package bus

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"regexp"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/nats-io/nats.go/jetstream"
)

// A module's state on the bus (novox/hq ADR 0202): key-value buckets the controller creates from what
// the module declared, and issues to each assignment in its membership by the name the module uses —
// its own state by the local name, another module's as `<module>.<name>`.
//
// **The runtime keeps each module to its own buckets.** One account per machine carries every module
// on it, so the bus enforces only the union; and a write the bus refuses reaches the writer as a
// timeout, not a refusal (measured, novox/hq research 024). So what a module may reach is decided here,
// from its membership, and refused with the reason before anything is sent.

// StateIssued is one bucket an assignment may reach (ADR 0202).
type StateIssued struct {
	Name   string `json:"name"`
	Bucket string `json:"bucket"`
	Writes bool   `json:"writes,omitempty"`
}

// StateEntry is one key's current value.
type StateEntry struct {
	Key      string          `json:"key"`
	Value    json.RawMessage `json:"value"`
	Revision uint64          `json:"revision"`
}

// StateChange is one change a watch delivers: a key put or deleted.
type StateChange struct {
	State    string          `json:"state"`
	Key      string          `json:"key"`
	Op       string          `json:"op"`
	Value    json.RawMessage `json:"value,omitempty"`
	Revision uint64          `json:"revision"`
	// Current is true for a value that was there when the watch began, false for a change since.
	Current bool `json:"current"`
}

// StateTimeout bounds one state operation on the bus.
var StateTimeout = 10 * time.Second

// stateKey is a key the bus can hold: letters, digits and `-/_=.`, no leading or trailing dot. A
// module's convention for naming a machine in a key (`all.<server>`, `<machine>.<server>`) fits it.
var stateKey = regexp.MustCompile(`^[-/_=a-zA-Z0-9]+(\.[-/_=a-zA-Z0-9]+)*$`)

// issuedState is the bucket a module may reach by a name, and whether it may write it — or the reason
// it may not reach it at all.
func (c *Conn) issuedState(module, name string) (StateIssued, error) {
	m := c.Membership(module)
	if m == nil {
		return StateIssued{}, fmt.Errorf("%s has no membership issued on %s yet, so no state of it is reachable "+
			"until the mesh issues one (novox/hq ADR 0202)", module, c.node)
	}
	var names []string
	for _, s := range m.State {
		if s.Name == name {
			return s, nil
		}
		names = append(names, s.Name)
	}
	sort.Strings(names)
	issued := "none"
	if len(names) > 0 {
		issued = strings.Join(names, ", ")
	}
	return StateIssued{}, fmt.Errorf("%s keeps and reads no state called %q: it declares what it keeps under "+
		"`state` and what it reads under `reads` as <module>.<name>, and was issued: %s (novox/hq ADR 0202)",
		module, name, issued)
}

func (c *Conn) bucket(ctx context.Context, s StateIssued) (jetstream.KeyValue, error) {
	js, err := jetstream.New(c.nc)
	if err != nil {
		return nil, err
	}
	kv, err := js.KeyValue(ctx, s.Bucket)
	if err != nil {
		if errors.Is(err, jetstream.ErrBucketNotFound) {
			return nil, fmt.Errorf("the state %q is issued and its bucket is not on the bus yet: the controller "+
				"creates it from the catalogue on its next raise", s.Name)
		}
		return nil, err
	}
	return kv, nil
}

func checkKey(key string) error {
	if !stateKey.MatchString(key) {
		return fmt.Errorf("%q is not a key the bus can hold: letters, digits and -/_=, in dot-separated "+
			"names", key)
	}
	return nil
}

// StateGet is one key's current value, or nil when it has none.
func (c *Conn) StateGet(module, name, key string) (*StateEntry, error) {
	s, err := c.issuedState(module, name)
	if err != nil {
		return nil, err
	}
	if err := checkKey(key); err != nil {
		return nil, err
	}
	ctx, cancel := context.WithTimeout(context.Background(), StateTimeout)
	defer cancel()
	kv, err := c.bucket(ctx, s)
	if err != nil {
		return nil, err
	}
	e, err := kv.Get(ctx, key)
	if errors.Is(err, jetstream.ErrKeyNotFound) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	return &StateEntry{Key: e.Key(), Value: valueOf(e.Value()), Revision: e.Revision()}, nil
}

// StatePut writes one key, as the module, where the module keeps the state. It answers the revision.
func (c *Conn) StatePut(module, name, key string, value json.RawMessage) (uint64, error) {
	s, err := c.writable(module, name)
	if err != nil {
		return 0, err
	}
	if err := checkKey(key); err != nil {
		return 0, err
	}
	if len(value) == 0 || !json.Valid(value) {
		return 0, fmt.Errorf("a state value is JSON")
	}
	if field := credentialField(value); field != "" {
		return 0, fmt.Errorf("%s's %s.%s carries a field %q, which names a credential: no secret is kept in state, "+
			"sealed or not — a bucket is a stream, and a machine joining a year later reads it whole. Name the "+
			"secret and fetch it on request/reply (novox/hq ADR 0202, design 32 §10)", module, name, key, field)
	}
	ctx, cancel := context.WithTimeout(context.Background(), StateTimeout)
	defer cancel()
	kv, err := c.bucket(ctx, s)
	if err != nil {
		return 0, err
	}
	return kv.Put(ctx, key, value)
}

// StateDelete removes one key, as the module, where the module keeps the state. A key that was not
// there is not an error: what is asked for is that it is gone.
func (c *Conn) StateDelete(module, name, key string) error {
	s, err := c.writable(module, name)
	if err != nil {
		return err
	}
	if err := checkKey(key); err != nil {
		return err
	}
	ctx, cancel := context.WithTimeout(context.Background(), StateTimeout)
	defer cancel()
	kv, err := c.bucket(ctx, s)
	if err != nil {
		return err
	}
	return kv.Delete(ctx, key)
}

// StateKeys is every key with a current value, sorted.
func (c *Conn) StateKeys(module, name string) ([]string, error) {
	s, err := c.issuedState(module, name)
	if err != nil {
		return nil, err
	}
	ctx, cancel := context.WithTimeout(context.Background(), StateTimeout)
	defer cancel()
	kv, err := c.bucket(ctx, s)
	if err != nil {
		return nil, err
	}
	lister, err := kv.ListKeys(ctx)
	if err != nil {
		return nil, err
	}
	defer func() { _ = lister.Stop() }()
	keys := []string{}
	for k := range lister.Keys() {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	return keys, nil
}

func (c *Conn) writable(module, name string) (StateIssued, error) {
	s, err := c.issuedState(module, name)
	if err != nil {
		return s, err
	}
	if !s.Writes {
		owner := name
		if dot := strings.LastIndex(name, "."); dot > 0 {
			owner = name[:dot]
		}
		return s, fmt.Errorf("%s reads %s and does not keep it: only %s's own instances write it (novox/hq ADR 0202)",
			module, name, owner)
	}
	return s, nil
}

// StateWatch hands deliver the current value of every key matching the pattern — none that is
// deleted — and then every change, in order (ADR 0202). It returns once the current values are
// delivered; deliver is called from one goroutine, one change at a time, and an error from it is said
// and the watch goes on: state is not a queue, and the next change, or the next start, reads it again.
// The pattern is a key, with `*` for one name and `**` for the rest; empty is every key.
func (c *Conn) StateWatch(module, name, pattern string, deliver func(StateChange) error) (stop func(), err error) {
	s, err := c.issuedState(module, name)
	if err != nil {
		return nil, err
	}
	filter := ">"
	if pattern != "" {
		parts := strings.Split(pattern, ".")
		for i, p := range parts {
			if p == "**" {
				if i != len(parts)-1 {
					return nil, fmt.Errorf("%q: `**` stands for the rest of a key, so it comes last", pattern)
				}
				parts[i] = ">"
				continue
			}
			if p != "*" && !stateKey.MatchString(p) {
				return nil, fmt.Errorf("%q is not a key pattern: names, `*` for one and `**` for the rest", pattern)
			}
		}
		filter = strings.Join(parts, ".")
	}
	ctx, cancel := context.WithTimeout(context.Background(), StateTimeout)
	kv, err := c.bucket(ctx, s)
	cancel()
	if err != nil {
		return nil, err
	}
	watching, stopWatching := context.WithCancel(context.Background())
	w, err := kv.Watch(watching, filter)
	if err != nil {
		stopWatching()
		return nil, err
	}
	var once sync.Once
	stop = func() {
		once.Do(func() {
			_ = w.Stop()
			stopWatching()
		})
	}
	current := make(chan struct{})
	go func() {
		initial := true
		for e := range w.Updates() {
			if e == nil {
				// The end of what was there when the watch began.
				if initial {
					initial = false
					close(current)
				}
				continue
			}
			change := StateChange{State: name, Key: e.Key(), Revision: e.Revision(), Current: initial}
			switch e.Operation() {
			case jetstream.KeyValuePut:
				change.Op = "put"
				change.Value = valueOf(e.Value())
			default:
				// A deletion among the current values is a key that is not there: not handed over
				// (measured, research 024 — the server sends its marker among the initial values).
				if initial {
					continue
				}
				change.Op = "delete"
			}
			if err := deliver(change); err != nil {
				c.Logf("[mesh-tools] %s did not take %s %s of %s: %v; its next change, or its next start, reads it again",
					module, change.Op, change.Key, name, err)
			}
		}
		if initial {
			close(current)
		}
	}()
	select {
	case <-current:
		return stop, nil
	case <-time.After(StateTimeout):
		stop()
		return nil, fmt.Errorf("the current values of %s did not arrive in %s", name, StateTimeout)
	}
}

func valueOf(raw []byte) json.RawMessage {
	if len(raw) == 0 || !json.Valid(raw) {
		b, _ := json.Marshal(string(raw))
		return b
	}
	return json.RawMessage(raw)
}

// credentialEndings are the ends of a field name that say its value is a credential. A guard against
// the ordinary mistake, not a determined one: a sealed value is plain text to anything inspecting it,
// so the rule is checked where it can be and said to be partial (ADR 0202).
var credentialEndings = []string{"password", "passwd", "secret", "token", "credential", "credentials",
	"authorization", "apikey", "privatekey", "accesskey", "cookie"}

// credentialField is the first field anywhere in a JSON value whose name says it is a credential, or "".
func credentialField(value json.RawMessage) string {
	var v any
	if json.Unmarshal(value, &v) != nil {
		return ""
	}
	var walk func(any) string
	walk = func(v any) string {
		switch t := v.(type) {
		case map[string]any:
			keys := make([]string, 0, len(t))
			for k := range t {
				keys = append(keys, k)
			}
			sort.Strings(keys)
			for _, k := range keys {
				norm := strings.NewReplacer("-", "", "_", "", " ", "").Replace(strings.ToLower(k))
				for _, end := range credentialEndings {
					if strings.HasSuffix(norm, end) {
						return k
					}
				}
				if found := walk(t[k]); found != "" {
					return found
				}
			}
		case []any:
			for _, x := range t {
				if found := walk(x); found != "" {
					return found
				}
			}
		}
		return ""
	}
	return walk(v)
}