reactbin/specs/015-library-pagination/spec.md

Feature Specification: Library Pagination UI

Feature Branch: 015-library-pagination Created: 2026-05-09 Status: Draft Input: User description: "Pagination UI for the image library"

User Scenarios & Testing (mandatory)

User Story 1 - Navigate Pages of Images (Priority: P1)

A user with a large image library currently sees at most 50 images and a "Load more" button that appends more images below. There is no way to jump to a specific point in the library or know how many images exist in total. This story replaces the append-on-load pattern with page-by-page navigation: Previous/Next buttons and a "Page N of M" indicator so the user always knows where they are.

Why this priority: The core usability gap — a library of any meaningful size is effectively unnavigable today. Without this, the feature has no value.

Independent Test: Load the library page. Confirm a page indicator ("Page 1 of N") is visible and the total image count is shown. Click "Next" — confirm the next set of images loads and the indicator updates. Click "Previous" — confirm the first set returns. On the first page, "Previous" is absent or disabled. On the last page, "Next" is absent or disabled. Changing a tag filter resets to page 1.

Acceptance Scenarios:

1. Given the library has more images than fit on one page, When the page loads, Then only the first page of images is shown with a "Next" button and "Page 1 of N" indicator visible.
2. Given the user is on page 1, When they click "Next", Then the next page of images replaces the current grid (not appended) and the indicator updates to "Page 2 of N".
3. Given the user is on the last page, When they view the page, Then the "Next" button is absent or disabled and "Previous" is present.
4. Given the user is on page 1, When they view the page, Then the "Previous" button is absent or disabled.
5. Given the library has fewer images than one page, When the page loads, Then no pagination controls are shown.
6. Given active tag filters are applied, When the user changes the filter, Then the page resets to 1 and the indicator updates.

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User Story 2 - Page State Reflected in URL (Priority: P2)

The current library URL is always /. After implementing page navigation, a user who shares or bookmarks a URL should land on the same page they were viewing, not always page 1.

Why this priority: Useful for bookmarking and sharing a specific point in the library, but the library is fully functional without it.

Independent Test: Navigate to page 3 of the library. Copy the URL from the browser address bar. Open it in a new tab. Confirm page 3 loads directly. Confirm the Back button in the browser returns to page 2.

Acceptance Scenarios:

1. Given the user navigates to page 3, When the page URL is copied and opened in a new tab, Then page 3 loads directly without navigating through prior pages.
2. Given the user navigates Next through several pages, When they press the browser Back button, Then the previous page is restored.
3. Given the URL includes a page number beyond the total pages available, When the page loads, Then page 1 is shown rather than an error.

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Edge Cases

• What happens when the total drops below the current page (e.g., images deleted in another session)? → Display page 1.
• What happens when the library is empty? → No pagination controls shown; existing empty state displayed.
• What happens when only one page of results exists? → No pagination controls shown.
• What happens when a filter change results in fewer pages than the current page? → Reset to page 1.

Requirements (mandatory)

Functional Requirements

• FR-001: The library MUST display images in discrete pages rather than an appending list.
• FR-002: The library MUST show a page indicator displaying the current page number and total page count (e.g., "Page 2 of 7").
• FR-003: The library MUST show the total number of images matching the current filters (e.g., "143 images").
• FR-004: A "Next" control MUST be available on all pages except the last; a "Previous" control MUST be available on all pages except the first.
• FR-005: Pagination controls MUST NOT be shown when all images fit on a single page.
• FR-006: Navigating to a new page MUST replace the displayed images, not append to them.
• FR-007: Changing a tag filter MUST reset the current page to 1.
• FR-008: The current page number MUST be reflected in the URL query string so that the URL is bookmarkable and shareable.
• FR-009: Loading a URL with a page parameter MUST display the correct page directly.
• FR-010: A page parameter beyond the available range MUST silently fall back to page 1.
• FR-011: The page size (number of images per page) MUST be 24 images.

Success Criteria (mandatory)

Measurable Outcomes

• SC-001: A user can navigate from page 1 to any other page using only Previous/Next controls within 2 clicks per page.
• SC-002: The total image count and current position are visible without scrolling on page load.
• SC-003: A bookmarked or shared page URL loads the correct page 100% of the time (within the valid range).
• SC-004: Changing a tag filter always resets to page 1 with no stale images from the previous page visible.
• SC-005: Pages with fewer images than the page size (the last page) display correctly without layout breakage.

Assumptions

• Page size is fixed at 24 images; no user-configurable page size is required.
• The API already supports limit and offset parameters; no backend changes are needed.
• The existing "Load more" / infinite-scroll pattern is fully replaced by page navigation.
• Browser history integration (Back/Forward) is satisfied by URL query parameter updates.
• Mobile responsiveness of pagination controls is required to match the existing library layout.