// Package activity holds the app's coordination state: the single active project
// (the repo/task currently in focus) and a bounded feed of what happened — user
// AND Claude actions. Both are in-memory (mirrored to the logs, no datastore —
// AGENT.md §1.3) and queryable so Claude can sync on any turn boundary; new
// events also fan out to subscribers for the browser SSE stream (§8.2). This is
// the foundation the graceful project handoff (§8.3) builds on.
package activity

import (
	"log/slog"
	"sync"
	"time"
)

// Actor is who caused an event.
type Actor string

const (
	ActorUser   Actor = "user"
	ActorClaude Actor = "claude"
	ActorSystem Actor = "system"
)

// Event is one entry in the activity feed.
type Event struct {
	ID     int64     `json:"id"`
	Time   time.Time `json:"time"`
	Actor  Actor     `json:"actor"`
	Kind   string    `json:"kind"`             // e.g. "active-project-changed"
	Repo   string    `json:"repo,omitempty"`   // repo path, when relevant
	Detail string    `json:"detail,omitempty"` // human-readable extra context
}

// Feed is the concurrency-safe active-project + activity store with fan-out.
type Feed struct {
	mu        sync.RWMutex
	active    string // active project path ("" = none)
	events    []Event
	maxEvents int
	nextID    int64
	subs      map[chan Event]struct{}
	log       *slog.Logger
}

// New builds a Feed keeping at most maxEvents recent events.
func New(log *slog.Logger, maxEvents int) *Feed {
	if maxEvents <= 0 {
		maxEvents = 200
	}
	return &Feed{
		maxEvents: maxEvents,
		nextID:    1,
		subs:      make(map[chan Event]struct{}),
		log:       log,
	}
}

// ActiveProject returns the current active project path ("" if none).
func (f *Feed) ActiveProject() string {
	f.mu.RLock()
	defer f.mu.RUnlock()
	return f.active
}

// SetActiveProject sets the active project and records an event. It is a no-op
// (changed=false, zero Event) when path already matches, so repeated sets don't
// spam the feed.
func (f *Feed) SetActiveProject(actor Actor, path string) (Event, bool) {
	f.mu.Lock()
	if f.active == path {
		f.mu.Unlock()
		return Event{}, false
	}
	f.active = path
	ev, subs := f.appendLocked(actor, "active-project-changed", path, "")
	f.mu.Unlock()

	publish(subs, ev)
	return ev, true
}

// Record adds an arbitrary event to the feed.
func (f *Feed) Record(actor Actor, kind, repo, detail string) Event {
	f.mu.Lock()
	ev, subs := f.appendLocked(actor, kind, repo, detail)
	f.mu.Unlock()

	publish(subs, ev)
	return ev
}

// Events returns up to limit of the most recent events, oldest first. limit<=0
// returns all retained events.
func (f *Feed) Events(limit int) []Event {
	f.mu.RLock()
	defer f.mu.RUnlock()
	if limit <= 0 || limit > len(f.events) {
		limit = len(f.events)
	}
	out := make([]Event, limit)
	copy(out, f.events[len(f.events)-limit:])
	return out
}

// Subscribe returns a channel of future events and an unsubscribe func the
// caller MUST invoke when done (e.g. via defer) to avoid leaking the channel.
func (f *Feed) Subscribe() (<-chan Event, func()) {
	ch := make(chan Event, 16)
	f.mu.Lock()
	f.subs[ch] = struct{}{}
	f.mu.Unlock()

	var once sync.Once
	unsub := func() {
		once.Do(func() {
			f.mu.Lock()
			delete(f.subs, ch)
			f.mu.Unlock()
			close(ch)
		})
	}
	return ch, unsub
}

// appendLocked assigns id/time, appends (trimming to maxEvents), logs, and
// returns the event plus a snapshot of subscriber channels to publish to after
// the lock is released. Caller must hold f.mu.
func (f *Feed) appendLocked(actor Actor, kind, repo, detail string) (Event, []chan Event) {
	ev := Event{ID: f.nextID, Time: time.Now(), Actor: actor, Kind: kind, Repo: repo, Detail: detail}
	f.nextID++
	f.events = append(f.events, ev)
	if len(f.events) > f.maxEvents {
		f.events = f.events[len(f.events)-f.maxEvents:]
	}
	if f.log != nil {
		f.log.Info("activity", "actor", actor, "kind", kind, "repo", repo, "detail", detail)
	}
	subs := make([]chan Event, 0, len(f.subs))
	for ch := range f.subs {
		subs = append(subs, ch)
	}
	return ev, subs
}

// publish does a non-blocking send to each subscriber; a full channel (slow
// consumer) drops the event rather than stalling the producer.
func publish(subs []chan Event, ev Event) {
	for _, ch := range subs {
		select {
		case ch <- ev:
		default:
		}
	}
}