# NixOS module for repertory-api
#
# This module fetches the application source directly from a self-hosted Forgejo instance at a pinned
# tag/commit, builds a Python environment, runs Alembic migrations on start,
# and manages the Flask service under systemd.
#
# ── Typical usage in configuration.nix ───────────────────────────────────────
#
#   imports = [ (fetchTarball {
#     url    = "https://git.yourdomain.com/yourusername/repertory-api/archive/v1.0.0.tar.gz";
#     sha256 = "0000000000000000000000000000000000000000000000000000";
#   } + "/nixos/module.nix") ];
#
# ── Secrets ──────────────────────────────────────────────────────────────────
#
# The module expects two sops-nix secrets to exist. Add to configuration.nix:
#
#   sops.secrets."repertory-api-key" = {};
#   sops.secrets."repertory-db-url"  = {};
#
# ── Minimal configuration.nix example ────────────────────────────────────────
#
#   services.repertory-api = {
#     enable  = true;
#     domain  = "git.yourdomain.com";
#     owner   = "yourusername";
#     version = "v1.0.0";
#     rev     = "abc123...";   # git commit SHA for the tag
#     sha256  = "sha256-...";  # `nix-prefetch-url --unpack <tarball url>`
#   };
#
# ── Updating ─────────────────────────────────────────────────────────────────
#
# 1. Push a new tag to your Forgejo instance (e.g. v1.1.0).
# 2. Get the new sha256:
#      nix-prefetch-url --unpack \
#        https://git.yourdomain.com/yourusername/repertory-api/archive/v1.1.0.tar.gz
# 3. Update `version`, `rev`, and `sha256` in your configuration.nix.
# 4. nixos-rebuild switch
#    → Nix fetches the new source, rebuilds the Python env, restarts the
#      service, and runs migrations automatically in preStart.
#
# ─────────────────────────────────────────────────────────────────────────────

{ config, lib, pkgs, ... }:

with lib;

let
  cfg = config.services.repertory-api;

  # Fetch the application source from the self-hosted Forgejo instance at the
  # pinned rev. Nix verifies the sha256 hash, so this is fully reproducible.
  appSrc = pkgs.fetchFromGitea {
    domain = cfg.domain;
    owner  = cfg.owner;
    repo   = "repertory-api";
    rev    = cfg.rev;
    sha256 = cfg.sha256;
  };

  # Build the Python environment with all runtime dependencies.
  # This mirrors pyproject.toml [project.dependencies].
  # uv is a local dev tool — on NixOS, Nix itself plays the role of
  # dependency resolver and the Python env is built at evaluation time.
  pythonEnv = pkgs.python3.withPackages (ps: with ps; [
    flask
    flask-sqlalchemy
    sqlalchemy
    psycopg2
    python-dotenv
    alembic
  ]);

in {

  options.services.repertory-api = {
    enable = mkEnableOption "Repertory API";

    domain = mkOption {
      type        = types.str;
      description = "Hostname of your self-hosted Forgejo instance.";
      example     = "git.yourdomain.com";
    };

    owner = mkOption {
      type        = types.str;
      description = "Forgejo username / org that owns the repertory-api repo.";
      example     = "yourusername";
    };

    version = mkOption {
      type        = types.str;
      description = "Human-readable version label (used only for documentation/logging).";
      example     = "v1.0.0";
    };

    rev = mkOption {
      type        = types.str;
      description = "Git commit SHA for the tag you want to deploy.";
      example     = "abc1234def5678";
    };

    sha256 = mkOption {
      type        = types.str;
      description = ''
        sha256 hash of the fetched source tarball.
        Obtain with:
          nix-prefetch-url --unpack \
            https://git.yourdomain.com/<owner>/repertory-api/archive/<rev>.tar.gz
      '';
      example = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";
    };

    port = mkOption {
      type        = types.port;
      default     = 5000;
      description = "Port the Flask app listens on.";
    };

    user = mkOption {
      type        = types.str;
      default     = "repertory";
      description = "Unix user to run the service as.";
    };

    group = mkOption {
      type        = types.str;
      default     = "repertory";
      description = "Unix group to run the service as.";
    };

    apiKeySecret = mkOption {
      type        = types.str;
      default     = "/run/secrets/repertory-api-key";
      description = "Path to the SOPS-decrypted file containing the raw API key.";
    };

    dbUrlSecret = mkOption {
      type        = types.str;
      default     = "/run/secrets/repertory-db-url";
      description = "Path to the SOPS-decrypted file containing the DATABASE_URL string.";
    };
  };

  config = mkIf cfg.enable {

    users.users.${cfg.user} = {
      isSystemUser = true;
      group        = cfg.group;
      home         = "/var/lib/repertory-api";
      createHome   = true;
    };

    users.groups.${cfg.group} = {};

    systemd.services.repertory-api = {
      description = "Repertory API (Flask) — ${cfg.version}";
      wantedBy    = [ "multi-user.target" ];
      after       = [ "network.target" "postgresql.service" ];

      serviceConfig = {
        User             = cfg.user;
        Group            = cfg.group;
        WorkingDirectory = appSrc;
        Restart          = "on-failure";
        RestartSec       = "5s";

        ExecStart = "${pythonEnv}/bin/python -m flask --app wsgi:app run --host=0.0.0.0 --port=${toString cfg.port}";

        # Secrets are injected via the env file written in preStart.
        EnvironmentFiles = [ "/run/repertory-api/env" ];

        # Security hardening
        ProtectSystem    = "strict";
        ProtectHome      = true;
        PrivateTmp       = true;
        NoNewPrivileges  = true;
        # /run/repertory-api is on tmpfs and holds only the mode-600 env file.
        ReadWritePaths   = [ "/run/repertory-api" ];
      };

      preStart = ''
        # Write secrets into a tmpfs env file so nothing is on-disk in plaintext.
        mkdir -p /run/repertory-api
        chmod 700 /run/repertory-api
        printf 'API_KEY=%s\n'      "$(cat ${cfg.apiKeySecret})" >  /run/repertory-api/env
        printf 'DATABASE_URL=%s\n' "$(cat ${cfg.dbUrlSecret})"  >> /run/repertory-api/env
        chmod 600 /run/repertory-api/env

        # Run any pending Alembic migrations before the server starts.
        # On a fresh database this creates all tables; on subsequent deploys
        # it applies only new migration files.
        export DATABASE_URL="$(cat ${cfg.dbUrlSecret})"
        cd ${appSrc}
        ${pythonEnv}/bin/python -m alembic upgrade head
      '';
    };
  };
}