Lazily register slider_plus() and slider_minus() methods (#80)

* Lazily register `slider_plus()` and `slider_minus()` methods

* NEWS bullet

* Just use `vctrs::s3_register()`

Since it is fully up to date now in vctrs 0.5.0

* Update slider information now that it is on CRAN

DESCRIPTION

@@ -32,6 +32,7 @@ Suggests:
     covr,
     knitr,
     rmarkdown,
+    slider (>= 0.3.0),
     testthat (>= 2.1.0)
 VignetteBuilder: 
     knitr

NEWS.md

@@ -1,5 +1,8 @@
 # almanac (development version)
 
+* almanac steppers created with `stepper()` now work as `.before` and
+  `.after` arguments of `slider::slide_index()` and friends (#80).
+
 * R >=3.4.0 is now required, which is in line with tidyverse standards.
 
 # almanac 0.1.1

R/aaa.R

@@ -4,6 +4,9 @@
   rrule_js_path <- system.file("js/rrule.js", package = pkgname)
   almanac_global_context$source(rrule_js_path)
 
+  vctrs::s3_register("slider::slider_plus", "Date.almanac_stepper", slider_plus.Date.almanac_stepper)
+  vctrs::s3_register("slider::slider_minus", "Date.almanac_stepper", slider_minus.Date.almanac_stepper)
+
   .Call(export_almanac_init)
 }
 

R/stepper.R

@@ -286,6 +286,19 @@ vec_cast.almanac_stepper.almanac_stepper <- function(x, to, ..., x_arg = "", to_
   x
 }
 
+# ------------------------------------------------------------------------------
+# slider_plus() / slider_minus()
+
+# @export - .onLoad()
+slider_plus.Date.almanac_stepper <- function(x, y) {
+  vec_arith("+", x, y)
+}
+
+# @export - .onLoad()
+slider_minus.Date.almanac_stepper <- function(x, y) {
+  vec_arith("-", x, y)
+}
+
 # ------------------------------------------------------------------------------
 
 stepper_rschedule <- function(x) {

tests/testthat/test-stepper.R

@@ -144,3 +144,79 @@ test_that("steppers are coercible if from the same rschedule", {
   expect_error(vec_cast(x, new_stepper()), class = "vctrs_error_incompatible_type")
 })
 
+# ------------------------------------------------------------------------------
+# slider_plus() / slider_minus()
+
+test_that("`slider_plus()` method is registered", {
+  skip_if_not_installed("slider", minimum_version = "0.3.0")
+
+  y <- workdays(1)
+
+  # friday
+  x <- as.Date("1970-01-09")
+
+  expect_identical(
+    slider::slider_plus(x, y),
+    as.Date("1970-01-12")
+  )
+
+  # monday
+  x <- as.Date("1970-01-12")
+
+  expect_identical(
+    slider::slider_plus(x, y),
+    as.Date("1970-01-13")
+  )
+})
+
+test_that("`slider_minus()` method is registered", {
+  skip_if_not_installed("slider", minimum_version = "0.3.0")
+
+  y <- workdays(1)
+
+  # monday
+  x <- as.Date("1970-01-12")
+
+  expect_identical(
+    slider::slider_minus(x, y),
+    as.Date("1970-01-09")
+  )
+
+  # friday
+  x <- as.Date("1970-01-09")
+
+  expect_identical(
+    slider::slider_minus(x, y),
+    as.Date("1970-01-08")
+  )
+})
+
+test_that("`slide_index()` works with steppers", {
+  skip_if_not_installed("slider", minimum_version = "0.3.0")
+
+  # wednesday -> wednesday
+  x <- 1:8
+  i <- as.Date("1970-01-07") + 0:7
+
+  out <- slider::slide_index(
+    .x = x,
+    .i = i,
+    .f = identity,
+    .before = workdays(1),
+    .after = workdays(1)
+  )
+
+  expect_identical(
+    out,
+    list(
+      1:2, # On Wed, Bounds Tue-Thu
+      1:3, # On Thu, Bounds Wed-Fri
+      2:6, # On Fri, Bounds Thu-Mon
+      3:6, # On Sat, Bounds Fri-Mon
+      3:6, # On Sun, Bounds Fri-Mon
+      3:7, # On Mon, Bounds Fri-Tue
+      6:8, # On Tue, Bounds Mon-Wed
+      7:8  # On Wed, Bounds Tue-Thu
+    )
+  )
+})