must-be-carbon/feat/2377 add supply endpoint for KLIMA & BCT (#2382)

* feat(app): add API endpoint for supply

* chore(github): fix typo in PR template

* feat(app): add support for supply by token

* feat(app): shorten api paths

* refactor(app): use getTokenDecimals

* refactor(app): make type a required param

.github/pull_request_template.md

@@ -16,7 +16,7 @@ Also related to <issue-number>
 
 ## How to Test
 <!--
- Pleas eprovide a shrot description of how a reviewer can confirm the changes
+ Please provide a short description of how a reviewer can confirm the changes
 -->
 
 1. _step1_

app/pages/api/supply.ts

@@ -0,0 +1,99 @@
+import {
+  getContract,
+  getStaticProvider,
+  getTokenDecimals,
+} from "@klimadao/lib/utils";
+import { formatUnits } from "ethers/lib/utils";
+import { DEFAULT_NETWORK } from "lib/constants";
+import type { NextApiRequest, NextApiResponse } from "next";
+
+export const config = {
+  api: {},
+  // Specifies the maximum allowed duration for this function to execute (in seconds)
+  maxDuration: 5,
+};
+
+type APIResponse =
+  | number
+  | {
+      totalSupply: number;
+      circulatingSupply: number;
+    }
+  | {
+      error: string;
+    };
+
+const DEFAULT_TOKENS = ["klima", "bct"];
+
+/**
+ * @description fetch total supply for a token
+ * @param req
+ * @param res
+ * @example GET /api/supply?type=total&token=klima Returns number
+ * @example GET /api/supply?type=circulating&token=klima Return number
+ */
+export default async function handler(
+  req: NextApiRequest,
+  res: NextApiResponse<APIResponse>
+) {
+  try {
+    switch (req.method) {
+      case "GET":
+        const { type, token } = req.query;
+
+        if (!token || !type) {
+          return res
+            .status(400)
+            .send({ error: "Token or type is missing from params" });
+        }
+
+        if (typeof token !== "string") {
+          return res.status(400).send({ error: "Token should be a string" });
+        }
+
+        const targetToken = DEFAULT_TOKENS.find((t) => t === token);
+
+        if (!targetToken) {
+          return res.status(400).send({ error: "Invalid token" });
+        }
+
+        const provider = getStaticProvider({
+          chain: "polygon",
+        });
+
+        const contract = getContract({
+          // TODO: Improve typing by exporting ContractName type from lib
+          contractName: targetToken as "klima" | "bct",
+          network: DEFAULT_NETWORK,
+          provider,
+        });
+
+        const totalSupply = await contract.totalSupply();
+
+        if (!totalSupply) {
+          return res.status(500).send({ error: "Failed to get total supply" });
+        }
+
+        const totalSupplyNum = Number(
+          formatUnits(totalSupply, getTokenDecimals(targetToken))
+        );
+
+        switch (type) {
+          case "total":
+          case "circulating":
+            return res.status(200).send(totalSupplyNum);
+          default:
+            return res.status(400).send({ error: "Invalid type" });
+        }
+
+      default:
+        res.setHeader("Allow", ["GET"]);
+        return res
+          .status(405)
+          .send({ error: `Method ${req.method} Not Allowed` });
+    }
+  } catch (error) {
+    console.error(error);
+    return res.status(500).send({ error: "Internal Server Error" });
+  }
+}