// Package catalogue is what modules are, and what a node gets when it is assigned some.
//
// novox/hq ADR 0009: everything is a module, a module declares what it provides and requires,
// and a module declares what it claims. This turns a set of assignments into the one declaration
// a node is sent — which is the first thing the control plane decides rather than relays.
package catalogue

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

// Scopes a claim can have.
//
// Not everything singular is singular per machine: a seat is one per node, a DHCP server is one
// per segment, and the hub is one per mesh. Scope says which, and it is the same idea the mesh
// already enforces by hand for the hub.
const (
	ScopeNode = "node"
	ScopeSite = "site"
	ScopeMesh = "mesh"
)

// name is what a module, a provision or a claim may be called.
//
// Constrained because these become resource identities, permission patterns and error messages,
// and a name that is valid in one and not the others is a fault found late.
var name = regexp.MustCompile(`^[a-z0-9][a-z0-9-]*(\.[a-z0-9][a-z0-9-]*)*$`)

// Claim is a singular resource a module takes over.
type Claim struct {
	Name string `json:"name"`
	// Scope defaults to the node, which is where nearly everything singular is singular.
	Scope string `json:"scope,omitempty"`
}

// At is this claim's scope, with the default applied.
func (c Claim) At() string {
	if c.Scope == "" {
		return ScopeNode
	}
	return c.Scope
}

// Manifest is everything a module says about itself.
type Manifest struct {
	Module  string `json:"module"`
	Version string `json:"version,omitempty"`

	// Provides are the names other modules may require. A module always provides its own name;
	// this is for the rest — `zsh` provides `shell`, `xorg` provides `display-server`.
	Provides []string `json:"provides,omitempty"`

	// Requires are names that must be provided by something assigned to the same node.
	Requires []string `json:"requires,omitempty"`

	// Claims are singular resources. Two modules claiming one thing within a scope cannot both
	// be assigned there — which is how exclusivity is expressed, rather than as a list of rivals
	// that every new module would force its predecessors to update.
	Claims []Claim `json:"claims,omitempty"`

	// Capabilities the machine must have. A different field from Requires because the remedy
	// differs: a missing module can be assigned, and a missing capability means the wrong
	// machine.
	Capabilities []string `json:"capabilities,omitempty"`

	// Resources are what this module puts on a node, in the host's own vocabulary.
	Resources []map[string]any `json:"resources,omitempty"`

	// Computed names something in the control plane that works this module's resources out per
	// node, instead of them being fixed here.
	//
	// Because some files cannot be written in advance. A machine's peer list on the private
	// network is derived from every other machine, so it differs on each one and changes when any
	// of them changes — there is nothing to put in a manifest.
	//
	// Being a module anyway is the point: it is assigned like anything else, so a machine that
	// should not be on the private network simply is not given it, and the network is worked out
	// over the machines that have it. Before this, connectivity was code beside the module system
	// doing the same job, and every machine with an address was on the network whether or not
	// anybody wanted it there.
	Computed string `json:"computed,omitempty"`
}

// ParseManifest reads a module manifest, refusing anything it cannot act on.
//
// Every problem is reported rather than the first, because somebody writing a manifest fixes
// them in one pass or in four.
func ParseManifest(raw []byte) (Manifest, error) {
	var m Manifest
	if err := json.Unmarshal(raw, &m); err != nil {
		return Manifest{}, fmt.Errorf("this is not a module manifest: %w", err)
	}

	var problems []string
	if !name.MatchString(m.Module) {
		problems = append(problems, fmt.Sprintf(
			"%q is not a usable module name: lower-case letters, digits, dashes and dots", m.Module))
	}
	for _, p := range m.Provides {
		if !name.MatchString(p) {
			problems = append(problems, fmt.Sprintf("%q is not a usable name to provide", p))
		}
		if p == m.Module {
			// Harmless and worth saying: a module always provides its own name, so writing it
			// suggests the author expected it not to.
			problems = append(problems, fmt.Sprintf(
				"%s provides its own name already; listing it says nothing", m.Module))
		}
	}
	for _, r := range m.Requires {
		if !name.MatchString(r) {
			problems = append(problems, fmt.Sprintf("%q is not a usable name to require", r))
		}
		if r == m.Module {
			problems = append(problems, fmt.Sprintf("%s requires itself", m.Module))
		}
	}
	for _, c := range m.Claims {
		if !name.MatchString(c.Name) {
			problems = append(problems, fmt.Sprintf("%q is not a usable claim name", c.Name))
		}
		switch c.At() {
		case ScopeNode, ScopeSite, ScopeMesh:
		default:
			problems = append(problems, fmt.Sprintf(
				"%s claims %s at scope %q; a claim is held per node, per site or per mesh",
				m.Module, c.Name, c.Scope))
		}
	}
	if m.Computed != "" && len(m.Resources) > 0 {
		// One or the other. A module that both ships files and has them computed would leave
		// nobody able to say where a given file came from.
		problems = append(problems, fmt.Sprintf(
			"%s has resources of its own and says they are computed by %q; it is one or the other",
			m.Module, m.Computed))
	}
	for i, r := range m.Resources {
		id, _ := r["id"].(string)
		if id == "" {
			problems = append(problems, fmt.Sprintf("resource %d has no id", i))
		}
		if _, ok := r["type"].(string); !ok {
			problems = append(problems, fmt.Sprintf("resource %q has no type", id))
		}
	}

	if len(problems) > 0 {
		sort.Strings(problems)
		return Manifest{}, fmt.Errorf("this manifest cannot be used:\n  - %s",
			strings.Join(problems, "\n  - "))
	}
	return m, nil
}

// Offers is everything this module can satisfy: its own name, and what it provides.
func (m Manifest) Offers() []string {
	out := append([]string{m.Module}, m.Provides...)
	sort.Strings(out)
	return out
}