package dialogue

import (
	"sync"
	"time"
)

// Slot names one field of Slots. Named type, not a free string, so a missing
// slot cannot be misspelled — the question phrasing switches on these.
type Slot string

const (
	SlotTime  Slot = "time"  // Slots.Time / HasTime
	SlotKey   Slot = "key"   // Slots.Key / HasKey
	SlotValue Slot = "value" // Slots.Value (paired with Key)
	SlotFn    Slot = "fn"    // Slots.Fn / HasFn
	SlotText  Slot = "text"  // Slots.Text
)

// DefaultMaxAttempts — how many questions she may ask about one request.
// Three, because after three tries the likely problem is that she misheard the
// whole request, not one slot — so another question about that slot won't help.
// Configurable: voice.clarify_max_attempts.
const DefaultMaxAttempts = 3

// PendingQuestion is what Maven holds while she waits for an answer to an open
// question. Unlike the yes/no confirms in cmd/mavend/voice.go, the answer here
// is free text that fills a missing slot rather than a verdict.
type PendingQuestion struct {
	Intent    Intent // what the router already guessed
	Slots     Slots  // what it already filled
	Missing   []Slot // what is still empty, in the order to ask about
	Utterance string // the user's original raw words
	Asked     time.Time
	TTL       time.Duration
	Attempts  int // questions already asked
	// MaxAttempts caps Attempts. 0 ⇒ DefaultMaxAttempts.
	MaxAttempts int
}

// Action reads the parked question as the typed action it is assembling
// (pending.go). Derived rather than stored: the question's fields stay the one
// copy of the truth, so a caller that fills them the old way cannot end up with
// a capability that disagrees with the intent.
func (q *PendingQuestion) Action() PendingAction {
	return PendingAction{
		Capability:  CapabilityFor(q.Intent),
		Slots:       q.Slots,
		Missing:     q.Missing,
		Utterance:   q.Utterance,
		Asked:       q.Asked,
		TTL:         q.TTL,
		Attempts:    q.Attempts,
		MaxAttempts: q.MaxAttempts,
	}
}

// IsExpired and CanAsk answer through the action, so there is exactly one copy
// of the TTL and attempt-cap rules and the widening cannot drift from them.
func (q *PendingQuestion) IsExpired(now time.Time) bool {
	a := q.Action()
	return a.IsExpired(now)
}

// CanAsk reports whether Maven may ask another question about this request.
func (q *PendingQuestion) CanAsk() bool {
	a := q.Action()
	return a.CanAsk()
}

// ClarifyStore holds the parked questions. Same shape and locking as
// SessionStore: keyed by dialogue id, expired entries dropped on read.
//
// Memory only, deliberately, unlike SessionStore — a restart expires every
// parked question and she does not announce that it happened (Vikunja #385,
// written down in docs/design.md). The 90s TTL and the attempt count measure a
// pause in one conversation, and a restart is a gap of unknown length, so a
// restored question would either be dead already or lying about its age. His
// next words route fresh, which is the right answer with or without a notice.
// Do not give this store a persister without re-arguing that.
type ClarifyStore struct {
	mu sync.RWMutex
	// stacks — one stack of parked questions per dialogue id, newest last. It
	// was a single question per id until V-559; a side query has to be able to
	// suspend the active flow and find it still there afterwards (V-561 does
	// the suspending, this only holds the room for it).
	stacks     map[string][]*PendingQuestion
	defaultTTL time.Duration
}

// MaxStackDepth — how many parked questions one dialogue id may hold.
//
// Two, not three. One is the flow he is in, one is the thing he interrupted it
// with, and out loud he does not nest deeper than that: a side query inside a
// side query is a shape typed conversation has and spoken conversation does
// not. The bound is also a promise — every level she keeps is a level she must
// be able to SPEAK when it dies (clarifyGaveUp, clarifyExpiredVariants), and
// two lines of "and the other thing I dropped" is already the limit of what a
// reply can carry.
const MaxStackDepth = 2

func NewClarifyStore(defaultTTL time.Duration) *ClarifyStore {
	if defaultTTL <= 0 {
		// Short, like confirmTTL in voice.go: a clarifying question is a
		// same-breath gesture, a stale one should not eat a later utterance.
		defaultTTL = 90 * time.Second
	}
	return &ClarifyStore{
		stacks:     make(map[string][]*PendingQuestion),
		defaultTTL: defaultTTL,
	}
}

// Put parks a question, replacing the one on top. Called on a clarify decision
// (cmd/mavend/clarify.go), and it is still what the daemon uses: re-asking the
// same request is a new question about the SAME action, so it overwrites rather
// than growing the stack. Push is the deeper one, and nothing calls it yet.
func (s *ClarifyStore) Put(id string, q *PendingQuestion) {
	s.fillTTL(q)
	s.mu.Lock()
	defer s.mu.Unlock()
	stack := s.stacks[id]
	if len(stack) == 0 {
		s.stacks[id] = []*PendingQuestion{q}
		return
	}
	stack[len(stack)-1] = q
}

// Push suspends whatever is parked and puts q on top. The returned question is
// one the depth bound forced out of the bottom of the stack, and the caller MUST
// tell him about it — a parked request that dies without a word leaves him
// thinking it landed, which is the whole reason clarifyGaveUp exists. nil is the
// ordinary case.
func (s *ClarifyStore) Push(id string, q *PendingQuestion) *PendingQuestion {
	s.fillTTL(q)
	s.mu.Lock()
	defer s.mu.Unlock()
	stack := append(s.stacks[id], q)
	var dropped *PendingQuestion
	if len(stack) > MaxStackDepth {
		dropped = stack[0]
		stack = stack[1:]
	}
	s.stacks[id] = stack
	return dropped
}

// Peek returns the live question on top, or nil when there is none. Expired
// entries below it are left alone: TakeExpired is what reports those, and
// dropping one here would be the silent death this store is careful about.
func (s *ClarifyStore) Peek(id string, now time.Time) *PendingQuestion {
	s.mu.RLock()
	stack := s.stacks[id]
	var q *PendingQuestion
	if len(stack) > 0 {
		q = stack[len(stack)-1]
	}
	s.mu.RUnlock()
	if q == nil {
		return nil
	}
	if q.IsExpired(now) {
		s.Delete(id)
		return nil
	}
	return q
}

// Get is Peek under the name every caller already uses. Kept because a clarify
// answer is always about the top of the stack, so the two are the same call.
func (s *ClarifyStore) Get(id string, now time.Time) *PendingQuestion {
	return s.Peek(id, now)
}

// Pop takes the live question off the top and returns it, so the flow beneath
// becomes current again. nil when the top is empty or expired — an expired top
// is dropped along with the rest of the stack, exactly as Peek does, because the
// clock that killed it has been running for everything underneath too.
func (s *ClarifyStore) Pop(id string, now time.Time) *PendingQuestion {
	s.mu.Lock()
	stack := s.stacks[id]
	if len(stack) == 0 {
		s.mu.Unlock()
		return nil
	}
	q := stack[len(stack)-1]
	if q.IsExpired(now) {
		delete(s.stacks, id)
		s.mu.Unlock()
		return nil
	}
	if len(stack) == 1 {
		delete(s.stacks, id)
	} else {
		s.stacks[id] = stack[:len(stack)-1]
	}
	s.mu.Unlock()
	return q
}

// Depth — how many questions are parked for this id, expired ones included.
// Diagnostic; the arbiter in V-560 reads it to know it is inside a flow.
func (s *ClarifyStore) Depth(id string) int {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return len(s.stacks[id])
}

// TakeExpired reports whether a question was parked here but its TTL ran out,
// and drops it. Get drops such a question silently, which leaves the user
// thinking his request is still alive — the caller uses this to tell him it is
// gone before treating his words as a fresh utterance.
//
// It looks at the top only, and drops the whole stack when that one is dead: one
// notice is what a reply can carry, and anything parked under a question that
// timed out has been waiting at least as long.
func (s *ClarifyStore) TakeExpired(id string, now time.Time) bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	stack := s.stacks[id]
	if len(stack) == 0 || !stack[len(stack)-1].IsExpired(now) {
		return false
	}
	delete(s.stacks, id)
	return true
}

// Delete drops every question parked for this id. The old single-slot Delete
// under the old name: at depth one the two are the same, and a caller that means
// "this exchange is over" means all of it.
func (s *ClarifyStore) Delete(id string) {
	s.mu.Lock()
	delete(s.stacks, id)
	s.mu.Unlock()
}

// fillTTL applies the store default to a question parked without one.
func (s *ClarifyStore) fillTTL(q *PendingQuestion) {
	if q.TTL <= 0 {
		q.TTL = s.defaultTTL
	}
}

// Answer merges the slots parsed from the user's answer into the parked ones.
// Only the slots listed in Missing are touched. Within those, a value the answer
// carries WINS over what was parked: she asked about this slot, so «нет, в пять»
// after «в три» must replace the time, not be thrown away.
//
// This is the clarify answer only. A correction in a fresh turn ("вообще-то
// перенеси на пять") is a different code path (followUpMerge) — not here.
//
// Parsing the answer text into `answer` is the caller's job; this package must
// stay free of internal/router.
func (q *PendingQuestion) Answer(text string, answer Slots) Slots {
	out := q.Slots
	for _, slot := range q.Missing {
		switch slot {
		case SlotTime:
			if answer.HasTime {
				out.Time = answer.Time
				out.HasTime = true
			}
		case SlotKey:
			if answer.HasKey {
				out.Key = answer.Key
				out.HasKey = true
			}
		case SlotValue:
			if answer.Value != "" {
				out.Value = answer.Value
			}
		case SlotFn:
			if answer.HasFn {
				out.Fn = answer.Fn
				out.HasFn = true
				out.Args = append([]string(nil), answer.Args...)
			}
		case SlotText:
			if answer.Text != "" {
				out.Text = answer.Text
			} else if out.Text == "" {
				// No parse for a text slot — the raw answer IS the text.
				out.Text = text
			}
		}
	}
	return out
}

// StillMissing lists the slots that are empty in s, out of the ones asked for.
// The caller uses it to decide between acting and dropping the request.
func StillMissing(want []Slot, s Slots) []Slot {
	var out []Slot
	for _, slot := range want {
		empty := false
		switch slot {
		case SlotTime:
			empty = !s.HasTime
		case SlotKey:
			empty = !s.HasKey
		case SlotValue:
			empty = s.Value == ""
		case SlotFn:
			empty = !s.HasFn
		case SlotText:
			empty = s.Text == ""
		}
		if empty {
			out = append(out, slot)
		}
	}
	return out
}