from odoo import api, models

class StockMove(models.Model):
    _inherit = 'stock.move'

    @api.depends('product_uom_qty', 'raw_material_production_id', 'raw_material_production_id.product_qty', 'raw_material_production_id.qty_producing')
    def _compute_unit_factor(self):
        super()._compute_unit_factor()
        for move in self:
            mo = move.raw_material_production_id or move.production_id
            # Prevent 3-decimal rounding drift if the move comes from a BOM Line!
            if mo and mo.bom_id and move.bom_line_id:
                # Use the exact, unrounded mathematical ratio directly from BOM line and UoMs.
                bom_line = move.bom_line_id
                bom = mo.bom_id
                
                # Fetch quantities directly converting to product matching formats without DB truncation
                line_qty = bom_line.product_uom_id._compute_quantity(bom_line.product_qty, bom_line.product_id.uom_id, round=False)
                bom_qty = bom.product_uom_id._compute_quantity(bom.product_qty, bom.product_tmpl_id.uom_id, round=False)
                
                if bom_qty:
                    move.unit_factor = round(line_qty / bom_qty, 8)

    def _set_quantity_done_prepare_vals(self, qty):
        # Workaround for Odoo UI onchange bug where move_line_ids (NewId) are sometimes passed 
        # from the browser without their product_id, causing "Expected singleton: uom.uom()" crashes.
        for ml in self.move_line_ids:
            if not ml.product_id and self.product_id:
                ml.product_id = self.product_id
        return super()._set_quantity_done_prepare_vals(qty)