# Generic scheduler helper — produces a scheduling artefact for any of the
# four runtime targets (K8s CronJob, systemd timer, cron.d entry, daemon
# task registration). Not coupled to backup nor to Kubernetes; any task in
# the repo that needs to be scheduled can build on top of this.
#
# Example:
#   let s = (import "scheduler.ncl").make_schedule {
#     name = "etcd-snapshot",
#     schedule_kind = 'cron, cron_expr = "0 */6 * * *",
#     target = { kind = 'systemd_timer, host_selector = "control_planes",
#                user = "root", unit_name = "prvng-etcd-snapshot" },
#     command = "/usr/local/bin/prvng-backup one-shot backup etcd-snapshot",
#     env = { …secret refs… },
#   } in s.systemd_units

{
  # === Target descriptors ===================================================

  K8sCronJobTarget = {
    kind            | [| 'k8s_cronjob |],
    namespace       | String,
    image           | String,
    image_pull_policy | [| 'IfNotPresent, 'Always, 'Never |] | default = 'IfNotPresent,
    service_account | String | optional,
    node_selector   | { _ | String } | default = {},
    restart_policy  | [| 'OnFailure, 'Never |] | default = 'OnFailure,
    successful_jobs_history_limit | Number | default = 3,
    failed_jobs_history_limit     | Number | default = 5,
  },

  SystemdTimerTarget = {
    kind          | [| 'systemd_timer |],
    unit_name     | String,
    host_selector | String | doc "Hostname pattern or role (e.g. 'control_planes')",
    user          | String | default = "root",
    after         | Array String | default = ["network-online.target"],
    persistent    | Bool   | default = true,
  },

  CronDTarget = {
    kind          | [| 'cron_d |],
    file_name     | String | doc "Filename under /etc/cron.d/",
    host_selector | String,
    user          | String | default = "root",
  },

  DaemonTaskTarget = {
    kind            | [| 'daemon_task |],
    task_id         | String,
    daemon_endpoint | String | default = "unix:///run/prvng-backup.sock",
  },

  # === Top-level builder ====================================================

  # make_schedule returns a record with one populated branch out of:
  # { manifests, systemd_units, cron_files, daemon_registrations }.
  # Callers serialise the appropriate branch.
  make_schedule = fun spec =>
    let target_kind = spec.target.kind in
    let cron_expr = spec.cron_expr in
    let name = spec.name in
    let command = spec.command in
    let env = spec.env in

    {
      manifests =
        if target_kind == 'k8s_cronjob then
          [{
            apiVersion = "batch/v1",
            kind = "CronJob",
            metadata = {
              name = name,
              namespace = spec.target.namespace,
            },
            spec = {
              schedule = cron_expr,
              successfulJobsHistoryLimit = spec.target.successful_jobs_history_limit,
              failedJobsHistoryLimit = spec.target.failed_jobs_history_limit,
              jobTemplate.spec.template.spec = {
                restartPolicy = std.string.from_enum spec.target.restart_policy,
                serviceAccountName = spec.target.service_account,
                nodeSelector = spec.target.node_selector,
                containers = [{
                  name = name,
                  image = spec.target.image,
                  imagePullPolicy = std.string.from_enum spec.target.image_pull_policy,
                  command = ["/bin/sh", "-c", command],
                  env = std.record.to_array env
                    |> std.array.map (fun e => { name = e.field, value = e.value }),
                }],
              },
            },
          }]
        else [],

      systemd_units =
        if target_kind == 'systemd_timer then
          [{
            host_selector = spec.target.host_selector,
            unit_name = spec.target.unit_name,
            service_unit = m%"
              [Unit]
              Description=%{name}
              After=%{std.string.join " " spec.target.after}

              [Service]
              Type=oneshot
              User=%{spec.target.user}
              ExecStart=%{command}
              EnvironmentFile=-/etc/prvng-backup/%{name}.env
            "%,
            timer_unit = m%"
              [Unit]
              Description=Timer for %{name}

              [Timer]
              OnCalendar=%{cron_expr}
              Persistent=%{if spec.target.persistent then "true" else "false"}

              [Install]
              WantedBy=timers.target
            "%,
          }]
        else [],

      cron_files =
        if target_kind == 'cron_d then
          [{
            host_selector = spec.target.host_selector,
            path = "/etc/cron.d/%{spec.target.file_name}",
            content = m%"
              %{cron_expr} %{spec.target.user} %{command}
            "%,
          }]
        else [],

      daemon_registrations =
        if target_kind == 'daemon_task then
          [{
            task_id = spec.target.task_id,
            daemon_endpoint = spec.target.daemon_endpoint,
            schedule = cron_expr,
            command = command,
            env = env,
          }]
        else [],
    },
}