#!/usr/bin/env bash
# 1. Shebang: run this file with the first `bash` on the PATH. On macOS that
#    can be the old /bin/bash 3.2, so this script avoids newer features.
#
# sample-script.sh: summarise a log file by level (INFO, WARN, ERROR).
# Free sample from 99helpers.com/file-types/sh
# Run:  bash sample-script.sh                 (uses a built-in sample log)
#       bash sample-script.sh -n 2 app.log    (show the last 2 errors)
#       bash sample-script.sh -f app.log      (exit with status 1 if errors)
#       chmod +x sample-script.sh && ./sample-script.sh -h

# 2. "Strict mode": stop on the first failing command (-e), treat unset
#    variables as errors (-u), and let a failure anywhere in a pipeline
#    count (-o pipefail). Not a cure-all, but it catches many mistakes.
set -euo pipefail

# 3. Read-only settings. ${0##*/} strips the folder from the script's path.
readonly SCRIPT_NAME="${0##*/}"
readonly VERSION="1.0"
show_errors=3
fail_on_error=false

# 4. A function. Here-documents (<<EOF) print several lines as written.
usage() {
  cat <<EOF
Usage: $SCRIPT_NAME [-n NUMBER] [-f] [-h] [FILE]
Count INFO, WARN and ERROR lines in FILE (or a built-in sample log)
and show the last NUMBER errors (default: $show_errors).
  -f  exit with status 1 if the log contains errors
EOF
}

sample_log() {
  cat <<'EOF'
2026-10-27 09:00:01 INFO  server started on port 8080
2026-10-27 09:00:05 INFO  connected to database
2026-10-27 09:12:44 WARN  slow request: /reports took 2.4 s
2026-10-27 09:13:02 ERROR upload failed: file too large
2026-10-27 09:15:10 INFO  user ada.example signed in
2026-10-27 09:20:31 ERROR template not found: invoice.html
2026-10-27 09:21:00 WARN  disk 81% full
2026-10-27 09:30:00 INFO  nightly report queued
EOF
}

# 5. Options with getopts: "n:" means -n takes a value, in $OPTARG.
while getopts ":n:fhv" option; do
  case "$option" in
    n) show_errors="$OPTARG" ;;
    f) fail_on_error=true ;;
    h) usage; exit 0 ;;
    v) echo "$SCRIPT_NAME $VERSION"; exit 0 ;;
    :) echo "$SCRIPT_NAME: -$OPTARG needs a value" >&2; exit 2 ;;
    *) usage >&2; exit 2 ;;
  esac
done
shift $((OPTIND - 1))

case "$show_errors" in
  '' | *[!0-9]*) echo "$SCRIPT_NAME: -n needs a whole number" >&2; exit 2 ;;
esac

# 6. Pick the input: a readable file, or the built-in sample.
#    ${1:-} gives "" instead of an error under set -u when there is no $1.
file="${1:-}"
if [[ -n "$file" && ! -r "$file" ]]; then
  echo "$SCRIPT_NAME: cannot read '$file'" >&2
  exit 1
fi

info=0 warn=0 error=0
errors=()

# 7. Read line by line. IFS= and -r keep spaces and backslashes intact;
#    case matches each line against glob patterns.
while IFS= read -r line || [[ -n "$line" ]]; do
  case "$line" in
    *" INFO "*)  info=$((info + 1)) ;;
    *" WARN "*)  warn=$((warn + 1)) ;;
    *" ERROR "*) error=$((error + 1)); errors+=("$line") ;;
  esac
done < <(if [[ -n "$file" ]]; then cat -- "$file"; else sample_log; fi)

# 8. printf rather than echo: it behaves the same in every shell.
#    Always "quote" variables, so spaces in values can't split them apart.
printf '%-6s %5d\n' INFO "$info" WARN "$warn" ERROR "$error"

# 9. Arrays: ${#errors[@]} is the count. Checking it first keeps bash 3.2
#    happy under set -u, where an empty array counts as unset.
if (( ${#errors[@]} > 0 && show_errors > 0 )); then
  start=$(( ${#errors[@]} > show_errors ? ${#errors[@]} - show_errors : 0 ))
  echo "Last errors:"
  for (( i = start; i < ${#errors[@]}; i++ )); do
    printf '  %s\n' "${errors[i]}"
  done
fi

# 10. The exit status: 0 means success, anything else failure. With -f, a
#     calling script or CI job can stop when the log contains errors.
if [[ "$fail_on_error" == true ]] && (( error > 0 )); then
  exit 1
fi
exit 0