// Command predefined refuses a change to predefined.json that removes a key a module still names (novox/hq ADR
// 0348 clause 7, design 57 package K2, issue 661).
//
// Mesh config and node config hold values only for the keys on the catalogue's list of predefined keys, at the
// root of the repository; a module's config value may fall back to one, `"predefined": "<key>"`. A key removed
// while a manifest still names it would leave that module falling back to nothing: the controller refuses its
// build then, at the next merge that touches it. So the removal is refused here, in the pull request that makes
// it, naming each module that names the key.
//
// **What it cannot know.** Whether a key still holds a value at the mesh or a node is mesh-config's to say (design
// 57 package K3): it holds the values, and the catalogue's check reads no store. Until mesh-config refuses that
// itself, removing a key nobody names is let through here, and said.
//
// The list it compares with is the trunk's at the merge base, given with -base; without one, nothing was removed.
// The controller the mesh runs reads the list itself (type, validation, every manifest against it) in the
// module check; this check reads only its keys.
//
//	go run . [-base <the trunk's predefined.json>] <catalogue root>
//
// Exits 1 on a finding.
package main

import (
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

// File is the list's file at the root of the catalogue.
const File = "predefined.json"

// Keys is the keys of a list, read as a JSON object; an absent file has none.
func Keys(path string) (map[string]bool, error) {
	raw, err := os.ReadFile(path)
	if errors.Is(err, fs.ErrNotExist) {
		return map[string]bool{}, nil
	}
	if err != nil {
		return nil, err
	}
	var keys map[string]json.RawMessage
	if err := json.Unmarshal(raw, &keys); err != nil {
		return nil, fmt.Errorf("%s is not a JSON object of keys: %w", path, err)
	}
	out := map[string]bool{}
	for k := range keys {
		out[k] = true
	}
	return out, nil
}

// Named is, per predefined key, the modules whose manifests name it: under `config`, or its alias `settings`.
func Named(root string) (map[string][]string, error) {
	manifests, err := filepath.Glob(filepath.Join(root, "modules", "*", "module.json"))
	if err != nil {
		return nil, err
	}
	sort.Strings(manifests)
	named := map[string][]string{}
	for _, path := range manifests {
		raw, err := os.ReadFile(path)
		if err != nil {
			return nil, err
		}
		var m struct {
			Module   string                     `json:"module"`
			Config   map[string]json.RawMessage `json:"config"`
			Settings map[string]json.RawMessage `json:"settings"`
		}
		if err := json.Unmarshal(raw, &m); err != nil {
			return nil, fmt.Errorf("%s: %w", path, err)
		}
		for _, declared := range []map[string]json.RawMessage{m.Config, m.Settings} {
			for _, d := range declared {
				var value struct {
					Predefined string `json:"predefined"`
				}
				if json.Unmarshal(d, &value) == nil && value.Predefined != "" {
					named[value.Predefined] = append(named[value.Predefined], m.Module)
				}
			}
		}
	}
	return named, nil
}

// Removed is each key the base list holds and the tree's does not, with the modules still naming it; a removed
// key nobody names is answered with none.
func Removed(base, tree map[string]bool, named map[string][]string) map[string][]string {
	out := map[string][]string{}
	for k := range base {
		if !tree[k] {
			out[k] = named[k]
		}
	}
	return out
}

func main() {
	basePath := flag.String("base", "", "the trunk's predefined.json at the merge base")
	flag.Parse()
	if flag.NArg() != 1 {
		fmt.Fprintln(os.Stderr, "usage: predefined [-base <the trunk's predefined.json>] <catalogue root>")
		os.Exit(2)
	}
	root := flag.Arg(0)
	tree, err := Keys(filepath.Join(root, File))
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
	if *basePath == "" {
		fmt.Printf("%s: %d key(s); no trunk list given, so none was removed\n", File, len(tree))
		return
	}
	base, err := Keys(*basePath)
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
	named, err := Named(root)
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
	removed := Removed(base, tree, named)
	keys := make([]string, 0, len(removed))
	for k := range removed {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	failed := false
	for _, k := range keys {
		if modules := removed[k]; len(modules) > 0 {
			failed = true
			fmt.Printf("%s: the key %q is removed and still named by %s: move each off it first (novox/hq ADR 0348 "+
				"clause 7)\n", File, k, strings.Join(modules, ", "))
		} else {
			fmt.Printf("%s: the key %q is removed and no module names it; whether the mesh or a node still holds a "+
				"value for it is mesh-config's to refuse, not this check's\n", File, k)
		}
	}
	if failed {
		os.Exit(1)
	}
	fmt.Printf("%s: %d key(s), none removed that a module names\n", File, len(tree))
}