contract TangentStake is Owned {
    // prevents overflows
    using SafeMath for uint;
    
    // represents a purchase object
    // addr is the buying address
    // amount is the number of wei in the purchase
    // sf is the sum of (purchase amount / sum of previous purchase amounts)
    struct Purchase {
        address addr;
        uint amount;
        uint sf;
    }
    
    // Purchase object array that holds entire purchase history
    Purchase[] purchases;
    
    // tangents are rewarded along with Ether upon cashing out
    Tangent tokenContract;
    
    // the rate of tangents to ether is multiplier / divisor
    uint multiplier;
    uint divisor;
    
    // accuracy multiplier
    uint acm;
    
    uint netStakes;
    
    // logged when a purchase is made
    event PurchaseEvent(uint index, address addr, uint eth, uint sf);
    
    // logged when a person cashes out or the contract is destroyed
    event CashOutEvent(uint index, address addr, uint eth, uint tangles);
    
    event NetStakesChange(uint netStakes);
    
    // logged when the rate of tangents to ether is decreased
    event Revaluation(uint oldMul, uint oldDiv, uint newMul, uint newDiv);
    
    // constructor, sets initial rate to 1000 TAN per 1 Ether
    function TangentStake(address tokenAddress) public {
        tokenContract = Tangent(tokenAddress);
        multiplier = 1000;
        divisor = 1;
        acm = 10**18;
        netStakes = 0;
    }
    
    // decreases the rate of Tangents to Ether, the contract cannot be told
    // to give out more Tangents per Ether, only fewer.
    function revalue(uint newMul, uint newDiv) public onlyOwner {
        require( (newMul.div(newDiv)) <= (multiplier.div(divisor)) );
        Revaluation(multiplier, divisor, newMul, newDiv);
        multiplier = newMul;
        divisor = newDiv;
        return;
    }
    
    // returns the current amount of wei that will be given for the purchase 
    // at purchases[index]
    function getEarnings(uint index) public constant returns (uint earnings, uint amount) {
        Purchase memory cpurchase;
        Purchase memory lpurchase;
        
        cpurchase = purchases[index];
        amount = cpurchase.amount;
        
        if (cpurchase.addr == address(0)) {
            return (0, amount);
        }
        
        earnings = (index == 0) ? acm : 0;
        lpurchase = purchases[purchases.length-1];
        earnings = earnings.add( lpurchase.sf.sub(cpurchase.sf) );
        earnings = earnings.mul(amount).div(acm);
        return (earnings, amount);
    }
    
    // Cash out Ether and Tangent at for the purchase at index "index".
    // All of the Ether and Tangent associated with with that purchase will
    // be sent to recipient, and no future withdrawals can be made for the
    // purchase.
    function cashOut(uint index) public {
        require(0 <= index && index < purchases.length);
        require(purchases[index].addr == msg.sender);
        
        uint earnings;
        uint amount;
        uint tangles;
        
        (earnings, amount) = getEarnings(index);
        purchases[index].addr = address(0);
        require(earnings != 0 && amount != 0);
        netStakes = netStakes.sub(amount);
        
        tangles = earnings.mul(multiplier).div(divisor);
        CashOutEvent(index, msg.sender, earnings, tangles);
        NetStakesChange(netStakes);
        
        tokenContract.transfer(msg.sender, tangles);
        msg.sender.transfer(earnings);
        return;
    }
    
    
    // The fallback function used to purchase stakes
    // sf is the sum of the proportions of:
    // (ether of current purchase / sum of ether prior to purchase)
    // It is used to calculate earnings upon withdrawal.
    function () public payable {
        require(msg.value != 0);
        
        uint index = purchases.length;
        uint sf;
        uint f;
        
        if (index == 0) {
            sf = 0;
        } else {
            f = msg.value.mul(acm).div(netStakes);
            sf = purchases[index-1].sf.add(f);
        }
        
        netStakes = netStakes.add(msg.value);
        purchases.push(Purchase(msg.sender, msg.value, sf));
        
        NetStakesChange(netStakes);
        PurchaseEvent(index, msg.sender, msg.value, sf);
        return;
    }
}
function getEarnings(uint index) public constant returns (uint earnings, uint amount) {
    Purchase memory cpurchase;
    Purchase memory lpurchase;
        
    cpurchase = purchases[index];
    amount = cpurchase.amount;
        
    if (cpurchase.addr == address(0)) {
        return (0, amount);
    }
        
    earnings = (index == 0) ? acm : 0;
    lpurchase = purchases[purchases.length-1];
    earnings = earnings.add( lpurchase.sf.sub(cpurchase.sf) );
    earnings = earnings.mul(amount).div(acm);
    return (earnings, amount);
}

// returns the current amount of wei that will be given for the purchase 
// at purchases[index]