#!/usr/bin/env bash

# Exit immediately if the script encounters a non-zero status.
set -e

# If set, Bash includes filenames beginning with a `.` in the results of
# filename expansion. The filenames `.` and `..` must always be matched
# explicitly, even if dotglob is set.
shopt -s dotglob extglob

# ============================================================
# PROLOGUE
# ============================================================

# Create a new top-level directory as fallback in case $BUILD (defined below)
# is ever empty.
mkdir -p "/tmp/bs.phoenix"

# Create an intermediate build directory. The final step of this script will
# copy the content from this directory to $OUT.
BUILD=$(mktemp -d -p "/tmp/bs.phoenix")

if [ -z "$BUILD" ]; then
  >&2 echo "Failed to create temp directory."
  exit 1
fi

# Deletes the intermediate build directory on exit. We use a concatenation of
# the intermediate directory with the basename of the generated temp directory
# to ensure we never evaluate to root (i.e. `/`). That should never actually
# happen but a good habit to establish nonetheless.
function cleanup {
  rm -r "/tmp/bs.phoenix/$(basename "$BUILD")"
}

trap cleanup EXIT

# ============================================================
# ENVIRONMENT
# ============================================================

if [ -z "$MODULE" ]; then
  MODULE_ARG=
else
  MODULE_ARG="--module '$MODULE'"
fi

if [ -n "$ECTO" ]; then
  ECTO_ARG=
else
  ECTO_ARG="--no-ecto"
fi

# ============================================================
# BUILD
# ============================================================

# Copy template contents over to the intermediate build directory.
cp -r template/!(README*) "$BUILD"

# Explicitly set permissions on all copied template files.
find "$BUILD" -type f -execdir chmod 644 {} +
find "$BUILD" -type d -execdir chmod 755 {} +
chmod 755 "$BUILD"/.githooks/pre-commit

# Generate a new project with the specified name using `mix`. Generate in a
# subdirectory to avoid interactive conflict resolution.
nix develop "$BUILD" \
  --command bash \
  -c "mix phx.new $BUILD/bs.project --app '$APP' $MODULE_ARG $ECTO_ARG"

# Copy the generated files into the intermediate build directory.
mv -f "$BUILD"/bs.project/* "$BUILD"
rmdir "$BUILD"/bs.project

# Overwrite the generated README in favor of that defined in our template.
if [ -n "$ECTO" ]; then
  cp template/README-ecto.md "$BUILD"/README.md
else
  cp template/README-no-ecto.md "$BUILD"/README.md
fi
chmod 644 "$BUILD"/README.md

# Include additional build files for our assets. Group into subdirectory so
# the `chmod` command can take advantage of globbing.
mkdir -p "$BUILD"/bs.assets
cp assets/* "$BUILD"/bs.assets
chmod 644 "$BUILD"/bs.assets/*
mv "$BUILD"/bs.assets/* "$BUILD"/assets
rmdir "$BUILD"/bs.assets

# Create a new database cluster.
if [ -n "$ECTO" ]; then
  nix develop "$BUILD" --command bash -c "pg_ctl initdb -D $BUILD/db"
fi

# ============================================================
# REWRITES
# ============================================================

# The mix generator would fail if $APP did not consist of just lowercase ASCII
# letters, numbers, or underscores. Thus $APP is safe to interpolate into the
# following command.
for file in flake.nix assets/{package.json,package-lock.json,node-packages.nix}
do
  sed -i "s/<APP>/$APP/g" "$BUILD/$file"
done

# Allow specifying a custom path to our :esbuild and :tailwind configs.
# Typically when building a Phoenix application, Mix will download
# esbuild/tailwind binaries on demand. Within nix environments this is not
# possible. Instead, specify them directly with these environment variables.
sed -i '/config :esbuild/, /^$/ {
  s/0.17.11/0.19.7/; s/]$/],/;
  s/^$/\ \ path: System.get_env("MIX_ESBUILD_PATH")\n/}' \
  "$BUILD"/config/config.exs

sed -i '/config :tailwind/, /^$/ {
  s/3.3.2/3.3.5/; s/]$/],/;
  s/^$/\ \ path: System.get_env("MIX_TAILWIND_PATH")\n/}' \
  "$BUILD"/config/config.exs

# By default Phoenix generates a postgres configuration with assumed username
# `postgres`. This flake encourages a local postgres database with username
# `$(whoami)`. Reflect this in the config.
sed -i "s/username: \"postgres\"/username: \"$(whoami)\"/g" "$BUILD/config/dev.exs"

# Append an additional rule to `.gitignore` to ignore the database cluster.
cat <<EOF >> "$BUILD"/.gitignore
# Directory used by \`direnv\` to hold \`use flake\`-generated profiles.
/.direnv/

# A symlink produced by default when running \`nix build\`.
/result
EOF

if [ -n "$ECTO" ]; then
  cat <<EOF >> "$BUILD"/.gitignore

# The default location of the generated database cluster.
/db/
EOF
fi

# ============================================================
# EPILOGUE
# ============================================================

# Success! Copy contents to target directory.
cp -a "$BUILD"/* "$OUT"