package main

import (
	"bufio"
	"compress/gzip"
	"context"
	"fmt"
	"io"
	"os"
	"strings"
	"sync/atomic"
	"time"

	"github.com/jackc/pgx/v5"
)

// Domain represents a host to process for feeds
// Status: hold (pending review), pass (approved), skip (not processing)
// CrawledAt: zero time = needs domain_check, +1 sec = needs feed_crawl, real time = done
type Domain struct {
	Host       string    `json:"host"`
	Status     string    `json:"status"`
	CrawledAt  time.Time `json:"crawled_at"`
	FeedsFound int       `json:"feeds_found,omitempty"`
	LastError  string    `json:"last_error,omitempty"`
	TLD        string    `json:"tld,omitempty"`
	MissCount  int       `json:"miss_count,omitempty"`
}

// MissCountThreshold is the number of consecutive errors before setting status to hold
const MissCountThreshold = 100

// ErrorRetryDelay is how long to wait before retrying a domain with errors (1 hour minimum)
// At 100 seconds actual rate due to queue, 100 misses = ~2.8 hours
// At 1 hour minimum delay, 100 misses = ~4+ days in practice
var ErrorRetryDelay = 1 * time.Hour

// FullHost returns the complete hostname (host + tld)
func (d *Domain) FullHost() string {
	return fullHost(d.Host, d.TLD)
}

// Sentinel values for domain processing state
var (
	DomainStateUnchecked = time.Time{}                  // 0001-01-01 00:00:00 - needs domain_check
	DomainStateChecked   = time.Time{}.Add(time.Second) // 0001-01-01 00:00:01 - needs feed_crawl
)

// shouldAutoSkipDomain checks if a domain should be auto-skipped based on patterns
func shouldAutoSkipDomain(host string) bool {
	// Never skip our own domain
	if strings.HasSuffix(host, "1440.news") || host == "1440.news" {
		return false
	}
	// Skip bare TLDs (no dot means it's just "com", "net", etc.)
	if !strings.Contains(host, ".") {
		return true
	}
	// Skip domains starting with a digit (spam pattern)
	if len(host) > 0 && host[0] >= '0' && host[0] <= '9' {
		return true
	}
	// Skip domains starting with letter-dash (spam pattern, e.g., "a-example.com")
	if len(host) > 1 && ((host[0] >= 'a' && host[0] <= 'z') || (host[0] >= 'A' && host[0] <= 'Z')) && host[1] == '-' {
		return true
	}
	return false
}

// saveDomain stores a domain in PostgreSQL
func (c *Crawler) saveDomain(domain *Domain) error {
	// Auto-skip domains matching spam patterns
	fh := domain.FullHost()
	status := domain.Status
	if shouldAutoSkipDomain(fh) {
		status = "skip"
	}

	_, err := c.db.Exec(`
		INSERT INTO domains (host, status, crawled_at, feeds_found, last_error, tld)
		VALUES ($1, $2, $3, $4, $5, $6)
		ON CONFLICT(host, tld) DO UPDATE SET
			status = EXCLUDED.status,
			crawled_at = EXCLUDED.crawled_at,
			feeds_found = EXCLUDED.feeds_found,
			last_error = EXCLUDED.last_error
	`, stripTLD(fh), status, domain.CrawledAt,
		domain.FeedsFound, NullableString(domain.LastError), domain.TLD)
	return err
}

// saveDomainTx stores a domain using a transaction
func (c *Crawler) saveDomainTx(tx pgx.Tx, domain *Domain) error {
	// Auto-skip domains matching spam patterns
	fh := domain.FullHost()
	status := domain.Status
	if shouldAutoSkipDomain(fh) {
		status = "skip"
	}

	_, err := tx.Exec(context.Background(), `
		INSERT INTO domains (host, status, crawled_at, feeds_found, last_error, tld)
		VALUES ($1, $2, $3, $4, $5, $6)
		ON CONFLICT(host, tld) DO NOTHING
	`, stripTLD(fh), status, domain.CrawledAt,
		domain.FeedsFound, NullableString(domain.LastError), domain.TLD)
	return err
}

// domainExists checks if a domain already exists in the database
func (c *Crawler) domainExists(host string) bool {
	host = normalizeHost(host)
	var exists bool
	err := c.db.QueryRow("SELECT EXISTS(SELECT 1 FROM domains WHERE host = $1 AND tld = $2)", stripTLD(host), getTLD(host)).Scan(&exists)
	return err == nil && exists
}

// getDomain retrieves a domain from PostgreSQL
func (c *Crawler) getDomain(host string) (*Domain, error) {
	host = normalizeHost(host)
	domain := &Domain{}
	var lastError *string

	err := c.db.QueryRow(`
		SELECT host, tld, status, crawled_at, feeds_found, last_error
		FROM domains WHERE host = $1 AND tld = $2
	`, stripTLD(host), getTLD(host)).Scan(
		&domain.Host, &domain.TLD, &domain.Status, &domain.CrawledAt,
		&domain.FeedsFound, &lastError,
	)

	if err == pgx.ErrNoRows {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}

	domain.LastError = StringValue(lastError)

	return domain, nil
}

// GetDomainsToCheck returns unchecked domains needing DNS lookup (domain_check)
// crawled_at = zero time means needs domain_check
func (c *Crawler) GetDomainsToCheck(limit int) ([]*Domain, error) {
	rows, err := c.db.Query(`
		SELECT host, status, crawled_at, feeds_found, last_error, tld
		FROM domains
		WHERE status = 'pass'
			AND crawled_at = '0001-01-01 00:00:00'
			AND last_error IS NULL
		LIMIT $1
	`, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	return c.scanDomains(rows)
}

// GetDomainsToCrawl returns DNS-verified domains needing feed discovery (feed_crawl)
// crawled_at = +1 sec means passed DNS check, ready for crawl
// Also includes domains with errors that are due for retry
func (c *Crawler) GetDomainsToCrawl(limit int) ([]*Domain, error) {
	now := time.Now()
	rows, err := c.db.Query(`
		SELECT host, status, crawled_at, feeds_found, last_error, tld
		FROM domains
		WHERE status = 'pass' AND (
			(crawled_at = '0001-01-01 00:00:01' AND last_error IS NULL)  -- passed DNS, ready to crawl
			OR (crawled_at < $1 AND crawled_at > '0001-01-01 00:00:01' AND last_error IS NOT NULL)  -- retry errors
		)
		ORDER BY last_error IS NULL DESC, crawled_at ASC
		LIMIT $2
	`, now, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	return c.scanDomains(rows)
}

// markDomainChecked updates a domain after domain_check (sets to +1 sec for feed_crawl)
// host parameter should be the stripped host (without TLD)
func (c *Crawler) markDomainChecked(host, tld, lastError string) error {
	if lastError != "" {
		// Increment miss_count, set to 'hold' only at threshold
		// Schedule retry after ErrorRetryDelay
		retryAt := time.Now().Add(ErrorRetryDelay)
		_, err := c.db.Exec(`
			UPDATE domains SET
				crawled_at = $1,
				last_error = $2,
				miss_count = miss_count + 1,
				status = CASE WHEN miss_count + 1 >= $3 THEN 'hold' ELSE status END
			WHERE host = $4 AND tld = $5
		`, retryAt, lastError, MissCountThreshold, host, tld)
		return err
	}
	// Success - reset miss_count
	_, err := c.db.Exec(`
		UPDATE domains SET crawled_at = $1, last_error = NULL, miss_count = 0
		WHERE host = $2 AND tld = $3
	`, DomainStateChecked, host, tld)
	return err
}

// scanDomains is a helper to scan multiple domain rows
func (c *Crawler) scanDomains(rows pgx.Rows) ([]*Domain, error) {
	var domains []*Domain
	for rows.Next() {
		domain := &Domain{}
		var lastError *string

		if err := rows.Scan(
			&domain.Host, &domain.Status, &domain.CrawledAt,
			&domain.FeedsFound, &lastError, &domain.TLD,
		); err != nil {
			continue
		}

		domain.LastError = StringValue(lastError)

		domains = append(domains, domain)
	}

	return domains, rows.Err()
}

// markDomainCrawled updates a domain after feed_crawl (sets to NOW())
// host parameter should be the stripped host (without TLD)
func (c *Crawler) markDomainCrawled(host, tld string, feedsFound int, lastError string) error {
	if lastError != "" {
		// Increment miss_count, set to 'hold' only at threshold
		// Schedule retry after ErrorRetryDelay
		retryAt := time.Now().Add(ErrorRetryDelay)
		_, err := c.db.Exec(`
			UPDATE domains SET
				crawled_at = $1,
				feeds_found = $2,
				last_error = $3,
				miss_count = miss_count + 1,
				status = CASE WHEN miss_count + 1 >= $4 THEN 'hold' ELSE status END
			WHERE host = $5 AND tld = $6
		`, retryAt, feedsFound, lastError, MissCountThreshold, host, tld)
		return err
	}
	// Success - reset miss_count
	now := time.Now()
	_, err := c.db.Exec(`
		UPDATE domains SET crawled_at = $1, feeds_found = $2, last_error = NULL, miss_count = 0
		WHERE host = $3 AND tld = $4
	`, now, feedsFound, host, tld)
	return err
}

// GetDomainCount returns the total number of domains and counts by status
func (c *Crawler) GetDomainCount() (total int, hold int, err error) {
	err = c.db.QueryRow("SELECT COUNT(*) FROM domains").Scan(&total)
	if err != nil {
		return 0, 0, err
	}
	err = c.db.QueryRow("SELECT COUNT(*) FROM domains WHERE status = 'hold'").Scan(&hold)
	return total, hold, err
}

// ImportTestDomains adds a list of specific domains for testing
func (c *Crawler) ImportTestDomains(domains []string) {
	for _, host := range domains {
		host = normalizeHost(host)
		_, err := c.db.Exec(`
			INSERT INTO domains (host, status, tld)
			VALUES ($1, 'pass', $2)
			ON CONFLICT(host, tld) DO NOTHING
		`, stripTLD(host), getTLD(host))
		if err != nil {
			fmt.Printf("Error adding test domain %s: %v\n", host, err)
		} else {
			fmt.Printf("Added test domain: %s\n", host)
		}
	}
}

// ImportDomainsFromFile reads a vertices file and stores new domains as "pass"
func (c *Crawler) ImportDomainsFromFile(filename string, limit int) (imported int, skipped int, err error) {
	file, err := os.Open(filename)
	if err != nil {
		return 0, 0, fmt.Errorf("failed to open file: %v", err)
	}
	defer file.Close()

	return c.parseAndStoreDomains(file, limit)
}

// ImportDomainsInBackground starts domain import in a background goroutine
func (c *Crawler) ImportDomainsInBackground(filename string) {
	go func() {
		file, err := os.Open(filename)
		if err != nil {
			fmt.Printf("Failed to open vertices file: %v\n", err)
			return
		}
		defer file.Close()

		var bodyReader io.Reader

		bufReader := bufio.NewReader(file)
		peekBytes, err := bufReader.Peek(2)
		if err != nil && err != io.EOF {
			fmt.Printf("Failed to peek at file: %v\n", err)
			return
		}

		if len(peekBytes) >= 2 && peekBytes[0] == 0x1f && peekBytes[1] == 0x8b {
			gzReader, err := gzip.NewReader(bufReader)
			if err != nil {
				fmt.Printf("Failed to create gzip reader: %v\n", err)
				return
			}
			defer gzReader.Close()
			bodyReader = gzReader
		} else {
			bodyReader = bufReader
		}

		scanner := bufio.NewScanner(bodyReader)
		buf := make([]byte, 0, 64*1024)
		scanner.Buffer(buf, 1024*1024)

		const batchSize = 100
		totalImported := 0
		batchCount := 0

		type domainEntry struct {
			host string
			tld  string
		}

		for {
			// Read and canonicalize batch
			var domains []domainEntry
			for len(domains) < batchSize && scanner.Scan() {
				line := scanner.Text()
				parts := strings.Split(line, "\t")
				if len(parts) >= 2 {
					reverseHostName := strings.TrimSpace(parts[1])
					if reverseHostName != "" {
						host := normalizeHost(reverseHost(reverseHostName))
						tld := getTLD(host)
						domains = append(domains, domainEntry{host: host, tld: tld})
					}
				}
			}

			if len(domains) == 0 {
				break
			}

			// Use COPY for bulk insert (much faster than individual INSERTs)
			ctx := context.Background()
			conn, err := c.db.Acquire(ctx)
			if err != nil {
				fmt.Printf("Failed to acquire connection: %v\n", err)
				break
			}

			// Build rows for copy, applying auto-skip for spam patterns
			rows := make([][]interface{}, len(domains))
			for i, d := range domains {
				status := "pass"
				if shouldAutoSkipDomain(d.host) {
					status = "skip"
				}
				rows[i] = []interface{}{stripTLD(d.host), status, d.tld}
			}

			// Use CopyFrom for bulk insert
			imported, err := conn.CopyFrom(
				ctx,
				pgx.Identifier{"domains"},
				[]string{"host", "status", "tld"},
				pgx.CopyFromRows(rows),
			)
			conn.Release()

			if err != nil {
				// Fall back to individual inserts with ON CONFLICT
				for _, d := range domains {
					status := "pass"
					if shouldAutoSkipDomain(d.host) {
						status = "skip"
					}
					c.db.Exec(`
						INSERT INTO domains (host, status, tld)
						VALUES ($1, $2, $3)
						ON CONFLICT(host, tld) DO NOTHING
					`, stripTLD(d.host), status, d.tld)
				}
				imported = int64(len(domains))
			}

			batchCount++
			totalImported += int(imported)
			atomic.AddInt32(&c.domainsImported, int32(imported))

			fmt.Printf("Import batch %d: %d domains (total: %d)\n", batchCount, imported, totalImported)

			// Wait 1 second before the next batch
			time.Sleep(1 * time.Second)
		}

		if err := scanner.Err(); err != nil {
			fmt.Printf("Error reading vertices file: %v\n", err)
		}

		fmt.Printf("Background import complete: %d domains imported\n", totalImported)
	}()
}

func (c *Crawler) parseAndStoreDomains(reader io.Reader, limit int) (imported int, skipped int, err error) {
	var bodyReader io.Reader

	bufReader := bufio.NewReader(reader)
	peekBytes, err := bufReader.Peek(2)
	if err != nil && err != io.EOF {
		return 0, 0, fmt.Errorf("failed to peek at file: %v", err)
	}

	if len(peekBytes) >= 2 && peekBytes[0] == 0x1f && peekBytes[1] == 0x8b {
		gzReader, err := gzip.NewReader(bufReader)
		if err != nil {
			return 0, 0, fmt.Errorf("failed to create gzip reader: %v", err)
		}
		defer gzReader.Close()
		bodyReader = gzReader
	} else {
		bodyReader = bufReader
	}

	scanner := bufio.NewScanner(bodyReader)
	buf := make([]byte, 0, 64*1024)
	scanner.Buffer(buf, 1024*1024)

	count := 0
	const batchSize = 100

	type domainEntry struct {
		host string
		tld  string
	}

	for {
		// Read and canonicalize batch
		var domains []domainEntry
		for len(domains) < batchSize && scanner.Scan() {
			if limit > 0 && count >= limit {
				break
			}
			line := scanner.Text()
			parts := strings.Split(line, "\t")
			if len(parts) >= 2 {
				reverseHostName := strings.TrimSpace(parts[1])
				if reverseHostName != "" {
					host := normalizeHost(reverseHost(reverseHostName))
					domains = append(domains, domainEntry{host: host, tld: getTLD(host)})
					count++
				}
			}
		}

		if len(domains) == 0 {
			break
		}

		// Insert with ON CONFLICT, applying auto-skip for spam patterns
		for _, d := range domains {
			status := "pass"
			if shouldAutoSkipDomain(d.host) {
				status = "skip"
			}
			result, err := c.db.Exec(`
				INSERT INTO domains (host, status, tld)
				VALUES ($1, $2, $3)
				ON CONFLICT(host, tld) DO NOTHING
			`, stripTLD(d.host), status, d.tld)
			if err != nil {
				skipped++
			} else if result > 0 {
				imported++
			} else {
				skipped++
			}
		}

		if limit > 0 && count >= limit {
			break
		}
	}

	if err := scanner.Err(); err != nil {
		return imported, skipped, fmt.Errorf("error reading file: %v", err)
	}

	return imported, skipped, nil
}