package session

import (
	"context"
	"database/sql"
	"fmt"
	"log/slog"
	"strings"
	"sync"
	"time"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/channel/adapter"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/logger"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/user"
)

// DDL for the channel↔session mapping. The composite primary key over
// (platform, channel_id) is the unique key the design requires: each real-world
// channel maps to exactly one internal session_id. created_at/updated_at follow
// the project's timestamp convention; actor_role records the identity lane so the
// mapping survives restarts.
//
// The created_at/updated_at DEFAULT expressions are a fallback only: every write
// path (insertOrIgnoreSessionSQL) supplies explicit fixed-width UTC timestamps
// via formatSessionTime, so the 3-digit-millisecond strftime defaults are never
// exercised and no row mixes timestamp widths.
const createTableSQL = `
CREATE TABLE IF NOT EXISTS channel_sessions (
    platform    TEXT NOT NULL,
    channel_id  TEXT NOT NULL,
    session_id  TEXT NOT NULL,
    actor_role  TEXT NOT NULL,
    created_at  TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now')),
    updated_at  TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now')),
    PRIMARY KEY (platform, channel_id)
)`

const createIndexSQL = `
CREATE INDEX IF NOT EXISTS idx_channel_sessions_actor_role ON channel_sessions(actor_role)`

const insertOrIgnoreSessionSQL = `
INSERT OR IGNORE INTO channel_sessions
    (platform, channel_id, session_id, actor_role, created_at, updated_at)
VALUES (?, ?, ?, ?, ?, ?)`

const selectSessionSQL = `
SELECT session_id FROM channel_sessions WHERE platform = ? AND channel_id = ?`

// listSessionsSQL selects every persisted channel mapping, newest first. Group
// sessions key on a channel_id carrying groupChannelPrefix; direct sessions use
// their channel id. created_at is fixed-width UTC text (see sessionTimeLayout),
// so its text order is its time order; rowid breaks created_at ties so mappings
// written in the same coarse clock tick still list in a stable order
// (channel_sessions is an ordinary rowid table, not WITHOUT ROWID).
const listSessionSQL = `
SELECT platform, channel_id, session_id, actor_role FROM channel_sessions
ORDER BY created_at DESC, rowid DESC`

// groupChannelPrefix marks a channel id as a group conversation so a session
// reconstructed from the backing table (where no IsGroup flag is persisted) can
// still report group membership.
const groupChannelPrefix = "group:"

// SessionManager owns the channel↔session mapping. It backs the map with the
// SQLite table channel_sessions so a channel keeps its internal session across
// restarts, and it caches lookups in memory to avoid a query per message. The
// cache is guarded by an RWMutex for concurrent adapter use.
type SessionManager struct {
	mu    sync.RWMutex
	db    *sql.DB
	log   *slog.Logger
	cache map[string]Session
}

// New builds a SessionManager, ensuring the channel_sessions table and its index
// exist. It performs no migration bookkeeping: the schema is created here so the
// module is self-contained. A nil db is rejected. ctx is used for DDL.
func New(ctx context.Context, db *sql.DB, log *slog.Logger) (*SessionManager, error) {
	if db == nil {
		return nil, ErrNilDB
	}
	log = logger.WithSource(log, "channel/session")
	if _, err := db.ExecContext(ctx, createTableSQL); err != nil {
		return nil, fmt.Errorf("session: ensure channel_sessions: %w", err)
	}
	if _, err := db.ExecContext(ctx, createIndexSQL); err != nil {
		return nil, fmt.Errorf("session: ensure channel_sessions index: %w", err)
	}
	return &SessionManager{db: db, log: log, cache: make(map[string]Session)}, nil
}

// GetOrCreate resolves the actor for msg and returns the Session bound to the
// (platform, channel) the message represents, creating the mapping on first
// sight. The owner whitelist is applied here (ResolveActor), so the owner flag
// is set structurally rather than from prompt text. Concurrent calls for the
// same channel return the same session.
func (m *SessionManager) GetOrCreate(ctx context.Context, msg adapter.UnifiedMessage, owner *user.OwnerProfile) (Session, error) {
	actor := ResolveActor(msg, owner)
	cid := channelID(msg)
	if cid == "" {
		return Session{}, fmt.Errorf("session: get-or-create %s: %w", msg.Platform, ErrInvalidChannel)
	}
	key := msg.Platform + "\x00" + cid

	if s, ok := m.lookupCached(key); ok {
		return s, nil
	}

	m.mu.Lock()
	defer m.mu.Unlock()
	if s, ok := m.cache[key]; ok {
		return s, nil
	}

	sessionID, err := m.persist(ctx, msg.Platform, cid, actor)
	if err != nil {
		return Session{}, err
	}

	s := Session{
		Platform:    msg.Platform,
		ChannelID:   cid,
		SessionID:   sessionID,
		ActorRole:   actor.Role,
		Owner:       actor.IsOwner(),
		IsGroup:     actor.IsGroupChat(),
		MemWritable: actor.IsOwner() && !actor.IsGroupChat(),
	}
	m.cache[key] = s
	return s, nil
}

// List returns every known session, newest first, across the backing table and
// the in-memory cache. Rows that are still in the cache are returned with their
// full derived metadata (Owner/IsGroup/MemWritable from the original resolve);
// rows recovered from the table (for example from a previous process) are
// reconstructed from the persisted actor role. The returned slice is non-nil. It
// is safe for concurrent use.
func (m *SessionManager) List(ctx context.Context) ([]Session, error) {
	rows, err := m.db.QueryContext(ctx, listSessionSQL)
	if err != nil {
		return nil, fmt.Errorf("session: list: %w", err)
	}
	defer func() { _ = rows.Close() }()

	sessions := make([]Session, 0)
	for rows.Next() {
		var platform, cid, sessionID, roleStr string
		if err := rows.Scan(&platform, &cid, &sessionID, &roleStr); err != nil {
			return nil, fmt.Errorf("session: scan list: %w", err)
		}
		key := platform + "\x00" + cid
		if cached, ok := m.lookupCached(key); ok {
			sessions = append(sessions, cached)
			continue
		}
		role := adapter.Role(roleStr)
		owner := role == adapter.RoleOwner
		isGroup := strings.HasPrefix(cid, groupChannelPrefix)
		sessions = append(sessions, Session{
			Platform:    platform,
			ChannelID:   cid,
			SessionID:   sessionID,
			ActorRole:   role,
			Owner:       owner,
			IsGroup:     isGroup,
			MemWritable: owner && !isGroup,
		})
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("session: iterate list: %w", err)
	}
	return sessions, nil
}

// lookupCached returns the cached session for key under a read lock.
func (m *SessionManager) lookupCached(key string) (Session, bool) {
	m.mu.RLock()
	defer m.mu.RUnlock()
	s, ok := m.cache[key]
	return s, ok
}

// persist writes the channel mapping if it does not exist yet and reads back the
// canonical session_id. INSERT OR IGNORE makes it safe under concurrency: the
// winning writer's session_id becomes the binding. It is called under the write
// lock so the in-memory cache and the table stay in agreement.
func (m *SessionManager) persist(ctx context.Context, platform, cid string, actor adapter.Actor) (string, error) {
	now := formatSessionTime(time.Now())
	if _, err := m.db.ExecContext(ctx, insertOrIgnoreSessionSQL, platform, cid, newSessionID(), string(actor.Role), now, now); err != nil {
		return "", fmt.Errorf("session: persist %s/%s: %w", platform, cid, err)
	}
	var sessionID string
	if err := m.db.QueryRowContext(ctx, selectSessionSQL, platform, cid).Scan(&sessionID); err != nil {
		return "", fmt.Errorf("session: read back %s/%s: %w", platform, cid, err)
	}
	if m.log != nil {
		m.log.Debug("channel session bound",
			"platform", platform, "channel_id", cid, "session_id", sessionID, "actor_role", actor.Role)
	}
	return sessionID, nil
}

// channelID derives the stable channel key used for session mapping. Group
// messages key on the group (prefixed so a group never collides with a direct
// channel of the same id); direct messages key on their channel id, falling back
// to the sender id when no explicit channel id is present.
func channelID(msg adapter.UnifiedMessage) string {
	if msg.IsGroup() {
		if msg.GroupID != "" {
			return groupChannelPrefix + msg.GroupID
		}
		return msg.ChannelID
	}
	if msg.ChannelID != "" {
		return msg.ChannelID
	}
	return msg.SenderID
}