Multi-Currency Accounting in Odoo 19:
Exchange Rates, Revaluation & Reporting

import requests
from odoo import models, fields, api


class ResCurrency(models.Model):
    _inherit = "res.currency"

    # Register the new provider in the selection field
    rate_provider = fields.Selection(
        selection_add=[("custom_treasury", "Internal Treasury Rates")],
        ondelete={"custom_treasury": "set default"},
    )

    @api.model
    def _get_custom_treasury_rates(self, company):
        """Fetch rates from internal treasury API.

        Returns dict: {'EUR': 1.0842, 'GBP': 0.7921, ...}
        Rates are expressed as 1 unit of base currency = X foreign.
        """
        endpoint = company.x_treasury_api_url  # custom field
        headers = {"Authorization": f"Bearer {company.x_treasury_api_key}"}

        response = requests.get(
            endpoint,
            headers=headers,
            params={"base": company.currency_id.name},
            timeout=30,
        )
        response.raise_for_status()
        data = response.json()

        # Odoo expects rates as: 1 base_currency = X foreign
        # Adjust if your API returns the inverse
        return {
            currency_code: rate
            for currency_code, rate in data["rates"].items()
        }

    def _update_currency_rates(self):
        """Override to route to custom provider when configured."""
        for company in self.env["res.company"].search([]):
            if company.currency_provider == "custom_treasury":
                rates = self._get_custom_treasury_rates(company)
                for currency_code, rate in rates.items():
                    currency = self.search([
                        ("name", "=", currency_code),
                        ("active", "=", True),
                    ], limit=1)
                    if currency:
                        currency.rate_ids.create({
                            "currency_id": currency.id,
                            "company_id": company.id,
                            "name": fields.Date.today(),
                            "rate": rate,
                        })
            else:
                super()._update_currency_rates()
        return True

# Journal entry lines created by Odoo:
# ┌───────────────────────┬──────────┬──────────┬──────────────┐
# │ Account               │ Debit    │ Credit   │ Amount (EUR) │
# ├───────────────────────┼──────────┼──────────┼──────────────┤
# │ 411000 Receivable     │ 10,800   │          │  10,000 EUR  │
# │ 701000 Revenue        │          │ 10,800   │ -10,000 EUR  │
# └───────────────────────┴──────────┴──────────┴──────────────┘
#
# Key fields on each account.move.line:
# - amount_currency: 10,000 / -10,000 (in EUR)
# - debit/credit: 10,800 / 10,800 (in USD, base currency)
# - currency_id: EUR
# - currency_rate: 1.08 (stored at posting time)

# Payment journal entry (rate = 1.04):
# ┌───────────────────────┬──────────┬──────────┬──────────────┐
# │ Account               │ Debit    │ Credit   │ Amount (EUR) │
# ├───────────────────────┼──────────┼──────────┼──────────────┤
# │ 512000 Bank EUR       │ 10,400   │          │  10,000 EUR  │
# │ 411000 Receivable     │          │ 10,400   │ -10,000 EUR  │
# └───────────────────────┴──────────┴──────────┴──────────────┘
#
# Reconciling the receivable triggers an automatic exchange entry:
# ┌───────────────────────┬──────────┬──────────┬──────────────┐
# │ Account               │ Debit    │ Credit   │ Amount (EUR) │
# ├───────────────────────┼──────────┼──────────┼──────────────┤
# │ 666000 Exchange Loss  │    400   │          │     0.00 EUR │
# │ 411000 Receivable     │          │    400   │     0.00 EUR │
# └───────────────────────┴──────────┴──────────┴──────────────┘
#
# The receivable was booked at $10,800 but settled at $10,400.
# The $400 difference is a realized exchange LOSS.
# Note: amount_currency = 0 on the exchange entry because
# in EUR terms, the full 10,000 was received.

eur = self.env.ref("base.EUR")
rate = eur._get_rates(
    self.env.company, fields.Date.today()
)[eur.id]

loan_amount_eur = 50000.0
loan_amount_base = loan_amount_eur / rate  # convert to base

move = self.env["account.move"].create({
    "journal_id": self.env.ref(
        "my_module.journal_general"
    ).id,
    "date": fields.Date.today(),
    "line_ids": [
        (0, 0, {
            "account_id": intercompany_receivable.id,
            "debit": loan_amount_base,
            "credit": 0,
            "currency_id": eur.id,
            "amount_currency": loan_amount_eur,
            "partner_id": subsidiary.partner_id.id,
        }),
        (0, 0, {
            "account_id": bank_account.id,
            "debit": 0,
            "credit": loan_amount_base,
            "currency_id": eur.id,
            "amount_currency": -loan_amount_eur,
            "partner_id": subsidiary.partner_id.id,
        }),
    ],
})
move.action_post()

from odoo import models


class AgedReceivableCustom(models.AbstractModel):
    _inherit = "account.aged.receivable"

    def _get_column_details(self, options):
        """Add a currency amount column to the report."""
        columns = super()._get_column_details(options)
        # Insert after the 'due_date' column
        currency_col = self._header_column(
            name="amount_currency",
            sortable=True,
        )
        columns.insert(2, currency_col)
        return columns

    def _get_aml_values(self, options, aml, rate):
        """Include amount_currency in each line's data."""
        values = super()._get_aml_values(options, aml, rate)
        values["amount_currency"] = {
            "name": f"{aml.amount_currency:.2f} "
                    f"{aml.currency_id.name}",
            "no_format": aml.amount_currency,
        }
        return values