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"
	"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, which is also what names the file.
	Consumer string
	// From is the module on that machine which asked, so the provider can name what it creates
	// after the thing using it rather than after the machine.
	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
	// 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
}

// 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.
	rules, err := r.Filtering(with.Generators)
	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,
			})
		}
		for _, to := range sortedKeys(m.Secrets) {
			var found *Needed
			for i, n := range r.Needs {
				if n.Name == to {
					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),
					"type":   "file",
					"path":   grantPath(m.Grants[to], g.Consumer),
					"sealed": g.Sealed,
				})
			}
		}
		for _, to := range sortedKeys(m.Binds) {
			var found *Needed
			for i, n := range r.Needs {
				if n.Name == to {
					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])
			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)
		}

		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
			}
			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"`
	// 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.
func grantPath(directory, consumer string) string {
	return strings.TrimRight(directory, "/") + "/" + consumer + ".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
		}
		return sorted[i].Consumer < sorted[j].Consumer
	})
	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,
			Secret: grantPath(directories[g.Provision], g.Consumer),
		})
	}
	for _, m := range modules {
		for _, to := range sortedKeys(m.Contributes) {
			// 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 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,
		"serves":    n.Serves,
		"generated": "by the mesh — do not edit; replaced whenever this changes. " +
			"It carries no credential: the mesh has no way to issue one yet",
	}, "", "  ")
	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
}

// ContributionsTo is what this node's set 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.
func (r Resolution) ContributionsTo(requirement string, settings SettingsBy) (
	string, map[string]any, error) {
	all, err := r.contributions(settings, nil, nil)
	if err != nil {
		return "", nil, err
	}
	given := all[requirement]
	if len(given) == 0 {
		return "", nil, nil
	}
	if len(given) > 1 {
		// Two modules on one machine wanting the same provision would share one credential, and
		// the provider would be told to create one thing under two names. Refused rather than
		// resolved by picking, which is the rule everywhere else here.
		var who []string
		for _, g := range given {
			who = append(who, g.From)
		}
		sort.Strings(who)
		return "", nil, fmt.Errorf(
			"%s has %d modules asking for %q and they would share one credential: %s",
			r.Node, len(given), requirement, strings.Join(who, ", "))
	}
	return given[0].From, given[0].Values, 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 {
		serves, said := m.Serves[requirement]
		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
}