"""
Declare and configure the models for the impress core application
"""
import hashlib
import json
import smtplib
import textwrap
import uuid
from datetime import timedelta
from logging import getLogger

from django.conf import settings
from django.contrib.auth import models as auth_models
from django.contrib.auth.base_user import AbstractBaseUser
from django.contrib.sites.models import Site
from django.core import exceptions, mail, validators
from django.core.files.base import ContentFile
from django.core.files.storage import default_storage
from django.db import models
from django.template.base import Template as DjangoTemplate
from django.template.context import Context
from django.template.loader import render_to_string
from django.utils import html, timezone
from django.utils.functional import lazy
from django.utils.translation import gettext_lazy as _
from django.utils.translation import override

import frontmatter
import markdown
from botocore.exceptions import ClientError
from timezone_field import TimeZoneField
from weasyprint import CSS, HTML
from weasyprint.text.fonts import FontConfiguration

logger = getLogger(__name__)


def get_resource_roles(resource, user):
    """Compute the roles a user has on a resource."""
    roles = []
    if user.is_authenticated:
        try:
            roles = resource.user_roles or []
        except AttributeError:
            teams = user.get_teams()
            try:
                roles = resource.accesses.filter(
                    models.Q(user=user) | models.Q(team__in=teams),
                ).values_list("role", flat=True)
            except (models.ObjectDoesNotExist, IndexError):
                roles = []
    return roles


class RoleChoices(models.TextChoices):
    """Defines the possible roles a user can have in a template."""

    MEMBER = "member", _("Member")
    ADMIN = "administrator", _("Administrator")
    OWNER = "owner", _("Owner")


class BaseModel(models.Model):
    """
    Serves as an abstract base model for other models, ensuring that records are validated
    before saving as Django doesn't do it by default.

    Includes fields common to all models: a UUID primary key and creation/update timestamps.
    """

    id = models.UUIDField(
        verbose_name=_("id"),
        help_text=_("primary key for the record as UUID"),
        primary_key=True,
        default=uuid.uuid4,
        editable=False,
    )
    created_at = models.DateTimeField(
        verbose_name=_("created on"),
        help_text=_("date and time at which a record was created"),
        auto_now_add=True,
        editable=False,
    )
    updated_at = models.DateTimeField(
        verbose_name=_("updated on"),
        help_text=_("date and time at which a record was last updated"),
        auto_now=True,
        editable=False,
    )

    class Meta:
        abstract = True

    def save(self, *args, **kwargs):
        """Call `full_clean` before saving."""
        self.full_clean()
        super().save(*args, **kwargs)


class User(AbstractBaseUser, BaseModel, auth_models.PermissionsMixin):
    """User model to work with OIDC only authentication."""

    sub_validator = validators.RegexValidator(
        regex=r"^[\w.@+-]+\Z",
        message=_(
            "Enter a valid sub. This value may contain only letters, "
            "numbers, and @/./+/-/_ characters."
        ),
    )

    sub = models.CharField(
        _("sub"),
        help_text=_(
            "Required. 255 characters or fewer. Letters, numbers, and @/./+/-/_ characters only."
        ),
        max_length=255,
        unique=True,
        validators=[sub_validator],
        blank=True,
        null=True,
    )
    email = models.EmailField(_("identity email address"), blank=True, null=True)

    # Unlike the "email" field which stores the email coming from the OIDC token, this field
    # stores the email used by staff users to login to the admin site
    admin_email = models.EmailField(
        _("admin email address"), unique=True, blank=True, null=True
    )

    language = models.CharField(
        max_length=10,
        choices=lazy(lambda: settings.LANGUAGES, tuple)(),
        default=settings.LANGUAGE_CODE,
        verbose_name=_("language"),
        help_text=_("The language in which the user wants to see the interface."),
    )
    timezone = TimeZoneField(
        choices_display="WITH_GMT_OFFSET",
        use_pytz=False,
        default=settings.TIME_ZONE,
        help_text=_("The timezone in which the user wants to see times."),
    )
    is_device = models.BooleanField(
        _("device"),
        default=False,
        help_text=_("Whether the user is a device or a real user."),
    )
    is_staff = models.BooleanField(
        _("staff status"),
        default=False,
        help_text=_("Whether the user can log into this admin site."),
    )
    is_active = models.BooleanField(
        _("active"),
        default=True,
        help_text=_(
            "Whether this user should be treated as active. "
            "Unselect this instead of deleting accounts."
        ),
    )

    objects = auth_models.UserManager()

    USERNAME_FIELD = "admin_email"
    REQUIRED_FIELDS = []

    class Meta:
        db_table = "impress_user"
        verbose_name = _("user")
        verbose_name_plural = _("users")

    def __str__(self):
        return self.email or self.admin_email or str(self.id)

    def save(self, *args, **kwargs):
        """
        If it's a new user, give its user access to the documents to which s.he was invited.
        """
        is_adding = self._state.adding
        super().save(*args, **kwargs)

        if is_adding:
            self._convert_valid_invitations()

    def _convert_valid_invitations(self):
        """
        Convert valid invitations to document accesses.
        Expired invitations are ignored.
        """
        valid_invitations = Invitation.objects.filter(
            email=self.email,
            created_at__gte=(
                timezone.now()
                - timedelta(seconds=settings.INVITATION_VALIDITY_DURATION)
            ),
        ).select_related("document")

        if not valid_invitations.exists():
            return

        DocumentAccess.objects.bulk_create(
            [
                DocumentAccess(
                    user=self, document=invitation.document, role=invitation.role
                )
                for invitation in valid_invitations
            ]
        )
        valid_invitations.delete()

    def email_user(self, subject, message, from_email=None, **kwargs):
        """Email this user."""
        if not self.email:
            raise ValueError("User has no email address.")
        mail.send_mail(subject, message, from_email, [self.email], **kwargs)

    def get_teams(self):
        """
        Get list of teams in which the user is, as a list of strings.
        Must be cached if retrieved remotely.
        """
        return []


class BaseAccess(BaseModel):
    """Base model for accesses to handle resources."""

    user = models.ForeignKey(
        User,
        on_delete=models.CASCADE,
        null=True,
        blank=True,
    )
    team = models.CharField(max_length=100, blank=True)
    role = models.CharField(
        max_length=20, choices=RoleChoices.choices, default=RoleChoices.MEMBER
    )

    class Meta:
        abstract = True

    def _get_abilities(self, resource, user):
        """
        Compute and return abilities for a given user taking into account
        the current state of the object.
        """
        roles = []
        if user.is_authenticated:
            teams = user.get_teams()
            try:
                roles = self.user_roles or []
            except AttributeError:
                try:
                    roles = resource.accesses.filter(
                        models.Q(user=user) | models.Q(team__in=teams),
                    ).values_list("role", flat=True)
                except (self._meta.model.DoesNotExist, IndexError):
                    roles = []

        is_owner_or_admin = bool(
            set(roles).intersection({RoleChoices.OWNER, RoleChoices.ADMIN})
        )
        if self.role == RoleChoices.OWNER:
            can_delete = (
                RoleChoices.OWNER in roles
                and resource.accesses.filter(role=RoleChoices.OWNER).count() > 1
            )
            set_role_to = [RoleChoices.ADMIN, RoleChoices.MEMBER] if can_delete else []
        else:
            can_delete = is_owner_or_admin
            set_role_to = []
            if RoleChoices.OWNER in roles:
                set_role_to.append(RoleChoices.OWNER)
            if is_owner_or_admin:
                set_role_to.extend([RoleChoices.ADMIN, RoleChoices.MEMBER])

        # Remove the current role as we don't want to propose it as an option
        try:
            set_role_to.remove(self.role)
        except ValueError:
            pass

        return {
            "destroy": can_delete,
            "update": bool(set_role_to),
            "retrieve": bool(roles),
            "set_role_to": set_role_to,
        }


class Document(BaseModel):
    """Pad document carrying the content."""

    title = models.CharField(_("title"), max_length=255)
    is_public = models.BooleanField(
        _("public"),
        default=False,
        help_text=_("Whether this document is public for anyone to use."),
    )

    _content = None

    class Meta:
        db_table = "impress_document"
        ordering = ("title",)
        verbose_name = _("Document")
        verbose_name_plural = _("Documents")

    def __str__(self):
        return self.title

    @property
    def file_key(self):
        """Key of the object storage file to which the document content is stored"""
        if not self.pk:
            return None
        return str(self.pk)

    @property
    def content(self):
        """Return the json content from object storage if available"""
        if self._content is None and self.id:
            try:
                response = self.get_content_response()
            except (FileNotFoundError, ClientError):
                pass
            else:
                self._content = response["Body"].read().decode('utf-8')
        return self._content

    @content.setter
    def content(self, content):
        """Cache the content, don't write to object storage yet"""
        if not isinstance(content, str):
            raise ValueError("content should be a string.")
        
        self._content = content

    def get_content_response(self, version_id=""):
        """Get the content in a specific version of the document"""
        return default_storage.connection.meta.client.get_object(
            Bucket=default_storage.bucket_name, Key=self.file_key, VersionId=version_id
        )

    def save(self, *args, **kwargs):
        """Write content to object storage only if _content has changed."""
        super().save(*args, **kwargs)

        if self._content:
            file_key = self.file_key
            bytes_content = self._content.encode("utf-8")

            if default_storage.exists(file_key):
                response = default_storage.connection.meta.client.head_object(
                    Bucket=default_storage.bucket_name, Key=file_key
                )
                has_changed = (
                    response["ETag"].strip('"')
                    != hashlib.md5(bytes_content).hexdigest()  # noqa
                )
            else:
                has_changed = True
            if has_changed:
                content_file = ContentFile(bytes_content)
                default_storage.save(file_key, content_file)

    def get_versions_slice(
        self, from_version_id="", from_datetime=None, page_size=None
    ):
        """Get document versions from object storage with pagination and starting conditions"""
        # /!\ Trick here /!\
        # The "KeyMarker" and "VersionIdMarker" fields must either be both set or both not set.
        # The error we get otherwise is not helpful at all.
        token = {}
        if from_version_id:
            token.update(
                {"KeyMarker": self.file_key, "VersionIdMarker": from_version_id}
            )

        if from_datetime:
            response = default_storage.connection.meta.client.list_object_versions(
                Bucket=default_storage.bucket_name,
                Prefix=self.file_key,
                MaxKeys=settings.S3_VERSIONS_PAGE_SIZE,
                **token,
            )

            # Find the first version after the given datetime
            version = None
            for version in response.get("Versions", []):
                if version["LastModified"] >= from_datetime:
                    token = {
                        "KeyMarker": self.file_key,
                        "VersionIdMarker": version["VersionId"],
                    }
                    break
            else:
                if version is None or version["LastModified"] < from_datetime:
                    if response["NextVersionIdMarker"]:
                        return self.get_versions_slice(
                            from_version_id=response["NextVersionIdMarker"],
                            page_size=settings.S3_VERSIONS_PAGE_SIZE,
                            from_datetime=from_datetime,
                        )
                    return {
                        "next_version_id_marker": "",
                        "is_truncated": False,
                        "versions": [],
                    }

        response = default_storage.connection.meta.client.list_object_versions(
            Bucket=default_storage.bucket_name,
            Prefix=self.file_key,
            MaxKeys=min(page_size, settings.S3_VERSIONS_PAGE_SIZE)
            if page_size
            else settings.S3_VERSIONS_PAGE_SIZE,
            **token,
        )
        return {
            "next_version_id_marker": response["NextVersionIdMarker"],
            "is_truncated": response["IsTruncated"],
            "versions": [
                {
                    key_snake: version[key_camel]
                    for key_camel, key_snake in [
                        ("ETag", "etag"),
                        ("IsLatest", "is_latest"),
                        ("LastModified", "last_modified"),
                        ("VersionId", "version_id"),
                    ]
                }
                for version in response.get("Versions", [])
            ],
        }

    def delete_version(self, version_id):
        """Delete a version from object storage given its version id"""
        return default_storage.connection.meta.client.delete_object(
            Bucket=default_storage.bucket_name, Key=self.file_key, VersionId=version_id
        )

    def get_abilities(self, user):
        """
        Compute and return abilities for a given user on the document.
        """
        roles = get_resource_roles(self, user)
        is_owner_or_admin = bool(
            set(roles).intersection({RoleChoices.OWNER, RoleChoices.ADMIN})
        )
        can_get = self.is_public or bool(roles)
        can_get_versions = bool(roles)

        return {
            "destroy": RoleChoices.OWNER in roles,
            "versions_destroy": is_owner_or_admin,
            "versions_list": can_get_versions,
            "versions_retrieve": can_get_versions,
            "manage_accesses": is_owner_or_admin,
            "update": is_owner_or_admin,
            "partial_update": is_owner_or_admin,
            "retrieve": can_get,
        }


class DocumentAccess(BaseAccess):
    """Relation model to give access to a document for a user or a team with a role."""

    document = models.ForeignKey(
        Document,
        on_delete=models.CASCADE,
        related_name="accesses",
    )

    class Meta:
        db_table = "impress_document_access"
        ordering = ("-created_at",)
        verbose_name = _("Document/user relation")
        verbose_name_plural = _("Document/user relations")
        constraints = [
            models.UniqueConstraint(
                fields=["user", "document"],
                condition=models.Q(user__isnull=False),  # Exclude null users
                name="unique_document_user",
                violation_error_message=_("This user is already in this document."),
            ),
            models.UniqueConstraint(
                fields=["team", "document"],
                condition=models.Q(team__gt=""),  # Exclude empty string teams
                name="unique_document_team",
                violation_error_message=_("This team is already in this document."),
            ),
            models.CheckConstraint(
                check=models.Q(user__isnull=False, team="")
                | models.Q(user__isnull=True, team__gt=""),
                name="check_document_access_either_user_or_team",
                violation_error_message=_("Either user or team must be set, not both."),
            ),
        ]

    def __str__(self):
        return f"{self.user!s} is {self.role:s} in document {self.document!s}"

    def get_abilities(self, user):
        """
        Compute and return abilities for a given user on the document access.
        """
        return self._get_abilities(self.document, user)


class Template(BaseModel):
    """HTML and CSS code used for formatting the print around the MarkDown body."""

    title = models.CharField(_("title"), max_length=255)
    description = models.TextField(_("description"), blank=True)
    code = models.TextField(_("code"), blank=True)
    css = models.TextField(_("css"), blank=True)
    is_public = models.BooleanField(
        _("public"),
        default=False,
        help_text=_("Whether this template is public for anyone to use."),
    )

    class Meta:
        db_table = "impress_template"
        ordering = ("title",)
        verbose_name = _("Template")
        verbose_name_plural = _("Templates")

    def __str__(self):
        return self.title

    def get_abilities(self, user):
        """
        Compute and return abilities for a given user on the template.
        """
        roles = get_resource_roles(self, user)
        is_owner_or_admin = bool(
            set(roles).intersection({RoleChoices.OWNER, RoleChoices.ADMIN})
        )
        can_get = self.is_public or bool(roles)

        return {
            "destroy": RoleChoices.OWNER in roles,
            "generate_document": can_get,
            "manage_accesses": is_owner_or_admin,
            "update": is_owner_or_admin,
            "partial_update": is_owner_or_admin,
            "retrieve": can_get,
        }

    def generate_document(self, body, body_type):
        """
        Generate and return a PDF document for this template around the
        body passed as argument.
        """
        document = frontmatter.loads(body)
        metadata = document.metadata
        strip_body = document.content.strip()

        if body_type == "html":
            body_html = strip_body
        else:
            body_html = (
                markdown.markdown(textwrap.dedent(strip_body)) if strip_body else ""
            )

        document_html = HTML(
            string=DjangoTemplate(self.code).render(
                Context({"body": html.format_html(body_html), **metadata})
            )
        )
        css = CSS(
            string=self.css,
            font_config=FontConfiguration(),
        )
        return document_html.write_pdf(stylesheets=[css], zoom=1)


class TemplateAccess(BaseAccess):
    """Relation model to give access to a template for a user or a team with a role."""

    template = models.ForeignKey(
        Template,
        on_delete=models.CASCADE,
        related_name="accesses",
    )

    class Meta:
        db_table = "impress_template_access"
        ordering = ("-created_at",)
        verbose_name = _("Template/user relation")
        verbose_name_plural = _("Template/user relations")
        constraints = [
            models.UniqueConstraint(
                fields=["user", "template"],
                condition=models.Q(user__isnull=False),  # Exclude null users
                name="unique_template_user",
                violation_error_message=_("This user is already in this template."),
            ),
            models.UniqueConstraint(
                fields=["team", "template"],
                condition=models.Q(team__gt=""),  # Exclude empty string teams
                name="unique_template_team",
                violation_error_message=_("This team is already in this template."),
            ),
            models.CheckConstraint(
                check=models.Q(user__isnull=False, team="")
                | models.Q(user__isnull=True, team__gt=""),
                name="check_template_access_either_user_or_team",
                violation_error_message=_("Either user or team must be set, not both."),
            ),
        ]

    def __str__(self):
        return f"{self.user!s} is {self.role:s} in template {self.template!s}"

    def get_abilities(self, user):
        """
        Compute and return abilities for a given user on the template access.
        """
        return self._get_abilities(self.template, user)


class Invitation(BaseModel):
    """User invitation to a document."""

    email = models.EmailField(_("email address"), null=False, blank=False)
    document = models.ForeignKey(
        Document,
        on_delete=models.CASCADE,
        related_name="invitations",
    )
    role = models.CharField(
        max_length=20, choices=RoleChoices.choices, default=RoleChoices.MEMBER
    )
    issuer = models.ForeignKey(
        User,
        on_delete=models.CASCADE,
        related_name="invitations",
    )

    class Meta:
        db_table = "impress_invitation"
        verbose_name = _("Document invitation")
        verbose_name_plural = _("Document invitations")
        constraints = [
            models.UniqueConstraint(
                fields=["email", "document"], name="email_and_document_unique_together"
            )
        ]

    def __str__(self):
        return f"{self.email} invited to {self.document}"

    def save(self, *args, **kwargs):
        """Make invitations read-only."""
        if self.created_at:
            raise exceptions.PermissionDenied()

        super().save(*args, **kwargs)
        self.email_invitation()

    def clean(self):
        """Validate fields."""
        super().clean()

        # Check if an identity already exists for the provided email
        if User.objects.filter(email=self.email).exists():
            raise exceptions.ValidationError(
                {"email": _("This email is already associated to a registered user.")}
            )

    @property
    def is_expired(self):
        """Calculate if invitation is still valid or has expired."""
        if not self.created_at:
            return None

        validity_duration = timedelta(seconds=settings.INVITATION_VALIDITY_DURATION)
        return timezone.now() > (self.created_at + validity_duration)

    def get_abilities(self, user):
        """Compute and return abilities for a given user."""
        can_delete = False
        roles = []

        if user.is_authenticated:
            teams = user.get_teams()
            try:
                roles = self.user_roles or []
            except AttributeError:
                try:
                    roles = self.document.accesses.filter(
                        models.Q(user=user) | models.Q(team__in=teams),
                    ).values_list("role", flat=True)
                except (self._meta.model.DoesNotExist, IndexError):
                    roles = []

            can_delete = bool(
                set(roles).intersection({RoleChoices.OWNER, RoleChoices.ADMIN})
            )

        return {
            "destroy": can_delete,
            "update": False,
            "partial_update": False,
            "retrieve": bool(roles),
        }

    def email_invitation(self):
        """Email invitation to the user."""
        try:
            with override(self.issuer.language):
                title = _("Invitation to join Impress!")
                template_vars = {"title": title, "site": Site.objects.get_current()}
                msg_html = render_to_string("mail/html/invitation.html", template_vars)
                msg_plain = render_to_string("mail/text/invitation.txt", template_vars)
                mail.send_mail(
                    title,
                    msg_plain,
                    settings.EMAIL_FROM,
                    [self.email],
                    html_message=msg_html,
                    fail_silently=False,
                )

        except smtplib.SMTPException as exception:
            logger.error("invitation to %s was not sent: %s", self.email, exception)