package cache

import (
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"sync"

	"github.com/MichaelMure/git-bug/bug"
	"github.com/MichaelMure/git-bug/entity"
	"github.com/MichaelMure/git-bug/identity"
	"github.com/MichaelMure/git-bug/repository"
	"github.com/MichaelMure/git-bug/util/process"
)

// 1: original format
// 2: added cache for identities with a reference in the bug cache
// 3: CreateUnixTime --> createUnixTime, EditUnixTime --> editUnixTime
const formatVersion = 3

var _ repository.RepoCommon = &RepoCache{}

// RepoCache is a cache for a Repository. This cache has multiple functions:
//
// 1. After being loaded, a Bug is kept in memory in the cache, allowing for fast
// 		access later.
// 2. The cache maintain in memory and on disk a pre-digested excerpt for each bug,
// 		allowing for fast querying the whole set of bugs without having to load
//		them individually.
// 3. The cache guarantee that a single instance of a Bug is loaded at once, avoiding
// 		loss of data that we could have with multiple copies in the same process.
// 4. The same way, the cache maintain in memory a single copy of the loaded identities.
//
// The cache also protect the on-disk data by locking the git repository for its
// own usage, by writing a lock file. Of course, normal git operations are not
// affected, only git-bug related one.
type RepoCache struct {
	// the underlying repo
	repo repository.ClockedRepo

	// the name of the repository, as defined in the MultiRepoCache
	name string

	muBug sync.RWMutex
	// excerpt of bugs data for all bugs
	bugExcerpts map[entity.Id]*BugExcerpt
	// bug loaded in memory
	bugs map[entity.Id]*BugCache

	muIdentity sync.RWMutex
	// excerpt of identities data for all identities
	identitiesExcerpts map[entity.Id]*IdentityExcerpt
	// identities loaded in memory
	identities map[entity.Id]*IdentityCache

	// the user identity's id, if known
	userIdentityId entity.Id
}

func NewRepoCache(r repository.ClockedRepo) (*RepoCache, error) {
	return NewNamedRepoCache(r, "")
}

func NewNamedRepoCache(r repository.ClockedRepo, name string) (*RepoCache, error) {
	c := &RepoCache{
		repo:       r,
		name:       name,
		bugs:       make(map[entity.Id]*BugCache),
		identities: make(map[entity.Id]*IdentityCache),
	}

	err := c.lock()
	if err != nil {
		return &RepoCache{}, err
	}

	err = c.load()
	if err == nil {
		return c, nil
	}

	// Cache is either missing, broken or outdated. Rebuilding.
	err = c.buildCache()
	if err != nil {
		return nil, err
	}

	return c, c.write()
}

// load will try to read from the disk all the cache files
func (c *RepoCache) load() error {
	err := c.loadBugCache()
	if err != nil {
		return err
	}
	return c.loadIdentityCache()
}

// write will serialize on disk all the cache files
func (c *RepoCache) write() error {
	err := c.writeBugCache()
	if err != nil {
		return err
	}
	return c.writeIdentityCache()
}

func (c *RepoCache) lock() error {
	lockPath := repoLockFilePath(c.repo)

	err := repoIsAvailable(c.repo)
	if err != nil {
		return err
	}

	err = os.MkdirAll(filepath.Dir(lockPath), 0777)
	if err != nil {
		return err
	}

	f, err := os.Create(lockPath)
	if err != nil {
		return err
	}

	pid := fmt.Sprintf("%d", os.Getpid())
	_, err = f.WriteString(pid)
	if err != nil {
		return err
	}

	return f.Close()
}

func (c *RepoCache) Close() error {
	c.muBug.Lock()
	defer c.muBug.Unlock()
	c.muIdentity.Lock()
	defer c.muIdentity.Unlock()

	c.identities = make(map[entity.Id]*IdentityCache)
	c.identitiesExcerpts = nil
	c.bugs = make(map[entity.Id]*BugCache)
	c.bugExcerpts = nil

	lockPath := repoLockFilePath(c.repo)
	return os.Remove(lockPath)
}

func (c *RepoCache) buildCache() error {
	c.muBug.Lock()
	defer c.muBug.Unlock()
	c.muIdentity.Lock()
	defer c.muIdentity.Unlock()

	_, _ = fmt.Fprintf(os.Stderr, "Building identity cache... ")

	c.identitiesExcerpts = make(map[entity.Id]*IdentityExcerpt)

	allIdentities := identity.ReadAllLocalIdentities(c.repo)

	for i := range allIdentities {
		if i.Err != nil {
			return i.Err
		}

		c.identitiesExcerpts[i.Identity.Id()] = NewIdentityExcerpt(i.Identity)
	}

	_, _ = fmt.Fprintln(os.Stderr, "Done.")

	_, _ = fmt.Fprintf(os.Stderr, "Building bug cache... ")

	c.bugExcerpts = make(map[entity.Id]*BugExcerpt)

	allBugs := bug.ReadAllLocalBugs(c.repo)

	for b := range allBugs {
		if b.Err != nil {
			return b.Err
		}

		snap := b.Bug.Compile()
		c.bugExcerpts[b.Bug.Id()] = NewBugExcerpt(b.Bug, &snap)
	}

	_, _ = fmt.Fprintln(os.Stderr, "Done.")
	return nil
}

func repoLockFilePath(repo repository.Repo) string {
	return path.Join(repo.GetPath(), "git-bug", lockfile)
}

// repoIsAvailable check is the given repository is locked by a Cache.
// Note: this is a smart function that will cleanup the lock file if the
// corresponding process is not there anymore.
// If no error is returned, the repo is free to edit.
func repoIsAvailable(repo repository.Repo) error {
	lockPath := repoLockFilePath(repo)

	// Todo: this leave way for a racey access to the repo between the test
	// if the file exist and the actual write. It's probably not a problem in
	// practice because using a repository will be done from user interaction
	// or in a context where a single instance of git-bug is already guaranteed
	// (say, a server with the web UI running). But still, that might be nice to
	// have a mutex or something to guard that.

	// Todo: this will fail if somehow the filesystem is shared with another
	// computer. Should add a configuration that prevent the cleaning of the
	// lock file

	f, err := os.Open(lockPath)

	if err != nil && !os.IsNotExist(err) {
		return err
	}

	if err == nil {
		// lock file already exist
		buf, err := ioutil.ReadAll(io.LimitReader(f, 10))
		if err != nil {
			return err
		}
		if len(buf) == 10 {
			return fmt.Errorf("the lock file should be < 10 bytes")
		}

		pid, err := strconv.Atoi(string(buf))
		if err != nil {
			return err
		}

		if process.IsRunning(pid) {
			return fmt.Errorf("the repository you want to access is already locked by the process pid %d", pid)
		}

		// The lock file is just laying there after a crash, clean it

		fmt.Println("A lock file is present but the corresponding process is not, removing it.")
		err = f.Close()
		if err != nil {
			return err
		}

		err = os.Remove(lockPath)
		if err != nil {
			return err
		}
	}

	return nil
}