from odoo import models, fields, api
from odoo.exceptions import ValidationError

class EducationTimetableSlot(models.Model):
    _name = 'education.timetable.slot'
    _description = 'Timetable Slot'
    _order = 'date desc, start_time'

    # Academic References (Student Population)
    program_id = fields.Many2one('education.program', string='Program', required=True)
    academic_year_id = fields.Many2one('education.academic.year', string='Academic Year', required=True)
    term_id = fields.Many2one('education.academic.term', string='Term')
    batch_id = fields.Many2one('education.batch', string='Batch')

    # Slot Details
    subject_id = fields.Many2one('education.subject', string='Subject', required=True)
    faculty_id = fields.Many2one('res.users', string='Faculty / Instructor', required=True)
    room_id = fields.Many2one('education.room', string='Room / Venue', required=True)

    # Schedule
    date = fields.Date(string='Date', required=True)
    start_time = fields.Float(string='Start Time', required=True)
    end_time = fields.Float(string='End Time', required=True)

    active = fields.Boolean(default=True)
    state = fields.Selection([
        ('draft', 'Draft'),
        ('confirmed', 'Confirmed'),
        ('cancelled', 'Cancelled')
    ], string='Status', default='draft')

    @api.constrains('start_time', 'end_time')
    def _check_time(self):
        for rec in self:
            if rec.start_time >= rec.end_time:
                raise ValidationError("Start time must be strictly earlier than end time.")

    @api.constrains('date', 'start_time', 'end_time', 'faculty_id', 'room_id', 'program_id', 'academic_year_id', 'term_id', 'batch_id')
    def _check_overlap(self):
        for rec in self:
            domain_base = [
                ('date', '=', rec.date),
                ('id', '!=', rec.id),
                # Interval logic: existing_start < new_end AND existing_end > new_start
                ('start_time', '<', rec.end_time),
                ('end_time', '>', rec.start_time),
            ]

            # 1. Check Faculty Conflict
            faculty_conflict = self.search(domain_base + [('faculty_id', '=', rec.faculty_id.id)], limit=1)
            if faculty_conflict:
                raise ValidationError(f"Faculty conflict: {rec.faculty_id.name} already has a class overlapping this time on {rec.date}.")

            # 2. Check Room Conflict
            room_conflict = self.search(domain_base + [('room_id', '=', rec.room_id.id)], limit=1)
            if room_conflict:
                raise ValidationError(f"Room conflict: {rec.room_id.name} is already booked for an overlapping time on {rec.date}.")

            # 3. Check Student Population Conflict
            # Population is defined by Program + Academic Year + Term + Batch
            # If a slot has NO term, it applies to the whole year, so it should conflict with ANY term in that year.
            # So if either the new slot or the existing slot has no term (or they match), it's a conflict.
            population_domain = domain_base + [
                ('program_id', '=', rec.program_id.id),
                ('academic_year_id', '=', rec.academic_year_id.id),
            ]
            
            # OR logic for term_id: either matches exactly, or one of them is False
            if rec.term_id:
                population_domain.append('|')
                population_domain.append(('term_id', '=', False))
                population_domain.append(('term_id', '=', rec.term_id.id))
                
            # OR logic for batch_id: either matches exactly, or one of them is False
            if rec.batch_id:
                population_domain.append('|')
                population_domain.append(('batch_id', '=', False))
                population_domain.append(('batch_id', '=', rec.batch_id.id))
            
            population_conflict = self.search(population_domain, limit=1)
            if population_conflict:
                raise ValidationError(f"Student Population conflict: This specific academic group already has a class overlapping this time on {rec.date}.")