#!/bin/sh
# Generates the self-signed dev CA and leaf certificate `server/` serves its
# TLS listener with. Run it once, ON THE MACHINE THAT RUNS THE BACKEND, before
# the first start; the server exits with a clear message if the certificates
# are missing.
#
# Same scheme as ../local-updater's: nothing on a device trusts this
# automatically -- the app embeds the CA certificate verbatim and pins to it
# (`PinnedCert.kt`), rather than relying on the device's system trust store.
# This server's API *is* remote code execution (it spawns AI sessions on
# request), so a MITM on it would be as bad as it gets -- hence pinning.
#
# WHERE THE KEYS LIVE, AND WHY NOT IN THE REPO
#
# Output goes to $XDG_CONFIG_HOME/ai-app/certs (0700), deliberately *not*
# beside this script. The repo is a virtiofs mount shared with the dev VM,
# and that VM is treated as untrusted -- a machine that isn't malicious but
# could become so. A CA private key it can read is a CA private key it can
# sign with, and a leaf signed by this CA is one the phone's pinned app
# accepts without question. Keeping the key off the shared mount is what
# makes pinning mean anything.
#
# The same reasoning says the CA key doesn't belong on the backend either,
# strictly: the server only ever reads leaf.pem and leaf-key.pem, and the CA
# key is needed solely to reissue a leaf. Moving ca-key.pem somewhere offline
# once the setup is stable costs nothing but having it to hand at reissue.
#
# Running this inside the VM is fine and expected for emulator work -- it
# just produces a *different*, throwaway CA there. Never install a build
# pinning that dev CA on the real phone.
#
# The CA is idempotent -- skipped if `certs/ca.pem` already exists, so
# re-running this doesn't invalidate the certificate the installed app has
# pinned against without a reason to. The leaf is cheap and reissued on
# every run (still signed by that same, unchanged CA), so adding another SAN
# entry only means rerunning this script, not touching anything pinned.
#
# The leaf's SANs must cover every address a device reaches this server at.
# In production that is exactly one: the backend's WireGuard address, which
# the phone uses from everywhere (see PLAN.md's off-network section).
# Override with SERVER_IP=... if your wg0 address differs.
#
# Outputs into `certs/` (gitignored -- private key material, and the whole
# thing is trivially regeneratable anyway):
#   ca.pem           the CA certificate (not its private key) -- what the
#                     app embeds and pins against.
#   ca-key.pem       the CA's private key -- only this script needs it, to
#                     sign the leaf below. Never shipped anywhere.
#   leaf.pem         the server's own certificate (CA-signed), presented on
#                     every TLS handshake.
#   leaf-key.pem     the leaf's private key -- what the server loads to
#                     terminate TLS.
#   ca-sha256.txt    the CA certificate's SPKI SHA-256 fingerprint, printed
#                     below too. Informational -- the app embeds the whole
#                     `ca.pem`, not this digest.
#   leaf-sha256.txt  the leaf's SPKI SHA-256 fingerprint. Informational --
#                     nothing pins the leaf; the app pins the CA and
#                     validates the chain.

set -eu

SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
CERTS_DIR="${AI_APP_CERTS:-${XDG_CONFIG_HOME:-$HOME/.config}/ai-app/certs}"
# The backend's WireGuard address -- the one address the phone ever dials in
# production (PLAN.md: single-path addressing, no home/away distinction).
SERVER_IP="${SERVER_IP:-10.66.0.1}"
# Also covered so development before the tunnel exists can complete a real
# handshake against the same pinned CA:
#   127.0.0.1  curl from the machine itself, and tests binding loopback
#   10.0.2.2   the Android emulator's alias for the host's loopback
#   LAN_IP     a real phone on the same LAN, pre-WireGuard
LOOPBACK_IP="127.0.0.1"
EMULATOR_HOST_IP="10.0.2.2"
LAN_IP="${LAN_IP:-192.168.1.168}"

# Private key material: owner-only from the moment it exists, rather than
# created world-readable and chmod'ed a beat later.
umask 077
mkdir -p "$CERTS_DIR"
chmod 700 "$CERTS_DIR"
cd "$CERTS_DIR"
echo "==> Writing certificates to $CERTS_DIR"

if [ -f ca.pem ]; then
    echo "==> ca.pem already exists, reusing existing CA."
else
    echo "==> Generating CA key + self-signed CA certificate"
    openssl ecparam -name prime256v1 -genkey -noout -out ca-key.pem
    # Explicit keyUsage: strict verifiers (e.g. Python 3.14's ssl) reject a
    # CA without it, and Android could follow -- cheap to be proper now,
    # expensive to regenerate after phones have pinned it.
    openssl req -new -x509 -key ca-key.pem -out ca.pem -days 3650 \
        -subj "/O=ai-app dev/CN=ai-app dev CA" \
        -addext "basicConstraints=critical,CA:TRUE" \
        -addext "keyUsage=critical,keyCertSign,cRLSign"
fi

echo "==> Generating leaf key + CSR for $SERVER_IP (+ dev addresses)"
openssl ecparam -name prime256v1 -genkey -noout -out leaf-key.pem
openssl req -new -key leaf-key.pem -out leaf.csr \
    -subj "/O=ai-app dev/CN=$SERVER_IP"

echo "==> Signing leaf certificate with the dev CA"
cat > leaf.ext <<EOF
subjectAltName = IP:$SERVER_IP,IP:$LOOPBACK_IP,IP:$EMULATOR_HOST_IP,IP:$LAN_IP
basicConstraints = CA:FALSE
keyUsage = digitalSignature
extendedKeyUsage = serverAuth
EOF
openssl x509 -req -in leaf.csr -CA ca.pem -CAkey ca-key.pem -CAcreateserial \
    -out leaf.pem -days 3650 -extfile leaf.ext
rm -f leaf.csr leaf.ext ca.srl

echo "==> Computing certificate fingerprints (SPKI SHA-256)"
CA_SHA256=$(openssl x509 -in ca.pem -pubkey -noout \
    | openssl pkey -pubin -outform der \
    | openssl dgst -sha256 -binary \
    | openssl base64)
echo "$CA_SHA256" > ca-sha256.txt
LEAF_SHA256=$(openssl x509 -in leaf.pem -pubkey -noout \
    | openssl pkey -pubin -outform der \
    | openssl dgst -sha256 -binary \
    | openssl base64)
echo "$LEAF_SHA256" > leaf-sha256.txt

echo
echo "==> Done."
echo "    CA fingerprint (base64):   $CA_SHA256"
echo "    Leaf fingerprint (base64): $LEAF_SHA256"
echo
echo "    Only relevant if the CA was regenerated just now (i.e. ca.pem did"
echo "    not already exist): the app embeds PINNED_CA_PEM and needs the new"
echo "    $CERTS_DIR/ca.pem contents pasted in, or it silently"
echo "    stops being able to reach this server. The app installs via Local"
echo "    Updater, so recovery is a reinstall through that -- but it's still"
echo "    a one-way door for the installed copy."
echo
echo "      app/androidApp/src/main/kotlin/com/example/aiapp/PinnedCert.kt"
echo
echo "    Only ca.pem is meant to leave this machine. Copy it by hand; do not"
echo "    put the certs directory back in the repo, which is shared with the"
echo "    VM (see this script's header)."