// Package firstview is the tool runner's picture of the four states it reads of the indexer and the assigner: the assigner's
// placement and seat-holders, the indexer's manifests and modules (novox/hq ADR 0615 §1, §3; ADR 0621 §2; issue 1966 TLS-5).
//
// **It never reads the owners' state.** At start it asks each owner's first-view tool until answered (the owner answers in a
// runtime of its own, never through this one: ADR 0621 §1), then follows the owner's views family, one event per changed key;
// a gap in the revisions, or an owner whose state was made again, asks the first view once more, said in the log. Past two
// minutes without an answer it writes a finding in its own state `findings`, which the condition keeper raises and clears.
package firstview

import (
	"context"
	"encoding/json"
	"fmt"
	conditions "git.novox.be/novox/mesh-contracts/health-and-repair/go/clients/meshconditionsclient"
	condseat "git.novox.be/novox/mesh-contracts/health-and-repair/go/seats/meshconditions"
	"sort"
	"sync"
	"time"

	"git.novox.be/novox/mesh-sdk/go/views"

	"github.com/novox/mesh-tools/node-tools/internal/bus"
)

// The owners and their first-view tools (the tools' addresses are `<owner>.<tool>`).
const (
	Indexer  = "mesh-delivery-indexer"
	Assigner = "mesh-delivery-assigner"
)

// Spec is one first view the runner holds.
type Spec struct{ Owner, Tool, State string }

// Specs are the four.
var Specs = []Spec{
	{Assigner, "placement", "placement"},
	{Assigner, "seat-holders", "seat-holders"},
	{Indexer, "manifests", "manifests"},
	{Indexer, "modules", "modules"},
}

// Name is the name a state is read by, `<owner>.<state>`: delivery.PlacementRead, delivery.SeatHoldersRead and the indexer's.
func (s Spec) Name() string { return s.Owner + "." + s.State }

// Views is the four followers.
type Views struct {
	logf      func(string, ...any)
	followers map[string]*views.Follower // by Spec.Name()
	byState   map[string]*views.Follower // by the state an event names
	ctx       context.Context
	cancel    context.CancelFunc
	wg        sync.WaitGroup
	deps      Deps
}

// FindingsState is the runner's own state the findings are written in.
const FindingsState = "findings"

// Deps is what the views reach the bus through: Start makes them from the runner's connection, a test from fakes.
type Deps struct {
	// Module is the runner's own name, the observer of its findings.
	Module string
	// Ask calls an owner's tool, `<owner>.<tool>`.
	Ask func(address string, body any) (json.RawMessage, error)
	// Consume hands each event of the owners' views families to deliver, until the stop is called.
	Consume func(deliver func(bus.Envelope) error) (stop func(), err error)
	// PutFinding and DeleteFinding keep and remove a finding in the runner's own state.
	PutFinding    func(key string, value json.RawMessage) error
	DeleteFinding func(key string) error
	// Bound and Wait are the follower's (zero: two minutes, five seconds).
	Bound, Wait time.Duration
}

// Start asks the four first views, each until answered, and follows the owners' views families on the runner's own
// consumers. It returns at once: the picture fills as the owners answer.
func Start(parent context.Context, conn *bus.Conn, logf func(string, ...any)) (*Views, func()) {
	return StartWith(parent, DepsOf(conn), logf)
}

// DepsOf is the views' reach through the runner's own connection: its tool calls, its consumer and its findings state.
func DepsOf(conn *bus.Conn) Deps {
	me := conn.Module()
	return Deps{Module: me,
		Ask: func(address string, body any) (json.RawMessage, error) {
			got, err := conn.Ask(address, body, "")
			return got.Result, err
		},
		Consume: func(deliver func(bus.Envelope) error) (func(), error) { return conn.ConsumeAs(me, deliver) },
		PutFinding: func(key string, value json.RawMessage) error {
			_, err := conn.StatePut(me, FindingsState, key, value)
			return err
		},
		DeleteFinding: func(key string) error { return conn.StateDelete(me, FindingsState, key) },
	}
}

// StartWith is Start over deps.
func StartWith(parent context.Context, d Deps, logf func(string, ...any)) (*Views, func()) {
	ctx, cancel := context.WithCancel(parent)
	v := &Views{logf: logf, ctx: ctx, cancel: cancel, followers: map[string]*views.Follower{}, byState: map[string]*views.Follower{}, deps: d}
	for _, s := range Specs {
		s := s
		call := func(tool string, body any) (json.RawMessage, error) { return d.Ask(s.Owner+"."+tool, body) }
		f := &views.Follower{Owner: s.Owner, Tool: s.Tool, State: s.State, Ask: views.AskVia(call, s.Tool), Logf: logf,
			Bound: d.Bound, Wait: d.Wait,
			Raise: func(st views.Status) { v.finding(st, true) },
			Clear: func(st views.Status) { v.finding(st, false) }}
		v.followers[s.Name()] = f
		v.byState[s.State] = f
		v.wg.Add(1)
		go func() { defer v.wg.Done(); _ = f.Start(ctx) }()
	}
	stop, err := d.Consume(v.hear)
	if err != nil {
		logf("[mesh-tools] the owners' views are not followed (%v): the pictures are the first views alone until the runner starts again", err)
		stop = func() {}
	}
	return v, func() { stop(); cancel(); v.wg.Wait() }
}

// hear applies one views event; a gap asks the first view once more.
func (v *Views) hear(env bus.Envelope) error {
	ev, err := views.DecodeEvent(env.Body)
	if err != nil {
		return nil // not a views event: nothing to hold, nothing to retry
	}
	f := v.byState[ev.State]
	if f == nil || f.Owner != ev.Owner {
		return nil
	}
	if gap, why := f.Apply(ev); gap {
		v.logf("[mesh-tools] a gap in %s's %s (%s): its first view %s is asked once more", f.Owner, f.State, why, f.Tool)
		go func() { _ = f.Again(v.ctx, "a gap: "+why) }()
	}
	return nil
}

// finding writes or removes the runner's finding of a first view unanswered past its bound, in its own state.
func (v *Views) finding(st views.Status, raised bool) {
	key, value, err := conditionOf(views.UnansweredFinding(v.deps.Module, st, time.Now()))
	if err != nil {
		v.logf("[mesh-tools] the finding of the first view %s is not made: %v", st.Tool, err)
		return
	}
	if raised {
		err = v.deps.PutFinding(key, value)
	} else {
		err = v.deps.DeleteFinding(key)
	}
	if err != nil {
		v.logf("[mesh-tools] the finding of the first view %s is not kept: %v", st.Tool, err)
	}
}

// State is the picture of the state spec names (`<owner>.<state>`), every current value by key; an error says the owner has
// not answered yet, so nothing is claimed of it.
func (v *Views) State(name string) (map[string][]byte, error) {
	f := v.followers[name]
	if f == nil {
		return nil, fmt.Errorf("the tool runner holds no first view of %s", name)
	}
	select {
	case <-f.Ready():
	default:
		return nil, fmt.Errorf("%s's first view %s has not been answered yet", f.Owner, f.Tool)
	}
	out := map[string][]byte{}
	for k, raw := range f.Values() {
		out[k] = raw
	}
	return out, nil
}

// Entry is one value of the picture, nil when the owner holds none.
func (v *Views) Entry(name, key string) ([]byte, error) {
	all, err := v.State(name)
	if err != nil {
		return nil, err
	}
	return all[key], nil
}

// Status is each first view as it stands, by `<owner>.<state>`, sorted.
func (v *Views) Status() []views.Status {
	var out []views.Status
	for _, f := range v.followers {
		out = append(out, f.Status())
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Owner+out[i].State < out[j].Owner+out[j].State })
	return out
}

// Again asks every first view once more, by hand, for why.
func (v *Views) Again(ctx context.Context, why string) []error {
	var errs []error
	for _, f := range v.followers {
		if err := f.Again(ctx, why); err != nil {
			errs = append(errs, err)
		}
	}
	return errs
}

// conditionOf is a finding in the layout of the seat mesh-conditions' state findings (its contract, ADR 0634 §1), about a
// module, a warning.
func conditionOf(f views.Finding) (string, []byte, error) {
	key := conditions.Key(scopeModule, f.ID, f.Kind)
	v := condseat.FindingsByKeyValue{V: 1, Key: key, Kind: f.Kind, Observer: f.Observer, Severity: conditions.Warning,
		Subject: condseat.Subject{Scope: scopeModule, ID: f.ID}, Summary: f.Summary, Headline: f.Headline,
		Explanation: f.Explanation, Source: f.Observer + "." + f.Kind, At: f.At.UTC().Format(time.RFC3339),
		Evidence: []condseat.Evidence{{At: f.At.UTC().Format(time.RFC3339), Said: f.Summary}}}
	if err := conditions.CheckFinding(v); err != nil {
		return "", nil, err
	}
	raw, err := json.Marshal(v)
	return key, raw, err
}

// scopeModule is the scope of a finding about a module.
const scopeModule = "module"