//go:build linux || freebsd
// +build linux freebsd

package ftp

import (
	"bufio"
	"context"
	"crypto/tls"
	"fmt"
	"io"
	"net"
	"net/textproto"
	"net/url"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"codeberg.org/petrbalvin/goget/internal/output"
	"codeberg.org/petrbalvin/goget/internal/pool"
)

type Client struct {
	conn      net.Conn
	reader    *textproto.Reader
	writer    *bufio.Writer
	host      string
	port      int
	user      string
	password  string
	url       string
	tlsConfig *tls.Config
	useTLS    bool
	passive   bool
	timeout   time.Duration
}

func NewClient(rawURL string, timeout time.Duration) (*Client, error) {
	u, err := url.Parse(rawURL)
	if err != nil {
		return nil, fmt.Errorf("invalid url: %w", err)
	}

	host := u.Hostname()
	port := 21
	if u.Port() != "" {
		p, err := strconv.Atoi(u.Port())
		if err != nil {
			return nil, fmt.Errorf("invalid port: %w", err)
		}
		port = p
	}

	user := "anonymous"
	password := "anonymous@"
	if u.User != nil {
		user = u.User.Username()
		if pass, ok := u.User.Password(); ok {
			password = pass
		}
	}

	useTLS := u.Scheme == "ftps"
	if !useTLS && (user != "anonymous" || (u.User != nil && u.User.Username() != "anonymous")) {
		fmt.Fprintf(os.Stderr, "Warning: FTP credentials sent in plaintext. Use ftps:// for encrypted transfers.\n")
	}

	c := &Client{
		host:     host,
		port:     port,
		user:     user,
		password: password,
		url:      rawURL,
		useTLS:   useTLS,
		passive:  true, // Default to passive mode
		timeout:  timeout,
		tlsConfig: &tls.Config{
			MinVersion:         tls.VersionTLS12,
			ServerName:         host,
			InsecureSkipVerify: false,
		},
	}

	return c, nil
}

func (c *Client) Connect() error {
	addr := net.JoinHostPort(c.host, fmt.Sprintf("%d", c.port))
	conn, err := net.DialTimeout("tcp", addr, c.timeout)
	if err != nil {
		return fmt.Errorf("failed to connect: %w", err)
	}

	c.conn = conn
	c.reader = textproto.NewReader(bufio.NewReader(conn))
	c.writer = bufio.NewWriter(conn)

	// Read greeting
	code, _, err := c.readResponse()
	if err != nil {
		return fmt.Errorf("failed to read greeting: %w", err)
	}
	if code != 220 {
		return fmt.Errorf("unexpected greeting code: %d", code)
	}

	// Upgrade to TLS if FTPS (explicit)
	if c.useTLS {
		if err := c.sendCommand("AUTH TLS"); err != nil {
			return err
		}
		code, _, err := c.readResponse()
		if err != nil {
			return fmt.Errorf("auth tls failed: %w", err)
		}
		if code != 234 && code != 334 {
			// Try AUTH SSL as fallback
			if err := c.sendCommand("AUTH SSL"); err != nil {
				return err
			}
			code, _, err = c.readResponse()
			if err != nil {
				return fmt.Errorf("auth ssl failed: %w", err)
			}
			if code != 234 && code != 334 {
				return fmt.Errorf("server does not support tls/ssl")
			}
		}

		// Wrap connection with TLS
		tlsConn := tls.Client(c.conn, c.tlsConfig)
		if err := tlsConn.Handshake(); err != nil {
			return fmt.Errorf("tls handshake failed: %w", err)
		}
		c.conn = tlsConn
		c.reader = textproto.NewReader(bufio.NewReader(tlsConn))
		c.writer = bufio.NewWriter(tlsConn)
	}

	// Send USER
	if err := c.sendCommand("USER %s", c.user); err != nil {
		return err
	}
	code, _, err = c.readResponse()
	if err != nil {
		return fmt.Errorf("user command failed: %w", err)
	}

	// 331 means password required, 230 means already logged in
	if code == 331 {
		// Send PASS
		if err := c.sendCommand("PASS %s", c.password); err != nil {
			return err
		}
		code, _, err = c.readResponse()
		if err != nil {
			return fmt.Errorf("pass command failed: %w", err)
		}
	}

	if code != 230 && code != 200 {
		return fmt.Errorf("login failed with code: %d", code)
	}

	// Set binary mode
	if err := c.sendCommand("TYPE I"); err != nil {
		return err
	}
	code, _, err = c.readResponse()
	if err != nil {
		return fmt.Errorf("type command failed: %w", err)
	}
	if code != 200 {
		return fmt.Errorf("failed to set binary mode")
	}

	return nil
}

func (c *Client) sendCommand(format string, args ...interface{}) error {
	cmd := fmt.Sprintf(format, args...)
	if _, err := c.writer.WriteString(cmd); err != nil {
		return fmt.Errorf("failed to send command: %w", err)
	}
	if _, err := c.writer.WriteString("\r\n"); err != nil {
		return fmt.Errorf("failed to send command terminator: %w", err)
	}
	if err := c.writer.Flush(); err != nil {
		return fmt.Errorf("failed to flush command: %w", err)
	}
	return nil
}

func (c *Client) readResponse() (int, string, error) {
	code, msg, err := c.reader.ReadResponse(0)
	if err != nil {
		return 0, "", err
	}
	return code, msg, nil
}

func (c *Client) getFileSize(path string) (int64, error) {
	if err := c.sendCommand("SIZE %s", path); err != nil {
		return 0, err
	}
	code, msg, err := c.readResponse()
	if err != nil {
		return 0, fmt.Errorf("size command failed: %w", err)
	}
	if code != 213 {
		return 0, fmt.Errorf("size command failed with code: %d", code)
	}

	size, err := strconv.ParseInt(strings.TrimSpace(msg), 10, 64)
	if err != nil {
		return 0, fmt.Errorf("failed to parse size: %w", err)
	}
	return size, nil
}

func (c *Client) establishDataConnection() (net.Conn, error) {
	if c.passive {
		return c.enterPassiveMode()
	}
	return c.enterActiveMode()
}

func (c *Client) enterPassiveMode() (net.Conn, error) {
	if err := c.sendCommand("PASV"); err != nil {
		return nil, err
	}
	code, msg, err := c.readResponse()
	if err != nil {
		return nil, fmt.Errorf("pasv command failed: %w", err)
	}
	if code != 227 {
		return nil, fmt.Errorf("pasv command failed with code: %d", code)
	}

	// Parse PASV response: 227 Entering Passive Mode (h1,h2,h3,h4,p1,p2)
	start := strings.Index(msg, "(")
	end := strings.Index(msg, ")")
	if start == -1 || end == -1 {
		return nil, fmt.Errorf("invalid pasv response")
	}

	parts := strings.Split(msg[start+1:end], ",")
	if len(parts) != 6 {
		return nil, fmt.Errorf("invalid pasv response format")
	}

	h1, _ := strconv.Atoi(parts[0])
	h2, _ := strconv.Atoi(parts[1])
	h3, _ := strconv.Atoi(parts[2])
	h4, _ := strconv.Atoi(parts[3])
	p1, _ := strconv.Atoi(parts[4])
	p2, _ := strconv.Atoi(parts[5])

	dataHost := fmt.Sprintf("%d.%d.%d.%d", h1, h2, h3, h4)
	dataPort := p1*256 + p2

	// Use original host for TLS connections to match certificate
	if c.useTLS {
		dataHost = c.host
	}

	conn, err := net.DialTimeout("tcp", fmt.Sprintf("%s:%d", dataHost, dataPort), c.timeout)
	if err != nil {
		return nil, fmt.Errorf("failed to connect to data port: %w", err)
	}

	if c.useTLS {
		tlsConn := tls.Client(conn, c.tlsConfig)
		if err := tlsConn.Handshake(); err != nil {
			conn.Close()
			return nil, fmt.Errorf("tls handshake on data connection failed: %w", err)
		}
		return tlsConn, nil
	}

	return conn, nil
}

func (c *Client) enterActiveMode() (net.Conn, error) {
	// Get local IP from the control connection to bind only to that interface
	ctrlAddr, ok := c.conn.LocalAddr().(*net.TCPAddr)
	if !ok || ctrlAddr.IP == nil {
		return nil, fmt.Errorf("failed to get local address for active mode")
	}
	ctrlIP := ctrlAddr.IP.To4()
	if ctrlIP == nil {
		return nil, fmt.Errorf("no ipv4 address available for active mode")
	}

	// Bind listener only to the interface of the control connection, not 0.0.0.0
	listener, err := net.Listen("tcp", net.JoinHostPort(ctrlIP.String(), "0"))
	if err != nil {
		return nil, fmt.Errorf("failed to create listener: %w", err)
	}
	defer listener.Close()

	// Set a deadline so Accept respects the timeout
	if tcpListener, ok := listener.(*net.TCPListener); ok {
		tcpListener.SetDeadline(time.Now().Add(c.timeout))
	}

	listenAddr := listener.Addr().(*net.TCPAddr)

	p1 := listenAddr.Port / 256
	p2 := listenAddr.Port % 256

	portCmd := fmt.Sprintf("PORT %d,%d,%d,%d,%d,%d",
		ctrlIP[0], ctrlIP[1], ctrlIP[2], ctrlIP[3], p1, p2)

	if err := c.sendCommand("%s", portCmd); err != nil {
		return nil, err
	}
	code, _, err := c.readResponse()
	if err != nil {
		return nil, fmt.Errorf("port command failed: %w", err)
	}
	if code != 200 {
		return nil, fmt.Errorf("port command failed with code: %d", code)
	}

	// Accept incoming connection
	connChan := make(chan net.Conn, 1)
	errChan := make(chan error, 1)

	go func() {
		conn, err := listener.Accept()
		if err != nil {
			errChan <- err
			return
		}
		connChan <- conn
	}()

	select {
	case conn := <-connChan:
		return conn, nil
	case err := <-errChan:
		return nil, fmt.Errorf("failed to accept data connection: %w", err)
	case <-time.After(c.timeout):
		return nil, fmt.Errorf("timeout waiting for data connection")
	}
}

func (c *Client) DownloadFile(ctx context.Context, remotePath, localPath string, resumeOffset int64, progressFunc func(current, total int64)) error {
	// Get file size
	totalSize, err := c.getFileSize(remotePath)
	if err != nil {
		return fmt.Errorf("failed to get file size: %w", err)
	}

	// Check if we need to resume
	var startOffset int64 = 0
	if resumeOffset > 0 && resumeOffset < totalSize {
		startOffset = resumeOffset
		if err := c.sendCommand("REST %d", startOffset); err != nil {
			return err
		}
		code, _, err := c.readResponse()
		if err != nil {
			return fmt.Errorf("rest command failed: %w", err)
		}
		if code != 350 {
			return fmt.Errorf("rest command failed with code: %d", code)
		}
	} else if resumeOffset >= totalSize {
		// File already complete
		return nil
	}

	// Open local file for writing
	mode := os.O_CREATE | os.O_WRONLY
	if startOffset > 0 {
		mode |= os.O_APPEND
	} else {
		mode |= os.O_TRUNC
	}

	localFile, err := os.OpenFile(localPath, mode, 0644)
	if err != nil {
		return fmt.Errorf("failed to open local file: %w", err)
	}
	defer localFile.Close()

	// Seek to start position if resuming
	if startOffset > 0 {
		if _, err := localFile.Seek(startOffset, io.SeekStart); err != nil {
			return fmt.Errorf("failed to seek: %w", err)
		}
	}

	// Establish data connection FIRST (before RETR command)
	dataConn, err := c.establishDataConnection()
	if err != nil {
		return fmt.Errorf("failed to establish data connection: %w", err)
	}
	defer dataConn.Close()

	// Send RETR command AFTER data connection is established
	if err := c.sendCommand("RETR %s", remotePath); err != nil {
		return err
	}

	// Read response (should be 150 or 125)
	code, _, err := c.readResponse()
	if err != nil {
		return fmt.Errorf("retr command failed: %w", err)
	}
	if code != 150 && code != 125 {
		// Try waiting a bit for the server to respond
		time.Sleep(100 * time.Millisecond)
		code, _, err = c.readResponse()
		if err != nil {
			return fmt.Errorf("retr command failed with code: %d", code)
		}
		if code != 150 && code != 125 {
			return fmt.Errorf("retr command failed with code: %d", code)
		}
	}

	// Copy data with progress. Polls ctx between reads so a SIGINT
	// arriving mid-transfer is detected on the next iteration and the
	// partial progress is saved to ResumeMetadata before returning.
	var copied int64 = startOffset
	buf := make([]byte, 32*1024)
	for {
		if ctx.Err() != nil {
			if err := saveFTPResume(c.url, localPath, copied, totalSize); err != nil {
				return fmt.Errorf("failed to save resume metadata: %w", err)
			}
			return ctx.Err()
		}
		n, err := dataConn.Read(buf)
		if n > 0 {
			written, werr := localFile.Write(buf[:n])
			copied += int64(written)
			if werr != nil {
				return fmt.Errorf("failed to write: %w", err)
			}
			if progressFunc != nil {
				progressFunc(copied, totalSize)
			}
		}
		if err == io.EOF {
			break
		}
		if err != nil {
			return fmt.Errorf("failed to read from data connection: %w", err)
		}
	}

	// Read final response
	code, _, err = c.readResponse()
	if err != nil {
		return fmt.Errorf("failed to read final response: %w", err)
	}
	if code != 226 && code != 250 {
		return fmt.Errorf("transfer failed with code: %d", code)
	}

	// Successful transfer — drop any stale resume sidecar.
	_ = output.DeleteResumeMetadata(localPath)
	return nil
}

func (c *Client) ListRemoteDir(path string) ([]string, error) {
	// Establish data connection
	dataConn, err := c.establishDataConnection()
	if err != nil {
		return nil, fmt.Errorf("failed to establish data connection: %w", err)
	}
	defer dataConn.Close()

	// Send LIST command
	cmd := "LIST"
	if path != "" {
		cmd = fmt.Sprintf("LIST %s", path)
	}
	if err := c.sendCommand("%s", cmd); err != nil {
		return nil, err
	}

	// Read response (should be 150 or 125)
	code, _, err := c.readResponse()
	if err != nil {
		return nil, fmt.Errorf("list command failed: %w", err)
	}
	if code != 150 && code != 125 {
		return nil, fmt.Errorf("list command failed with code: %d", code)
	}

	// Read directory listing
	var lines []string
	scanner := bufio.NewScanner(dataConn)
	for scanner.Scan() {
		lines = append(lines, scanner.Text())
	}
	if err := scanner.Err(); err != nil {
		return nil, fmt.Errorf("failed to read directory listing: %w", err)
	}

	// Read final response
	code, _, err = c.readResponse()
	if err != nil {
		return nil, fmt.Errorf("failed to read final response: %w", err)
	}
	if code != 226 && code != 250 {
		return nil, fmt.Errorf("list command failed with code: %d", code)
	}

	return lines, nil
}

func (c *Client) ChangeDir(path string) error {
	if err := c.sendCommand("CWD %s", path); err != nil {
		return err
	}
	code, _, err := c.readResponse()
	if err != nil {
		return fmt.Errorf("cwd command failed: %w", err)
	}
	if code != 250 {
		return fmt.Errorf("cwd command failed with code: %d", code)
	}
	return nil
}

func (c *Client) GetCurrentDir() (string, error) {
	if err := c.sendCommand("PWD"); err != nil {
		return "", err
	}
	code, msg, err := c.readResponse()
	if err != nil {
		return "", fmt.Errorf("pwd command failed: %w", err)
	}
	if code != 257 {
		return "", fmt.Errorf("pwd command failed with code: %d", code)
	}

	// Extract path from response (usually quoted)
	start := strings.Index(msg, "\"")
	end := strings.LastIndex(msg, "\"")
	if start != -1 && end > start {
		return msg[start+1 : end], nil
	}
	return strings.TrimSpace(msg), nil
}

func (c *Client) Close() error {
	if err := c.sendCommand("QUIT"); err != nil {
		return err
	}
	_, _, _ = c.readResponse() // Ignore errors on close
	if c.conn != nil {
		return c.conn.Close()
	}
	return nil
}

// Helper function to download entire directory recursively
func (c *Client) DownloadDirectory(ctx context.Context, remotePath, localPath string, progressFunc func(file string, current, total int64)) error {
	// Create local directory
	if err := os.MkdirAll(localPath, 0755); err != nil {
		return fmt.Errorf("failed to create local directory: %w", err)
	}

	// Save current directory
	origDir, err := c.GetCurrentDir()
	if err != nil {
		return err
	}
	defer func() {
		c.ChangeDir(origDir)
	}()

	// Change to remote directory
	if err := c.ChangeDir(remotePath); err != nil {
		return err
	}

	// List directory contents
	entries, err := c.ListRemoteDir("")
	if err != nil {
		return err
	}

	// Parse entries and download files
	for _, entry := range entries {
		fields := strings.Fields(entry)
		if len(fields) < 9 {
			continue
		}

		name := fields[len(fields)-1]
		if name == "." || name == ".." {
			continue
		}

		isDir := fields[0][0] == 'd'
		remoteFilePath := filepath.Join(remotePath, name)
		localFilePath := filepath.Join(localPath, name)

		if isDir {
			if err := c.DownloadDirectory(ctx, remoteFilePath, localFilePath, progressFunc); err != nil {
				return err
			}
		} else {
			if progressFunc != nil {
				progressFunc(name, 0, 0)
			}
			if err := c.DownloadFile(ctx, remoteFilePath, localFilePath, 0, nil); err != nil {
				return err
			}
		}
	}

	return nil
}

// saveFTPResume persists partial FTP download progress to the standard
// `.goget.meta` sidecar so a subsequent `goget --resume` can continue
// from `downloaded` bytes. Errors are wrapped to surface failures
// without aborting the cancellation handling.
func saveFTPResume(url, localPath string, downloaded, total int64) error {
	if localPath == "" || localPath == "-" || downloaded <= 0 {
		return nil
	}
	meta := output.NewResumeMetadata(url, "", "", downloaded, total)
	return meta.Save(localPath)
}

// clientPool holds N pre-connected FTP clients. A single shared pool
// removes the need to open/close connections for every file in a
// recursive download, and is required for the parallel recursive
// implementation because each *Client owns its own TCP control
// connection and is not safe for concurrent use.
type clientPool struct {
	available chan *Client
	all       []*Client
}

// newClientPool opens `size` independent FTP connections to the same
// server. Connections are kept open until close() is called.
func newClientPool(rawURL string, timeout time.Duration, size int) (*clientPool, error) {
	if size < 1 {
		size = 1
	}
	all := make([]*Client, 0, size)
	avail := make(chan *Client, size)
	for i := 0; i < size; i++ {
		c, err := NewClient(rawURL, timeout)
		if err != nil {
			for _, existing := range all {
				_ = existing.Close()
			}
			return nil, err
		}
		if err := c.Connect(); err != nil {
			for _, existing := range all {
				_ = existing.Close()
			}
			return nil, err
		}
		all = append(all, c)
		avail <- c
	}
	return &clientPool{available: avail, all: all}, nil
}

// acquire blocks until a client is available, then returns it. The
// caller must call release() when done.
func (p *clientPool) acquire() *Client {
	return <-p.available
}

// release returns a client to the pool. It must be called exactly once
// per acquire().
func (p *clientPool) release(c *Client) {
	p.available <- c
}

// size returns the number of clients in the pool.
func (p *clientPool) size() int {
	return len(p.all)
}

// close shuts down every client in the pool. The pool must not be used
// after this call.
func (p *clientPool) close() {
	for _, c := range p.all {
		_ = c.Close()
	}
}

// ftpTask represents a unit of work for the concurrent recursive
// download: either a directory to list or a file to download.
type ftpTask struct {
	remotePath string
	localPath  string
	isDir      bool
	name       string
}

// ftpTaskHandler processes one ftpTask. For directories it lists the
// contents and submits child tasks for each entry. For files it
// acquires a client from the pool and downloads.
func ftpTaskHandler(cpool *clientPool, progressFunc func(file string, current, total int64)) func(ctx context.Context, t ftpTask) {
	return func(ctx context.Context, t ftpTask) {
		if ctx.Err() != nil {
			return
		}

		if err := os.MkdirAll(t.localPath, 0755); err != nil {
			pool.Get[ftpTask](ctx).AddError(fmt.Errorf("failed to create local dir %s: %w", t.localPath, err))
			return
		}

		if !t.isDir {
			c := cpool.acquire()
			defer cpool.release(c)
			if progressFunc != nil {
				progressFunc(t.name, 0, 0)
			}
			var fileProgress func(current, total int64)
			if progressFunc != nil {
				fileProgress = func(current, total int64) {
					progressFunc(t.name, current, total)
				}
			}
			if err := c.DownloadFile(ctx, t.remotePath, t.localPath, 0, fileProgress); err != nil {
				pool.Get[ftpTask](ctx).AddError(fmt.Errorf("download %s: %w", t.remotePath, err))
			}
			return
		}

		c := cpool.acquire()
		entries, err := c.ListRemoteDir(t.remotePath)
		cpool.release(c)
		if err != nil {
			pool.Get[ftpTask](ctx).AddError(fmt.Errorf("list %s: %w", t.remotePath, err))
			return
		}

		p := pool.Get[ftpTask](ctx)
		for _, entry := range entries {
			fields := strings.Fields(entry)
			if len(fields) < 9 {
				continue
			}
			name := fields[len(fields)-1]
			if name == "." || name == ".." {
				continue
			}
			childIsDir := fields[0][0] == 'd'
			p.Submit(ftpTask{
				remotePath: filepath.Join(t.remotePath, name),
				localPath:  filepath.Join(t.localPath, name),
				isDir:      childIsDir,
				name:       name,
			})
		}
	}
}

// DownloadDirectoryConcurrent downloads a remote directory to localPath
// using a pool of N FTP connections. All operations (LIST, RETR) use
// absolute paths so concurrent workers never share or mutate CWD state
// on the server side. The returned error is the first error encountered
// by any worker; other workers continue in the background until they
// hit ctx cancellation or finish their tasks.
func DownloadDirectoryConcurrent(ctx context.Context, rawURL string, timeout time.Duration, remotePath, localPath string, parallel int, progressFunc func(file string, current, total int64)) error {
	if parallel < 1 {
		parallel = 1
	}
	cpool, err := newClientPool(rawURL, timeout, parallel)
	if err != nil {
		return err
	}
	defer cpool.close()

	p := pool.New(ctx, parallel, ftpTaskHandler(cpool, progressFunc))
	p.Submit(ftpTask{
		remotePath: remotePath,
		localPath:  localPath,
		isDir:      true,
	})

	if errs := p.Wait(); len(errs) > 0 {
		return errs[0]
	}
	return nil
}