package main

import (
	"bufio"
	"fmt"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"golang.org/x/net/html"
)

// webCrawlerInit is called during init on program start
func webCrawlerInit() {
	go func() {
		// First run immediately
		runCrawlerAndIndexer()

		// Then run periodically based on CrawlingInterval
		ticker := time.NewTicker(config.CrawlingInterval)
		for range ticker.C {
			runCrawlerAndIndexer()
		}
	}()
}

// runCrawlerAndIndexer reads domains.csv -> crawls -> writes to data_to_index.txt -> reindexes
func runCrawlerAndIndexer() {
	// 1. Read domains.csv
	domains, err := readDomainsCSV(filepath.Join(config.DriveCache.Path, "domains.csv"))
	if err != nil {
		printErr("Error reading domains.csv: %v", err)
		return
	}

	// 2. Crawl each domain and write results to data_to_index.txt
	outFile := filepath.Join(config.DriveCache.Path, "data_to_index.txt")
	if err := crawlDomainsToFile(domains, outFile, config.MaxPagesPerDomain, config.ConcurrentCrawlers); err != nil {
		printErr("Error crawling domains: %v", err)
		return
	}

	// 3. Re-index data_to_index.txt periodically based on IndexRefreshInterval
	startPeriodicIndexing(outFile, config.IndexRefreshInterval)

	printDebug("Crawl + index refresh completed.")
}

// readDomainsCSV returns a slice of (rank,domain) from a local CSV file
func readDomainsCSV(csvPath string) ([][2]string, error) {
	f, err := os.Open(csvPath)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	var result [][2]string
	scanner := bufio.NewScanner(f)
	// Skip header line
	scanner.Scan()

	for scanner.Scan() {
		line := scanner.Text()
		// Split by commas, not tabs
		fields := strings.SplitN(line, ",", 3) // Splits into up to 3 parts (rank, domain, popularity)
		if len(fields) < 2 {
			printDebug("Skipping malformed line: %s", line)
			continue
		}
		// Remove quotes around fields, if present
		rank := strings.Trim(fields[0], `"`)
		domain := strings.Trim(fields[1], `"`)
		result = append(result, [2]string{rank, domain})
	}
	return result, scanner.Err()
}

// crawlDomainsToFile visits each domain, extracts minimal data, writes results to outFile
func crawlDomainsToFile(domains [][2]string, outFile string, maxPages int, concurrentCrawlers int) error {
	existingEntries := make(map[string]bool)
	var mu sync.Mutex // Mutex to protect access to the map

	if _, err := os.Stat(outFile); err == nil {
		file, err := os.Open(outFile)
		if err != nil {
			return fmt.Errorf("unable to open %s: %v", outFile, err)
		}
		defer file.Close()

		scanner := bufio.NewScanner(file)
		for scanner.Scan() {
			line := scanner.Text()
			parts := strings.SplitN(line, "|", 5)
			if len(parts) >= 1 {
				existingEntries[parts[0]] = true
			}
		}
	}

	// Open file for writing (truncate if existing)
	file, err := os.OpenFile(outFile, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
	if err != nil {
		return fmt.Errorf("unable to open %s for writing: %v", outFile, err)
	}
	defer file.Close()

	semaphore := make(chan struct{}, concurrentCrawlers)
	var wg sync.WaitGroup

	for _, d := range domains {
		wg.Add(1)
		semaphore <- struct{}{}
		go func(domain [2]string) {
			defer wg.Done()
			defer func() { <-semaphore }()

			rank := domain[0]
			domainName := domain[1]
			fullURL := "https://" + domainName

			mu.Lock()
			if domainName == "" || existingEntries[fullURL] {
				mu.Unlock()
				return
			}
			existingEntries[fullURL] = true
			mu.Unlock()

			title, desc, keywords := fetchPageMetadata(fullURL)
			if title == "" {
				title = "Unknown Title"
			}
			if desc == "" {
				desc = "No Description"
			}

			line := fmt.Sprintf("%s|%s|%s|%s|%s\n",
				fullURL,
				sanitize(title),
				sanitize(keywords),
				sanitize(desc),
				rank,
			)
			file.WriteString(line)
		}(d)
	}

	wg.Wait()
	return nil
}

// fetchPageMetadata does a simple GET and parses <title>, meta[name=description], meta[name=keywords]
func fetchPageMetadata(pageURL string) (string, string, string) {
	// Generate a User-Agent using your GetUserAgent function
	userAgent, err := GetUserAgent("crawler")
	if err != nil {
		printWarn("Failed to generate User-Agent: %v", err)
		return "", "", ""
	}

	client := &http.Client{Timeout: 15 * time.Second}
	req, err := http.NewRequest("GET", pageURL, nil)
	if err != nil {
		printWarn("Failed to create request for %s: %v", pageURL, err)
		return "", "", ""
	}

	// Set the dynamically generated User-Agent
	req.Header.Set("User-Agent", userAgent)

	resp, err := client.Do(req)
	if err != nil {
		printWarn("Failed to GET %s: %v", pageURL, err)
		return "", "", ""
	}
	defer resp.Body.Close()

	// Handle non-200 responses
	if resp.StatusCode == 403 || resp.StatusCode == 401 {
		printWarn("Skipping %s: HTTP %d", pageURL, resp.StatusCode)
		return "", "", ""
	} else if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		printWarn("Non-200 for %s: %d", pageURL, resp.StatusCode)
		return "", "", ""
	}

	// Parse HTML
	doc, err := html.Parse(resp.Body)
	if err != nil {
		printWarn("HTML parse error for %s: %v", pageURL, err)
		return "", "", ""
	}

	var title, desc, keywords string
	var f func(*html.Node)
	f = func(n *html.Node) {
		if n.Type == html.ElementNode && n.Data == "title" && n.FirstChild != nil {
			title = n.FirstChild.Data
		}
		if n.Type == html.ElementNode && n.Data == "meta" {
			var nameVal, contentVal string
			for _, attr := range n.Attr {
				switch strings.ToLower(attr.Key) {
				case "name":
					nameVal = strings.ToLower(attr.Val)
				case "content":
					contentVal = attr.Val
				}
			}
			if nameVal == "description" {
				desc = contentVal
			} else if nameVal == "keywords" {
				keywords = contentVal
			}
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			f(c)
		}
	}
	f(doc)

	return title, desc, keywords
}

// sanitize is a quick helper to remove newlines/pipes from fields
func sanitize(input string) string {
	input = strings.ReplaceAll(input, "|", " ")
	input = strings.ReplaceAll(input, "\n", " ")
	input = strings.TrimSpace(input)
	return input
}