Implementing Workflow State Machines in Odoo: Advanced Logic

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

class ReturnRequest(models.Model):
    _name = 'return.request'
    _description = 'Customer Return Request'
    _inherit = ['mail.thread', 'mail.activity.mixin']  # Enable Chatter
    
    state = fields.Selection([
        ('draft', 'Draft'),
        ('approved', 'Approved'),
        ('received', 'Received'),
        ('inspected', 'Inspected'),
        ('refunded', 'Refunded'),
        ('rejected', 'Rejected'),
    ], string='Status', default='draft', tracking=True, required=True)
    
    # Other fields
    tracking_number = fields.Char(string="Tracking #")
    quality_check = fields.Selection([('pass', 'Pass'), ('fail', 'Fail')])

def action_approve(self):
    """Move from Draft -> Approved"""
    for rec in self:
        if rec.state != 'draft':
            continue  # Idempotency check
        rec.state = 'approved'
        # Logic: Send Email with Label

def action_receive(self):
    """Move from Approved -> Received"""
    for rec in self:
        if not rec.tracking_number:
            raise UserError(_("You must enter a tracking number before receiving."))
        rec.state = 'received'

def action_inspect(self):
    """Move from Received -> Inspected"""
    for rec in self:
        if not rec.quality_check:
            raise UserError(_("Please select Pass or Fail."))
        if rec.quality_check == 'fail':
            rec.state = 'rejected'
        else:
            rec.state = 'inspected'

def action_refund(self):
    """Move from Inspected -> Refunded"""
    for rec in self:
        if rec.state != 'inspected':
            raise UserError(_("Only inspected items can be refunded."))
        # Logic: Create Credit Note
        rec.state = 'refunded'

def action_reset_draft(self):
    """Reset to Draft (for corrections)"""
    for rec in self:
        if rec.state == 'refunded':
            raise UserError(_("Cannot reset a refunded return."))
        rec.state = 'draft'

<form>
    <header>
        <!-- Buttons define the "Arrows" of the state machine -->
        
        <!-- Visible only in Draft -->
        <button name="action_approve" string="Approve Return" type="object"
                class="oe_highlight" states="draft" groups="base.group_user"/>
        
        <!-- Visible only in Approved -->
        <button name="action_receive" string="Mark Received" type="object"
                class="oe_highlight" states="approved"/>
        
        <!-- Visible only in Received -->
        <button name="action_inspect" string="Complete Inspection" type="object"
                class="oe_highlight" states="received"/>
        
        <!-- Visible only in Inspected -->
        <button name="action_refund" string="Issue Refund" type="object"
                class="oe_highlight" states="inspected" groups="account.group_account_manager"/>
        
        <!-- Reset Button (Visible in specific states) -->
        <button name="action_reset_draft" string="Reset to Draft" type="object"
                states="approved,received,rejected"/>
        
        <!-- The Status Bar itself -->
        <field name="state" widget="statusbar" 
               statusbar_visible="draft,approved,received,inspected,refunded"/>
    </header>
    
    <sheet>
        <!-- Make fields readonly in later stages to prevent tampering -->
        <group>
            <field name="tracking_number" 
                   attrs="{'readonly': [('state', 'in', ['refunded', 'rejected'])]}"/>
            <field name="quality_check" 
                   attrs="{'invisible': [('state', 'in', ['draft', 'approved'])]}"/>
        </group>
    </sheet>
</form>

@api.model
def create(self, vals):
    # Force new records to be draft
    vals['state'] = 'draft'
    return super().create(vals)

def write(self, vals):
    if 'state' in vals:
        # Prevent manual writing to state unless via our specific methods
        # (This is strict, but effective)
        # You might implement a context flag check here.
        pass
    return super().write(vals)

def action_confirm(self):
    if self.amount_total > 5000:
        self.state = 'vp_approve'
    elif self.amount_total > 1000:
        self.state = 'to_approve'
    else:
        super().action_confirm()  # Standard logic