package main

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"slices"
	"sort"
	"strings"
	"sync"

	"git.novox.be/novox/mesh-sdk/go/catalogue"
	"git.novox.be/novox/mesh-sdk/go/compose"
	"git.novox.be/novox/mesh-sdk/go/validate"
	"github.com/novox/mesh-controller/internal/inventory"
)

// The controller's composition on mesh-sdk's (novox/hq ADR 0453 clause 3, design 47 R4b, issues 1386 to 1388): every
// caller that planned or composed a node reads the Input once for its operation (compose_input.go), asks the SDK to
// compose over it, and, when it sends, performs what the composition names foreseen (compose_perform.go) and composes again.

// inputCacheKey carries an operation's Input in its context, so the planning of every node of one verb reads the stores once.
type inputCacheKey struct{}

type inputCache struct {
	mu sync.Mutex
	by map[string]*meshInput
}

// withInputCache is ctx for an operation: the Input read for it is kept until a send changes what it read. A context that
// carries none reads the stores for each composition, which is correct and slow.
func withInputCache(ctx context.Context) context.Context {
	if _, ok := ctx.Value(inputCacheKey{}).(*inputCache); ok {
		return ctx
	}
	return context.WithValue(ctx, inputCacheKey{}, &inputCache{by: map[string]*meshInput{}})
}

// freshInput is ctx for one composition whose Input is read afresh and kept only until the composition makes something: a
// send that is composed after another one made and recorded things (a push's machines, one after the other).
func freshInput(ctx context.Context) context.Context {
	return context.WithValue(ctx, inputCacheKey{}, &inputCache{by: map[string]*meshInput{}})
}

// keptSignature is what the Input read depends on in ctx: which recorded modules each machine keeps at the build it runs
// (recorded_kept.go), so an Input read for a person's push is never taken for one read for a gated send.
func keptSignature(ctx context.Context) string {
	skip, on := keptExcept(ctx)
	var names []string
	for m := range skip {
		names = append(names, m)
	}
	sort.Strings(names)
	every, _ := ctx.Value(keepEveryBuildKey{}).(string)
	settings, _ := ctx.Value(keepForSettingsKey{}).(string)
	return fmt.Sprintf("kept=%v;except=%v;every=%s;settings=%s", on, names, every, settings)
}

// inputFor is the Input for ctx's operation.
func inputFor(ctx context.Context, open *stores) (*meshInput, error) {
	cache, ok := ctx.Value(inputCacheKey{}).(*inputCache)
	if !ok {
		return readComposeInput(ctx, open)
	}
	sig := keptSignature(ctx)
	cache.mu.Lock()
	defer cache.mu.Unlock()
	if in := cache.by[sig]; in != nil {
		return in, nil
	}
	in, err := readComposeInput(ctx, open)
	if err != nil {
		return nil, err
	}
	cache.by[sig] = in
	return in, nil
}

// forgetInput drops what the operation read, because a send made or recorded something it read.
func forgetInput(ctx context.Context) {
	if cache, ok := ctx.Value(inputCacheKey{}).(*inputCache); ok {
		cache.mu.Lock()
		cache.by = map[string]*meshInput{}
		cache.mu.Unlock()
	}
}

// resolveNode works out everything a node should run, from what was assigned to it (planFor on the SDK): over the Input,
// writing nothing. A failure to compose the node's own modules is marked notResolvable, as planFor marked it; every other
// failure is returned as it is.
func resolveNode(ctx context.Context, open *stores, node string) (catalogue.Resolution, catalogue.SettingsBy, error) {
	in, err := inputFor(ctx, open)
	if err != nil {
		return catalogue.Resolution{}, nil, err
	}
	if err := in.refused[node]; err != nil {
		return catalogue.Resolution{}, nil, err
	}
	resolved, err := compose.Resolve(in.Input, node)
	if err != nil {
		if compose.IsUnresolvable(err) {
			return catalogue.Resolution{}, nil, notResolvable{err}
		}
		return catalogue.Resolution{}, nil, err
	}
	logUnheld(node, resolved.Plan.Unheld)
	return resolved.Plan, resolved.Settings, nil
}

// generatorsOf is what every node's declaration is composed with, over the whole mesh (generators on the SDK).
func generatorsOf(ctx context.Context, open *stores) (map[string]catalogue.Generator, error) {
	in, err := inputFor(ctx, open)
	if err != nil {
		return nil, err
	}
	return compose.Generators(in.Input)
}

// renderingOf is what a machine is rendered with as a question reads it (nothing made), with the private network: what the
// filter's rules, the roster and the like are derived from.
func renderingOf(ctx context.Context, open *stores, node string) (catalogue.Rendering, error) {
	in, err := inputFor(ctx, open)
	if err != nil {
		return catalogue.Rendering{}, err
	}
	rendered, err := compose.Render(in.Input, node, compose.Reading)
	if err != nil {
		return catalogue.Rendering{}, markUnresolvable(err)
	}
	with := rendered.Rendering
	if with.Generators, err = compose.Generators(in.Input); err != nil {
		return catalogue.Rendering{}, err
	}
	return with, nil
}

// whoResolvesOn is the machines whose resolution answers a requirement, and why the others did not (whoResolves over the
// Input): by what a module provides, not by its name. A machine whose set does not compose is in refused, said; one the mesh
// could not be asked about is an error, never a refusal (novox/hq 04-ISSUES/152).
func whoResolvesOn(ctx context.Context, open *stores, requirement string) (map[string]bool, map[string]string, error) {
	in, err := inputFor(ctx, open)
	if err != nil {
		return nil, nil, err
	}
	on := map[string]bool{}
	refused := map[string]string{}
	for _, n := range in.sortedNodes() {
		if err := in.refused[n.Name]; err != nil {
			return nil, nil, fmt.Errorf("whether %s answers %q cannot be read: %w", n.Name, requirement, err)
		}
		resolved, err := compose.Resolve(in.Input, n.Name)
		switch {
		case compose.IsUnresolvable(err):
			refused[n.Name] = err.Error()
			continue
		case err != nil:
			return nil, nil, fmt.Errorf("whether %s answers %q cannot be read: %w", n.Name, requirement, err)
		}
		for _, m := range resolved.Plan.Modules {
			for _, offered := range m.Offers() {
				if offered == requirement {
					on[n.Name] = true
				}
			}
		}
	}
	return on, refused, nil
}

// sortedNodes is the Input's nodes by name, the order the controller reads them in.
func (in *meshInput) sortedNodes() []compose.Node {
	out := append([]compose.Node(nil), in.Nodes...)
	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
	return out
}

// composeQuestion composes a node's declaration as a question asks it: nothing is made, and what a send would make is a
// stand-in (Foreseeing) or left out (Reading). It also answers what the node-engine's validator refuses of it. The lines the
// composition found are said where the controller says its own (standard error, or the writer an act gave).
//
// withOrder says the declaration carries the order it was last sent under (composedAndValidated's, which a comparison with the
// last send needs); without it the order is none, as declarationWith left it for the sender to stamp.
func composeQuestion(ctx context.Context, open *stores, node string, mode compose.Mode, withOrder bool) (sendable, []string, error) {
	in, err := inputFor(ctx, open)
	if err != nil {
		return sendable{}, nil, err
	}
	if err := in.refused[node]; err != nil {
		return sendable{}, nil, err
	}
	d, problems, err := compose.ComposeIn(in.Input, node, mode)
	if err != nil {
		return sendable{}, nil, markUnresolvable(err)
	}
	if err := refusedBus(in, node); err != nil {
		return sendable{}, nil, err
	}
	sayFound(ctx, d)
	out := sendableOf(d)
	if !withOrder {
		out.Sequence, out.Epoch, out.Generation = 0, 0, 0
	}
	return out, problems, nil
}

// refusedBus is why the node cannot be composed because it runs the bus and the bus's user list cannot be: no user has a
// credential, so the list would refuse every connection in the mesh (busUserList). The controller's own composition refused that
// machine with those words; no other machine is refused for it. nil when nothing refuses the node.
func refusedBus(in *meshInput, node string) error {
	if in.busRefused == nil {
		return nil
	}
	resolved, err := compose.Resolve(in.Input, node)
	if err != nil {
		return nil // it does not compose for its own reasons, which are said
	}
	for _, m := range resolved.Plan.Modules {
		if m.BusUsers != "" && m.ClaimsSeat("mesh-broker") {
			return in.busRefused
		}
	}
	return nil
}

// markUnresolvable is an error of a node whose own set does not compose, as planFor marked it.
func markUnresolvable(err error) error {
	if compose.IsUnresolvable(err) {
		return notResolvable{err}
	}
	return err
}

// composeSend composes a node's declaration to send it, as the Allocating composition did: composed over what is read,
// then what it named foreseen is made (perform), the stores are read again and it is composed again. A declaration that
// still names anything foreseen is refused, said, and never sent.
func composeSend(ctx context.Context, open *stores, node string) (sendable, error) {
	declared, _, err := composeSendValidated(ctx, open, node)
	return declared, err
}

// composeSendValidated is composeSend and what the node-engine's validator refuses of the declaration it composed, for the
// merge gate's two passes (composedAndValidated in its Allocating mode).
func composeSendValidated(ctx context.Context, open *stores, node string) (sendable, []string, error) {
	// The core modules whose credentials the controller sealed itself because the vault was silent and no box was kept
	// (ADR 0396): the composition stands in a vault box for each, and a send carries the controller's own seal instead.
	byController, err := prepareSend(ctx, open, node)
	if err != nil {
		return sendable{}, nil, err
	}
	for attempt := 0; ; attempt++ {
		in, err := inputFor(ctx, open)
		if err != nil {
			return sendable{}, nil, err
		}
		if err := in.refused[node]; err != nil {
			return sendable{}, nil, err
		}
		d, problems, err := compose.ComposeIn(in.Input, node, compose.Foreseeing)
		if err != nil {
			return sendable{}, nil, markUnresolvable(err)
		}
		if err := refusedBus(in, node); err != nil {
			return sendable{}, nil, err
		}
		if len(byController) > 0 {
			if d, problems, err = sealedByTheController(in, node, d, byController); err != nil {
				return sendable{}, nil, err
			}
		}
		left := stillForeseen(d)
		resolved, rerr := compose.Resolve(in.Input, node)
		if rerr != nil {
			return sendable{}, nil, markUnresolvable(rerr)
		}
		if len(resolved.Foreseen) > 0 {
			left = append(left, resolved.Foreseen...)
		}
		if len(left) == 0 && len(in.wouldMake) == 0 {
			sayFound(ctx, d)
			out := sendableOf(d)
			// The sender stamps the order it allots (order.stamp); a composition for a send carries none of its own.
			out.Sequence, out.Epoch, out.Generation = 0, 0, 0
			here, _ := nodeOf(in.Input, node)
			out.Builds = buildsOf(in.Input, here, resolved.Plan, d.LeftOutWhy)
			out.Bindings = boundToData(resolved.Plan, d.LeftOutWhy)
			if len(d.Filled) > 0 {
				if out.plans, err = handedPlans(in, node, resolved); err != nil {
					return sendable{}, nil, err
				}
			}
			return out, problems, nil
		}
		if attempt > 0 {
			return sendable{}, nil, fmt.Errorf("%s was composed twice and still names what only a send makes (%s): nothing is sent "+
				"that stands in for a value", node, strings.Join(left, "; "))
		}
		if _, err := perform(ctx, open, in, node, d); err != nil {
			return sendable{}, nil, err
		}
		// What was made is in the stores now: the next read is a fresh one.
		forgetInput(ctx)
	}
}

// restOfTheMesh is what every other machine holds and offers (theRestOfTheMesh over the Input), for a question: the lines it
// finds are said where the controller says its own, and a seat it would pass on is passed by the next send (perform), not by
// the question. shelf, when given, replaces the Input's catalogue: a caller composing a change's shelf.
func restOfTheMesh(ctx context.Context, open *stores, shelf map[string]catalogue.Manifest, exclude string) (catalogue.World, error) {
	in, err := inputFor(ctx, open)
	if err != nil {
		return catalogue.World{}, err
	}
	input := in.Input
	if shelf != nil {
		input.Catalogue = shelf
	}
	world, passes, left, err := compose.TheRestOfTheMesh(input, exclude)
	if err != nil {
		return catalogue.World{}, err
	}
	var w io.Writer = os.Stderr
	if lw, ok := ctx.Value(leftOutKey{}).(io.Writer); ok {
		w = lw
	}
	for _, l := range left {
		fmt.Fprintln(w, l.String())
	}
	for _, line := range passes.Said {
		fmt.Fprintln(w, line)
	}
	return world, nil
}

// restOfTheMeshOf is restOfTheMesh for a caller that holds the inventory alone: the other stores the Input reads are opened for
// the call and let go of again.
func restOfTheMeshOf(ctx context.Context, inv *inventory.Inventory, shelf map[string]catalogue.Manifest, exclude string) (catalogue.World, error) {
	open := &stores{inventory: inv}
	defer func() {
		if open.licences != nil {
			open.licences.Close()
		}
		if open.identity != nil {
			open.identity.Close()
		}
	}()
	return restOfTheMesh(ctx, open, shelf, exclude)
}

// sayFound says the lines a composition found while composing, once each: a machine left out of the rest of the mesh, a seat
// that two claimants could take, the bus's users left out for want of a credential.
func sayFound(ctx context.Context, d compose.Declared) {
	if len(d.Said) == 0 {
		return
	}
	var w io.Writer = os.Stderr
	if lw, ok := ctx.Value(leftOutKey{}).(io.Writer); ok {
		w = lw
	}
	for _, line := range d.Said {
		fmt.Fprintln(w, line)
	}
}

// sendableOf is a composed declaration as the controller's sends know it.
func sendableOf(d compose.Declared) sendable {
	out := sendable{Resources: d.Resources, Sequence: d.Sequence, Epoch: d.Epoch, Generation: d.Generation,
		ReadsModules: d.ReadsModules, moduleOf: d.ModuleOf, buildIDs: d.BuildIDs, modules: d.Modules,
		localNetwork: d.LocalNetwork, Received: d.Received, Mesh: d.Mesh, BusUsers: d.BusUsers,
		LeftOut: d.LeftOut, leftOutWhy: d.LeftOutWhy, withheld: d.Withheld, unbound: d.Unbound, foreseen: d.Foreseen,
		unplaced: d.Unplaced, handedOnly: d.HandedOnly, Filled: d.Filled, Provisioner: d.Provisioner,
		requiredBy: d.RequiredBy}
	if d.Adoption != nil {
		out.Adoption = &adoptionEnvelope{Taken: d.Adoption.Taken, Untaken: d.Adoption.Untaken}
	}
	return out
}

// buildsOf is the build of each module a declaration for the node carries, as a send records it (novox/hq issue 259): the
// module's current build for each module in it, the build it was last sent for one left out of it, and a module kept at the
// build the machine runs carried at that one (ADR 0245). Never nil.
func buildsOf(in compose.Input, node compose.Node, plan catalogue.Resolution, leftOut map[string]string) map[string]string {
	before := node.SentBuilds
	if !node.SentKnown {
		before = nil
	}
	out := map[string]string{}
	for _, m := range plan.Modules {
		if _, left := leftOut[m.Module]; left {
			if was, kept := before[m.Module]; kept {
				out[m.Module] = was
			}
			continue
		}
		out[m.Module] = in.CurrentBuilds[m.Module]
	}
	for m, was := range node.KeptBuilds {
		if _, carried := out[m]; carried {
			out[m] = was
		}
	}
	return out
}

// handedPlans is the plan of each module handed to the provisioner, which the assignments mirror keeps with the send (design
// 57 P6): the composition's declaration does not carry it, so it is composed from the same rendering again.
func handedPlans(in *meshInput, node string, resolved compose.Resolved) (map[string]catalogue.Plan, error) {
	rendered, err := compose.Render(in.Input, node, compose.Foreseeing)
	if err != nil {
		return nil, err
	}
	gens, err := compose.Generators(in.Input)
	if err != nil {
		return nil, err
	}
	with := rendered.Rendering
	with.Generators = gens
	composed, err := resolved.Plan.Compose(with)
	if err != nil {
		return nil, err
	}
	return composed.Plans, nil
}

// sealedByTheController is the declaration with the controller's own seal in place of the vault's box for each core module the
// vault did not answer for and no box was kept for (core_box.go, ADR 0396): the file carries "sealed", as the controller's
// composition sent it, until the vault holds the credential. What the composition stood in for the box is replaced and no longer
// wanted; the validator is run again over the body.
func sealedByTheController(in *meshInput, node string, d compose.Declared, modules []string) (compose.Declared, []string, error) {
	rendered, err := compose.Render(in.Input, node, compose.Foreseeing)
	if err != nil {
		return d, nil, err
	}
	stood, _ := compactBox(catalogue.ForeseenVaultBox)
	var wanted []compose.CoreBoxWanted
	var foreseen []string
	for _, w := range d.CoreBoxesWanted {
		if !slices.Contains(modules, w.Module) {
			wanted = append(wanted, w)
			continue
		}
		sealed := rendered.Rendering.Needed[w.Module][w.Name]
		if sealed == "" {
			return d, nil, fmt.Errorf("%s/%s on %s has no seal of the controller's to carry until the vault holds it", w.Module, w.Name, node)
		}
		for _, r := range d.Resources {
			box, isBox := r[catalogue.VaultSealedField]
			// By the resource's id alone: its path is the manifest's with the machine's words filled in, and so is not the
			// manifest's own.
			if !isBox || r["id"] != w.Module+"."+catalogue.NeedID(w.Name) {
				continue
			}
			if had, err := compactBox(box); err != nil || had != stood {
				continue
			}
			delete(r, catalogue.VaultSealedField)
			r["sealed"] = sealed
		}
	}
	// A stand-in box that is left is said by its resource, never sent and never guessed at.
	for _, r := range d.Resources {
		if box, has := r[catalogue.VaultSealedField]; has {
			if had, err := compactBox(box); err == nil && had == stood {
				if id, _ := r["id"].(string); slices.ContainsFunc(modules, func(m string) bool { return strings.HasPrefix(id, m+".") }) {
					return d, nil, fmt.Errorf("%s on %s still carries a stand-in for the vault's box, and the controller has "+
						"no seal of its own for it", id, node)
				}
			}
		}
	}
	d.CoreBoxesWanted = wanted
	for _, f := range d.Foreseen {
		module, _, _ := strings.Cut(f, "/")
		if !slices.Contains(modules, module) {
			foreseen = append(foreseen, f)
		}
	}
	d.Foreseen = foreseen
	body, err := d.Body()
	if err != nil {
		return d, nil, err
	}
	return d, validate.Declaration(body), nil
}

// compactBox is a value as the compact JSON it marshals to, so a box is compared by what it says and not by the type that
// holds it.
func compactBox(v any) (string, error) {
	raw, err := json.Marshal(v)
	if err != nil {
		return "", err
	}
	var out bytes.Buffer
	if err := json.Compact(&out, raw); err != nil {
		return "", err
	}
	return out.String(), nil
}