// Package manager orchestrates the high-level lifecycle of WireGuard tunnels
// and their associated network namespaces.
//
// Architecture:
// wg-wrap provides a transparent data path:
// Linux Application -> Linux Kernel Routing -> TUN Device -> Userspace WireGuard -> UDP Socket -> Internet.
//
// Persistent Namespaces & Shared Sessions:
// To support multiple concurrent commands on the same WireGuard tunnel without re-establishing
// connections, wg-wrap employs session-based persistent, unprivileged namespaces.
//
//  1. Tracking: Process usage is tracked using active PID files inside the runtime base directory.
//  2. Ref-Counting & Cleanup: Active PIDs are regularly pruned. When the last active process exits,
//     the namespace is unpinned and resources are reclaimed.
//  3. Setns Join: When a new process is executed on an active profile, it discovers an active PID
//     and attaches itself to the existing User, Mount, and Network namespaces of the active tunnel.
package manager

import (
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"

	"git.theodohertyfamily.com/wg-wrap/internal/config"
	"git.theodohertyfamily.com/wg-wrap/internal/namespace"
	"git.theodohertyfamily.com/wg-wrap/internal/paths"
	"git.theodohertyfamily.com/wg-wrap/internal/wireguard"
	"git.theodohertyfamily.com/wg-wrap/pkg/wgconf"
)

type Manager struct {
	// PM is the path manager used to resolve configuration and runtime directories.
	PM *paths.PathManager
	// NS handles the network namespace operations.
	NS namespace.Ops
}

// New creates a new Manager with the given path manager and namespace operations.
func New(pm *paths.PathManager, ns namespace.Ops) *Manager {
	return &Manager{PM: pm, NS: ns}
}

// Bootstrap ensures the process is running in an isolated user and network namespace.
// If an active session already exists for the profile, it joins it.
func (m *Manager) Bootstrap(cfg *config.Config) error {
	if m.NS.IsIsolated() {
		return nil
	}

	// Preserve the host runtime base dir in the environment before bootstrapping.
	_ = os.Setenv("WG_WRAP_HOST_RUNTIME_BASE_DIR", m.PM.RuntimeBaseDir())

	// Acquire startup lock to prevent concurrent bootstrap/joining races.
	lockFile, lockErr := m.NS.AcquireProfileLock(m.PM, cfg.Profile)
	if lockErr == nil {
		defer m.NS.ReleaseProfileLock(lockFile)
	}

	// Before bootstrapping, see if an active namespace/process for the profile exists.
	activePid, err := m.NS.FindActiveProfilePid(m.PM, cfg.Profile)
	if err == nil && activePid > 0 {
		// Release the lock before executing the command to allow others to join.
		m.NS.ReleaseProfileLock(lockFile)

		// Register this PID before joining to prevent the race where the joining process
		// hasn't registered itself yet, causing the existing process to think it's the last one.
		_ = m.NS.RegisterProcess(m.PM, cfg.Profile)

		if err := m.NS.BootstrapJoin(activePid); err != nil {
			return fmt.Errorf("failed to join existing namespace: %w", err)
		}
		return nil
	}

	if err := m.NS.Bootstrap(); err != nil {
		return fmt.Errorf("bootstrap failed: %w", err)
	}

	return nil
}

// Execute manages the full execution lifecycle inside an isolated namespace:
// lock acquisition, PID registration, tunnel initialization, command execution, and cleanup.
func (m *Manager) Execute(cfg *config.Config, verbose bool) error {
	if !m.NS.IsIsolated() {
		return fmt.Errorf("Execute called without namespace isolation")
	}

	// Acquire execution lock during configuration and startup inside the namespace.
	lockFile, lockErr := m.NS.AcquireProfileLock(m.PM, cfg.Profile)
	var lockFileReleased bool
	if lockErr == nil {
		defer func() {
			if !lockFileReleased {
				m.NS.ReleaseProfileLock(lockFile)
			}
		}()
	}

	if err := m.NS.PruneStalePids(m.PM, cfg.Profile); err != nil {
		fmt.Fprintf(os.Stderr, "failed to prune stale pids: %v\n", err)
	}
	if err := m.NS.RegisterProcess(m.PM, cfg.Profile); err != nil {
		return fmt.Errorf("failed to register process: %w", err)
	}

	defer func() {
		var cleanupLock *os.File
		var cleanupErr error

		if lockErr == nil && !lockFileReleased {
			cleanupLock = lockFile
		} else {
			cleanupLock, cleanupErr = m.NS.AcquireProfileLock(m.PM, cfg.Profile)
		}

		if cleanupErr == nil {
			if err := m.NS.UnregisterProcess(m.PM, cfg.Profile); err != nil {
				fmt.Fprintf(os.Stderr, "failed to unregister process: %v\n", err)
			}

			if err := m.NS.PruneStalePids(m.PM, cfg.Profile); err != nil {
				fmt.Fprintf(os.Stderr, "failed to prune stale pids during cleanup: %v\n", err)
			}

			last, lastErr := m.NS.IsLastProcess(m.PM, cfg.Profile)

			if lastErr == nil && last {
				if err := m.NS.UnpinNamespace(m.PM, cfg.Profile); err != nil {
					fmt.Fprintf(os.Stderr, "failed to unpin namespace: %v\n", err)
				}
			}
			if lockErr == nil && !lockFileReleased {
				lockFileReleased = true
			}
			m.NS.ReleaseProfileLock(cleanupLock)
		} else {
			if err := m.NS.UnregisterProcess(m.PM, cfg.Profile); err != nil {
				fmt.Fprintf(os.Stderr, "failed to unregister process: %v\n", err)
			}
		}
	}()

	if os.Getenv("WG_WRAP_JOINED") == "1" {
		if verbose {
			fmt.Printf("Joining active WireGuard tunnel session for profile %s...\n", cfg.Profile)
		}
	} else {
		if verbose {
			fmt.Printf("Initializing WireGuard tunnel for profile %s...\n", cfg.Profile)
		}

		profilesDir := m.PM.ConfigDir()
		profilePath := filepath.Join(profilesDir, cfg.Profile+".conf")

		if _, err := os.Stat(profilePath); err == nil {
			wgCfg, err := wgconf.Parse(profilePath)
			if err != nil {
				return fmt.Errorf("failed to parse profile %s: %w", cfg.Profile, err)
			}

			dnsServer := cfg.DNSServer
			if dnsServer == "" {
				dnsServer = wgCfg.DNS
			}
			if dnsServer == "" {
				dnsServer = "1.1.1.1"
				hasDefaultRoute := false
				for _, peer := range wgCfg.Peers {
					for _, ip := range peer.AllowedIPs {
						trimmed := strings.TrimSpace(ip)
						if trimmed == "0.0.0.0/0" || trimmed == "::/0" {
							hasDefaultRoute = true
							break
						}
					}
					if hasDefaultRoute {
						break
					}
				}
				if !hasDefaultRoute {
					fmt.Fprintf(os.Stderr, "warning: Falling back to 1.1.1.1, but your profile does not route all traffic (0.0.0.0/0). DNS resolution may fail.\n")
				}
			}

			tunnel, err := wireguard.NewTunnelManager().StartTunnel(m.PM, cfg.Profile, wgCfg, dnsServer)
			if err != nil {
				return fmt.Errorf("failed to start WireGuard tunnel: %w", err)
			}
			defer tunnel.Close(wireguard.NewTunnelManager())

			if err := m.NS.PinNamespace(m.PM, cfg.Profile); err != nil {
				fmt.Fprintf(os.Stderr, "warning: failed to pin namespace: %v\n", err)
			}
		} else {
			if cfg.Profile != "default" {
				return fmt.Errorf("profile %s not found", cfg.Profile)
			}
			fmt.Fprintf(os.Stderr, "warning: default profile configuration not found. Executing command in bare isolation.\n")
		}
	}

	lockFileReleased = true
	m.NS.ReleaseProfileLock(lockFile)

	cmd := exec.Command(cfg.Command[0], cfg.Command[1:]...)
	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	cmd.Env = os.Environ()

	if err := cmd.Run(); err != nil {
		return fmt.Errorf("command execution failed: %w", err)
	}

	return nil
}

// StopProfile stops a profile session by unpinning its namespace.
func (m *Manager) StopProfile(profile string) error {
	if err := m.NS.UnpinNamespace(m.PM, profile); err != nil {
		return fmt.Errorf("failed to stop profile: %w", err)
	}
	return nil
}

// VerifyLifecycle checks for an active session for the given profile.
func (m *Manager) VerifyLifecycle(profile string) error {
	activePid, err := m.NS.FindActiveProfilePid(m.PM, profile)
	if err != nil || activePid <= 0 {
		return fmt.Errorf("no active session found for profile %s", profile)
	}

	fmt.Printf("Active session found for profile %s (PID: %d)\n", profile, activePid)
	return nil
}