package postcard

import (
	"context"
	"fmt"
	"log/slog"
	netmail "net/mail"
	"strings"
	"sync"
	"time"

	gomail "github.com/wneessen/go-mail"
)

// Driver delivers a fully rendered message.
type Driver interface {
	Send(ctx context.Context, msg RenderedMessage) error
}

// RenderedMessage is the validated payload a driver transmits.
type RenderedMessage struct {
	To      []string
	Cc      []string
	Bcc     []string
	From    string
	ReplyTo string
	Subject string
	HTML    string
	Text    string
}

// SMTPConfig is the compass mail.smtp section used by the SMTP driver.
type SMTPConfig struct {
	Host     string
	Port     int
	Username string
	Password string
	TLS      string
	Timeout  time.Duration
}

// MemoryDriver stores rendered messages for tests. It is concurrency-safe.
type MemoryDriver struct {
	mu       sync.Mutex
	messages []RenderedMessage
}

// NewMemoryDriver returns an empty in-memory driver.
func NewMemoryDriver() *MemoryDriver {
	return &MemoryDriver{}
}

// Send appends msg to the in-memory log.
func (d *MemoryDriver) Send(_ context.Context, msg RenderedMessage) error {
	if d == nil {
		return fmt.Errorf("postcard: memory driver is nil")
	}
	d.mu.Lock()
	defer d.mu.Unlock()
	d.messages = append(d.messages, cloneRendered(msg))
	return nil
}

// Messages returns a copy of stored messages in send order.
func (d *MemoryDriver) Messages() []RenderedMessage {
	if d == nil {
		return nil
	}
	d.mu.Lock()
	defer d.mu.Unlock()
	out := make([]RenderedMessage, len(d.messages))
	for i, msg := range d.messages {
		out[i] = cloneRendered(msg)
	}
	return out
}

// LogDriver writes rendered headers and the text part to a logger.
type LogDriver struct {
	log *slog.Logger
}

// NewLogDriver logs through log. slog.Default is used when log is nil.
func NewLogDriver(log *slog.Logger) *LogDriver {
	if log == nil {
		log = slog.Default()
	}
	return &LogDriver{log: log}
}

// Send logs From/To/Cc/Bcc/ReplyTo/Subject and the text part. It never
// logs SMTP credentials or the HTML body.
func (d *LogDriver) Send(_ context.Context, msg RenderedMessage) error {
	if d == nil || d.log == nil {
		return fmt.Errorf("postcard: log driver is nil")
	}
	d.log.Info("postcard mail",
		slog.String("from", msg.From),
		slog.Any("to", msg.To),
		slog.Any("cc", msg.Cc),
		slog.Any("bcc", msg.Bcc),
		slog.String("reply_to", msg.ReplyTo),
		slog.String("subject", msg.Subject),
		slog.String("text", msg.Text),
	)
	return nil
}

// SMTPDriver sends through go-mail with an explicit TLS policy.
type SMTPDriver struct {
	client *gomail.Client
}

// NewSMTPDriver builds a go-mail client. TLS defaults to mandatory; NoTLS
// is opt-in for local Mailpit and is never inferred.
func NewSMTPDriver(cfg SMTPConfig) (*SMTPDriver, error) {
	if strings.TrimSpace(cfg.Host) == "" {
		return nil, fmt.Errorf("postcard: mail.smtp.host is empty")
	}
	port := cfg.Port
	if port == 0 {
		port = 587
	}
	timeout := cfg.Timeout
	if timeout <= 0 {
		timeout = 10 * time.Second
	}
	policy, err := parseTLSPolicy(cfg.TLS)
	if err != nil {
		return nil, err
	}
	opts := []gomail.Option{
		gomail.WithPort(port),
		gomail.WithTLSPolicy(policy),
		gomail.WithTimeout(timeout),
	}
	if strings.TrimSpace(cfg.Username) != "" {
		opts = append(opts,
			gomail.WithSMTPAuth(gomail.SMTPAuthPlain),
			gomail.WithUsername(cfg.Username),
			gomail.WithPassword(cfg.Password),
		)
	}
	client, err := gomail.NewClient(cfg.Host, opts...)
	if err != nil {
		return nil, fmt.Errorf("postcard: smtp client: %w", err)
	}
	return &SMTPDriver{client: client}, nil
}

// Send validates headers and recipients, then delivers with context.
func (d *SMTPDriver) Send(ctx context.Context, msg RenderedMessage) error {
	if d == nil || d.client == nil {
		return fmt.Errorf("postcard: smtp driver is nil")
	}
	if err := validateRendered(msg, true); err != nil {
		return err
	}
	gm, err := buildSMTPMessage(msg)
	if err != nil {
		return err
	}
	if err := d.client.DialAndSendWithContext(ctx, gm); err != nil {
		return fmt.Errorf("smtp: %w", err)
	}
	return nil
}

// FailDriver returns Err from Send. Tests use it as a deterministic failure.
type FailDriver struct {
	Err     error
	sends   int
	sendsMu sync.Mutex
}

// Send returns Err without retrying.
func (d *FailDriver) Send(context.Context, RenderedMessage) error {
	if d == nil {
		return fmt.Errorf("postcard: fail driver is nil")
	}
	d.sendsMu.Lock()
	d.sends++
	d.sendsMu.Unlock()
	if d.Err == nil {
		return fmt.Errorf("postcard: driver failed")
	}
	return d.Err
}

func (d *FailDriver) sendCount() int {
	d.sendsMu.Lock()
	defer d.sendsMu.Unlock()
	return d.sends
}

func cloneRendered(msg RenderedMessage) RenderedMessage {
	msg.To = append([]string(nil), msg.To...)
	msg.Cc = append([]string(nil), msg.Cc...)
	msg.Bcc = append([]string(nil), msg.Bcc...)
	return msg
}

func parseTLSPolicy(v string) (gomail.TLSPolicy, error) {
	switch strings.ToLower(strings.TrimSpace(v)) {
	case "", "mandatory", "tls":
		return gomail.TLSMandatory, nil
	case "opportunistic", "starttls":
		return gomail.TLSOpportunistic, nil
	case "none", "notls", "off":
		return gomail.NoTLS, nil
	default:
		return 0, fmt.Errorf("postcard: unknown mail.smtp.tls %q (use mandatory, starttls, or none)", v)
	}
}

func buildSMTPMessage(msg RenderedMessage) (*gomail.Msg, error) {
	gm := gomail.NewMsg()
	if err := gm.From(msg.From); err != nil {
		return nil, fmt.Errorf("postcard: from: %w", err)
	}
	if len(msg.To) > 0 {
		if err := gm.To(msg.To...); err != nil {
			return nil, fmt.Errorf("postcard: to: %w", err)
		}
	}
	if len(msg.Cc) > 0 {
		if err := gm.Cc(msg.Cc...); err != nil {
			return nil, fmt.Errorf("postcard: cc: %w", err)
		}
	}
	if len(msg.Bcc) > 0 {
		if err := gm.Bcc(msg.Bcc...); err != nil {
			return nil, fmt.Errorf("postcard: bcc: %w", err)
		}
	}
	if msg.ReplyTo != "" {
		if err := gm.ReplyTo(msg.ReplyTo); err != nil {
			return nil, fmt.Errorf("postcard: reply-to: %w", err)
		}
	}
	gm.Subject(msg.Subject)
	gm.SetBodyString(gomail.TypeTextPlain, msg.Text)
	gm.AddAlternativeString(gomail.TypeTextHTML, msg.HTML)
	return gm, nil
}

func validateRendered(msg RenderedMessage, requireFrom bool) error {
	if err := rejectCRLF("subject", msg.Subject); err != nil {
		return err
	}
	if err := rejectCRLF("from", msg.From); err != nil {
		return err
	}
	if requireFrom || msg.From != "" {
		if err := validateAddr("from", msg.From); err != nil {
			return err
		}
	}
	if err := rejectCRLF("reply-to", msg.ReplyTo); err != nil {
		return err
	}
	if msg.ReplyTo != "" {
		if err := validateAddr("reply-to", msg.ReplyTo); err != nil {
			return err
		}
	}
	for _, addr := range msg.To {
		if err := validateAddr("to", addr); err != nil {
			return err
		}
	}
	for _, addr := range msg.Cc {
		if err := validateAddr("cc", addr); err != nil {
			return err
		}
	}
	for _, addr := range msg.Bcc {
		if err := validateAddr("bcc", addr); err != nil {
			return err
		}
	}
	return nil
}

func validateAddr(kind, addr string) error {
	if err := rejectCRLF(kind, addr); err != nil {
		return err
	}
	if strings.TrimSpace(addr) == "" {
		return fmt.Errorf("postcard: empty %s address", kind)
	}
	if _, err := netmail.ParseAddress(addr); err != nil {
		return fmt.Errorf("postcard: invalid %s address", kind)
	}
	return nil
}

func rejectCRLF(kind, value string) error {
	if strings.ContainsAny(value, "\r\n") {
		return fmt.Errorf("postcard: %s contains CR/LF", kind)
	}
	return nil
}