+" Parameters:
+"
+" - step +1 for right, -1 for left
+"
+" TODO: multiple lines.
+"
+function! s:FindCornerOfSyntax(lnum, col, step)
+ let l:col = a:col
+ let l:syn = synIDattr(synID(a:lnum, l:col, 1), 'name')
+ while synIDattr(synID(a:lnum, l:col, 1), 'name') ==# l:syn
+ let l:col += a:step
+ endwhile
+ return l:col - a:step
+endfunction
+
+" Return the next position of the given syntax name,
+" inclusive on the given position.
+"
+" TODO: multiple lines
+"
+function! s:FindNextSyntax(lnum, col, name)
+ let l:col = a:col
+ let l:step = 1
+ while synIDattr(synID(a:lnum, l:col, 1), 'name') !=# a:name
+ let l:col += l:step
+ endwhile
+ return [a:lnum, l:col]
+endfunction
+
+function! s:FindCornersOfSyntax(lnum, col)
+ return [<sid>FindLeftOfSyntax(a:lnum, a:col), <sid>FindRightOfSyntax(a:lnum, a:col)]
+endfunction
+
+function! s:FindRightOfSyntax(lnum, col)
+ return <sid>FindCornerOfSyntax(a:lnum, a:col, 1)
+endfunction
+
+function! s:FindLeftOfSyntax(lnum, col)
+ return <sid>FindCornerOfSyntax(a:lnum, a:col, -1)
+endfunction
+
+" Returns:
+"
+" - a string with the the URL for the link under the cursor
+" - an empty string if the cursor is not on a link
+"
+" `b:` instead of `s:` to make it testable.
+"
+" TODO
+"
+" - multiline support
+" - give an error if the separator does is not on a link
+"
+function! b:Markdown_GetUrlForPosition(lnum, col)
+ let l:lnum = a:lnum
+ let l:col = a:col
+ let l:syn = synIDattr(synID(l:lnum, l:col, 1), 'name')
+
+ if l:syn ==# 'mkdInlineURL' || l:syn ==# 'mkdURL' || l:syn ==# 'mkdLinkDefTarget'
+ " Do nothing.
+ elseif l:syn ==# 'mkdLink'
+ let [l:lnum, l:col] = <sid>FindNextSyntax(l:lnum, l:col, 'mkdURL')
+ let l:syn = 'mkdURL'
+ elseif l:syn ==# 'mkdDelimiter'
+ let l:line = getline(l:lnum)
+ let l:char = l:line[col - 1]
+ if l:char ==# '<'
+ let l:col += 1
+ elseif l:char ==# '>' || l:char ==# ')'
+ let l:col -= 1
+ elseif l:char ==# '[' || l:char ==# ']' || l:char ==# '('
+ let [l:lnum, l:col] = <sid>FindNextSyntax(l:lnum, l:col, 'mkdURL')
+ else
+ return ''
+ endif
+ else
+ return ''
+ endif
+
+ let [l:left, l:right] = <sid>FindCornersOfSyntax(l:lnum, l:col)
+ return getline(l:lnum)[l:left - 1 : l:right - 1]
+endfunction
+
+" Front end for GetUrlForPosition.
+"
+function! s:OpenUrlUnderCursor()
+ let l:url = b:Markdown_GetUrlForPosition(line('.'), col('.'))
+ if l:url != ''
+ call netrw#NetrwBrowseX(l:url, 0)
+ else
+ echomsg 'The cursor is not on a link.'
+ endif
+endfunction
+