Gist shows two attempts to create csv import rules for transactions in "foreign" currency with cost in "home" currency

init.journal

2019-01-01 init
  equity:opening balances
  assets:bank   $100

rules1

fields date,description,amt,fx_ccy,fx_amt,balance_
skip 1
account1 assets:bank

amount -%fx_ccy%fx_amt @@ $%amt
balance $ %balance_

if
transaction1
  account2  expenses:one

if
transaction2
  account2  expenses:two

;; With these rules account balances dont work, and even if we ignore them, cost is not being recorded:
;; hledger print -f source.csv --rules rules1 
;; 2019/01/02 transaction1
;;     assets:bank        £-2 @@ $1 = $ 99
;;     expenses:one              $1
;; 
;; 2019/01/03 transaction2
;;     assets:bank        £-4 @@ $2 = $ 97
;;     expenses:two              $2
;; 
;;
;; (cat init.journal; hledger print -f source.csv --rules rules1) | hledger balance -f - 
;; hledger: balance assertion: "-" (line 5, column 34)
;; transaction:
;; 2019/01/02 transaction1
;;     assets:bank        £-2 @@ $1 = $ 99
;;     expenses:one
;; 
;; assertion details:
;; date:       2019/01/02
;; account:    assets:bank
;; commodity:  $
;; calculated: 100
;; asserted:   99
;; difference: -1
;; 

rules2

fields date,description,amt,fx_ccy,fx_amt,balance_
skip 1
account2 assets:bank

amount %fx_ccy %fx_amt @@ $%amt
balance $ %balance_

if
transaction1
  account1  expenses:one

if
transaction2
  account1  expenses:two

;; With these rules, costs are recorded in the right place, but balance assertions are now on the wrong account:
;; hledger print -f source.csv --rules rules2
;; 2019/01/02 transaction1
;;     expenses:one       £ 2 @@ $1 = $ 99
;;     assets:bank              $-1
;; 
;; 2019/01/03 transaction2
;;     expenses:two       £ 4 @@ $2 = $ 97
;;     assets:bank              $-2
;; 
;;> (cat init.journal; hledger print -f source.csv --rules rules2) | hledger balance -f - 
;; hledger: balance assertion: "-" (line 5, column 34)
;; transaction:
;; 2019/01/02 transaction1
;;     expenses:one       £ 2 @@ $1 = $ 99
;;     assets:bank
;; 
;; assertion details:
;; date:       2019/01/02
;; account:    expenses:one
;; commodity:  $
;; calculated: 0
;; asserted:   99
;; difference: 99
;; 

source.csv

target.journal

;;
;; This is the journal that we want to produce through CSV import. Assets:bank is in $$$, expenses are in foreign currency, and we know
;; dollar cost for them, and want to record it
;;
2019-01-01 init
  equity:opening balances
  assets:bank   $100

2019-01-02 transaction1
   assets:bank    -$1 = $99
   expenses:one   £2 @@ $1

2019-01-03 transaction3
   assets:bank   -$2  = $97
   expenses:two   £4 @@ $2


;; Now we can produce balance report in foreign currency and in dollar cost:
;; % hledger -f target.journal balance
;;                  $97  assets:bank
;;                $-100  equity:opening balances
;;                   £6  expenses
;;                   £2    one
;;                   £4    two
;; --------------------
;;                  $-3
;;                   £6
;;
;;
;;  hledger -f target.journal balance --cost 
;;                  $97  assets:bank
;;                $-100  equity:opening balances
;;                   $3  expenses
;;                   $1    one
;;                   $2    two
;; --------------------
;;                    0