package backthink

import (
	"fmt"
	"time"
)

// Importance is the estimated severity of an event that woke a thinking pass. It
// is the primary positive signal in the interrupt decision: a low-importance
// heartbeat almost never interrupts, while a critical safety event normally does.
type Importance int

const (
	// ImportanceLow is a routine trigger (e.g. the periodic heartbeat).
	ImportanceLow Importance = iota
	// ImportanceNormal is an ordinary event worth reflecting on (device change).
	ImportanceNormal
	// ImportanceHigh is a notable event (a reminder the user set firing).
	ImportanceHigh
	// ImportanceCritical is a safety-critical event that may override work/busy.
	ImportanceCritical
)

// String returns a stable label for logs and records.
func (i Importance) String() string {
	switch i {
	case ImportanceLow:
		return "low"
	case ImportanceNormal:
		return "normal"
	case ImportanceHigh:
		return "high"
	case ImportanceCritical:
		return "critical"
	default:
		return fmt.Sprintf("importance(%d)", int(i))
	}
}

// highBoredomThreshold is the boredom (0..1) above which a normal daytime event
// is worth interrupting a bored, otherwise idle user. It is a const so no magic
// number appears in the decision path.
const highBoredomThreshold = 0.7

// UserState describes the user's current condition as observed from device
// telemetry (heart rate, sleep) and schedule (work, busy). It is the negative
// signal in the interrupt decision: a sleeping, working or busy user is left
// alone. Boredom (0..1) is the soft positive dial that widens interruption.
type UserState struct {
	// HeartRateBPM is the current heart rate, 0 when unknown.
	HeartRateBPM int
	// Sleeping reports whether the user is currently asleep from sleep tracking.
	Sleeping bool
	// Working reports whether the user is in a work/scheduled block.
	Working bool
	// Busy reports whether the user is marked busy (calendar / do-not-disturb).
	Busy bool
	// Boredom ranges 0..1. Higher boredom means the user is idle and more open
	// to a gentle interruption.
	Boredom float64
}

// String returns a concise human-readable summary for logs/records.
func (s UserState) String() string {
	return fmt.Sprintf("bpm=%d sleeping=%v working=%v busy=%v boredom=%.2f",
		s.HeartRateBPM, s.Sleeping, s.Working, s.Busy, s.Boredom)
}

// DecisionInput is the set of signals Decide weighs: the event's importance, the
// current wall-clock time, the user's current state and their boredom.
type DecisionInput struct {
	// Trigger is a human-readable source label, recorded for traceability.
	Trigger string
	// Import is the event's estimated importance.
	Import Importance
	// At is the current wall-clock time, in the local timezone used for the
	// do-not-disturb window.
	At time.Time
	// UserState carries the user's physiological/schedule condition.
	UserState UserState
}

// Decision is the outcome of Decide.
type Decision struct {
	// ShouldPush reports whether the user should be interrupted.
	ShouldPush bool
	// Reason is a short human-readable justification, surfaced on the panel.
	Reason string
}

// Decide applies the interrupt rule from design/12 §2 (and design/11 §6) with
// "不打扰 (do not interrupt) as the first principle" as its bias. It is a pure
// method on Backthink only so it can read the configured quiet-hours window; it
// does not touch state.
//
// The evaluation order is deliberately fail-closed (prefer not interrupting):
//
//  1. A sleeping user is never interrupted.
//  2. A working or busy user is interrupted only by a critical event.
//  3. Inside the quiet-hours (deep-night) window only high/critical events
//     interrupt; low/normal events are deferred.
//  4. In the daytime, high/critical events always interrupt; a normal event
//     interrupts only when the user is quite bored; a low event never does.
func (b *Backthink) Decide(in DecisionInput) Decision {
	s := in.UserState
	if s.Sleeping {
		return Decision{ShouldPush: false, Reason: "user is asleep; not interrupting"}
	}
	if (s.Working || s.Busy) && in.Import < ImportanceCritical {
		return Decision{ShouldPush: false, Reason: "user is working/busy; not interrupting"}
	}
	if b.inQuietHours(in.At) {
		if in.Import >= ImportanceHigh {
			return Decision{ShouldPush: true, Reason: "quiet hours but event is important"}
		}
		return Decision{ShouldPush: false, Reason: "quiet hours; not interrupting"}
	}
	switch in.Import {
	case ImportanceCritical, ImportanceHigh:
		return Decision{ShouldPush: true, Reason: "high/critical importance during daytime"}
	case ImportanceNormal:
		if s.Boredom >= highBoredomThreshold {
			return Decision{ShouldPush: true, Reason: "normal importance and user is bored"}
		}
		return Decision{ShouldPush: false, Reason: "normal importance; not worth interrupting"}
	default:
		return Decision{ShouldPush: false, Reason: "low importance; not interrupting"}
	}
}

// disturbAllowed is the hard "do not disturb" safety gate for an autonomous push
// (design/12 §2 first principle). Unlike Decide it deliberately ignores trigger
// importance — which design/20 P2 replaces with her own judgment — and only blocks
// when it is genuinely inappropriate to interrupt: the user is asleep, working or
// busy, or it is inside the quiet-hours window. The frequency gate (PushGate)
// applies separately inside the pusher.
func (b *Backthink) disturbAllowed(at time.Time, s UserState) bool {
	if s.Sleeping || s.Working || s.Busy {
		return false
	}
	return !b.inQuietHours(at)
}

// interruptReason is the short human-readable note recorded/logged when no push
// goes out (or as the pre-push intent). It keeps the panel self-explanatory:
// either she concluded no push, or the do-not-disturb gate refused a push she
// wanted.
func (b *Backthink) interruptReason(push bool, at time.Time, s UserState) string {
	switch {
	case !push:
		return "conclusion requested no push"
	case !b.disturbAllowed(at, s):
		return "proactive push blocked by do-not-disturb"
	default:
		return "proactive push approved"
	}
}

// inQuietHours reports whether at falls inside the configured do-not-disturb
// window. The window may wrap midnight (e.g. 23:00-07:00); two equal non-zero
// hours disable it.
func (b *Backthink) inQuietHours(at time.Time) bool {
	h := at.Hour()
	start, end := b.cfg.QuietStartHour, b.cfg.QuietEndHour
	if start <= end {
		return h >= start && h < end
	}
	return h >= start || h < end
}