#!/usr/bin/env bash

# Compare the current tmux version against one or more version constraints.
#
# Each constraint pairs an operator and version in a single argument,
# e.g. ">= 3.2". Multiple constraints can be joined with the logical operators
# `and` / `or`, where `and` binds tighter than `or` (standard precedence). This
# allows a single invocation to express a range without spawning the script
# multiple times.
#
# Exit: 0 if the whole expression is true, 1 if false
#
# Examples:
#   check-version.sh ">= 3.2"
#   check-version.sh ">= 3.2" and "< 3.3"
#   check-version.sh "< 2.9" or ">= 3.4"

set -euo pipefail

usage() {
  cat >&2 <<'EOF'
usage: check-version.sh <constraint> [and|or <constraint> ...]
  constraint: <operator> <version>, e.g. ">= 3.2"
  operators:  < <= == >= >
  logical:    and or  (and binds tighter than or)
EOF
}

if [[ ${1:-} == "-h" || ${1:-} == "--help" ]]; then
  usage
  exit 0
fi

if [[ $# -eq 0 ]]; then
  usage
  exit 1
fi

# Extract tmux version (e.g., "tmux 3.3a" -> "3.3a")
current_version=$(tmux -V | sed 's/^tmux //')

# Compare two version strings
# Returns: -1 if v1 < v2, 0 if v1 == v2, 1 if v1 > v2
compare_versions() {
  local v1="$1"
  local v2="$2"

  # Strip trailing letters (e.g., "3.3a" -> "3.3") and save them
  local v1_suffix="${v1##*[0-9]}"
  local v2_suffix="${v2##*[0-9]}"
  v1="${v1%[a-zA-Z]*}"
  v2="${v2%[a-zA-Z]*}"

  # Split into components
  IFS='.' read -ra v1_parts <<< "$v1"
  IFS='.' read -ra v2_parts <<< "$v2"

  # Compare numeric parts
  local max_len=$(( ${#v1_parts[@]} > ${#v2_parts[@]} ? ${#v1_parts[@]} : ${#v2_parts[@]} ))
  for ((i = 0; i < max_len; i++)); do
    local p1="${v1_parts[i]:-0}"
    local p2="${v2_parts[i]:-0}"
    if ((p1 < p2)); then
      echo -1
      return
    elif ((p1 > p2)); then
      echo 1
      return
    fi
  done

  # Numeric parts equal, compare suffixes (no suffix < a < b < ...)
  # A letter suffix indicates a patch release, so 3.6a > 3.6
  if [[ -z "$v1_suffix" && -n "$v2_suffix" ]]; then
    echo -1
    return
  elif [[ -n "$v1_suffix" && -z "$v2_suffix" ]]; then
    echo 1
    return
  elif [[ "$v1_suffix" < "$v2_suffix" ]]; then
    echo -1
    return
  elif [[ "$v1_suffix" > "$v2_suffix" ]]; then
    echo 1
    return
  fi

  echo 0
}

# Evaluate a single constraint (e.g. ">= 3.2") against the current version.
# Returns 0 (true) or 1 (false); exits on a malformed constraint.
eval_constraint() {
  local constraint="$1"
  local operator version
  read -r operator version <<< "$constraint"

  if [[ -z "$operator" || -z "$version" ]]; then
    echo "error: invalid constraint: '$constraint' (expected '<operator> <version>', e.g. '>= 3.2')" >&2
    usage
    exit 1
  fi

  local result
  result=$(compare_versions "$current_version" "$version")

  case "$operator" in
    '<')  [[ "$result" -eq -1 ]] ;;
    '<=') [[ "$result" -le 0 ]] ;;
    '==') [[ "$result" -eq 0 ]] ;;
    '>=') [[ "$result" -ge 0 ]] ;;
    '>')  [[ "$result" -eq 1 ]] ;;
    *)
      echo "error: invalid operator: '$operator'" >&2
      usage
      exit 1 ;;
  esac
}

# Walk the alternating constraint/logical sequence, accumulating each `and`
# group (1 = true) and folding completed groups into the `or` result. Truth
# values are tracked as ints and converted to an exit code at the end.
or_result=0
and_result=1
expect=constraint

for token in "$@"; do
  if [[ "$expect" == "constraint" ]]; then
    case "$token" in
      and | or)
        echo "error: expected a constraint, got logical operator: $token" >&2
        usage
        exit 1 ;;
    esac
    if eval_constraint "$token"; then
      and_result=$(( and_result & 1 ))
    else
      and_result=$(( and_result & 0 ))
    fi
    expect=logical
  else
    case "$token" in
      and)
        ;;
      or)
        or_result=$(( or_result | and_result ))
        and_result=1 ;;
      *)
        echo "error: expected 'and' or 'or', got: $token" >&2
        usage
        exit 1 ;;
    esac
    expect=constraint
  fi
done

if [[ "$expect" == "constraint" ]]; then
  echo "error: expression ends with a logical operator" >&2
  usage
  exit 1
fi

or_result=$(( or_result | and_result ))

[[ "$or_result" -eq 1 ]] && exit 0 || exit 1