package catalogue

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

// The list of predefined keys (novox/hq ADR 0348 §7, design 57 package K2, issue 661).
//
// **A fixed, reviewable list, owned by the build.** Mesh config and node config hold values only for the keys
// in the catalogue's `predefined.json`, at the root of its repository: each key with its type, a description
// including its unit, its validation (enum, minimum and maximum, pattern) and whether it is trusted. A module's
// value may fall back to one of them, of the same type (ADR 0348 §2, §4).
//
// **Read where a manifest is judged, from the tree it is judged in.** A build reads the file at the root of the
// repository at the commit it builds, `module check` at the root of the repository above each manifest, the
// merge gate at the root of the tree under check; each refuses a file that is not exactly a list of keys, and
// judges every manifest it reads against it (ParseManifestWith). Everywhere else — registration, a stored build
// read again — a manifest is judged against the list the mesh published (PublishedPredefined): the newest trunk
// build's of the catalogue, which the controller keeps and loads with its store.

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

// CatalogueRepository is the name of the repository whose list the mesh publishes: the catalogue's, by the name
// a check finds it beside under (internal/builder's check, ADR 0121).
const CatalogueRepository = "mesh-catalog"

// PredefinedKey is one key of the list: its type, its description, its validation and whether it is trusted
// (ADR 0348 §7). It has no default: a module's value falling back to it has its own.
type PredefinedKey struct {
	Type        string   `json:"type"`
	Description string   `json:"description"`
	Enum        []any    `json:"enum,omitempty"`
	Minimum     *float64 `json:"minimum,omitempty"`
	Maximum     *float64 `json:"maximum,omitempty"`
	Pattern     string   `json:"pattern,omitempty"`
	Trusted     bool     `json:"trusted,omitempty"`
}

// PredefinedList is the list by key. Nil is no list at all, which is not the same as an empty one: a value
// naming a key is refused then saying the list is not present.
type PredefinedList map[string]PredefinedKey

// ParsePredefined reads predefined.json strictly: one JSON object of keys, each with exactly the fields of a
// PredefinedKey, and every key judged as a module's config value is (PredefinedProblems). Anything else is
// refused whole, naming each problem — a list half read would let a module fall back to a key nobody reviewed.
func ParsePredefined(raw []byte) (PredefinedList, error) {
	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", PredefinedFile, err)
	}
	if keys == nil {
		return nil, fmt.Errorf("%s is not a JSON object of keys: it says null", PredefinedFile)
	}
	list := PredefinedList{}
	var problems []string
	for _, key := range sortedKeys(keys) {
		decoder := json.NewDecoder(bytes.NewReader(keys[key]))
		decoder.DisallowUnknownFields()
		var k PredefinedKey
		if err := decoder.Decode(&k); err != nil {
			problems = append(problems, fmt.Sprintf("%q is not a predefined key's declaration (type, description, "+
				"enum, minimum, maximum, pattern, trusted): %v", key, err))
			continue
		}
		list[key] = k
	}
	problems = append(problems, PredefinedProblems(list)...)
	if len(problems) > 0 {
		return nil, fmt.Errorf("%s is refused: %s", PredefinedFile, strings.Join(problems, "; "))
	}
	return list, nil
}

// PredefinedProblems is every way a key of the list is declared wrongly, by the rules a module's config value
// is held to (ADR 0348 §4, §7, §11): a usable name that is not placement, a type, a description, validation
// that fits the type, and an object or a list only when trusted.
func PredefinedProblems(list PredefinedList) []string {
	var problems []string
	for _, key := range sortedKeys(list) {
		k := list[key]
		say := func(format string, args ...any) {
			problems = append(problems, fmt.Sprintf("the predefined key %q: ", key)+fmt.Sprintf(format, args...))
		}
		if !settingRef.MatchString("${setting:" + key + "}") {
			say("not a usable key: lower-case letters, digits, dots, dashes and underscores")
			continue
		}
		if meshWords[key] || accountFacts[key] {
			say("%q is placement, which the mesh decides, never a config value (novox/hq ADR 0348 §11)", key)
			continue
		}
		switch k.Type {
		case ConfigNumber, ConfigString, ConfigBoolean:
		case ConfigObject, ConfigList:
			if !k.Trusted {
				say("is %s and not trusted: an object or a list is trusted, \"trusted\": true (novox/hq ADR 0348 §4)", k.Type)
			}
		case "":
			say("no type: say \"type\": number, string or boolean, or object or list when trusted (novox/hq ADR 0348 §4)")
		default:
			say("type %q is none of number, string, boolean, object and list (novox/hq ADR 0348 §4)", k.Type)
		}
		if strings.TrimSpace(k.Description) == "" {
			say("no description: say in a sentence what the value is, including its unit (novox/hq ADR 0348 §7)")
		}
		for _, wrong := range validationProblems(SettingDeclaration{Type: k.Type, Enum: k.Enum, Minimum: k.Minimum,
			Maximum: k.Maximum, Pattern: k.Pattern}) {
			say("%s", wrong)
		}
	}
	return problems
}

// ReadPredefined is the list in predefined.json at a repository's root, and nil with no error when the root
// holds none: a repository other than the catalogue, or the catalogue before the file.
func ReadPredefined(root string) (PredefinedList, error) {
	path := filepath.Join(root, PredefinedFile)
	info, err := os.Lstat(path)
	if errors.Is(err, fs.ErrNotExist) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	if !info.Mode().IsRegular() {
		return nil, fmt.Errorf("%s is %s, not a plain file", path, kindOf(info.Mode()))
	}
	raw, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	return ParsePredefined(raw)
}

// RepositoryRoot is the nearest directory at or above dir holding `.git`: the root of the repository a manifest
// is in, where `module check` reads the list. Empty when none is: a manifest outside a repository is judged
// against no list.
func RepositoryRoot(dir string) string {
	at, err := filepath.Abs(dir)
	if err != nil {
		return ""
	}
	for {
		if _, err := os.Lstat(filepath.Join(at, ".git")); err == nil {
			return at
		}
		up := filepath.Dir(at)
		if up == at {
			return ""
		}
		at = up
	}
}

// PredefinedAbove is the list at the root of the repository above dir (RepositoryRoot), nil when there is no
// repository or it holds no list.
func PredefinedAbove(dir string) (PredefinedList, error) {
	root := RepositoryRoot(dir)
	if root == "" {
		return nil, nil
	}
	return ReadPredefined(root)
}

// Canonical is the list as JSON with its keys sorted: what a build carries and the controller keeps, so one list
// is one text.
func (l PredefinedList) Canonical() ([]byte, error) {
	if l == nil {
		return nil, nil
	}
	return json.Marshal(map[string]PredefinedKey(l))
}

// Keys is the list's keys, sorted.
func (l PredefinedList) Keys() []string {
	out := make([]string, 0, len(l))
	for k := range l {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

// NamesPredefined is whether any value of the manifest falls back to a predefined key.
func (m Manifest) NamesPredefined() bool {
	for _, d := range m.Settings {
		if d.Predefined != "" {
			return true
		}
	}
	return false
}

// publishedPredefined is the list the mesh published, which a manifest is judged against where no tree is read.
var publishedPredefined struct {
	sync.RWMutex
	list PredefinedList
}

// UsePredefined makes list the one a manifest is judged against where no tree is read: what the controller
// loads from its store, and what it keeps when a newer trunk build of the catalogue publishes one. Nil leaves
// the list it has: a store that holds none yet never empties one already loaded.
func UsePredefined(list PredefinedList) {
	if list == nil {
		return
	}
	publishedPredefined.Lock()
	defer publishedPredefined.Unlock()
	publishedPredefined.list = list
}

// PublishedPredefined is the list a manifest is judged against where no tree is read; nil when none is loaded.
func PublishedPredefined() PredefinedList {
	publishedPredefined.RLock()
	defer publishedPredefined.RUnlock()
	return publishedPredefined.list
}

// ReplacePublished sets the published list, nil included, and answers the one it replaced: for a test that
// judges against a list of its own and puts the mesh's back.
func ReplacePublished(list PredefinedList) (was PredefinedList) {
	publishedPredefined.Lock()
	defer publishedPredefined.Unlock()
	was, publishedPredefined.list = publishedPredefined.list, list
	return was
}