package frombus

import (
	"context"
	"encoding/json"
	"fmt"
	"regexp"
	"slices"
	"sort"
	"strings"

	"git.novox.be/novox/mesh-sdk/go/catalogue"
	"git.novox.be/novox/mesh-sdk/go/compose"
	"git.novox.be/novox/mesh-sdk/go/declaration"
	"git.novox.be/novox/mesh-sdk/go/delivery"
)

// Answer is a node's answer to its proposal's placement candidates (novox/hq ADR 0567 §3, ADR 0559 §4): s.Node composed in shadow with
// s.Placements laid over the trunk's placement (compose.CompositionsShadow, its own sealed values and boxes through r as
// for its own composition), compared with what it runs (delivery.CompareComposed). It applies nothing and writes
// nothing; the proposal and the revision are the candidate's, said back in the answer.
//
// The node's own composition is compared only where the node runs one. fps gives the build each module is composed at: what the node runs, and for a module the candidate places that the
// node does not run, the build the trunk holds; a placed module with none is added, with no build of it known. What the
// composition stands in for is judged: a value of a module the proposal adds (on this node or another: its credential, own
// secrets and boxes are made only once it is placed, ADR 0549 §5) is not yet issued, which is no refusal; any other
// stand-in is a value missing for a module the node runs, a refusal naming it ("node" when it is the node's own).
func Answer(ctx context.Context, r Reader, mesh Mesh, s Scope, fps map[string]string, running []delivery.Composed, proposal string, revision uint64) delivery.CandidateAnswer {
	a := delivery.CandidateAnswer{Proposal: proposal, Revision: revision}
	refuse := func(err error) delivery.CandidateAnswer {
		a.Refused = err.Error()
		a.Verdict = delivery.CandidateRefused
		return a
	}
	trunk, err := r.Placements(ctx)
	if err != nil {
		return refuse(fmt.Errorf("frombus: placement: %w", err))
	}
	if s.Running == nil {
		s.Running = running
	}
	// Every module it cannot compose is named, not the first only (issue 1126): a build it cannot read or take in, and
	// below, a module the composition refuses, each composed as a stub so the rest is composed and compared.
	failed := map[string]string{}
	in, err := input(ctx, r, mesh, s, func(module string, err error) { failed[module] = err.Error() })
	if err != nil {
		return refuse(err)
	}
	asConsumer, asProvider, err := compose.CredentialsNeeded(in, s.Node)
	if err != nil {
		return refuse(err)
	}
	// What the node runs, by module. A consumer's credential is asked only for a module it runs: the vault refuses the
	// whole ask for a consuming module not assigned to the node (mesh-vault's own), and a module the candidate adds is
	// assigned only after the merge (ADR 0549 §5), so its credential is left missing, a stand-in answered as not yet
	// issued under Added (review of L2b, round 1, finding 1).
	runs := map[string]bool{}
	for _, c := range running {
		if c.Module != "" {
			runs[c.Module] = true
		}
	}
	var consumed []compose.CredentialKey
	for _, k := range asConsumer {
		if runs[k.ConsumerModule] {
			consumed = append(consumed, k)
		}
	}
	asConsumer = consumed
	if len(asConsumer)+len(asProvider) > 0 {
		if in.Credentials, in.Issued, err = r.Credentials(ctx, s.Node, asConsumer, asProvider); err != nil {
			return refuse(fmt.Errorf("frombus: the credentials of %s: %w", s.Node, err))
		}
	}
	composed, skipped, stood, err := composeEach(in, s.Node, fps, false, s.Running, failed)
	if err != nil {
		// Not one module's: the node's own (a value served elsewhere, the mesh's network), said once as the node's.
		if len(failed) == 0 {
			return refuse(err)
		}
		failed[delivery.HaveNodeWord] = err.Error()
		composed, skipped, stood = nil, nil, nil
	}
	// The node's own composition is judged only where the node runs one: one that runs none applies it only once a want
	// names it (the node agent's own composer hands it on that want alone), so a candidate does not add it.
	runsOwn := false
	for _, c := range running {
		runsOwn = runsOwn || c.Module == ""
	}
	if !runsOwn {
		for key, c := range composed {
			if c.Module == "" {
				delete(composed, key)
			}
		}
	}
	if _, whole := failed[delivery.HaveNodeWord]; whole {
		// Nothing composed to compare: every refusal is said, and nothing else.
		for _, m := range sortedKeys(failed) {
			a.Refusals = append(a.Refusals, delivery.ModuleRefused{Module: m, Why: failed[m]})
		}
		heldAsToday(&a, s.HeldToday)
		a.Verdict = delivery.VerdictOf(a)
		return a
	}
	// A module the composition folds inside the node's own is judged there: the agent also says it runs by module, from
	// the declaration it kept before the switch (agent.Everything), which is no removal (issue 1126, seed #531).
	if len(s.InOwn) > 0 {
		var judged []delivery.Composed
		for _, c := range running {
			if c.Module == "" || !slices.Contains(s.InOwn, c.Module) {
				judged = append(judged, c)
			}
		}
		running = judged
	}
	cmp := delivery.CompareComposedWith(composed, running, s.SameValue)
	// The answer rides in the node's have key: its shown bodies are bounded, the rest named only.
	budget := MaxShown
	for i := range cmp.Differs {
		kept := cmp.Differs[i].Bodies[:0]
		for _, b := range cmp.Differs[i].Bodies {
			if n := len(b.Composed) + len(b.Running); n <= budget {
				budget -= n
				kept = append(kept, b)
			} else {
				kept = append(kept, delivery.ResourceBodies{ID: b.ID, Why: b.Why})
				a.Note = "some differing resources are named without their bodies: the answer holds at most " +
					fmt.Sprint(MaxShown) + " bytes of them"
			}
		}
		cmp.Differs[i].Bodies = kept
	}
	// A refused module was composed as a stub: what it composed is no difference; its refusal is said.
	notFailed := func(m string) bool { _, ok := failed[m]; return !ok }
	a.Same = slices.DeleteFunc(cmp.Same, func(m string) bool { return !notFailed(m) })
	a.Removed = slices.DeleteFunc(cmp.Removed, func(m string) bool { return !notFailed(m) })
	a.Differs = slices.DeleteFunc(cmp.Differs, func(d delivery.ModuleDiffers) bool { return !notFailed(d.Module) })
	cmp.Added = slices.DeleteFunc(cmp.Added, func(d delivery.ModuleAdded) bool { return !notFailed(d.Module) })
	skipped = slices.DeleteFunc(skipped, func(m string) bool { return !notFailed(m) })

	// What the proposal adds, by node and module: placed by a candidate and not by the trunk on that node.
	added := map[string]bool{}
	for node, p := range s.Placements {
		if p == nil {
			continue
		}
		was := map[string]bool{}
		for _, m := range trunk[node].Modules {
			was[m.Module] = true
		}
		for _, m := range p.Modules {
			if !was[m.Module] {
				added[node+"/"+m.Module] = true
			}
		}
	}
	unissued := map[string][]string{}
	refusals := map[string][]string{}
	for _, x := range stood {
		node, module := standsInFor(x, s.Node)
		switch {
		case node == s.Node && runs[module]:
			// A value missing for a module the node runs is a refusal, whatever the trunk places (the seed's trunk is
			// empty, and every module counts as the group's).
			refusals[module] = append(refusals[module], x)
		case module != "" && added[node+"/"+module]:
			if node == s.Node {
				unissued[module] = append(unissued[module], x)
			} // another node's addition: the module here that carries it differs, which the assigner judges
		case module == "" || node != s.Node:
			// The node's own, or a value this node holds for a module elsewhere (a grant it provides): said as the node's.
			refusals[delivery.HaveNodeWord] = append(refusals[delivery.HaveNodeWord], x)
		default:
			refusals[module] = append(refusals[module], x)
		}
	}
	addedHere := map[string]delivery.ModuleAdded{}
	for _, m := range cmp.Added {
		addedHere[m.Module] = m
	}
	for _, m := range skipped { // placed, and no build given to compose it at
		addedHere[m] = delivery.ModuleAdded{Module: m, Unissued: []string{"no build of " + m + " is known to compose it at"}}
	}
	for m, xs := range unissued {
		got := addedHere[m]
		got.Module = m
		got.Unissued = append(got.Unissued, xs...)
		addedHere[m] = got
	}
	for _, m := range sortedKeys(addedHere) {
		a.Added = append(a.Added, addedHere[m])
	}
	for _, m := range sortedKeys(refusals) {
		if _, isAdded := addedHere[m]; isAdded {
			continue // a module the candidate adds here: what it lacks is said under Added
		}
		if _, isFailed := failed[m]; isFailed {
			continue // said below, as why it could not be composed
		}
		a.Refusals = append(a.Refusals, delivery.ModuleRefused{Module: m, Why: "stands in for " + strings.Join(refusals[m], ", ")})
	}
	for _, m := range sortedKeys(failed) {
		a.Refusals = append(a.Refusals, delivery.ModuleRefused{Module: m, Why: failed[m]})
	}
	sort.Slice(a.Refusals, func(i, j int) bool { return a.Refusals[i].Module < a.Refusals[j].Module })
	heldAsToday(&a, s.HeldToday)
	a.Verdict = delivery.VerdictOf(a)
	return a
}

// heldAsToday moves each refusal of a module the node holds today (Scope.HeldToday) into Held: the candidate holds it as
// the node does, which is no change (issue 1126: a seed reproduces today, and today holds it too).
func heldAsToday(a *delivery.CandidateAnswer, today []string) {
	if len(today) == 0 {
		return
	}
	kept := a.Refusals[:0]
	for _, r := range a.Refusals {
		if slices.Contains(today, r.Module) {
			a.Held = append(a.Held, r)
		} else {
			kept = append(kept, r)
		}
	}
	a.Refusals = kept
	if len(a.Refusals) == 0 {
		a.Refusals = nil
	}
}

// maxCulprits bounds the modules one refusal is tried on, each a whole composition.
const maxCulprits = 8

// MaxShown bounds the bytes of shown resource bodies in one answer (delivery.ModuleDiffers.Bodies).
const MaxShown = 256 << 10

var (
	grantStandIn = regexp.MustCompile(`^the grant of \S+ for (\S+) on (\S+)$`)
	needsStandIn = regexp.MustCompile(`^(\S+) on (\S+) needs `)
)

// standsInFor is the node and module a stand-in of compose's words is for: an own secret `module/name`, a port
// `port module:port`, a grant `the grant of <provision> for <module> on <node>`, a need `<module> on <node> needs ...`;
// the module empty when the words name none (the certificate, the authority).
func standsInFor(x, node string) (string, string) {
	if m := grantStandIn.FindStringSubmatch(x); m != nil {
		return m[2], m[1]
	}
	if m := needsStandIn.FindStringSubmatch(x); m != nil {
		return m[2], m[1]
	}
	if rest, ok := strings.CutPrefix(x, "port "); ok {
		if module, _, ok := strings.Cut(rest, ":"); ok {
			return node, module
		}
	}
	if module, _, ok := strings.Cut(x, "/"); ok && !strings.Contains(x, " ") {
		return node, module
	}
	return node, ""
}

// composeEach is the one rule, for the node that applies and for its answer to a candidate alike, by which a module's
// own refusal refuses that module and never the node (issue 1126: seed-8 fixed it in the answer alone, and the
// applying path still refused all of novox for de-spiegel's unset route names). The node is composed; a refusal is laid
// on the module whose stub (compose.Stub) changes it (culprit), that module is held (compose.Node.Held) and said in
// failed with the refusal's words, and the rest is composed again, until it composes or the refusal is no single
// module's, which is answered as the node's (err). Applied composes as the node applies (compose.Reading) and holds the
// module placed here each stand-in is for; one for no module placed here (the node's own, a value this node holds for a
// module elsewhere) refuses the node (compose.ErrStoodIn). Not applied, it composes in compose.Foreseeing and answers
// every stand-in for the caller to judge (Answer).
//
// **A held module is what runs of it** (review of the apply, round 1): composed from what running holds of it
// (compose.Carried of its own composition there; the node's own carries it wherever it runs there), so what the others
// read of it (the machine ports its containers publish, the routes reaching it) is what runs, and none of its own
// composition is in out: the node keeps what it last applied. **What depends on how it is held is held too:** a module
// whose composition differs when the held ones are composed as their stubs instead is held with them, and a node's own
// composition that differs (but for the held modules' own resources) refuses the node. And since a held module is
// composed from its new manifest, which may not be the build's that runs, what reads that manifest is held with it
// (dependents): the providers of what it contributes to (the proxy its routes), and, when it listens, the filter.
func composeEach(in compose.Input, node string, fps map[string]string, applied bool, running []delivery.Composed, failed map[string]string) (out map[string]delivery.Composed, skipped, stood []string, err error) {
	mode := compose.Foreseeing
	if applied {
		mode = compose.Reading
	}
	runs := map[string]*delivery.Composed{}
	for i := range running {
		if m := running[i].Module; m != "" {
			runs[m] = &running[i]
		}
	}
	src := map[string]catalogue.Manifest{} // each held module's manifest before it was held
	bareOf := map[string]bool{}
	var hold func(m, why string, bare bool)
	hold = func(m, why string, bare bool) {
		if _, done := failed[m]; !done {
			failed[m] = why // a held module tried bare keeps the words it was first held for
		}
		first := false
		if _, ok := src[m]; !ok {
			man, ok := manifestOn(in, node, m)
			if !ok {
				return
			}
			src[m], first = man, true
		}
		bareOf[m] = bareOf[m] || bare
		in = heldAs(in, node, m, src[m], bareOf[m], runs[m])
		if !first {
			return
		}
		// What the others read of its manifest (what it contributes, what it listens on) is its new manifest's, not
		// necessarily the build's that runs: what reads it is held with it (review of the apply, round 2).
		for _, r := range dependents(in, node, src[m], failed) {
			hold(r, "it reads what "+m+" contributes or listens on, and "+m+" is held", false)
		}
	}
	for _, m := range sortedKeys(failed) {
		hold(m, failed[m], false)
	}
	for {
		out, skipped, stood, err = compose.CompositionsIn(in, node, fps, mode)
		if err != nil {
			module, bare := culprit(in, node, fps, mode, failed, err)
			if module == "" {
				return nil, nil, nil, err
			}
			hold(module, err.Error(), bare)
			continue
		}
		again := false
		if applied && len(stood) > 0 {
			placed := map[string]bool{}
			for _, m := range assignedOn(in, node) {
				placed[m] = true
			}
			of := map[string][]string{}
			var nodes []string
			for _, x := range stood {
				if n, m := standsInFor(x, node); n == node && placed[m] {
					of[m] = append(of[m], x)
				} else {
					nodes = append(nodes, x)
				}
			}
			for _, m := range sortedKeys(of) {
				if _, done := failed[m]; !done {
					hold(m, "stands in for "+strings.Join(of[m], ", "), false)
					again = true
				}
			}
			if !again && len(nodes) > 0 {
				return nil, nil, nil, fmt.Errorf("%w on %s: %s", compose.ErrStoodIn, node, strings.Join(nodes, ", "))
			}
		}
		if !again && len(failed) > 0 {
			dependent, own := dependsOnHeld(in, node, fps, mode, out, src, bareOf, failed)
			if own {
				return nil, nil, nil, fmt.Errorf("frombus: %s's own composition depends on how %s, held, is composed, and is not applied",
					node, strings.Join(sortedKeys(failed), ", "))
			}
			for _, m := range dependent {
				hold(m, "what it composes of "+strings.Join(sortedKeys(failed), ", ")+", held, is not what runs of them", false)
				again = true
			}
		}
		if !again {
			break
		}
	}
	skipped = slices.DeleteFunc(skipped, func(m string) bool { _, held := failed[m]; return held })
	return out, skipped, stood, nil
}

// dependsOnHeld composes in again with each held module as its stub rather than as what runs of it, and answers the
// modules, not held, whose composition differs between the two (sorted), and own when the node's own composition does
// but for the held modules' own resources. A composition of stubs that fails says nothing more: what runs composed.
func dependsOnHeld(in compose.Input, node string, fps map[string]string, mode compose.Mode, asRuns map[string]delivery.Composed,
	src map[string]catalogue.Manifest, bareOf map[string]bool, failed map[string]string) (dependent []string, own bool) {
	stubs := in
	for _, m := range sortedKeys(failed) {
		if man, ok := src[m]; ok {
			stubs = heldAs(stubs, node, m, man, bareOf[m], nil)
		}
	}
	asStubs, _, _, err := compose.CompositionsIn(stubs, node, fps, mode)
	if err != nil {
		return nil, false
	}
	isHeld := func(m string) bool { _, ok := failed[m]; return ok }
	keys := map[string]bool{}
	for k := range asRuns {
		keys[k] = true
	}
	for k := range asStubs {
		keys[k] = true
	}
	for _, k := range sortedKeys(keys) {
		a, inA := asRuns[k]
		b, inB := asStubs[k]
		m := a.Module
		if !inA {
			m = b.Module
		}
		if m != "" && isHeld(m) {
			continue
		}
		if m == "" {
			a, b = withoutHeld(a, isHeld), withoutHeld(b, isHeld)
		}
		da, errA := delivery.ComposedDigestOf(a)
		db, errB := delivery.ComposedDigestOf(b)
		if inA == inB && errA == nil && errB == nil && da == db {
			continue
		}
		if m == "" {
			own = true
			continue
		}
		dependent = append(dependent, m)
	}
	return dependent, own
}

// withoutHeld is the node's own composition c without the resources of a held module (its id naming it) and without
// its filled paths, for comparing the rest.
func withoutHeld(c delivery.Composed, isHeld func(string) bool) delivery.Composed {
	out := c
	out.Filled = nil
	out.Resources = nil
	for _, raw := range c.Resources {
		var head struct {
			ID     string `json:"id"`
			Module string `json:"module"`
		}
		_ = json.Unmarshal(raw, &head)
		owner := head.Module
		if owner == "" {
			owner, _ = declaration.ModuleGuess(head.ID)
		}
		if owner != "" && isHeld(owner) {
			continue
		}
		out.Resources = append(out.Resources, raw)
	}
	return out
}

// dependents is, of the modules placed on node and not held, those that read what man says to them: each that provides
// what man contributes to (the proxy its routes), and, when man listens on a port, each that holds the filter (the
// openings).
func dependents(in compose.Input, node string, man catalogue.Manifest, failed map[string]string) []string {
	to := map[string]bool{}
	for p := range man.Contributes {
		to[p] = true
	}
	for p := range man.ContributesMany {
		to[p] = true
	}
	listens := len(man.Listens) > 0
	if len(to) == 0 && !listens {
		return nil
	}
	var out []string
	for _, m := range assignedOn(in, node) {
		if _, held := failed[m]; held || m == man.Module {
			continue
		}
		pm, ok := manifestOn(in, node, m)
		if !ok {
			continue
		}
		if listens && pm.Filtering != nil {
			out = append(out, m)
			continue
		}
		for _, o := range pm.Provides {
			if to[o.Name] {
				out = append(out, m)
				break
			}
		}
	}
	return out
}

// assignedOn is the modules placed on node, in placement order.
func assignedOn(in compose.Input, node string) []string {
	for _, n := range in.Nodes {
		if n.Name == node {
			return n.Assigned
		}
	}
	return nil
}

// manifestOn is the manifest node composes module from: its Kept, else the catalogue's.
func manifestOn(in compose.Input, node, module string) (catalogue.Manifest, bool) {
	for _, n := range in.Nodes {
		if n.Name == node {
			if man, ok := n.Kept[module]; ok {
				return man, true
			}
		}
	}
	man, ok := in.Catalogue[module]
	return man, ok
}

// culprit is the module placed on node whose composition the error is of: the first, in placement order, whose stub
// (compose.Stub) makes the composition in mode succeed or fail otherwise; empty when none does (the error is not one
// module's). Modules already refused are passed over. A module whose stub still fails the same is tried bare (its stub
// contributing nothing, bare true): a refusal of what it contributes is its own, which the stub keeps (issue 1126,
// seed-8: de-spiegel's route names on novox, an unset required value, refused the whole node).
func culprit(in compose.Input, node string, fps map[string]string, mode compose.Mode, failed map[string]string, err error) (string, bool) {
	var assigned []string
	for _, n := range in.Nodes {
		if n.Name == node {
			assigned = n.Assigned
		}
	}
	// Only the modules the error names: the words of a module's refusal name it. Each try is a whole composition, so a
	// refusal naming none is no module's, answered at once rather than after a composition per module (issue 1126: ace's
	// answer took 7m46s).
	var order []string
	for _, m := range assigned {
		if strings.Contains(err.Error(), m) && len(order) < maxCulprits {
			order = append(order, m)
		}
	}
	changes := func(m string, bare bool) bool {
		_, _, _, again := compose.CompositionsIn(stubbed(in, node, m, bare), node, fps, mode)
		return again == nil || again.Error() != err.Error()
	}
	for _, m := range order {
		if _, done := failed[m]; done {
			continue
		}
		if changes(m, false) {
			return m, false
		}
	}
	var kept map[string]catalogue.Manifest
	for _, n := range in.Nodes {
		if n.Name == node {
			kept = n.Kept
		}
	}
	for _, m := range order {
		// One already held is tried bare too, once: held for its build, its stub may still refuse (its own secret
		// never issued, issue 1126).
		if _, done := failed[m]; done && isBare(kept[m]) {
			continue
		}
		if changes(m, true) {
			return m, true
		}
	}
	return "", false
}

// isBare says a stub contributes nothing and declares no own secret (stubbed, bare).
func isBare(m catalogue.Manifest) bool {
	return len(m.Contributes) == 0 && len(m.ContributesMany) == 0 && len(m.OwnSecrets) == 0
}

// stubbed is in with module held on node as its stub alone (heldAs, nothing of it running), from the manifest node
// composes it from: a culprit's try.
func stubbed(in compose.Input, node, module string, bare bool) compose.Input {
	man, ok := manifestOn(in, node, module)
	if !ok {
		return in
	}
	return heldAs(in, node, module, man, bare, nil)
}

// heldAs is in with module held on node (compose.Node.Held): composed from man as what runs of it (compose.Carried of
// runs; its stub, compose.Stub, when runs is nil or holds nothing of it), as node's Kept; bare, contributing nothing to
// what it requires and declaring no own secret: none of a held module's own composition is applied, so what it has not
// been issued (restic's repository on a node it never ran on) is no refusal of the rest.
func heldAs(in compose.Input, node, module string, man catalogue.Manifest, bare bool, runs *delivery.Composed) compose.Input {
	out := in
	out.Nodes = append([]compose.Node(nil), in.Nodes...)
	for i := range out.Nodes {
		if out.Nodes[i].Name != node {
			continue
		}
		if bare {
			man.Contributes, man.ContributesMany, man.OwnSecrets = nil, nil, nil
		}
		kept := make(map[string]catalogue.Manifest, len(out.Nodes[i].Kept)+1)
		for k, v := range out.Nodes[i].Kept {
			kept[k] = v
		}
		kept[module] = compose.Carried(man, module, runs)
		out.Nodes[i].Kept = kept
		held := make(map[string]bool, len(out.Nodes[i].Held)+1)
		for k, v := range out.Nodes[i].Held {
			held[k] = v
		}
		held[module] = true
		out.Nodes[i].Held = held
	}
	return out
}