package main

import (
	"context"
	"fmt"
	"github.com/novox/mesh-controller/internal/broker"
	"slices"
	"sort"
	"strings"

	"github.com/novox/mesh-controller/internal/catalogue"
)

// The things the mesh can be asked to do, separated from how it was asked.
//
// **A surface is an adapter with no decisions in it** (novox/hq ADR 0035). The command line and
// the command API call the same functions here, so an assignment refused at one is refused at the
// other for the same reason and in the same words. The moment a surface can accept something
// another would reject, the mesh has two answers to one question and people learn which to trust.
//
// Each returns what happened as text a person can read and a caller can pass on. Neither surface
// composes its own explanation, because two explanations of one refusal drift.

// assign puts a module on a node, and says at once what in the mesh no longer works out.
//
// The assignment is kept even when the node does not resolve: it is what a person meant, and
// assignment is not an ordering. A consumer assigned before its provider does not resolve for as
// long as it takes to assign the provider, and refusing the first half of a pair would make the
// order somebody types two commands in part of the mesh's rules.
//
// **What is checked is the mesh, not the one machine** — because that is what the assignment
// changes. novox/hq 04-ISSUES/017 names the shape: an action can succeed into a state its own
// verify rejects, and it happens when the action's test is not the test the verify uses. Here the
// action tested one node and the verify is resolution over all of them, so an assignment could be
// reported as fine while it took a provision away from every other machine — a module offering a
// mesh-scoped provision stops offering it the moment its own node stops resolving, and every
// consumer elsewhere is then told *nothing in this mesh provides it*, with a remedy that names a
// module already assigned. That was found on a four-node raise and read as a version bump breaking
// provider recognition; it was neither the version nor the provider.
//
// It costs a resolution per machine. Assignment is a person typing a command, and being told which
// machines this just blocked is worth more than the milliseconds.
func assign(ctx context.Context, open *stores, node string, modules ...string) (string, error) {
	if len(modules) == 0 {
		return "", fmt.Errorf("assign %s names no module", node)
	}
	// Held while it is recorded, so it cannot land between a converge's preview and its flip and
	// be taken without ever having been previewed (novox/hq ADR 0100).
	ctx, release, err := holdNodes(ctx, open, []string{node})
	if err != nil {
		return "", err
	}
	defer release()
	// **The one assignment refused for what the node lacks** (novox/hq ADR 0207). Everything else
	// an assignment leaves unresolved is kept, because assignment is not an ordering; a module whose
	// resources are applied through a seat nothing on the node holds is refused, because that order
	// — the service manager, the package manager and the runtime before anything that installs,
	// runs or contains — is the mesh's to keep. Several modules in one act are judged together, so
	// holders that depend on each other go on in one command.
	shelf, before, err := seatDependenciesOnAssign(ctx, open, node, modules)
	if err != nil {
		return "", err
	}
	// **Before the new assignment can unsettle a seat somebody holds only by being alone**
	// (novox/hq 04-ISSUES/170): what the mesh derived so far is written down, and then the
	// assignment resolves against a record rather than against a coincidence.
	settled, err := recordDerivedHolders(ctx, open)
	if err != nil {
		return "", err
	}
	var lines []string
	var added []string
	for _, module := range modules {
		fresh, err := open.inventory.Assign(ctx, node, module)
		if err != nil {
			return strings.Join(lines, "\n"), err
		}
		if !fresh {
			// Nothing changed, and saying "is assigned" would read as an action. One node runs one
			// of each — the module's name is the assignment's identity (novox/hq ADR 0115).
			lines = append(lines, fmt.Sprintf(
				"%s already runs %s — one node runs one of each (ADR 0115); nothing changed", node, module))
			continue
		}
		added = append(added, module)
		lines = append(lines, fmt.Sprintf("%s is assigned %s", node, module))
	}
	if len(added) == 0 {
		return strings.Join(lines, "\n"), nil
	}
	answer := strings.Join(lines, "\n")
	for _, line := range settled {
		answer += "\n  " + line
	}
	// What this act changed about this node's unmet seat dependencies, and nothing else (novox/hq
	// ADR 0207): a dependency of a module just assigned, or one this assignment met. The rest of the
	// node's list, and every other node's, is `status`'s.
	for _, line := range unheldChange(shelf, node, before, append(append([]string(nil), before...), added...)) {
		answer += "\n  " + line
	}
	// Its bus credential, in the same act (novox/hq issue 203): an assignment pushed before its
	// credential exists delivers a process that cannot authenticate and crash-loops until somebody
	// runs a second verb and a second push. Issued here when the module speaks on the bus and has
	// no credential yet; kept when it has one, so re-assigning rotates nothing.
	for _, module := range added {
		if line := issueOnAssign(ctx, open, node, module); line != "" {
			answer += "\n  " + line
		}
	}
	plan, _, err := planFor(ctx, open, node)
	if err != nil {
		// Kept, and still refused. Both halves are the answer, and the rest of the mesh is still
		// worth reporting: this machine's refusal is rarely the only consequence.
		return answer + blockedElsewhere(ctx, open, node), err
	}
	// Kept, and cannot be hosted here. Said at once rather than discovered at push: a module whose
	// capability the machine lacks is on the wrong machine, and the assignment records what a person
	// meant while this line says it will not run until it moves. The rest of the node still pushes.
	isAdded := map[string]bool{}
	for _, m := range added {
		isAdded[m] = true
	}
	for _, u := range plan.Unhostable {
		if !isAdded[u.Module] {
			continue
		}
		for _, c := range u.Missing {
			answer += "\n  but " + catalogue.WrongMachine(u.Module, c, node)
		}
	}
	return answer + fmt.Sprintf("\n  run `push %s` to send it", node) +
		blockedElsewhere(ctx, open, node), nil
}

// seatDependenciesOnAssign is the refusal ADR 0207 makes at assignment, or nothing, with the
// catalogue and the node's assignments it was judged against. Modules already assigned are not new
// and are not judged again.
func seatDependenciesOnAssign(ctx context.Context, open *stores, node string, modules []string) (
	map[string]catalogue.Manifest, []string, error) {
	shelf, err := open.inventory.Catalogue(ctx)
	if err != nil {
		return nil, nil, err
	}
	assigned, err := open.inventory.Assigned(ctx, node)
	if err != nil {
		return nil, nil, err
	}
	already := map[string]bool{}
	for _, a := range assigned {
		already[a] = true
	}
	var adding []string
	for _, m := range modules {
		if !already[m] {
			adding = append(adding, m)
		}
	}
	// The lines AssignRefusal says beside an assignment it lets through are said by unheldChange
	// with everything else this act changed, so they are not said twice.
	if _, err := catalogue.AssignRefusal(shelf, node, assigned, adding); err != nil {
		return nil, nil, err
	}
	// Two modules declaring one package, path or unit is refused before anything is recorded
	// (novox/hq ADR 0210, 04-ISSUES/235): kept, the node would not resolve until one came off again.
	if err := catalogue.CollisionRefusal(shelf, node, assigned, adding); err != nil {
		return nil, nil, err
	}
	return shelf, assigned, nil
}

// unassign takes modules off a node. What they leave behind is the host's business: a directory
// holding anything the mesh did not put there is kept (novox/hq ADR 0030).
//
// It reports the rest of the mesh for the same reason assign does, and more sharply: taking a
// module off one machine is the ordinary way to stop providing something to another, and nothing
// about the command's own output would ever have said so.
//
// **Refused when it takes away the last holder of a seat a module left on the node depends on**
// (novox/hq ADR 0207) — the other side of refusing that module's assignment without one. Several
// modules in one act are judged together, so a holder and its dependents come off in one command.
func unassign(ctx context.Context, open *stores, node string, modules ...string) (string, error) {
	if len(modules) == 0 {
		return "", fmt.Errorf("unassign %s names no module", node)
	}
	ctx, release, err := holdNodes(ctx, open, []string{node})
	if err != nil {
		return "", err
	}
	defer release()
	shelf, err := open.inventory.Catalogue(ctx)
	if err != nil {
		return "", err
	}
	assigned, err := open.inventory.Assigned(ctx, node)
	if err != nil {
		return "", err
	}
	// Every one checked before any is taken off, so a refusal leaves the node as it was.
	runs := map[string]bool{}
	for _, a := range assigned {
		runs[a] = true
	}
	for _, module := range modules {
		if !runs[module] {
			return "", fmt.Errorf("%s is not assigned to %s", module, node)
		}
	}
	if err := catalogue.UnassignRefusal(shelf, node, assigned, modules); err != nil {
		return "", err
	}
	for _, module := range modules {
		if err := open.inventory.Unassign(ctx, node, module); err != nil {
			return "", err
		}
	}
	answer := fmt.Sprintf("%s no longer runs %s — run `push %s` to make it so",
		node, strings.Join(modules, ", "), node)
	var left []string
	for _, a := range assigned {
		if !slices.Contains(modules, a) {
			left = append(left, a)
		}
	}
	for _, line := range unheldChange(shelf, node, assigned, left) {
		answer += "\n  " + line
	}
	// What it leaves behind that is irreplaceable is kept and retired, never removed (novox/hq ADR 0233).
	for _, line := range keptOnUnassign(ctx, open.inventory, node, modules) {
		answer += "\n  " + line
	}
	return answer + blockedElsewhere(ctx, open, node), nil
}

// splitModules is a surface's one `module` field as the modules it names: several, comma-separated,
// are one act (novox/hq ADR 0207), so the holders that depend on each other go on together from the
// command API and the controller seat's verbs as they do from the command line.
func splitModules(field string) []string {
	var out []string
	for _, m := range strings.Split(field, ",") {
		if m = strings.TrimSpace(m); m != "" {
			out = append(out, m)
		}
	}
	return out
}

// blockedElsewhere is every OTHER machine that cannot be worked out as things now stand.
//
// **The state, not the cause.** Saying "this assignment broke laptop" would mean resolving the
// whole mesh twice and would still be a guess about which of several changes did it; saying
// "laptop cannot be worked out, and here is what it says" is true, is what somebody has to fix,
// and cannot mislead. The machine that was just changed is left out because its own refusal is
// already the answer beside this one.
//
// Nothing here can fail the act it reports on. A mesh that cannot be read is worth saying and is
// not a reason to claim the assignment did not happen — it did.
func blockedElsewhere(ctx context.Context, open *stores, except string) string {
	nodes, err := open.inventory.Nodes(ctx)
	if err != nil {
		return "\n\nThe rest of the mesh could not be checked: " + err.Error()
	}
	blocked := map[string]string{}
	for _, n := range nodes {
		if n.Name == except {
			continue
		}
		if _, _, err := planFor(ctx, open, n.Name); err != nil {
			blocked[n.Name] = err.Error()
		}
	}
	if len(blocked) == 0 {
		return ""
	}
	names := make([]string, 0, len(blocked))
	for name := range blocked {
		names = append(names, name)
	}
	sort.Strings(names)

	var out strings.Builder
	fmt.Fprintf(&out, "\n\nAND %d other machine(s) cannot be worked out as things stand, so "+
		"nothing will be sent to them:\n", len(names))
	for _, name := range names {
		fmt.Fprintf(&out, "  %s\n", name)
		for _, line := range strings.Split(strings.TrimRight(blocked[name], "\n"), "\n") {
			fmt.Fprintf(&out, "    %s\n", strings.TrimSpace(line))
		}
	}
	out.WriteString("\nThis may or may not be what just changed — it is what is true now.")
	return out.String()
}

// issueOnAssign gives a newly assigned module its bus credential, the way `module issue` does, and
// says what it did in one line. Nothing for a module that declares no broker secret; nothing for one
// whose user is already minted (a credential is rotated on purpose, never by re-assigning); and when
// the bus cannot be reached from here, the line names the verb and the push that would refuse the
// module until it is run — never a silent placeholder (novox/hq issue 203).
func issueOnAssign(ctx context.Context, open *stores, node, module string) string {
	inv := open.inventory
	shelf, err := inv.Catalogue(ctx)
	if err != nil {
		return ""
	}
	m, known := shelf[module]
	if !known || mayIssue(m) != nil {
		return ""
	}
	user := broker.Principal{Kind: broker.KindModule, Node: node, Module: module}.Username()
	if _, minted, err := inv.BusUserHash(ctx, user); err != nil || minted {
		return ""
	}
	busAddress, err := broker.BusAddress()
	if err == nil {
		err = issueOnTheNewBus(ctx, inv, m, node, busAddress)
	}
	if err != nil {
		return fmt.Sprintf("its bus credential is not issued (%v): `module issue %s --node %s` first — "+
			"`push %s` refuses to send %s until it is", err, module, node, node, module)
	}
	return fmt.Sprintf("its bus credential is issued and sealed to %s, and arrives with the push", node)
}