// Package service exposes domain services. opslog provides a lightweight
// in-memory pub/sub for streaming admin log events without persisting them.
package service

import (
	"sync"
	"sync/atomic"
	"time"
)

// OpsLogEntry is one streamed log event. All fields are optional except Time
// — any missing data simply renders as empty in the admin UI.
type OpsLogEntry struct {
	Time          time.Time `json:"time"`
	Method        string    `json:"method,omitempty"`
	Path          string    `json:"path,omitempty"`
	Status        int       `json:"status"`
	LatencyMs     int64     `json:"latency_ms"`
	Model         string    `json:"model,omitempty"`
	Stream        bool      `json:"stream,omitempty"`
	AccountID     int64     `json:"account_id,omitempty"`
	GroupID       int64     `json:"group_id,omitempty"`
	APIKeyID      int64     `json:"api_key_id,omitempty"`
	UserID        int64     `json:"user_id,omitempty"`
	Turns         int       `json:"turns,omitempty"`
	PromptChars   int       `json:"prompt_chars,omitempty"`
	ErrorMessage  string    `json:"error_message,omitempty"`
	ErrorDetail   string    `json:"error_detail,omitempty"`
	UpstreamCode  int       `json:"upstream_status,omitempty"`
}

// OpsLogFilter restricts which entries a subscriber receives. Empty fields
// match everything; non-empty fields are AND-combined.
type OpsLogFilter struct {
	MinStatus     int
	Model         string
	AccountID     int64
	GroupID       int64
	MinLatencyMs  int64
}

// matches reports whether the entry passes the filter.
func (f OpsLogFilter) matches(e *OpsLogEntry) bool {
	if f.MinStatus > 0 && e.Status < f.MinStatus {
		return false
	}
	if f.Model != "" && e.Model != f.Model {
		return false
	}
	if f.AccountID > 0 && e.AccountID != f.AccountID {
		return false
	}
	if f.GroupID > 0 && e.GroupID != f.GroupID {
		return false
	}
	if f.MinLatencyMs > 0 && e.LatencyMs < f.MinLatencyMs {
		return false
	}
	return true
}

// OpsLogBroadcaster is a lock-free-ish fan-out broadcaster with a bounded
// ring buffer for history (so freshly connected clients can prime their UI)
// and per-subscriber non-blocking sends (so a slow client never stalls a
// publish on the hot request path).
type OpsLogBroadcaster struct {
	subsMu      sync.RWMutex
	subscribers map[int64]*opsLogSubscription
	nextID      atomic.Int64

	historyMu sync.Mutex
	history   []OpsLogEntry
	histHead  int
	histLen   int
	histCap   int

	// publishedTotal / droppedTotal expose simple ops counters for an
	// admin dashboard cell. Atomic so callers don't need to lock.
	publishedTotal atomic.Int64
	droppedTotal   atomic.Int64
}

type opsLogSubscription struct {
	ch     chan OpsLogEntry
	filter OpsLogFilter
	// closed is set atomically by unsubscribe() before any cleanup. Publish
	// reads this flag under subsMu.RLock and skips closed subscriptions
	// instead of attempting a send-on-closed-channel (which would panic).
	closed atomic.Bool
}

// NewOpsLogBroadcaster constructs a broadcaster. historyCap controls how
// many recent entries are kept for newly connected clients; 1000 is a sane
// default. Pass historyCap<=0 to disable the buffer entirely.
func NewOpsLogBroadcaster(historyCap int) *OpsLogBroadcaster {
	if historyCap < 0 {
		historyCap = 0
	}
	b := &OpsLogBroadcaster{
		subscribers: make(map[int64]*opsLogSubscription),
		histCap:     historyCap,
	}
	if historyCap > 0 {
		b.history = make([]OpsLogEntry, historyCap)
	}
	return b
}

// Publish fans the entry out to every matching subscriber and appends it to
// the history buffer. Never blocks: if a subscriber's channel is full, the
// entry is dropped for that subscriber and the broadcaster's drop counter
// is incremented. Hot-path safe.
//
// The same entry value is delivered (by value) to all subscribers and to
// the ring buffer — no shared mutable pointer is leaked, so subscribers
// holding references to past entries cannot observe later mutations.
func (b *OpsLogBroadcaster) Publish(entry OpsLogEntry) {
	if entry.Time.IsZero() {
		entry.Time = time.Now()
	}
	b.publishedTotal.Add(1)

	b.appendHistory(entry)

	b.subsMu.RLock()
	subs := make([]*opsLogSubscription, 0, len(b.subscribers))
	for _, s := range b.subscribers {
		subs = append(subs, s)
	}
	b.subsMu.RUnlock()

	for _, s := range subs {
		// Skip subscriptions that have been unsubscribed since we snapped
		// the list. Without this check, a concurrent unsubscribe → close(ch)
		// would race the send below and panic on send-to-closed-channel.
		if s.closed.Load() {
			continue
		}
		if !s.filter.matches(&entry) {
			continue
		}
		select {
		case s.ch <- entry:
		default:
			b.droppedTotal.Add(1)
		}
	}
}

// Subscribe registers a new listener. The returned channel is buffered;
// callers MUST drain it. Cancel by calling the returned unsubscribe func
// (idempotent and safe from any goroutine).
//
// IMPORTANT: unsubscribe does NOT close the channel. Closing it would race
// with concurrent Publish goroutines that may already be holding a snapshot
// of the subscription pointer (causing a panic on send-to-closed-channel).
// Instead, unsubscribe (a) sets the closed atomic flag — Publish skips sends
// to flagged subs — and (b) removes from the subscriber map. Any in-flight
// send that slips past the flag check still proceeds harmlessly into the
// channel buffer and is garbage-collected with the channel once the caller
// drops its reference. Subscribers that need to know the broadcaster is
// done with them should rely on the parent ctx, not channel close.
func (b *OpsLogBroadcaster) Subscribe(filter OpsLogFilter, bufSize int) (<-chan OpsLogEntry, func()) {
	if bufSize <= 0 {
		bufSize = 1024
	}
	id := b.nextID.Add(1)
	sub := &opsLogSubscription{
		ch:     make(chan OpsLogEntry, bufSize),
		filter: filter,
	}
	b.subsMu.Lock()
	b.subscribers[id] = sub
	b.subsMu.Unlock()

	var unsubOnce sync.Once
	unsubscribe := func() {
		unsubOnce.Do(func() {
			sub.closed.Store(true)
			b.subsMu.Lock()
			delete(b.subscribers, id)
			b.subsMu.Unlock()
		})
	}
	return sub.ch, unsubscribe
}

// Snapshot returns a copy of the recent history (oldest → newest), filtered
// by the given filter. Used by /admin/ops/logs/recent to prime newly opened
// dashboards before live events arrive.
func (b *OpsLogBroadcaster) Snapshot(filter OpsLogFilter, maxEntries int) []OpsLogEntry {
	b.historyMu.Lock()
	defer b.historyMu.Unlock()

	if b.histLen == 0 {
		return nil
	}
	out := make([]OpsLogEntry, 0, b.histLen)
	start := b.histHead - b.histLen
	if start < 0 {
		start += b.histCap
	}
	for i := 0; i < b.histLen; i++ {
		idx := (start + i) % b.histCap
		e := b.history[idx]
		if !filter.matches(&e) {
			continue
		}
		out = append(out, e)
	}
	if maxEntries > 0 && len(out) > maxEntries {
		out = out[len(out)-maxEntries:]
	}
	return out
}

// Stats reports cumulative publish/drop counts and the current subscriber
// count for diagnostics.
func (b *OpsLogBroadcaster) Stats() (published, dropped int64, subscribers int) {
	b.subsMu.RLock()
	subscribers = len(b.subscribers)
	b.subsMu.RUnlock()
	return b.publishedTotal.Load(), b.droppedTotal.Load(), subscribers
}

func (b *OpsLogBroadcaster) appendHistory(e OpsLogEntry) {
	if b.histCap == 0 {
		return
	}
	b.historyMu.Lock()
	defer b.historyMu.Unlock()
	b.history[b.histHead] = e
	b.histHead = (b.histHead + 1) % b.histCap
	if b.histLen < b.histCap {
		b.histLen++
	}
}