iterator: add functionality to move indices

Extract the index acrobatics from the message store and move it to
iterator package for re-use and to add unit tests.

Signed-off-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>
This commit is contained in:
Koni Marti 2022-10-20 16:43:42 +02:00 committed by Robin Jarry
parent c5face0b6f
commit 206665a2d9
2 changed files with 184 additions and 0 deletions

51
lib/iterator/index.go Normal file
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@ -0,0 +1,51 @@
package iterator
// IndexProvider implements a subset of the Interator interface
type IndexProvider interface {
StartIndex() int
EndIndex() int
}
// FixBounds will force the index i to either its lower- or upper-bound value
// if out-of-bound
func FixBounds(i, lower, upper int) int {
switch {
case i > upper:
i = upper
case i < lower:
i = lower
}
return i
}
// WrapBounds will wrap the index i around its upper- or lower-bound if
// out-of-bound
func WrapBounds(i, lower, upper int) int {
switch {
case i > upper:
i = lower + (i-upper-1)%upper
case i < lower:
i = upper - (lower-i-1)%upper
}
return i
}
type BoundsCheckFunc func(int, int, int) int
// MoveIndex moves the index variable idx forward by delta steps and ensures
// that the boundary policy as defined by the CheckBoundsFunc is enforced.
//
// If CheckBoundsFunc is nil, fix boundary checks are performed.
func MoveIndex(idx, delta int, indexer IndexProvider, cb BoundsCheckFunc) int {
lower, upper := indexer.StartIndex(), indexer.EndIndex()
sign := 1
if upper < lower {
lower, upper = upper, lower
sign = -1
}
result := idx + sign*delta
if cb == nil {
return FixBounds(result, lower, upper)
}
return cb(result, lower, upper)
}

133
lib/iterator/index_test.go Normal file
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package iterator_test
import (
"testing"
"git.sr.ht/~rjarry/aerc/lib/iterator"
)
type indexer struct {
start int
end int
}
func (ip *indexer) StartIndex() int {
return ip.start
}
func (ip *indexer) EndIndex() int {
return ip.end
}
func TestMoveIndex(t *testing.T) {
tests := []struct {
idx int
delta int
start int
end int
cb iterator.BoundsCheckFunc
expected int
}{
{
idx: 0,
delta: 1,
start: 0,
end: 2,
cb: iterator.FixBounds,
expected: 1,
},
{
idx: 0,
delta: 5,
start: 0,
end: 2,
cb: iterator.FixBounds,
expected: 2,
},
{
idx: 0,
delta: -1,
start: 0,
end: 2,
cb: iterator.FixBounds,
expected: 0,
},
{
idx: 0,
delta: 2,
start: 0,
end: 2,
cb: iterator.WrapBounds,
expected: 2,
},
{
idx: 0,
delta: 3,
start: 0,
end: 2,
cb: iterator.WrapBounds,
expected: 0,
},
{
idx: 0,
delta: -1,
start: 0,
end: 2,
cb: iterator.WrapBounds,
expected: 2,
},
{
idx: 2,
delta: 2,
start: 0,
end: 2,
cb: iterator.WrapBounds,
expected: 1,
},
{
idx: 0,
delta: -2,
start: 0,
end: 2,
cb: iterator.WrapBounds,
expected: 1,
},
{
idx: 1,
delta: 1,
start: 2,
end: 0,
cb: iterator.FixBounds,
expected: 0,
},
{
idx: 0,
delta: 1,
start: 2,
end: 0,
cb: iterator.FixBounds,
expected: 0,
},
{
idx: 0,
delta: 1,
start: 2,
end: 0,
cb: iterator.WrapBounds,
expected: 2,
},
}
for i, test := range tests {
idx := iterator.MoveIndex(
test.idx,
test.delta,
&indexer{test.start, test.end},
test.cb,
)
if idx != test.expected {
t.Errorf("test %d [%#v] failed: got %d but expected %d",
i, test, idx, test.expected)
}
}
}