Add Plutus txin script documentation and example

doc/reference/plutus/plutus-minting-script-example.md

@@ -0,0 +1,119 @@
+# Plutus Scripts
+
+## What is a Plutus spending script?
+
+This is a type of Plutus script that is required to validate the spending of a tx output at its own script address. The tx output at the Plutus script address *must* be associated with a datum hash, otherwise, the tx output will be unspendable! The purpose of this datum hash is to encode the state of the contract. A demonstration of this can be seen in [lecture #7](https://youtu.be/oJupInqvJUI) of the Plutus Pioneers Program. The Plutus spending script expects a datum and a redeemer in order to successfully validate the spending of the tx output at its own script address; note that the redeemer is considered to be the user input. These are supplied in the transaction being submitted along with the Plutus script itself and specified transaction execution units.
+
+The transaction execution units are an upper bound or budget of what will be spent to execute the Plutus script. If you don't specify a high enough value to cover script execution, your transaction will still be successful (provided it is a valid tx) but you will lose your collateral. The collateral is the transaction input(s) you specify to be consumed if your script fails to execute. There is a protocol parameter `collateralPercent` that determines what percentage of your inputs you must supply as collateral.
+
+*Note that in order to use a tx input as collateral, it **cannot** reside at a script address; it must reside at a ‘normal’ payment address and it cannot contain any multi-assets.*
+
+### An example of using a Plutus spending script
+
+Below is an example that shows how to use a Plutus spending script. This is a step-by-step
+process involving:
+
++ the creation of the `AlwaysSucceeds` Plutus txin script
++ sending ADA to the Plutus script address
++ spending ADA at the Plutus script address
+
+In this example we will use the [AlwaysSucceeds](../../../plutus-example/plutus-example/src/Cardano/PlutusExample/AlwaysSucceeds.hs) Plutus spending script. In order to execute a Plutus spending script, we require the following:
+
+- Collateral tx input(s) - these are provided and are forfeited in the event the Plutus script fails to execute.
+- A Plutus tx output with accompanying datum hash. This is the tx output that sits at the Plutus script address. It must have a datum hash, otherwise, it is unspendable.
+- The Plutus script serialized in the text envelope format. `cardano-cli` expects Plutus scripts to be serialized in the text envelope format.
+
+#### Creating the `AlwaysSucceeds` Plutus spending script
+
+The plutus-example executable will automagically generate several Plutus scripts in the CLI-compatiable text envelope format.
+
+Run the following commands:
+
+```bash
+cd plutus-example
+
+cabal run exe:plutus-example
+```
+
+This will output `always-succeeds-txin.plutus` in the `generated-plutus-scripts` dir.
+
+#### Setting up a local Alonzo node cluster
+
+There is a convenient script that will set up an Alonzo cluster immediately on your local machine.
+
+Run the following command:
+
+```bash
+cabal install cardano-cli
+cabal install cardano-node
+./scripts/byron-to-alonzo/mkfiles.sh alonzo
+```
+
+Follow the instructions displayed in the terminal to start your Alonzo cluster.
+
+#### Sending ADA to the script address
+
+In order to require a Plutus script to validate the spending of a tx ouput, we must put the tx output at the script address of the said Plutus script. However, before we do that, we must create a datum hash:
+
+```bash
+> cardano-cli transaction hash-script-data --script-data-value 42
+> 9e1199a988ba72ffd6e9c269cadb3b53b5f360ff99f112d9b2ee30c4d74ad88b
+```
+In this example, the script we are using always succeeds so we can use any datum hash. We calculate the script address as follows:
+
+```bash
+> cardano-cli address build --payment-script-file plutus-example/generated-plutus-scripts/always-succeeds-txin.plutus  --testnet-magic 42
+> addr_test1wzeqkp6ne3xm6gz39l874va4ujgl4kr0e46pf3ey8xsu3jsgkpcj2
+```
+
+Now, we should create the tx that will send ADA to the script address of our `AlwaysSucceeds` script:
+
+```bash
+cardano-cli transaction build-raw \
+  --alonzo-era \
+  --fee 0 \
+  --tx-in $txin \
+  --tx-out "addr_test1wzeqkp6ne3xm6gz39l874va4ujgl4kr0e46pf3ey8xsu3jsgkpcj2+$lovelace" \
+  --tx-out-datum-hash 9e1199a988ba72ffd6e9c269cadb3b53b5f360ff99f112d9b2ee30c4d74ad88b \
+  --out-file create-datum-output.body
+
+cardano-cli transaction sign \
+  --tx-body-file create-datum-output.body \
+  --testnet-magic 42 \
+  --signing-key-file $UTXO_SKEY \
+  --out-file create-datum-output.tx
+```
+
+#### Spending ADA at the script address
+
+Now that there is ADA at our script address, we must construct the appropriate transaction in order to spend it.
+
+`$plutusutxotxin` - This is the tx input that sits at the Plutus script address (NB: It has a datum hash).
+`$plutusrequiredtime` and `$plutusrequiredspace` - These make up the Plutus script execution budget and are part of the `$txfee`
+`tx-in-redeemer-value` - We must also supply a redeemer value even though the Plutus script will succeed regardless of the redeemer.
+
+```bash
+cardano-cli transaction build-raw \
+  --alonzo-era \
+  --fee "$txfee" \
+  --tx-in $plutusutxotxin \
+  --tx-in-collateral $txinCollateral \
+  --tx-out "$dummyaddress+$spendable" \
+  --tx-in-script-file $plutusscriptinuse \
+  --tx-in-datum-value 42  \
+  --protocol-params-file pparams.json\
+  --tx-in-redeemer-value 42 \
+  --tx-in-execution-units "($plutusrequiredtime, $plutusrequiredspace)" \
+  --out-file test-alonzo.body
+
+cardano-cli transaction sign \
+  --tx-body-file test-alonzo.body \
+  --testnet-magic 42 \
+  --signing-key-file "${UTXO_SKEY}" \
+  --out-file alonzo.tx
+```
+
+If there is ADA at `$dummyaddress` then the Plutus script was successfully executed. Conversely, if the Plutus script failed, the collateral input would have been consumed.
+
+You can use the [example-txin-locking-plutus-script.sh](../../../scripts/plutus/example-txin-locking-plutus-script.sh) in conjunction with [mkfiles.sh alonzo](../../../scripts/byron-to-alonzo/mkfiles.sh) script to automagically run the `AlwaysSucceeds` script.
+

doc/reference/simple-scripts.md

@@ -1,4 +1,4 @@
-# Scripts
+# Simple Scripts
 
 From the Shelley era onwards, Cardano has supported scripts and script
 addresses.