// Package composer is mesh-sdk's composition and validator as one function over a plain request (novox/hq ADR 0482
// clause 4, issue 1621): what the command mesh-compose runs, so a program that links any one mesh-sdk can have the
// composition of another commit judged by building that commit's command and reading its verdict.
//
// **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"
	"sort"

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

// 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 (in mesh-sdk's own module, or in
// a module that requires mesh-sdk, at the version it pins).
const Package = "git.novox.be/novox/mesh-sdk/go/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.
	Input compose.Input `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) that
	// every config value falling back to a key is judged against, when the asker has it (mesh-compose -catalogue
	// reads it). Without it a fallback is read as catalogue.ParseManifestForInputs reads it: against the list the mesh
	// published when this process holds one, else each key as its value declares it, for the merge gate judges the
	// fallback in the catalogue and a manifest that only carries one is not refused here.
	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.
type Case struct {
	Name      string                         `json:"name"`
	Manifests map[string]Manifest            `json:"manifests"`
	Kept      map[string]map[string]Manifest `json:"kept,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 the reader's words.
type ManifestRead struct {
	Accepted bool   `json:"accepted"`
	Refused  string `json:"refused,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
}

// Run composes every case of r and answers the verdict, its SDK this binary's mesh-sdk. An error is a request it
// cannot run (an unknown depth, a case named twice, a manifest left as a digest); a machine that does not compose is a
// verdict.
func Run(r Request) (Verdict, error) {
	depth := r.Depth
	if depth == "" {
		depth = DepthCompose
	}
	if depth != DepthResolve && depth != DepthCompose {
		return Verdict{}, fmt.Errorf("composer: the depth %q is not resolve or compose", r.Depth)
	}
	v := Verdict{V: Version, SDK: sdkversion.Version()}
	seen := map[string]bool{}
	for _, c := range r.Cases {
		if seen[c.Name] {
			return Verdict{}, fmt.Errorf("composer: the case %q is named twice", c.Name)
		}
		seen[c.Name] = true
		cv, err := runCase(r, c, depth)
		if err != nil {
			return Verdict{}, err
		}
		v.Cases = append(v.Cases, cv)
	}
	return v, nil
}

// readManifest reads one manifest as this run reads every one: against the request's list of predefined keys when it
// has one, else as the indexer and the builder read it (Request.Predefined).
func readManifest(raw []byte, predefined catalogue.PredefinedList) (catalogue.Manifest, error) {
	if predefined != nil {
		return catalogue.ParseManifestWith(raw, predefined)
	}
	return catalogue.ParseManifestForInputs(raw)
}

func parse(m map[string]Manifest, reads map[string]ManifestRead, predefined catalogue.PredefinedList) (map[string]catalogue.Manifest, error) {
	out := map[string]catalogue.Manifest{}
	for name, man := range m {
		if len(man.Raw) == 0 {
			return nil, fmt.Errorf("%w: %s (digest %s)", ErrUnfilled, name, man.Digest)
		}
		parsed, err := readManifest(man.Raw, predefined)
		if reads != nil {
			if err != nil {
				reads[name] = ManifestRead{Refused: err.Error()}
			} else {
				reads[name] = ManifestRead{Accepted: true}
			}
		}
		if err == nil {
			out[name] = parsed
		}
	}
	return out, nil
}

func runCase(r Request, c Case, depth string) (CaseVerdict, error) {
	cv := CaseVerdict{Name: c.Name, Manifests: map[string]ManifestRead{}}
	shelf, err := parse(c.Manifests, cv.Manifests, r.Predefined)
	if err != nil {
		return CaseVerdict{}, err
	}
	in := r.Input
	in.Catalogue = shelf
	in.Nodes = slices.Clone(in.Nodes)
	in.Holdings = slices.Clone(in.Holdings)
	for i := range in.Nodes {
		in.Nodes[i].Kept = nil
		if kept := c.Kept[in.Nodes[i].Name]; len(kept) > 0 {
			k, err := parse(kept, nil, r.Predefined)
			if err != nil {
				return CaseVerdict{}, err
			}
			in.Nodes[i].Kept = k
		}
	}
	if r.HoldingsFromClaims {
		in.Holdings = append(in.Holdings, HoldingsOf(shelf, in.Nodes)...)
	}
	if len(r.Machines) == 0 {
		return cv, nil
	}
	cv.Machines = map[string]Machine{}
	for _, node := range r.Machines {
		cv.Machines[node] = machine(in, node, depth, r.Declarations)
	}
	return cv, nil
}

// HoldingsOf is every seat an assigned module claims, held on the node it is assigned to, in node order: the holdings
// of an input that has none of record (the assigner's, mesh-delivery-assigner internal/assign input).
func HoldingsOf(shelf map[string]catalogue.Manifest, nodes []compose.Node) []catalogue.Held {
	var out []catalogue.Held
	sorted := slices.Clone(nodes)
	sort.Slice(sorted, func(i, j int) bool { return sorted[i].Name < sorted[j].Name })
	for _, n := range sorted {
		for _, mod := range n.Assigned {
			for _, cl := range shelf[mod].Claims {
				scope := cl.Scope
				if seat, ok := catalogue.SeatNamed(cl.Name); ok && scope == "" {
					scope = seat.Scope
				}
				out = append(out, catalogue.Held{Claim: cl.Name, Scope: scope, Node: n.Name, Module: mod})
			}
		}
	}
	return out
}

func machine(in compose.Input, node, depth string, declarations bool) Machine {
	if depth == DepthResolve {
		if _, err := compose.Resolve(in, node); err != nil {
			return Machine{Reason: err.Error()}
		}
		return Machine{Composes: true}
	}
	d, problems, err := compose.Compose(in, node)
	if err != nil {
		return Machine{Reason: err.Error()}
	}
	m := Machine{Composes: len(problems) == 0, Problems: problems, Refusals: d.Refusals()}
	if len(problems) > 0 {
		m.Reason = "the node-engine's validator refuses the declaration"
	}
	if declarations {
		m.Declared = pathsOf(d)
	}
	return m
}

// pathsOf is every resource of a declaration that names a path, with its owner, group and mode as declared, sorted by
// path.
func pathsOf(d compose.Declared) []Path {
	var out []Path
	str := func(r map[string]any, key string) string {
		if v, ok := r[key]; ok && v != nil {
			return fmt.Sprint(v)
		}
		return ""
	}
	for _, r := range d.Resources {
		p := str(r, "path")
		if p == "" {
			continue
		}
		out = append(out, Path{Path: p, Kind: str(r, "type"), Owner: str(r, "owner"), Group: str(r, "group"),
			Mode: str(r, "mode"), Module: d.ModuleOf[str(r, "id")]})
	}
	sort.Slice(out, func(i, j int) bool {
		if out[i].Path != out[j].Path {
			return out[i].Path < out[j].Path
		}
		return out[i].Kind < out[j].Kind
	})
	return out
}