package grants

import (
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"sort"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"git.novox.be/novox/mesh-sdk/go/asks"
	"git.novox.be/novox/mesh-sdk/go/delivery"
)

// The part's own states, as its manifest declares them, and the keys of the two that hold one value.
const (
	StateUserList    = "user-list"
	StateMemberships = "memberships"
	StateAssertions  = "assertions"
	StateTakeover    = "takeover"
	KeyList          = "list"
	KeySwitch        = "switch"
	// KeyPass is the last pass's result, and KeyAsked a tool's ask to compose again now, both in StateUserList.
	KeyPass  = "pass"
	KeyAsked = "asked"
)

// States is every state the part keeps.
var States = []string{StateAssertions, StateMemberships, StateTakeover, StateUserList}

// The events the part says.
const (
	EventUserList   = "user-list-changed"
	EventMembership = "membership-changed"
	// EventAsserted is said when the part created a bucket, log or stream a manifest declares (issue 1790).
	EventAsserted = "asserted"
)

// Emits is every event the part says.
var Emits = []string{EventAsserted, EventMembership, EventUserList}

// Store is the part's own state, by local name: the only thing the part writes.
type Store interface {
	Get(state, key string) ([]byte, uint64, bool, error)
	Put(state, key string, value []byte) (uint64, error)
}

// Emitter says one of the part's events.
type Emitter interface {
	Emit(event string, body any) error
}

// UserListState is the value of `user-list` in shadow: the list the grants part composed (users and grants, no hashes),
// what the bus loaded, and how they differ. Inputs is the digest of all it says but At: a value is written again only
// when it changes.
type UserListState struct {
	V      int    `json:"v"`
	Mode   string `json:"mode"`
	Inputs string `json:"inputs"`
	Digest string `json:"digest"`
	Users  int    `json:"users"`
	// LeftOut are the assignments the shadow list leaves out, each with why.
	LeftOut []Gap                     `json:"left_out"`
	Compare Comparison                `json:"compare"`
	Loaded  *delivery.UserListWritten `json:"loaded,omitempty"`
	// Credentials says per user whether the vault holds its hash and how its line would differ (ADR 0547 clause 9).
	Credentials Credentials `json:"credentials"`
	BusNode     string      `json:"bus_node,omitempty"`
	Gaps        []Gap       `json:"gaps"`
	At          time.Time   `json:"at"`
}

func (s UserListState) inputs() string {
	s.At, s.Inputs = time.Time{}, ""
	raw, _ := json.Marshal(s)
	sum := sha256.Sum256(raw)
	return "sha256:" + hex.EncodeToString(sum[:])
}

// Result is what one composition did.
type Result struct {
	UserList           UserListState `json:"user_list"`
	Revision           uint64        `json:"revision"`
	Written            bool          `json:"written"`
	Memberships        int           `json:"memberships"`
	MembershipsWritten int           `json:"memberships_written"`
	Published          []string      `json:"published,omitempty"`
	NotPublished       []string      `json:"not_published,omitempty"`
	Assertions         int           `json:"assertions"`
	AssertionsWritten  int           `json:"assertions_written"`
	// Asserted is each module whose declared streams this pass created, `<module> at <digest>: created …`, and
	// NotAsserted each creation refused, `<module> <stream>: <why>` (issue 1790).
	Asserted    []string `json:"asserted,omitempty"`
	NotAsserted []string `json:"not_asserted,omitempty"`
	// Refused is every manifest the indexer holds that this pass could not read, `manifest of <module>: <why>`: its
	// module counts as placed nowhere (issue 1945).
	Refused []string `json:"refused,omitempty"`
	// RootNotFree is each machine the composition needed a root-free word for and did not get one, `<machine>: not
	// free, <why>`: a verified sender is composed as from no root-free machine there (issue 1945).
	RootNotFree []string `json:"root_not_free,omitempty"`
	// Sealed is the list sealed to the bus node as the key `user-list.sealed` names it (ADR 0547 clause 7).
	Sealed              *SealedState `json:"sealed,omitempty"`
	Errors              []string     `json:"errors,omitempty"`
	PublishedOrAsserted string       `json:"published_or_asserted"`
}

// NothingTakesEffect is what every composition says it did on the bus beyond its own state and the memberships.
const NothingTakesEffect = "memberships (on the assignments stream, a first one or one that only adds to the last published or drops only a verb the seat catalogue retired; any other loss stays a shadow difference), and each bucket, log or stream a manifest declares that the bus lacks, created once with the manifest's limits (the operator, 2026-10-26 08:54); the user list, the grants and any change to a stream the bus holds stay in shadow until take-over"

// Part is the grants part: it reads, calls and writes through these, and nothing else.
type Part struct {
	Read  Reader
	Call  Caller
	Store Store
	Emit  Emitter
	// Publish publishes memberships: the process's connection; nil in the tools, which ask the process instead.
	Publish Publisher
	// Create creates a declared stream the bus lacks: the process's connection; nil in the tools, which ask the process.
	Create Creator
	// Asker asks the operator (take-over, hand-back): the process's client of the router; nil in the tools, which write
	// the request and let the process ask it.
	Asker Asker
	// Logf logs what no state or condition says (an error of acting on an answer): the process's; nil in the tools.
	Logf func(string, ...any)
	// Objects is the part's object bucket of sealed lists: the process's connection; nil in the tools.
	Objects Objects
	// Say says a condition to the operator: the process's; nil in the tools.
	Say func(asks.Condition) error
	// Forget takes away the record the asker kept of an ask it failed to publish; Nonce is a test's id suffix.
	Forget func(id string) error
	Nonce  func() string
	// deciding is set while a take-over is decided, so the composition it makes asks and reconciles nothing.
	deciding atomic.Bool
	Now      func() time.Time

	cache Manifests
	mu    sync.Mutex
	last  Result
	made  creations
	// askSeen is the revision of the last ask to compose (KeyAsked) this part acted on.
	askSeen uint64
	// heldSaid is the reason of the held-list condition last said (empty: none raised); heldKnown is whether one was said
	// since the start, so the first pass after a start always says its state (a condition raised before a restart is cleared
	// by it). holdMu guards both.
	holdMu    sync.Mutex
	heldSaid  string
	heldKnown bool
}

// Ask is the value of KeyAsked: a tool's ask to compose now, and, from grants_assert, to create one module's missing
// streams again even where they were created at this manifest before.
type Ask struct {
	By     string    `json:"by"`
	At     time.Time `json:"at"`
	Assert string    `json:"assert,omitempty"`
}

// askedAssert is the module a new ask names to assert by hand, read once per ask; empty when none.
func (p *Part) askedAssert() string {
	raw, rev, found, err := p.Store.Get(StateUserList, KeyAsked)
	if err != nil || !found || rev == p.askSeen {
		return ""
	}
	p.askSeen = rev
	var a Ask
	_ = json.Unmarshal(raw, &a)
	return a.Assert
}

func (p *Part) now() time.Time {
	if p.Now == nil {
		return time.Now().UTC()
	}
	return p.Now().UTC()
}

// Compose composes the user list, the memberships and the assertions from what the bus holds now, compares them, and
// writes each of its own keys whose value changed, saying each change. It never stops at a refusal: a read refused is
// a gap, a write refused is said in Errors, and the next event composes again.
func (p *Part) Compose() Result {
	// No lock is held across a round trip on the bus: the reads, calls, publishes and writes below take none, and the
	// lock is taken only to keep the result, so a tool answers while a pass waits on the bus.
	res := Result{PublishedOrAsserted: NothingTakesEffect}
	defer func() {
		p.mu.Lock()
		p.last = res
		p.mu.Unlock()
	}()
	in := ReadInputs(p.Read, &p.cache)
	for _, g := range in.Refused {
		res.Refused = append(res.Refused, g.Input+": "+g.Why)
	}
	recs, left := Records(in)
	res.RootNotFree = WithRootFree(&recs, p.Call)
	st := UserListState{V: 1, Mode: p.SwitchState(), LeftOut: left, Loaded: in.Loaded, BusNode: in.BusNode,
		Gaps: append(append([]Gap(nil), in.Gaps...), MembershipGaps...), At: p.now()}
	if st.LeftOut == nil {
		st.LeftOut = []Gap{}
	}
	users, err := ComposeUsers(recs)
	if err != nil {
		res.Errors = append(res.Errors, "the shadow list could not be composed: "+err.Error())
	}
	users = WithHashes(users, in.Hashes)
	st.Digest, st.Users = Digest(users), len(users)
	loaded, err := LoadedUsers(p.Call)
	st.Compare = Compare(users, loaded, Placed(in)).Excusing(ExcusedBy(MultiHeld(recs)))
	if err != nil {
		st.Compare.Unread = err.Error()
	}
	st.Credentials = CredentialsOf(users, loaded, in.Hashes)
	st.Inputs = st.inputs()
	res.UserList = st
	if raw, rev, found, err := p.Store.Get(StateUserList, KeyList); err != nil {
		res.Errors = append(res.Errors, fmt.Sprintf("its own %s cannot be read: %v", StateUserList, err))
	} else {
		var was UserListState
		if found && json.Unmarshal(raw, &was) == nil && was.Inputs == st.Inputs {
			res.Revision = rev
		} else if data, err := json.Marshal(st); err == nil {
			if rev, err := p.Store.Put(StateUserList, KeyList, data); err != nil {
				res.Errors = append(res.Errors, fmt.Sprintf("its own %s cannot be written: %v", StateUserList, err))
			} else {
				res.Revision, res.Written = rev, true
				p.say(&res, EventUserList, map[string]any{"digest": st.Digest, "revision": rev, "users": st.Users,
					"differing": len(st.Compare.Differing()), "mode": Shadow})
			}
		}
	}
	// The list itself, sealed to the bus node and named in `user-list.sealed` (ADR 0547 clause 7).
	if list, n, leftOut, err := ComposeList(recs, in.Hashes); err != nil {
		res.Errors = append(res.Errors, "the user list could not be composed whole: "+err.Error())
	} else {
		// The users the bus loaded: what a first list after take-over must keep where the part has not yet written one.
		var bus []string
		if st.Compare.Unread == "" {
			bus = names(loaded)
		}
		p.writeSealed(&res, list, n, leftOut, in, bus)
	}
	ms := Memberships(recs)
	res.Memberships = len(ms)
	for _, key := range sortedKeys(ms) {
		m, now := publish(p.Publish, ms[key])
		switch {
		case now:
			res.Published = append(res.Published, key)
			p.say(&res, EventMembership, map[string]any{"node": m.Node, "module": m.Module, "digest": m.Digest, "published": true})
		case m.Published != MembershipUnchanged:
			res.NotPublished = append(res.NotPublished, key+": "+m.Published)
		}
		data, _ := json.Marshal(m)
		if p.changed(&res, StateMemberships, key, data) {
			res.MembershipsWritten++
		}
	}
	held, heldErr := HeldStreams(p.Call)
	forced := ""
	if p.Create != nil {
		forced = p.askedAssert()
	}
	for _, module := range sortedKeys(in.Manifests) {
		if !assigned(in, module) {
			continue
		}
		a := Assert(module, in.Digests[module], in.Manifests[module], held, heldErr)
		// Created only where the bus was read and lacks it, never changed where it holds it (issue 1790).
		if p.Create != nil && heldErr == nil {
			if made := createMissing(p.Create, &p.made, &a, in.Manifests[module], forced == module); len(made) > 0 {
				res.Asserted = append(res.Asserted, fmt.Sprintf("%s at %s: created %s", module, a.Manifest, strings.Join(made, ", ")))
				p.say(&res, EventAsserted, map[string]any{"module": module, "manifest": a.Manifest, "created": made})
			}
			for _, why := range notCreated(a) {
				res.NotAsserted = append(res.NotAsserted, module+" "+why)
			}
		}
		res.Assertions++
		data, _ := json.Marshal(a)
		if p.changed(&res, StateAssertions, module, data) {
			res.AssertionsWritten++
		}
	}
	if _, _, found, err := p.Store.Get(StateTakeover, KeySwitch); err == nil && !found {
		data, _ := json.Marshal(Switch{V: 1, State: Shadow, Acts: []Act{}})
		if _, err := p.Store.Put(StateTakeover, KeySwitch, data); err != nil {
			res.Errors = append(res.Errors, fmt.Sprintf("its own %s cannot be written: %v", StateTakeover, err))
		}
	}
	if !p.deciding.Load() {
		if err := p.RaiseRequested(); err != nil {
			res.Errors = append(res.Errors, err.Error())
		}
		if err := p.Reconcile(); err != nil {
			res.Errors = append(res.Errors, err.Error())
		}
	}
	return res
}

// Last is the result of the last pass this part made, kept under the lock alone.
func (p *Part) Last() Result {
	p.mu.Lock()
	defer p.mu.Unlock()
	return p.last
}

func assigned(in Inputs, module string) bool {
	for _, ms := range in.Assigned {
		for _, m := range ms {
			if m == module {
				return true
			}
		}
	}
	return false
}

// changed writes key when its value differs from the one held, and says whether it wrote.
func (p *Part) changed(res *Result, state, key string, data []byte) bool {
	raw, _, found, err := p.Store.Get(state, key)
	if err != nil {
		res.Errors = append(res.Errors, fmt.Sprintf("its own %s %s cannot be read: %v", state, key, err))
		return false
	}
	if found && bytes.Equal(raw, data) {
		return false
	}
	if _, err := p.Store.Put(state, key, data); err != nil {
		res.Errors = append(res.Errors, fmt.Sprintf("its own %s %s cannot be written: %v", state, key, err))
		return false
	}
	return true
}

func (p *Part) say(res *Result, event string, body any) {
	if p.Emit == nil {
		return
	}
	if err := p.Emit.Emit(event, body); err != nil {
		res.Errors = append(res.Errors, fmt.Sprintf("the event %s could not be said: %v", event, err))
	}
}

func sortedKeys[V any](m map[string]V) []string {
	out := make([]string, 0, len(m))
	for k := range m {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

func names(us []User) []string {
	out := make([]string, 0, len(us))
	for _, u := range us {
		out = append(out, u.User)
	}
	return out
}