package grants

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

	occ "git.novox.be/novox/mesh-contracts/operator-and-conversation/go/clients/operatorchannelclient"
	oc "git.novox.be/novox/mesh-contracts/operator-and-conversation/go/seats/operatorchannel"
	"git.novox.be/novox/mesh-delivery/contracts/go/clients/meshcatalogclient"
	"git.novox.be/novox/mesh-delivery/contracts/go/seats/meshcatalog"
	"git.novox.be/novox/mesh-sdk/go/keys"
	"git.novox.be/novox/mesh-sdk/go/views"
)

// **The grants part's first views** (novox/hq ADR 0615 §1, §4 to §6, ADR 0621, ADR 0622; design 25 § 12.2; DLV-F4r,
// DLV-R1). The part reads the assigner's assignments and wants and the indexer's manifests, modules and verdicts no longer
// from their buckets, but by each owner's first-view tool, asked once at its start, then from the owner's views family
// alone (each event one changed key with its revision), asking once more only on a gap in revisions, never on a timer.
// The verdicts alone are followed on the seat mesh-catalog's manifest-accepted and manifest-refused, which carry the revision
// (ADR 0622 §2), not on its views family (HearVerdict).
// Started while an owner is down it keeps asking and never reads the owner's state; past the bound (two minutes) it
// raises FirstViewUnanswered naming the owner and the tool, cleared by the answer.
//
// **An answer empty at revision 0 drops no login**: until an owner answers above revision 0 the state reads as a failed
// read, so the part keeps the user list it has in force, and FirstViewEmpty stands, naming the owner and the operator's
// step (the owner writes its state again from its sources, then grants_first_view_again); an answer above 0 clears it.

// FirstView is one owner's state the part reads by its first view: the owner, the tool its `invokes` names, the state,
// and the read it stands for in the part's inputs (`<owner>.<state>`).
type FirstView struct {
	Owner string `json:"owner"`
	Tool  string `json:"tool"`
	State string `json:"state"`
	Read  string `json:"read"`
}

// The owners.
const (
	AssignerModule = "mesh-delivery-assigner"
	IndexerModule  = "mesh-delivery-indexer"
)

// FirstViews are the five (ADR 0615 §3 as ADR 0622 §1 amends it: the grants part's assignments, wants, manifests,
// modules and verdicts).
var FirstViews = []FirstView{
	{Owner: AssignerModule, Tool: AssignerModule + ".assignments", State: "assignments", Read: ReadAssignments},
	{Owner: AssignerModule, Tool: AssignerModule + ".wants", State: "wants", Read: ReadWants},
	{Owner: IndexerModule, Tool: IndexerModule + ".manifests", State: "manifests", Read: ReadManifests},
	{Owner: IndexerModule, Tool: IndexerModule + ".modules", State: "modules", Read: ReadModules},
	{Owner: IndexerModule, Tool: IndexerModule + ".verdicts", State: "verdicts", Read: ReadVerdicts},
}

// The conditions of the first views, each naming the owner and its state.
const (
	FirstViewUnanswered = "mesh-grants.first-view-unanswered"
	FirstViewEmpty      = "mesh-grants.first-view-empty"
)

// KeyFirstViews is the key of the part's own state user-list where its process keeps what each first view holds, which
// grants_first_views reads.
const KeyFirstViews = "first-views"

// ErrFirstViewNotYet is a read of a first view not answered above revision 0: the part composes as from a failed read.
var ErrFirstViewNotYet = errors.New("not answered above revision 0 yet")

// Views is the part's reads of the five owners' states through their first views: a Reader and a Watcher for those
// states, every other read going to Rest.
type Views struct {
	// Followers are the five, by the read they stand for.
	Followers map[string]*views.Follower
	// Rest reads every other state, and Watching watches it (nil: watched by nobody, as in a tool).
	Rest     Reader
	Watching Watcher

	said *untilSaid
}

// NewViews makes the five followers: ask calls an owner's tool (through the part's own account), say says a condition,
// changed wakes a pass. Started by Start.
func NewViews(ask func(tool string) func(context.Context, string) (views.Answer, error), say func(oc.Condition) error,
	changed func(), logf func(string, ...any)) *Views {
	v := &Views{Followers: map[string]*views.Follower{}}
	sayer := &untilSaid{say: say, logf: logf, unsaid: map[string]oc.Condition{}}
	v.said = sayer
	for _, fv := range FirstViews {
		fv := fv
		f := &views.Follower{Owner: fv.Owner, Tool: fv.Tool, State: fv.State, Ask: ask(fv.Tool), Logf: logf,
			Changed: func(string, json.RawMessage, bool, time.Time) { changed() }}
		f.Raise = func(s views.Status) {
			sayer.Say(unansweredCondition(fv, s, true))
			changed()
		}
		f.Clear = func(s views.Status) {
			sayer.Say(unansweredCondition(fv, s, false))
			changed()
		}
		v.Followers[fv.Read] = f
	}
	return v
}

// untilSaid says a first view's condition; one the condition keeper did not take is logged and kept, and said again at
// the part's next pass (SayUnsaid), until it lands or a newer word on the same key replaces it: a raise or a clear is
// never dropped on a failed publish, and nothing waits on a timer for it.
type untilSaid struct {
	say    func(oc.Condition) error
	logf   func(string, ...any)
	mu     sync.Mutex
	unsaid map[string]oc.Condition
}

// Say says c; when it fails it is kept to be said again.
func (u *untilSaid) Say(c oc.Condition) {
	if u.say == nil {
		return
	}
	err := u.say(c)
	u.mu.Lock()
	defer u.mu.Unlock()
	if err == nil {
		delete(u.unsaid, c.Key)
		return
	}
	u.unsaid[c.Key] = c
	if u.logf != nil {
		u.logf("the condition %s (%s) could not be said: %v; said again at the next pass", c.Key, c.State, err)
	}
}

// SayUnsaid says again every condition not taken yet: the part's pass calls it.
func (v *Views) SayUnsaid() {
	if v == nil || v.said == nil {
		return
	}
	u := v.said
	u.mu.Lock()
	pending := make([]oc.Condition, 0, len(u.unsaid))
	for _, k := range slices.Sorted(maps.Keys(u.unsaid)) {
		pending = append(pending, u.unsaid[k])
	}
	u.mu.Unlock()
	for _, c := range pending {
		u.mu.Lock()
		current, still := u.unsaid[c.Key]
		u.mu.Unlock()
		if still && current.State == c.State {
			u.Say(c)
		}
	}
}

// Start asks each first view on a goroutine of its own, until it is answered or ctx ends; each answer wakes a pass.
func (v *Views) Start(ctx context.Context, changed func()) {
	for _, f := range v.Followers {
		f := f
		go func() {
			if f.Start(ctx) == nil {
				changed()
			}
		}()
	}
}

// Following says the follower of the owner's views event state, or nil.
func (v *Views) Following(owner, state string) *views.Follower {
	for _, fv := range FirstViews {
		if fv.Owner == owner && fv.State == state {
			return v.Followers[fv.Read]
		}
	}
	return nil
}

// ready is the follower of read, answered above revision 0; nil and why when it is not one of the five, or not yet.
func (v *Views) ready(read string) (*views.Follower, bool, error) {
	f, ok := v.Followers[read]
	if !ok {
		return nil, false, nil
	}
	select {
	case <-f.Ready():
	default:
		return f, true, fmt.Errorf("%s by %s: %w", read, f.Tool, ErrFirstViewNotYet)
	}
	if s := f.Status(); s.Revision == 0 {
		return f, true, fmt.Errorf("%s by %s answered empty at revision 0: %w", read, f.Tool, ErrFirstViewNotYet)
	}
	return f, true, nil
}

// Get reads one key: from its first view for the five, else from Rest.
func (v *Views) Get(state, key string) ([]byte, bool, error) {
	f, mine, err := v.ready(state)
	if !mine {
		return v.Rest.Get(state, key)
	}
	if err != nil {
		return nil, false, err
	}
	raw, ok := f.Get(key)
	return raw, ok, nil
}

// Keys lists a state's keys: from its first view for the five, else from Rest.
func (v *Views) Keys(state string) ([]string, error) {
	f, mine, err := v.ready(state)
	if !mine {
		return v.Rest.Keys(state)
	}
	if err != nil {
		return nil, err
	}
	values := f.Values()
	out := make([]string, 0, len(values))
	for k := range values {
		out = append(out, k)
	}
	sort.Strings(out)
	return out, nil
}

// Watch watches Rest's states; the five are followed by their first views and events, never watched.
func (v *Views) Watch(state string, changed func(key string, value []byte), ended func(error)) error {
	if _, mine := v.Followers[state]; mine || v.Watching == nil {
		return nil
	}
	return v.Watching.Watch(state, changed, ended)
}

// Statuses are what each first view holds now, in FirstViews' order.
func (v *Views) Statuses() []views.Status {
	out := make([]views.Status, 0, len(FirstViews))
	for _, fv := range FirstViews {
		out = append(out, v.Followers[fv.Read].Status())
	}
	return out
}

// Again asks the first view of one state (its state name, `assignments`, or its tool) once more, or every one when state is
// empty, each on a goroutine of its own; it answers which it asked, or refuses a state that is none of the five.
func (v *Views) Again(ctx context.Context, state, why string) ([]string, error) {
	var asked []string
	for _, fv := range FirstViews {
		if state != "" && state != fv.State && state != fv.Tool && state != fv.Read {
			continue
		}
		f := v.Followers[fv.Read]
		go func() { _ = f.Again(ctx, why) }()
		asked = append(asked, fv.Tool)
	}
	if len(asked) == 0 {
		return nil, fmt.Errorf("%q is no first view of the grants part: one of assignments, wants, manifests, modules, verdicts, or none for all", state)
	}
	return asked, nil
}

// VerdictEvents are the seat mesh-catalog's two events the part follows the verdicts on after their first view (ADR 0622 §2), as its
// manifest's consumes name them.
var VerdictEvents = []string{meshcatalog.Seat + "." + meshcatalog.EventManifestAccepted, meshcatalog.Seat + "." + meshcatalog.EventManifestRefused}

// HearVerdict takes one of the seat mesh-catalog's manifest-accepted or manifest-refused (event, its name) into the verdicts' first
// view, as one change of the verdicts state at the revision it carries (ADR 0622 §2): the manifest's digest its key, the
// verdict it says its value. A revision past the one after the picture's is a gap, and so is an event carrying no
// revision (an indexer that does not say it) or one saying no manifest above the picture's revision (the empty accepted
// verdict of a module leaving the trunk): the first view is asked once more on its own goroutine, said in the log. A
// revision already in the picture is passed over. Data that does not read is answered as an error, and nothing is asked.
func (v *Views) HearVerdict(ctx context.Context, event string, data []byte, logf func(string, ...any)) error {
	f := v.Followers[ReadVerdicts]
	if f == nil {
		return nil
	}
	var verdict meshcatalog.VerdictsByDigestValue
	var digest string
	var revision uint64
	switch event {
	case meshcatalog.EventManifestAccepted:
		var a meshcatalog.ManifestAcceptedEvent
		if err := json.Unmarshal(data, &a); err != nil {
			return fmt.Errorf("%s does not read: %w", event, err)
		}
		verdict = meshcatalog.VerdictsByDigestValue{V: keys.Version, Module: a.Module, State: meshcatalogclient.VerdictAccepted, Judge: a.Judge}
		digest, revision = a.Digest, uint64(a.Revision)
	case meshcatalog.EventManifestRefused:
		var r meshcatalog.ManifestRefusedEvent
		if err := json.Unmarshal(data, &r); err != nil {
			return fmt.Errorf("%s does not read: %w", event, err)
		}
		verdict = meshcatalog.VerdictsByDigestValue{V: keys.Version, Module: r.Module, State: meshcatalogclient.VerdictRefused, Judge: r.Judge, Problems: r.Problems}
		digest, revision = r.Digest, uint64(r.Revision)
	default:
		return fmt.Errorf("%q is not a verdict event of the indexer", event)
	}
	held := f.Status()
	gap := func(why string) error {
		logf("views: a gap in %s (%s): its first view %s is asked once more", f.State, why, f.Tool)
		go func() { _ = f.Gap(ctx, why) }()
		return nil
	}
	if revision == 0 {
		return gap(fmt.Sprintf("the indexer's %s of %s carries no revision", event, verdict.Module))
	}
	key, err := meshcatalogclient.VerdictsKey(digest)
	if err != nil {
		if revision <= held.Revision {
			return nil
		}
		return gap(fmt.Sprintf("the indexer's %s of %s at revision %d names no manifest", event, verdict.Module, revision))
	}
	// A revision below the picture's is a gap (ADR 0615 §5): the verdict events carry no mark of when the indexer's verdicts
	// were made, so one made again shows only as revisions starting low. A redelivery of a verdict the picture already
	// holds for its manifest is passed over, so a consumer's backlog after a restart asks nothing.
	if revision < held.Revision {
		if raw, found := f.Get(key); found {
			if was, err := meshcatalogclient.DecodeVerdict(raw); err == nil && sameVerdict(was, verdict) {
				return nil
			}
		}
		return gap(fmt.Sprintf("the indexer's %s of %s at revision %d, below the picture's %d: its verdicts were made again, or this verdict was missed",
			event, verdict.Module, revision, held.Revision))
	}
	value, err := json.Marshal(verdict)
	if err != nil {
		return err
	}
	if g, why := f.Apply(views.Event{V: 1, Owner: f.Owner, State: f.State, Key: key, Revision: revision, Created: held.Created,
		Value: value, At: time.Now().UTC()}); g {
		return gap(why)
	}
	return nil
}

// sameVerdict says two verdicts of one manifest say the same: its module, accepted or refused, the judge and the problems.
func sameVerdict(a, b meshcatalog.VerdictsByDigestValue) bool {
	return a.Module == b.Module && a.State == b.State && a.Judge == b.Judge && slices.Equal(a.Problems, b.Problems)
}

// unansweredCondition is FirstViewUnanswered for one first view, raised or cleared.
func unansweredCondition(fv FirstView, s views.Status, raised bool) oc.Condition {
	c := oc.Condition{Key: FirstViewUnanswered + "." + fv.Owner + "." + fv.State, Subject: oc.ConditionSubject{Scope: "module", ID: Module}}
	if !raised {
		c.State = occ.StateCleared
		c.Resolved = fv.Tool + " answered at revision " + fmt.Sprint(s.Revision)
		return c
	}
	c.State, c.Severity = occ.StateRaised, occ.SeverityWarning
	c.Summary = fmt.Sprintf("the grants part has no first view of %s's %s: %s has not answered since %s (%s)", fv.Owner, fv.State,
		fv.Tool, s.Asked.Format(time.RFC3339), strings.TrimSpace(s.Error))
	c.Headline = "The grants part waits for " + fv.Owner
	c.Explanation = "The grants part reads " + fv.Owner + "'s " + fv.State + " only through " + fv.Tool + ", and keeps asking it; " +
		"it never reads the state itself, and keeps what it composed meanwhile (novox/hq ADR 0615 §6). The answer clears this."
	c.Needs = "a look at " + fv.Owner + "'s runtime of its own: is it running and connected?"
	return c
}

// emptyCondition is FirstViewEmpty for one first view: raised while it answered empty at revision 0, with the
// operator's step, cleared by an answer above 0.
func emptyCondition(fv FirstView, raised bool) oc.Condition {
	c := oc.Condition{Key: FirstViewEmpty + "." + fv.Owner + "." + fv.State, Subject: oc.ConditionSubject{Scope: "module", ID: Module}}
	if !raised {
		c.State = occ.StateCleared
		c.Resolved = fv.Tool + " answered above revision 0"
		return c
	}
	step := "the indexer takes each module in again (indexer_take_in)"
	if fv.Owner == AssignerModule {
		step = "the assigner composes the wants again at its next composition"
	}
	c.State, c.Severity = occ.StateRaised, occ.SeverityWarning
	c.Summary = fmt.Sprintf("%s answered %s's %s empty at revision 0, so the grants part keeps the user list in force", fv.Tool, fv.Owner, fv.State)
	c.Headline = fv.Owner + "'s " + fv.State + " is empty"
	c.Explanation = occ.NeedsYou + "a step. The owner holds nothing of " + fv.State + " (its state rebuilt by a recreate that could " +
		"not keep the data, or a fresh mesh), so the grants part drops no login and keeps what it holds; a login revoked meanwhile " +
		"stays until the owner's first change (novox/hq design 25 § 12.2)."
	c.Needs = "let the owner write its state again from its sources (" + step + "), then grants_first_view_again"
	return c
}

// firstViewsSaid is what the part last said and kept of its first views (sayFirstViews).
type firstViewsSaid struct {
	mu    sync.Mutex
	empty map[string]bool
	known bool
}

// FirstViewsState is the value of KeyFirstViews: each first view's status, as the part's process last kept it.
type FirstViewsState struct {
	V     int            `json:"v"`
	Views []views.Status `json:"views"`
}

// sayFirstViews keeps the first views' statuses in the part's own state (for grants_first_views) when they change, and
// raises or clears FirstViewEmpty for each answered at revision 0. Each pass calls it; nil Views is none.
func (p *Part) sayFirstViews(res *Result) {
	if p.Views == nil {
		return
	}
	statuses := p.Views.Statuses()
	for i := range statuses {
		statuses[i].Asked, statuses[i].Answered = statuses[i].Asked.Truncate(time.Second), statuses[i].Answered.Truncate(time.Second)
	}
	data, _ := json.Marshal(FirstViewsState{V: 1, Views: statuses})
	p.changed(res, StateUserList, KeyFirstViews, data)
	p.fvSaid.mu.Lock()
	defer p.fvSaid.mu.Unlock()
	if p.fvSaid.empty == nil {
		p.fvSaid.empty = map[string]bool{}
	}
	for i, fv := range FirstViews {
		s := statuses[i]
		empty := !s.Answered.IsZero() && s.Revision == 0
		if p.fvSaid.known && p.fvSaid.empty[fv.Read] == empty {
			continue
		}
		if s.Answered.IsZero() && !p.fvSaid.known {
			continue // not answered yet: nothing to say of its emptiness
		}
		if p.Say == nil || p.Say(emptyCondition(fv, empty)) == nil {
			p.fvSaid.empty[fv.Read] = empty
		}
	}
	p.fvSaid.known = true
}

// FirstViewsOf answers the tool grants_first_views: what the part's process last kept of each first view (owner, tool,
// state, revision, when asked and answered, asks, hand acts, whether its condition is raised).
func (p *Part) FirstViewsOf() (any, error) {
	raw, rev, found, err := p.Store.Get(StateUserList, KeyFirstViews)
	if err != nil {
		return nil, fmt.Errorf("its own %s %s cannot be read: %w", StateUserList, KeyFirstViews, err)
	}
	if !found {
		return map[string]any{"views": []any{}, "said": "the part's process has kept no first view yet: it has not passed since it started"}, nil
	}
	var st FirstViewsState
	if err := json.Unmarshal(raw, &st); err != nil {
		return nil, fmt.Errorf("its own %s %s does not read: %w", StateUserList, KeyFirstViews, err)
	}
	return map[string]any{"views": st.Views, "revision": rev, "first-views": FirstViews}, nil
}

// AskFirstViewAgain answers the tool grants_first_view_again: it asks the part's process to ask one first view (by its
// state, or every one when state is empty) once more now, and records the hand act through record (the seat
// mesh-hand-acts); a state that is none of the five is refused before anything is asked.
func (p *Part) AskFirstViewAgain(caller, state, why string, record func(what, why string) error) (any, error) {
	which := AllFirstViews
	if state != "" {
		which = ""
		for _, fv := range FirstViews {
			if state == fv.State || state == fv.Tool || state == fv.Read {
				which = fv.State
			}
		}
		if which == "" {
			return nil, fmt.Errorf("%q is no first view of the grants part: one of assignments, wants, manifests, modules, verdicts, or none for all", state)
		}
	}
	if strings.TrimSpace(why) == "" {
		return nil, errors.New("grants_first_view_again needs why: it is recorded as a hand act")
	}
	if record != nil {
		if err := record("grants_first_view_again "+which, why); err != nil {
			return nil, fmt.Errorf("the hand act could not be recorded, so nothing was asked: %w", err)
		}
	}
	ask, _ := json.Marshal(Ask{By: caller, At: p.now(), FirstView: which})
	rev, err := p.Store.Put(StateUserList, KeyAsked, ask)
	if err != nil {
		return nil, fmt.Errorf("the ask could not be written: %w", err)
	}
	return map[string]any{"asked": rev, "first-view": which,
		"says": "the part's process asks it once more at this ask; grants_first_views shows its answer"}, nil
}

// Unwrapped is a call whose answer is read as the tool's own text where the runtime wraps it as content (unwrap), as
// a first view's answer is decoded (views.AskVia).
func Unwrapped(call func(key string, body any) (json.RawMessage, error)) func(key string, body any) (json.RawMessage, error) {
	return func(key string, body any) (json.RawMessage, error) {
		raw, err := call(key, body)
		if err != nil {
			return nil, err
		}
		return unwrap(raw), nil
	}
}