// Package routine is maven's scheduled-behavior engine: things she does on a
// cron schedule, independent of any reactive request or care predicate.
//
// A Routine is the third proactive class, distinct from the two that already
// exist:
//
//   - a Reminder (internal/store) is a USER-stated one-off/recurring intent —
//     "напомни завтра позвонить маме". It exists because the user asked.
//   - a care Rule (internal/loop) fires on WORLD-STATE predicates — water/meal/
//     break/service_down. It exists because a snapshot crossed a threshold.
//   - a Routine is OPERATOR-declared clockwork — an 08:00 morning briefing, a
//     22:00 wind-down. It exists purely because the clock said so.
//
// This package is pure: no store, no clock of its own, no I/O. The daemon's tick
// driver owns the impurity (it holds the last-fired map and calls Due each tick),
// exactly as it does for the loop package. That keeps the schedule logic here
// unit-testable without time side effects.
package routine

import (
	"fmt"
	"time"

	"github.com/robfig/cron/v3"
)

// Routine — one scheduled behavior. Cron is a standard 5-field expression
// (minute hour dom month dow). Body is the RU text delivered verbatim through
// the normal dispatcher (routines are NOT LLM-phrased: the operator writes the
// line, so it's deterministic and can't hallucinate). Severity (1-4) drives
// routing the same way a nudge's does — care-class (≤2) is suppressed by quiet
// hours and drops when away; ops-class (3-4) reaches away channels.
type Routine struct {
	Name     string
	Cron     string
	Body     string
	Severity int
}

// Validate reports the first structural problem with a routine set: a missing
// name/cron/body or an unparseable cron expression. Called at config load so a
// typo surfaces at startup, not as a silently-never-firing routine at runtime.
func Validate(routines []Routine) error {
	for _, r := range routines {
		if r.Name == "" {
			return fmt.Errorf("routine: name is required")
		}
		if r.Body == "" {
			return fmt.Errorf("routine %q: body is required", r.Name)
		}
		if _, err := cron.ParseStandard(r.Cron); err != nil {
			return fmt.Errorf("routine %q: bad cron %q: %w", r.Name, r.Cron, err)
		}
	}
	return nil
}

// Due returns the routines whose schedule crossed since their last fire and
// records now as the new last-fire time for each one returned. The caller owns
// `last` (the tick driver holds it across ticks); Due mutates it in place.
//
// Cold-start guard: a routine absent from `last` (never seen — fresh daemon, or
// a newly-added routine) is SEEDED to now WITHOUT firing. Without this, a daemon
// restart at 12:00 would replay the 08:00 briefing, because Next() computed from
// the zero time is always in the past. The cost is that a routine can't fire in
// the same tick the daemon booted — an acceptable trade for never replaying a
// missed schedule on restart.
//
// A routine whose cron fails to parse is skipped (Validate rejects those at
// load; this is defence in depth so a bad expression can't fire every tick).
func Due(routines []Routine, last map[string]time.Time, now time.Time) []Routine {
	var out []Routine
	for _, r := range routines {
		sched, err := cron.ParseStandard(r.Cron)
		if err != nil {
			continue
		}
		prev, seen := last[r.Name]
		if !seen {
			last[r.Name] = now // seed on first sight — don't fire (cold-start guard)
			continue
		}
		if next := sched.Next(prev); !next.After(now) {
			last[r.Name] = now
			out = append(out, r)
		}
	}
	return out
}