package pdfinfo

import (
	"fmt"
	"strings"
	"testing"
)

// fakePDF builds a minimal but structurally scannable PDF with a page-tree
// /Count and N /Type /Page objects.
func fakePDF(pages, declared int) []byte {
	var objs []string
	for i := 1; i <= pages; i++ {
		objs = append(objs, fmt.Sprintf("%d 0 obj<</Type/Page/Parent 99 0 R>>endobj", i))
	}
	objs = append(objs, fmt.Sprintf("99 0 obj<</Type/Pages/Count %d/Kids[1 0 R]>>endobj", declared))
	body := strings.Join(objs, "\n")
	return []byte("%PDF-1.7\n" + body + "\n%%EOF")
}

func TestPagesCount(t *testing.T) {
	for _, n := range []int{1, 2, 7, 23} {
		got, err := Pages(fakePDF(n, n))
		if err != nil {
			t.Fatalf("n=%d: %v", n, err)
		}
		if got != n {
			t.Fatalf("n=%d got %d", n, got)
		}
	}
}

func TestPagesFallsBackToPageObjects(t *testing.T) {
	// No /Pages /Count reachable: count /Type /Page objects instead.
	pdf := []byte("%PDF-1.7\n1 0 obj<</Type/Page>>endobj\n2 0 obj<</Type/Page>>endobj\n%%EOF")
	got, err := Pages(pdf)
	if err != nil || got != 2 {
		t.Fatalf("got=%d err=%v", got, err)
	}
}

func TestPagesRejectsNonPDF(t *testing.T) {
	if _, err := Pages([]byte("hello")); err == nil {
		t.Fatal("want error for non-PDF")
	}
	if _, err := Pages(nil); err == nil {
		t.Fatal("want error for empty input")
	}
}

func TestPagesDoesNotCountPagesType(t *testing.T) {
	// "/Type /Pages" must not match the /Type /Page fallback.
	pdf := []byte("%PDF-1.7\n1 0 obj<</Type/Page>>endobj\n2 0 obj<</Type/Pages/Count 5>>endobj\n%%EOF")
	got, err := Pages(pdf)
	if err != nil || got != 5 {
		t.Fatalf("got=%d err=%v", got, err)
	}
}