#!/usr/bin/env bash
#
# A minimal HabitGrid backend that has nothing to do with markdown, Obsidian or
# Syncthing. It exists to prove the plugin's front-end talks to the *contract*
# and not to one particular implementation: if this bash script works, so does
# a REST client, a SQLite reader, or anything else that prints the same JSON.
#
# Counts live in HABITGRID_OPT_STATE_FILE, one `name=count` line per habit.
# Everything it needs arrives the way the contract says it does: the verb as
# argv, the options as HABITGRID_OPT_* environment variables.

set -euo pipefail

state_file="${HABITGRID_OPT_STATE_FILE:-}"
today="${HABITGRID_TODAY:-$(date +%F)}"
yesterday="$(date -d "$today -1 day" +%F)"

if [[ -z "$state_file" ]]; then
  echo "fake-backend: HABITGRID_OPT_STATE_FILE is not set" >&2
  exit 1
fi

# Two habits, one with a goal and one without, so the front-end's two level
# formulas both get exercised.
habit_names=(coffee walk)
habit_goals=(3 null)

count_of() {
  local name="$1"
  [[ -f "$state_file" ]] || { echo 0; return; }
  local line
  line="$(grep -m1 "^$name=" "$state_file" || true)"
  echo "${line#*=}" | grep -qE '^[0-9]+$' && echo "${line#*=}" || echo 0
}

set_count() {
  local name="$1" value="$2" rest=""
  [[ -f "$state_file" ]] && rest="$(grep -v "^$name=" "$state_file" || true)"
  { [[ -n "$rest" ]] && printf '%s\n' "$rest"; printf '%s=%s\n' "$name" "$value"; } >"$state_file"
}

goal_of() {
  local name="$1" index=0
  for known in "${habit_names[@]}"; do
    [[ "$known" == "$name" ]] && { echo "${habit_goals[$index]}"; return; }
    index=$((index + 1))
  done
  echo "null"
}

is_known() {
  local name="$1"
  for known in "${habit_names[@]}"; do
    [[ "$known" == "$name" ]] && return 0
  done
  return 1
}

# {"name":..,"goal":..,"today":..,"history":{..}} -- yesterday is always 1 so
# the tests have a streak to look at.
print_habit() {
  local name="$1"
  printf '{"name":"%s","goal":%s,"today":%s,"history":{"%s":%s,"%s":1}}' \
    "$name" "$(goal_of "$name")" "$(count_of "$name")" \
    "$today" "$(count_of "$name")" "$yesterday"
}

case "${1:-}" in
  list)
    printf '{"habits":['
    separator=""
    for name in "${habit_names[@]}"; do
      printf '%s' "$separator"
      print_habit "$name"
      separator=","
    done
    printf ']}\n'
    ;;
  increment)
    name="${2:-}"
    if ! is_known "$name"; then
      echo "fake-backend: no such habit: $name" >&2
      exit 1
    fi
    set_count "$name" "$(( $(count_of "$name") + 1 ))"
    print_habit "$name"
    printf '\n'
    ;;
  *)
    echo "fake-backend: usage: fake-backend list|increment <name>" >&2
    exit 2
    ;;
esac