// Copyright (c) 2026 Storm Dragon
// SPDX-License-Identifier: GPL-3.0-or-later

package tentacle

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"git.stormux.org/storm/cthulhu/internal/input"
)

type Limits struct {
	Processes         int
	Starting          int
	PendingPerProcess int
	PendingTotal      int
	StartupTimeout    time.Duration
	RequestTimeout    time.Duration
	ShutdownTimeout   time.Duration
}

func DefaultLimits() Limits {
	return Limits{Processes: 16, Starting: 2, PendingPerProcess: 8, PendingTotal: 64,
		StartupTimeout: 3 * time.Second, RequestTimeout: 2 * time.Second, ShutdownTimeout: 250 * time.Millisecond}
}

// Spec is a validated launch description, independent of package metadata.
// Program[0] must be absolute; arguments are never interpreted by a shell.
type Spec struct {
	ID           string
	Program      []string
	Directory    string
	Presentation bool // Explicit local grant for command speech/braille results.
	Interaction  bool // Internal forms and explicit focused-item/clipboard exchanges.
}

type Stats struct {
	Processes int
	Starting  int
	Pending   int
}

type Manager struct {
	mutex        sync.Mutex
	limits       Limits
	sessions     map[string]*Session
	starting     chan struct{}
	pending      chan struct{}
	closed       bool
	coreBindings map[input.KeyboardLayout]input.CommandBindings
	containment  *containment
	delegation   *Delegation
	cleanupError error
}

// NewDelegatedManager keeps exec inside the delegated service. This is required
// when the reader's own cgroup is outside that service's delegation boundary.
func NewDelegatedManager(delegation *Delegation) (*Manager, error) {
	manager, err := NewContainedManager(DefaultLimits(), nil, delegation.Parent, DefaultResourceLimits())
	if err == nil {
		manager.delegation = delegation
	}
	return manager, err
}

// NewManager is the uncontained host for explicit trusted protocol fixtures.
// Reader integration must use NewContainedManager; there is no implicit fallback.
func NewManager(limits Limits, overrides []input.BindingOverride) (*Manager, error) {
	if limits.Processes < 1 || limits.Starting < 1 || limits.Starting > limits.Processes ||
		limits.PendingPerProcess < 1 || limits.PendingTotal < limits.PendingPerProcess ||
		limits.StartupTimeout <= 0 || limits.RequestTimeout <= 0 || limits.ShutdownTimeout <= 0 {
		return nil, errors.New("invalid tentacle host limits")
	}
	if err := input.ValidateBindingOverrides(overrides); err != nil {
		return nil, err
	}
	coreBindings := make(map[input.KeyboardLayout]input.CommandBindings)
	for _, layout := range []input.KeyboardLayout{input.DesktopKeyboardLayout, input.LaptopKeyboardLayout} {
		bindings, err := input.ResolveCommandBindings(layout, true, overrides)
		if err != nil {
			return nil, err
		}
		coreBindings[layout] = bindings
	}
	return &Manager{limits: limits, sessions: make(map[string]*Session), coreBindings: coreBindings,
		starting: make(chan struct{}, limits.Starting), pending: make(chan struct{}, limits.PendingTotal)}, nil
}

// Start reserves capacity and returns immediately. Ready closes after the child
// has either staged a valid registration or failed; Done includes worker joins.
// Rejected admission starts no process and changes no desired enablement.
func (manager *Manager) Start(ctx context.Context, spec Spec) (*Session, error) {
	if ctx == nil {
		return nil, errors.New("nil tentacle context")
	}
	if err := ctx.Err(); err != nil {
		return nil, err
	}
	if err := validate_spec(spec); err != nil {
		return nil, err
	}
	manager.mutex.Lock()
	defer manager.mutex.Unlock()
	if manager.cleanupError != nil {
		return nil, manager.cleanupError
	}
	if manager.closed {
		return nil, ErrUnavailable
	}
	if len(manager.sessions) >= manager.limits.Processes || manager.sessions[spec.ID] != nil {
		return nil, ErrBusy
	}
	select {
	case manager.starting <- struct{}{}:
	default:
		return nil, ErrBusy
	}
	var identity [16]byte
	if _, err := rand.Read(identity[:]); err != nil {
		<-manager.starting
		return nil, err
	}
	spec.Program = append([]string{}, spec.Program...)
	sessionContext, cancel := context.WithCancel(ctx)
	outputContext, revokeOutput := context.WithCancel(sessionContext)
	session := &Session{manager: manager, spec: spec, identity: hex.EncodeToString(identity[:]),
		outputContext: outputContext, revokeOutput: revokeOutput,
		ctx: sessionContext, cancel: cancel, state: Starting, ready: make(chan struct{}), done: make(chan struct{}),
		stop: make(chan struct{}), revoked: make(chan struct{}), outbound: make(chan outgoing, manager.limits.PendingPerProcess+2),
		pending: make(map[string]*pendingCall)}
	manager.sessions[spec.ID] = session
	go session.run()
	return session, nil
}

func (manager *Manager) Stats() Stats {
	manager.mutex.Lock()
	defer manager.mutex.Unlock()
	return Stats{Processes: len(manager.sessions), Starting: len(manager.starting), Pending: len(manager.pending)}
}

// Shutdown may wait for children and is intended for the lifecycle worker.
// Disable itself is nonblocking and revokes dispatch before requesting exit.
func (manager *Manager) Shutdown(ctx context.Context) error {
	manager.mutex.Lock()
	manager.closed = true
	sessions := make([]*Session, 0, len(manager.sessions))
	for _, session := range manager.sessions {
		sessions = append(sessions, session)
		session.Disable()
	}
	manager.mutex.Unlock()
	for _, session := range sessions {
		select {
		case <-session.Done():
		case <-ctx.Done():
			return ctx.Err()
		}
	}
	manager.mutex.Lock()
	defer manager.mutex.Unlock()
	if manager.cleanupError != nil {
		return manager.cleanupError
	}
	if manager.containment != nil {
		if err := manager.containment.group.remove(); err != nil {
			manager.cleanupError = err
			return err
		}
		manager.containment = nil
	}
	return nil
}

func validate_spec(spec Spec) error {
	if spec.Interaction && !spec.Presentation || !valid_id(spec.ID) || len(spec.Program) == 0 || len(spec.Program) > 32 ||
		!filepath.IsAbs(spec.Program[0]) || (spec.Directory != "" && !filepath.IsAbs(spec.Directory)) {
		return errors.New("invalid local tentacle launch")
	}
	for _, argument := range append(append([]string{}, spec.Program...), spec.Directory) {
		if len(argument) > 4096 || strings.ContainsRune(argument, 0) {
			return errors.New("invalid local tentacle argument")
		}
	}
	return nil
}