Fix it is possible to gain cash by repeatedly buying and selling shares of other arcologies

src/neighbor/neighborInteract.js

@@ -119,6 +119,7 @@ App.Neighbor.Interact = function() {
 
 	const interact = (function() {
 		let nd = new App.Neighbor.Display((id) => replaceDetails(id));
+		const DEMAND_PER_PERCENT = 2;
 
 		return list;
 
@@ -183,8 +184,7 @@ App.Neighbor.Interact = function() {
 					App.UI.DOM.appendNewElement("p", frag, `Your arcology's culture is capable of starting to exert cultural sway over other arcologies. It can project ${desc[0]}.`);
 				}
 			} else {
-				const ownershipCost = 500 * Math.trunc(V.arcologies[arcID].prosperity * (1 + (V.arcologies[arcID].demandFactor / 100)));
-				frag.append(`A 1% interest in this arcology is worth ${cashFormat(ownershipCost)}. `);
+				frag.append(`A 1% interest in this arcology is worth ${cashFormat(buyValue(V.arcologies[arcID], 1))}. `);
 				if (V.arcologies[arcID].ownership + V.arcologies[arcID].PCminority + V.arcologies[arcID].minority < 100) {
 					frag.append(`The transaction fee is ${cashFormat(10000)}.`);
 				}
@@ -192,18 +192,16 @@ App.Neighbor.Interact = function() {
 				if (V.arcologies[arcID].ownership + V.arcologies[arcID].PCminority + V.arcologies[arcID].minority < 100) {
 					let links = [];
 					links.push(App.UI.DOM.link("Buy", () => {
-						cashX(forceNeg(ownershipCost), "war");
-						cashX(-10000, "war");
+						cashX(-(buyValue(V.arcologies[arcID], 1) + 10000), "war");
 						V.arcologies[arcID].PCminority += 1;
-						V.arcologies[arcID].demandFactor += 2;
+						V.arcologies[arcID].demandFactor += DEMAND_PER_PERCENT;
 					}, [], "Neighbor Interact"));
 					if (V.arcologies[arcID].ownership + V.arcologies[arcID].PCminority + V.arcologies[arcID].minority <= 90) {
-						if (V.cash > ownershipCost * 10) {
+						if (V.cash > buyValue(V.arcologies[arcID], 10) + 10000) {
 							const link = App.UI.DOM.link("10%", () => {
-								cashX(forceNeg(ownershipCost * 10), "war");
-								cashX(-10000, "war");
+								cashX(-(buyValue(V.arcologies[arcID], 10) + 10000), "war");
 								V.arcologies[arcID].PCminority += 10;
-								V.arcologies[arcID].demandFactor += 20;
+								V.arcologies[arcID].demandFactor += DEMAND_PER_PERCENT * 10;
 							}, [], "Neighbor Interact");
 							links.push(link);
 						}
@@ -217,9 +215,9 @@ App.Neighbor.Interact = function() {
 				if (V.arcologies[arcID].PCminority > 0) {
 					let links = [];
 					links.push(App.UI.DOM.link("Sell", () => {
-						cashX(ownershipCost, "war");
+						cashX(sellValue(V.arcologies[arcID], 1), "war");
 						V.arcologies[arcID].PCminority -= 1;
-						V.arcologies[arcID].demandFactor -= 2;
+						V.arcologies[arcID].demandFactor -= DEMAND_PER_PERCENT;
 						if (V.arcologies[arcID].government !== "your agent" && V.arcologies[arcID].government !== "your trustees" && V.arcologies[arcID].rival !== 1) {
 							if (V.arcologies[arcID].ownership + V.arcologies[arcID].PCminority + V.arcologies[arcID].minority < 10) {
 								V.arcologies[arcID].ownership += 10;
@@ -229,9 +227,9 @@ App.Neighbor.Interact = function() {
 					}, [], "Neighbor Interact"));
 					if (V.arcologies[arcID].PCminority >= 10) {
 						links.push(App.UI.DOM.link("10%", () => {
-							cashX((ownershipCost * 10), "war");
+							cashX(sellValue(V.arcologies[arcID], 10), "war");
 							V.arcologies[arcID].PCminority -= 10;
-							V.arcologies[arcID].demandFactor -= 20;
+							V.arcologies[arcID].demandFactor -= DEMAND_PER_PERCENT * 10;
 							if (V.arcologies[arcID].government !== "your agent" && V.arcologies[arcID].government !== "your trustees" && V.arcologies[arcID].rival !== 1) {
 								if (V.arcologies[arcID].ownership + V.arcologies[arcID].PCminority + V.arcologies[arcID].minority < 10) {
 									V.arcologies[arcID].ownership += 10;
@@ -273,6 +271,34 @@ App.Neighbor.Interact = function() {
 			return frag;
 		}
 
+		/**
+		 * How much does it cost to buy x percent of a given arcology
+		 * @param {FC.ArcologyState} arc
+		 * @param {number} percent
+		 * @returns {number}
+		 */
+		function buyValue(arc, percent) {
+			const baseValue = 500 * arc.prosperity;
+			// scale the demand in such a way that buying twice in a row costs the same as buying double once.
+			const scaledDemand = arc.demandFactor + (DEMAND_PER_PERCENT * (percent / 2));
+			const scalingFactor = 1 + (scaledDemand / 100);
+			return Math.round(baseValue * scalingFactor * percent);
+		}
+
+		/**
+		 * How much does the player get when selling x percent of a given arcology
+		 * @param {FC.ArcologyState} arc
+		 * @param {number} percent
+		 * @returns {number}
+		 */
+		function sellValue(arc, percent) {
+			const baseValue = 500 * arc.prosperity;
+			// scale the demand in such a way that selling twice in a row gives the same as selling double once.
+			const scaledDemand = arc.demandFactor - (DEMAND_PER_PERCENT * (percent / 2));
+			const scalingFactor = 1 + (scaledDemand / 100);
+			return Math.round(baseValue * scalingFactor * percent);
+		}
+
 		/** Create a div containing actions specific to arcologies that are under the player's control
 		 * @param {number} arcID
 		 * @returns {Element}