{ config, ... }:

# CouchDB, tuned as the backend for Obsidian Self-hosted LiveSync
# (vrtmrz/obsidian-livesync). The plugin replicates the vault into CouchDB
# chunk-by-chunk over PouchDB's replication protocol, so this is a plain
# CouchDB 3 node — nothing Obsidian-specific runs here.
#
# Published PUBLICLY as https://notes.mgaction.town via neptun's caddy (see
# hosts/neptun/configuration.nix), because Obsidian's mobile apps refuse
# cleartext HTTP and jupiter's *.jupiter.sol names cannot get a real cert.
# That makes the settings below security-relevant, not cosmetic:
#
#   - `require_valid_user` in BOTH [chttpd] and [chttpd_auth]: without it
#     CouchDB answers unauthenticated GETs on the open internet.
#   - neptun's vhost allowlists only the endpoints the plugin uses, so Fauxton
#     (/_utils) and the cluster/config endpoints are not reachable from
#     outside at all — reach them over the tailnet instead.
#   - Turn ON end-to-end encryption in the plugin (Settings → Remote Database
#     → End-to-End Encryption, plus "Obfuscate Properties", which covers the
#     paths and timestamps that E2EE alone leaves readable). Then this server
#     only ever holds ciphertext, which is what makes a publicly-reachable
#     credentialed database an acceptable trade rather than a bad one.
#
#     Its passphrase is a SEPARATE secret from couchdb_admin_password below —
#     deliberately, and it must stay that way. The couchdb password
#     authenticates to this server and is stored here (hashed) and in
#     secrets/jupiter.yaml; the E2EE passphrase never leaves the Obsidian
#     clients and CouchDB has no idea it exists. Reusing one string for both
#     hands whoever obtains that credential the decryption key as well, which
#     is precisely the failure E2EE is here to prevent. The passphrase is
#     therefore NOT in sops (nothing on this host consumes it) — it lives in
#     the HomeLab Proton Pass vault, with the deploy credentials.
#
#     Losing it costs the remote database, not the notes: wipe it and
#     re-initialize from a device that still holds the plaintext vault.
{
  services.couchdb = {
    enable = true;

    # Listens on all interfaces, same reasoning as immich: :5984 is NOT opened
    # in the firewall, so it is reachable over tailscale0 (trusted in
    # common.nix) and localhost only. That is the path neptun's caddy takes.
    bindAddress = "0.0.0.0";
    port = 5984;

    # The vault database is the ONLY copy of the notes once LiveSync is the
    # source of truth, so it belongs on the array, not the 29G eMMC. All three
    # of these default under /var/lib/couchdb and have to move together —
    # configFile especially, since CouchDB writes to it at runtime (below).
    databaseDir = "/mnt/data/AppData/couchdb";
    viewIndexDir = "/mnt/data/AppData/couchdb";
    configFile = "/mnt/data/AppData/couchdb/local.ini";

    # The admin password, as an [admins] ini fragment from sops.
    # services.couchdb.adminPass would render it into the world-readable
    # store; extraConfigFiles is the module's own documented hook for this
    # (hosts/jupiter/secrets.nix renders the template).
    #
    # ⚠️ CouchDB hashes a plaintext admin password at startup and persists the
    # hash to the LAST, writable file in its ini chain — local.ini above,
    # which then takes precedence over this fragment. So changing the sops
    # value alone does NOT rotate the password: delete the `[admins]` line
    # from /mnt/data/AppData/couchdb/local.ini and restart as well.
    extraConfigFiles = [ config.sops.templates."couchdb-admins.ini".path ];

    # Values taken from LiveSync's own CouchDB setup documentation; the plugin
    # refuses to replicate (or silently truncates) without them.
    extraConfig = {
      couchdb = {
        # Creates _users/_replicator on first boot instead of leaving the node
        # in the un-set-up state where every request 500s.
        single_node = "true";
        # LiveSync splits notes into chunks, but a big pasted image still
        # arrives as one document. 8MB (the default) is too small.
        max_document_size = "50000000";
      };

      chttpd = {
        require_valid_user = "true";
        max_http_request_size = "4294967296";
        enable_cors = "true";
      };

      chttpd_auth = {
        require_valid_user = "true";
        authentication_redirect = "/_utils/session.html";
      };

      httpd = {
        # Makes CouchDB answer 401 with a WWW-Authenticate challenge rather
        # than a bare 401 body — the plugin's basic-auth flow depends on it.
        "WWW-Authenticate" = ''Basic realm="couchdb"'';
        enable_cors = "true";
      };

      # Obsidian is an Electron/Capacitor app, so its requests carry these
      # non-http origins. Without them desktop and mobile both fail CORS
      # preflight and the plugin reports a bare "cannot connect".
      cors = {
        credentials = "true";
        origins = "app://obsidian.md,capacitor://localhost,http://localhost";
        headers = "accept, authorization, content-type, origin, referer";
        methods = "GET, PUT, POST, HEAD, DELETE";
        max_age = "3600";
      };

      # The module points [log] file at /var/log/couchdb.log, which nothing
      # rotates — on a 29G eMMC an info-level log of every replication request
      # is a slow disk-fill. stderr hands it to journald's capped storage
      # instead (the file setting is then ignored).
      log = {
        writer = "stderr";
        level = "warning";
      };
    };
  };

  # /mnt/data/AppData is drwx--x--- darman:users, so the couchdb user needs
  # group "users" just to traverse into its own database dir. The dir itself
  # is created couchdb:couchdb by the module's tmpfiles rule.
  users.users.couchdb.extraGroups = [ "users" ];

  # databaseDir is outside /var/lib, so systemd derives no mount dependency
  # from it. Without this CouchDB starts with the array missing, creates an
  # empty database on the eMMC, and LiveSync sees a remote vault that lost
  # every note — which it would then happily replicate back to the clients.
  systemd.services.couchdb.unitConfig.RequiresMountsFor = [ "/mnt/data" ];
}