#!/bin/sh
# loadupd.sh - fetch the newest upd binary for this machine.
#
# The one thing upd cannot do for itself: `upd --update` needs an upd to run
# it. Everything after this first one is upd's own job.
#
#   ./loadupd.sh              # into the current directory
#   ./loadupd.sh ~/bin        # into a directory of your choosing
#
# Plain POSIX sh, and nothing beyond uname, sed, grep and one of curl or wget:
# it has to run on the machines upd exists for, before upd is on them.
set -e

REPO=${UPD_REPO_URL:-https://git.micw.org/mike/upd}
NAME=upd
DEST=${1:-.}

die() {
	echo "loadupd: $*" >&2
	exit 1
}

# https://host/owner/repo -> https://host/api/v1/repos/owner/repo
api=$(echo "$REPO" | sed -e 's#/*$##' -e 's#\.git$##' \
	-e 's#^\(https\{0,1\}://[^/]*\)/\(.*\)$#\1/api/v1/repos/\2#')
case "$api" in
*/api/v1/repos/*/*) ;;
*) die "cannot read $REPO, expected https://host/owner/repo" ;;
esac

os=$(uname -s | tr 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' 'abcdefghijklmnopqrstuvwxyz')
case "$os" in
darwin | linux | freebsd) ;;
*) die "unsupported system: $(uname -s)" ;;
esac

# The names are Go's, not uname's, because that is what the release assets are
# called.
case "$(uname -m)" in
x86_64 | amd64) arch=amd64 ;;
aarch64 | arm64) arch=arm64 ;;
i386 | i686) arch=386 ;;
armv7* | armv6*) arch=arm ;;
*) die "unsupported architecture: $(uname -m)" ;;
esac

asset="$NAME-$os-$arch"

# curl on an old machine may be the very thing that cannot speak TLS 1.2 any
# more - which is half the reason upd exists - so wget gets its turn before we
# give up.
fetch() { # url outfile
	if command -v curl >/dev/null 2>&1; then
		curl -fsSL -o "$2" "$1" && return 0
	fi
	if command -v wget >/dev/null 2>&1; then
		wget -q -O "$2" "$1" && return 0
	fi
	return 1
}

tmp=$(mktemp -d "${TMPDIR:-/tmp}/loadupd.XXXXXX") || die "cannot create a temporary directory"
trap 'rm -rf "$tmp"' EXIT INT TERM

echo "Looking for the newest release of $NAME ..."
fetch "$api/releases/latest" "$tmp/release.json" ||
	die "cannot reach $api
  If the TLS handshake failed, this machine is too old to fetch it itself -
  copy $asset over from somewhere else."

tag=$(sed -n 's/.*"tag_name"[[:space:]]*:[[:space:]]*"\([^"]*\)".*/\1/p' "$tmp/release.json" | head -n 1)
[ -n "$tag" ] || die "no release found in $REPO"

# One asset per line, then pick ours by name. The JSON arrives as one long
# line, so the comma is what separates the fields.
urls=$(tr ',' '\n' <"$tmp/release.json" |
	sed -n 's/.*"browser_download_url"[[:space:]]*:[[:space:]]*"\([^"]*\)".*/\1/p')
url=$(echo "$urls" | grep "/$asset\$" | head -n 1)
if [ -z "$url" ]; then
	die "release $tag has no $asset (only: $(echo "$urls" | sed 's#.*/##' | tr '\n' ' '))"
fi

echo "Downloading $asset $tag ..."
fetch "$url" "$tmp/$NAME" || die "download failed: $url"
chmod 755 "$tmp/$NAME"

# A truncated file or one built for the wrong platform shows up here, not on
# first use.
"$tmp/$NAME" --version >/dev/null 2>&1 || die "the downloaded binary does not run"

[ -d "$DEST" ] || mkdir -p "$DEST" || die "cannot create $DEST"
# Spelled out in full: "." says nothing in a message, and even less in the
# comparison against $PATH below.
dir=$(cd "$DEST" && pwd) || die "cannot use $DEST"
target="$dir/$NAME"

# Via a file alongside, so that replacing an upd that is currently running is
# one atomic step and not half a copy.
cp "$tmp/$NAME" "$target.new.$$" || die "no write permission in $dir"
chmod 755 "$target.new.$$"
mv "$target.new.$$" "$target" || {
	rm -f "$target.new.$$"
	die "cannot replace $target"
}

echo "$NAME $tag installed at $target"
case ":$PATH:" in
*":$dir:"*) ;;
*) echo "Note: $dir is not in \$PATH." ;;
esac
echo "From here on: $NAME --update"