package runtime

import (
	"encoding/json"
	"io/ioutil"
	"os"
	"path/filepath"
	"syscall"

	"github.com/Sirupsen/logrus"
)

type Container interface {
	// ID returns the container ID
	ID() string
	// Path returns the path to the bundle
	Path() string
	// Start starts the init process of the container
	Start(checkpoint string, s Stdio) (Process, error)
	// Exec starts another process in an existing container
	Exec(string, ProcessSpec, Stdio) (Process, error)
	// Delete removes the container's state and any resources
	Delete() error
	// Processes returns all the containers processes that have been added
	Processes() ([]Process, error)
	// State returns the containers runtime state
	State() State
	// Resume resumes a paused container
	Resume() error
	// Pause pauses a running container
	Pause() error
	// RemoveProcess removes the specified process from the container
	RemoveProcess(string) error
	// Checkpoints returns all the checkpoints for a container
	Checkpoints() ([]Checkpoint, error)
	// Checkpoint creates a new checkpoint
	Checkpoint(Checkpoint) error
	// DeleteCheckpoint deletes the checkpoint for the provided name
	DeleteCheckpoint(name string) error
	// Labels are user provided labels for the container
	Labels() []string
	// Pids returns all pids inside the container
	Pids() ([]int, error)
	// Stats returns realtime container stats and resource information
	Stats() (*Stat, error)
	// Name or path of the OCI compliant runtime used to execute the container
	Runtime() string
	// OOM signals the channel if the container received an OOM notification
	// OOM() (<-chan struct{}, error)
}

type Stdio struct {
	Stdin  string
	Stdout string
	Stderr string
}

func NewStdio(stdin, stdout, stderr string) Stdio {
	for _, s := range []*string{
		&stdin, &stdout, &stderr,
	} {
		if *s == "" {
			*s = "/dev/null"
		}
	}
	return Stdio{
		Stdin:  stdin,
		Stdout: stdout,
		Stderr: stderr,
	}
}

// New returns a new container
func New(root, id, bundle, runtimeName string, labels []string) (Container, error) {
	c := &container{
		root:      root,
		id:        id,
		bundle:    bundle,
		labels:    labels,
		processes: make(map[string]*process),
		runtime:   runtimeName,
	}
	if err := os.Mkdir(filepath.Join(root, id), 0755); err != nil {
		return nil, err
	}
	f, err := os.Create(filepath.Join(root, id, StateFile))
	if err != nil {
		return nil, err
	}
	defer f.Close()
	if err := json.NewEncoder(f).Encode(state{
		Bundle:  bundle,
		Labels:  labels,
		Runtime: runtimeName,
	}); err != nil {
		return nil, err
	}
	return c, nil
}

func Load(root, id string) (Container, error) {
	var s state
	f, err := os.Open(filepath.Join(root, id, StateFile))
	if err != nil {
		return nil, err
	}
	defer f.Close()
	if err := json.NewDecoder(f).Decode(&s); err != nil {
		return nil, err
	}
	c := &container{
		root:      root,
		id:        id,
		bundle:    s.Bundle,
		labels:    s.Labels,
		runtime:   s.Runtime,
		processes: make(map[string]*process),
	}
	dirs, err := ioutil.ReadDir(filepath.Join(root, id))
	if err != nil {
		return nil, err
	}
	for _, d := range dirs {
		if !d.IsDir() {
			continue
		}
		pid := d.Name()
		s, err := readProcessState(filepath.Join(root, id, pid))
		if err != nil {
			return nil, err
		}
		p, err := loadProcess(filepath.Join(root, id, pid), pid, c, s)
		if err != nil {
			logrus.WithField("id", id).WithField("pid", pid).Debug("containerd: error loading process %s", err)
			continue
		}
		c.processes[pid] = p
	}
	return c, nil
}

func readProcessState(dir string) (*ProcessState, error) {
	f, err := os.Open(filepath.Join(dir, "process.json"))
	if err != nil {
		return nil, err
	}
	defer f.Close()
	var s ProcessState
	if err := json.NewDecoder(f).Decode(&s); err != nil {
		return nil, err
	}
	return &s, nil
}

type container struct {
	// path to store runtime state information
	root      string
	id        string
	bundle    string
	runtime   string
	processes map[string]*process
	stdio     Stdio
	labels    []string
}

func (c *container) ID() string {
	return c.id
}

func (c *container) Path() string {
	return c.bundle
}

func (c *container) Labels() []string {
	return c.labels
}

func (c *container) readSpec() (*PlatformSpec, error) {
	var spec PlatformSpec
	f, err := os.Open(filepath.Join(c.bundle, "config.json"))
	if err != nil {
		return nil, err
	}
	defer f.Close()
	if err := json.NewDecoder(f).Decode(&spec.Spec); err != nil {
		return nil, err
	}
	return &spec, nil
}

func (c *container) State() State {
	proc := c.processes["init"]
	if proc == nil || proc.pid == 0 {
		return Stopped
	}
	err := syscall.Kill(proc.pid, 0)
	if err != nil && err == syscall.ESRCH {
		return Stopped
	}
	return Running
}

func (c *container) Delete() error {
	return os.RemoveAll(filepath.Join(c.root, c.id))
}

func (c *container) Processes() ([]Process, error) {
	out := []Process{}
	for _, p := range c.processes {
		out = append(out, p)
	}
	return out, nil
}

func (c *container) RemoveProcess(pid string) error {
	delete(c.processes, pid)
	return os.RemoveAll(filepath.Join(c.root, c.id, pid))
}