// Package facts is the mesh's facts snapshot: what a check needs to judge a change against the mesh
// that runs, and nothing it could leak (novox/hq to-be 45 §9, ADR 0227 rule 9).
//
// **Why it exists.** Every check the mesh had was right about the world it was given, and none was
// given the mesh's world: a module passed every test and refused the anchor's whole declaration because
// a real machine's name made its identity 23 characters (issue 263); a manifest passed the catalogue
// check and was refused by the node-engine (issue 236); a resolver answer that glibc forgave was final
// to musl (issue 262). The controller holds those facts. It writes them here, the build seat reads them,
// and a merge check composes every machine of the snapshot with the change applied.
//
// **What it holds, and what it never holds.** Every machine — under a stable pseudonym of the same length
// as its name, because the length is what a name limit meets — with its roles, system, C library,
// architecture, builds, what it reported it can do, what is assigned there, its pins and settings;
// every seat and its holders; every module the mesh holds, as its manifest; the sources the mesh built
// them from; the versions of the bus, the store and the node-engine it runs; and how each machine's
// declaration composes today. **No secret and no address**: a setting whose key or value reads as a
// secret is withheld, an address is replaced by one from a documentation range, and a machine's name, a
// site, an account and a public domain are replaced wherever they appear. So a snapshot can be copied
// into a test, a replay or a pull request without carrying anything of the installation it came from.
package facts

import (
	"crypto/sha256"
	"encoding/json"
	"fmt"
	"sort"
	"time"
)

// Format is the snapshot's version. A reader refuses one newer than it knows: a field it cannot read
// is a fact it would judge without.
const Format = 1

// Repository and Tag are where the controller keeps the newest snapshot in the artifact store, and
// MediaType what it is kept as.
const (
	Repository = "facts"
	Tag        = "latest"
	MediaType  = "application/vnd.novox.mesh.facts.v1+json"
)

// Facts is one snapshot.
type Facts struct {
	Format int `json:"facts"`
	// Taken is when the controller composed it.
	Taken time.Time `json:"taken"`
	// Controller is the controller build that composed it — the one the mesh runs, which is the one a
	// change to the catalogue must be readable by (version skew).
	Controller Build `json:"controller"`
	// Versions are what the mesh runs of the things its tests stand in for.
	Versions Versions `json:"versions"`
	// Sources are the repositories the mesh builds modules from, each with the newest commit it built.
	Sources []Source `json:"sources"`
	// Machines, in name order of their pseudonyms.
	Machines []Machine `json:"machines"`
	// Seats are every seat held, with its holders.
	Seats []Seat `json:"seats"`
	// Modules are every module the mesh holds, as it holds them.
	Modules []Module `json:"modules"`
	// Settings are the mesh-wide layer of every module's settings, scrubbed.
	Settings []Settings `json:"settings,omitempty"`
	// Edges are the build dependencies between modules, as the mesh recorded them — what a merge's
	// rebuild width is computed from.
	Edges []Edge `json:"edges,omitempty"`
}

// Build names one build of a core component.
type Build struct {
	Version string `json:"version,omitempty"`
	Commit  string `json:"commit,omitempty"`
}

// Versions are what the mesh runs.
type Versions struct {
	// Bus is the bus server's release, as the server tells a client that connects.
	Bus string `json:"bus,omitempty"`
	// Store is the store's server version, as the store answers it.
	Store string `json:"store,omitempty"`
	// NodeEngines are the node-engine builds the machines report, each once.
	NodeEngines []string `json:"node-engines,omitempty"`
}

// Source is a repository the mesh builds from, and the newest commit it built a module of.
type Source struct {
	Repository string `json:"repository"`
	Commit     string `json:"commit,omitempty"`
	Modules    int    `json:"modules"`
}

// Machine is one machine, under its pseudonym.
type Machine struct {
	Name string `json:"name"`
	// Length is the length of its real name, which the pseudonym keeps.
	Length int `json:"length"`
	// Roles are what it is to the mesh, in words: the control node, the hub, the bus's machine, a
	// holder of a mesh seat. What a check names when it fails one.
	Roles []string `json:"roles,omitempty"`
	// System is the node-engine's system (arch, alpine, …), Libc its C library, as far as the mesh knows.
	System       string `json:"system,omitempty"`
	Libc         string `json:"libc,omitempty"`
	Architecture string `json:"architecture,omitempty"`
	Kernel       string `json:"kernel,omitempty"`
	// NodeEngine and NodeTools are the builds it runs.
	NodeEngine string `json:"node-engine,omitempty"`
	NodeTools  string `json:"node-tools,omitempty"`
	// Capabilities are what it reported it can do; the detail kept only where it is a version.
	Capabilities []Capability `json:"capabilities,omitempty"`
	// Site, Hub, Public: where it is on the private network — its site (a pseudonym), whether it is the
	// hub, whether others can dial it. No address.
	Site   string `json:"site,omitempty"`
	Hub    bool   `json:"hub,omitempty"`
	Public bool   `json:"public,omitempty"`
	// OnNetwork is whether it has a place on the private network at all.
	OnNetwork bool `json:"on-network,omitempty"`
	// Adopted is whether the mesh adopted it rather than converged it.
	Adopted bool `json:"adopted,omitempty"`
	// Account is the operator's login there (a pseudonym of the same length), and AccountHome where its
	// home is when that is not the derived one.
	Account     string `json:"account,omitempty"`
	AccountHome string `json:"account-home,omitempty"`
	// PublicDomain is the domain it answers for, its labels replaced.
	PublicDomain string `json:"public-domain,omitempty"`
	// Assigned is every module assigned there.
	Assigned []string `json:"assigned,omitempty"`
	// Pins are where it was told a provision comes from.
	Pins []Pin `json:"pins,omitempty"`
	// Settings are its own layer of each module's settings, scrubbed.
	Settings []Settings `json:"settings,omitempty"`
	// Accepted are the secrets a person gave the mesh for modules here, by name only: the mesh cannot
	// make them, so a check composing this machine gives each a stand-in instead of refusing it.
	Accepted []Accepted `json:"accepted,omitempty"`
	// Declaration is how its declaration composes today, as the controller that took this saw it.
	Declaration Declaration `json:"declaration"`
}

// Capability is one thing a machine reported it can or cannot do.
type Capability struct {
	Name    string `json:"name"`
	Present bool   `json:"present"`
	Detail  string `json:"detail,omitempty"`
}

// Pin is one provision a machine was told where to take from.
type Pin struct {
	Provision string `json:"provision"`
	Machine   string `json:"machine"`
	Module    string `json:"module,omitempty"`
}

// Accepted is one secret a person gave: the module's own when Provider is empty, else the credential it
// takes from that machine's provider under Local.
type Accepted struct {
	Module   string `json:"module"`
	Name     string `json:"name"`
	Provider string `json:"provider,omitempty"`
	Local    string `json:"local,omitempty"`
}

// Settings is one layer of one module's settings.
type Settings struct {
	Module string         `json:"module"`
	Values map[string]any `json:"values"`
}

// Declaration is how one machine's declaration composed when the snapshot was taken.
type Declaration struct {
	// Composes is whether it composed and the node-engine's validator took it.
	Composes bool `json:"composes"`
	// Digest is its body's digest — composed as the next push would, so it moves with what the mesh
	// would send, and is not the digest of what was last sent.
	Digest string `json:"digest,omitempty"`
	// Resources are what it declares, as `type:id`, sorted.
	Resources []string `json:"resources,omitempty"`
	// Problems are why it does not compose or validate, scrubbed.
	Problems []string `json:"problems,omitempty"`
	// LeftOut are the modules assigned there and left out of it, each with why.
	LeftOut map[string]string `json:"left-out,omitempty"`
	// Withheld are the consumers its grants leave out because an identity overflows the provision's
	// bound (ADR 0225), and Unbound the credentials on record for consumers bound elsewhere (issue 274),
	// each said in words.
	Withheld []string `json:"withheld,omitempty"`
	Unbound  []string `json:"unbound,omitempty"`
}

// Seat is one seat and the machines holding it.
type Seat struct {
	Name    string   `json:"name"`
	Scope   string   `json:"scope"`
	Holders []Holder `json:"holders"`
}

// Holder is one module on one machine holding a seat.
type Holder struct {
	Machine string `json:"machine"`
	Module  string `json:"module"`
}

// Module is one module the mesh holds.
type Module struct {
	Name string `json:"name"`
	// Repository and Path are where it is built from; empty for one that came with the controller.
	Repository string `json:"repository,omitempty"`
	Path       string `json:"path,omitempty"`
	// Commit is the commit the manifest the mesh holds was read at.
	Commit string `json:"commit,omitempty"`
	// Provided is a module that came with the controller rather than from a repository.
	Provided bool `json:"provided,omitempty"`
	// RollOut is its upgrade policy: rolled out when built, or recorded.
	RollOut bool `json:"roll-out,omitempty"`
	// Reads are the other repositories its build read source from.
	Reads []string `json:"reads,omitempty"`
	// Manifest is the module as the mesh holds it: artifacts resolved to the builds it runs.
	Manifest json.RawMessage `json:"manifest"`
}

// Edge is one build dependency: From is built standing on To.
type Edge struct {
	From string `json:"from"`
	To   string `json:"to"`
	Kind string `json:"kind,omitempty"`
}

// Sorted puts every list in a fixed order, so two snapshots of one mesh are the same bytes apart from
// when they were taken.
func (f *Facts) Sorted() {
	sort.Slice(f.Machines, func(i, j int) bool { return f.Machines[i].Name < f.Machines[j].Name })
	for i := range f.Machines {
		m := &f.Machines[i]
		sort.Strings(m.Roles)
		sort.Strings(m.Assigned)
		sort.Slice(m.Capabilities, func(a, b int) bool { return m.Capabilities[a].Name < m.Capabilities[b].Name })
		sort.Slice(m.Pins, func(a, b int) bool { return m.Pins[a].Provision < m.Pins[b].Provision })
		sort.Slice(m.Settings, func(a, b int) bool { return m.Settings[a].Module < m.Settings[b].Module })
		sort.Slice(m.Accepted, func(a, b int) bool {
			x, y := m.Accepted[a], m.Accepted[b]
			return x.Module+"\x00"+x.Name+"\x00"+x.Provider+"\x00"+x.Local < y.Module+"\x00"+y.Name+"\x00"+y.Provider+"\x00"+y.Local
		})
		sort.Strings(m.Declaration.Resources)
	}
	sort.Slice(f.Seats, func(i, j int) bool {
		if f.Seats[i].Name != f.Seats[j].Name {
			return f.Seats[i].Name < f.Seats[j].Name
		}
		return f.Seats[i].Scope < f.Seats[j].Scope
	})
	for i := range f.Seats {
		h := f.Seats[i].Holders
		sort.Slice(h, func(a, b int) bool {
			if h[a].Machine != h[b].Machine {
				return h[a].Machine < h[b].Machine
			}
			return h[a].Module < h[b].Module
		})
	}
	sort.Slice(f.Modules, func(i, j int) bool { return f.Modules[i].Name < f.Modules[j].Name })
	sort.Slice(f.Sources, func(i, j int) bool { return f.Sources[i].Repository < f.Sources[j].Repository })
	sort.Slice(f.Settings, func(i, j int) bool { return f.Settings[i].Module < f.Settings[j].Module })
	sort.Slice(f.Edges, func(i, j int) bool {
		if f.Edges[i].From != f.Edges[j].From {
			return f.Edges[i].From < f.Edges[j].From
		}
		return f.Edges[i].To < f.Edges[j].To
	})
	sort.Strings(f.Versions.NodeEngines)
}

// Encode is the snapshot as it is kept: sorted, indented, so a person can read the one the build seat
// read and a diff of two says what moved.
func (f Facts) Encode() ([]byte, error) {
	f.Sorted()
	return json.MarshalIndent(f, "", " ")
}

// Content is the digest of everything but when it was taken: two snapshots of an unchanged mesh have
// the same content, which is how the controller tells a change from another day.
func (f Facts) Content() (string, error) {
	f.Taken = time.Time{}
	body, err := f.Encode()
	if err != nil {
		return "", err
	}
	sum := sha256.Sum256(body)
	return fmt.Sprintf("sha256:%x", sum), nil
}

// Decode reads a snapshot, refusing one newer than this reader knows and one that is not a snapshot.
func Decode(body []byte) (Facts, error) {
	var f Facts
	if err := json.Unmarshal(body, &f); err != nil {
		return Facts{}, fmt.Errorf("not a facts snapshot: %w", err)
	}
	switch {
	case f.Format == 0:
		return Facts{}, fmt.Errorf("not a facts snapshot: it says no format")
	case f.Format > Format:
		return Facts{}, fmt.Errorf("a facts snapshot of format %d, and this reads format %d: a newer controller "+
			"took it, and what it says beyond %d would be judged without", f.Format, Format, Format)
	}
	return f, nil
}

// Longest is the length of the longest machine name in the snapshot — what a consumer's identity is
// judged on (novox/hq ADR 0225).
func (f Facts) Longest() int {
	longest := 0
	for _, m := range f.Machines {
		if m.Length > longest {
			longest = m.Length
		}
	}
	return longest
}

// Machine is the machine of that pseudonym.
func (f Facts) Machine(name string) (Machine, bool) {
	for _, m := range f.Machines {
		if m.Name == name {
			return m, true
		}
	}
	return Machine{}, false
}

// Described is how a check names a machine: its roles, then its pseudonym.
func (m Machine) Described() string {
	if len(m.Roles) == 0 {
		return "a machine (" + m.Name + ")"
	}
	out := m.Roles[0]
	for _, r := range m.Roles[1:] {
		out += ", " + r
	}
	return out + " (" + m.Name + ")"
}