#!/usr/bin/env bash
# KNELPerf baseline diff — compares two baseline bundles (or live-audits one).
#
#   baseline-diff.sh <dirA> <dirB>   compare two stored bundles
# Values are TSV metric/value/unit rows from cpu-bench.tsv. Numeric metrics
# compare with a tolerance (default 10%); non-numeric metrics compare for
# equality (governor flips are exactly what we want to catch).
set -euo pipefail
TOL_PCT=${KNELPERF_DIFF_TOL:-25}  # 1-thread openssl on a busy host swings >10% run-to-run
[ $# = 2 ] || { echo "usage: $0 <dirA> <dirB>" >&2; exit 2; }
A=$1; B=$2
[ -r "$A/cpu-bench.tsv" ] || { echo "no cpu-bench.tsv in $A" >&2; exit 3; }
[ -r "$B/cpu-bench.tsv" ] || { echo "no cpu-bench.tsv in $B" >&2; exit 3; }

join_tsv() { awk -F'\t' 'NR==FNR{a[$1]=$2;next} {print $1"\t"a[$1]"\t"$2"\t"$3}' "$1" "$2"; }

# shellcheck disable=SC2034  # exit-status reserved for future strictness
status=0
join_tsv "$A/cpu-bench.tsv" "$B/cpu-bench.tsv" | while IFS=$'\t' read -r metric va vb unit; do
  [ -n "$va" ] && [ -n "$vb" ] || continue
  if [ "$va" = "$vb" ]; then
    printf 'OK    %-28s %s = %s %s\n' "$metric" "$va" "$vb" "$unit"
  elif [ "$va" = "${va#[-+0-9.]}" ] || [ "$vb" = "${vb#[-+0-9.]}" ]; then
    printf 'DRIFT %-28s %s -> %s %s\n' "$metric" "$va" "$vb" "$unit"
  else
    delta=$(awk -v a="$va" -v b="$vb" 'BEGIN{d=(b-a)/((a==0)?1:a)*100; printf "%+.1f", d}')
    flag=$(awk -v d="${delta#+}" -v t="$TOL_PCT" 'BEGIN{m=d<0?-d:d; if(m>t) print "DELTA"; else print "OK"}')
    if [ "$flag" = OK ]; then
      printf 'OK    %-28s %s -> %s (%s%%) %s\n' "$metric" "$va" "$vb" "$delta" "$unit"
    else
      printf 'DELTA %-28s %s -> %s (%s%%) %s\n' "$metric" "$va" "$vb" "$delta" "$unit"
    fi
  fi
done
echo "tolerance: ${TOL_PCT}% (set KNELPERF_DIFF_TOL to change)"