refactor UTXO selection

UTXO-select.md

@@ -4,7 +4,7 @@ Creates dummy inputs and outputs. Builds a TX with them.
 ```
 =btc -build-file %/lib/btc/hoon
 =bwsl -build-file %/lib/btc-wallet-store/hoon
-=u (utxo:btc [pos=0 (hash256:btc [wid=32 dat=0xc493.f6f1.4668.5f76.b44f.0c77.ca88.120c.b8bc.89f5.34fe.69b6.8288.27b9.74e6.8849]) height=3 value=0])
+=u (utxo:btc [pos=0 (hash256:btc [wid=32 dat=0xc493.f6f1.4668.5f76.b44f.0c77.ca88.120c.b8bc.89f5.34fe.69b6.8288.27b9.74e6.8849]) height=3 value=0 ~])
 =val0 200.000
 =val1 500.000
 =val2 30
@@ -12,10 +12,10 @@ Creates dummy inputs and outputs. Builds a TX with them.
 
 =eny1 0v3uc.iuebi.5qilc.l8d87.c1k6n.7iksq.nkobs.8s5he.raq40.9ff0b.5tj3u.kjtg7.aq59e.hatv7.oioam.mlsr4.pqqcd.cnbjn.pnpi2.1m5rt.k4scg
 =eny2 0v1gt.mc4ca.lfs0m.q1dal.lqobu.mmlbd.2umnp.lj9dr.4pf4s.pvclr.dps96.4a6i8.rt6n9.krp0r.11kqu.ckqe4.1tmat.gr754.463aj.a4b41.jj7qg
+=w *walt:bwsl
+=w w(bipt %bip84, confs 6)
 =inputs ~[[u(value val0) %0 0] [u(value val1) %0 2] [u(value val2) %0 1] [u(value val3) %1 2]]
 =outputs ~[[[%bech32 'bc1q59u5epktervh6fxqay2dlph0wxu9hjnx6v8n66'] value=200.100] [[%bech32 'bc1qlwd7mw33uea5m8r2lsnsrkc7gp2qynrxsfxpfm'] value=200.000]]
-=w *walt:bwsl
-=w w(bipt %bip84)
 
 (~(single-random-draw sut:bwsl [w eny1 923 ~ 100 outputs]) inputs)
 (~(single-random-draw sut:bwsl [w eny2 923 ~ 100 outputs]) inputs)

app/btc-wallet-hook.hoon

@@ -55,7 +55,7 @@
     def   ~(. (default-agent this %|) bowl)
     hc    ~(. +> bowl)
 ::
-++  on-init
+++  on-initb
   ^-  (quip card _this)
   ~&  >  '%btc-wallet-hook initialized'
   :_  this(fam-limit.state fam-limit:defaults)

app/btc-wallet-store.hoon

@@ -128,16 +128,43 @@
     ::
       %generate-address
     (generate-address +.act)
+    ::  TODO: end to end tests
+    ::  %generate-txbu
+    ::  - get txbu and change amount
+    ::  - if txbu is blank, fail
+    ::  - if change is blank, send txbu as update
+    ::  - if change:
+    ::    - generate new change address
+    ::    - add that address+change value to the txbu
+    ::    - send txbu update
+    ::    - send address update
+    ::    - send a request for info on the address (watch it)
     ::
       %generate-txbu
-    =+  w=(~(get by walts) xpub.act)
+    =+  uw=(~(get by walts) xpub.act)
-    ?~  w  ~&(>>> "btc-wallet-store: non-existent xpub" `state)
+    ?~  uw
-    =/  t=(unit txbu)
+      ~|("btc-wallet-store: non-existent xpub" !!)
-      %~  select-utxos  sut
+    ?.  scanned.u.uw
-      [u.w eny.bowl last-block payee.act feyb.act txos.act]
+    ~|("btc-wallet-store: wallet not scanned yet" !!)
-    ?~  t  ~&(>>> "btc-wallet-store: insufficient balance" `state)
+    =/  [tb=(unit txbu) chng=(unit sats)]
-    :_  state
+      %~  with-change  sut
-    ~[(send-update [%generate-txbu xpub.act u.t])]
+      [u.uw eny.bowl last-block payee.act feyb.act txos.act]
+    ?~  tb  ~&(>>> "btc-wallet-store: insufficient balance" `state)
+    ::  if no change, just return txbu
+    ::
+    ?~  chng
+      [~[(send-update [%generate-txbu xpub.act u.tb])] state]
+    =/  [addr=address:btc =idx w=walt]
+      ~(gen-address wad u.uw %1)
+    =+  new-txbu=(~(add-output txb u.tb) addr u.chng)
+    :_  state(walts (~(put by walts) xpub.act w))
+    :~  (send-update [%generate-txbu xpub.act new-txbu])
+        (send-update [%generate-address xpub.act addr ~])
+        %+  send-request  ~[requests-path]
+          :*  %address-info  last-block
+              addr  xpub.act  %1  idx
+          ==
+    ==
     ::
       %add-history-entry
     :: TODO
@@ -294,6 +321,7 @@
 ::
 ++  generate-address
   |=  [=xpub =chyg =peta]
+  ^-  (quip card _state)
   =+  uw=(~(get by walts) xpub)
   ?~  uw
     ~|("btc-wallet-store: non-existent xpub" !!)

lib/btc-wallet-store.hoon

@@ -71,6 +71,30 @@
       (fall max-gap max-gap:defaults)
       (fall confs confs:defaults)
   ==
+::  txb: transaction builder helpers
+::
+++  txb
+  |_  t=txbu
+  ++  value
+    ^-  [in=sats out=sats]
+    :-  %+  roll
+          %+  turn  txis.t
+          |=(=txi value.utxo.txi)
+        add
+    %+  roll
+      (turn txos.t |=(=txo value.txo))
+    add
+  ::
+  ++  fee
+    =/  [in=sats out=sats]  value
+    (sub in out)
+  ::
+  ++  add-output
+    |=  [=address:btc value=sats]
+    ^-  txbu
+    =/  ntxo=txo  [address value]
+    t(txos [ntxo txos.t])
+  --
 ::  wad: door for processing walts (wallets)
 ::        parameterized on a walt and it's chyg account
 ::
@@ -139,6 +163,7 @@
 |_  [w=walt eny=@uvJ last-block=@ud payee=(unit ship) =feyb txos=(list txo)]
   ++  meta-weight  10
   ++  output-weight  31
+  ++  n-txos  (lent txos)
   ::
   ++  target-value
     ^-  sats
@@ -146,9 +171,10 @@
     |=([a=sats b=sats] (add a b))
   ::
   ++  base-weight
+    |=  num-txos=@ud
     ^-  vbytes
     %+  add  meta-weight
-    (mul (lent txos) output-weight)
+    (mul num-txos output-weight)
   ::
   ++  input-weight
     ^-  vbytes
@@ -156,10 +182,15 @@
       ~|("Only bech32 wallets supported" !!)
     102
   ::
+  ++  min-tx-fee
+    ^-  sats
+    %+  mul  feyb
+    (add (base-weight 1) input-weight)
+  ::
   ++  total-vbytes
     |=  selected=(list input)
     ^-  vbytes
-    %+  add  base-weight
+    %+  add  (base-weight n-txos)
     (mul input-weight (lent selected))
   ::  value of an input after fee
   ::  0 if net is <= 0
@@ -169,15 +200,32 @@
     =/  cost  (mul input-weight feyb)
     ?:  (lte val cost)  0
     (sub val cost)
+  ::
   ::  +spendable: whether utxo has enough confs to spend
   ::
   ++  spendable
     |=  =utxo:btc  ^-  ?
     (gte (num-confs last-block utxo) confs.w)
+  ::  +with-change:
+  ::    - choose UTXOs, if there are enough
+  ::    - return txbu and amount of change (if any)
+  ::
+  ++  with-change
+    ^-  [tb=(unit txbu) chng=(unit sats)]
+    =+  tb=select-utxos
+    ?~  tb  [~ ~]
+    =+  fee=~(fee txb u.tb)
+    =/  costs=sats                      ::  cost of this tx + sending another
+      %+  add  min-tx-fee
+      (mul feyb vbytes.u.tb)
+    ?.  (gth fee costs)
+      [tb ~]
+    :-  tb
+    `(sub fee costs)
   ::  Uses naive random selection. Should switch to branch-and-bound later.
   ::
   ++  select-utxos
-    |^  ^-  (unit =txbu)
+    |^  ^-  (unit txbu)
     =/  is=(unit (list input))
       %-  single-random-draw
       %-  zing
@@ -209,7 +257,7 @@
     |=  is=(list input)
     ^-  (unit (list input))
     =/  rng  ~(. og eny)
-    =/  target  (add target-value (mul feyb base-weight))   ::  add base fees to target
+    =/  target  (add target-value (mul feyb (base-weight n-txos)))   ::  add base fees to target
     =|  [select=(list input) total=sats:btc]
     |-  ?:  =(~ is)  ~
     =^  n  rng  (rads:rng (lent is))