using Test, Dates

# will export `YearMonth` type
using YearMonths

# constructors
ym = YearMonth(2018, 12)
@test ym == YearMonth("2018-12") # accepts yyyy-mm format
@test ym == YearMonth("201812")  # accepts yyyymm format
@test ym == YearMonth(201812) # accepts Int

# algebra
@test ym - Month(1) == YearMonth(2018, 11)
@test ym - Year(1) == YearMonth(2017, 12)
@test ym + Month(1) == YearMonth(2019, 1)
@test Month(1) + ym == YearMonth(2019, 1)
@test ym + Year(1) == YearMonth(2019, 12)
@test Year(1) + ym == YearMonth(2019, 12)
@test ym + Month(12) == YearMonth(2019, 12)
@test ym - YearMonth(2018, 12) == Month(0)
@test ym - YearMonth(2019, 12) == -Month(12)
@test ym - YearMonth(2017, 12) == Month(12)

# comparison
ym1 = YearMonth(2020, 1)
ym2 = YearMonth(2019, 12)
@test ym1 > ym2

# Basic `Dates` API
ym = YearMonth(2018, 5)
@test firstdayofmonth(ym) == Date(2018, 5, 1)
@test lastdayofmonth(ym) == Date(2018, 5, 31)
@test month(ym) == 5
@test year(ym) == 2018
@test yearmonth(ym) == (2018, 5)