EA to switch between 2 symbols according to trading parameters (with code for MT4 & MT5)

GENERAL IDEA
-- we specify 2 symbols (ex. input symbol 1 = Microsoft & symbol 2 = Apple);

-- we specify input initial amount to trade (ex. $10,000);

-- we specify the interval at which the EA will check the trading conditions (ex. input interval_X = 10M)

-- we specify the trading parameters (ex. input conditions X = 1.0%; & Y = 1.5%)

ACTIONS:

1) UNIQUE ACTION = FIRST BUY:

-- if there is no open position by this EA, immediately buy X shares (= lot1) of symbol 1 at current ask_price (using the initial amount to calculate the lot);

-- register the quotes of BOTH symbol_1 & symbol_2 at the time of the transaction (let's call the "LAST-TRADE-QUOTE-1 & LAST-TRADE-QUOTE-2): those values will be used for trading condition X.

2) REGULAR/REPEATED ACTIONS: (obs. after the first buy, there'll always be an open position)

at every interval_X, check which symbol is the current open position;
-- if symbol 1 is current position, check if condition_X or condition_Y is true
  -- if symbol 1 is current position & (X or Y is true) --> sell symbol 1 

-- use the money from the sell to calculate lot2 (# of shares) --> buy  symbol 2

-- register quotes of both symbols (last-trade-quote-1 & last-trade-quote-2);

-- if symbol 2 is current position, check if condition_X or condition_Y is true
-- if symbol 2 is current position & (X or Y is true) --> sell symbol 2

-- use the money from the sell to calculate the new lot1 (# of shares) --> buy  symbol 1;

-- register quotes of both symbols (last-trade-quote-1 & last-trade-quote-2);

Bottom line:

-- after the first buy, there will always be an open position;

-- the EA will check the trading conditions: if they are true, sell symbol 1 & buy symbol 2 (or sell symbol 2 & buy symbol 1);

-- repeat the process at the defined interval

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GENERAL IDEA WITH MORE DETAILS: 

An important part of this EA is the "dynamic calculation" of the lots, meaning: after we close a position, the money generated by the sell of symbol_1 (or symbol_2) will be used to calculate how many shares we can buy of symbol_2 (or symbol_1). 

I think this can be achieved with the use of the following variables: 

double BUYMONEY (the available money to make the buy), SELLMONEY (the money generated by the sell), STANDBYCASH (the money not used in the buy after rounding down to min-lot). 

As there is a MIN LOT requirement, we never use the total amount of available money. We'll call this the STANDBYCASH. 

1) calculating the STANDBYCASH
let's say we have 10,000 to start with and Microsoft is $98. 
let's say the MIN-LOT = 1.0. 
so we could buy 102 shares of Microsoft. 
now: 102 lots at $98 = $9,996, which means that $4 are not used: that's the standbycash = $4
so standbycash = previous available money to make a buy (or BUYMONEY) - amount spent in the buy (which can be calculate by lot * ask.price). 

2) so, after the first buy, we will (always) have an open position.
let's say the trading conditions are true, so it's time to sell. 
let's say the bid price for Microsoft is $104. 
the amount generated by this sell (SELLMONEY) = lot1 * bid1 = 102 * 104 = $10,608 
so the new total amount available to make a buy (let's call it BUYMONEY = standbycash ($4) + sellmoney ($10,608) = $10,612
{obs. later on we can also include TRADEFEES: buymoney = standbycash + sellmoney - tradefees}
With that, we can calculate LOT2 (the # of shares of symbol_2 to be bought): 
LOT2 = buymoney / ask2 (the ask price of symbol2) (rounding to min lot). 
Let's say the ask_price of Apple is $84. 
With $10,612 we could buy 126 shares of Apple. 
Now, 126 * 84 = 10,584 meaning that we will have $28 left in the account. 
new standbycash = 10,612 - 10,584 = $28

Next time, we will sell Apple, say, at 90.

126 shares * 90 = $11,340 (sellmoney)
new buymoney = sellmoney + standbycash = 11,340 + 28 = $11,368

With that, we calculate the new lot of Microsoft to buy.
Let's say Microsoft is now $112.
With $11,364 at $112, we can buy 101 Microsoft (always rounding to min lot). 
Amount spent = 101*112 = $11,312, meaning the new standbycash = 11,364 - 11,312 = $52

And so on.

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SPECIFICATIONS ABOUT THE CONDITIONS X & Y

input periods = 50;

input condition_X = 1.0%
input condition_Y = 1.5%

X1 = (bid1 / last-trade-quote-1) - (ask2 / last-trade-quote-2);  // X1 is the condition X when symbol_1 is the current/open position
X2 = (bid2 / last-trade-quote-2) - (ask1 / last-trade-quote-1); // X2 is the condition X when symbol_2 is the current/open position

Y1 = bid1 / avg1 (= average of 50 periods of symbol1) - ask2 / avg2   // Y1 is the condition Y when symbol_1 is the current/open position
Y2 = bid2 / avg2 (= average of 50 periods of symbol2) - ask1 / avg1  // Y2 is the condition Y when symbol_1 is the current/open position

if (X1 >= condition_X || Y1>= condition_Y) bool sell_1_buy_2 is true
if (X2 >= condition_X || Y2>= condition_Y) bool sell_2_buy_1 is true

PS2. I have developed this myself and works well in the strategy tester, but I want/need it to be protected against potential errors.

So, the developer who accepts the job may either revise/adapt/protect the code I already have or create his own.