from typing import override

from django.core.validators import RegexValidator
from django.db import models
from django.utils.translation import gettext_lazy as _

from apps.core.models import BaseModel

EVENT_TYPE_KEY_PATTERN = r"^[A-Za-z][A-Za-z0-9_]*$"


class EventType(BaseModel):
    name = models.CharField(
        max_length=100,
        unique=True,
        verbose_name=_("name"),
        validators=[
            RegexValidator(
                regex=EVENT_TYPE_KEY_PATTERN,
                message=(
                    "Event type name must follow snake_case, "
                    "camelCase, or PascalCase."
                ),
            )
        ],
    )
    display_name = models.CharField(
        max_length=200,
        verbose_name=_("display name"),
    )
    description = models.TextField(
        blank=True,
        verbose_name=_("description"),
    )
    is_exposure = models.BooleanField(
        default=False,
        verbose_name=_("is exposure"),
        help_text=_(
            "When True, this event type represents an exposure "
            "(fact of showing a variant to a user)."
        ),
    )
    requires_exposure = models.BooleanField(
        default=False,
        verbose_name=_("requires exposure"),
        help_text=_(
            "When True, events of this type are only attributed "
            "if a matching exposure exists for the same decision_id."
        ),
    )
    required_fields = models.JSONField(
        default=list,
        blank=True,
        verbose_name=_("required fields"),
        help_text=_(
            "List of property field names that must be present "
            "in event properties."
        ),
    )
    is_active = models.BooleanField(
        default=True,
        db_index=True,
        verbose_name=_("is active"),
    )
    created_at = models.DateTimeField(
        auto_now_add=True,
        verbose_name=_("created at"),
    )
    updated_at = models.DateTimeField(
        auto_now=True,
        verbose_name=_("updated at"),
    )

    class Meta:
        verbose_name = _("event type")
        verbose_name_plural = _("event types")
        ordering = ["name"]

    @override
    def __str__(self) -> str:
        return self.name


class Exposure(BaseModel):
    decision_id = models.CharField(
        max_length=100,
        unique=True,
        verbose_name=_("decision ID"),
    )
    experiment_id = models.UUIDField(
        null=True,
        blank=True,
        verbose_name=_("experiment ID"),
        db_index=True,
    )
    variant_id = models.UUIDField(
        null=True,
        blank=True,
        verbose_name=_("variant ID"),
    )
    subject_id = models.CharField(
        max_length=200,
        db_index=True,
        verbose_name=_("subject ID"),
    )
    timestamp = models.DateTimeField(
        verbose_name=_("event timestamp"),
    )
    created_at = models.DateTimeField(
        auto_now_add=True,
        verbose_name=_("created at"),
    )

    class Meta:
        verbose_name = _("exposure")
        verbose_name_plural = _("exposures")
        ordering = ["-timestamp"]
        indexes = [
            models.Index(
                fields=["experiment_id", "variant_id", "timestamp"],
                name="idx_exposure_exp_var_ts",
            ),
        ]

    @override
    def __str__(self) -> str:
        return f"Exposure({self.decision_id})"


class Decision(BaseModel):
    decision_id = models.CharField(
        max_length=100,
        unique=True,
        verbose_name=_("decision ID"),
    )
    flag_key = models.CharField(
        max_length=100,
        verbose_name=_("flag key"),
    )
    subject_id = models.CharField(
        max_length=200,
        db_index=True,
        verbose_name=_("subject ID"),
    )
    experiment_id = models.UUIDField(
        null=True,
        blank=True,
        verbose_name=_("experiment ID"),
    )
    variant_id = models.UUIDField(
        null=True,
        blank=True,
        verbose_name=_("variant ID"),
    )
    value = models.CharField(
        max_length=500,
        blank=True,
        verbose_name=_("resolved value"),
    )
    reason = models.CharField(
        max_length=50,
        verbose_name=_("reason"),
    )
    created_at = models.DateTimeField(
        auto_now_add=True,
        verbose_name=_("created at"),
    )

    class Meta:
        verbose_name = _("decision")
        verbose_name_plural = _("decisions")
        ordering = ["-created_at"]
        indexes = [
            models.Index(
                fields=["flag_key", "subject_id"],
                name="idx_decision_flag_subject",
            ),
        ]

    @override
    def __str__(self) -> str:
        return f"Decision({self.decision_id}, {self.flag_key})"


class Event(BaseModel):
    event_id = models.CharField(
        max_length=200,
        unique=True,
        verbose_name=_("event ID"),
        help_text=_("Client-provided idempotency key"),
    )
    event_type = models.ForeignKey(
        EventType,
        on_delete=models.PROTECT,
        related_name="events",
        verbose_name=_("event type"),
    )
    decision_id = models.CharField(
        max_length=100,
        db_index=True,
        verbose_name=_("decision ID"),
    )
    subject_id = models.CharField(
        max_length=200,
        db_index=True,
        verbose_name=_("subject ID"),
    )
    timestamp = models.DateTimeField(
        verbose_name=_("event timestamp"),
    )
    properties = models.JSONField(
        default=dict,
        blank=True,
        verbose_name=_("properties"),
    )
    is_attributed = models.BooleanField(
        default=True,
        db_index=True,
        verbose_name=_("is attributed"),
        help_text=_(
            "False when event requires exposure but none was found yet."
        ),
    )
    created_at = models.DateTimeField(
        auto_now_add=True,
        verbose_name=_("created at"),
    )

    class Meta:
        verbose_name = _("event")
        verbose_name_plural = _("events")
        ordering = ["-timestamp"]
        indexes = [
            models.Index(
                fields=["decision_id", "event_type"],
                name="idx_event_decision_type",
            ),
            models.Index(
                fields=["event_type", "subject_id", "timestamp"],
                name="idx_event_type_subj_ts",
            ),
        ]

    @override
    def __str__(self) -> str:
        return f"Event({self.event_id}, {self.event_type})"


class PendingEvent(BaseModel):
    event_id = models.CharField(
        max_length=200,
        unique=True,
        verbose_name=_("event ID"),
    )
    event_type = models.ForeignKey(
        EventType,
        on_delete=models.PROTECT,
        related_name="pending_events",
        verbose_name=_("event type"),
    )
    decision_id = models.CharField(
        max_length=100,
        db_index=True,
        verbose_name=_("decision ID"),
    )
    subject_id = models.CharField(
        max_length=200,
        verbose_name=_("subject ID"),
    )
    timestamp = models.DateTimeField(
        verbose_name=_("event timestamp"),
    )
    properties = models.JSONField(
        default=dict,
        blank=True,
        verbose_name=_("properties"),
    )
    expires_at = models.DateTimeField(
        db_index=True,
        verbose_name=_("expires at"),
    )
    created_at = models.DateTimeField(
        auto_now_add=True,
        verbose_name=_("created at"),
    )

    class Meta:
        verbose_name = _("pending event")
        verbose_name_plural = _("pending events")
        ordering = ["-created_at"]
        indexes = [
            models.Index(
                fields=["decision_id"],
                name="idx_pending_decision",
            ),
        ]

    @override
    def __str__(self) -> str:
        return f"PendingEvent({self.event_id}, {self.decision_id})"