// Package composer is the shape of a composition over a plain request (novox/hq ADR 0482 clause 4, issue 1621, as ADR
// 0593 §7 changes it): the request the command mesh-compose reads and the verdict it answers. The command and the
// composer that runs it are the node-engine's (mesh-host cmd/mesh-compose), built from its repository at a group's
// head, so a change to its composition code is judged by that code.
//
// **It reads its request and nothing else.** No bus, store, network, file or environment: the manifests come inside the
// request (raw, as their repository holds them), the rest of the mesh is a compose.Input, and the answer is a value.
// A manifest named only by its digest in the delivery indexer's bucket is filled before the run by Fill, by whoever
// holds the bus (the Go build module's compose job); Run refuses a digest left unfilled.
package composer

import (
	"encoding/json"
	"errors"
	"fmt"
	"slices"

	"git.novox.be/novox/mesh-sdk/go/catalogue"
	"git.novox.be/novox/mesh-sdk/go/delivery"
)

// Version is the version of a Request and of a Verdict; a reader refuses another.
const Version = 1

// Package is the import path of the command, which a compose job builds at a commit of the node-engine's repository
// (novox/hq ADR 0593 §7).
const Package = "github.com/novox/mesh-host/cmd/mesh-compose"

// The depths of a composition.
const (
	// DepthResolve resolves each machine's set over the rest of the mesh (compose.Resolve): what the assigner judges
	// while the facts snapshot is not on the bus (issue 1461).
	DepthResolve = "resolve"
	// DepthCompose composes each machine's whole declaration and runs the node-engine's validator over it
	// (compose.Compose).
	DepthCompose = "compose"
)

// Request is everything one run composes: the rest of the mesh, one or more cases of manifests composed over it, and
// the machines composed in each case.
type Request struct {
	V int `json:"v"`
	// Input is the composition's input without its catalogue (and without each node's kept manifests): the cases give
	// those. A Catalogue or Kept it holds is ignored. It is the node-engine's composition input as JSON, which only the
	// composer decodes (novox/hq ADR 0593 §7), so this shape imports no composition.
	Input json.RawMessage `json:"input"`
	// Cases are composed one after the other over Input, each with its own manifests; their names are unique.
	Cases []Case `json:"cases"`
	// Machines are the nodes composed in every case; none means the manifests are only read.
	Machines []string `json:"machines,omitempty"`
	// Depth is DepthResolve or DepthCompose; empty is DepthCompose.
	Depth string `json:"depth,omitempty"`
	// HoldingsFromClaims adds to Input's holdings every seat an assigned module claims, held on its node (the
	// assigner's input, which has no holdings of record).
	HoldingsFromClaims bool `json:"holdings_from_claims,omitempty"`
	// Declarations asks each composed machine's declared paths (DepthCompose only).
	Declarations bool `json:"declarations,omitempty"`
	// Predefined is the list of predefined keys at the catalogue's root (predefined.json, novox/hq ADR 0348 §7). No
	// longer read: the composer judges no manifest (novox/hq ADR 0578 §5), the indexer's judge does, and its verdicts
	// come in each case's Verdicts. Kept so an asker that still sends it is read.
	Predefined catalogue.PredefinedList `json:"predefined,omitempty"`
}

// Case is one catalogue composed: every module's manifest by name, and per node the manifests kept at the build it runs.
//
// Placements are, by node, the placement the case composes that node with in place of what Input says of it: a change's
// own placement files, so a check composes a catalogue pull request's placement (issue 1126, frombus.Placed); a null
// placement leaves nothing placed on the node. A case without them composes Input's.
//
// Verdicts are, by module, the indexer's judge's verdict on its manifest in Manifests (novox/hq ADR 0578 §5), put in by
// the assigner or the checker that runs the composer: a refused one is held, composed as its stub so what it offers
// still shapes the rest, and named in the case's verdict. A module without one is accepted (delivery.TakeManifestVerdict).
type Case struct {
	Name       string                              `json:"name"`
	Manifests  map[string]Manifest                 `json:"manifests"`
	Verdicts   map[string]delivery.ManifestVerdict `json:"verdicts,omitempty"`
	Kept       map[string]map[string]Manifest      `json:"kept,omitempty"`
	Placements map[string]*delivery.Placement      `json:"placements,omitempty"`
}

// Manifest is a module's manifest as its repository holds it (Raw, the bytes), or the digest the delivery indexer keeps
// it under (Digest), which Fill replaces by the bytes. On the wire it is the manifest itself, or {"digest": "..."}.
type Manifest struct {
	Raw    json.RawMessage
	Digest string
}

// MarshalJSON writes the raw manifest, or {"digest": ...} when only the digest is known.
func (m Manifest) MarshalJSON() ([]byte, error) {
	if len(m.Raw) > 0 {
		return m.Raw, nil
	}
	return json.Marshal(map[string]string{"digest": m.Digest})
}

// UnmarshalJSON reads {"digest": "..."} (an object with that one key) as a digest, and any other value as the raw
// manifest.
func (m *Manifest) UnmarshalJSON(raw []byte) error {
	var probe map[string]json.RawMessage
	if json.Unmarshal(raw, &probe) == nil && len(probe) == 1 {
		if d, ok := probe["digest"]; ok {
			var digest string
			if err := json.Unmarshal(d, &digest); err != nil {
				return fmt.Errorf("a manifest's digest is not a string: %w", err)
			}
			*m = Manifest{Digest: digest}
			return nil
		}
	}
	*m = Manifest{Raw: slices.Clone(raw)}
	return nil
}

// Verdict is what one run answers: the mesh-sdk the command was built with, and each case's verdict in the order asked.
type Verdict struct {
	V     int           `json:"v"`
	SDK   string        `json:"sdk"`
	Cases []CaseVerdict `json:"cases"`
}

// CaseVerdict is one case's: every manifest read or refused, every machine composed or not.
type CaseVerdict struct {
	Name      string                  `json:"name"`
	Manifests map[string]ManifestRead `json:"manifests"`
	Machines  map[string]Machine      `json:"machines,omitempty"`
}

// ManifestRead is one manifest as this mesh-sdk reads it: accepted, or refused with why: the indexer's verdict
// (Case.Verdicts) or bytes that do not decode. A field the decoder does not know is set aside, named in SetAside, and
// the manifest still accepted (novox/hq ADR 0578 §6).
type ManifestRead struct {
	Accepted bool   `json:"accepted"`
	Refused  string `json:"refused,omitempty"`
	SetAside string `json:"set_aside,omitempty"`
}

// Machine is one machine composed: whether it composes (resolves, at DepthResolve), why not, the node-engine
// validator's problems and the composition's refusals (DepthCompose), and its declared paths when asked.
type Machine struct {
	Composes bool     `json:"composes"`
	Reason   string   `json:"reason,omitempty"`
	Problems []string `json:"problems,omitempty"`
	Refusals []string `json:"refusals,omitempty"`
	Declared []Path   `json:"declared,omitempty"`
}

// Path is one path a declaration puts on the machine, with its kind (the resource's type), owner, group and mode as
// declared, and the module it is of.
type Path struct {
	Path   string `json:"path"`
	Kind   string `json:"kind"`
	Owner  string `json:"owner,omitempty"`
	Group  string `json:"group,omitempty"`
	Mode   string `json:"mode,omitempty"`
	Module string `json:"module,omitempty"`
}

// ErrUnfilled is a manifest named by a digest that nobody replaced by its bytes.
var ErrUnfilled = errors.New("composer: a manifest is named by its digest and was not filled")

// Decode reads a request; it refuses one that is not JSON or of another version.
func Decode(data []byte) (Request, error) {
	var r Request
	if err := json.Unmarshal(data, &r); err != nil {
		return Request{}, fmt.Errorf("composer: the request is not JSON of its shape: %w", err)
	}
	if r.V != Version {
		return Request{}, fmt.Errorf("composer: a request of version %d, this composer reads %d", r.V, Version)
	}
	return r, nil
}

// Fill replaces every manifest named by its digest by the bytes get answers for that digest; a digest get cannot answer
// stops it, named.
func Fill(r *Request, get func(digest string) ([]byte, error)) error {
	fill := func(m map[string]Manifest) error {
		for name, man := range m {
			if len(man.Raw) > 0 {
				continue
			}
			raw, err := get(man.Digest)
			if err != nil {
				return fmt.Errorf("composer: the manifest of %s (digest %s): %w", name, man.Digest, err)
			}
			m[name] = Manifest{Raw: raw}
		}
		return nil
	}
	for _, c := range r.Cases {
		if err := fill(c.Manifests); err != nil {
			return err
		}
		for _, kept := range c.Kept {
			if err := fill(kept); err != nil {
				return err
			}
		}
	}
	return nil
}