Working out a reporting challenge from HN, part 2. See also part 1: https://gist.github.com/simonmichael/3bb42cd82b4afd437305d10ad914b9ec

avodonosov.journal

; avodonosov problem, HN 2021-09-05
; part of https://gist.github.com/simonmichael/3bb42cd82b4afd437305d10ad914b9ec

; "For example
; Jan 1
;   Received 1000 EUR for a contract
;   The rate 1 EUR = 2 BYN
; Jan 2
;   Exchanged 300 EUR to BYN
;   The rate 1 EUR = 2.1 BYN
; Jan 3
;   Received 2000 EUR for a contract
;   The rate 1 EUR = 2.2 BYN
; Jan 5
;   Exchanged 600 EUR to BYN
;   The rate 1 EUR = 2.3 BYN
; Jan 30:
;   The rate 1 EUR = 2.5 BYN
; I need reports net worth, total income for the month, capital gains.
; First generate the report in BYN, then in EUR, then in USD. 
; Let's assume the commissions are zero.
; Net worth is easy - current sum in original currencies and then convert to the currency of the report using the current rate
; But what ledger was failing to do, for me, is to compute capital gains.
; And, as I remember, it was unable to even balance the ledger
; How would one describe this use case in ledger format?"


P 1/1 EUR 2 BYN

1/1 acquire euros when price is 2 BYN
    revenues                                   -2000 BYN  ; 1000 EUR @ 2 BYN          ; recognise the revenue in local currency immediately, it's more useful for reporting
    assets:eur:2021-01-01                       1000 EUR @ 2 BYN = 1000 EUR @ 2 BYN   ; the money is not converted immediately, so we track it as a lot with a cost basis

1/2 convert some euros at 2.1 BYN
    assets:eur:2021-01-01                       -300 EUR @ 2 BYN = 700 EUR @ 2 BYN    ; we're disposing of euros acquired with this cost
    assets:byn                                   630 BYN                              ; selling them for this much (300 EUR @ 2.1 BYN)
    revenues:forex gain                          -30 BYN                              ; resulting in this gain

P 1/3 EUR 2.2 BYN

1/3 acquire euros when price is 2.2 BYN
    revenues                                   -4400 BYN  ; 2000 EUR @ 2.2 BYN
    assets:eur:2021-01-03                       2000 EUR @ 2.2 BYN = 2000 EUR @ 2.2 BYN  ; new date and cost, new lot

1/5 convert some euros at 2.3 BYN
    assets:eur:2021-01-01                       -600 EUR @ 2 BYN = 100 EUR @ 2 BYN    ; we assume FIFO rule, disposing from the oldest lot first
    assets:byn                                  1380 BYN                              ; 600 EUR @ 2.3 BYN
    revenues:forex gain                         -180 BYN

P 1/30 EUR 1.21 USD
P 1/30 EUR 2.5 BYN

; Now to see a zero balance in bse (confirming "balanced books"), there are two steps:
; 1. convert all balances to the base currency, at the reporting date. 
;    This also involves recognising forex gain/loss as usual.
; 2. merge revenues/expenses to equity.

;comment

1/30 temporary for reporting: convert all to base currency, at current rate (2.5)
    assets:eur:2021-01-01                       -100 EUR @ 2 BYN = 0 EUR @ 2 BYN
    assets:eur:2021-01-01:value on 1/30          250 BYN  ; 100 EUR @ 2.5 BYN
    revenues:forex gain:unrealised               -50 BYN
    assets:eur:2021-01-03                      -2000 EUR @ 2.2 BYN = 0 EUR @ 2.2 BYN
    assets:eur:2021-01-03:value on 1/30         5000 BYN  ; 2000 EUR @ 2.5 BYN
    revenues:forex gain:unrealised              -600 BYN

;comment

1/30 temporary for reporting: retain earnings
    revenues                                    6400 BYN == 0
    revenues:forex gain                          210 BYN == 0
    revenues:forex gain:unrealised               650 BYN == 0
    equity:retained earnings


comment

$ hledger -f avodonosov.journal bse
Balance Sheet With Equity 2021-01-30

                                     || 2021-01-30
=====================================++============
 Assets                              ||
-------------------------------------++------------
 assets:byn                          || 2010.0 BYN
 assets:eur:2021-01-01:value on 1/30 ||  250.0 BYN
 assets:eur:2021-01-03:value on 1/30 || 5000.0 BYN
-------------------------------------++------------
                                     || 7260.0 BYN
=====================================++============
 Liabilities                         ||
-------------------------------------++------------
-------------------------------------++------------
                                     ||
=====================================++============
 Equity                              ||
-------------------------------------++------------
 equity:retained earnings            || 7260.0 BYN
-------------------------------------++------------
                                     || 7260.0 BYN
=====================================++============
 Net:                                ||          0


Questions:

1. What are the ways to report unrealised capital/forex gains/losses ?

1.1. Add a "convert all to base currency" txn working out the gain

As above.

1.2. Run cost and value reports and compare the difference

$ hledger bal assets:eur -B
           200.0 BYN  assets:eur:2021-01-01
          4400.0 BYN  assets:eur:2021-01-03
--------------------
          4600.0 BYN  
$ hledger bal assets:eur -V
           250.0 BYN  assets:eur:2021-01-01
          5000.0 BYN  assets:eur:2021-01-03
--------------------
          5250.0 BYN  

1.3. Use bal --gain in hledger master

$ hledger bal assets:eur --gain
            50.0 BYN  assets:eur:2021-01-01
           600.0 BYN  assets:eur:2021-01-03
--------------------
           650.0 BYN  

1.4. use roi ?

I don't know how; something like 

$ hledger roi --inv assets:eur --pnl 'revenues:forex gain'


2. In the "convert some euros" txns, how to use trading accounts
   (equity:conversion postings) instead of @ notation, while also
   respecting cost basis ?