Discount, give away the least, percent or fixed whichever is lesser

discounter.php

<?php

$discount_that_was_probably_applied = quick_calc_discount_used(1.21,10,11.99);

print_r($discount_that_was_probably_applied);

function quick_calc_discount_used($fixed = 0, $percent = 0, $sell_price) {
    $gave_away = 0;
    $method_used = false;
    $final_sell = 0;
    
	$percent_sell = 0;
    $percent_giveaway = 0;
    
	if ($percent) {
		$percent_sell = sprintf("%.2f", ($sell_price * (1-($percent/100))));
        //echo $percent_sell;
        $percent_giveaway = $sell_price - $percent_sell; 
        //echo ' {'.$percent_giveaway;
	}
    
    
    // -- fixed
    $fixed_sell = 0;
    $fixed_giveaway = 0;
    
	if ($fixed) {
		$fixed_sell = $sell_price - $fixed;
        //echo $fixed_sell;
        $fixed_giveaway = $sell_price - $fixed_sell; 
        //echo ' {'.$fixed_giveaway;
	}
    
    
    // -- where did we win? -- give away least theory
    if ($percent_giveaway > $fixed_giveaway) {
        $final_sell = $fixed_sell;
        $gave_away = $fixed_giveaway;
        $method_used = 'fixed';
    } else {
        $final_sell = $percent_sell;
        $gave_away = $percent_giveaway;
        $method_used = 'percent';
    }
     
    
    // -- fail safe 
    if ($final_sell < 0.01) {
        // cant do that
        $final_sell = $sell_price; // reset with no discount 
    }
    
    
    return compact('gave_away','method_used','final_sell');
        
    
}

?>

<?php

$discount_that_was_probably_applied = quick_calc_discount_used(100.21,100,11.99);

print_r($discount_that_was_probably_applied);

function quick_calc_discount_used($fixed = 0, $percent = 0, $sell_price) {
    $gave_away = 0;
    $method_used = false;
    $final_sell = 0;
    
	$percent_sell = 0;
    $percent_giveaway = 0;
    
	if ($percent) {
		$percent_sell = sprintf("%.2f", ($sell_price * (1-($percent/100))));
        //echo $percent_sell;
        $percent_giveaway = $sell_price - $percent_sell; 
        //echo ' {'.$percent_giveaway;
	}
    
    
    // -- fixed
    $fixed_sell = 0;
    $fixed_giveaway = 0;
    
	if ($fixed) {
		$fixed_sell = $sell_price - $fixed;
        //echo $fixed_sell;
        $fixed_giveaway = $sell_price - $fixed_sell; 
        //echo ' {'.$fixed_giveaway;
	}
    
    
    // -- where did we win? -- give away least theory
    if ($percent_giveaway > $fixed_giveaway) {
        $final_sell = $fixed_sell;
        $gave_away = $fixed_giveaway;
        $method_used = 'fixed';
    } else {
        $final_sell = $percent_sell;
        $gave_away = $percent_giveaway;
        $method_used = 'percent';
    }
     
    
    // -- fail safe 
    if ($final_sell < 0.01) {
        // cant do that
        $final_sell = $sell_price; // reset with no discount 
        $method_used = 'fallthrough';
        $gave_away = 0;
    }
    
    
    return compact('gave_away','method_used','final_sell');
        
    
}

?>