Improve search functionality

* Addresses issues ArtifexSoftware#78 & ArtifexSoftware#98
  Fix the issue where the search results on the current page would be skipped when clicking the "Next" search button for the first time.
  Improve the search experience for the Chinese input method.

* Add an Enter key handler for the search input.
  Enter: search "Next"
  Shift + Enter: search "Prev"

* Display page number based on 1

examples/simple-viewer/index.html

@@ -84,8 +84,8 @@
 			size="40"
 			placeholder="Search..."
 		>
-		<button onclick="run_search(-1, 1)">Prev</button>
-		<button onclick="run_search(1, 1)">Next</button>
+		<button id="search-prev" onclick="run_search(-1, 1)">Prev</button>
+		<button id="search-next" onclick="run_search(1, 1)">Next</button>
 		<div id="search-status" style="flex-grow:1"></div>
 		<button onclick="hide_search_panel()">X</button>
 	</footer>

examples/simple-viewer/viewer.js

@@ -582,10 +582,19 @@ let search_status = document.getElementById("search-status")
 let search_input = document.getElementById("search-input")
 
 var current_search_needle = ""
-var current_search_page = 0
+var last_search_page = -1
 
-search_input.oninput = function (event) {
-	run_search(event.shiftKey ? -1 : 1, 0)
+search_input.onchange = function (event) {
+	last_search_page = -1
+}
+
+search_input.onkeyup = function (event) {
+	if (event.key === 'Enter') {
+		if (event.shiftKey)
+			document.getElementById("search-prev").click()
+		else
+			document.getElementById("search-next").click()
+	}
 }
 
 function show_search_panel() {
@@ -619,34 +628,38 @@ async function run_search(direction, step) {
 	// start search from visible page
 	set_search_needle(search_input.value)
 
-	current_search_page = find_visible_page()
-
-	let next_page = current_search_page
-	if (step)
-		next_page += direction
+	let page = 0;
+	if (last_search_page === -1)
+		page = find_visible_page()
+	else {
+		page = last_search_page
+		if (step)
+			page += direction
+	}
 
-	while (next_page >= 0 && next_page < page_list.length) {
+	while (page >= 0 && page < page_list.length) {
 		// We run the check once per loop iteration,
 		// in case the search was cancel during the 'await' below.
 		if (current_search_needle === "") {
 			search_status.textContent = ""
 			return
 		}
 
-		search_status.textContent = `Searching page ${next_page}.`
+		search_status.textContent = `Searching page ${page + 1}.`
 
-		if (page_list[next_page].loadNeedle !== page_list[next_page].needle)
-			await page_list[next_page]._loadSearch()
+		if (page_list[page].loadNeedle !== page_list[page].needle)
+			await page_list[page]._loadSearch()
 
-		const hits = page_list[next_page].searchData
+		const hits = page_list[page].searchData
 		if (hits && hits.length > 0) {
-			page_list[next_page].rootNode.scrollIntoView()
-			current_search_page = next_page
-			search_status.textContent = `${hits.length} hits on page ${next_page}.`
+			page_list[page].rootNode.scrollIntoView()
+			last_search_page = page
+			const word = hits.length === 1 ? "hit" : "hits"
+			search_status.textContent = `${hits.length} ${word} on page ${page + 1}.`
 			return
 		}
 
-		next_page += direction
+		page += direction
 	}
 
 	search_status.textContent = "No more search hits."
@@ -735,7 +748,7 @@ async function init_document(title) {
 	clear_message()
 
 	current_search_needle = ""
-	current_search_page = 0
+	last_search_page = -1
 }
 
 async function open_document_from_buffer(buffer, magic, title) {