fix(trades): normalize the rate against deuterium like the other resources

README.md

@@ -373,6 +373,13 @@ Ogame.Trader.parseRate('3:2:1', 'deut');
 // → { rateMetal: 3, rateCrystal: 2, rateDeut: 1 }
 ```
 
+The reference term always comes back as `1`, so a rate and any multiple of it are the same rate, whichever resource you sell:
+
+```javascript
+Ogame.Trader.parseRate('4:3:2', 'deut');
+// → { rateMetal: 2, rateCrystal: 1.5, rateDeut: 1 }  — same as '2:1.5:1'
+```
+
 ### `Ogame.i18n`
 
 Every model entry carries `names: { en, fr }`.

src/trades/deut.test.js

@@ -6,4 +6,11 @@ describe('A deut trade', () => {
     expect(metal).toBe(100000);
     expect(crystal).toBe(75000);
   });
+
+  // `4:3:2` is the same rate as `2:1.5:1`; it used to pay twice as much.
+  it('Sells the same deut for the same amount at an equivalent rate', () => {
+    const { metal, crystal } = sellDeut(100000, 50, 50, '4:3:2');
+    expect(metal).toBe(100000);
+    expect(crystal).toBe(75000);
+  });
 });

src/trades/parseRate.js

@@ -20,9 +20,14 @@ function extract(rate, type) {
       rateDeut: deut / crystal,
     };
   } else if (type === 'deut') {
+    // Like the two branches above: express the other terms in units of the one
+    // being sold, so its own term becomes 1. Reading `metal` and `crystal` raw
+    // here only happened to work because rates are usually written against 1
+    // deuterium — `4:3:2` is the same rate as `2:1.5:1`, but used to pay twice
+    // as much for the very same deuterium.
     res = {
-      rateMetal: metal,
-      rateCrystal: crystal,
+      rateMetal: metal / deut,
+      rateCrystal: crystal / deut,
       rateDeut: 1,
     };
   } else {

src/trades/parseRate.test.js

@@ -27,6 +27,26 @@ describe('Parse rate given a resource and a rate', () => {
     });
   });
 
+  // Normalizing means expressing the other two terms in units of the reference
+  // resource, whichever one it is. The deut branch used to read the metal and
+  // crystal terms raw, so a rate written against anything but 1 deuterium came
+  // back scaled.
+  it('Parse rate by selling deut when the deut term is not 1', () => {
+    const res = parseRate('4:3:2', 'deut');
+    expect(res).toEqual({
+      rateMetal: 2,
+      rateCrystal: 1.5,
+      rateDeut: 1,
+    });
+  });
+
+  it('Reads equivalent rates identically, whichever resource is sold', () => {
+    ['metal', 'crystal', 'deut'].forEach((type) => {
+      expect(parseRate('4:3:2', type)).toEqual(parseRate('2:1.5:1', type));
+      expect(parseRate('10:7.5:5', type)).toEqual(parseRate('2:1.5:1', type));
+    });
+  });
+
   it('Should return an error if rate is not correctly specified', () => {
     try {
       const res = parseRate('3:toto:1');