// Package audit appends rows to the audit_log table. Every mutation
// in the API funnels through this so the operator can answer
// "who did what when?" from a single SELECT.
package audit

import (
	"context"
	"encoding/json"
	"sync"
	"time"

	"github.com/jackc/pgx/v5/pgxpool"
)

type Repo struct {
	Pool *pgxpool.Pool

	subsMu sync.RWMutex
	subs   map[chan Entry]struct{}
}

func New(pool *pgxpool.Pool) *Repo {
	return &Repo{Pool: pool, subs: map[chan Entry]struct{}{}}
}

// Subscribe gibt einen Channel für Live-Audit-Events zurück + ein
// Unsubscribe-Cleanup. Channel-Buffer 32 — bei stehenden Clients
// werden Events gedropt (non-blocking-send).
func (r *Repo) Subscribe() (<-chan Entry, func()) {
	c := make(chan Entry, 32)
	r.subsMu.Lock()
	if r.subs == nil {
		r.subs = map[chan Entry]struct{}{}
	}
	r.subs[c] = struct{}{}
	r.subsMu.Unlock()
	return c, func() {
		r.subsMu.Lock()
		delete(r.subs, c)
		r.subsMu.Unlock()
		close(c)
	}
}

func (r *Repo) broadcast(e Entry) {
	r.subsMu.RLock()
	subs := make([]chan Entry, 0, len(r.subs))
	for c := range r.subs {
		subs = append(subs, c)
	}
	r.subsMu.RUnlock()
	for _, c := range subs {
		select {
		case c <- e:
		default:
		}
	}
}

// Entry mirrors one audit_log row — ListRecent returns these for
// the dashboard's recent-activity card.
type Entry struct {
	ID        int64           `json:"id"`
	Actor     string          `json:"actor"`
	Action    string          `json:"action"`
	Subject   *string         `json:"subject,omitempty"`
	Detail    json.RawMessage `json:"detail,omitempty"`
	NodeID    *string         `json:"node_id,omitempty"`
	CreatedAt time.Time       `json:"created_at"`
}

// ListRecent returns the most recent audit entries, newest first.
// Pass 0 for a sensible default (10).
func (r *Repo) ListRecent(ctx context.Context, limit int) ([]Entry, error) {
	if r == nil || r.Pool == nil {
		return []Entry{}, nil
	}
	if limit <= 0 || limit > 100 {
		limit = 10
	}
	rows, err := r.Pool.Query(ctx, `
SELECT id, actor, action, subject, detail, node_id, created_at
FROM audit_log
ORDER BY created_at DESC, id DESC
LIMIT $1`, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := make([]Entry, 0, limit)
	for rows.Next() {
		var e Entry
		if err := rows.Scan(&e.ID, &e.Actor, &e.Action, &e.Subject, &e.Detail, &e.NodeID, &e.CreatedAt); err != nil {
			return nil, err
		}
		out = append(out, e)
	}
	return out, rows.Err()
}

// Log writes one audit_log row. detail is JSON-encodable (typically a
// map[string]any) — empty map means "no payload". If pool is nil
// (e.g. dev env without DB), Log silently no-ops so handlers don't
// have to guard each call site.
func (r *Repo) Log(ctx context.Context, actor, action, subject string, detail any, nodeID string) error {
	if r == nil || r.Pool == nil {
		return nil
	}
	var detailJSON []byte
	if detail != nil {
		var err error
		detailJSON, err = json.Marshal(detail)
		if err != nil {
			return err
		}
	}
	var subjectArg any = subject
	if subject == "" {
		subjectArg = nil
	}
	var nodeArg any = nodeID
	if nodeID == "" {
		nodeArg = nil
	}
	// RETURNING id+created_at damit der Subscribe-Channel direkt einen
	// vollständigen Entry verteilen kann — Subscriber müssen nicht
	// erneut die DB hitten für die Anzeige.
	var e Entry
	e.Actor = actor
	e.Action = action
	if subject != "" {
		s := subject
		e.Subject = &s
	}
	if len(detailJSON) > 0 {
		e.Detail = json.RawMessage(detailJSON)
	}
	if nodeID != "" {
		n := nodeID
		e.NodeID = &n
	}
	err := r.Pool.QueryRow(ctx, `
INSERT INTO audit_log (actor, action, subject, detail, node_id)
VALUES ($1, $2, $3, $4, $5)
RETURNING id, created_at`,
		actor, action, subjectArg, detailJSON, nodeArg).
		Scan(&e.ID, &e.CreatedAt)
	if err != nil {
		return err
	}
	// Broadcast nach erfolgreichem INSERT — wenn DB ablehnt, sollen
	// Subscribers das Event auch nicht sehen.
	r.broadcast(e)
	return nil
}