Uniswap-like market maker with single-token contributions

gistfile1.txt

{
	init: `{
		$asset = 'n9y3VomFeWFeZZ2PcSEcmyBb/bI7kzZduBJigNetnkY=';
		$mm_asset = var['mm_asset'];
	}`,
	messages: {
		cases: [
			{ // define share asset
				if: `{ trigger.data.define AND !$mm_asset }`,
				messages: [
					{
						app: 'asset',
						payload: {
							// without cap
							is_private: false,
							is_transferrable: true,
							auto_destroy: false,
							fixed_denominations: false,
							issued_by_definer_only: true,
							cosigned_by_definer: false,
							spender_attested: false,
						}
					},
					{
						app: 'state',
						state: `{
							var['mm_asset'] = response_unit;
							response['mm_asset'] = response_unit;
						}`
					}
				]
			},
			{ // invest in MM
				if: `{
					$base_amount = trigger.output[[asset=base]];
					$asset_amount = trigger.output[[asset=$asset]];
					$both = $base_amount > 1e5 AND $asset_amount > 0;
					$asset_only = $base_amount == 1e4 AND $asset_amount > 0;
					$base_only = $base_amount > 1e5 AND $asset_amount == 0;
					$mm_asset AND ($both OR trigger.data.contribute AND ($asset_only OR $base_only))
				}`,
				init: `{
					$asset_balance = balance[$asset] - $asset_amount;
					$bytes_balance = balance[base] - $base_amount;
					if ($asset_balance == 0 OR $bytes_balance == 0){ // initial deposit
						if (!$both)
							bounce("initial contribution must have both tokens");
						$issue_amount = balance[base];
						return;
					}
					
					if ($both){
						$current_ratio = $asset_balance / $bytes_balance;
						$expected_asset_amount = round($current_ratio * $base_amount);
						if ($expected_asset_amount != $asset_amount)
							bounce('wrong ratio of amounts, expected ' || $expected_asset_amount || ' of asset');
						$investor_share_of_prev_balance = $base_amount / $bytes_balance;
					}
					else if ($asset_only){
						$investor_share_of_prev_balance = sqrt(1 + $asset_amount/$asset_balance) - 1;
					}
					else if ($base_only){
						$investor_share_of_prev_balance = sqrt(1 + $base_amount/$bytes_balance) - 1;
					}
					$issue_amount = round($investor_share_of_prev_balance * var['mm_asset_outstanding']);
				}`,
				messages: [
					{
						app: 'payment',
						payload: {
							asset: "{$mm_asset}",
							outputs: [
								{address: "{trigger.address}", amount: "{ $issue_amount }"}
							]
						}
					},
					{
						app: 'state',
						state: `{
							var['mm_asset_outstanding'] += $issue_amount;
						}`
					},
				]
			},
			{ // divest MM shares 
				// (user is already paying 10000 bytes bounce fee which is a divest fee)
				// the price slightly moves due to fees received and paid in bytes
				if: `{$mm_asset AND trigger.output[[asset=$mm_asset]]}`,
				init: `{
					$mm_asset_amount = trigger.output[[asset=$mm_asset]];
					$investor_share = $mm_asset_amount / var['mm_asset_outstanding'];
				}`,
				messages: [
					{
						app: 'payment',
						payload: {
							asset: "{$asset}",
							outputs: [
								{address: "{trigger.address}", amount: "{ round($investor_share * balance[$asset]) }"}
							]
						}
					},
					{
						app: 'payment',
						payload: {
							asset: "base",
							outputs: [
								{address: "{trigger.address}", amount: "{ round($investor_share * balance[base]) }"}
							]
						}
					},
					{
						app: 'state',
						state: `{
							var['mm_asset_outstanding'] -= trigger.output[[asset=$mm_asset]];
						}`
					},
				]
			},
			{ // exchange bytes to asset
				if: `{trigger.output[[asset=base]] > 1e5 AND trigger.output[[asset=$asset]] == 0 AND var['mm_asset_outstanding']}`,
				init: `{
					$asset_balance = balance[$asset] - trigger.output[[asset=$asset]];
					$bytes_balance = balance[base] - trigger.output[[asset=base]];
					// other formula can be used for product, e.g. $asset_balance * $bytes_balance ^ 2
					$p = $asset_balance * $bytes_balance;
					$new_asset_balance = round($p / balance[base]);
					$amount = $asset_balance - $new_asset_balance; // we can deduct exchange fees here
				}`,
				messages: [
					{
						app: 'payment',
						payload: {
							asset: "{$asset}",
							outputs: [
								{address: "{trigger.address}", amount: "{ $amount }"}
							]
						}
					},
				]
			},
			{ // exchange asset to bytes
				if: `{trigger.output[[asset=$asset]] > 0 AND var['mm_asset_outstanding']}`,
				init: `{
					$asset_balance = balance[$asset] - trigger.output[[asset=$asset]];
					$bytes_balance = balance[base] - trigger.output[[asset=base]]; // 10Kb fee
					// other formula can be used for product, e.g. $asset_balance * $bytes_balance ^ 2
					$p = $asset_balance * $bytes_balance;
					$new_bytes_balance = round($p / balance[$asset]);
					$amount = $bytes_balance - $new_bytes_balance; // we can deduct exchange fees here
				}`,
				messages: [
					{
						app: 'payment',
						payload: {
							asset: "base",
							outputs: [
								{address: "{trigger.address}", amount: "{ $amount }"}
							]
						}
					},
				]
			},
		]
	}
}