#!/bin/bash

# Mastodon install hooks.

# Web Push identity.
# ---------------------------------------------------------------------------
# The two VAPID values are not independent secrets — they are the two halves of
# one P-256 keypair, and the browser verifies that the push request is signed by
# the private key matching the public key it subscribed with. The framework's
# RANDOMIZED* generators mint each placeholder on its own, so they can produce
# two well-formed strings but never a *pair*: what shipped before was two
# unrelated random values, and web push could not work with them. Stoat hits the
# same wall and solves it the same way, in its own install hook.
#
# Mastodon's webpush gem expects unpadded URL-safe base64 of the raw key
# material: the 32-byte private scalar (43 chars) and the 65-byte uncompressed
# public point (87 chars). Both are sliced out of the SEC1 DER, whose layout for
# prime256v1 is a fixed 121 bytes — a 2-byte SEQUENCE header, INTEGER 1, then
# `04 20` introducing the private scalar at offset 7, and the public point as
# the trailing field. Both slices were cross-checked against `openssl ec -text`.
#
# Runs at install_post_setup: the deployed config exists by then (so there is
# something to write to) and the compose has not been templated yet (so the pair
# reaches the compose on this same install).
#
# Generated once, then left alone. Rotating the pair invalidates every push
# subscription clients are holding, so an existing well-formed pair is never
# replaced — including across reinstalls.
mastodon_install_post_setup()
{
    local app_name="${1:-mastodon}"
    local config_file="$(appDir "$app_name")/${app_name}.config"
    [[ -f "$config_file" ]] || return 0

    # Keep a pair that already has the right shape. The length test is also what
    # retires the old values: two independent RANDOMIZEDVAPID strings are the
    # wrong length for the public half, so an install carrying them regenerates
    # once and is correct from then on.
    if [[ "$CFG_MASTODON_VAPID_PRIVATE_KEY_1" =~ ^[A-Za-z0-9_-]{43}$ \
       && "$CFG_MASTODON_VAPID_PUBLIC_KEY_1"  =~ ^[A-Za-z0-9_-]{87}$ ]]; then
        return 0
    fi

    local pem der
    pem=$(mktemp) || return 0
    der=$(mktemp) || { rm -f "$pem"; return 0; }

    if ! openssl ecparam -name prime256v1 -genkey -noout -out "$pem" 2>/dev/null \
       || ! openssl ec -in "$pem" -outform DER -out "$der" 2>/dev/null; then
        rm -f "$pem" "$der"
        isError "Could not generate a VAPID keypair for $app_name — web push will not work."
        return 0
    fi

    local vapid_private vapid_public
    vapid_private=$(head -c 39 "$der" | tail -c 32 | base64 | tr -d '\n' | tr '+/' '-_' | tr -d '=')
    vapid_public=$(tail -c 65 "$der" | base64 | tr -d '\n' | tr '+/' '-_' | tr -d '=')
    rm -f "$pem" "$der"

    # Refuse to write a malformed pair over a working one — a short read or an
    # openssl build with a different DER layout would otherwise quietly break
    # push instead of leaving it as it was.
    if [[ ! "$vapid_private" =~ ^[A-Za-z0-9_-]{43}$ || ! "$vapid_public" =~ ^[A-Za-z0-9_-]{87}$ ]]; then
        isError "Generated VAPID keypair had an unexpected shape — leaving $app_name's push keys alone."
        return 0
    fi

    updateConfigOption "CFG_MASTODON_VAPID_PRIVATE_KEY_1" "$vapid_private" "$config_file"
    updateConfigOption "CFG_MASTODON_VAPID_PUBLIC_KEY_1" "$vapid_public" "$config_file"
    isSuccessful "Generated a VAPID keypair for $app_name web push."
}