Epoch summary corrections function and cron script (#230)

## Description
Function compares block / transaction totals currently recorded in epoch
table with reality and performs corrections if necessary. First time the
job is run it scans epochs 0 till current and creates control table
entry, on subsequent runs it scans 2 most recent epochs looking for
discrepancies. Function is invoked from a shell script that gets
installed as a part of cron job setup in guild-operators repository
change.

---------

Co-authored-by: RdLrT <[email protected]>

files/grest/cron/jobs/epoch-summary-corrections-update.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+DB_NAME=cexplorer
+
+tip=$(psql ${DB_NAME} -qbt -c "SELECT EXTRACT(EPOCH FROM time)::integer FROM block ORDER BY id DESC LIMIT 1;" | xargs)
+
+if [[ $(( $(date +%s) - tip )) -gt 300 ]]; then
+  echo "$(date +%F_%H:%M:%S) Skipping as database has not received a new block in past 300 seconds!" && exit 1
+fi
+
+echo "$(date +%F_%H:%M:%S) Running epoch summary corrections update..."
+psql ${DB_NAME} -qbt -c "SELECT GREST.EPOCH_SUMMARY_CORRECTIONS_UPDATE();" 1>/dev/null 2>&1
+echo "$(date +%F_%H:%M:%S) Job done!"

files/grest/rpc/epoch/epoch_summary_corrections_update.sql

@@ -0,0 +1,65 @@
+CREATE OR REPLACE function grest.epoch_summary_corrections_update()
+RETURNS void
+LANGUAGE plpgsql
+AS $$
+DECLARE
+  curr_epoch_record record := null;
+  latest_epoch bigint = (SELECT MAX(no) FROM epoch);
+  last_epoch_checked bigint = coalesce((SELECT last_value::bigint FROM grest.control_table WHERE key = 'last_epoch_summary_data_checked'), -1);
+BEGIN
+  RAISE NOTICE 'Last validated epoch was %', last_epoch_checked;
+  IF last_epoch_checked < 0 THEN
+    RAISE NOTICE 'Inserting initial record for key last_epoch_summary_data_checked';
+    INSERT INTO grest.control_table values('last_epoch_summary_data_checked', 0, null);
+  END IF;
+  FOR curr_epoch_record IN (
+    SELECT b.epoch_no
+    FROM
+      (SELECT
+        no,
+        blk_count AS epoch_blk_count,
+        tx_count AS epoch_tx_count
+      FROM epoch
+      WHERE no > last_epoch_checked - 2) AS e,
+      (SELECT
+        epoch_no,
+        COUNT(block_no) AS block_blk_count,
+        SUM(tx_count) AS block_tx_count
+      FROM block
+      WHERE epoch_no > (last_epoch_checked - 2)
+      GROUP BY epoch_no) AS b
+      WHERE e.no = b.epoch_no
+        AND (e.epoch_blk_count != b.block_blk_count OR e.epoch_tx_count != b.block_tx_count)
+      ORDER BY b.epoch_no
+  ) LOOP
+    RAISE NOTICE 'Need to fix up data for epoch %', curr_epoch_record;
+    WITH agg_table AS
+      ( SELECT
+          MIN(block.epoch_no) AS epoch_no,
+          SUM(tx.out_sum) AS out_sum,
+          SUM(tx.fee) AS fee_sum,
+          MIN(block.time) AS start_time,
+          MAX(block.time) AS end_time,
+          COUNT(tx.id) AS tx_count,
+          COUNT(distinct block.block_no) AS blk_count
+        FROM block
+        LEFT JOIN tx ON block.id = tx.block_id
+        WHERE block.epoch_no = curr_epoch_record.epoch_no
+      )
+
+    UPDATE epoch
+      SET
+        out_sum = COALESCE(agg_table.out_sum, 0),
+        fees = COALESCE(agg_table.fee_sum, 0),
+        tx_count = agg_table.tx_count,
+        blk_count = agg_table.blk_count,
+        start_time = agg_table.start_time,
+        end_time = agg_table.end_time
+      FROM agg_table
+      WHERE no = agg_table.epoch_no ;
+
+    RAISE NOTICE 'Epoch row for epoch % corrected', curr_epoch_record;
+  END LOOP;
+  UPDATE grest.control_table SET last_value = latest_epoch::text WHERE key = 'last_epoch_summary_data_checked';
+END;
+$$;