from odoo import models, _
from odoo.exceptions import UserError


class MrpProduction(models.Model):
    _inherit = 'mrp.production'

    def _prepare_stock_lot_values(self):
        self.ensure_one()
        name = False
        product = self.product_id
        tmpl = product.product_tmpl_id
        seq = getattr(tmpl, 'lot_sequence_id', False)
        if seq:
            tried = set()
            # Try generating a unique candidate from the per-product sequence
            for _i in range(10):
                candidate = seq.next_by_id()
                if not candidate:
                    break
                if candidate in tried:
                    continue
                tried.add(candidate)
                exist_lot = self.env['stock.lot'].search([
                    ('product_id', '=', product.id),
                    '|', ('company_id', '=', False), ('company_id', '=', self.company_id.id),
                    ('name', '=', candidate),
                ], limit=1)
                if not exist_lot:
                    name = candidate
                    break

        # Fallback to default behavior if no per-product candidate was found
        if not name:
            name = self.env['ir.sequence'].next_by_code('stock.lot.serial')
            exist_lot = (not name) or self.env['stock.lot'].search([
                ('product_id', '=', product.id),
                '|', ('company_id', '=', False), ('company_id', '=', self.company_id.id),
                ('name', '=', name),
            ], limit=1)
            if exist_lot:
                name = self.env['stock.lot']._get_next_serial(self.company_id, product)
            if not name:
                raise UserError(_("Please set the first Serial Number or a default sequence"))

        return {
            'product_id': product.id,
            'name': name,
        }