FX Rates fetcher

Edge function to fetch fx rates every hour and write to a DB in Supabase

---

Tech used

1. Deno edge functions from Supabase
2. Supabase tables to store data in Postgres
3. PG_NET plugin from Supabase to make edge function calls to add data table
4. PG_CRON plugin to call a corn job to add data periodically.
5. Oak server. Think express for Deno runtime.
6. Deno runtime because supabase supports it. (Almost has Node.js parity for APIs, making porting over easy)

---

Dev setup

1. Sign up for some service that provides FX rates.
2. Sign up for supabase
3. Create a table called 'fx-rates' that is of the schema described below

  create table
  public.fx - rates (
    id uuid not null default gen_random_uuid (),
    timestamp timestamp with time zone null default now(),
    base character varying null,
    quote character varying null,
    price real null,
    constraint fx - rates_pkey primary key (id)
  ) tablespace pg_default;

4. Setup RLS policies to allow access to our DB
5. Enable extension PG_CRON and PG_NET to allow for cron jobs and requests over https
6. Install the supabase CLI locally and link your project.
7. supabase functions new [FUNCTION_NAME] will create a edge function
8. supabase function deploy [FUNCTION_NAME] will deploy them to the edge.
9. supabase secrets set KEY VALUE to set the secret obtained from step 1.
10. Run the below query in SQL_EDITOR to enable the cron job.

select
  cron.schedule(
    'fetch-fxrates-every-hr', -- name of cron
    '1 * * * *', -- every hour
    $$
    select
      net.http_post(
          url:='PROJECT_URL/functions/v1/fetch-fxrates',
          headers:='{"Content-Type": "application/json", "Authorization": "Bearer SERVICE_ROLE_TOKEN"}'::jsonb
        ) as request_id;
    $$
  );

11. Get the SERVICE_ANON_TOKEN from your project to make the requests.

---

Edge functions

1. fetch-fxrates

This will fetch the fxrates from here and store them in our PG table in supabase

To hit the only endpoint of this function

curl -i --location --request POST 'PROJECT_URL/functions/v1/fetch-fxrates' \
  --header 'Authorization: Bearer SERVICE_ROLE_TOKEN' \
  --header 'Content-Type: application/json'

---

2. fx-server

This exposes a endpoint to read and set data to our table with the endpoint PROJECT_URL/functions/v1/fx-server/

ENDPOINT = PROJECT_URL/functions/v1/fx-server/

For health check of this server hit /

curl -i --location --request GET ENDPOINT \
  --header 'Authorization: Bearer SERVICE_ROLE_TOKEN

---

To get all fx rates entries of a base and quote currency. Both are 3 letter uppercase country codes like INR, USD etc.

curl -i --location --request GET ENDPOINT/[base_currency]/[quote_currency] \
  --header 'Authorization: Bearer SERVICE_ROLE_TOKEN'

---

To set a price for a base and quote currency.

Make sure base, quote are 3 letter currency code. price needs to be a float

curl -i --location --request PSOT ENDPOINT \
  --header 'Authorization: Bearer SERVICE_ROLE_TOKEN' \
  --header 'Content-Type: application/json' \
  --data '{"base":"USD", "quote":"INR", "price": 81.01}'

---

Project env variables

PROJECT_URL is https://qodaqyywtayabxzvhjoc.supabase.co

SERVICE_ANON_TOKEN is ...