Add How to create a Crypto Coin example (#4)

my-crypto-coin/.gitignore

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+.idea
+.vscode

my-crypto-coin/cli/mcc/balances.go

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+package main
+
+import (
+	"github.com/spf13/cobra"
+	"my-crypto-coin/ledger"
+	"fmt"
+	"os"
+)
+
+func balancesCmd() *cobra.Command {
+	var balancesCmd = &cobra.Command{
+		Use:   "balances",
+		Short: "Interact with balances (list...).",
+		Run: func(cmd *cobra.Command, args []string) {
+		},
+	}
+
+	balancesCmd.AddCommand(balancesListCmd)
+
+	return balancesCmd
+}
+
+var balancesListCmd = &cobra.Command{
+	Use:   "list",
+	Short: "Lists all balances.",
+	Run: func(cmd *cobra.Command, args []string) {
+		state, err := ledger.SyncState()
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		defer state.Close()
+
+		fmt.Println("Accounts balances:")
+		fmt.Println("__________________")
+		fmt.Println("")
+		for account, balance := range state.Balances {
+			fmt.Println(fmt.Sprintf("%s: %d", account, balance))
+		}
+	},
+}

my-crypto-coin/cli/mcc/main.go

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+package main
+
+import (
+	"github.com/spf13/cobra"
+	"os"
+	"fmt"
+)
+
+func main() {
+	var mccCmd = &cobra.Command{
+		Use:   "mcc",
+		Short: "My Crypto Coin CLI",
+		Run: func(cmd *cobra.Command, args []string) {
+		},
+	}
+
+	mccCmd.AddCommand(versionCmd)
+	mccCmd.AddCommand(balancesCmd())
+	mccCmd.AddCommand(txCmd())
+
+	err := mccCmd.Execute()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}

my-crypto-coin/cli/mcc/tx.go

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+package main
+
+import (
+	"github.com/spf13/cobra"
+	"my-crypto-coin/ledger"
+	"fmt"
+	"os"
+)
+
+func txCmd() *cobra.Command {
+	var txsCmd = &cobra.Command{
+		Use:   "tx",
+		Short: "Interact with transactions (new...).",
+		Run: func(cmd *cobra.Command, args []string) {
+		},
+	}
+
+	txsCmd.AddCommand(newTxCmd())
+
+	return txsCmd
+}
+
+
+func newTxCmd() *cobra.Command {
+	var cmd = &cobra.Command{
+		Use:   "new",
+		Short: "Adds new TX to the ledger.",
+		Run: func(cmd *cobra.Command, args []string) {
+			from, _ := cmd.Flags().GetString("from")
+			to, _ := cmd.Flags().GetString("to")
+			value, _ := cmd.Flags().GetUint("value")
+
+			tx := ledger.NewTx(ledger.NewAccount(from), ledger.NewAccount(to), value)
+
+			state, err := ledger.SyncState()
+			if err != nil {
+				fmt.Fprintln(os.Stderr, err)
+				os.Exit(1)
+			}
+			defer state.Close()
+
+			err = state.WriteToLedger(tx)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, err)
+				os.Exit(1)
+			}
+
+			fmt.Println("TX successfully added to the ledger.")
+		},
+	}
+
+	cmd.Flags().String("from", "", "From what account to send coins")
+	cmd.MarkFlagRequired("from")
+
+	cmd.Flags().String("to", "", "To what account to send coins")
+	cmd.MarkFlagRequired("to")
+
+	cmd.Flags().Uint("value", 0, "How many coins to send")
+	cmd.MarkFlagRequired("value")
+
+	return cmd
+}

my-crypto-coin/cli/mcc/version.go

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+package main
+
+import (
+	"fmt"
+	"github.com/spf13/cobra"
+)
+
+const Major = "0"
+const Minor = "1"
+const Fix = "0"
+const Verbal = "Genesis"
+
+var versionCmd = &cobra.Command{
+	Use:   "version",
+	Short: "Describes version.",
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Println(fmt.Sprintf("Version: %s.%s.%s-beta %s", Major, Minor, Fix, Verbal))
+	},
+}

my-crypto-coin/go.mod

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+module my-crypto-coin
+
+go 1.16
+
+require github.com/spf13/cobra v1.4.0 // indirect

my-crypto-coin/go.sum

@@ -0,0 +1,10 @@
+github.com/cpuguy83/go-md2man/v2 v2.0.1/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
+github.com/inconshreveable/mousetrap v1.0.0 h1:Z8tu5sraLXCXIcARxBp/8cbvlwVa7Z1NHg9XEKhtSvM=
+github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANytuPF1OarO4DADm73n8=
+github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/spf13/cobra v1.4.0 h1:y+wJpx64xcgO1V+RcnwW0LEHxTKRi2ZDPSBjWnrg88Q=
+github.com/spf13/cobra v1.4.0/go.mod h1:Wo4iy3BUC+X2Fybo0PDqwJIv3dNRiZLHQymsfxlB84g=
+github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
+github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=

my-crypto-coin/ledger/genesis.go

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+package ledger
+
+import (
+	"io/ioutil"
+	"encoding/json"
+)
+
+type Genesis struct {
+	Balances map[Account]uint `json:"balances"`
+}
+
+func loadGenesis(path string) (Genesis, error) {
+	genesisFileContent, err := ioutil.ReadFile(path)
+	if err != nil {
+		return Genesis{}, err
+	}
+
+	var loadedGenesis Genesis
+
+	err = json.Unmarshal(genesisFileContent, &loadedGenesis)
+	if err != nil {
+		return Genesis{}, err
+	}
+
+	return loadedGenesis, nil
+} 

my-crypto-coin/ledger/genesis.json

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+{
+  "genesis_time": "2022-04-12T00:00:00.000000000Z",
+  "chain_id": "our-blockchain",
+  "balances": {
+    "alice": 1000000
+  }
+}

my-crypto-coin/ledger/ledger.db

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+{"from":"alice","to":"bob","value":10}
+{"from":"alice","to":"alice","value":3}
+{"from":"alice","to":"alice","value":500}
+{"from":"alice","to":"bob","value":100}
+{"from":"bob","to":"alice","value":5}
+{"from":"bob","to":"carol","value":10}
+{"from":"alice","to":"carol","value":10}

my-crypto-coin/ledger/state.go

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+package ledger
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"bufio"
+	"encoding/json"
+)
+
+type State struct {
+	Balances  map[Account]uint
+	txMempool []Tx
+
+	dbFile *os.File
+}
+
+
+func SyncState() (*State, error)  {
+	cwd, err := os.Getwd()
+	if err != nil {
+		return nil, err
+	}
+
+	gen, err := loadGenesis(filepath.Join(cwd, "ledger", "genesis.json"))
+	if err != nil {
+		return nil, err
+	}
+
+	balances := make(map[Account]uint)
+	for account, balance := range gen.Balances {
+		balances[account] = balance
+	}
+
+	file, err := os.OpenFile(filepath.Join(cwd, "ledger", "ledger.db"), os.O_APPEND|os.O_RDWR, 0600)
+	if err != nil {
+		return nil, err
+	}
+
+	scanner := bufio.NewScanner(file)
+
+	state := &State{balances, make([]Tx, 0), file}
+
+	for scanner.Scan() {
+		if err := scanner.Err(); err != nil {
+			return nil, err
+		}
+
+		var transaction Tx
+		json.Unmarshal(scanner.Bytes(), &transaction)
+
+		if err := state.writeTransaction(transaction); err != nil {
+			return nil, err
+		}
+	}
+
+	return state, nil
+}
+
+func (s *State) writeTransaction(tx Tx) error {
+	if s.Balances[tx.From] < tx.Value {
+		return fmt.Errorf("insufficient balance")
+	}
+
+	s.Balances[tx.From] -= tx.Value
+	s.Balances[tx.To] += tx.Value
+
+	return nil
+}
+
+func (s *State) Close() {
+	s.dbFile.Close()
+}
+
+func (s *State) WriteToLedger(tx Tx) error {
+	if err := s.writeTransaction(tx); err != nil {
+		return err
+	}
+
+	s.txMempool = append(s.txMempool, tx)
+
+	mempool := make([]Tx, len(s.txMempool))
+	copy(mempool, s.txMempool)
+
+	for i := 0; i < len(mempool); i++ {
+		txJson, err := json.Marshal(mempool[i])
+		if err != nil {
+			return err
+		}
+
+		if _, err = s.dbFile.Write(append(txJson, '\n')); err != nil {
+			return err
+		}
+		s.txMempool = s.txMempool[1:]
+	}
+
+	return nil
+}

my-crypto-coin/ledger/tx.go

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+package ledger
+
+type Account string
+
+type Tx struct {
+	From  Account `json:"from"`
+	To    Account `json:"to"`
+	Value uint    `json:"value"`
+}
+
+func NewAccount(value string) Account {
+	return Account(value)
+}
+
+func NewTx(from Account, to Account, value uint) Tx {
+	return Tx{from, to, value}
+}