// Package unit generates the systemd user units cronr manages. Pure
// text generation — systemd does the scheduling, cronr owns no daemon.
package unit

import (
	"fmt"
	"regexp"
	"strings"
)

// Prefix namespaces everything cronr creates so list/rm can never
// touch units it does not own.
const Prefix = "cronr-"

var nameRe = regexp.MustCompile(`^[a-zA-Z0-9][a-zA-Z0-9_-]*$`)

// ValidName reports whether a job name is safe for unit/file names.
func ValidName(name string) bool {
	return len(name) <= 64 && nameRe.MatchString(name)
}

// Script wraps the job command in an executable shell script — the
// unit ExecStart points here, so arbitrary quoting in the command
// never meets systemd's ExecStart parsing.
func Script(cmd string) string {
	return "#!/bin/sh\n# generated by cronr - the job's command lives here so systemd\n# unit quoting never mangles it\n" + cmd + "\n"
}

// Service renders the .service unit. PATH gets ~/.local/bin first so
// jobs can call agent tools (notifyr, svgc, agy, ...) like a login
// shell would.
func Service(name, scriptPath string) string {
	return fmt.Sprintf(`[Unit]
Description=cronr job %s

[Service]
Type=oneshot
Environment=PATH=%%h/.local/bin:/usr/local/bin:/usr/bin:/bin
ExecStart=/bin/sh %s
`, name, scriptPath)
}

// Timer renders the .timer unit. Recurring jobs get Persistent=true
// (a missed run fires at next boot/login); one-shots do not.
func Timer(name, calendarSpec string, oneshot bool) string {
	persistent := "true"
	if oneshot {
		persistent = "false"
	}
	return fmt.Sprintf(`[Unit]
Description=cronr timer for %s

[Timer]
OnCalendar=%s
Persistent=%s

[Install]
WantedBy=timers.target
`, name, calendarSpec, persistent)
}

// UnitNames returns the service and timer unit names for a job.
func UnitNames(name string) (service, timer string) {
	return Prefix + name + ".service", Prefix + name + ".timer"
}

// JobName extracts the job name from a cronr unit filename, or ""
// if the filename is not cronr's.
func JobName(unitFile string) string {
	base := unitFile
	if i := strings.LastIndex(base, "/"); i >= 0 {
		base = base[i+1:]
	}
	if !strings.HasPrefix(base, Prefix) {
		return ""
	}
	base = strings.TrimPrefix(base, Prefix)
	for _, suffix := range []string{".timer", ".service"} {
		if strings.HasSuffix(base, suffix) {
			return strings.TrimSuffix(base, suffix)
		}
	}
	return ""
}

// AtToCalendar converts "YYYY-MM-DD HH:MM" (or with seconds) to a
// systemd calendar spec for one-shot jobs. systemd accepts the format
// as-is; this just validates the shape early with a helpful error.
var atRe = regexp.MustCompile(`^\d{4}-\d{2}-\d{2} \d{2}:\d{2}(:\d{2})?$`)

func AtToCalendar(at string) (string, error) {
	if !atRe.MatchString(at) {
		return "", fmt.Errorf("--at must be \"YYYY-MM-DD HH:MM[:SS]\", got %q", at)
	}
	return at, nil
}