package store

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"sync"
	"time"
)

// KeptName is the file, beside the node's state, of every shared folder the engine keeps (novox/hq ADR 0325 §5):
// whose entries it added, on which filesystem it was placed, whether it was taken and under which warrant, and how
// far its sweep got. Its own file for the reason the hand-overs have theirs: the take act, the watch and the sweep
// run beside an apply, whose save of the state would lose a record written into it meanwhile.
const KeptName = "kept-folders.json"

// KeptPath is that file beside the state at statePath.
func KeptPath(statePath string) string {
	return filepath.Join(filepath.Dir(statePath), KeptName)
}

// KeptUser is one identity the mesh keeps an entry for on a folder: its name, its number, its use and where it
// runs (a container, or the tool runner standing for every module whose tools use the folder, ADR 0325 §4).
type KeptUser struct {
	Identity string `json:"identity"`
	UID      uint32 `json:"uid"`
	Use      string `json:"use"`
	From     string `json:"from"`
}

// How a folder came to be kept.
const (
	// KeptByWarrant is a folder that held data, taken on the operator's word (ADR 0325 §8).
	KeptByWarrant = "warrant"
	// KeptEmpty is a folder that held nothing yet when it was first kept (§5).
	KeptEmpty = "empty"
	// KeptMade is a folder the engine made under a parent on its placed filesystem (§9).
	KeptMade = "made"
)

// KeptFolder is one shared folder the engine keeps, or has seen and waits to keep. Counts and mount points only
// beside its own path: never a path under it.
type KeptFolder struct {
	Path string `json:"path"`
	// Mount is the mount point of the filesystem the folder was placed on when the engine first saw it there:
	// later, a nearest existing parent on another one is the disk not there (ADR 0325 §9).
	Mount string `json:"mount,omitempty"`
	// Kept is that the mesh keeps it; How why (KeptByWarrant, KeptEmpty, KeptMade); Warrant and By the warrant and
	// who asked, for a folder taken on one; At since when.
	Kept    bool      `json:"kept,omitempty"`
	How     string    `json:"how,omitempty"`
	Warrant string    `json:"warrant,omitempty"`
	By      string    `json:"by,omitempty"`
	At      time.Time `json:"at,omitzero"`
	// Users are the identities whose entries are on everything under the folder; Want what the last apply
	// declared. Where they differ a walk adds or removes exactly the difference.
	Users []KeptUser `json:"users,omitempty"`
	Want  []KeptUser `json:"want,omitempty"`
	// IDs are the accesses that last named the folder: what a leftover is said under once none does.
	IDs []string `json:"ids,omitempty"`
	// TakenOn is the mount point the operator's warrant was carried out on (ADR 0325 §8): the controller's word
	// that the folder was taken holds for that filesystem alone, and a folder moved to another asks again.
	TakenOn string `json:"taken_on,omitempty"`
	// Left is the entries the mesh added on a filesystem no longer at the folder (a disk mounted over it, or
	// one gone): taken out by a drop walk once that filesystem holds the folder again, said until then.
	Left []KeptLeft `json:"left,omitempty"`
	// Act is the last walk under the folder: a take, an add or a drop.
	Act *KeptAct `json:"act,omitempty"`
	// Sweep is how far the sweep got (ADR 0325 §10).
	Sweep KeptSweep `json:"sweep"`
	// Watches is how many folders under it are watched; OutOfWatches that the machine's watch limit was met, and
	// the sweep alone finds what is made where no watch is (§6).
	Watches      int  `json:"watches,omitempty"`
	OutOfWatches bool `json:"out_of_watches,omitempty"`
}

// KeptLeft is the mesh's entries left on one filesystem: its mount point and whose entries they are.
type KeptLeft struct {
	Mount string     `json:"mount"`
	Users []KeptUser `json:"users"`
}

// KeptAct is one walk under a kept folder, as the engine records it. Counts only: never a path.
type KeptAct struct {
	// Act is take, add or drop.
	Act     string    `json:"act"`
	Warrant string    `json:"warrant,omitempty"`
	By      string    `json:"by,omitempty"`
	State   string    `json:"state"`
	Started time.Time `json:"started"`
	Ended   time.Time `json:"ended,omitzero"`
	// Folders and Files are the entries changed; Kept the ones that already had what they need; Links the links
	// passed by unfollowed; Other the entries neither a file nor a folder; Mounts the folders on another
	// filesystem not entered.
	Folders int `json:"folders,omitempty"`
	Files   int `json:"files,omitempty"`
	Kept    int `json:"kept,omitempty"`
	Links   int `json:"links,omitempty"`
	Other   int `json:"other,omitempty"`
	Mounts  int `json:"mounts,omitempty"`
	// Why is what stopped or failed it, in words with no path.
	Why string `json:"why,omitempty"`
}

// KeptSweep is the sweep's place in a kept folder: where the last look stopped, below the folder, by the names
// of each level (never said, only resumed from); when it last covered the folder whole; and what this pass found.
type KeptSweep struct {
	Cursor  []string  `json:"cursor,omitempty"`
	Covered time.Time `json:"covered,omitzero"`
	// Read is how many entries this pass read so far; Narrowed how many gave a user less than its right and were
	// put back; Unrepaired how many could not be (an owner's bits, which the mesh never changes, or a write that
	// failed).
	Read       int `json:"read,omitempty"`
	Narrowed   int `json:"narrowed,omitempty"`
	Unrepaired int `json:"unrepaired,omitempty"`
	// LastUnrepaired is what the last whole pass could not put back: said until the next pass is through.
	LastUnrepaired int `json:"last_unrepaired,omitempty"`
	// Bound is that the last look ran out of its bound before the folder was covered.
	Bound bool `json:"bound,omitempty"`
}

// KeptFile is the kept folders' file, one writer at a time in this process.
type KeptFile struct {
	path string
	mu   sync.Mutex
}

// NewKeptFile is the kept folders' file beside the state at statePath.
func NewKeptFile(statePath string) *KeptFile { return &KeptFile{path: KeptPath(statePath)} }

// All is every kept or seen folder, by path. None is an empty map; a file that cannot be read is an error.
func (k *KeptFile) All() (map[string]KeptFolder, error) {
	k.mu.Lock()
	defer k.mu.Unlock()
	return k.load()
}

// Update changes the record of one folder under the file's lock: change is given the record (empty when there is
// none) and whether there was one, and says whether to keep it; a record not kept is removed.
func (k *KeptFile) Update(path string, change func(f *KeptFolder, had bool) bool) error {
	k.mu.Lock()
	defer k.mu.Unlock()
	all, err := k.load()
	if err != nil {
		return err
	}
	f, had := all[path]
	f.Path = path
	if change(&f, had) {
		all[path] = f
	} else {
		delete(all, path)
	}
	return k.save(all)
}

func (k *KeptFile) load() (map[string]KeptFolder, error) {
	raw, err := os.ReadFile(k.path)
	if errors.Is(err, fs.ErrNotExist) {
		return map[string]KeptFolder{}, nil
	}
	if err != nil {
		return nil, fmt.Errorf("reading the kept folders: %w", err)
	}
	out := map[string]KeptFolder{}
	if err := json.Unmarshal(raw, &out); err != nil {
		return nil, fmt.Errorf("the kept folders (%s) are unreadable: %w", k.path, err)
	}
	return out, nil
}

func (k *KeptFile) save(all map[string]KeptFolder) error {
	raw, err := json.MarshalIndent(all, "", "  ")
	if err != nil {
		return err
	}
	tmp, err := os.CreateTemp(filepath.Dir(k.path), ".kept-folders-*.json")
	if err != nil {
		return err
	}
	defer os.Remove(tmp.Name())
	if _, err := tmp.Write(append(raw, '\n')); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Sync(); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Close(); err != nil {
		return err
	}
	return os.Rename(tmp.Name(), k.path)
}