// Package streammonitor produces a normalized "live streams" snapshot grouped by
// user from the authoritative server-side monitoring records written by
// internal/nodesessions. It backs an async enforcement loop and admin views.
//
// EXISTENCE is server-observed on every path and never gated by a client report,
// so a "hidden stream" (a disguised client that pulls bytes but withholds
// progress) is always counted:
//   - Edge (multi-node): a record exists in Redis for the whole connection
//     (direct/remux Track..Remove) or while segments are pulled (transcode Touch),
//     and BytesServed/LastServedAt advance only on real bytes.
//   - Integrated: the FuncSource reflects SessionManager.AllSessions(), and a
//     session is unreapable while it holds an in-flight transport marker
//     (BeginTransport/EndTransport around every byte pour) — no client progress
//     required to stay visible.
//
// TIMING is server-observed on every path. LastServedAt advances only when the
// server begins, ends, or writes a media transport. A session that has not
// served media projects an empty LastServedAt and sorts as the stalest over-cap
// victim. See internal/nodesessions for record production.
package streammonitor

import (
	"context"
	"encoding/json"
	"log/slog"
	"time"

	"github.com/redis/go-redis/v9"

	"github.com/Silo-Server/silo-server/internal/nodesessions"
	"github.com/Silo-Server/silo-server/internal/playback"
)

// sessionKeyPrefix is the Redis key prefix under which nodesessions.Tracker
// stores its SessionInfo records — the tracker's own exported constant, so the
// write and read sides can never drift.
const sessionKeyPrefix = nodesessions.KeyPrefix

// scanCount is the COUNT hint passed to SCAN. It bounds the amount of work per
// round trip while keeping the number of round trips reasonable.
const scanCount = 256

// LiveStream is a normalized view of a single active streaming session.
type LiveStream struct {
	SessionID        string
	LogicalSessionID string
	UserID           int // from SessionInfo.AuthUserID
	ProfileID        string
	NodeName         string
	NodeURL          string
	Type             string // play method: direct_play | remux | transcode
	Route            string // origin protocol: native | jellycompat
	MediaFileID      int
	ClientIP         string
	ClientName       string
	Position         float64 // last known playback position (seconds); secondary timing
	HWAccel          string
	LastServedAt     time.Time // parsed from SessionInfo.LastServedAt (zero if absent)
	BytesServed      int64
	StartedAt        time.Time // parsed from SessionInfo.StartedAt (zero if unparseable)
}

// Snapshot is a point-in-time picture of the live streams.
type Snapshot struct {
	Streams []LiveStream
}

// CountByUser returns the number of live streams owned by userID.
func (s Snapshot) CountByUser(userID int) int {
	n := 0
	for _, st := range s.Streams {
		if st.UserID == userID {
			n++
		}
	}
	return n
}

// StreamsForUser returns the live streams owned by userID.
func (s Snapshot) StreamsForUser(userID int) []LiveStream {
	out := make([]LiveStream, 0)
	for _, st := range s.Streams {
		if st.UserID == userID {
			out = append(out, st)
		}
	}
	return out
}

// ByUser groups the live streams by owning user id.
func (s Snapshot) ByUser() map[int][]LiveStream {
	out := make(map[int][]LiveStream)
	for _, st := range s.Streams {
		out[st.UserID] = append(out[st.UserID], st)
	}
	return out
}

// Source yields the current live picture.
type Source interface {
	Snapshot(ctx context.Context) (Snapshot, error)
}

// MultiSource unions several sources into one snapshot, de-duplicating sessions
// that appear in more than one backend (e.g. a session held both in the central
// session manager and mirrored by an edge's Redis record) by keeping the most-
// recently-served copy. A source that errors is skipped (logged), so one
// unavailable backend never blinds the enforcer to the others. This is what lets
// the enforcer see BOTH locally-served (integrated) and edge-served (multi-node)
// streams regardless of whether Redis is configured.
type MultiSource struct {
	sources []Source
}

// NewMultiSource builds a union source over the given sources (nil entries are
// ignored).
func NewMultiSource(sources ...Source) *MultiSource {
	return &MultiSource{sources: sources}
}

// Snapshot merges every sub-source's snapshot, de-duplicated by canonical
// logical session identity when available.
func (m *MultiSource) Snapshot(ctx context.Context) (Snapshot, error) {
	var all []LiveStream
	for _, src := range m.sources {
		if src == nil {
			continue
		}
		snap, err := src.Snapshot(ctx)
		if err != nil {
			slog.Warn("streammonitor: source snapshot failed; skipping", "error", err)
			continue
		}
		all = append(all, snap.Streams...)
	}
	return Snapshot{Streams: mergeStreams(all)}, nil
}

// toLiveStream converts a nodesessions.SessionInfo into a LiveStream, parsing
// the RFC3339 timestamps and tolerating empty/unparseable values (which map to
// the zero time).
func toLiveStream(info nodesessions.SessionInfo) LiveStream {
	return LiveStream{
		SessionID:        info.SessionID,
		LogicalSessionID: info.LogicalSessionID,
		UserID:           info.AuthUserID,
		ProfileID:        info.ProfileID,
		NodeName:         info.NodeName,
		NodeURL:          info.NodeURL,
		Type:             info.Type,
		Route:            info.Route,
		MediaFileID:      info.MediaFileID,
		ClientIP:         info.ClientIP,
		ClientName:       info.ClientName,
		Position:         info.Position,
		HWAccel:          info.HWAccel,
		LastServedAt:     parseTime(info.LastServedAt),
		BytesServed:      info.BytesServed,
		StartedAt:        parseTime(info.StartedAt),
	}
}

// sessionIdentity returns the stable identity used to merge and enforce a
// playback stream. SessionID remains the transport-addressing key on raw node
// records; a logical id, when present, takes precedence only in monitoring.
func sessionIdentity(sessionID, logicalSessionID string) string {
	if logicalSessionID != "" {
		return logicalSessionID
	}
	return sessionID
}

// parseTime parses an RFC3339 timestamp, returning the zero time for empty or
// unparseable input.
func parseTime(s string) time.Time {
	if s == "" {
		return time.Time{}
	}
	t, err := time.Parse(time.RFC3339, s)
	if err != nil {
		slog.Debug("streammonitor: unparseable timestamp", "value", s, "error", err)
		return time.Time{}
	}
	return t
}

// mergeStreams collapses records that share a canonical identity (the logical
// session id when present, otherwise the transport SessionID). The same stream
// can be tracked by more than one node or transport generation. The freshest
// record wins; genuinely distinct logical sessions are retained. The relative
// order of kept records is not guaranteed.
//
// Ownership and attribution are carried forward independently of the freshness
// pick: the transcode node's own start record has no resolved owner (UserID 0)
// and thinner attribution, while the proxy record fronting it does. If the
// ownerless node record happened to be the freshest copy, taking it wholesale
// would bucket the session under user 0 (which the enforcer skips — silently
// exempting it from the concurrency cap) and drop route/client detail from the
// monitor view. So a merged record adopts a resolved owner from either candidate
// and backfills any empty attribution/display field from the other copy.
func mergeStreams(streams []LiveStream) []LiveStream {
	bySession := make(map[string]LiveStream, len(streams))
	for _, st := range streams {
		key := sessionIdentity(st.SessionID, st.LogicalSessionID)
		existing, ok := bySession[key]
		if !ok {
			st.SessionID = key
			bySession[key] = st
			continue
		}
		winner := existing
		other := st
		if st.LastServedAt.After(existing.LastServedAt) {
			winner, other = st, existing
		}
		// If the freshest copy is ownerless, adopt a resolved owner from either
		// candidate so the session is still attributed (and enforced) correctly.
		if winner.UserID <= 0 {
			for _, cand := range []LiveStream{existing, st} {
				if cand.UserID > 0 {
					winner.UserID = cand.UserID
					winner.ProfileID = cand.ProfileID
					winner.MediaFileID = cand.MediaFileID
					break
				}
			}
		}
		// Backfill display/attribution fields the freshest copy lacks so the
		// merged record is as complete as possible for the monitor view.
		if winner.Route == "" {
			winner.Route = other.Route
		}
		if winner.ClientIP == "" {
			winner.ClientIP = other.ClientIP
		}
		if winner.ClientName == "" {
			winner.ClientName = other.ClientName
		}
		if winner.HWAccel == "" {
			winner.HWAccel = other.HWAccel
		}
		if winner.Position == 0 {
			winner.Position = other.Position
		}
		// These are observers of one pour, not independent byte sources.
		winner.BytesServed = max(winner.BytesServed, other.BytesServed)
		winner.SessionID = key
		bySession[key] = winner
	}
	out := make([]LiveStream, 0, len(bySession))
	for _, st := range bySession {
		out = append(out, st)
	}
	return out
}

// DedupeSessionInfos collapses raw monitoring records that share a canonical
// identity, applying the same rules as mergeStreams — keep the most-recently-
// served copy, carry a resolved owner forward, backfill missing attribution —
// but preserving the SessionInfo shape and transport SessionID for surfaces
// whose wire format IS the raw record. Kept as a sibling of mergeStreams rather
// than a shared generic because mergeStreams operates on parsed LiveStream.
func DedupeSessionInfos(infos []nodesessions.SessionInfo) []nodesessions.SessionInfo {
	bySession := make(map[string]nodesessions.SessionInfo, len(infos))
	order := make([]string, 0, len(infos))
	for _, in := range infos {
		key := sessionIdentity(in.SessionID, in.LogicalSessionID)
		existing, ok := bySession[key]
		if !ok {
			bySession[key] = in
			order = append(order, key)
			continue
		}
		winner, other := existing, in
		if parseTime(in.LastServedAt).After(parseTime(existing.LastServedAt)) {
			winner, other = in, existing
		}
		if winner.AuthUserID <= 0 && other.AuthUserID > 0 {
			winner.AuthUserID = other.AuthUserID
			winner.ProfileID = other.ProfileID
			winner.MediaFileID = other.MediaFileID
		}
		if winner.Route == "" {
			winner.Route = other.Route
		}
		if winner.ClientIP == "" {
			winner.ClientIP = other.ClientIP
		}
		if winner.ClientName == "" {
			winner.ClientName = other.ClientName
		}
		if winner.HWAccel == "" {
			winner.HWAccel = other.HWAccel
		}
		if winner.Position == 0 {
			winner.Position = other.Position
		}
		winner.BytesServed = max(winner.BytesServed, other.BytesServed)
		bySession[key] = winner
	}
	out := make([]nodesessions.SessionInfo, 0, len(bySession))
	for _, id := range order {
		out = append(out, bySession[id])
	}
	return out
}

// LiveLocalSessions maps in-process playback sessions into monitoring records
// so integrated streams are visible to both the enforcer and admin view.
func LiveLocalSessions(sm *playback.SessionManager, nodeName string) []nodesessions.SessionInfo {
	if sm == nil {
		return nil
	}
	live := sm.AllSessions()
	out := make([]nodesessions.SessionInfo, 0, len(live))
	for _, s := range live {
		lastServedAt := ""
		if !s.LastServedAt.IsZero() {
			lastServedAt = s.LastServedAt.UTC().Format(time.RFC3339)
		}
		out = append(out, nodesessions.SessionInfo{
			SessionID:    s.ID,
			NodeName:     nodeName,
			AuthUserID:   s.UserID,
			ProfileID:    s.ProfileID,
			Type:         string(s.PlayMethod),
			Route:        s.Origin(),
			MediaFileID:  s.MediaFileID,
			ClientIP:     s.ClientIP,
			ClientName:   s.ClientName,
			Position:     s.Position,
			Resolution:   s.TargetResolution,
			HWAccel:      s.TranscodeHWAccel,
			StartedAt:    s.StartedAt.UTC().Format(time.RFC3339),
			LastServedAt: lastServedAt,
			BytesServed:  s.BytesServed,
		})
	}
	return out
}

// RedisSource reads silo:sessions:* records, producing the multi-node
// authoritative picture.
type RedisSource struct {
	rdb *redis.Client
}

// NewRedisSource creates a RedisSource backed by rdb.
func NewRedisSource(rdb *redis.Client) *RedisSource {
	return &RedisSource{rdb: rdb}
}

// Snapshot SCANs every silo:sessions:* record, decodes it, and returns the
// deduped live picture. The same logical session appearing on multiple nodes or
// transport generations is collapsed to the record with the newest liveness.
func (r *RedisSource) Snapshot(ctx context.Context) (Snapshot, error) {
	if r.rdb == nil {
		return Snapshot{Streams: []LiveStream{}}, nil
	}

	// Fully iterate the cursor to collect matching keys. SCAN (not KEYS) keeps
	// this non-blocking against a large keyspace.
	var keys []string
	var cursor uint64
	for {
		batch, next, err := r.rdb.Scan(ctx, cursor, sessionKeyPrefix+"*", scanCount).Result()
		if err != nil {
			return Snapshot{}, err
		}
		keys = append(keys, batch...)
		cursor = next
		if cursor == 0 {
			break
		}
	}

	if len(keys) == 0 {
		return Snapshot{Streams: []LiveStream{}}, nil
	}

	vals, err := r.rdb.MGet(ctx, keys...).Result()
	if err != nil {
		return Snapshot{}, err
	}

	streams := make([]LiveStream, 0, len(vals))
	for i, v := range vals {
		if v == nil {
			// Key expired between SCAN and MGET; skip.
			continue
		}
		var raw string
		switch val := v.(type) {
		case string:
			raw = val
		case []byte:
			raw = string(val)
		default:
			slog.Debug("streammonitor: unexpected redis value type", "key", keys[i])
			continue
		}
		var info nodesessions.SessionInfo
		if err := json.Unmarshal([]byte(raw), &info); err != nil {
			slog.Debug("streammonitor: unmarshal session record failed", "key", keys[i], "error", err)
			continue
		}
		streams = append(streams, toLiveStream(info))
	}

	return Snapshot{Streams: mergeStreams(streams)}, nil
}

// FuncSource adapts an in-process provider (integrated single-node) that returns
// the local tracker records.
type FuncSource struct {
	fn func(ctx context.Context) ([]nodesessions.SessionInfo, error)
}

// NewFuncSource creates a FuncSource backed by fn.
func NewFuncSource(fn func(ctx context.Context) ([]nodesessions.SessionInfo, error)) *FuncSource {
	return &FuncSource{fn: fn}
}

// Snapshot invokes the wrapped provider and returns the deduped live picture.
func (f *FuncSource) Snapshot(ctx context.Context) (Snapshot, error) {
	if f.fn == nil {
		return Snapshot{Streams: []LiveStream{}}, nil
	}
	infos, err := f.fn(ctx)
	if err != nil {
		return Snapshot{}, err
	}
	streams := make([]LiveStream, 0, len(infos))
	for _, info := range infos {
		streams = append(streams, toLiveStream(info))
	}
	return Snapshot{Streams: mergeStreams(streams)}, nil
}