// Package manifest reads and writes the two manifests of the model.
//
// The suite manifest declares three things: the language the suite's rules are
// written in, its live and retired topics, and its live and retired rule
// prefixes together with the paths of their files. The tool knows no topic and
// no prefix in advance — that whole list arrives from here.
//
// Both manifests are data the tool edits, so both are decoded into structs and
// written back out of them. They carry no comments: a file a machine rewrites
// cannot keep a comment through the round trip, and pretending otherwise costs
// the comment on a day nobody is watching. What a topic is for is said in the
// documents next to the manifest, which no command touches.
//
// Because a write goes out of the structs, a key the tool does not know would
// disappear on the next edit. So it does not write at all while one is there:
// a refusal naming the key is the only outcome that neither loses it nor hides
// it.
package manifest

import (
	"bytes"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"github.com/BurntSushi/toml"
)

// Name is the name of a suite manifest. Which of the two manifests lies next
// to you tells you where you are, and both start with a dot for the same
// reason: a manifest is data the tool writes, not a document of the repository,
// and it sits with the rest of the service files rather than among the
// conventions themselves.
const Name = ".conventions-suite.toml"

// DefaultLanguageCode is the suite's natural language when the manifest says
// nothing about it. The key is optional on purpose: the vocabulary lives in the
// binary, and making every suite declare what is already implied buys nothing.
const DefaultLanguageCode = "ru"

// Language is the [language] section: the version of the conventions language,
// the natural language its words are written in, and the two documents about
// it. The full description stays with the author of the suite, the short one
// travels into the copy.
//
// Source is where those two documents live. Empty means the suite itself, which
// is where they lie while the specification of the language has no repository
// of its own; once it moves out, the same key names it without anything else
// changing — the vocabulary is picked by version and code either way.
type Language struct {
	Version     int    `toml:"version"`
	Lang        string `toml:"lang,omitempty"`
	Source      string `toml:"source,omitempty"`
	Description string `toml:"description,omitempty"`
	Reading     string `toml:"reading,omitempty"`
}

// Section is a part of the manifest split into a live and a retired half.
// Retired entries are kept rather than deleted: a topic name and a rule prefix
// live on in foreign repositories, and neither may ever be reused.
type Section struct {
	Live    map[string]string `toml:"live,omitempty"`
	Retired map[string]string `toml:"retired,omitempty"`
}

// Add puts an entry into the live half, making the map if there is none.
func (s *Section) Add(key, value string) {
	if s.Live == nil {
		s.Live = make(map[string]string)
	}
	s.Live[key] = value
}

// Retire moves an entry out of the live half into the retired one. A name is
// never deleted and never reissued: it lives on in foreign repositories, and a
// name handed out twice starts pointing at something else there.
func (s *Section) Retire(key, note string) {
	delete(s.Live, key)
	if s.Retired == nil {
		s.Retired = make(map[string]string)
	}
	s.Retired[key] = note
}

// Manifest is a parsed suite manifest.
type Manifest struct {
	Language Language `toml:"language"`
	Topics   Section  `toml:"topics,omitempty"`
	Prefixes Section  `toml:"prefixes,omitempty"`

	// Path is where the manifest was read from.
	Path string `toml:"-"`
	// Undecoded lists keys the tool does not know. A typo in the manifest
	// would otherwise pass in silence, and it costs a subscription or a
	// whole file.
	Undecoded []string `toml:"-"`
}

// Load reads the suite manifest from directory root.
func Load(root string) (*Manifest, error) {
	path := filepath.Join(root, Name)
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("reading the suite manifest: %w", err)
	}

	var m Manifest
	meta, err := toml.Decode(string(data), &m)
	if err != nil {
		return nil, fmt.Errorf("parsing %s: %w", path, err)
	}
	m.Path = path
	for _, key := range meta.Undecoded() {
		m.Undecoded = append(m.Undecoded, key.String())
	}
	sort.Strings(m.Undecoded)

	if m.Language.Lang == "" {
		m.Language.Lang = DefaultLanguageCode
	}
	return &m, nil
}

// Save writes the manifest back to where it was read from.
func (m *Manifest) Save() error {
	return save(m.Path, m, m.Undecoded)
}

// save encodes a manifest and puts it in place.
func save(path string, value any, undecoded []string) error {
	if len(undecoded) > 0 {
		return fmt.Errorf("%s holds %s the tool does not know (%s); a write goes out of what the tool understands, so the key would be dropped — fix the spelling first",
			path, plural(len(undecoded), "key"), strings.Join(undecoded, ", "))
	}
	var b bytes.Buffer
	enc := toml.NewEncoder(&b)
	enc.Indent = ""
	if err := enc.Encode(value); err != nil {
		return fmt.Errorf("encoding %s: %w", path, err)
	}
	return os.WriteFile(path, b.Bytes(), 0o644)
}

func plural(n int, noun string) string {
	if n == 1 {
		return fmt.Sprintf("%d %s", n, noun)
	}
	return fmt.Sprintf("%d %ss", n, noun)
}

// Find walks up from start looking for a directory that holds a suite
// manifest, so that `convy suite check` works from any subdirectory of a suite.
func Find(start string) (string, error) {
	return findUp(start, Name)
}

// findUp walks up from start looking for a directory holding the named file.
func findUp(start, name string) (string, error) {
	dir, err := filepath.Abs(start)
	if err != nil {
		return "", err
	}
	for {
		if _, err := os.Stat(filepath.Join(dir, name)); err == nil {
			return dir, nil
		}
		parent := filepath.Dir(dir)
		if parent == dir {
			return "", ErrNotFound
		}
		dir = parent
	}
}

// ErrNotFound means there is no suite manifest here or above.
var ErrNotFound = errors.New("suite manifest not found")

// LivePrefixes lists the live prefixes in an order stable between runs: the
// output of a check must not depend on map iteration.
func (m *Manifest) LivePrefixes() []string {
	return sortedKeys(m.Prefixes.Live)
}

// LiveTopics lists the live topics in a stable order.
func (m *Manifest) LiveTopics() []string {
	return sortedKeys(m.Topics.Live)
}

// PrefixOf returns the prefix declared for a file, if there is one. Paths are
// compared in slash form, the way the manifest writes them.
func (m *Manifest) PrefixOf(path string) (string, bool) {
	want := filepath.ToSlash(path)
	for prefix, declared := range m.Prefixes.Live {
		if filepath.ToSlash(declared) == want {
			return prefix, true
		}
	}
	return "", false
}

// PathOf returns the path declared for a live prefix.
func (m *Manifest) PathOf(prefix string) (string, bool) {
	path, ok := m.Prefixes.Live[prefix]
	return path, ok
}

// TopicLive reports whether the topic is declared among the live ones.
func (m *Manifest) TopicLive(topic string) bool {
	_, ok := m.Topics.Live[topic]
	return ok
}

// TopicRetired reports whether the topic is listed among the retired ones.
func (m *Manifest) TopicRetired(topic string) bool {
	_, ok := m.Topics.Retired[topic]
	return ok
}

// PrefixRetired reports whether the prefix is listed among the retired ones.
func (m *Manifest) PrefixRetired(prefix string) bool {
	_, ok := m.Prefixes.Retired[prefix]
	return ok
}

// ValidPrefix checks the shape of a prefix: four uppercase Latin letters. The
// letter X in first position is reserved for consuming repositories, and the
// suite never takes it.
func ValidPrefix(prefix string) error {
	if len(prefix) != 4 {
		return fmt.Errorf("prefix %q is not four letters", prefix)
	}
	for _, r := range prefix {
		if r < 'A' || r > 'Z' {
			return fmt.Errorf("prefix %q holds a character that is not an uppercase Latin letter", prefix)
		}
	}
	if strings.HasPrefix(prefix, "X") {
		return fmt.Errorf("prefix %q starts with X, a letter reserved for the local rules of consumers", prefix)
	}
	return nil
}

func sortedKeys(m map[string]string) []string {
	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	return keys
}