package api

import (
	"encoding/json"
	"fmt"
	"io"
	"strconv"
	"sync"
	"time"
)

const (
	// OriginStart and OriginEnd are the available parameters for the origin
	// argument when streaming a file. They respectively offset from the start
	// and end of a file.
	OriginStart = "start"
	OriginEnd   = "end"
)

// AllocFileInfo holds information about a file inside the AllocDir
type AllocFileInfo struct {
	Name     string
	IsDir    bool
	Size     int64
	FileMode string
	ModTime  time.Time
}

// StreamFrame is used to frame data of a file when streaming
type StreamFrame struct {
	Offset    int64  `json:",omitempty"`
	Data      []byte `json:",omitempty"`
	File      string `json:",omitempty"`
	FileEvent string `json:",omitempty"`
}

// IsHeartbeat returns if the frame is a heartbeat frame
func (s *StreamFrame) IsHeartbeat() bool {
	return len(s.Data) == 0 && s.FileEvent == "" && s.File == "" && s.Offset == 0
}

// AllocFS is used to introspect an allocation directory on a Nomad client
type AllocFS struct {
	client *Client
}

// AllocFS returns an handle to the AllocFS endpoints
func (c *Client) AllocFS() *AllocFS {
	return &AllocFS{client: c}
}

// getNodeClient returns a Client that will dial the node. If the QueryOptions
// is set, the function will ensure that it is initialized and that the Params
// field is valid.
func (a *AllocFS) getNodeClient(node *Node, allocID string, q **QueryOptions) (*Client, error) {
	if node.HTTPAddr == "" {
		return nil, fmt.Errorf("http addr of the node where alloc %q is running is not advertised", allocID)
	}

	region := ""
	if q != nil && *q != nil && (*q).Region != "" {
		region = (*q).Region
	} else if a.client.config.Region != "" {
		// Use the region from the client
		region = a.client.config.Region
	} else {
		// Use the region from the agent
		agentRegion, err := a.client.Agent().Region()
		if err != nil {
			return nil, err
		}
		region = agentRegion
	}

	// Get an API client for the node
	conf := a.client.config.CopyConfig(node.HTTPAddr, node.TLSEnabled)
	conf.TLSConfig.TLSServerName = fmt.Sprintf("client.%s.nomad", region)
	nodeClient, err := NewClient(conf)
	if err != nil {
		return nil, err
	}

	// Set the query params
	if q == nil {
		return nodeClient, nil
	}

	if *q == nil {
		*q = &QueryOptions{}
	}
	if actQ := *q; actQ.Params == nil {
		actQ.Params = make(map[string]string)
	}
	return nodeClient, nil
}

// List is used to list the files at a given path of an allocation directory
func (a *AllocFS) List(alloc *Allocation, path string, q *QueryOptions) ([]*AllocFileInfo, *QueryMeta, error) {
	node, _, err := a.client.Nodes().Info(alloc.NodeID, &QueryOptions{})
	if err != nil {
		return nil, nil, err
	}
	nodeClient, err := a.getNodeClient(node, alloc.ID, &q)
	if err != nil {
		return nil, nil, err
	}
	q.Params["path"] = path

	var resp []*AllocFileInfo
	qm, err := nodeClient.query(fmt.Sprintf("/v1/client/fs/ls/%s", alloc.ID), &resp, q)
	if err != nil {
		return nil, nil, err
	}

	return resp, qm, nil
}

// Stat is used to stat a file at a given path of an allocation directory
func (a *AllocFS) Stat(alloc *Allocation, path string, q *QueryOptions) (*AllocFileInfo, *QueryMeta, error) {
	node, _, err := a.client.Nodes().Info(alloc.NodeID, &QueryOptions{})
	if err != nil {
		return nil, nil, err
	}
	nodeClient, err := a.getNodeClient(node, alloc.ID, &q)
	if err != nil {
		return nil, nil, err
	}
	q.Params["path"] = path

	var resp AllocFileInfo
	qm, err := nodeClient.query(fmt.Sprintf("/v1/client/fs/stat/%s", alloc.ID), &resp, q)
	if err != nil {
		return nil, nil, err
	}
	return &resp, qm, nil
}

// ReadAt is used to read bytes at a given offset until limit at the given path
// in an allocation directory. If limit is <= 0, there is no limit.
func (a *AllocFS) ReadAt(alloc *Allocation, path string, offset int64, limit int64, q *QueryOptions) (io.ReadCloser, error) {
	node, _, err := a.client.Nodes().Info(alloc.NodeID, &QueryOptions{})
	if err != nil {
		return nil, err
	}

	nodeClient, err := a.getNodeClient(node, alloc.ID, &q)
	if err != nil {
		return nil, err
	}
	q.Params["path"] = path
	q.Params["offset"] = strconv.FormatInt(offset, 10)
	q.Params["limit"] = strconv.FormatInt(limit, 10)

	r, err := nodeClient.rawQuery(fmt.Sprintf("/v1/client/fs/readat/%s", alloc.ID), q)
	if err != nil {
		return nil, err
	}
	return r, nil
}

// Cat is used to read contents of a file at the given path in an allocation
// directory
func (a *AllocFS) Cat(alloc *Allocation, path string, q *QueryOptions) (io.ReadCloser, error) {
	node, _, err := a.client.Nodes().Info(alloc.NodeID, &QueryOptions{})
	if err != nil {
		return nil, err
	}

	nodeClient, err := a.getNodeClient(node, alloc.ID, &q)
	if err != nil {
		return nil, err
	}
	q.Params["path"] = path

	r, err := nodeClient.rawQuery(fmt.Sprintf("/v1/client/fs/cat/%s", alloc.ID), q)
	if err != nil {
		return nil, err
	}
	return r, nil
}

// Stream streams the content of a file blocking on EOF.
// The parameters are:
// * path: path to file to stream.
// * offset: The offset to start streaming data at.
// * origin: Either "start" or "end" and defines from where the offset is applied.
// * cancel: A channel that when closed, streaming will end.
//
// The return value is a channel that will emit StreamFrames as they are read.
func (a *AllocFS) Stream(alloc *Allocation, path, origin string, offset int64,
	cancel <-chan struct{}, q *QueryOptions) (<-chan *StreamFrame, error) {

	node, _, err := a.client.Nodes().Info(alloc.NodeID, q)
	if err != nil {
		return nil, err
	}

	nodeClient, err := a.getNodeClient(node, alloc.ID, &q)
	if err != nil {
		return nil, err
	}
	q.Params["path"] = path
	q.Params["offset"] = strconv.FormatInt(offset, 10)
	q.Params["origin"] = origin

	r, err := nodeClient.rawQuery(fmt.Sprintf("/v1/client/fs/stream/%s", alloc.ID), q)
	if err != nil {
		return nil, err
	}

	// Create the output channel
	frames := make(chan *StreamFrame, 10)

	go func() {
		// Close the body
		defer r.Close()

		// Create a decoder
		dec := json.NewDecoder(r)

		for {
			// Check if we have been cancelled
			select {
			case <-cancel:
				return
			default:
			}

			// Decode the next frame
			var frame StreamFrame
			if err := dec.Decode(&frame); err != nil {
				close(frames)
				return
			}

			// Discard heartbeat frames
			if frame.IsHeartbeat() {
				continue
			}

			frames <- &frame
		}
	}()

	return frames, nil
}

// Logs streams the content of a tasks logs blocking on EOF.
// The parameters are:
// * allocation: the allocation to stream from.
// * follow: Whether the logs should be followed.
// * task: the tasks name to stream logs for.
// * logType: Either "stdout" or "stderr"
// * origin: Either "start" or "end" and defines from where the offset is applied.
// * offset: The offset to start streaming data at.
// * cancel: A channel that when closed, streaming will end.
//
// The return value is a channel that will emit StreamFrames as they are read.
func (a *AllocFS) Logs(alloc *Allocation, follow bool, task, logType, origin string,
	offset int64, cancel <-chan struct{}, q *QueryOptions) (<-chan *StreamFrame, error) {

	node, _, err := a.client.Nodes().Info(alloc.NodeID, q)
	if err != nil {
		return nil, err
	}

	nodeClient, err := a.getNodeClient(node, alloc.ID, &q)
	if err != nil {
		return nil, err
	}
	q.Params["follow"] = strconv.FormatBool(follow)
	q.Params["task"] = task
	q.Params["type"] = logType
	q.Params["origin"] = origin
	q.Params["offset"] = strconv.FormatInt(offset, 10)

	r, err := nodeClient.rawQuery(fmt.Sprintf("/v1/client/fs/logs/%s", alloc.ID), q)
	if err != nil {
		return nil, err
	}

	// Create the output channel
	frames := make(chan *StreamFrame, 10)

	go func() {
		// Close the body
		defer r.Close()

		// Create a decoder
		dec := json.NewDecoder(r)

		for {
			// Check if we have been cancelled
			select {
			case <-cancel:
				return
			default:
			}

			// Decode the next frame
			var frame StreamFrame
			if err := dec.Decode(&frame); err != nil {
				close(frames)
				return
			}

			// Discard heartbeat frames
			if frame.IsHeartbeat() {
				continue
			}

			frames <- &frame
		}
	}()

	return frames, nil
}

// FrameReader is used to convert a stream of frames into a read closer.
type FrameReader struct {
	frames   <-chan *StreamFrame
	cancelCh chan struct{}

	closedLock sync.Mutex
	closed     bool

	unblockTime time.Duration

	frame       *StreamFrame
	frameOffset int

	byteOffset int
}

// NewFrameReader takes a channel of frames and returns a FrameReader which
// implements io.ReadCloser
func NewFrameReader(frames <-chan *StreamFrame, cancelCh chan struct{}) *FrameReader {
	return &FrameReader{
		frames:   frames,
		cancelCh: cancelCh,
	}
}

// SetUnblockTime sets the time to unblock and return zero bytes read. If the
// duration is unset or is zero or less, the read will block til data is read.
func (f *FrameReader) SetUnblockTime(d time.Duration) {
	f.unblockTime = d
}

// Offset returns the offset into the stream.
func (f *FrameReader) Offset() int {
	return f.byteOffset
}

// Read reads the data of the incoming frames into the bytes buffer. Returns EOF
// when there are no more frames.
func (f *FrameReader) Read(p []byte) (n int, err error) {
	f.closedLock.Lock()
	closed := f.closed
	f.closedLock.Unlock()
	if closed {
		return 0, io.EOF
	}

	if f.frame == nil {
		var unblock <-chan time.Time
		if f.unblockTime.Nanoseconds() > 0 {
			unblock = time.After(f.unblockTime)
		}

		select {
		case frame, ok := <-f.frames:
			if !ok {
				return 0, io.EOF
			}
			f.frame = frame

			// Store the total offset into the file
			f.byteOffset = int(f.frame.Offset)
		case <-unblock:
			return 0, nil
		case <-f.cancelCh:
			return 0, io.EOF
		}
	}

	// Copy the data out of the frame and update our offset
	n = copy(p, f.frame.Data[f.frameOffset:])
	f.frameOffset += n

	// Clear the frame and its offset once we have read everything
	if len(f.frame.Data) == f.frameOffset {
		f.frame = nil
		f.frameOffset = 0
	}

	return n, nil
}

// Close cancels the stream of frames
func (f *FrameReader) Close() error {
	f.closedLock.Lock()
	defer f.closedLock.Unlock()
	if f.closed {
		return nil
	}

	close(f.cancelCh)
	f.closed = true
	return nil
}