#!/usr/bin/env bash
#
# Get latest release version, branch tag, or latest commit from GitHub
# Usage: x-gh-get-latest-version <repo>
# Author: Ismo Vuorinen <https://github.com/ivuorinen> 2024

set -euo pipefail

# Environment variables, more under get_release_version() and get_latest_branch_tag()
# functions. These can be overridden by the user.
GITHUB_API_URL="${GITHUB_API_URL:-https://api.github.com/repos}"
VERBOSE="${VERBOSE:-0}"

# Prints a message if VERBOSE=1
msg()
{
  [[ "$VERBOSE" -eq 1 ]] && echo "$1"
}

# Show usage information
usage()
{
  cat << EOF
Usage: $0 <repo> (e.g. ivuorinen/dotfiles)

Fetches the latest release version, latest branch tag, or latest commit SHA from GitHub.

Options:
  - INCLUDE_PRERELEASES=1  Include prerelease versions (default: only stable releases).
  - OLDEST_RELEASE=1       Fetch the oldest release instead of the latest.
  - BRANCH=<branch>        Fetch the latest tag from a specific branch (default: main).
  - LATEST_COMMIT=1        Fetch the latest commit SHA from the specified branch.
  - OUTPUT=json            Return output as JSON (default: plain text).
  - GITHUB_API_URL=<url>   Override GitHub API URL (useful for GitHub Enterprise).
  - GITHUB_TOKEN=<token>   Use GitHub API token to increase rate limits (default: unauthenticated).

Requirements:
  - curl
  - jq (for JSON processing)

Examples:
  # Fetch the latest stable release
  $0 ivuorinen/dotfiles

  # Fetch the latest release including prereleases
  INCLUDE_PRERELEASES=1 $0 ivuorinen/dotfiles

  # Fetch the oldest release
  OLDEST_RELEASE=1 $0 ivuorinen/dotfiles

  # Fetch the latest tag from the 'develop' branch
  BRANCH=develop $0 ivuorinen/dotfiles

  # Fetch the latest commit SHA from 'main' branch
  LATEST_COMMIT=1 $0 ivuorinen/dotfiles

  # Output result in JSON format
  OUTPUT=json $0 ivuorinen/dotfiles

  # Use GitHub API token for higher rate limits
  GITHUB_TOKEN="your_personal_access_token" $0 ivuorinen/dotfiles

  # Use GitHub Enterprise API
  GITHUB_API_URL="https://github.example.com/api/v3/repos" $0 ivuorinen/dotfiles
EOF
  exit 1
}

# Check that required dependencies are installed
check_dependencies()
{
  for cmd in curl jq; do
    if ! command -v "$cmd" &> /dev/null; then
      echo "Error: '$cmd' is required but not installed." >&2
      exit 1
    fi
  done
}

# Fetches the latest release or the oldest if OLDEST_RELEASE=1
# $1 - GitHub repository (string)
get_release_version()
{
  local repo="$1"
  local include_prereleases="${INCLUDE_PRERELEASES:-0}"
  local oldest_release="${OLDEST_RELEASE:-0}"
  local api_url="${GITHUB_API_URL}/${repo}/releases"

  local auth_header=()
  if [[ -n "${GITHUB_TOKEN:-}" ]]; then
    auth_header=(-H "Authorization: token $GITHUB_TOKEN")
  fi

  msg "Fetching release data from: $api_url (Include prereleases: $include_prereleases, Oldest: $oldest_release)"

  local json_response
  json_response=$(curl -sSL "${auth_header[@]}" "$api_url")

  # Check for API errors
  if echo "$json_response" | jq -e 'has("message")' > /dev/null; then
    msg "GitHub API error: $(echo "$json_response" | jq -r '.message')"
    exit 1
  fi

  local filter='.[] | select(.tag_name)'
  [[ "$include_prereleases" -eq 0 ]] && filter+='.prerelease == false'

  local version
  if [[ "$oldest_release" -eq 1 ]]; then
    version=$(echo "$json_response" | jq -r "[${filter}] | last.tag_name // empty")
  else
    version=$(echo "$json_response" | jq -r "[${filter}] | first.tag_name // empty")
  fi

  if [[ -z "$version" ]]; then
    msg "Failed to fetch release version for repository: $repo"
    exit 1
  fi

  echo "$version"
}

# Fetches the latest tag from the specified branch
get_latest_branch_tag()
{
  local repo="$1"
  local branch="${BRANCH:-main}"
  local api_url="${GITHUB_API_URL}/${repo}/git/refs/tags"

  msg "Fetching latest tag for branch '$branch' from: $api_url"

  local json_response
  json_response=$(curl -sSL "$api_url")

  local version
  version=$(echo "$json_response" | jq -r "[.[] | select(.ref | contains(\"refs/tags/$branch\"))] | last.ref | sub(\"refs/tags/\"; \"\") // empty")

  if [[ -z "$version" ]]; then
    msg "Failed to fetch latest tag for branch: $branch"
    exit 1
  fi

  echo "$version"
}

# Fetches the latest commit SHA from the specified branch
get_latest_commit()
{
  local repo="$1"
  local branch="${BRANCH:-main}"
  local api_url="${GITHUB_API_URL}/${repo}/commits/$branch"

  msg "Fetching latest commit SHA from: $api_url"

  local json_response
  json_response=$(curl -sSL "$api_url")

  local sha
  sha=$(echo "$json_response" | jq -r '.sha // empty')

  if [[ -z "$sha" ]]; then
    msg "Failed to fetch latest commit SHA for branch: $branch"
    exit 1
  fi

  echo "$sha"
}

# Main function
# $1 - GitHub repository (string)
main()
{
  if [[ $# -ne 1 ]]; then
    usage
  fi

  check_dependencies

  local repo="$1"
  local result

  if [[ "${LATEST_COMMIT:-0}" -eq 1 ]]; then
    result=$(get_latest_commit "$repo")
  elif [[ -n "${BRANCH:-}" ]]; then
    result=$(get_latest_branch_tag "$repo")
  else
    result=$(get_release_version "$repo")
  fi

  if [[ "${OUTPUT:-text}" == "json" ]]; then
    echo "{\"repository\": \"$repo\", \"result\": \"$result\"}"
  else
    echo "$result"
  fi
}

main "$@"

# vim: set ts=2 sw=2 ft=sh et: