Better pagination support for > 9 pages at once (#114)

internal/app/controller/web/index.go

@@ -16,7 +16,7 @@ type Index struct {
 	controller.Super
 	Journals   []model.Journal
 	Pages      []int
-	Pagination database.PaginationInformation
+	Pagination database.PaginationDisplay
 	Saved      bool
 }
 
@@ -26,25 +26,29 @@ func (c *Index) Run(response http.ResponseWriter, request *http.Request) {
 	container := c.Super.Container.(*app.Container)
 	js := model.Journals{Container: container, Gs: model.GiphyAdapter(container)}
 
-	pagination := database.PaginationQuery{Page: 1, ResultsPerPage: container.Configuration.ArticlesPerPage}
+	paginationQuery := database.PaginationQuery{Page: 1, ResultsPerPage: container.Configuration.ArticlesPerPage}
 	query := request.URL.Query()
 	if query["page"] != nil {
 		page, err := strconv.Atoi(query["page"][0])
 		if err == nil {
-			pagination.Page = page
+			paginationQuery.Page = page
 		}
 	}
 
-	c.Journals, c.Pagination = js.FetchPaginated(pagination)
+	var paginationInfo database.PaginationInformation
+	c.Journals, paginationInfo = js.FetchPaginated(paginationQuery)
+	c.Pagination = database.DisplayPagination(paginationInfo)
 	c.Saved = false
 	flash := c.Session.GetFlash()
 	if flash != nil && flash[0] == "saved" {
 		c.Saved = true
 	}
 
-	c.Pages = make([]int, c.Pagination.TotalPages)
-	for i := range c.Pages {
-		c.Pages[i] = i + 1
+	c.Pages = make([]int, database.PAGINATION_MAX_PAGES)
+	i := 0
+	for p := c.Pagination.FirstPage; p <= c.Pagination.LastPage; p++ {
+		c.Pages[i] = p
+		i++
 	}
 
 	c.SessionStore.Save(response)

pkg/database/pagination.go

@@ -1,5 +1,19 @@
 package database
 
+import "math"
+
+const PAGINATION_MAX_PAGES = 9
+
+// PaginationDisplay describes the information needed to display a pagination component
+type PaginationDisplay struct {
+	ShowLeft    bool
+	ShowRight   bool
+	CurrentPage int
+	FirstPage   int
+	LastPage    int
+	TotalPages  int
+}
+
 // PaginationInformation is used to return information from a pagination query
 type PaginationInformation struct {
 	Page           int
@@ -8,7 +22,7 @@ type PaginationInformation struct {
 	TotalResults   int
 }
 
-// PaginationQuery accepts current page and resuilts per page to generate a query
+// PaginationQuery accepts current page and results per page to generate a query
 type PaginationQuery struct {
 	Page           int
 	ResultsPerPage int
@@ -18,3 +32,27 @@ type PaginationQuery struct {
 type PaginationResult struct {
 	TotalResults int `json:"total"`
 }
+
+func DisplayPagination(info PaginationInformation) PaginationDisplay {
+	display := PaginationDisplay{false, false, info.Page, 1, info.TotalPages, info.TotalPages}
+	if info.TotalPages <= PAGINATION_MAX_PAGES {
+		return display
+	}
+	half := int(math.Floor(PAGINATION_MAX_PAGES / 2))
+	if info.Page-half > 1 {
+		display.ShowLeft = true
+		display.FirstPage = info.Page - half
+		if info.TotalPages-half <= info.Page {
+			display.FirstPage = info.TotalPages - PAGINATION_MAX_PAGES + 1
+		}
+	}
+	if info.Page+half < info.TotalPages {
+		display.ShowRight = true
+		display.LastPage = info.Page + half
+		if info.Page-half <= 1 {
+			display.LastPage = PAGINATION_MAX_PAGES
+		}
+	}
+
+	return display
+}

pkg/database/pagination_test.go

@@ -0,0 +1,44 @@
+package database
+
+import (
+	"testing"
+)
+
+func TestDisplayPagination(t *testing.T) {
+	tables := []struct {
+		input  PaginationInformation
+		output PaginationDisplay
+	}{
+		{
+			PaginationInformation{1, 1, 20, 1},
+			PaginationDisplay{false, false, 1, 1, 1, 1},
+		},
+		{
+			PaginationInformation{1, 4, 20, 70},
+			PaginationDisplay{false, false, 1, 1, 4, 4},
+		},
+		{
+			PaginationInformation{1, 9, 20, 175},
+			PaginationDisplay{false, false, 1, 1, 9, 9},
+		},
+		{
+			PaginationInformation{1, 15, 20, 299},
+			PaginationDisplay{false, true, 1, 1, 9, 15},
+		},
+		{
+			PaginationInformation{15, 15, 20, 299},
+			PaginationDisplay{true, false, 15, 7, 15, 15},
+		},
+		{
+			PaginationInformation{7, 15, 20, 299},
+			PaginationDisplay{true, true, 7, 3, 11, 15},
+		},
+	}
+
+	for _, table := range tables {
+		actual := DisplayPagination(table.input)
+		if actual != table.output {
+			t.Errorf("Expected DisplayPagination() to produce result of '%v', got '%v'", table.output, actual)
+		}
+	}
+}

web/templates/index.html.tmpl

@@ -23,12 +23,14 @@
 {{if gt .Pagination.TotalPages 1}}
     <nav class="pagination">
         <ol>
-            {{$currentPage := .Pagination.Page}}
+            {{if .Pagination.ShowLeft}}<li class="first">1 ...</li>{{end}}
+            {{$currentPage := .Pagination.CurrentPage}}
             {{range .Pages}}
                 <li class="{{if eq . $currentPage}}current{{end}}">
                     <a href="/?page={{.}}">{{.}}</a>
                 </li>
             {{end}}
+            {{if .Pagination.ShowRight}}<li class="last">... {{.Pagination.TotalPages}}</li>{{end}}
         </ol>
     </nav>
 {{end}}