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## Example unit test for `AmountFormatter` module | |
defmodule GroceryBudget.AmountFormatterTest do | |
use ExUnit.Case | |
alias GroceryBudget.Utils.AmountFormatter | |
describe "AmountFormatter" do | |
@tag :amount_formatter | |
test "to_db/1 should multiply by 100" do | |
assert AmountFormatter.to_db(500) == 50000 | |
end | |
@tag :amount_formatter | |
test "to_db/1 should convert the decimal to whole number" do | |
assert AmountFormatter.to_db(500.25) == 50025 | |
end | |
@tag :amount_formatter | |
test "to_db/1 should not convert" do | |
assert AmountFormatter.to_db("hellowrold") == {:error, :invalid_number} | |
end | |
@tag :amount_formatter | |
test "from_db/1 should format amount" do | |
assert AmountFormatter.from_db(5000) == 50 | |
end | |
end | |
end | |
defmodule GroceryBudget.Utils.AmountFormatter do | |
@moduledoc """ | |
We do not store decimal to amount fields in database. In order to | |
retain the decimal place when fetching, We multiply or divide it by 100. This way, | |
we only deal with whole number. If we want to fetch the original value | |
we have to use this `AmountFormatter` module. | |
Example Usage: | |
iex> AmountFormatter.to_db(123.50) | |
iex> 12350 | |
iex> AmountFormatter.from_db(12350) | |
iex> 123.50 | |
""" | |
def to_db(amount) when is_binary(amount) do | |
if Regex.match?(~r/^\d+$/, amount) do | |
amount | |
|> Decimal.new() | |
|> Decimal.mult(100) | |
|> Decimal.to_integer() | |
else | |
{:error, :invalid_number} | |
end | |
end | |
def to_db(amount) when is_float(amount) do | |
trunc(amount * 100) | |
end | |
def to_db(amount) when is_integer(amount) do | |
trunc(amount * 100) | |
end | |
def from_db(amount) when is_float(amount) do | |
trunc(amount / 100) | |
end | |
def from_db(amount) when is_integer(amount) do | |
amount | |
|> Decimal.new() | |
|> Decimal.div(100) | |
|> Decimal.normalize() | |
|> Decimal.round() | |
|> Decimal.to_integer() | |
end | |
def from_db(amount) when is_binary(amount) do | |
trunc(String.to_float(amount) / 100) | |
end | |
# Sometimes `Ecto` returns `Decimal` struct | |
# so we need to support it. | |
def from_db(%Decimal{} = amount) do | |
amount = | |
amount | |
|> Decimal.div(100) | |
|> Decimal.to_string() | |
converted_amount = | |
case Regex.match?(~r/\d\.\d/, amount) do | |
true -> String.to_float(amount) | |
false -> String.to_integer(amount) * 1.0 | |
end | |
trunc(converted_amount) | |
# |> case do | |
# "0" -> | |
# 0 | |
# amount -> | |
# String.to_float(amount) | |
# end | |
end | |
@doc """ | |
Allow users to format amount to string | |
""" | |
def from_db(amount, :string) do | |
amount | |
|> Decimal.new() | |
|> Decimal.div(100) | |
|> Decimal.normalize() | |
|> Decimal.to_string(:normal) | |
end | |
end |
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