package pdf

import (
	"fmt"
	"os"
	"regexp"
	"strconv"
)

// CountPDFPages counts the number of pages in a PDF file.
// It reads the PDF and extracts the page count from its internal structure.
func CountPDFPages(filePath string) (int, error) {
	// Check if file exists
	if _, err := os.Stat(filePath); err != nil {
		return 0, fmt.Errorf("file not found: %w", err)
	}

	// Read the PDF file
	data, err := os.ReadFile(filePath)
	if err != nil {
		return 0, fmt.Errorf("failed to read file: %w", err)
	}

	// Convert to string for regex matching
	content := string(data)

	// Try to find /Type /Pages /Count pattern
	// This is the most reliable indicator of page count in PDF structure
	pageCountRegex := regexp.MustCompile(`/Type\s+/Pages\s+/Kids\s*\[(.*?)\]\s+/Count\s+(\d+)`)
	matches := pageCountRegex.FindStringSubmatch(content)
	if len(matches) >= 3 {
		count, err := strconv.Atoi(matches[2])
		if err == nil && count > 0 {
			return count, nil
		}
	}

	// Fallback: count individual /Type /Page objects
	pageRegex := regexp.MustCompile(`/Type\s+/Page[\s/\(\)]`)
	pageMatches := pageRegex.FindAllString(content, -1)
	if len(pageMatches) > 0 {
		return len(pageMatches), nil
	}

	// If we can't determine page count, return 0 (indicates error or unknown)
	return 0, fmt.Errorf("unable to determine page count")
}