feat(regions): Add support for updating countries in a region (#6432)

**What**
Add missing support for updating countries on the POST /admin/regions/:id route.
Furthermore, the PR refactors how the normalization and validation was handled in both create and update scenarios.
Finally, the PR adds a unique index on the country entity, which ensures at the DB level that we cannot have a duplicate country in the DB for a single region.

packages/region/integration-tests/__tests__/region-module.spec.ts

@@ -127,7 +127,7 @@ describe("Region Module Service", () => {
         currency_code: "USD",
         countries: ["neverland"],
       })
-    ).rejects.toThrowError("Countries with codes neverland does not exist")
+    ).rejects.toThrowError('Countries with codes: "neverland" do not exist')
   })
 
   it("should throw when country is already assigned to a region", async () => {
@@ -144,7 +144,7 @@ describe("Region Module Service", () => {
         countries: ["us"],
       })
     ).rejects.toThrowError(
-      "Country with code us is already assigned to a region"
+      'Countries with codes: "us" are already assigned to a region'
     )
   })
 
@@ -163,7 +163,163 @@ describe("Region Module Service", () => {
         },
       ])
     ).rejects.toThrowError(
-      "Country with code us is already assigned to a region"
+      'Countries with codes: "us" are already assigned to a region'
+    )
+  })
+
+  it("should update the region successfully", async () => {
+    const createdRegion = await service.create({
+      name: "North America",
+      currency_code: "USD",
+      countries: ["us", "ca"],
+    })
+
+    await service.update(createdRegion.id, {
+      name: "Americas",
+      currency_code: "MXN",
+      countries: ["us", "mx"],
+    })
+
+    const latestRegion = await service.retrieve(createdRegion.id, {
+      relations: ["currency", "countries"],
+    })
+
+    expect(latestRegion).toMatchObject({
+      id: createdRegion.id,
+      name: "Americas",
+      currency_code: "mxn",
+    })
+
+    expect(latestRegion.countries.map((c) => c.iso_2)).toEqual(["mx", "us"])
+  })
+
+  it("should update the region without affecting countries if countries are undefined", async () => {
+    const createdRegion = await service.create({
+      name: "North America",
+      currency_code: "USD",
+      countries: ["us", "ca"],
+    })
+
+    await service.update(createdRegion.id, {
+      name: "Americas",
+      currency_code: "MXN",
+    })
+
+    const updatedRegion = await service.retrieve(createdRegion.id, {
+      relations: ["currency", "countries"],
+    })
+
+    expect(updatedRegion).toMatchObject({
+      id: createdRegion.id,
+      name: "Americas",
+      currency_code: "mxn",
+    })
+
+    expect(updatedRegion.countries.map((c) => c.iso_2)).toEqual(["ca", "us"])
+  })
+
+  it("should remove the countries in a region successfully", async () => {
+    const createdRegion = await service.create({
+      name: "North America",
+      currency_code: "USD",
+      countries: ["us", "ca"],
+    })
+
+    await service.update(createdRegion.id, {
+      name: "Americas",
+      currency_code: "MXN",
+      countries: [],
+    })
+
+    const updatedRegion = await service.retrieve(createdRegion.id, {
+      relations: ["currency", "countries"],
+    })
+
+    expect(updatedRegion).toMatchObject({
+      id: createdRegion.id,
+      name: "Americas",
+      currency_code: "mxn",
+    })
+
+    expect(updatedRegion.countries).toHaveLength(0)
+  })
+
+  it("should fail updating the region currency to a non-existent one", async () => {
+    const createdRegion = await service.create({
+      name: "North America",
+      currency_code: "USD",
+      countries: ["us", "ca"],
+    })
+
+    await expect(
+      service.update(
+        { id: createdRegion.id },
+        {
+          currency_code: "DOGECOIN",
+        }
+      )
+    ).rejects.toThrowError('Currencies with codes: "dogecoin" were not found')
+  })
+
+  it("should fail updating the region countries to non-existent ones", async () => {
+    const createdRegion = await service.create({
+      name: "North America",
+      currency_code: "USD",
+      countries: ["us", "ca"],
+    })
+
+    await expect(
+      service.update(
+        { id: createdRegion.id },
+        {
+          countries: ["us", "neverland"],
+        }
+      )
+    ).rejects.toThrowError('Countries with codes: "neverland" do not exist')
+  })
+
+  it("should fail updating the region if there are duplicate countries", async () => {
+    const createdRegion = await service.create({
+      name: "North America",
+      currency_code: "USD",
+      countries: ["us", "ca"],
+    })
+
+    await expect(
+      service.update(
+        { id: createdRegion.id },
+        {
+          countries: ["us", "us"],
+        }
+      )
+    ).rejects.toThrowError(
+      'Countries with codes: "us" are already assigned to a region'
+    )
+  })
+
+  it("should fail updating the region if country is already used", async () => {
+    const [createdRegion] = await service.create([
+      {
+        name: "North America",
+        currency_code: "USD",
+        countries: ["us", "ca"],
+      },
+      {
+        name: "Americas",
+        currency_code: "USD",
+        countries: ["mx"],
+      },
+    ])
+
+    await expect(
+      service.update(
+        { id: createdRegion.id },
+        {
+          countries: ["us", "mx"],
+        }
+      )
+    ).rejects.toThrowError(
+      'Countries with codes: "mx" are already assigned to a region'
     )
   })
 
@@ -173,6 +329,6 @@ describe("Region Module Service", () => {
         name: "Europe",
         currency_code: "DOGECOIN",
       })
-    ).rejects.toThrowError("Currency with code: DOGECOIN was not found")
+    ).rejects.toThrowError('Currencies with codes: "dogecoin" were not found')
   })
 })