// Package ws provides the LiveKit companion process manager.
//
// LiveKitProcess manages the lifecycle of a livekit-server binary running
// alongside chatserver. It auto-generates a minimal livekit.yaml config,
// starts the process, monitors health, and restarts on crash.
package ws

import (
	"context"
	"fmt"
	"log/slog"
	"net/http"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"

	"github.com/J3vb/OwnCord/Server/config"
	"github.com/J3vb/OwnCord/Server/syncutil"
)

// LiveKitProcess manages the companion livekit-server binary.
type LiveKitProcess struct {
	cfg        *config.VoiceConfig
	tlsCfg     *config.TLSConfig
	dataDir    string
	httpClient *http.Client // for health checks — no redirect following

	mu       syncutil.Mutex
	cmd      *exec.Cmd
	cancel   context.CancelFunc
	stopped  bool
	runDone  chan struct{} // closed by runLoop when cmd.Wait() returns
	loopDone chan struct{} // closed when runLoop exits entirely
}

// NewLiveKitProcess creates a new process manager. It does not start the
// process — call Start() to launch the LiveKit server.
// The tlsCfg is used to configure TLS on the LiveKit server using the same
// certs as OwnCord (avoids mixed-content blocks in WebView2).
func NewLiveKitProcess(cfg *config.VoiceConfig, tlsCfg *config.TLSConfig, dataDir string) *LiveKitProcess {
	return &LiveKitProcess{
		cfg:     cfg,
		tlsCfg:  tlsCfg,
		dataDir: dataDir,
		httpClient: &http.Client{
			// Own the transport rather than inheriting http.DefaultTransport:
			// its pool is shared process-wide, and httptest.Server.Close closes
			// its idle connections, which severs in-flight health checks.
			Transport: http.DefaultTransport.(*http.Transport).Clone(),
			CheckRedirect: func(*http.Request, []*http.Request) error {
				return http.ErrUseLastResponse
			},
		},
	}
}

// autoGeneratedMarker identifies a livekit.yaml written by OwnCord. A file
// without this marker is treated as user-managed and never overwritten.
const autoGeneratedMarker = "Auto-generated by OwnCord"

// generateConfig writes a minimal livekit.yaml for the companion process.
// If the file exists and lacks the auto-generated marker, it is treated as
// user-managed and left untouched so operators can set LiveKit options
// OwnCord does not model (ips.includes, interfaces, stun_servers, ...).
func (p *LiveKitProcess) generateConfig() (string, error) {
	cfgPath := filepath.Join(p.dataDir, "livekit.yaml")

	if existing, err := os.ReadFile(cfgPath); err == nil {
		// An empty/whitespace-only file is a truncated leftover, not a
		// user-managed config — regenerate it rather than wedging LiveKit.
		if len(strings.TrimSpace(string(existing))) > 0 &&
			!strings.Contains(string(existing), autoGeneratedMarker) {
			slog.Info("livekit: livekit.yaml is user-managed (auto-generated marker absent), not overwriting", "path", cfgPath)
			slog.Warn("livekit: ensure the keys entry in your livekit.yaml matches voice.livekit_api_key / voice.livekit_api_secret")
			return cfgPath, nil
		}
	} else if !os.IsNotExist(err) {
		return "", fmt.Errorf("reading existing livekit config: %w", err)
	}

	// No TURN TLS config — LiveKit signaling is proxied through OwnCord's
	// HTTPS server at /livekit/*, so no separate TLS is needed on LiveKit.

	// Sanitize credentials for safe YAML interpolation: reject strings
	// containing characters that could break YAML structure.
	//
	// The error names the offending config field but never echoes the
	// offending byte: this error is wrapped by Start() and logged by the
	// caller, so quoting a character from the key or secret would write a
	// byte of a credential to the server log in clear text.
	const unsafeYAML = ":#{}\n\r\"\\"
	for _, cred := range []struct {
		field string
		value string
	}{
		{"voice.livekit_api_key", p.cfg.LiveKitAPIKey},
		{"voice.livekit_api_secret", p.cfg.LiveKitAPISecret},
	} {
		if strings.ContainsAny(cred.value, unsafeYAML) {
			return "", fmt.Errorf(`%s contains a character that cannot be safely written to livekit.yaml (one of : # { } " \ CR LF)`, cred.field)
		}
	}
	// Build node_ip line only when configured (required for remote users behind NAT).
	// Validate: must be a plain IP address (no YAML-breaking chars).
	nodeIPLine := ""
	if p.cfg.NodeIP != "" {
		for _, ch := range p.cfg.NodeIP {
			if ch == '"' || ch == '\\' || ch == '\n' || ch == '\r' || ch == '#' || ch == '{' || ch == '}' {
				return "", fmt.Errorf("node_ip contains unsafe character %q", string(ch))
			}
		}
		nodeIPLine = fmt.Sprintf("\n  node_ip: %q", p.cfg.NodeIP)
	}
	// Advertise LAN host candidates alongside the external mapping so clients
	// on the local network can reach a dual-homed (LAN + public IP) server.
	advertiseInternalLine := ""
	if p.cfg.AdvertiseInternalIP {
		advertiseInternalLine = "\n  advertise_internal_ip: true"
	}

	content := fmt.Sprintf(`# Auto-generated by OwnCord — regenerated on every server start.
# To manage this file yourself (custom rtc options, multiple interfaces, etc.),
# delete the first line above; OwnCord will then leave the file untouched.
# Your keys entry must still match voice.livekit_api_key /
# voice.livekit_api_secret in config.yaml.
port: 7880

rtc:
  port_range_start: 50000
  port_range_end: 60000
  use_external_ip: true%s%s
  pli_throttle:
    low_quality: 500ms
    mid_quality: 1s
    high_quality: 1s

keys:
  "%s": "%s"

logging:
  level: info
`, nodeIPLine, advertiseInternalLine, p.cfg.LiveKitAPIKey, p.cfg.LiveKitAPISecret)

	if err := os.MkdirAll(p.dataDir, 0o750); err != nil {
		return "", fmt.Errorf("creating data dir: %w", err)
	}
	if err := os.WriteFile(cfgPath, []byte(content), 0o600); err != nil {
		return "", fmt.Errorf("writing livekit config: %w", err)
	}

	return cfgPath, nil
}

// Start launches the livekit-server binary. If LiveKitBinaryPath is empty
// and auto-download is disabled, this is a no-op (assumes LiveKit is managed
// externally). With auto-download enabled, the binary is fetched (and
// checksum-verified) in the background before the process starts, so server
// startup is never blocked on the download.
func (p *LiveKitProcess) Start() error {
	if p.cfg.LiveKitBinaryPath == "" && !p.cfg.AutoDownloadLiveKit {
		slog.Info("livekit: no binary path configured, assuming externally managed")
		return nil
	}

	p.mu.Lock()
	defer p.mu.Unlock()

	if p.cmd != nil {
		return fmt.Errorf("livekit process already running")
	}

	cfgPath, err := p.generateConfig()
	if err != nil {
		return fmt.Errorf("generating livekit config: %w", err)
	}

	ctx, cancel := context.WithCancel(context.Background())
	p.cancel = cancel
	p.loopDone = make(chan struct{})

	go func() {
		defer func() {
			p.mu.Lock()
			if p.loopDone != nil {
				close(p.loopDone)
			}
			p.mu.Unlock()
		}()

		binPath := p.cfg.LiveKitBinaryPath
		if binPath == "" {
			resolved, dlErr := p.resolveBinary(ctx)
			if dlErr != nil {
				if ctx.Err() == nil {
					slog.Error("livekit: auto-download failed — voice stays offline until livekit-server is available",
						"error", dlErr,
						"hint", "check the network, or set voice.livekit_binary in config.yaml to a binary you provide")
				}
				return
			}
			binPath = resolved
		}
		p.runLoop(ctx, cfgPath, binPath)
	}()

	return nil
}

// resolveBinary downloads (or reuses a cached copy of) the pinned
// livekit-server release, retrying a few times so a transient network hiccup
// at boot does not permanently disable voice until the next restart.
func (p *LiveKitProcess) resolveBinary(ctx context.Context) (string, error) {
	const (
		attempts   = 3
		retryDelay = 15 * time.Second
	)
	var lastErr error
	for i := range attempts {
		if i > 0 {
			slog.Warn("livekit: retrying download", "attempt", i+1, "error", lastErr)
			select {
			case <-time.After(retryDelay):
			case <-ctx.Done():
				return "", ctx.Err()
			}
		}
		attemptCtx, cancel := context.WithTimeout(ctx, 10*time.Minute)
		path, err := EnsureLiveKitBinary(attemptCtx, p.dataDir, p.cfg.LiveKitVersion)
		cancel()
		if err == nil {
			return path, nil
		}
		lastErr = err
	}
	return "", lastErr
}

// runLoop starts and restarts the process until stopped or context cancelled.
// Uses exponential backoff (3s → 6s → 12s … up to 60s) and stops after 10
// consecutive rapid failures (process exits within 30 seconds). loopDone is
// closed by the Start goroutine that calls this.
func (p *LiveKitProcess) runLoop(ctx context.Context, cfgPath, binPath string) {
	const (
		baseDelay   = 3 * time.Second
		maxDelay    = 60 * time.Second
		maxRetries  = 10
		stableAfter = 30 * time.Second // reset counter if process runs longer than this
	)

	rapidFailures := 0
	delay := baseDelay

	for {
		if ctx.Err() != nil {
			return
		}

		cmd := exec.CommandContext(ctx, binPath, "--config", cfgPath) //nolint:gosec // G204: binary path from trusted server config or verified download
		cmd.Stdout = os.Stdout
		cmd.Stderr = os.Stderr
		cmd.WaitDelay = 6 * time.Second // bound Wait to prevent goroutine leak on Windows
		if attr := liveKitSysProcAttr(); attr != nil {
			// Linux: die with a parent that never ran its teardown (kill -9,
			// OOM, restart-backstop force-exit) instead of orphaning with
			// 7880/UDP still bound.
			cmd.SysProcAttr = attr
		}

		slog.Info("livekit: starting process",
			"binary", binPath,
			"config", cfgPath,
			"rapid_failures", rapidFailures)

		startTime := time.Now()
		p.mu.Lock()
		if p.stopped {
			p.mu.Unlock()
			return
		}
		// Start inside the critical section that publishes p.cmd: Start is
		// what writes cmd.Process, which IsRunning and Stop read under p.mu —
		// started after the unlock, that write races every such read.
		err := cmd.Start()
		if err == nil {
			p.cmd = cmd
			p.runDone = make(chan struct{})
		}
		p.mu.Unlock()

		if err == nil {
			err = cmd.Wait()
		}

		p.mu.Lock()
		p.cmd = nil
		if p.runDone != nil {
			close(p.runDone)
			p.runDone = nil
		}
		stopped := p.stopped
		p.mu.Unlock()

		if stopped || ctx.Err() != nil {
			slog.Info("livekit: process stopped")
			return
		}

		// If the process ran for a while, it was stable — reset backoff.
		if time.Since(startTime) > stableAfter {
			rapidFailures = 0
			delay = baseDelay
		} else {
			rapidFailures++
		}

		if err != nil {
			slog.Error("livekit: process exited unexpectedly",
				"error", err,
				"rapid_failures", rapidFailures,
				"restart_delay", delay)
		}

		if rapidFailures >= maxRetries {
			slog.Error("livekit: too many rapid failures, giving up",
				"rapid_failures", rapidFailures)
			return
		}

		select {
		case <-time.After(delay):
			slog.Info("livekit: restarting process")
		case <-ctx.Done():
			return
		}

		// Exponential backoff capped at maxDelay.
		delay *= 2
		if delay > maxDelay {
			delay = maxDelay
		}
	}
}

// IsRunning returns true if the companion process is currently running.
func (p *LiveKitProcess) IsRunning() bool {
	p.mu.Lock()
	defer p.mu.Unlock()
	return p.cmd != nil && p.cmd.Process != nil
}

// HealthCheck probes the LiveKit HTTP endpoint to verify it is accepting
// connections. Returns true if the server responds (any status code).
func (p *LiveKitProcess) HealthCheck(ctx context.Context) (bool, error) {
	httpURL := wsToHTTP(p.cfg.LiveKitURL)

	ctx, cancel := context.WithTimeout(ctx, 3*time.Second)
	defer cancel()

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, httpURL, nil)
	if err != nil {
		return false, fmt.Errorf("creating health check request: %w", err)
	}

	resp, err := p.httpClient.Do(req)
	if err != nil {
		return false, fmt.Errorf("livekit health check failed: %w", err)
	}
	_ = resp.Body.Close()

	return true, nil
}

// Stop gracefully stops the companion process.
// It cancels the context (which signals runLoop) and waits up to 5 seconds
// for the process to exit. The actual cmd.Wait() is done by runLoop — we only
// monitor the process here to avoid calling exec.Cmd.Wait() twice (which has
// undefined behavior).
func (p *LiveKitProcess) Stop() {
	p.mu.Lock()
	p.stopped = true
	cancel := p.cancel
	cmd := p.cmd
	done := p.runDone
	loopDone := p.loopDone
	p.mu.Unlock()

	if cancel != nil {
		cancel()
	}

	// Wait for runLoop's cmd.Wait() to return (which closes runDone).
	// This avoids calling cmd.Wait() or cmd.Process.Wait() from a second
	// goroutine, which is unsafe on Windows.
	if done != nil {
		select {
		case <-done:
			slog.Info("livekit: process exited cleanly")
		case <-time.After(5 * time.Second):
			slog.Warn("livekit: process did not exit in time, killing")
			if cmd != nil && cmd.Process != nil {
				_ = cmd.Process.Kill()
			}
		}
	}

	// Wait for the entire runLoop goroutine to finish, ensuring no
	// new iteration can start after Stop returns.
	if loopDone != nil {
		select {
		case <-loopDone:
		case <-time.After(5 * time.Second):
		}
	}
}