package catalogue

// Turning a resolution into the declaration a node is sent.
//
// Separate from resolving because they answer different questions. Resolving asks *what should
// this machine run*; this asks *what does that look like as resources*, and the second is where
// settings are applied, generators are called, contributions are collected and credentials are
// placed. Both lived in one file until it was doing four jobs at once — which is the shape the
// system this replaces failed in, one import at a time.

import (
	"encoding/json"
	"fmt"
	"sort"
	"strconv"
	"strings"
)

// SettingsBy is the layers that apply to each module, keyed by module name.
type SettingsBy map[string][]Layer

// Generator works out a module's resources for one node, where they cannot be written in advance.
type Generator interface {
	// Resources for this node. Absent means the node is not part of whatever this generates,
	// which is an ordinary answer rather than a failure — a machine assigned the module before it
	// has an address on the network is in exactly that state.
	Resources(node string) ([]map[string]any, bool, error)
}

// OpensPorts is a generator that also says what its resources accept connections on.
//
// **Separate from Generator, because most generators have nothing to say here** and requiring an
// empty method of each would be a cost paid everywhere for one caller.
//
// It exists because a static field cannot express this. A hub accepts connections from every node
// at other sites; a machine that is not a hub dials out and needs nothing open — and they are the
// same module. `listens` in a manifest is one answer for every machine that runs it, so the
// machine that most needs filtering, the one facing the public internet, was the one whose rule
// set would have closed its own overlay.
type OpensPorts interface {
	// Listens is what this node accepts on because of what was computed for it. Nothing is the
	// ordinary answer: most machines running a computed module open no port at all.
	Listens(node string) ([]Listening, error)
}

// Grant is one consumer's credential, on the machine that must create it.
type Grant struct {
	// Provision is what was required.
	Provision string
	// Consumer is the node that will use it.
	Consumer string
	// From is the module on that machine which asked.
	//
	// **Part of who this credential is for, not a label** (novox/hq 04-ISSUES/022). Together with
	// Consumer it names one consumer; the node alone does not, because a machine routinely runs
	// several modules wanting the same thing. It is also what the provider names the role or the
	// bucket or the client after, so withdrawing one consumer does not take another's away.
	From string
	// Values are what that module contributed — the name it wants, and anything else the
	// provision's own vocabulary defines.
	Values map[string]any
	// Slug is the consumer module's identity slug, if it declared one — carried on the grant so the
	// provider side derives the same login the consumer does, even across nodes where the consumer's
	// manifest is not in view (novox/hq ADR 0049). Empty means "use the module name".
	Slug string
	// At is where the consuming machine is on the private network, empty if it is not on one.
	//
	// Passed in with the grant because it is a fact about another machine, and resolution answers
	// questions about one. A provider that must reach back to its consumer — a reverse proxy is
	// the whole reason this exists — otherwise has to know how the mesh names machines.
	At string
	// Sealed is the credential, closed to the providing node.
	Sealed string
}

// Rendering is everything needed to turn a resolution into the declaration a node is sent.
type Rendering struct {
	// Certificate is what the mesh issued for this machine's internal name, and the mesh's own
	// certificate. Both public — the key they belong to never left the machine.
	Certificate string
	Authority   string

	// Needed is each module's own secrets, sealed to this node, keyed by module and then by the
	// name the module gave it.
	Needed map[string]map[string]string

	// Mesh is every node's address on the private network, which is what a rule saying "from the
	// mesh" resolves to. Passed in for the same reason grants are: who else is on the network is
	// a fact about the mesh, and resolution answers questions about one machine.
	Mesh []string

	// Names is every machine's internal name and its address, for containers to be given.
	//
	// **A container does not inherit the machine's names**, so every internal name the mesh wrote
	// is invisible to what the machine runs. Given here rather than looked up on the machine,
	// because which machines exist is a fact about the mesh.
	Names map[string]string

	Settings   SettingsBy
	Generators map[string]Generator
	// Grants are the credentials this node must create, for the provisions it offers. Passed in
	// rather than resolved, because who consumes a node is a fact about the rest of the mesh and
	// resolution answers questions about one machine.
	Grants []Grant

	// Ports is where this machine puts what each module needs reachable, by module and by the
	// port the software itself uses (novox/hq ADR 0038).
	//
	// **The one place the number now lives.** A module used to write it three times — for the rule
	// set, for what a consumer is told, and for what the runtime publishes — and nothing checked
	// that the three agreed. They are all derived from this.
	Ports map[string]map[int]int
}

// machinePort is where a module's port lives on this machine, or the port itself when the mesh has
// not been asked. Unassigned is not an error here: a module with no `listens` never needed one,
// and a caller composing a declaration without a store still gets something coherent.
func (r Rendering) machinePort(module string, wanted int) int {
	if at, known := r.Ports[module][wanted]; known {
		return at
	}
	return wanted
}

// Declaration is everything the resolved modules put on the node, with settings applied.
//
// Resource identities are prefixed with the module they came from. Two modules may reasonably
// both call something "config", and without this the second would silently replace the first —
// the node applying one of them and reporting success.
func (r Resolution) Declaration(with Rendering) ([]map[string]any, error) {
	// Where each provision's credentials land, so a contribution can name the file rather than
	// carry a value the mesh does not have.
	directories := map[string]string{}
	for _, m := range r.Modules {
		for provision, where := range m.Grants {
			directories[provision] = where
		}
	}
	given, err := r.contributions(with.Settings, with.Grants, directories)
	if err != nil {
		return nil, err
	}

	// Once, from every module's listens -- not per module. A module receiving only its own ports
	// would write a rule set that closed every other module on the machine. Each module's per-node
	// exposure settings override its listens' source first (novox/hq ADR 0046).
	exposure := map[string]map[int]string{}
	for _, m := range r.Modules {
		e, err := Exposure(m, with.Settings[m.Module])
		if err != nil {
			return nil, err
		}
		if e != nil {
			exposure[m.Module] = e
		}
	}
	rules, err := r.Filtering(with.Generators, with.Ports, exposure)
	if err != nil {
		return nil, err
	}
	filtering := AsNftables(rules, with.Mesh)

	var out []map[string]any
	for _, m := range r.Modules {
		resources := m.Resources

		// What the mesh computes for this module goes FIRST, before the module's own resources.
		//
		// **Order is stated, not derived — the host does not sort** (novox/hq ADR 0005), so
		// whatever the mesh writes down is the order a machine applies. A module's service or
		// container routinely depends on one of these files; nothing here ever depends on a
		// module's resources, because none of it is computed from them.
		//
		// Appended, this was wrong in a way that only showed on the first apply and then healed:
		// the service started before its certificate or its rule set existed, failed, and the next
		// reconcile fixed it. A fault that repairs itself on the second attempt is worse than one
		// that does not, because what gets remembered is that it works.
		var first []map[string]any
		if f := m.Filtering; f != nil {
			first = append(first, map[string]any{
				"id": FilteringID(), "type": "file", "path": f.Into,
				"content": filtering, "mode": "0600",
			})
		}
		if c := m.Certificate; c != nil {
			if with.Certificate == "" {
				// Asked for and not issued. Refused rather than skipped: a module that serves TLS
				// with no certificate does not start, and the reason is somewhere else entirely.
				return nil, fmt.Errorf(
					"%s wants a certificate for this machine and none was issued", m.Module)
			}
			first = append(first, map[string]any{
				"id": CertificateID(), "type": "file", "path": c.Into,
				// Public. It travels in the open like any other file, because it is a statement
				// about a key rather than the key.
				"content": with.Certificate, "mode": "0644",
			})
			if c.Authority != "" {
				first = append(first, map[string]any{
					"id": AuthorityID(), "type": "file", "path": c.Authority,
					"content": with.Authority, "mode": "0644",
				})
			}
		}
		for _, name := range sortedKeys(m.OwnSecrets) {
			sealed := with.Needed[m.Module][name]
			if sealed == "" {
				// Declared and not made. Refused rather than skipped: a module whose own
				// credential is silently absent starts, fails to authenticate, and the reason is
				// three layers away from the machine reporting it.
				return nil, fmt.Errorf(
					"%s needs a secret called %q and none was made for it", m.Module, name)
			}
			first = append(first, map[string]any{
				"id": NeedID(name), "type": "file", "path": m.OwnSecrets[name], "sealed": sealed,
			})
		}
		// Operator-owned paths this module is granted use of (novox/hq ADR 0051). Written before
		// the module's own resources, and so before the container that mounts them: the host must
		// find each present — refusing clearly if the operator has not provided it — before it
		// starts anything that depends on it. The mesh creates, chowns and reconciles none of it;
		// an `access` resource says only *this path must exist, and this module reaches it*.
		for _, a := range m.Accesses {
			first = append(first, map[string]any{
				"id": AccessID(a.Path), "type": "access", "path": a.Path, "mode": a.At(),
			})
		}
		for _, to := range sortedKeys(m.Secrets) {
			var found *Needed
			for i, n := range r.Needs {
				// **This module's need, not the provision's** (novox/hq 04-ISSUES/022). Matching
				// on the name alone, every consumer of a provision took whichever credential
				// happened to be last in the list — so on a node with two of them, one module
				// would be given the other's password and fail to authenticate with a valid
				// credential belonging to somebody else.
				if n.Name == to && n.For == m.Module {
					found = &r.Needs[i]
				}
			}
			if found != nil && found.ByRecord && found.Sealed == "" {
				// Answered by a record whose key has not been supplied since this consumer was
				// put on it. **Refused, not skipped.** The mesh discarded the plaintext when the
				// key was accepted and cannot seal another, so a machine that resolved cleanly
				// would receive no file at all and fail at whatever tried to read it — which is
				// the outcome ADR 0024 exists to avoid, arrived at politely.
				return nil, fmt.Errorf(
					"%s on this machine uses the licence %q and no key has been sealed to it. "+
						"The mesh cannot make one; supply it again with `licence key %s`",
					m.Module, found.From, found.From)
			}
			if found == nil || found.Sealed == "" {
				// Answered on this machine, or answered by a node the mesh could not seal to.
				// Nothing to write either way, and writing an empty credential file would be
				// worse than none: something would read it and fail authenticating.
				continue
			}
			first = append(first, map[string]any{
				"id": SecretID(to), "type": "file", "path": m.Secrets[to],
				"sealed": found.Sealed,
			})
		}
		for _, to := range sortedKeys(m.Grants) {
			for _, g := range with.Grants {
				if g.Provision != to {
					continue
				}
				if g.From == "" {
					// Nothing on that machine asks for this any more. Skipped here rather than
					// where grants are gathered, so the rule holds whoever gathers them.
					//
					// **This is how a credential is withdrawn.** The provisioner removes what
					// nobody asks for, and it can only do that if the mesh stops asking — a
					// consumer that was unassigned would otherwise keep a working login for ever,
					// and nothing would say so.
					continue
				}
				first = append(first, map[string]any{
					"id":     GrantID(to, g.Consumer+"."+g.From),
					"type":   "file",
					"path":   grantPath(m.Grants[to], g.Consumer, g.From),
					"sealed": g.Sealed,
				})
			}
		}
		for _, to := range sortedKeys(m.Binds) {
			var found *Needed
			for i, n := range r.Needs {
				if n.Name == to && n.For == m.Module {
					found = &r.Needs[i]
				}
			}
			if found == nil {
				// Answered on this same machine rather than from elsewhere in the mesh.
				//
				// **Still written.** It used to be skipped, reasoning that "it is on this node"
				// is a fact nobody needs — and that is true of the *location* and false of
				// everything beside it. A binding also carries what the provider said a consumer
				// must know, which is the port; a consumer cannot invent that, and got an absent
				// file with no explanation. A build machine sharing a node with the registry it
				// pushes to sat in a loop saying it could not read its own binding.
				here := here(r, to)
				if here == nil {
					// Nothing in this node's set offers it either, so there is genuinely nothing
					// to say. Resolution has already refused anything unanswerable, so this is a
					// requirement met by the module itself.
					continue
				}
				found = here
			}
			file, err := boundFile(*found, m.Binds[to], ConsumerIdentity(r.Node, IdentitySource(m.Slug, m.Module)))
			if err != nil {
				return nil, err
			}
			first = append(first, file)
		}
		for _, to := range sortedKeys(m.Receives) {
			file, err := receivedFile(to, m.Receives[to], given[to])
			if err != nil {
				return nil, err
			}
			first = append(first, file)
		}
		if m.Computed != "" {
			generator, known := with.Generators[m.Computed]
			if !known {
				return nil, fmt.Errorf(
					"%s says its resources are computed by %q, and this control plane has no %q",
					m.Module, m.Computed, m.Computed)
			}
			generated, part, err := generator.Resources(r.Node)
			if err != nil {
				return nil, err
			}
			if !part {
				// Assigned, and not yet part of what this generates. Nothing to put on the
				// machine, which is different from an error: a node given the network module
				// before it has an address is in exactly that state, briefly.
				continue
			}
			resources = generated
		}

		// Now, and not before: a module whose resources are computed replaces them wholesale, and
		// merging earlier would throw away the files it still needs.
		resources = append(append([]map[string]any{}, first...), resources...)

		// Every container is given the mesh's names. Not a choice a module makes: a module that
		// listed them would go stale the day a machine joins, and one that did not would be a
		// module whose containers cannot reach anything by name.
		//
		// A container that was given names of its own keeps them and gets the mesh's beside them:
		// the mesh does not know what else a workload needs to reach, and taking something away
		// to add something is not what "also" means.
		if len(with.Names) > 0 {
			resources = withMeshNames(resources, with.Names)
		}

		// What this module may name from inside one of its own files. Gathered once per module
		// rather than per file, because it is a fact about the module.
		sealed, err := sealedFor(m, r.Needs, with)
		if err != nil {
			return nil, err
		}
		// And what its bindings say, for the half of a connection that is not secret.
		known := knownFor(m, r.Needs, r.Node)

		for _, unsettled := range resources {
			resource, err := ApplySettings(unsettled, with.Settings[m.Module])
			if err != nil {
				return nil, err
			}
			copied := map[string]any{}
			for k, v := range resource {
				copied[k] = v
			}
			// **After settings, and that is the whole reason it is here.** A module's file
			// content is where a setting lands, so a placeholder may only exist once the setting
			// has been put in — filling secrets first would look at content that is not yet what
			// the machine receives.
			if err := intoFile(copied, sealed, m.Module); err != nil {
				return nil, err
			}
			// **Substituted here, not on the machine.** A bound value is not secret — the mesh
			// holds it in the clear — so there is nothing for the host to be the only witness of,
			// and sending it already filled in means the host learns no new field.
			if err := boundInto(copied, known, m.Module); err != nil {
				return nil, err
			}
			if err := pinned(copied, m.Module); err != nil {
				return nil, err
			}
			publishedOn(copied, m.Module, with)
			copied["id"] = m.Module + "." + fmt.Sprint(resource["id"])
			// A service saying what it reflects names resources within its own module, so those
			// are prefixed too or they would point at nothing.
			//
			// **Unless it already names one.** A module may reflect a file another module put on
			// the machine — the case this exists for is a resolver restarting when the mesh
			// rewrites the names, which are computed by the mesh and belong to its module, not to
			// the daemon's. Written `<module>.<id>`, and a dot is what marks it as already
			// answered: prefixing it again would point at nothing, silently, and the daemon would
			// serve the old names for ever while everything reported success.
			if reflects, ok := resource["restart-on"].([]any); ok {
				var renamed []any
				for _, id := range reflects {
					named := fmt.Sprint(id)
					if strings.Contains(named, ".") {
						renamed = append(renamed, named)
						continue
					}
					renamed = append(renamed, m.Module+"."+named)
				}
				copied["restart-on"] = renamed
			}
			out = append(out, copied)
		}
	}
	return out, nil
}

// Contribution is one module telling the answer to a requirement what it needs from it.
type Contribution struct {
	// From is the module that said it, so the provider and a person reading the file can tell
	// which route belongs to what.
	From string `json:"from"`
	// Node is the machine it said it from, empty when that is this one.
	//
	// A provision answered from anywhere in the mesh has consumers on other machines, and the
	// provider has to know who they are — a database told to create a password and not who for
	// cannot do anything with it. Contributions were node-local until this, which meant the one
	// case that most needed them was the one they did not reach.
	Node string `json:"node,omitempty"`
	// At is where that machine is on the private network, empty when it is not on one or when it
	// is this machine.
	//
	// The mesh knows it and a provider should not have to derive it. A reverse proxy is told
	// *send traffic to this consumer* and has to open a connection — so without this every
	// provider that reaches back to a consumer would have to know how the mesh names machines,
	// which is a convention leaking into every module that implements a provision.
	At string `json:"at,omitempty"`
	// As is who this consumer is: what the provider should call the login it creates.
	//
	// **Said by the mesh rather than invented by the provisioner** (novox/hq 04-ISSUES/023). It
	// used to be neither — the provisioner made a name, and the consumer, which has to present it
	// to authenticate, had no way to learn it. One derivation reaches both ends, so they agree by
	// construction.
	// Omitted when there is none. A contribution that is not a credential grant — a module
	// offering something to another on its own machine — has nobody to be identified to, and a
	// field that is always present and usually empty teaches a reader to ignore it.
	As string `json:"as,omitempty"`
	// Secret is the file on this machine holding that consumer's credential, sealed to it.
	//
	// Named rather than carried, for the same reason the private network's key is: the mesh
	// discarded the value and could not put it here if it wanted to. What is here is where to
	// find it.
	Secret string `json:"secret,omitempty"`
	// Values are the module's own, with settings applied. What the keys mean is agreed by the
	// requirement's name — everything providing `reverse-proxy` understands the same shape, which
	// is what makes swapping one for another cost nothing.
	Values map[string]any `json:"values"`
}

// grantPath is where one consumer's sealed credential lands on the providing machine.
//
// Suffixed, so the directory can also hold whatever the module writing it keeps there and so a
// node named like something else in that directory cannot collide with it.
// One file per consumer, and a consumer is a module on a machine (novox/hq 04-ISSUES/022).
//
// Named after both. Named after the machine alone, two modules on one node wrote to one path: the
// second overwrote the first, and the provisioner — reading a directory — saw one consumer where
// there were two.
func grantPath(directory, consumer, module string) string {
	return strings.TrimRight(directory, "/") + "/" + consumer + "." + module + ".secret"
}

// contributions collects what every module in this set contributes, by requirement.
//
// Ordered by contributing module, because the result becomes a file on a machine and a file whose
// lines move about is a file that looks changed when nothing changed.
func (r Resolution) contributions(settings SettingsBy, grants []Grant,
	directories map[string]string) (map[string][]Contribution, error) {
	out := map[string][]Contribution{}
	modules := append([]Manifest{}, r.Modules...)
	sort.Slice(modules, func(i, j int) bool { return modules[i].Module < modules[j].Module })

	// What consumers on other machines asked for. Merged in with this machine's own, because from
	// the provider's side they are the same thing — somebody wanting something — and a provider
	// that had to read two lists would be a provider that reads one of them.
	sorted := append([]Grant{}, grants...)
	sort.Slice(sorted, func(i, j int) bool {
		if sorted[i].Provision != sorted[j].Provision {
			return sorted[i].Provision < sorted[j].Provision
		}
		if sorted[i].Consumer != sorted[j].Consumer {
			return sorted[i].Consumer < sorted[j].Consumer
		}
		return sorted[i].From < sorted[j].From
	})
	// A consumer already carried by the grants loop, keyed (provision, module). When provider and
	// consumer are co-located, `grantsFor` enumerates the same-node consumer too, so without this the
	// module would be emitted a second time by the m.Contributes loop below — once full (with the
	// grant's secret/as) and once partial — which is the duplicate seen in a co-located mesh.json.
	granted := map[string]map[string]bool{}
	for _, g := range sorted {
		if g.From == "" {
			// As above: nothing on that machine asks for this any more, so the provider is not
			// told about it and withdraws the login on its next pass.
			continue
		}
		out[g.Provision] = append(out[g.Provision], Contribution{
			From: g.From, Node: g.Consumer, At: g.At, Values: g.Values,
			As:     ConsumerIdentity(g.Consumer, IdentitySource(g.Slug, g.From)),
			Secret: grantPath(directories[g.Provision], g.Consumer, g.From),
		})
		if granted[g.Provision] == nil {
			granted[g.Provision] = map[string]bool{}
		}
		granted[g.Provision][g.From] = true
	}
	for _, m := range modules {
		for _, to := range sortedKeys(m.Contributes) {
			// The grants loop already emitted this module's contribution to this provision, with its
			// minted secret — emitting the partial copy again would duplicate it. A contribution with
			// no grant (a reverse-proxy route names a host, not a credential) is not in `granted`, so
			// it still reaches the provider from here.
			if granted[to][m.Module] {
				continue
			}
			// Settings reach a contribution the same way they reach a file. A route's hostname is
			// exactly the kind of thing that differs between one mesh and the next, and a module
			// that could not have it set would have to be edited to be reused.
			values, err := settle(m.Contributes[to], settings[m.Module], nil,
				m.Module+" contributing to "+to)
			if err != nil {
				return nil, fmt.Errorf("%s contributing to %s: %w", m.Module, to, err)
			}
			out[to] = append(out[to], Contribution{From: m.Module, Values: values})
		}
	}
	return out, nil
}

// receivedFile is the file a provider is given its consumers' contributions in.
func receivedFile(requirement, path string, given []Contribution) (map[string]any, error) {
	if given == nil {
		// Nobody contributed. The file is still written, empty, rather than left absent: a
		// provider that finds no file cannot tell "nothing asked for me" from "the mesh never
		// wrote it", and the two want completely different responses.
		given = []Contribution{}
	}
	// The note goes *inside* the document, not above it. The first version wrote a `//` header
	// and produced a file that says "do not edit" to a person and fails to parse for the program
	// meant to read it — which is the whole audience.
	body, err := json.MarshalIndent(map[string]any{
		"contributions": 1,
		"requirement":   requirement,
		"generated": "by the mesh — do not edit; replaced whenever a module contributing to " +
			requirement + " arrives or leaves",
		"given": given,
	}, "", "  ")
	if err != nil {
		return nil, err
	}
	return map[string]any{
		"id": ReceivedID(requirement), "type": "file", "path": path, "mode": "0644",
		"content": string(body) + "\n",
	}, nil
}

// sortedKeys is map iteration made repeatable, which everything written to a machine needs.
func sortedKeys[V any](m map[string]V) []string {
	out := make([]string, 0, len(m))
	for k := range m {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

// boundFile is what a module is told about something it requires from another machine.
//
// Where it is and what the providing module said about using it. **No credential**, and the file
// says so rather than leaving a reader to wonder whether one was meant to be there — a missing
// field looks like a bug, and a stated absence looks like a boundary.
func boundFile(n Needed, path, as string) (map[string]any, error) {
	// A record has no machine and no address. Saying so is the difference between a reader
	// concluding "somewhere with no address" and concluding the mesh failed to fill something in.
	where := any(n.At)
	if n.ByRecord {
		where = "a record in this mesh, not a machine"
	}
	body, err := json.MarshalIndent(map[string]any{
		"binding":   1,
		"provision": n.Name,
		"from":      n.From,
		"at":        where,
		// Who this module is at the other end. **The half that was missing** (novox/hq
		// 04-ISSUES/023): a consumer was told the address, the port and where its password is,
		// and not the name it must present — which the provisioner had invented.
		"as":     as,
		"serves": n.Serves,
		// **Where the credential is, not what it is.** It stopped being true that the mesh
		// cannot issue one when 021 was fixed, and a comment asserting a fact about the mesh that
		// has become false is worse than none — somebody reads it and stops looking.
		"generated": "by the mesh — do not edit; replaced whenever this changes. " +
			"The credential is not here: it is sealed, in the file this module's manifest " +
			"names under `secrets`",
	}, "", "  ")
	if err != nil {
		return nil, err
	}
	return map[string]any{
		"id": BoundID(n.Name), "type": "file", "path": path, "mode": "0644",
		"content": string(body) + "\n",
	}, nil
}

// ContributionsFrom is what one module on this node asked of one requirement, settled.
//
// Exported because a provider's grants are assembled from its consumers' resolutions, one machine
// at a time, and the alternative was for the control plane to reimplement settling.
//
// **One module, not one machine** (novox/hq 04-ISSUES/022). This used to take a requirement alone
// and refuse whenever two modules wanted it — correctly, given what it had: the credential was
// keyed by node, so the two would have shared one, and sharing is worse than refusing. But the
// arrangement refused is the ordinary one. A node running eight services against one database is
// not an edge case; it is what a machine looks like. Now each consumer has its own credential and
// there is nothing left to refuse.
func (r Resolution) ContributionsFrom(requirement, module string, settings SettingsBy) (
	map[string]any, bool, error) {
	all, err := r.contributions(settings, nil, nil)
	if err != nil {
		return nil, false, err
	}
	for _, g := range all[requirement] {
		if g.From == module {
			return g.Values, true, nil
		}
	}
	// It contributes no payload — but a require-only consumer of a parameterless provision (one whose
	// `serves` names no consumer-supplied key: `redis-cache`, `amqp`) still ASKS for it and must be
	// granted a credential. Keying "asks" on contributions alone marked those grants withdrawn
	// (From=""), so the provider never created the account and the consumer authenticated nowhere. A
	// module asks iff it still requires the provision, whether or not it hands anything up with it.
	for _, m := range r.Modules {
		if m.Module != module {
			continue
		}
		for _, req := range m.Requires {
			if req == requirement {
				return map[string]any{}, true, nil
			}
		}
	}
	// Nothing on that machine asks for this any more. Said as "not found" rather than as an
	// error: it is how a credential is withdrawn, and the provider removes what nobody asks for.
	return nil, false, nil
}

// here is the module on this same machine that answers a requirement, as a binding.
//
// **Only when the provider said something a consumer must know.** That is the line: the original
// reasoning — a file saying "it is on this node" is a fact nobody needs — is right about the
// location and wrong about everything beside it. A shell is answered here and there is nothing to
// say about it. A registry is answered here and the consumer still cannot guess the port.
//
// The address is this machine's own name on the private network when it has one, and loopback
// when it does not — a machine not on the network still reaches itself, and naming it by a name
// nothing resolves would be worse than naming it by an address that always works.
func here(r Resolution, requirement string) *Needed {
	for _, m := range r.Modules {
		_, said := m.Serves[requirement]
		serves := ServedOn(m, requirement, nil)
		if !said || len(serves) == 0 {
			continue
		}
		at := r.At
		if at == "" {
			at = "127.0.0.1"
		}
		return &Needed{Name: requirement, From: r.Node, At: at, Serves: serves}
	}
	return nil
}

// withMeshNames gives every container in a set the mesh's names.
//
// Copied rather than edited in place: these maps come from a module's manifest, and mutating one
// would change what the catalogue holds for every other machine running that module.
func withMeshNames(resources []map[string]any, names map[string]string) []map[string]any {
	out := make([]map[string]any, 0, len(resources))
	for _, r := range resources {
		if r["type"] != "container" {
			out = append(out, r)
			continue
		}
		// A container on the machine's own network shares its hosts file already, and a runtime
		// refuses to write one for it. Adding names there would be an argument the runtime
		// rejects, which fails the whole container for something it did not need.
		if network, on := r["network"].(string); on && network == "host" {
			out = append(out, r)
			continue
		}

		copied := map[string]any{}
		for k, v := range r {
			copied[k] = v
		}
		var given []any
		if already, ok := copied["hosts"].([]any); ok {
			given = append(given, already...)
		}
		for _, name := range sortedKeys(names) {
			given = append(given, name+":"+names[name])
		}
		copied["hosts"] = given
		out = append(out, copied)
	}
	return out
}

// pinned refuses an image that is not really pinned, on its way to a machine.
//
// **Here and not at parse** (novox/hq 04-ISSUES/025). A manifest in a repository names artifacts
// and the manifest the mesh holds names digests — they are deliberately not the same document, so
// a file awaiting a pin is legitimate exactly as the bundle's is. What must never happen is a
// placeholder reaching a machine, and this is the last moment before one does.
//
// The host checks only the *shape* of a reference, and cannot do more: verifying a digest exists
// means reaching a registry, which is the one thing a host must never have to do. So sixty-four
// zeros satisfies every gate in the system and stops on the machine at `docker pull` — which is
// how eighteen of them shipped across five modules that parse, resolve and compose cleanly.
func pinned(resource map[string]any, module string) error {
	image, ok := resource["image"].(string)
	if !ok {
		return nil
	}
	_, digest, found := strings.Cut(image, "@")
	if !found || strings.Trim(strings.TrimPrefix(digest, "sha256:"), "0") != "" {
		return nil
	}
	return fmt.Errorf(
		"%s would send %v to a machine pinned to a placeholder digest, which is never a real "+
			"image — it would be fetched and fail there. Resolve the tag to a digest first",
		module, resource["id"])
}

// publishedOn puts the machine's own port on the outside of a container's mapping.
//
// **A module writes the port the software uses; the mesh says where the machine puts it**
// (novox/hq ADR 0038). So `"5432"` means *publish what the software calls 5432*, and this fills in
// the half only the mesh can know.
//
// A mapping written the long way — `"5433:5432"` — is left exactly as it is. Some things genuinely
// must be pinned down by hand, and quietly overruling somebody who wrote both halves would be
// worse than not offering the short form at all.
func publishedOn(resource map[string]any, module string, with Rendering) {
	if fmt.Sprint(resource["type"]) != "container" {
		return
	}
	listed, ok := resource["ports"].([]any)
	if !ok {
		return
	}
	out := make([]any, 0, len(listed))
	for _, entry := range listed {
		written := fmt.Sprint(entry)
		if strings.Contains(written, ":") {
			out = append(out, written)
			continue
		}
		wanted, err := strconv.Atoi(strings.TrimSpace(written))
		if err != nil {
			// Not a port at all. Passed through, so the host refuses it with its own words rather
			// than this quietly dropping something somebody meant.
			out = append(out, written)
			continue
		}
		out = append(out, fmt.Sprintf("%d:%d", with.machinePort(module, wanted), wanted))
	}
	resource["ports"] = out
}

// ServedOn is what a provider tells a consumer, with the port that machine actually uses.
//
// **The module writes the port once, in `listens`** (novox/hq ADR 0038). It used to write it three
// times — for the rule set, for what a consumer is told, and for what the runtime publishes — and
// nothing checked that the three agreed. This is what fills the second in.
//
// The assignment wins when there is one, and the declared port stands in when there is not: a
// caller composing without a store still gets something coherent, and a mesh that has assigned one
// tells the truth about where it put it.
//
// Only when the module offers exactly one port. A module offering several has not said which
// belongs to which provision, and guessing would give a consumer a port that answers something
// else — so it keeps whatever the manifest said, which may be nothing.
func ServedOn(m Manifest, provision string, ports map[int]int) map[string]any {
	serves := m.Serves[provision]

	out := make(map[string]any, len(serves)+1)
	for k, v := range serves {
		out[k] = v
	}
	if _, said := out["port"]; said {
		// Written by hand. Redirected to wherever the machine put it, and otherwise left alone.
		if number, ok := asPort(out["port"]); ok {
			if at, known := ports[number]; known {
				out["port"] = at
			}
		}
		return out
	}
	if len(m.Listens) != 1 {
		return out
	}
	wanted := m.Listens[0].Port
	if at, known := ports[wanted]; known {
		out["port"] = at
	} else {
		out["port"] = wanted
	}
	return out
}

func asPort(v any) (int, bool) {
	switch n := v.(type) {
	case int:
		return n, true
	case float64:
		return int(n), true
	}
	return 0, false
}