//go:build linux

package agent

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"syscall"
	"time"

	processharness "github.com/nezhahq/nezha/integration/agentcompat/internal/process"
)

type ProcessIdentity struct {
	Generation     uint64
	PID            int
	ProcessGroupID int
}

type ProcessTransition struct {
	Previous ProcessIdentity
	Current  ProcessIdentity
}

type processGeneration struct {
	supervisor *processharness.Supervisor
	identity   ProcessIdentity
	record     processharness.CleanupRecord
}

func (agent *Agent) RuntimeIdentity() ProcessIdentity {
	agent.processMu.Lock()
	defer agent.processMu.Unlock()
	if agent.currentProcess == nil {
		return ProcessIdentity{}
	}
	return agent.currentProcess.identity
}

func (agent *Agent) StartProcess(ctx context.Context) (ProcessTransition, error) {
	agent.processMu.Lock()
	defer agent.processMu.Unlock()
	if agent.closed {
		return ProcessTransition{}, errors.New("agent is closed")
	}
	if agent.currentProcess != nil {
		return ProcessTransition{}, errors.New("agent process is already running")
	}
	agent.generation++
	logFile, err := agent.workspace.Log(fmt.Sprintf("agent-%s-generation-%d", strings.ReplaceAll(agent.uuid, "-", ""), agent.generation))
	if err != nil {
		return ProcessTransition{}, err
	}
	agent.logPath = logFile.Name()
	newSupervisor := processharness.NewSupervisor
	if agent.startConfig.newSupervisor != nil {
		newSupervisor = agent.startConfig.newSupervisor
	}
	supervisor := newSupervisor(ctx, processharness.Spec{
		Name: "agent", Path: agent.binaryPath, Args: []string{"-c", agent.configPath}, Env: agent.environment,
		Stdout: logFile, Stderr: logFile, MaxLogBytes: agentMaxLogBytes,
		TerminateTimeout: agentStopTimeout, KillTimeout: agentKillTimeout,
		Credential: agent.startConfig.Credential,
	})
	if err := supervisor.Start(); err != nil {
		return ProcessTransition{}, err
	}
	identity := ProcessIdentity{Generation: agent.generation, PID: supervisor.PID(), ProcessGroupID: supervisor.ProcessGroupID()}
	generation := &processGeneration{supervisor: supervisor, identity: identity, record: supervisor.CleanupRecord()}
	// Register the started generation before post-start setup so failures remain cleanup-owned.
	agent.currentProcess = generation
	agent.supervisor = supervisor
	agent.processes = append(agent.processes, generation)
	if err := agent.trackPID(identity.PID); err != nil {
		return agent.rollbackStartedProcess(ctx, generation, err)
	}
	if err := agent.trackProcessGroup(identity.ProcessGroupID); err != nil {
		return agent.rollbackStartedProcess(ctx, generation, err)
	}
	previous := ProcessIdentity{}
	return ProcessTransition{Previous: previous, Current: identity}, nil
}

func (agent *Agent) rollbackStartedProcess(ctx context.Context, generation *processGeneration, trackingErr error) (ProcessTransition, error) {
	agent.currentProcess = nil
	agent.supervisor = nil
	rollbackContext, cancel := context.WithTimeout(context.WithoutCancel(ctx), 15*time.Second)
	defer cancel()
	rollbackErr := generation.supervisor.Stop(rollbackContext)
	generation.record = generation.supervisor.CleanupRecord()
	return ProcessTransition{}, errors.Join(trackingErr, rollbackErr)
}

func (agent *Agent) StopProcess(ctx context.Context) (ProcessTransition, error) {
	agent.processMu.Lock()
	process := agent.currentProcess
	if process == nil {
		agent.processMu.Unlock()
		return ProcessTransition{}, errors.New("agent process is not running")
	}
	agent.currentProcess = nil
	agent.supervisor = nil
	agent.processMu.Unlock()
	if err := process.supervisor.Stop(ctx); err != nil {
		return ProcessTransition{Previous: process.identity}, fmt.Errorf("stop agent process: %w", err)
	}
	process.record = process.supervisor.CleanupRecord()
	return ProcessTransition{Previous: process.identity}, nil
}

func (agent *Agent) RestartProcess(ctx context.Context) (ProcessTransition, error) {
	stopped, err := agent.StopProcess(ctx)
	if err != nil {
		return stopped, err
	}
	started, err := agent.StartProcess(ctx)
	if err != nil {
		return ProcessTransition{Previous: stopped.Previous}, err
	}
	return ProcessTransition{Previous: stopped.Previous, Current: started.Current}, nil
}

func (agent *Agent) Restart(ctx context.Context) error {
	_, err := agent.RestartProcess(ctx)
	return err
}

func (agent *Agent) Close(ctx context.Context) error {
	agent.processMu.Lock()
	agent.closed = true
	agent.processMu.Unlock()
	return agent.Stop(ctx)
}

func (agent *Agent) closeProcesses(ctx context.Context) error {
	agent.processMu.Lock()
	processes := append([]*processGeneration(nil), agent.processes...)
	agent.processMu.Unlock()
	var cleanupError error
	for _, process := range processes {
		stopContext, cancel := context.WithTimeout(ctx, 15*time.Second)
		cleanupError = errors.Join(cleanupError, process.supervisor.Stop(stopContext))
		cancel()
		process.record = process.supervisor.CleanupRecord()
	}
	return cleanupError
}

func (agent *Agent) processesQuiescent() bool {
	agent.processMu.Lock()
	processes := append([]*processGeneration(nil), agent.processes...)
	agent.processMu.Unlock()
	for _, process := range processes {
		select {
		case <-process.supervisor.Exited():
		default:
			return false
		}
		err := syscall.Kill(-process.identity.ProcessGroupID, 0)
		if err == nil || errors.Is(err, syscall.EPERM) {
			return false
		}
		if !errors.Is(err, syscall.ESRCH) {
			return false
		}
	}
	return true
}