package delivery

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

	"git.novox.be/novox/mesh-sdk/go/declaration"
)

// **A node's declared packages, worked out by its engine** (novox/hq ADR 0565 §1, §6; issue 1953): the derivation and
// the comparison of the node-engine's state `packages` (EnginePackagesState, layout DeclaredPackages), so the engine
// that writes the key, the node seat's verb that compares it with the controller's mirror, and any reader work them out
// one way. The controller's own copy of the derivation (mesh-controller internal/inventory DeclaredPackagesValue) is
// not changed (ADR 0547 §1) and ends with its lease.

// EnginePackagesRead is the engine's state `packages` as a reader names it in `reads`: the node-engine's manifest is
// mesh-host's, so its bucket is mesh-host_packages, read as disk-load reads mesh-host.data (EngineDataRead).
const EnginePackagesRead = "mesh-host." + EnginePackagesState

// DeclaredPackagesOf is a node's key of `packages` from the compositions its engine composed for the node's wants:
// each resource of type package, by its name and whether it is declared absent, with the modules that declare it so,
// in the mirror's layout and order (names sorted, absent after present, modules sorted). A resource's module is the
// one it names, else its composition's, else the guess from its id (declaration.ModuleGuess); a package of no module
// lists none.
func DeclaredPackagesOf(node string, compositions []Composed) (DeclaredPackages, error) {
	by := map[packageKey]map[string]bool{}
	for _, c := range compositions {
		for _, raw := range c.Resources {
			var r struct {
				ID      string `json:"id"`
				Type    string `json:"type"`
				Package string `json:"package"`
				Absent  bool   `json:"absent"`
				Module  string `json:"module"`
			}
			if err := json.Unmarshal(raw, &r); err != nil {
				return DeclaredPackages{}, fmt.Errorf("delivery: a resource of %s's composition %q is not readable: %w", node, c.Module, err)
			}
			if r.Type != "package" || r.Package == "" {
				continue
			}
			k := packageKey{r.Package, r.Absent}
			if by[k] == nil {
				by[k] = map[string]bool{}
			}
			module := r.Module
			if module == "" {
				module = c.Module
			}
			if module == "" {
				module, _ = declaration.ModuleGuess(r.ID)
			}
			if module != "" {
				by[k][module] = true
			}
		}
	}
	v := DeclaredPackages{Node: node, Packages: []PackageDeclared{}}
	for _, k := range sortedPackageKeys(by) {
		modules := make([]string, 0, len(by[k]))
		for m := range by[k] {
			modules = append(modules, m)
		}
		sort.Strings(modules)
		v.Packages = append(v.Packages, PackageDeclared{Package: k.name, Modules: modules, Absent: k.absent})
	}
	return v, nil
}

// PackageDifference is one package two declarations of a node hold differently: the modules each side declares it
// with (present, or absent when Absent), none on a side that does not hold it.
type PackageDifference struct {
	Package string   `json:"package"`
	Absent  bool     `json:"absent"`
	Engine  []string `json:"engine"`
	Mirror  []string `json:"mirror"`
}

// DiffDeclaredPackages is every package the engine's key and the controller's mirror hold differently for one node, in
// the layout's order: what the node seat's verb packages answers until the lease write (ADR 0565 §6). Empty when they
// agree.
func DiffDeclaredPackages(engine, mirror DeclaredPackages) []PackageDifference {
	index := func(d DeclaredPackages) map[packageKey][]string {
		out := map[packageKey][]string{}
		for _, p := range d.Packages {
			out[packageKey{p.Package, p.Absent}] = append([]string{}, p.Modules...)
		}
		return out
	}
	e, m := index(engine), index(mirror)
	union := map[packageKey]bool{}
	for k := range e {
		union[k] = true
	}
	for k := range m {
		union[k] = true
	}
	out := []PackageDifference{}
	for _, k := range sortedPackageKeys(union) {
		em, inE := e[k]
		mm, inM := m[k]
		if inE && inM && slices.Equal(em, mm) {
			continue
		}
		if em == nil {
			em = []string{}
		}
		if mm == nil {
			mm = []string{}
		}
		out = append(out, PackageDifference{Package: k.name, Absent: k.absent, Engine: em, Mirror: mm})
	}
	return out
}

// packageKey is a package as the layout tells it apart: its name, and whether it is declared absent.
type packageKey struct {
	name   string
	absent bool
}

// sortedPackageKeys is the keys of m by name, absent after present.
func sortedPackageKeys[V any](m map[packageKey]V) []packageKey {
	keys := make([]packageKey, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Slice(keys, func(i, j int) bool {
		if keys[i].name != keys[j].name {
			return keys[i].name < keys[j].name
		}
		return !keys[i].absent && keys[j].absent
	})
	return keys
}