notifications-api/notifications_utils/template.py

import math
import re
from abc import ABC, abstractmethod
from datetime import datetime
from functools import lru_cache
from html import unescape
from os import path

from jinja2 import Environment, FileSystemLoader, select_autoescape
from markupsafe import Markup

from notifications_utils import (
    LETTER_MAX_PAGE_COUNT,
    MAGIC_SEQUENCE,
    SMS_CHAR_COUNT_LIMIT,
)
from notifications_utils.countries.data import Postage
from notifications_utils.field import Field, PlainTextField
from notifications_utils.formatters import (
    add_prefix,
    add_trailing_newline,
    autolink_urls,
    escape_html,
    formatted_list,
    make_quotes_smart,
    nl2br,
    normalise_multiple_newlines,
    normalise_whitespace,
    normalise_whitespace_and_newlines,
    remove_smart_quotes_from_email_addresses,
    remove_whitespace_before_punctuation,
    replace_hyphens_with_en_dashes,
    replace_hyphens_with_non_breaking_hyphens,
    sms_encode,
    strip_leading_whitespace,
    strip_unsupported_characters,
    unlink_govuk_escaped,
)
from notifications_utils.insensitive_dict import InsensitiveDict
from notifications_utils.markdown import (
    notify_email_markdown,
    notify_email_preheader_markdown,
    notify_letter_preview_markdown,
    notify_plain_text_email_markdown,
)
from notifications_utils.postal_address import (
    PostalAddress,
    address_lines_1_to_7_keys,
)
from notifications_utils.sanitise_text import SanitiseSMS
from notifications_utils.take import Take
from notifications_utils.template_change import TemplateChange

template_env = Environment(
    autoescape=select_autoescape(),
    loader=FileSystemLoader(
        path.join(
            path.dirname(path.abspath(__file__)),
            "jinja_templates",
        )
    ),
)


class Template(ABC):
    encoding = "utf-8"

    def __init__(
        self,
        template,
        values=None,
        redact_missing_personalisation=False,
    ):
        if not isinstance(template, dict):
            raise TypeError("Template must be a dict")
        if values is not None and not isinstance(values, dict):
            raise TypeError("Values must be a dict")
        if template.get("template_type") != self.template_type:
            raise TypeError(
                f"Cannot initialise {self.__class__.__name__} "
                f'with {template.get("template_type")} template_type'
            )
        self.id = template.get("id", None)
        self.name = template.get("name", None)
        self.content = template["content"]
        self.values = values
        self._template = template
        self.redact_missing_personalisation = redact_missing_personalisation

    def __repr__(self):
        return '{}("{}", {})'.format(self.__class__.__name__, self.content, self.values)

    @abstractmethod
    def __str__(self):
        pass

    @property
    def content_with_placeholders_filled_in(self):
        return str(
            Field(
                self.content,
                self.values,
                html="passthrough",
                redact_missing_personalisation=self.redact_missing_personalisation,
                markdown_lists=True,
            )
        ).strip()

    @property
    def values(self):
        if hasattr(self, "_values"):
            return self._values
        return {}

    @values.setter
    def values(self, value):
        if not value:
            self._values = {}
        else:
            placeholders = InsensitiveDict.from_keys(self.placeholders)
            self._values = InsensitiveDict(value).as_dict_with_keys(
                self.placeholders
                | set(
                    key
                    for key in value.keys()
                    if InsensitiveDict.make_key(key) not in placeholders.keys()
                )
            )

    @property
    def placeholders(self):
        return get_placeholders(self.content)

    @property
    def missing_data(self):
        return list(
            placeholder
            for placeholder in self.placeholders
            if self.values.get(placeholder) is None
        )

    @property
    def additional_data(self):
        return self.values.keys() - self.placeholders

    def get_raw(self, key, default=None):
        return self._template.get(key, default)

    def compare_to(self, new):
        return TemplateChange(self, new)

    @property
    def content_count(self):
        return len(self.content_with_placeholders_filled_in)

    def is_message_empty(self):
        if not self.content:
            return True

        if not self.content.startswith("((") or not self.content.endswith("))"):
            # If the content doesn’t start or end with a placeholder we
            # can guarantee it’s not empty, no matter what
            # personalisation has been provided.
            return False

        return self.content_count == 0

    def is_message_too_long(self):
        return False


class BaseSMSTemplate(Template):
    template_type = "sms"

    def __init__(
        self,
        template,
        values=None,
        prefix=None,
        show_prefix=True,
        sender=None,
    ):
        self.prefix = prefix
        self.show_prefix = show_prefix
        self.sender = sender
        self._content_count = None
        super().__init__(template, values)

    @property
    def values(self):
        return super().values

    @values.setter
    def values(self, value):
        # If we change the values of the template it’s possible the
        # content count will have changed, so we need to reset the
        # cached count.
        if self._content_count is not None:
            self._content_count = None

        # Assigning to super().values doesn’t work here. We need to get
        # the property object instead, which has the special method
        # fset, which invokes the setter it as if we were
        # assigning to it outside this class.
        super(BaseSMSTemplate, type(self)).values.fset(self, value)

    @property
    def content_with_placeholders_filled_in(self):
        # We always call SMSMessageTemplate.__str__ regardless of
        # subclass, to avoid any HTML formatting. SMS templates differ
        # in that the content can include the service name as a prefix.
        # So historically we’ve returned the fully-formatted message,
        # rather than some plain-text represenation of the content. To
        # preserve compatibility for consumers of the API we maintain
        # that behaviour by overriding this method here.
        return SMSMessageTemplate.__str__(self)

    @property
    def prefix(self):
        return self._prefix if self.show_prefix else None

    @prefix.setter
    def prefix(self, value):
        self._prefix = value

    @property
    def content_count(self):
        """
        Return the number of characters in the message. Note that we don't distinguish between GSM and non-GSM
        characters at this point, as `get_sms_fragment_count` handles that separately.

        Also note that if values aren't provided, will calculate the raw length of the unsubstituted placeholders,
        as in the message `foo ((placeholder))` has a length of 19.
        """
        if self._content_count is None:
            self._content_count = len(self._get_unsanitised_content())
        return self._content_count

    @property
    def content_count_without_prefix(self):
        # subtract 2 extra characters to account for the colon and the space,
        # added max zero in case the content is empty the __str__ methods strips the white space.
        if self.prefix:
            return max((self.content_count - len(self.prefix) - 2), 0)
        else:
            return self.content_count

    @property
    def fragment_count(self):
        """
        A fragment is up to 140 bytes, which could consist of 160 GSM chars, 140 ascii chars, or 70 ucs-2 chars,
        or any combination thereof.

        Since we are supporting more or less "all" languages, it doesn't seem like we really want to count chars,
        and that counting bytes should suffice.
        """

        # check if all chars are in the GSM-7 character set
        def gsm_check(x):
            rule = re.compile(
                r'^[\sa-zA-Z0-9_@?£!1$"¥#è?¤é%ù&ì\\ò(Ç)*:Ø+;ÄäøÆ,<LÖlöæ\-=ÑñÅß.>ÜüåÉ/§à¡¿\']+$'
            )
            gsm_match = rule.search(x)
            if gsm_match is None:
                return False
            return True

        message_str = self.content_with_placeholders_filled_in

        content_len = len(message_str)

        """
        Checks for GSM-7 char set, calculates msg size, and
        then fragments based on multipart message rules. ASCII
        was not specifically called out as almost all messages will
        switch from 7bit GSM to Unicode.

        Calculations are based on https://messente.com/documentation/tools/sms-length-calculator
        """
        if gsm_check(message_str):
            if content_len <= 160:
                return math.ceil(content_len / 160)
            else:
                return math.ceil(content_len / 153)
        else:
            if content_len <= 70:
                return math.ceil(content_len / 70)
            else:
                return math.ceil(content_len / 67)

    def is_message_too_long(self):
        """
        Message is validated with out the prefix.
        We have decided to be lenient and let the message go over the character limit. The SMS provider will
        send messages well over our limit. There were some inconsistencies with how we were validating the
        length of a message. This should be the method used anytime we want to reject a message for being too long.
        """
        return self.content_count_without_prefix > SMS_CHAR_COUNT_LIMIT

    def is_message_empty(self):
        return self.content_count_without_prefix == 0

    def _get_unsanitised_content(self):
        # This is faster to call than SMSMessageTemplate.__str__ if all
        # you need to know is how many characters are in the message
        if self.values:
            values = self.values
        else:
            values = {key: MAGIC_SEQUENCE for key in self.placeholders}
        return (
            Take(PlainTextField(self.content, values, html="passthrough"))
            .then(add_prefix, self.prefix)
            .then(remove_whitespace_before_punctuation)
            .then(normalise_whitespace_and_newlines)
            .then(normalise_multiple_newlines)
            .then(str.strip)
            .then(str.replace, MAGIC_SEQUENCE, "")
        )


class SMSMessageTemplate(BaseSMSTemplate):
    def __str__(self):
        return sms_encode(self._get_unsanitised_content())


class SMSBodyPreviewTemplate(BaseSMSTemplate):
    def __init__(
        self,
        template,
        values=None,
    ):
        super().__init__(template, values, show_prefix=False)

    def __str__(self):
        return Markup(
            Take(
                Field(
                    self.content,
                    self.values,
                    html="escape",
                    redact_missing_personalisation=True,
                )
            )
            .then(sms_encode)
            .then(remove_whitespace_before_punctuation)
            .then(normalise_whitespace_and_newlines)
            .then(normalise_multiple_newlines)
            .then(str.strip)
        )


class SMSPreviewTemplate(BaseSMSTemplate):
    jinja_template = template_env.get_template("sms_preview_template.jinja2")

    def __init__(
        self,
        template,
        values=None,
        prefix=None,
        show_prefix=True,
        sender=None,
        show_recipient=False,
        show_sender=False,
        downgrade_non_sms_characters=True,
        redact_missing_personalisation=False,
    ):
        self.show_recipient = show_recipient
        self.show_sender = show_sender
        self.downgrade_non_sms_characters = downgrade_non_sms_characters
        super().__init__(template, values, prefix, show_prefix, sender)
        self.redact_missing_personalisation = redact_missing_personalisation

    def __str__(self):
        return Markup(
            self.jinja_template.render(
                {
                    "sender": self.sender,
                    "show_sender": self.show_sender,
                    "recipient": Field(
                        "((phone number))",
                        self.values,
                        with_brackets=False,
                        html="escape",
                    ),
                    "show_recipient": self.show_recipient,
                    "body": Take(
                        Field(
                            self.content,
                            self.values,
                            html="escape",
                            redact_missing_personalisation=self.redact_missing_personalisation,
                        )
                    )
                    .then(
                        add_prefix,
                        (
                            (escape_html(self.prefix) or None)
                            if self.show_prefix
                            else None
                        ),
                    )
                    .then(sms_encode if self.downgrade_non_sms_characters else str)
                    .then(remove_whitespace_before_punctuation)
                    .then(normalise_whitespace_and_newlines)
                    .then(normalise_multiple_newlines)
                    .then(nl2br)
                    .then(
                        autolink_urls,
                        classes="govuk-link govuk-link--no-visited-state",
                    ),
                }
            )
        )


class BaseBroadcastTemplate(BaseSMSTemplate):
    template_type = "broadcast"

    MAX_CONTENT_COUNT_GSM = 1_395
    MAX_CONTENT_COUNT_UCS2 = 615

    @property
    def encoded_content_count(self):
        if self.non_gsm_characters:
            return self.content_count
        return self.content_count + count_extended_gsm_chars(
            self.content_with_placeholders_filled_in
        )

    @property
    def non_gsm_characters(self):
        return non_gsm_characters(self.content)

    @property
    def max_content_count(self):
        if self.non_gsm_characters:
            return self.MAX_CONTENT_COUNT_UCS2
        return self.MAX_CONTENT_COUNT_GSM

    @property
    def content_too_long(self):
        return self.encoded_content_count > self.max_content_count


class BroadcastPreviewTemplate(BaseBroadcastTemplate, SMSPreviewTemplate):
    jinja_template = template_env.get_template("broadcast_preview_template.jinja2")


class BroadcastMessageTemplate(BaseBroadcastTemplate, SMSMessageTemplate):
    @classmethod
    def from_content(cls, content):
        return cls(
            template={
                "template_type": cls.template_type,
                "content": content,
            },
            values=None,  # events have already done interpolation of any personalisation
        )

    @classmethod
    def from_event(cls, broadcast_event):
        """
        should be directly callable with the results of the BroadcastEvent.serialize() function from api/models.py
        """
        return cls.from_content(broadcast_event["transmitted_content"]["body"])

    def __str__(self):
        return (
            Take(
                Field(
                    self.content.strip(),
                    self.values,
                    html="escape",
                )
            )
            .then(sms_encode)
            .then(remove_whitespace_before_punctuation)
            .then(normalise_whitespace_and_newlines)
            .then(normalise_multiple_newlines)
        )


class SubjectMixin:
    def __init__(self, template, values=None, **kwargs):
        self._subject = template["subject"]
        super().__init__(template, values, **kwargs)

    @property
    def subject(self):
        return Markup(
            Take(
                Field(
                    self._subject,
                    self.values,
                    html="escape",
                    redact_missing_personalisation=self.redact_missing_personalisation,
                )
            )
            .then(do_nice_typography)
            .then(normalise_whitespace)
        )

    @property
    def placeholders(self):
        return get_placeholders(self._subject) | super().placeholders


class BaseEmailTemplate(SubjectMixin, Template):
    template_type = "email"

    @property
    def html_body(self):
        return (
            Take(
                Field(
                    self.content,
                    self.values,
                    html="escape",
                    markdown_lists=True,
                    redact_missing_personalisation=self.redact_missing_personalisation,
                )
            )
            .then(unlink_govuk_escaped)
            .then(strip_unsupported_characters)
            .then(add_trailing_newline)
            .then(notify_email_markdown)
            .then(do_nice_typography)
        )

    @property
    def content_size_in_bytes(self):
        return len(self.content_with_placeholders_filled_in.encode("utf8"))

    def is_message_too_long(self):
        """
        SES rejects email messages bigger than 10485760 bytes (just over 10 MB per message (after base64 encoding)):
        https://docs.aws.amazon.com/ses/latest/DeveloperGuide/quotas.html#limits-message

        Base64 is apparently wasteful because we use just 64 different values per byte, whereas a byte can represent
        256 different characters. That is, we use bytes (which are 8-bit words) as 6-bit words. There is
        a waste of 2 bits for each 8 bits of transmission data. To send three bytes of information
        (3 times 8 is 24 bits), you need to use four bytes (4 times 6 is again 24 bits). Thus the base64 version
        of a file is 4/3 larger than it might be. So we use 33% more storage than we could.
        https://lemire.me/blog/2019/01/30/what-is-the-space-overhead-of-base64-encoding/

        That brings down our max safe size to 7.5 MB == 7500000 bytes before base64 encoding

        But this is not the end! The message we send to SES is structured as follows:
        "Message": {
            'Subject': {
                'Data': subject,
            },
            'Body': {'Text': {'Data': body}, 'Html': {'Data': html_body}}
        },
        Which means that we are sending the contents of email message twice in one request: once in plain text
        and once with html tags. That means our plain text content needs to be much shorter to make sure we
        fit within the limit, especially since HTML body can be much byte-heavier than plain text body.

        Hence, we decided to put the limit at 1MB, which is equivalent of between 250 and 500 pages of text.
        That's still an extremely long email, and should be sufficient for all normal use, while at the same
        time giving us safe margin while sending the emails through Amazon SES.

        EDIT: putting size up to 2MB as GOV.UK email digests are hitting the limit.
        """
        return self.content_size_in_bytes > 2000000


class PlainTextEmailTemplate(BaseEmailTemplate):
    def __str__(self):
        return (
            Take(
                Field(
                    self.content, self.values, html="passthrough", markdown_lists=True
                )
            )
            .then(unlink_govuk_escaped)
            .then(strip_unsupported_characters)
            .then(add_trailing_newline)
            .then(notify_plain_text_email_markdown)
            .then(do_nice_typography)
            .then(unescape)
            .then(strip_leading_whitespace)
            .then(add_trailing_newline)
        )

    @property
    def subject(self):
        return Markup(
            Take(
                Field(
                    self._subject,
                    self.values,
                    html="passthrough",
                    redact_missing_personalisation=self.redact_missing_personalisation,
                )
            )
            .then(do_nice_typography)
            .then(normalise_whitespace)
        )


class HTMLEmailTemplate(BaseEmailTemplate):
    jinja_template = template_env.get_template("email_template.jinja2")

    PREHEADER_LENGTH_IN_CHARACTERS = 256

    def __init__(
        self,
        template,
        values=None,
        govuk_banner=True,
        complete_html=True,
        brand_logo=None,
        brand_text=None,
        brand_colour=None,
        brand_banner=False,
        brand_name=None,
    ):
        super().__init__(template, values)
        self.govuk_banner = govuk_banner
        self.complete_html = complete_html
        self.brand_logo = brand_logo
        self.brand_text = brand_text
        self.brand_colour = brand_colour
        self.brand_banner = brand_banner
        self.brand_name = brand_name

    @property
    def preheader(self):
        return " ".join(
            Take(
                Field(
                    self.content,
                    self.values,
                    html="escape",
                    markdown_lists=True,
                )
            )
            .then(unlink_govuk_escaped)
            .then(strip_unsupported_characters)
            .then(add_trailing_newline)
            .then(notify_email_preheader_markdown)
            .then(do_nice_typography)
            .split()
        )[: self.PREHEADER_LENGTH_IN_CHARACTERS].strip()

    def __str__(self):
        return self.jinja_template.render(
            {
                "subject": self.subject,
                "body": self.html_body,
                "preheader": self.preheader,
                "govuk_banner": self.govuk_banner,
                "complete_html": self.complete_html,
                "brand_logo": self.brand_logo,
                "brand_text": self.brand_text,
                "brand_colour": self.brand_colour,
                "brand_banner": self.brand_banner,
                "brand_name": self.brand_name,
            }
        )


class EmailPreviewTemplate(BaseEmailTemplate):
    jinja_template = template_env.get_template("email_preview_template.jinja2")

    def __init__(
        self,
        template,
        values=None,
        from_name=None,
        from_address=None,
        reply_to=None,
        show_recipient=True,
        redact_missing_personalisation=False,
    ):
        super().__init__(
            template,
            values,
            redact_missing_personalisation=redact_missing_personalisation,
        )
        self.from_name = from_name
        self.from_address = from_address
        self.reply_to = reply_to
        self.show_recipient = show_recipient

    def __str__(self):
        return Markup(
            self.jinja_template.render(
                {
                    "body": self.html_body,
                    "subject": self.subject,
                    "from_name": escape_html(self.from_name),
                    "from_address": self.from_address,
                    "reply_to": self.reply_to,
                    "recipient": Field(
                        "((email address))", self.values, with_brackets=False
                    ),
                    "show_recipient": self.show_recipient,
                }
            )
        )

    @property
    def subject(self):
        return (
            Take(
                Field(
                    self._subject,
                    self.values,
                    html="escape",
                    redact_missing_personalisation=self.redact_missing_personalisation,
                )
            )
            .then(do_nice_typography)
            .then(normalise_whitespace)
        )


class BaseLetterTemplate(SubjectMixin, Template):
    template_type = "letter"

    address_block = "\n".join(
        f'(({line.replace("_", " ")}))' for line in address_lines_1_to_7_keys
    )

    def __init__(
        self,
        template,
        values=None,
        contact_block=None,
        admin_base_url="http://localhost:6012",
        logo_file_name=None,
        redact_missing_personalisation=False,
        date=None,
    ):
        self.contact_block = (contact_block or "").strip()
        super().__init__(
            template,
            values,
            redact_missing_personalisation=redact_missing_personalisation,
        )
        self.admin_base_url = admin_base_url
        self.logo_file_name = logo_file_name
        self.date = date or datetime.utcnow()

    @property
    def subject(self):
        return (
            Take(
                Field(
                    self._subject,
                    self.values,
                    redact_missing_personalisation=self.redact_missing_personalisation,
                    html="escape",
                )
            )
            .then(do_nice_typography)
            .then(normalise_whitespace)
        )

    @property
    def placeholders(self):
        return get_placeholders(self.contact_block) | super().placeholders

    @property
    def postal_address(self):
        return PostalAddress.from_personalisation(InsensitiveDict(self.values))

    @property
    def _address_block(self):
        if (
            self.postal_address.has_enough_lines
            and not self.postal_address.has_too_many_lines
        ):
            return self.postal_address.normalised_lines

        if "address line 7" not in self.values and "postcode" in self.values:
            self.values["address line 7"] = self.values["postcode"]

        return Field(
            self.address_block,
            self.values,
            html="escape",
            with_brackets=False,
        ).splitlines()

    @property
    def _contact_block(self):
        return (
            Take(
                Field(
                    "\n".join(line.strip() for line in self.contact_block.split("\n")),
                    self.values,
                    redact_missing_personalisation=self.redact_missing_personalisation,
                    html="escape",
                )
            )
            .then(remove_whitespace_before_punctuation)
            .then(nl2br)
        )

    @property
    def _date(self):
        return self.date.strftime("%-d %B %Y")

    @property
    def _message(self):
        return (
            Take(
                Field(
                    self.content,
                    self.values,
                    html="escape",
                    markdown_lists=True,
                    redact_missing_personalisation=self.redact_missing_personalisation,
                )
            )
            .then(add_trailing_newline)
            .then(notify_letter_preview_markdown)
            .then(do_nice_typography)
            .then(replace_hyphens_with_non_breaking_hyphens)
        )


class LetterPreviewTemplate(BaseLetterTemplate):
    jinja_template = template_env.get_template("letter_pdf/preview.jinja2")

    def __str__(self):
        return Markup(
            self.jinja_template.render(
                {
                    "admin_base_url": self.admin_base_url,
                    "logo_file_name": self.logo_file_name,
                    # logo_class should only ever be None, svg or png
                    "logo_class": (
                        self.logo_file_name.lower()[-3:]
                        if self.logo_file_name
                        else None
                    ),
                    "subject": self.subject,
                    "message": self._message,
                    "address": self._address_block,
                    "contact_block": self._contact_block,
                    "date": self._date,
                }
            )
        )


class LetterPrintTemplate(LetterPreviewTemplate):
    jinja_template = template_env.get_template("letter_pdf/print.jinja2")


class LetterImageTemplate(BaseLetterTemplate):
    jinja_template = template_env.get_template("letter_image_template.jinja2")
    first_page_number = 1
    allowed_postage_types = (
        Postage.FIRST,
        Postage.SECOND,
        Postage.EUROPE,
        Postage.REST_OF_WORLD,
    )

    def __init__(
        self,
        template,
        values=None,
        image_url=None,
        page_count=None,
        contact_block=None,
        postage=None,
    ):
        super().__init__(template, values, contact_block=contact_block)
        if not image_url:
            raise TypeError("image_url is required")
        if not page_count:
            raise TypeError("page_count is required")
        if postage not in [None] + list(self.allowed_postage_types):
            raise TypeError(
                "postage must be None, {}".format(
                    formatted_list(
                        self.allowed_postage_types,
                        conjunction="or",
                        before_each="'",
                        after_each="'",
                    )
                )
            )
        self.image_url = image_url
        self.page_count = int(page_count)
        self._postage = postage

    @property
    def postage(self):
        if self.postal_address.international:
            return self.postal_address.postage
        return self._postage

    @property
    def last_page_number(self):
        return min(self.page_count, LETTER_MAX_PAGE_COUNT) + self.first_page_number

    @property
    def page_numbers(self):
        return list(range(self.first_page_number, self.last_page_number))

    @property
    def postage_description(self):
        return {
            Postage.FIRST: "first class",
            Postage.SECOND: "second class",
            Postage.EUROPE: "international",
            Postage.REST_OF_WORLD: "international",
        }.get(self.postage)

    @property
    def postage_class_value(self):
        return {
            Postage.FIRST: "letter-postage-first",
            Postage.SECOND: "letter-postage-second",
            Postage.EUROPE: "letter-postage-international",
            Postage.REST_OF_WORLD: "letter-postage-international",
        }.get(self.postage)

    def __str__(self):
        return Markup(
            self.jinja_template.render(
                {
                    "image_url": self.image_url,
                    "page_numbers": self.page_numbers,
                    "address": self._address_block,
                    "contact_block": self._contact_block,
                    "date": self._date,
                    "subject": self.subject,
                    "message": self._message,
                    "show_postage": bool(self.postage),
                    "postage_description": self.postage_description,
                    "postage_class_value": self.postage_class_value,
                }
            )
        )


def get_sms_fragment_count(character_count, non_gsm_characters):
    if non_gsm_characters:
        return 1 if character_count <= 70 else math.ceil(float(character_count) / 67)
    else:
        return 1 if character_count <= 160 else math.ceil(float(character_count) / 153)


def non_gsm_characters(content):
    """
    Returns a set of all the non gsm characters in a text. this doesn't include characters that we will downgrade (eg
    emoji, ellipsis, ñ, etc). This only includes welsh non gsm characters that will force the entire SMS to be encoded
    with UCS-2.
    """
    return set(content) & set(SanitiseSMS.WELSH_NON_GSM_CHARACTERS)


def count_extended_gsm_chars(content):
    return sum(map(content.count, SanitiseSMS.EXTENDED_GSM_CHARACTERS))


def do_nice_typography(value):
    return (
        Take(value)
        .then(remove_whitespace_before_punctuation)
        .then(make_quotes_smart)
        .then(remove_smart_quotes_from_email_addresses)
        .then(replace_hyphens_with_en_dashes)
    )


@lru_cache(maxsize=1024)
def get_placeholders(content):
    return Field(content).placeholders