Build a SaaS-based Inventory Management + POS + Basic Accounting system using Laravel (backend) and MySQL.

The system must follow multi-tenant architecture with strict data isolation.

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1. MULTI-TENANT (SAAS)
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- Each tenant = one customer account
- Each tenant can have multiple companies (restricted by subscription plan)

Tables:
- tenants: id, name, plan_id, subscription_status
- plans: id, name, price, max_companies (nullable), max_users

Rules:
- Restrict company creation based on plan.max_companies

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2. COMPANY MASTER
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- companies:
  - id, tenant_id
  - name, gst_number, state, address
  - invoice_prefix

- One tenant → multiple companies
- Each company has separate:
  - GST
  - stock
  - invoices
  - accounting

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3. USER MANAGEMENT
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- users belong to tenant
- user_companies:
  - user_id, company_id, role

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4. LEDGER SYSTEM (ACCOUNTING BASE)
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Create unified ledger table instead of separate customer/supplier:

TABLE: ledgers
- id
- tenant_id
- company_id
- name
- type (customer, supplier)
- group (sundry_debtors, sundry_creditors)
- gst_number
- state
- opening_balance
- balance_type (debit/credit)

RULES:
- Customers → Sundry Debtors
- Suppliers → Sundry Creditors

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5. PRODUCTS
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- products:
  - id, tenant_id, company_id
  - name, sku
  - purchase_price, selling_price
  - gst_rate, hsn_code
  - stock_quantity

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6. PURCHASE MODULE
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- purchases
- purchase_items

On Purchase:
- Increase stock
- Increase creditor balance

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7. SALES (POS SYSTEM)
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Support BOTH:

A. B2C (Retail)
- Fast billing
- GST inclusive pricing

B. B2B (Business)
- GST invoice required

Tables:
- sales
- sale_items

sale_items fields:
- quantity
- price
- discount
- taxable_value
- cgst_amount
- sgst_amount
- igst_amount
- total

On Sale:
- Decrease stock
- If credit sale → increase debtor balance

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8. CREDIT NOTE (SALES RETURN)
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- credit_notes
- credit_note_items

LOGIC:
- Customer returns goods
- Increase stock
- Reduce debtor balance
- Reverse GST

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9. DEBIT NOTE (PURCHASE RETURN)
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- debit_notes
- debit_note_items

LOGIC:
- Return goods to supplier
- Decrease stock
- Reduce creditor balance
- Reverse GST

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10. PAYMENTS
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TABLE: payments
- id
- tenant_id
- company_id
- ledger_id
- type (receipt/payment)
- amount
- payment_mode (cash, UPI, card)
- reference

LOGIC:
- Receipt → reduce debtor
- Payment → reduce creditor

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11. GST RULES (INDIA)
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- Product has gst_rate

Tax logic:
IF company_state == customer_state:
    apply CGST + SGST
ELSE:
    apply IGST

Support:
- Tax inclusive
- Tax exclusive

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12. STOCK MANAGEMENT
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Maintain in products.stock_quantity

Updates:
- Purchase → increase
- Sale → decrease
- Credit Note → increase
- Debit Note → decrease

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13. VALIDATIONS
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- Prevent negative stock
- Prevent company creation beyond plan limit
- Ensure tenant_id and company_id in ALL tables
- Always filter queries:
  WHERE tenant_id = ? AND company_id = ?

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14. ARCHITECTURE
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- Laravel API (clean architecture)
- Service Layer:
  - SaleService
  - PurchaseService
  - LedgerService
  - CreditNoteService
  - DebitNoteService

- Middleware:
  - TenantMiddleware
  - CompanyMiddleware

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15. DELIVERABLES
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Generate:

1. Database migrations
2. Eloquent models with relationships
3. Controllers (CRUD + POS APIs)
4. Service classes (business logic)
5. GST helper functions
6. API routes

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IMPORTANT NOTES
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- Do NOT mix tenant/company data
- Use ledger instead of separate customer/supplier tables
- Keep system scalable (SaaS ready)
- Follow Laravel best practices