Managing Complexity

background-image: url(../img/fp-tower/website-background.svg)

class: center, middle, white

.title[Managing Complexity]

---

.sixty-two-left[.center[
## "Software systems get replaced not when they .hl2[wear out] but when they crumble under their own weight because they have become .hl2[too complex]"

### Plain Functional Programming by Martin Odersky
]]

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# FP Function

.sixty-two-left[.center[
<img src="../img/foundation/fp-function-string-diagram-1.svg" style="width:600px;"/>
]]

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# Function composition

.sixty-two-left[.center[
<img src="../img/foundation/fp-function-compose-1.svg" style="width:800px;"/>
]]

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# Function composition

.sixty-two-left[.center[
<img src="../img/foundation/fp-function-compose-2.svg" style="width:800px;"/>
]]

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# Function composition

.sixty-two-left[.center[
<img src="../img/foundation/fp-function-compose-3.svg" style="width:800px;"/>
]]

---

.sixty-two-left[.center[
<img src="../img/screenshot/shopping-basket.png" style="width:1000px;"/>
]]

---

---
# Generate an invoice
.fifty-two-left[
<img src="../img/foundation/order-to-invoice-1.svg" style="width:500px;"/>
]

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# Golden Tests

.sixty-two-left[
```scala
def invoiceTest(
  order   : Order,
  customer: Customer,
  fileName: String
) =
  test(s"check invoice $fileName"){
    val expected = readFile(fileName)
    val result   = generateInvoice(order, customer)

assert(result == expected)
  }

invoiceTest(order1, bob, "invoice-bob-1.pdf")
invoiceTest(order2, bob, "invoice-bob-2.pdf")
invoiceTest(order2, eda, "invoice-eda-2.pdf")
```
]

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# Generate an invoice

.fifty-two-left[
<img src="../img/foundation/order-to-invoice-2a.svg" style="width:500px;"/>
]

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# Generate an invoice

.fifty-two-left[
<img src="../img/foundation/order-to-invoice-2b.svg" style="width:500px;"/>
]

---

.forty-seven-left[
#    English
.center[

]]

.forty-seven-right[
#    French
.center[

]]

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# Generate an invoice in different languages
.seventy-two-left[
<img src="../img/foundation/order-to-invoices-0.svg" style="width:600px;"/>
]

---
# Generate an invoice in different languages
.seventy-two-left[
<img src="../img/foundation/order-to-invoices-1.svg" style="width:600px;"/>
]

---
# Generate an invoice in different languages
.seventy-two-left[
<img src="../img/foundation/order-to-invoices-2.svg" style="width:600px;"/>
]

---
# Generate an invoice in different languages
.seventy-two-left[
<img src="../img/foundation/order-to-invoices-2b.svg" style="width:600px;"/>
]

---
# Generate an invoice in different languages

.fifty-two-left[
<img src="../img/foundation/order-to-invoice-3a.svg" style="width:500px;"/>
]

---

# Generate an invoice in different languages

.fifty-two-left[.center[
<img src="../img/screenshot/invoice-en-fr.png" style="width:550px;"/>
]]

---
# Generate an invoice (FP version)

.fifty-two-left[
<img src="../img/foundation/order-to-invoice-fp-1.svg" style="width:600px;"/>
]

---
# Generate an invoice (FP version)

.fifty-two-left[
<img src="../img/foundation/order-to-invoice-fp-2.svg" style="width:600px;"/>
]

.thirty-seven-right[
```scala
case class Invoice(
  invoiceNumber  : String,
  createdAt      : LocalDate,
  customerName   : String,
  customerAddress: Address,
  items          : List[Item],
  totalNet       : Double,
  totalAfterTax  : Double,
)
```
]

---

# Generate invoices (FP version)

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# FP vs non-FP functions

.center[
<img src="../img/foundation/order-to-invoice-comparison-2.svg" style="width:1000px;"/>
]

---
class: white

background-image: url(../img/fp-tower/website-background.svg)
 
# .white[Summary]

## .white[1.] .white[Easier to test (Dependency injection)]

## .white[2.] .white[Easier to build (Lego effect)]

## .white[3.] .white[Faster to onboard developers]