%% From https://github.com/madnight/benchmarksgame/blob/9f5a20ba09e668a20bb0f9765b33071fa9bb3f1d/LICENSE
%%
%% Copyright © 2004-2008 Brent Fulgham, 2005-2017 Isaac Gouy
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%%    of "The Computer Language Shootout Benchmarks" nor the names of its
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% The Computer Language Benchmarks Game
% http://benchmarksgame.alioth.debian.org/
%% Contributed by Johan Karlsson based on Fredrik Svahn's mandelbrot program

-module(mandelbrot2).
-export([main/2]).
-define(LIM_SQR, 4.0).
-define(ITER, 50).
-define(SR, -1.5).
-define(SI, -1).

main(Io, N) ->
    NStr = integer_to_list(N),
    file:write(Io, ["P4\n", NStr, " ", NStr, "\n"]),

    %% Spawn one process per row
    Row = fun(NextProc,Y)-> row(Io, NextProc, N-1, 0, ?SI+Y*2/N, N, 0, [], 7) end,
    spawn_proc_chain(Row, N).

%% A function that spawns a chain of processes.
spawn_proc_chain(Row, N) ->
    Spawn = fun(S,F,I,NN) -> spawn(fun() -> do_spawn_proc_chain(S,F,I,NN) end) end,
    Spawn(Spawn,Row,first,N).

do_spawn_proc_chain(_,_,Max,Max) ->
    receive _ -> ok end;
do_spawn_proc_chain(Spawn,Row,first,Max) ->
    NextProc = Spawn(Spawn,Row,1,Max),
    %% I'm the first process in the chain. Inform my self that I can finish.
    self() ! done,
    %% Execute the row function
    Row(NextProc,0);
do_spawn_proc_chain(Spawn,Row,N,Max) ->
    NextProc = Spawn(Spawn,Row,N+1,Max),
    Row(NextProc,N).


%% Iterate over a row, collect bits, bytes and finally print the row
row(Io,NextProc,X,X, _, _, Bits, Bytes, C) ->
    Char = case C of
               7 -> lists:reverse(Bytes);
               C -> lists:reverse([Bits bsl (C+1) | Bytes])
           end,
    %% Wait for the previous process to finish before printing
    receive _ -> ok end,
    ok = file:write(Io, Char),
    NextProc ! done;

row(Io,NP,M,X, Y2, N, Bits, Bytes, 0) ->
    row(Io,NP,M,X+1, Y2, N, 0, [Bits bsl 1 + m(?ITER, ?SR+(X+X)/N, Y2) | Bytes], 7);

row(Io,NP,M,X, Y2, N, Bits, Bytes, BitC) ->
    row(Io,NP,M,X+1, Y2, N, Bits bsl 1 + m(?ITER, ?SR+(X+X)/N, Y2), Bytes, BitC-1).


%Mandelbrot algorithm
m(Iter, CR,CI) -> m(Iter - 1, CR, CI, CR, CI).

m(Iter, R, I, CR, CI) ->
    case R*R+I*I > ?LIM_SQR of
	false when Iter > 0 -> m(Iter-1, R*R-I*I+CR, 2*R*I+CI, CR, CI);
	false -> 1;
	true -> 0
    end.