[bugfix] self-referencing collection pages for status replies (#2364)

4 files changed, 124 insertions, 75 deletions

diff --git a/internal/paging/boundary.go b/internal/paging/boundary.go
index 15af65e0c..83d265515 100644
--- a/internal/paging/boundary.go
+++ b/internal/paging/boundary.go
@@ -131,3 +131,20 @@ func (b Boundary) Find(in []string) int {
 	}
 	return -1
 }
+
+// Boundary_FindFunc is functionally equivalent to Boundary{}.Find() but for an arbitrary type with ID.
+// Note: this is not a Boundary{} method as Go generics are not supported in method receiver functions.
+func Boundary_FindFunc[T any](b Boundary, in []T, get func(T) string) int { //nolint:revive
+	if get == nil {
+		panic("nil function")
+	}
+	if b.Value == "" {
+		return -1
+	}
+	for i := range in {
+		if get(in[i]) == b.Value {
+			return i
+		}
+	}
+	return -1
+}
diff --git a/internal/paging/page.go b/internal/paging/page.go
index a56f674dd..a1cf76c74 100644
--- a/internal/paging/page.go
+++ b/internal/paging/page.go
@@ -19,9 +19,8 @@ package paging
 
 import (
 	"net/url"
+	"slices"
 	"strconv"
-
-	"golang.org/x/exp/slices"
 )
 
 type Page struct {
@@ -117,7 +116,7 @@ func (p *Page) Page(in []string) []string {
 
 			// Output slice must
 			// ALWAYS be descending.
-			in = Reverse(in)
+			slices.Reverse(in)
 		}
 	} else {
 		// Default sort is descending,
@@ -143,6 +142,66 @@ func (p *Page) Page(in []string) []string {
 	return in
 }
 
+// Page_PageFunc is functionally equivalent to Page{}.Page(), but for an arbitrary type with ID.
+// Note: this is not a Page{} method as Go generics are not supported in method receiver functions.
+func Page_PageFunc[WithID any](p *Page, in []WithID, get func(WithID) string) []WithID { //nolint:revive
+	if p == nil {
+		// no paging.
+		return in
+	}
+
+	if p.order().Ascending() {
+		// Sort type is ascending, input
+		// data is assumed to be ascending.
+
+		if minIdx := Boundary_FindFunc(p.Min, in, get); minIdx != -1 {
+			// Reslice skipping up to min.
+			in = in[minIdx+1:]
+		}
+
+		if maxIdx := Boundary_FindFunc(p.Max, in, get); maxIdx != -1 {
+			// Reslice stripping past max.
+			in = in[:maxIdx]
+		}
+
+		if p.Limit > 0 && p.Limit < len(in) {
+			// Reslice input to limit.
+			in = in[:p.Limit]
+		}
+
+		if len(in) > 1 {
+			// Clone input before
+			// any modifications.
+			in = slices.Clone(in)
+
+			// Output slice must
+			// ALWAYS be descending.
+			slices.Reverse(in)
+		}
+	} else {
+		// Default sort is descending,
+		// catching all cases when NOT
+		// ascending (even zero value).
+
+		if maxIdx := Boundary_FindFunc(p.Max, in, get); maxIdx != -1 {
+			// Reslice skipping up to max.
+			in = in[maxIdx+1:]
+		}
+
+		if minIdx := Boundary_FindFunc(p.Min, in, get); minIdx != -1 {
+			// Reslice stripping past min.
+			in = in[:minIdx]
+		}
+
+		if p.Limit > 0 && p.Limit < len(in) {
+			// Reslice input to limit.
+			in = in[:p.Limit]
+		}
+	}
+
+	return in
+}
+
 // Next creates a new instance for the next returnable page, using
 // given max value. This preserves original limit and max key name.
 func (p *Page) Next(lo, hi string) *Page {
@@ -225,21 +284,24 @@ func (p *Page) ToLinkURL(proto, host, path string, queryParams url.Values) *url.
 	if queryParams == nil {
 		// Allocate new query parameters.
 		queryParams = make(url.Values)
+	} else {
+		// Before edit clone existing params.
+		queryParams = cloneQuery(queryParams)
 	}
 
 	if p.Min.Value != "" {
 		// A page-minimum query parameter is available.
-		queryParams.Add(p.Min.Name, p.Min.Value)
+		queryParams.Set(p.Min.Name, p.Min.Value)
 	}
 
 	if p.Max.Value != "" {
 		// A page-maximum query parameter is available.
-		queryParams.Add(p.Max.Name, p.Max.Value)
+		queryParams.Set(p.Max.Name, p.Max.Value)
 	}
 
 	if p.Limit > 0 {
 		// A page limit query parameter is available.
-		queryParams.Add("limit", strconv.Itoa(p.Limit))
+		queryParams.Set("limit", strconv.Itoa(p.Limit))
 	}
 
 	// Build URL string.
@@ -250,3 +312,12 @@ func (p *Page) ToLinkURL(proto, host, path string, queryParams url.Values) *url.
 		RawQuery: queryParams.Encode(),
 	}
 }
+
+// cloneQuery clones input map of url values.
+func cloneQuery(src url.Values) url.Values {
+	dst := make(url.Values, len(src))
+	for k, vs := range src {
+		dst[k] = slices.Clone(vs)
+	}
+	return dst
+}
diff --git a/internal/paging/page_test.go b/internal/paging/page_test.go
index 9eeb90882..3046dfcdd 100644
--- a/internal/paging/page_test.go
+++ b/internal/paging/page_test.go
@@ -19,12 +19,12 @@ package paging_test
 
 import (
 	"math/rand"
+	"slices"
 	"testing"
 	"time"
 
 	"github.com/oklog/ulid"
 	"github.com/superseriousbusiness/gotosocial/internal/paging"
-	"golang.org/x/exp/slices"
 )
 
 // random reader according to current-time source seed.
@@ -77,9 +77,7 @@ func TestPage(t *testing.T) {
 var cases = []Case{
 	CreateCase("minID and maxID set", func(ids []string) ([]string, *paging.Page, []string) {
 		// Ensure input slice sorted ascending for min_id
-		slices.SortFunc(ids, func(a, b string) bool {
-			return a > b // i.e. largest at lowest idx
-		})
+		slices.SortFunc(ids, ascending)
 
 		// Select random indices in slice.
 		minIdx := randRd.Intn(len(ids))
@@ -93,7 +91,7 @@ var cases = []Case{
 		expect := slices.Clone(ids)
 		expect = cutLower(expect, minID)
 		expect = cutUpper(expect, maxID)
-		expect = paging.Reverse(expect)
+		slices.Reverse(expect)
 
 		// Return page and expected IDs.
 		return ids, &paging.Page{
@@ -103,9 +101,7 @@ var cases = []Case{
 	}),
 	CreateCase("minID, maxID and limit set", func(ids []string) ([]string, *paging.Page, []string) {
 		// Ensure input slice sorted ascending for min_id
-		slices.SortFunc(ids, func(a, b string) bool {
-			return a > b // i.e. largest at lowest idx
-		})
+		slices.SortFunc(ids, ascending)
 
 		// Select random parameters in slice.
 		minIdx := randRd.Intn(len(ids))
@@ -120,7 +116,7 @@ var cases = []Case{
 		expect := slices.Clone(ids)
 		expect = cutLower(expect, minID)
 		expect = cutUpper(expect, maxID)
-		expect = paging.Reverse(expect)
+		slices.Reverse(expect)
 
 		// Now limit the slice.
 		if limit < len(expect) {
@@ -136,9 +132,7 @@ var cases = []Case{
 	}),
 	CreateCase("minID, maxID and too-large limit set", func(ids []string) ([]string, *paging.Page, []string) {
 		// Ensure input slice sorted ascending for min_id
-		slices.SortFunc(ids, func(a, b string) bool {
-			return a > b // i.e. largest at lowest idx
-		})
+		slices.SortFunc(ids, ascending)
 
 		// Select random parameters in slice.
 		minIdx := randRd.Intn(len(ids))
@@ -152,7 +146,7 @@ var cases = []Case{
 		expect := slices.Clone(ids)
 		expect = cutLower(expect, minID)
 		expect = cutUpper(expect, maxID)
-		expect = paging.Reverse(expect)
+		slices.Reverse(expect)
 
 		// Return page and expected IDs.
 		return ids, &paging.Page{
@@ -163,9 +157,7 @@ var cases = []Case{
 	}),
 	CreateCase("sinceID and maxID set", func(ids []string) ([]string, *paging.Page, []string) {
 		// Ensure input slice sorted descending for since_id
-		slices.SortFunc(ids, func(a, b string) bool {
-			return a < b // i.e. smallest at lowest idx
-		})
+		slices.SortFunc(ids, descending)
 
 		// Select random indices in slice.
 		sinceIdx := randRd.Intn(len(ids))
@@ -188,9 +180,7 @@ var cases = []Case{
 	}),
 	CreateCase("maxID set", func(ids []string) ([]string, *paging.Page, []string) {
 		// Ensure input slice sorted descending for max_id
-		slices.SortFunc(ids, func(a, b string) bool {
-			return a < b // i.e. smallest at lowest idx
-		})
+		slices.SortFunc(ids, descending)
 
 		// Select random indices in slice.
 		maxIdx := randRd.Intn(len(ids))
@@ -209,9 +199,7 @@ var cases = []Case{
 	}),
 	CreateCase("sinceID set", func(ids []string) ([]string, *paging.Page, []string) {
 		// Ensure input slice sorted descending for since_id
-		slices.SortFunc(ids, func(a, b string) bool {
-			return a < b
-		})
+		slices.SortFunc(ids, descending)
 
 		// Select random indices in slice.
 		sinceIdx := randRd.Intn(len(ids))
@@ -230,9 +218,7 @@ var cases = []Case{
 	}),
 	CreateCase("minID set", func(ids []string) ([]string, *paging.Page, []string) {
 		// Ensure input slice sorted ascending for min_id
-		slices.SortFunc(ids, func(a, b string) bool {
-			return a > b // i.e. largest at lowest idx
-		})
+		slices.SortFunc(ids, ascending)
 
 		// Select random indices in slice.
 		minIdx := randRd.Intn(len(ids))
@@ -243,7 +229,7 @@ var cases = []Case{
 		// Create expected output.
 		expect := slices.Clone(ids)
 		expect = cutLower(expect, minID)
-		expect = paging.Reverse(expect)
+		slices.Reverse(expect)
 
 		// Return page and expected IDs.
 		return ids, &paging.Page{
@@ -296,3 +282,21 @@ func generateSlice(len int) []string {
 	}
 	return in
 }
+
+func ascending(a, b string) int {
+	if a > b {
+		return 1
+	} else if a < b {
+		return -1
+	}
+	return 0
+}
+
+func descending(a, b string) int {
+	if a < b {
+		return 1
+	} else if a > b {
+		return -1
+	}
+	return 0
+}
diff --git a/internal/paging/util.go b/internal/paging/util.go
deleted file mode 100644
index dd941dd88..000000000
--- a/internal/paging/util.go
+++ /dev/null
@@ -1,43 +0,0 @@
-// GoToSocial
-// Copyright (C) GoToSocial Authors admin@gotosocial.org
-// SPDX-License-Identifier: AGPL-3.0-or-later
-//
-// This program is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Affero General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// This program is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU Affero General Public License for more details.
-//
-// You should have received a copy of the GNU Affero General Public License
-// along with this program.  If not, see <http://www.gnu.org/licenses/>.
-
-package paging
-
-// Reverse will reverse the given input slice.
-func Reverse(in []string) []string {
-	var (
-		// Start at front.
-		i = 0
-
-		// Start at back.
-		j = len(in) - 1
-	)
-
-	for i < j {
-		// Swap i,j index values in slice.
-		in[i], in[j] = in[j], in[i]
-
-		// incr + decr,
-		// looping until
-		// they meet in
-		// the middle.
-		i++
-		j--
-	}
-
-	return in
-}