package msg

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"mime/multipart"
	"net/http"
	"net/url"
	"slices"
	"strings"
	"time"

	"git.sr.ht/~rjarry/aerc/app"
	"git.sr.ht/~rjarry/aerc/commands"
	"git.sr.ht/~rjarry/aerc/config"
	"git.sr.ht/~rjarry/aerc/lib"
	"git.sr.ht/~rjarry/aerc/lib/auth"
	"git.sr.ht/~rjarry/aerc/lib/log"
	"github.com/emersion/go-message/mail"
)

// Unsubscribe helps people unsubscribe from mailing lists by way of the
// List-Unsubscribe header.
type Unsubscribe struct {
	Edit       bool `opt:"-e" desc:"Force [compose].edit-headers = true."`
	NoEdit     bool `opt:"-E" desc:"Force [compose].edit-headers = false."`
	SkipEditor bool `opt:"-s" desc:"Skip the editor and go directly to the review screen."`
}

func init() {
	commands.Register(Unsubscribe{})
}

func (Unsubscribe) Description() string {
	return "Attempt to automatically unsubscribe from mailing lists."
}

func (Unsubscribe) Context() commands.CommandContext {
	return commands.MESSAGE_LIST | commands.MESSAGE_VIEWER
}

// Aliases returns a list of aliases for the :unsubscribe command
func (Unsubscribe) Aliases() []string {
	return []string{"unsubscribe"}
}

// Execute runs the Unsubscribe command
func (u Unsubscribe) Execute(args []string) error {
	editHeaders := (config.Compose.EditHeaders || u.Edit) && !u.NoEdit

	widget := app.SelectedTabContent().(app.ProvidesMessage)
	msg, err := widget.SelectedMessage()
	if err != nil {
		return err
	}

	headers := msg.RFC822Headers

	details, err := auth.CreateParser(auth.DKIM)(headers, widget.SelectedAccount().AccountConfig().TrustedAuthRes)
	switch {
	case err != nil:
		return errors.New("Failed to validate DKIM signature")
	case slices.Contains(details.Results, auth.ResultFail):
		return errors.New("DKIM validation failed")
	case !slices.Contains(details.Results, auth.ResultPass):
		return errors.New("No passing DKIM signature found")
	}

	if !headers.Has("list-unsubscribe") {
		return errors.New("No List-Unsubscribe header found")
	}
	text, err := headers.Text("List-Unsubscribe")
	if err != nil {
		return err
	}
	methods := parseUnsubscribeMethods(text)
	if len(methods) == 0 {
		return fmt.Errorf("no methods found to unsubscribe")
	}
	log.Debugf("unsubscribe: found %d methods", len(methods))

	unsubscribe := func(method *url.URL) {
		log.Debugf("unsubscribe: trying to unsubscribe using %s", method.Scheme)
		var err error
		switch strings.ToLower(method.Scheme) {
		case "mailto":
			err = unsubscribeMailto(method, editHeaders, u.SkipEditor)
		case "http", "https":
			err = unsubscribeHTTP(method, headers.Values("List-Unsubscribe-Post"))
		default:
			err = fmt.Errorf("unsubscribe: skipping unrecognized scheme: %s", method.Scheme)
		}
		if err != nil {
			app.PushError(err.Error())
		}
	}

	var title string = "Select method to unsubscribe"
	if msg != nil && msg.Envelope != nil && len(msg.Envelope.From) > 0 {
		title = fmt.Sprintf("%s from %s", title, msg.Envelope.From[0])
	}

	options := make([]string, len(methods))
	for i, method := range methods {
		options[i] = method.Scheme
	}

	if len(methods) == 1 {
		unsubscribe(methods[0])
		return nil
	}

	dialog := app.NewSelectorDialog(
		title,
		"Press <Enter> to confirm or <ESC> to cancel",
		options, 0, app.SelectedAccountUiConfig(),
		func(option string, err error) {
			app.CloseDialog()
			if err != nil {
				if errors.Is(err, app.ErrNoOptionSelected) {
					app.PushStatus("Unsubscribe: "+err.Error(),
						5*time.Second)
				} else {
					app.PushError("Unsubscribe: " + err.Error())
				}
				return
			}
			for _, m := range methods {
				if m.Scheme == option {
					unsubscribe(m)
					return
				}
			}
			app.PushError("Unsubscribe: selected method not found")
		},
	)
	app.AddDialog(dialog)

	return nil
}

// parseUnsubscribeMethods reads the list-unsubscribe header and parses it as a
// list of angle-bracket <> deliminated URLs. See RFC 2369.
func parseUnsubscribeMethods(header string) (methods []*url.URL) {
	r := bufio.NewReader(strings.NewReader(header))
	for {
		// discard until <
		_, err := r.ReadSlice('<')
		if err != nil {
			return
		}
		// read until <
		m, err := r.ReadSlice('>')
		if err != nil {
			return
		}
		m = m[:len(m)-1]
		if u, err := url.Parse(string(m)); err == nil {
			methods = append(methods, u)
		}
	}
}

func unsubscribeMailto(u *url.URL, editHeaders, skipEditor bool) error {
	widget := app.SelectedTabContent().(app.ProvidesMessage)
	acct := widget.SelectedAccount()
	if acct == nil {
		return errors.New("No account selected")
	}

	h := &mail.Header{}
	h.SetSubject(u.Query().Get("subject"))
	if to, err := mail.ParseAddressList(u.Opaque); err == nil {
		h.SetAddressList("to", to)
	}

	composer, err := app.NewComposer(
		acct,
		acct.AccountConfig(),
		acct.Worker(),
		editHeaders,
		"",
		h,
		nil,
		strings.NewReader(u.Query().Get("body")),
	)
	if err != nil {
		return err
	}
	composer.Tab = app.NewTab(composer, "unsubscribe")
	if skipEditor {
		composer.Terminal().Close()
	} else {
		composer.FocusTerminal()
	}
	return nil
}

func unsubscribeHTTP(u *url.URL, postData []string) error {
	confirm := app.NewSelectorDialog(
		"Do you want to unsubscribe?",
		u.String(),
		[]string{"No", "Yes", "Open in Browser"}, 0, app.SelectedAccountUiConfig(),
		func(option string, _ error) {
			app.CloseDialog()
			switch option {
			case "Yes":
				go func() {
					defer log.PanicHandler()

					buf := bytes.NewBuffer([]byte{})
					wr := multipart.NewWriter(buf)

					for dat := range slices.Values(postData) {
						header := strings.SplitN(dat, "=", 2)
						if len(header) < 2 {
							header = append(header, "")
						}
						_ = wr.WriteField(header[0], header[1]) // can't reasonably fail
					}

					data, err := http.Post(u.String(), "multipart/form-data", buf)
					if err != nil {
						app.PushError(fmt.Sprintf("Unsubscribe: failed to POST data: %v", err))
						return
					}

					responseData, err := io.ReadAll(data.Body)
					response := string(responseData)
					if err != nil {
						response = fmt.Sprintf("failed to read response-data: %v", err)
					}

					body := fmt.Sprintf(
						"Success: %s\nReceived data:\n%s",
						data.Status,
						response,
					)

					confirmation := app.NewSelectorDialog(
						fmt.Sprintf("Sent request. Status %d", data.StatusCode),
						body,
						[]string{"OK"}, 0, app.SelectedAccountUiConfig(),
						func(_ string, _ error) { app.CloseDialog() },
					)
					app.AddDialog(confirmation)
				}()
			case "Open in Browser":
				go func() {
					defer log.PanicHandler()
					mime := fmt.Sprintf("x-scheme-handler/%s", u.Scheme)
					if err := lib.XDGOpenMime(u.String(), mime, ""); err != nil {
						app.PushError("Unsubscribe:" + err.Error())
					}
				}()
			default:
				app.PushError("Unsubscribe: link will not be opened")
			}
		},
	)
	app.AddDialog(confirm)
	return nil
}