package main

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"os"
	"strings"
	"time"

	"github.com/novox/mesh-control/internal/broker"
	"github.com/novox/mesh-control/internal/catalogue"
	"github.com/novox/mesh-control/internal/inventory"
	"github.com/novox/mesh-control/internal/link"
)

// reportUnhostable says which of a node's assigned modules the machine cannot run, once per push.
//
// A module whose declared capability has no detector on the machine is on the wrong machine. It is
// kept out of what the node is sent — the healthy modules beside it still converge — and named here
// so it is neither silently dropped nor a reason the whole node fails to push.
func reportUnhostable(node string, plan catalogue.Resolution) {
	for _, u := range plan.Unhostable {
		for _, c := range u.Missing {
			fmt.Printf("%s not applied — %s\n", node, catalogue.WrongMachine(u.Module, c, node))
		}
	}
}

// sending it, and holding the link that carries it.
//
// Split out of main.go, which had reached 2,769 lines because appending was always the
// cheapest next step. That is how novox/hq ADR 0001 records `hal/sdk` reaching 34,636:
// nothing in it was wrong, and no one edit was the one that should have been a new file.

// serve is the control plane running: one connection to the broker, one queue, one consumer.
func serve(ctx context.Context) error {
	open, err := openStores(ctx)
	if err != nil {
		return err
	}
	defer open.Close()
	inv := open.inventory

	ident, err := openIdentity(ctx)
	if err != nil {
		return err
	}
	defer ident.Close()

	// Established at start rather than on first use. A control plane that cannot sign is one
	// whose declarations every node correctly refuses, and that should be a startup failure
	// rather than something discovered at the first declaration.
	key, err := ident.Establish(ctx)
	if err != nil {
		return err
	}
	fmt.Printf("signing as %s\n", key.Fingerprint()[:16])

	management, err := broker.ManagementFromEnvironment()
	if err != nil && !errors.Is(err, broker.ErrNotConfigured) {
		return err
	}

	// Where the broker is and what to expect there, so a node can be told how to come back
	// without a person and a new token.
	known, err := broker.FromEnvironment()
	if err != nil && !errors.Is(err, broker.ErrNotConfigured) {
		return err
	}
	if errors.Is(err, broker.ErrNotConfigured) {
		fmt.Printf("no broker address configured, so enrolled nodes will not be told how to "+
			"reconnect. Set %s and %s.\n", broker.AddressVar, broker.CertificateVar)
	}

	work := link.Enrolment{Inventory: inv, Identity: ident, Management: management, Broker: known}
	server, err := link.Connect(work, work)
	if err != nil {
		return err
	}
	defer server.Close()
	// And build results nobody was waiting for. A build triggered any other way than `build`
	// would otherwise be reported into the void, which is the same as not reporting it.
	server.Records(builds{inv})

	return server.Serve(ctx)
}

// declare sends one node a declaration, signed.
//
// Signed here rather than trusted from the broker: a node connects to the broker and takes
// instruction from the control plane behind it, and those are two identities. If a node believed
// whatever arrived on its queue, a compromised broker could forge declarations — and since the
// host applies whatever the link delivers, that is the whole machine (novox/hq ADR 0004).
func declare(ctx context.Context, args []string) error {
	if len(args) != 2 {
		return errors.New("declare <node> <declaration.json>")
	}
	node, path := args[0], args[1]

	raw, err := os.ReadFile(path)
	if err != nil {
		return err
	}

	ident, err := openIdentity(ctx)
	if err != nil {
		return err
	}
	defer ident.Close()

	// The node has to exist before it can be told anything. Publishing to a queue nobody consumes
	// would sit there looking like success.
	open, err := openStores(ctx)
	if err != nil {
		return err
	}
	defer open.Close()
	inv := open.inventory
	if _, err := inv.NodeByName(ctx, node); err != nil {
		return err
	}

	server, err := link.Connect(nil, nil)
	if err != nil {
		return err
	}
	defer server.Close()

	if err := link.Declare(ctx, server.Channel(), ident, node, raw, 15*time.Second); err != nil {
		return err
	}
	fmt.Printf("sent %s a signed declaration (%d bytes)\n", node, len(raw))
	return nil
}

// OverlayCIDRVar is the range the mesh allocates node addresses from.
const OverlayCIDRVar = "MESH_OVERLAY_CIDR"

// pushCommand sends nodes everything they should be: their place on the network, and what their
// assignments resolve to.
//
// One declaration, not two. A node holding its network and not its modules, or the reverse, is
// half-configured for as long as that lasts — and the two are computed from the same picture of
// the mesh, so sending them apart would let them disagree.
func pushCommand(ctx context.Context, args []string) error {
	set := flag.NewFlagSet("push", flag.ContinueOnError)
	// Only the machines that need it.
	//
	// **A command rather than a timer, to begin with.** Something that re-pushes on a schedule is
	// a scheduler over this, and building the scheduler first would mean two paths to one act
	// with nothing to compare them against. A person can run this; so can cron; so can whatever
	// eventually watches.
	behind := set.Bool("behind", false,
		"only machines whose last declaration was refused or partly failed")
	positionals, err := parseAround(set, args)
	if err != nil {
		return err
	}
	args = positionals
	if len(args) > 1 {
		return errors.New("push [<node>] [--behind] — one node, or all of them")
	}
	if len(args) == 1 && *behind {
		// Naming a machine and asking for the ones that need it are two different requests, and
		// guessing which was meant would sometimes push to a machine somebody did not name.
		return errors.New("push <node> or push --behind, not both: one names a machine and the " +
			"other asks which machines need one")
	}
	open, err := openStores(ctx)
	if err != nil {
		return err
	}
	defer open.Close()
	inv := open.inventory

	ident, err := openIdentity(ctx)
	if err != nil {
		return err
	}
	defer ident.Close()

	// Every node, not only the ones on the private network. A machine that was never given the
	// network module still takes modules, and iterating the network here is what used to make
	// "on the network" and "managed" the same thing.
	nodes, err := inv.Nodes(ctx)
	if err != nil {
		return err
	}

	// Which machines are not in the state they were sent, when that is what was asked for.
	var needsOne map[string]inventory.Doing
	if *behind {
		wrong, err := inv.NotDoingWhatTheyWereTold(ctx)
		if err != nil {
			return err
		}
		needsOne = map[string]inventory.Doing{}
		for _, d := range wrong {
			needsOne[d.Node] = d
		}
		// **And every machine not running what the mesh would send it.** "Behind" used to mean
		// only "failed or refused", so a machine that applied cleanly and whose declaration has
		// since changed was not behind — and novox/hq ADR 0010's question, *did my change go
		// out?*, was answerable only for the machines that broke.
		would, err := wouldSend(ctx, open, nodes)
		if err != nil {
			return err
		}
		waiting, err := inv.Waiting(ctx, would)
		if err != nil {
			return err
		}
		for _, m := range waiting {
			if _, already := needsOne[m.Node]; already {
				continue
			}
			needsOne[m.Node] = inventory.Doing{Node: m.Node, Outcome: "waiting"}
		}
		if len(needsOne) == 0 {
			// Said rather than doing nothing quietly. "Nothing needed one" and "this did not run"
			// must never look the same.
			fmt.Println("every machine is doing what it was told")
			return nil
		}
	}
	gens, err := generators(ctx, open)
	if err != nil {
		return err
	}

	server, err := link.Connect(nil, nil)
	if err != nil {
		return err
	}
	defer server.Close()

	// Which machines this push is about, before any of them is worked out.
	var asked []string
	for _, n := range nodes {
		if len(args) == 1 && n.Name != args[0] {
			continue
		}
		if *behind {
			doing, needs := needsOne[n.Name]
			if !needs {
				continue
			}
			// A machine that has been failing the same way for a long time is not going to stop
			// because it was asked again. Said, and pushed to anyway — refusing would leave no
			// way to retry after fixing the cause, and this is a command somebody ran.
			//
			// Only for machines that reported something. One that is merely waiting has no report
			// to be old, and saying it had been failing since the zero time would be a sentence
			// about nothing.
			if since := time.Since(doing.At); doing.Outcome != "waiting" && since > 6*time.Hour {
				fmt.Printf("%s has been %s since %s; pushing again anyway, but the cause is "+
					"unlikely to be timing\n",
					n.Name, doing.Outcome, doing.At.Local().Format("2006-01-02 15:04"))
			}
		}
		asked = append(asked, n.Name)
	}

	sending, refusals := composeEach(asked, func(node string) ([]map[string]any, error) {
		plan, settings, err := planFor(ctx, open, node)
		if err != nil {
			return nil, err
		}
		// A module assigned here that this machine cannot host is said and left out, not fatal: the
		// healthy modules beside it are still resolved and sent. Reported so it is not silently
		// dropped — the remedy is to move it, and until then the rest of the node converges.
		reportUnhostable(node, plan)
		// The private network is in here with everything else. It used to be composed separately
		// and prepended, which meant every machine with an address was on it and no machine could
		// be kept off. It is a module now, so it arrives the way a module does.
		return declarationWith(ctx, open, node, plan, settings, gens, Allocating)
	})

	for _, s := range sending {
		body, err := json.Marshal(map[string]any{"declaration": 1, "resources": s.resources})
		if err != nil {
			return err
		}
		if err := link.Declare(ctx, server.Channel(), ident, s.node, body, 15*time.Second); err != nil {
			return err
		}
		// After it is away, not before. A digest recorded for something that failed to send would
		// make the machine look current for a declaration it never received.
		record, err := inv.NodeByName(ctx, s.node)
		if err != nil {
			return err
		}
		if err := inv.RecordSent(ctx, record.ID, digestOf(body)); err != nil {
			return err
		}
		fmt.Printf("sent %s %d resource(s)\n", s.node, len(s.resources))
	}
	fmt.Printf("\n%d node(s) told\n", len(sending))
	return couldNotBeResolved(refusals, len(sending))
}

// readyNode is one machine and the declaration it would be sent.
type readyNode struct {
	node      string
	resources []map[string]any
}

// composeEach works out what each named machine should be, and never lets one machine's answer
// decide another's.
//
// **A machine whose set cannot be worked out is that machine's problem** (novox/hq ADR 0056). A
// whole-mesh push used to refuse outright when any one node failed to resolve, so a single
// unanswerable requirement on a single machine — one module requiring a provision nobody had
// assigned a provider for — left every other machine in the mesh unconverged, including machines
// with no relation to it at all. Nothing was sent anywhere, and the machines that could not be sent
// were the ones with nothing wrong with them.
//
// It is the same rule a92c11b established one level down, where an un-hostable module stopped
// taking down the healthy modules beside it, applied one level up: **the blast radius of a fault is
// the thing that has it.** What could not be worked out is named and returned, so a push still ends
// with a non-zero outcome and nobody mistakes a partial convergence for a whole one.
//
// The all-or-nothing rule is kept where it means something — sendTo, which rotates a credential
// across two machines that must agree — and dropped here, where it never did.
func composeEach(names []string,
	compose func(node string) ([]map[string]any, error)) ([]readyNode, []string) {

	var sending []readyNode
	var refusals []string
	for _, name := range names {
		resources, err := compose(name)
		if err != nil {
			refusals = append(refusals, fmt.Sprintf("%s:\n%v", name, err))
			continue
		}
		if len(resources) == 0 {
			fmt.Printf("%s is assigned nothing — skipped\n", name)
			continue
		}
		sending = append(sending, readyNode{name, resources})
	}
	return sending, refusals
}

// couldNotBeResolved is what a push ends with when some machines could not be worked out.
//
// **After the rest have been sent, never instead of sending them.** It is still an error, because
// the mesh is not in the state somebody asked for and a command that exits cleanly having skipped a
// machine is a command that lies. What it must not do is decide anything about the machines beside
// it, which is why it says how many were sent.
func couldNotBeResolved(refusals []string, sent int) error {
	if len(refusals) == 0 {
		return nil
	}
	return fmt.Errorf(
		"%d node(s) could not be resolved and were not sent. %d other node(s) were:\n\n%s",
		len(refusals), sent, strings.Join(refusals, "\n\n"))
}

// sendTo resolves and sends to exactly the machines named, or refuses without sending anything.
//
// The all-or-nothing rule push deliberately does NOT follow, and for a reason that holds here and
// not there: a rotation that reached the
// consumer and refused on the provider would leave one end holding a credential the other has
// never heard of — which is the state this whole mechanism exists to make impossible.
func sendTo(ctx context.Context, open *stores, names []string) error {
	inv := open.inventory
	ident, err := openIdentity(ctx)
	if err != nil {
		return err
	}
	defer ident.Close()

	gens, err := generators(ctx, open)
	if err != nil {
		return err
	}

	type ready struct {
		node      string
		resources []map[string]any
	}
	var sending []ready
	var refusals []string
	for _, name := range names {
		plan, settings, err := planFor(ctx, open, name)
		if err != nil {
			refusals = append(refusals, fmt.Sprintf("%s:\n%v", name, err))
			continue
		}
		reportUnhostable(name, plan)
		resources, err := declarationWith(ctx, open, name, plan, settings, gens, Allocating)
		if err != nil {
			refusals = append(refusals, fmt.Sprintf("%s:\n%v", name, err))
			continue
		}
		sending = append(sending, ready{name, resources})
	}
	if len(refusals) > 0 {
		return fmt.Errorf("nothing was sent. %d machine(s) could not be resolved:\n\n%s",
			len(refusals), strings.Join(refusals, "\n\n"))
	}

	server, err := link.Connect(nil, nil)
	if err != nil {
		return err
	}
	defer server.Close()

	for _, s := range sending {
		body, err := json.Marshal(map[string]any{"declaration": 1, "resources": s.resources})
		if err != nil {
			return err
		}
		if err := link.Declare(ctx, server.Channel(), ident, s.node, body, 15*time.Second); err != nil {
			return err
		}
		record, err := inv.NodeByName(ctx, s.node)
		if err != nil {
			return err
		}
		if err := inv.RecordSent(ctx, record.ID, digestOf(body)); err != nil {
			return err
		}
		fmt.Printf("  sent %s %d resource(s)\n", s.node, len(s.resources))
	}
	return nil
}

// digestOf is what the mesh compares to answer "has this machine been sent what it should be".
//
// Over the same bytes that are sent, so the comparison is of the thing itself rather than of
// something derived beside it that could drift from it.
func digestOf(body []byte) string {
	sum := sha256.Sum256(body)
	return hex.EncodeToString(sum[:])
}

// wouldSend is the digest of what each machine should be right now.
//
// Machines that do not resolve are left out rather than reported as waiting: "this machine cannot
// be worked out" is a different problem with a different remedy, and `plan` is where it is said.
func wouldSend(ctx context.Context, open *stores,
	nodes []inventory.Node) (map[string]string, error) {

	gens, err := generators(ctx, open)
	if err != nil {
		return nil, err
	}
	out := map[string]string{}
	for _, n := range nodes {
		plan, settings, err := planFor(ctx, open, n.Name)
		if err != nil {
			continue
		}
		resources, err := declarationWith(ctx, open, n.Name, plan, settings, gens, Reading)
		if err != nil {
			continue
		}
		body, err := json.Marshal(map[string]any{"declaration": 1, "resources": resources})
		if err != nil {
			return nil, err
		}
		out[n.Name] = digestOf(body)
	}
	return out, nil
}