How to add slash to the line and locate words? [closed]

Question

I wish to draw the graph like in the picture, however, there are three problems here, 1. how to add the words "OnMess" and "h" on top of the rectangles 2. how to add the word "ac" above the line as described in the picture 3. how to add slash to the line.

Here is my code, however the three problems haven't solved, can someone help me?:

 \documentclass[tikz]{standalone}
\usetikzlibrary{
    shapes.geometric,
    positioning,
    fit,
    calc
}
\tikzset{
    cir/.style={
       shape=circle,
       minimum size=1em,
    },
    dia/.style={
        shape=diamond,
        minimum size=2em,
    },
    dia cross/.style={
        dia,
        path picture={
            \draw (path picture bounding box.west) -- (path picture bounding box.east)
                  (path picture bounding box.north) -- (path picture bounding box.south);
        }
    }
}
\begin{document}
\begin{tikzpicture}[
    every node/.append style={draw,minimum width=3em,minimum height=1.5em},
    >=latex
]

%%% Left side
%% nodes with text
\node(a) {get flight(gf)};
\node[below=.5 of a] (b) {book flight(bf)};

\node[right=of a]    (c) {gc};
\node[below=.5 of c] (d) {bc};

%% rectangles around nodes with text
\node[fit=(a)(b)] (ab) {};
\node[fit=(c)(d)] (cd) {};

%% top diamond
\node[dia] at ([yshift=.5cm]$(ab.north)!.5!(cd.north)$) (dia1) {};

%%% Right side
\node[right=2 of d] (f) {bh};
\node[label={[inner sep=0pt,minimum height=2ex]above:h}] at (f |- dia1) (e) {gh};

% fake f to get the same spacing as on the left side (text with draw=gray)
\node[fit=(f),draw=none] (f') {};

%%% Big rectangles
\node[inner sep=1em,fit=(ab)(cd)(dia1)] (left) {};
\node[inner sep=1em,fit=(f')(dia1.north -| e)] (right) {};

%%%the first top diamond
\node[dia cross] at ([yshift=4.5cm]$(left.south)!.5!(right.south)$) (dia0) {};
\node[above=.5 of dia0](top){fu};
\node[cir,above=.5 of top,fill=black](ini){};

%%% Diamond below
\node[dia cross] at ([yshift=-.5cm]$(left.south)!.5!(right.south)$) (dia2) {};
\node[dia,below=.5 of dia2](dia3){};
\node[right=of dia3](atc){atc;
\node[below=0.5 of dia3](ru){ru};
\node[cir,below=0.5 of ru,fill=black](end){};
%%% Arrows
\foreach \pp/\pf/\pt in {--/a/b,
                         --/c/d,
                         --/e/f,
                         --/ini/top,
                         --/top/dia0,
                         --/dia2/dia3,
                         --/dia3/ru,
                         --/ru/end,
                         --/dia3/atc,
                         -|/dia1/ab,
                         -|/dia1/cd,
                         -|/dia0/left,
                         -|/dia0/right,
                         |-/left/dia2,
                         |-/atc/ru,
                         |-/right/dia2}
\draw[
    shorten >=\pgflinewidth,
    ->
] (\pf) \pp (\pt);
\end{tikzpicture}
\end{document}