package scheduler

import (
	"errors"
	"fmt"
	"time"

	"github.com/warmbly/warmbly/internal/config"
)

var (
	// ErrWarmupNotEnabled is returned when warmup is not enabled for an account
	ErrWarmupNotEnabled = errors.New("warmup not enabled for this account")

	// ErrCampaignNotActive is returned when a campaign is not active
	ErrCampaignNotActive = errors.New("campaign is not active")

	// ErrCampaignCompleted is returned when all emails in a campaign have been sent
	ErrCampaignCompleted = errors.New("campaign completed - no more emails to send")

	// ErrCampaignEnded is returned when a campaign has passed its end date
	ErrCampaignEnded = errors.New("campaign ended - past end date")

	// ErrNoEmailAccounts is returned when no email accounts are available for sending
	ErrNoEmailAccounts = errors.New("no email accounts available for this campaign")

	// ErrNoEligibleMailbox is the narrower case: the campaign HAS mailboxes,
	// but none can send under its current settings, and waiting will not
	// change that (a sending-behaviour profile with no working days). A gate
	// that lifts on its own, such as a spent daily budget, a closed sending
	// window or a warmup health hold, is a deferral instead, never this.
	// Reporting this as ErrNoEmailAccounts sent people looking at their tag
	// configuration for a problem that was never there.
	//
	// It wraps ErrNoEmailAccounts so existing callers that pause the campaign
	// on errors.Is(err, ErrNoEmailAccounts) keep behaving exactly as before.
	ErrNoEligibleMailbox = fmt.Errorf(
		"%w: no mailbox can send under its current sending settings", ErrNoEmailAccounts)

	// ErrDomainAuthFailing is the narrower case again: every mailbox in the
	// campaign's pool was gated by the sending-domain authentication check.
	// Reporting that as ErrNoEligibleMailbox would send people to check
	// timezones and daily caps for a DNS problem, which is exactly the class of
	// mislabelling ErrNoEligibleMailbox was introduced to fix.
	//
	// It wraps ErrNoEmailAccounts so existing callers that pause the campaign
	// keep behaving as before; callers that want the specific reason must test
	// for it BEFORE ErrNoEligibleMailbox and ErrNoEmailAccounts.
	ErrDomainAuthFailing = fmt.Errorf(
		"%w: every mailbox is sending from a domain that fails SPF/DMARC authentication", ErrNoEmailAccounts)

	// ErrDailyLimitReached is returned when the daily limit has been reached
	ErrDailyLimitReached = errors.New("daily email limit reached")

	// ErrCampaignDeferred is returned when there ARE valid contacts to send but
	// nothing can go right now — every usable mailbox has spent its daily
	// budget or is outside its hours, the daily new-lead cap is reached, the
	// step's own wait has not elapsed, or every due lead was refused for a
	// reason of its own (see ErrLeadDeferred). The caller must reschedule at the
	// returned (defer) time WITHOUT sending. The returned pair is always nil on
	// this path so it can never be mistaken for a sendable contact; the returned
	// accountID is a nominal pool mailbox for the wakeup task only (the next
	// invocation re-evaluates selection from scratch).
	ErrCampaignDeferred = errors.New("campaign send deferred - no eligible mailbox for this contact right now")

	// ErrLeadDeferred is the deferral that belongs to ONE lead rather than to
	// the campaign: this recipient cannot be placed right now (ESP-strict finds
	// no same-provider mailbox for their domain, their own mailbox is busy,
	// their preferred hours are hours away), while the pool itself is fine and
	// the lead behind them may well be sendable this second.
	//
	// The scheduler answers it by moving to the next routed lead instead of
	// parking the campaign. Before that, one such lead at the head of the
	// routing order stopped every other lead in the campaign from ever being
	// sent: the tick deferred, woke, routed to the same lead, and deferred
	// again, forever (issue #437).
	//
	// It wraps ErrCampaignDeferred so every caller outside the scheduler —
	// which only ever reschedules on a deferral — behaves exactly as before.
	ErrLeadDeferred = fmt.Errorf("%w: this lead cannot be placed right now", ErrCampaignDeferred)

	// ErrSenderBusy is the narrower lead deferral: this lead's sequence belongs
	// to one mailbox, and that mailbox has nothing left today. Every step of a
	// conversation comes from the address the contact first heard from, so the
	// lead waits for it rather than being written to by a stranger.
	//
	// It wraps ErrLeadDeferred (and so ErrCampaignDeferred), so the scheduler
	// moves on to the next lead and every other caller reschedules exactly as
	// before; only the contact drawer, which words the reason, tests for it.
	ErrSenderBusy = fmt.Errorf("%w: the mailbox this lead's sequence belongs to has no capacity left today", ErrLeadDeferred)
)

// DeferSlot is the wakeup time a caller must use after CalculateNextCampaignTime
// returns ErrCampaignDeferred. The returned instant is the campaign's real
// next-due moment, which is the honest answer to "when could this send" but the
// wrong answer to "when should this chain look again": a campaign is one
// self-perpetuating task, so parking it at a next-due three days out also means
// nothing re-reads the campaign for three days. Leads imported in the meantime
// sit at "Queued / Not started" until then.
//
// So a deferral is capped at config.CampaignMaxDeferMinutes. Anything sooner is
// kept as-is, because a near-term defer is already a precise wakeup. Sends are
// unaffected: a tick that fires early and still has nothing due simply defers
// again, and a tick that DID send parks its successor at the paced interval,
// which never goes through here.
func DeferSlot(at time.Time) time.Time {
	horizon := time.Now().Add(config.CampaignMaxDeferMinutes * time.Minute)
	if at.IsZero() || at.After(horizon) {
		return horizon
	}
	return at
}