from django.db import models, transaction
from django.contrib.auth.models import AbstractUser
from django.utils import timezone


class User(AbstractUser):
    """Custom User model with role and admin flag"""
    ROLE_CHOICES = [
        ('employee', 'Employee'),
        ('viewer', 'Viewer'),
    ]

    role = models.CharField(max_length=20, choices=ROLE_CHOICES, default='viewer')
    is_admin = models.BooleanField(default=False)
    can_measure = models.BooleanField(default=False)
    can_manually_measure = models.BooleanField(default=False)
    can_manage_entities = models.BooleanField(default=False)
    can_edit_documents = models.BooleanField(default=False)

    class Meta:
        db_table = 'api_user'

    def __str__(self):
        return f"{self.username} ({self.get_role_display()})"


class ComPortReading(models.Model):
    """Model to store serial port readings"""
    port = models.CharField(max_length=20)
    data = models.TextField()
    timestamp = models.DateTimeField(auto_now_add=True)
    source_ip = models.GenericIPAddressField(null=True, blank=True)

    class Meta:
        ordering = ['-timestamp']
        indexes = [
            models.Index(fields=['-timestamp']),
            models.Index(fields=['port', '-timestamp']),
        ]

    def __str__(self):
        return f"{self.port} - {self.timestamp}"


class Report(models.Model):
    """Model to store report templates for the report editor"""
    MATRIX = 'matrix'
    A4 = 'a4'
    KIND_CHOICES = [
        (MATRIX, 'Character matrix'),
        (A4, 'A4 free positioning'),
    ]

    name = models.CharField(max_length=255)
    kind = models.CharField(max_length=10, choices=KIND_CHOICES, default=MATRIX)
    page_width = models.IntegerField(default=80)
    page_height = models.IntegerField(default=66)
    api_endpoint = models.CharField(max_length=500, blank=True, default='')
    elements = models.JSONField(default=list)
    # mm page setup for kind='a4': page, orientation, margins{top,right,bottom,left},
    # defaultFont, defaultFontSize
    page_setup = models.JSONField(default=dict, blank=True)
    created_by = models.ForeignKey(
        User, on_delete=models.SET_NULL, null=True, blank=True,
        related_name='reports'
    )
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        ordering = ['-updated_at']

    def __str__(self):
        return self.name


class ScaleProtocol(models.Model):
    """How to read a particular scale indicator.

    Definitions live here rather than in the serial bridge so a new scale type
    is a configuration change, not a new binary on every station PC. The bridge
    only moves bytes; the frontend parses them using these rules.
    """
    FIXED_COLUMN = 'fixed_column'
    SIMULATOR = 'simulator'
    TOLEDO_CONTINUOUS = 'toledo_continuous'
    SICS = 'sics'

    KIND_CHOICES = [
        (FIXED_COLUMN, 'Fixed column'),
        (SIMULATOR, 'Simulator (ST/US)'),
        (TOLEDO_CONTINUOUS, 'Toledo Continuous'),
        (SICS, 'Mettler-Toledo SICS'),
    ]

    name = models.CharField(max_length=100, unique=True)
    kind = models.CharField(max_length=20, choices=KIND_CHOICES, default=FIXED_COLUMN)
    # Empty poll_command means the scale streams on its own (continuous mode).
    poll_command = models.CharField(max_length=20, blank=True, default='')
    poll_interval = models.FloatField(default=0.2)
    # Kind-specific parameters. For fixed_column: weight_start, weight_length,
    # stable_pos, stable_char, stable_means_balanced, decimals. Offsets are 0-based.
    config = models.JSONField(default=dict, blank=True)
    is_builtin = models.BooleanField(default=False)
    is_active = models.BooleanField(default=True)

    class Meta:
        ordering = ['name']

    def __str__(self):
        return self.name


class License(models.Model):
    """The installed licence. Single row - enforced by save()."""
    key_blob = models.TextField(blank=True, default='')
    installed_at = models.DateTimeField(auto_now=True)
    # Grace period start, stored here rather than in a file so it cannot be reset
    # by deleting something on disk, and is included in database backups.
    grace_started = models.DateTimeField(null=True, blank=True)

    def save(self, *args, **kwargs):
        if not self.pk and License.objects.exists():
            self.pk = License.objects.first().pk
        super().save(*args, **kwargs)

    def __str__(self):
        return 'License' if self.key_blob else 'License (none installed)'


class StationSlot(models.Model):
    """A station that has recently reported in.

    Slots are counted against the licence limit. The frontend refreshes every
    30s and a slot is released after SLOT_TIMEOUT_SECONDS, so switching off a
    station PC frees its slot automatically.
    """
    station_key = models.CharField(max_length=64, unique=True)
    bridge_version = models.CharField(max_length=20, blank=True, default='')
    com_port = models.CharField(max_length=20, blank=True, default='')
    first_seen = models.DateTimeField(auto_now_add=True)
    last_seen = models.DateTimeField(auto_now=True)

    class Meta:
        ordering = ['first_seen']

    def __str__(self):
        return f"{self.station_key} ({self.com_port})"


class DocumentCounter(models.Model):
    year = models.IntegerField(unique=True)
    last_number = models.IntegerField(default=0)


def generate_doc_number(year):
    with transaction.atomic():
        counter, _ = DocumentCounter.objects.select_for_update().get_or_create(
            year=year, defaults={'last_number': 0}
        )
        counter.last_number += 1
        counter.save()
        return f"{year}-{counter.last_number:06d}"