feat(examples): add grc20factory (gnolang#1913)

Signed-off-by: moul <94029+moul@users.noreply.github.com>

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<details><summary>Contributors' checklist...</summary>

- [ ] Added new tests, or not needed, or not feasible
- [ ] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [ ] Updated the official documentation or not needed
- [ ] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
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- [ ] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

---------

Signed-off-by: moul <94029+moul@users.noreply.github.com>

examples/gno.land/r/demo/grc20factory/gno.mod

@@ -0,0 +1,6 @@
+module gno.land/r/demo/grc20factory
+
+require (
+	gno.land/p/demo/avl v0.0.0-latest
+	gno.land/p/demo/grc/grc20 v0.0.0-latest
+)

examples/gno.land/r/demo/grc20factory/grc20factory.gno

@@ -0,0 +1,164 @@
+package foo20
+
+import (
+	"std"
+	"strconv"
+	"strings"
+
+	"gno.land/p/demo/avl"
+	"gno.land/p/demo/grc/grc20"
+)
+
+// XXX: the p/grc20 library needs a refactor to change names (i.e., adminToken)
+
+type token struct {
+	adminToken *grc20.AdminToken
+	admin      std.Address
+}
+
+var tokens avl.Tree // symbol -> token
+
+func NewToken(name, symbol string, decimals uint, initialMint uint64) {
+	admin := std.PrevRealm().Addr()
+	NewTokenWithAdmin(name, symbol, decimals, initialMint, admin)
+}
+
+func NewTokenWithAdmin(name, symbol string, decimals uint, initialMint uint64, admin std.Address) {
+	exists := tokens.Has(symbol)
+	if exists {
+		panic("token already exists")
+	}
+
+	newToken := grc20.NewAdminToken(name, symbol, decimals)
+	newToken.Mint(admin, initialMint)
+	t := token{
+		adminToken: newToken,
+		admin:      admin,
+	}
+	tokens.Set(symbol, &t)
+}
+
+// method proxies as public functions.
+//
+
+// getters.
+
+func TotalSupply(symbol string) uint64 {
+	token := mustTokenBySymbol(symbol)
+	return token.adminToken.TotalSupply()
+}
+
+func BalanceOf(symbol string, owner std.Address) uint64 {
+	token := mustTokenBySymbol(symbol)
+	balance, err := token.adminToken.BalanceOf(owner)
+	checkErr(err)
+	return balance
+}
+
+func Allowance(symbol string, owner, spender std.Address) uint64 {
+	token := mustTokenBySymbol(symbol)
+	allowance, err := token.adminToken.Allowance(owner, spender)
+	checkErr(err)
+	return allowance
+}
+
+// setters.
+
+func Transfer(symbol string, to std.Address, amount uint64) {
+	token := mustTokenBySymbol(symbol)
+	caller := std.PrevRealm().Addr()
+	err := token.adminToken.Transfer(caller, to, amount)
+	checkErr(err)
+}
+
+func Approve(symbol string, spender std.Address, amount uint64) {
+	token := mustTokenBySymbol(symbol)
+	caller := std.PrevRealm().Addr()
+	err := token.adminToken.Approve(caller, spender, amount)
+	checkErr(err)
+}
+
+func TransferFrom(symbol string, from, to std.Address, amount uint64) {
+	token := mustTokenBySymbol(symbol)
+	caller := std.PrevRealm().Addr()
+	err := token.adminToken.TransferFrom(caller, from, to, amount)
+	if err != nil {
+		panic(err)
+	}
+}
+
+// faucet.
+func Faucet(symbol string) {
+	token := mustTokenBySymbol(symbol)
+	// FIXME: add limits?
+	// FIXME: add payment in gnot?
+	caller := std.PrevRealm().Addr()
+	err := token.adminToken.Mint(caller, 1000*10000) // 1k
+	checkErr(err)
+}
+
+// administration.
+
+func Mint(symbol string, address std.Address, amount uint64) {
+	token := mustTokenBySymbol(symbol)
+	caller := std.PrevRealm().Addr()
+	assertIsAdmin(caller, token.admin)
+	err := token.adminToken.Mint(address, amount)
+	checkErr(err)
+}
+
+func Burn(symbol string, address std.Address, amount uint64) {
+	token := mustTokenBySymbol(symbol)
+	caller := std.PrevRealm().Addr()
+	assertIsAdmin(caller, token.admin)
+	err := token.adminToken.Burn(address, amount)
+	checkErr(err)
+}
+
+// render.
+//
+
+func Render(path string) string {
+	parts := strings.Split(path, "/")
+	c := len(parts)
+
+	switch {
+	case path == "":
+		return "TODO: list existing tokens and admins"
+	case c == 1:
+		symbol := parts[0]
+		token := mustTokenBySymbol(symbol)
+		return token.adminToken.RenderHome()
+	case c == 3 && parts[1] == "balance":
+		symbol := parts[0]
+		token := mustTokenBySymbol(symbol)
+		owner := std.Address(parts[2])
+		balance, _ := token.adminToken.BalanceOf(owner)
+		return strconv.FormatUint(balance, 10)
+	default:
+		return "404\n"
+	}
+}
+
+// helpers.
+//
+
+func assertIsAdmin(caller, admin std.Address) {
+	if caller != admin {
+		panic("restricted access")
+	}
+}
+
+func mustTokenBySymbol(symbol string) *token {
+	t, exists := tokens.Get(symbol)
+	if !exists {
+		panic("token does not exist")
+	}
+	return t.(*token)
+}
+
+func checkErr(err error) {
+	if err != nil {
+		panic(err)
+	}
+}

examples/gno.land/r/demo/grc20factory/grc20factory_test.gno

@@ -0,0 +1,58 @@
+package foo20
+
+import (
+	"std"
+	"testing"
+)
+
+func TestReadOnlyPublicMethods(t *testing.T) {
+	admin := std.Address("g1us8428u2a5satrlxzagqqa5m6vmuze025anjlj")
+	manfred := std.Address("g1u7y667z64x2h7vc6fmpcprgey4ck233jaww9zq")
+	unknown := std.Address("g1jg8mtutu9khhfwc4nxmuhcpftf0pajdhfvsqf5") // valid but never used.
+	NewTokenWithAdmin("Foo", "FOO", 4, 10000000000, admin)
+	NewTokenWithAdmin("Bar", "BAR", 4, 10000000, admin)
+	mustTokenBySymbol("FOO").adminToken.Mint(manfred, 100000000)
+
+	type test struct {
+		name    string
+		balance uint64
+		fn      func() uint64
+	}
+
+	// check balances #1.
+	{
+		tests := []test{
+			{"TotalSupply", 10100000000, func() uint64 { return TotalSupply("FOO") }},
+			{"BalanceOf(admin)", 10000000000, func() uint64 { return BalanceOf("FOO", admin) }},
+			{"BalanceOf(manfred)", 100000000, func() uint64 { return BalanceOf("FOO", manfred) }},
+			{"Allowance(admin, manfred)", 0, func() uint64 { return Allowance("FOO", admin, manfred) }},
+			{"BalanceOf(unknown)", 0, func() uint64 { return BalanceOf("FOO", unknown) }},
+		}
+		for _, tc := range tests {
+			if tc.fn() != tc.balance {
+				t.Errorf("%s: have: %d want: %d", tc.name, tc.fn(), tc.balance)
+			}
+		}
+	}
+	return
+
+	// unknown uses the faucet.
+	std.TestSetOrigCaller(unknown)
+	Faucet("FOO")
+
+	// check balances #2.
+	{
+		tests := []test{
+			{"TotalSupply", 10110000000, func() uint64 { return TotalSupply("FOO") }},
+			{"BalanceOf(admin)", 10000000000, func() uint64 { return BalanceOf("FOO", admin) }},
+			{"BalanceOf(manfred)", 100000000, func() uint64 { return BalanceOf("FOO", manfred) }},
+			{"Allowance(admin, manfred)", 0, func() uint64 { return Allowance("FOO", admin, manfred) }},
+			{"BalanceOf(unknown)", 10000000, func() uint64 { return BalanceOf("FOO", unknown) }},
+		}
+		for _, tc := range tests {
+			if tc.fn() != tc.balance {
+				t.Errorf("%s: have: %d want: %d", tc.name, tc.fn(), tc.balance)
+			}
+		}
+	}
+}