subseq of points from start

frontend/src/Point.elm

@@ -1,4 +1,4 @@
-module Point exposing(Pos, Point, decoder, downsample, duration)
+module Point exposing(Pos, Point, decoder, downsample, duration, subseq)
 
 import Json.Decode as D
 
@@ -62,3 +62,13 @@ duration points =
     case points of
         (p::ps) -> (last p ps).time - p.time
         _ -> 0
+
+subseq points start dur =
+    case points of
+        [] -> []
+        (p::ps) ->
+            if p.time < start
+            then subseq ps start dur
+            else if p.time >= (start + dur)
+                 then []
+                 else p::(subseq ps start dur)

frontend/tests/PointTest.elm

@@ -1,6 +1,6 @@
 module PointTest exposing (specs)
 
-import Point exposing (Point, Pos, downsample)
+import Point exposing (Point, Pos, downsample, subseq)
 import Test exposing (..)
 import Expect exposing (Expectation)
 
@@ -19,7 +19,8 @@ maybe default val =
 
 specs: Test
 specs =
-    describe "downsample"
+    describe "Point"
+        [ describe "downsample"
               [ test "it returns no more points than requested" <|
                     \_ ->
                     let orig = (points 10)
@@ -31,5 +32,21 @@ specs =
                           sampled = Point.downsample 10 orig
                           idx p = maybe 0 p.power
                       in Expect.equalLists [0, 500, 1000] (List.map idx sampled)
-
+              ]
+        , describe "subseq"
+            [ test "chooses only points in the time range" <|
+                  \_ ->
+                  let orig = (points 50)
+                      s = 1731437087
+                      d = 40
+                      subs = subseq orig s d
+                  in Expect.equal True
+                      (List.all (\ p -> p.time >= s && p.time <= s + d) subs)
+            , test "is empty if no points" <|
+                  \_ ->
+                      Expect.equalLists [] (subseq [] 10 10)
+            , test "is empty if no time" <|
+                  \_ ->
+                      Expect.equalLists (subseq (points 50) 1731437067 0) []
+            ]
         ]