from typing import override

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

from apps.core.models import BaseModel

METRIC_KEY_PATTERN = r"^[a-z][a-z0-9_]*$"


class MetricType(models.TextChoices):
    RATIO = "ratio", _("Ratio")
    COUNT = "count", _("Count")
    AVERAGE = "average", _("Average")
    PERCENTILE = "percentile", _("Percentile")


class MetricDirection(models.TextChoices):
    HIGHER_IS_BETTER = "higher_is_better", _("Higher is better")
    LOWER_IS_BETTER = "lower_is_better", _("Lower is better")
    NEUTRAL = "neutral", _("Neutral")


class MetricDefinition(BaseModel):
    key = models.CharField(
        max_length=100,
        unique=True,
        verbose_name=_("key"),
        validators=[
            django.core.validators.RegexValidator(
                regex=METRIC_KEY_PATTERN,
                message=(
                    "Metric key must start with a lowercase letter "
                    "and contain only lowercase letters, digits, "
                    "and underscores."
                ),
            )
        ],
    )
    name = models.CharField(
        max_length=200,
        verbose_name=_("name"),
    )
    description = models.TextField(
        blank=True,
        verbose_name=_("description"),
    )
    metric_type = models.CharField(
        max_length=20,
        choices=MetricType.choices,
        verbose_name=_("metric type"),
    )
    direction = models.CharField(
        max_length=20,
        choices=MetricDirection.choices,
        default=MetricDirection.NEUTRAL,
        verbose_name=_("direction"),
    )
    calculation_rule = models.JSONField(
        verbose_name=_("calculation rule"),
    )
    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 = _("metric definition")
        verbose_name_plural = _("metric definitions")
        ordering = ["key"]

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


class ExperimentMetric(BaseModel):
    experiment = models.ForeignKey(
        "experiments.Experiment",
        on_delete=models.CASCADE,
        related_name="experiment_metrics",
        verbose_name=_("experiment"),
    )
    metric = models.ForeignKey(
        MetricDefinition,
        on_delete=models.PROTECT,
        related_name="experiment_usages",
        verbose_name=_("metric"),
    )
    is_primary = models.BooleanField(
        default=False,
        verbose_name=_("is primary metric"),
    )
    created_at = models.DateTimeField(
        auto_now_add=True,
        verbose_name=_("created at"),
    )

    class Meta:
        verbose_name = _("experiment metric")
        verbose_name_plural = _("experiment metrics")
        constraints = [
            models.UniqueConstraint(
                fields=["experiment", "metric"],
                name="unique_experiment_metric",
            ),
        ]
        indexes = [
            models.Index(
                fields=["experiment", "is_primary"],
                name="idx_exp_metric_primary",
            ),
        ]

    @override
    def __str__(self) -> str:
        primary = " [primary]" if self.is_primary else ""
        return f"{self.experiment.name} → {self.metric.key}{primary}"