for(x=o=0;*s=*s-39?s[x=0]:8216+x|o&!s[x=1]|o>64&s[1]>64;o=*s++);}

Try it online!

Answer 5

Sed

Here's a shorter version of matteo_c's answer:

:z;s/'''/''’/g;t z;
s/''/‘’/g
s/'/’/g
s/^’/‘/g
s/ ’/ ‘/g

Answer 6

brev, 70 bytes

(strse x "'""’""’(’+)"(conc "‘" (m 1))" ’"" ‘""^’""‘")

Not sure how many bytes this is because Unicode but Steffan kindly counted them and here's the algo:

1. Replace all ' with ’.
2. Do "rule six" specially
3. Replace ^’ and ’ with opens