Convert from Absolute to Relative Paths

[David Bovill]

function file_GetRelativePath someFileOrFolder, baseFolder, @commonPath
    put the itemdelimiter into originalDelim
    set the itemdelimiter to "/"
    put empty into commonPath
    put someFileOrFolder into relativePath
    put 0 into itemNum
    repeat with itemNum = 1 to the number of items of baseFolder
        put item itemNum of baseFolder into basePathComponent
        put item itemNum of someFileOrFolder into somePathComponent

        if somePathComponent is basePathComponent then
            next repeat
        else
            subtract 1 from itemNum
            exit repeat
        end if
    end repeat

    put item 1 to itemNum of someFileOrFolder into commonPath
    delete item 1 to itemNum of relativePath

    delete item 1 to itemNum of baseFolder
    put the number of items of baseFolder into upBits
    repeat upBits
        put "../" before relativePath
    end repeat

    set the itemdelimiter to originalDelim
    put "/" after commonpath
    return relativePath
end file_GetRelativePath