package model

/*

Locking
=======

These methods are never called from the outside so don't follow the locking
policy in model.go.

TODO(jb): Refactor this into smaller and cleaner pieces.
TODO(jb): Increase performance by taking apparent peer bandwidth into account.

*/

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"log"
	"os"
	"path"
	"sync"
	"time"

	"github.com/calmh/syncthing/buffers"
	"github.com/calmh/syncthing/protocol"
)

func (m *Model) pullFile(name string) error {
	m.RLock()
	var localFile = m.local[name]
	var globalFile = m.global[name]
	var nodeIDs = m.whoHas(name)
	m.RUnlock()

	if len(nodeIDs) == 0 {
		return fmt.Errorf("%s: no connected nodes with file available", name)
	}

	filename := path.Join(m.dir, name)
	sdir := path.Dir(filename)

	_, err := os.Stat(sdir)
	if err != nil && os.IsNotExist(err) {
		os.MkdirAll(sdir, 0777)
	}

	tmpFilename := tempName(filename, globalFile.Modified)
	tmpFile, err := os.Create(tmpFilename)
	if err != nil {
		return err
	}

	contentChan := make(chan content, 32)
	var applyDone sync.WaitGroup
	applyDone.Add(1)
	go func() {
		applyContent(contentChan, tmpFile)
		tmpFile.Close()
		applyDone.Done()
	}()

	local, remote := BlockDiff(localFile.Blocks, globalFile.Blocks)
	var fetchDone sync.WaitGroup

	// One local copy routine

	fetchDone.Add(1)
	go func() {
		for _, block := range local {
			data, err := m.Request("<local>", name, block.Offset, block.Length, block.Hash)
			if err != nil {
				break
			}
			contentChan <- content{
				offset: int64(block.Offset),
				data:   data,
			}
		}
		fetchDone.Done()
	}()

	// N remote copy routines

	var remoteBlocks = blockIterator{blocks: remote}
	for i := 0; i < m.paralllelReqs; i++ {
		curNode := nodeIDs[i%len(nodeIDs)]
		fetchDone.Add(1)

		go func(nodeID string) {
			for {
				block, ok := remoteBlocks.Next()
				if !ok {
					break
				}
				data, err := m.requestGlobal(nodeID, name, block.Offset, block.Length, block.Hash)
				if err != nil {
					break
				}
				contentChan <- content{
					offset: int64(block.Offset),
					data:   data,
				}
			}
			fetchDone.Done()
		}(curNode)
	}

	fetchDone.Wait()
	close(contentChan)
	applyDone.Wait()

	err = hashCheck(tmpFilename, globalFile.Blocks)
	if err != nil {
		return fmt.Errorf("%s: %s (deleting)", path.Base(name), err.Error())
	}

	err = os.Chtimes(tmpFilename, time.Unix(globalFile.Modified, 0), time.Unix(globalFile.Modified, 0))
	if err != nil {
		return err
	}

	err = os.Chmod(tmpFilename, os.FileMode(globalFile.Flags&0777))
	if err != nil {
		return err
	}

	err = os.Rename(tmpFilename, filename)
	if err != nil {
		return err
	}

	return nil
}

func (m *Model) puller() {
	for {
		time.Sleep(time.Second)

		var ns []string
		m.RLock()
		for n := range m.need {
			ns = append(ns, n)
		}
		m.RUnlock()

		if len(ns) == 0 {
			continue
		}

		var limiter = make(chan bool, m.parallellFiles)
		var allDone sync.WaitGroup

		for _, n := range ns {
			limiter <- true
			allDone.Add(1)

			go func(n string) {
				defer func() {
					allDone.Done()
					<-limiter
				}()

				m.RLock()
				f, ok := m.global[n]
				m.RUnlock()

				if !ok {
					return
				}

				var err error
				if f.Flags&protocol.FlagDeleted == 0 {
					if m.trace["file"] {
						log.Printf("FILE: Pull %q", n)
					}
					err = m.pullFile(n)
				} else {
					if m.trace["file"] {
						log.Printf("FILE: Remove %q", n)
					}
					// Cheerfully ignore errors here
					_ = os.Remove(path.Join(m.dir, n))
				}
				if err == nil {
					m.Lock()
					m.updateLocal(f)
					m.Unlock()
				}
			}(n)
		}

		allDone.Wait()
	}
}

type content struct {
	offset int64
	data   []byte
}

func applyContent(cc <-chan content, dst io.WriterAt) error {
	var err error

	for c := range cc {
		_, err = dst.WriteAt(c.data, c.offset)
		buffers.Put(c.data)
		if err != nil {
			return err
		}
	}

	return nil
}

func hashCheck(name string, correct []Block) error {
	rf, err := os.Open(name)
	if err != nil {
		return err
	}
	defer rf.Close()

	current, err := Blocks(rf, BlockSize)
	if err != nil {
		return err
	}
	if len(current) != len(correct) {
		return errors.New("incorrect number of blocks")
	}
	for i := range current {
		if bytes.Compare(current[i].Hash, correct[i].Hash) != 0 {
			return fmt.Errorf("hash mismatch: %x != %x", current[i], correct[i])
		}
	}

	return nil
}

type blockIterator struct {
	sync.Mutex
	blocks []Block
}

func (i *blockIterator) Next() (b Block, ok bool) {
	i.Lock()
	defer i.Unlock()

	if len(i.blocks) == 0 {
		return
	}

	b, i.blocks = i.blocks[0], i.blocks[1:]
	ok = true

	return
}