package session

import (
	"context"
	"crypto/rand"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"ollie/agent"
	"ollie/backend"
	olog "ollie/log"
	"ollie/paths"
	"ollie/toolsrv"
)

// Config is the configuration for creating a session with an agent.
type Config struct {
	Backend        backend.Backend
	ModelName      string
	Profile        string // config profile name (e.g. "default")
	AgentsDir      string
	SessionsDir    string
	SessionID      string
	AgentID        string
	CWD            string
	History        *agent.History
	Runtime        *agent.Runtime
	NewToolServer  func() toolsrv.Runner
	NewBackend     func(string) (backend.Backend, error)
	Log            *olog.Logger
	MaxSteps       int
	ReadPlanStep   func() string
	ListHandlers   map[string]func() []string
	PromptEnvExtra []string
	Remote         string
	SystemPrompt   string
	EnvBlock       string
	Output         agent.EventHandler
}

// Session owns all session-level state: identity, agents, tool server lifecycle.
type Session struct {
	// Identity
	id    string // immutable UUID, set at creation
	name  string // mutable friendly name, defaults to id prefix
	uname string // immutable user principal (numeric UID)

	// Context lifecycle
	ctx    context.Context
	cancel context.CancelFunc

	// Agent state
	agents       []*agent.Agent
	log          *olog.Logger
	auditLog     *olog.Logger
	sessionsDir  string
	listHandlers map[string]func() []string
	remote       string

	// Environment
	envMu      sync.RWMutex
	env        map[string]string
	plan       []byte
	prevPrompt string

	// Tool server lifecycle
	proc      *toolsrv.Process       // toolsrv subprocess
	keeper    *toolsrv.ProcessKeeper // resilient process manager
	toolsConn toolsrv.Runner         // multiplexed RPC connection
	paused    bool                   // true when paused

	// Tool restrictions
	disallowTools map[string]struct{}

	// Synchronization
	mu sync.RWMutex

	// Autosave
	saveMu    sync.Mutex
	saveDirty bool
	saveTimer *time.Timer
}

// NewSessionID generates a UUIDv4 session identifier.
func NewSessionID() string {
	b := make([]byte, 16)
	rand.Read(b)                //nolint:errcheck
	b[6] = (b[6] & 0x0f) | 0x40 // version 4
	b[8] = (b[8] & 0x3f) | 0x80 // variant 10xx
	return fmt.Sprintf("%08x-%04x-%04x-%04x-%012x",
		b[0:4], b[4:6], b[6:8], b[8:10], b[10:16])
}

// NextUncheckedStep returns the first unchecked step from plan bytes.
func NextUncheckedStep(data []byte) string {
	for _, line := range strings.Split(string(data), "\n") {
		trimmed := strings.TrimSpace(line)
		if strings.HasPrefix(trimmed, "- [ ]") {
			return strings.TrimSpace(trimmed[5:])
		}
	}
	return ""
}

var sweepTmpOnce sync.Once

func ollieTmpDir() string {
	return filepath.Join(paths.DataDir(), "tmp")
}

func sweepStaleTmpDirs() {
	sweepTmpOnce.Do(func() {
		base := ollieTmpDir()
		os.RemoveAll(base)      //nolint:errcheck
		os.MkdirAll(base, 0700) //nolint:errcheck
	})
}

// New creates a session with an owned agent from the given configuration.
func New(cfg Config) *Session {
	sweepStaleTmpDirs()
	if cfg.ModelName != "" {
		cfg.Backend.SetModel(cfg.ModelName)
	}
	if cfg.NewBackend == nil {
		cfg.NewBackend = backend.NewWithName
	}
	rt := cfg.Runtime
	if rt == nil {
		rt = &agent.Runtime{}
	}
	rt.Backend = cfg.Backend
	if cfg.MaxSteps > 0 {
		rt.MaxSteps = cfg.MaxSteps
	}
	if cfg.SessionID != "" {
		os.MkdirAll(filepath.Join(ollieTmpDir(), cfg.SessionID), 0700) //nolint:errcheck
	}

	log := cfg.Log
	if log == nil {
		log = olog.NewWriter("core", olog.LevelError+1, io.Discard, io.Discard)
	}

	auditLog := log.Sub("audit")

	name := cfg.SessionID
	if idx := strings.IndexByte(cfg.SessionID, '-'); idx > 0 {
		name = cfg.SessionID[:idx]
	}

	s := &Session{
		id:           cfg.SessionID,
		name:         name,
		env:          make(map[string]string),
		agents:       make([]*agent.Agent, 0, 1),
		log:          log,
		auditLog:     auditLog,
		sessionsDir:  cfg.SessionsDir,
		remote:       cfg.Remote,
		listHandlers: cfg.ListHandlers,
	}

	ag := agent.NewAgent(agent.AgentCfg{
		History:        cfg.History,
		Runtime:        rt,
		Profile:        cfg.Profile,
		AgentsDir:      cfg.AgentsDir,
		ID:             cfg.AgentID,
		Cwd:            paths.ExpandHome(cfg.CWD),
		SystemPrompt:   cfg.SystemPrompt,
		EnvBlock:       cfg.EnvBlock,
		PromptEnvExtra: cfg.PromptEnvExtra,
		NewToolServer:  cfg.NewToolServer,
		NewBackend:     cfg.NewBackend,
		Output:         cfg.Output,
		Log:            log,
		AuditLog:       auditLog,
		SessionID:      cfg.SessionID,
		StartupMsgs:    rt.Messages,
		ReadPlanStep:   cfg.ReadPlanStep,
		Save:           s.saveSession,
		Flush:          s.flushSave,
	})

	s.agents = append(s.agents, ag)
	ag.SetSessionEnv(s.id)
	return s
}

// FindAgent returns the agent matching the given name or ID, or nil.
func (s *Session) FindAgent(nameOrID string) *agent.Agent {
	for _, ag := range s.agents {
		if ag.Name() == nameOrID || ag.ID() == nameOrID {
			return ag
		}
	}
	return nil
}

// Agents returns the full agent slice.
func (s *Session) Agents() []*agent.Agent { return s.agents }

// AgentAt returns the agent at the given index, or nil.
func (s *Session) AgentAt(idx int) *agent.Agent {
	if idx < 0 || idx >= len(s.agents) {
		return nil
	}
	return s.agents[idx]
}

// AgentCount returns the number of agents.
func (s *Session) AgentCount() int { return len(s.agents) }

// SaveFuncs returns save and flush callbacks suitable for use as
// SaveFuncs returns the save and flush callbacks for use in
// agent.AgentCfg.Save and Flush when adding agents to this session.
func (s *Session) SaveFuncs() (save func(), flush func()) {
	return s.saveSession, s.flushSave
}

// AddAgent appends an agent to the session.
func (s *Session) AddAgent(ag *agent.Agent) {
	s.agents = append(s.agents, ag)
	ag.SetSessionEnv(s.id)
}

// RemoveAgent removes an agent by ID and closes it.
// Returns false if the agent was not found.
func (s *Session) RemoveAgent(id string) bool {
	idx := -1
	for i, ag := range s.agents {
		if ag.ID() == id {
			idx = i
			break
		}
	}
	if idx < 0 {
		return false
	}
	s.agents[idx].Close()
	s.agents = append(s.agents[:idx], s.agents[idx+1:]...)
	return true
}

// Close releases resources for this session.
func (s *Session) Close() {
	s.log.Debug("Close() session=%q", s.id)
	s.flushSave()
	for _, ag := range s.agents {
		ag.Close()
	}
	if s.id != "" {
		os.RemoveAll(filepath.Join(ollieTmpDir(), s.id)) //nolint:errcheck
	}
}

// SetEnv stores a session-scoped variable and propagates to all agents.
func (s *Session) SetEnv(key, value string) {
	s.envMu.Lock()
	s.env[key] = value
	s.envMu.Unlock()
	for _, ag := range s.agents {
		ag.SetEnv(key, value)
	}
}

// Remote returns the remote target (e.g., SSH host) if any.
func (s *Session) Remote() string {
	return s.remote
}

// SetRemote sets the remote target for this session.
func (s *Session) SetRemote(remote string) {
	s.remote = remote
}

// SetSessionID renames the session.
func (s *Session) SetSessionID(newID string) error {
	oldID := s.id
	if oldID == newID {
		return nil
	}
	if s.sessionsDir != "" && oldID != "" {
		for _, suffix := range []string{".json", ".compaction.jsonl"} {
			oldPath := s.activeSessionPath(oldID, suffix)
			if _, err := os.Stat(oldPath); err == nil {
				if err := os.Rename(oldPath, s.activeSessionPath(newID, suffix)); err != nil {
					return fmt.Errorf("rename %s: %w", suffix, err)
				}
			}
		}
	}
	s.id = newID
	for _, ag := range s.agents {
		ag.RenamePreamble(oldID, newID)
	}
	oldTemp := filepath.Join(ollieTmpDir(), oldID)
	newTemp := filepath.Join(ollieTmpDir(), newID)
	if _, err := os.Stat(oldTemp); err == nil {
		os.Rename(oldTemp, newTemp) //nolint:errcheck
	}
	for _, ag := range s.agents {
		ag.SetSessionEnv(newID)
	}
	return nil
}

func (s *Session) activeSessionPath(id, suffix string) string {
	return filepath.Join(s.sessionsDir, "active", id+suffix)
}

func (s *Session) saveSession() {
	s.saveMu.Lock()
	s.saveDirty = true
	if s.saveTimer == nil {
		s.saveTimer = time.AfterFunc(2*time.Second, s.flushSave)
	}
	s.saveMu.Unlock()
}

func (s *Session) flushSave() {
	s.saveMu.Lock()
	dirty := s.saveDirty
	s.saveDirty = false
	if s.saveTimer != nil {
		s.saveTimer.Stop()
		s.saveTimer = nil
	}
	s.saveMu.Unlock()
	if !dirty || s.id == "" || s.sessionsDir == "" {
		return
	}
	// Use PersistSession for consistent format (writes Name field correctly)
	if err := PersistSession(s.Name()); err != nil {
		s.log.Error("session save: %v", err)
	}
}

// Save writes the current session state via PersistSession.
func (s *Session) Save() error {
	return PersistSession(s.Name())
}

// --- Identity accessors ---

// ID returns the immutable session UUID.
func (s *Session) ID() string { return s.id }

// Name returns the mutable friendly name.
func (s *Session) Name() string {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.name
}

// SetName sets the friendly name.
func (s *Session) SetName(name string) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.name = name
}

// Uname returns the immutable user principal.
func (s *Session) Uname() string { return s.uname }

// SetUname sets the user principal (should only be called during init).
func (s *Session) SetUname(uname string) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.uname = uname
}

// --- Context lifecycle ---

// Ctx returns the session context.
func (s *Session) Ctx() context.Context { return s.ctx }

// Cancel cancels the session context.
func (s *Session) Cancel() {
	if s.cancel != nil {
		s.cancel()
	}
}

// SetContext sets the session context and cancel func.
func (s *Session) SetContext(ctx context.Context, cancel context.CancelFunc) {
	s.ctx = ctx
	s.cancel = cancel
}

// --- Tool server lifecycle ---

// Proc returns the tool server process.
func (s *Session) Proc() *toolsrv.Process {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.proc
}

// SetProc sets the tool server process.
func (s *Session) SetProc(proc *toolsrv.Process) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.proc = proc
}

// Keeper returns the process keeper.
func (s *Session) Keeper() *toolsrv.ProcessKeeper {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.keeper
}

// SetKeeper sets the process keeper.
func (s *Session) SetKeeper(keeper *toolsrv.ProcessKeeper) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.keeper = keeper
}

// ToolsConn returns the tool server connection.
func (s *Session) ToolsConn() toolsrv.Runner {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.toolsConn
}

// SetToolsConn sets the tool server connection.
func (s *Session) SetToolsConn(conn toolsrv.Runner) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.toolsConn = conn
}

// IsPaused returns true if the session is paused.
func (s *Session) IsPaused() bool {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.paused
}

// SetPaused sets the paused state directly (used during restore).
func (s *Session) SetPaused(paused bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.paused = paused
}

// IsConnected returns true if the tool server connection is alive.
// Returns false if the session is paused.
func (s *Session) IsConnected() bool {
	s.mu.RLock()
	paused := s.paused
	conn := s.toolsConn
	s.mu.RUnlock()
	if paused || conn == nil {
		return false
	}
	if pinger, ok := conn.(interface{ Ping() error }); ok {
		return pinger.Ping() == nil
	}
	return true
}

// Pause stops the tool server to save resources.
// It cancels the session context (stopping all agent operations),
// kills the tool server process, and marks the session as paused.
func (s *Session) Pause() error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.paused {
		return fmt.Errorf("session already paused")
	}
	// Cancel the session context to stop all agent operations.
	if s.cancel != nil {
		s.cancel()
	}
	// Close the tool server process.
	if s.keeper != nil {
		s.keeper.Close()
	} else if s.proc != nil {
		s.proc.Close()
	}
	// Close any existing connection.
	if s.toolsConn != nil {
		if c, ok := s.toolsConn.(interface{ Close() }); ok {
			c.Close()
		}
		s.toolsConn = nil
	}
	s.paused = true
	// Persist the paused state.
	go s.saveSession()
	return nil
}

// Resume restarts the tool server after a Pause.
// It creates a fresh session context and respawns the tool server.
// For sessions restored in paused state (no keeper), it sets up the tool server from scratch.
func (s *Session) Resume() error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if !s.paused {
		return fmt.Errorf("session not paused")
	}

	// Create a fresh context since the old one was cancelled on pause.
	ctx, cancel := context.WithCancel(serverCtx)
	s.ctx = ctx
	s.cancel = cancel

	// If we have a keeper, use it to respawn. Otherwise set up from scratch.
	if s.keeper != nil {
		s.keeper.SetContext(ctx)
		conn, err := s.keeper.Dial()
		if err != nil {
			return fmt.Errorf("resume failed: %w", err)
		}
		s.toolsConn = conn
	} else {
		// Session was restored paused without infra - set up per-agent.
		for i, ag := range s.agents {
			cwd := ag.Cwd()
			if cwd == "" {
				cwd, _ = os.Getwd()
			}

			// First agent spawns the tool server, others reuse
			var reuseFrom *InfraConfig
			if s.proc != nil {
				reuseFrom = &InfraConfig{
					Proc:      s.proc,
					Keeper:    s.keeper,
					ToolsConn: s.toolsConn,
				}
			}

			infra, err := SetupToolServer(ToolServerConfig{
				Ctx:          ctx,
				CWD:          cwd,
				RemoteTarget: s.remote,
				Yolo:         pkgYolo,
				ReuseFrom:    reuseFrom,
			})
			if err != nil {
				return fmt.Errorf("resume setup for agent %s failed: %w", ag.ID(), err)
			}

			// First agent sets session infra
			if i == 0 {
				s.proc = infra.Proc
				s.keeper = infra.Keeper
				s.toolsConn = infra.ToolsConn
			}

			ag.SetToolServer(infra.NewToolServer, infra.ToolsConn)
		}
	}

	s.paused = false
	// Persist the resumed state.
	go s.saveSession()
	return nil
}

// --- Tool loading ---

// SetDisallowTools sets the tool disallow list.
func (s *Session) SetDisallowTools(disallow map[string]struct{}) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.disallowTools = disallow
}

// LoadTool loads a tool into the tool server.
func (s *Session) LoadTool(name string, ag *agent.Agent) error {
	name = strings.TrimSpace(name)
	if name == "" {
		return nil
	}
	s.mu.RLock()
	_, blocked := s.disallowTools[name]
	s.mu.RUnlock()
	if blocked {
		return fmt.Errorf("tool %q is disallowed for this session", name)
	}
	var runner toolsrv.Runner
	if s.toolsConn != nil {
		runner = s.toolsConn
	} else if ag != nil {
		runner = ag.ToolServer()
	}
	return LoadToolOnRunner(runner, name)
}

// LoadToolOnRunner loads a tool on the given runner.
func LoadToolOnRunner(runner toolsrv.Runner, name string) error {
	if runner == nil {
		return nil
	}
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	args, _ := json.Marshal(map[string]string{"name": name})
	if _, err := runner.CallTool(ctx, "tool_load", json.RawMessage(args)); err != nil {
		return fmt.Errorf("remote load: %w", err)
	}
	return nil
}

// --- Constructor for empty session ---

// NewEmpty creates an empty session without an agent.
func NewEmpty(id string, ctx context.Context, cancel context.CancelFunc) *Session {
	name := id
	if idx := strings.IndexByte(id, '-'); idx > 0 {
		name = id[:idx]
	}
	log := pkgSink.NewLogger("session")
	return &Session{
		id:          id,
		name:        name,
		ctx:         ctx,
		cancel:      cancel,
		env:         make(map[string]string),
		agents:      make([]*agent.Agent, 0),
		log:         log,
		auditLog:    log.Sub("audit"),
		sessionsDir: pkgSessionsDir,
	}
}