package lexicon

import (
	"errors"
	"io/fs"
	"os"
	"strings"
	"unicode/utf8"

	"github.com/prosolis/dreamdict/dictionary"
)

// DreamDict is a read-only handle on a built dict.db — one SQLite file holding
// English, French, European Portuguese, Spanish and Mandarin.
//
// It is a second database beside petal.db and is never written to: the file is
// built by DreamDict's own import CLI a few times a year, and Petal only reads
// it. That is what makes importing the package the right shape rather than
// running DreamDict as a service — a hover gloss should not depend on a second
// process being up, still less on one reachable across a VPN.
type DreamDict struct {
	d *dictionary.Dictionary
}

// OpenDreamDict opens dict.db read-only.
//
// A missing file returns (nil, nil), not an error. Petal is expected to run
// without dict.db — a laptop checkout has never had one, and the zh pair does
// not need one — so "the file isn't there" is a deployment state the caller
// handles by carrying on. A file that is *present but unusable* (corrupt, or
// never imported) does return an error, because that one is a mistake someone
// should hear about.
func OpenDreamDict(path string) (*DreamDict, error) {
	if strings.TrimSpace(path) == "" {
		return nil, nil
	}
	if _, err := os.Stat(path); err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return nil, nil
		}
		return nil, err
	}
	d, err := dictionary.NewReadOnly(path)
	if err != nil {
		return nil, err
	}
	return &DreamDict{d: d}, nil
}

// Close releases the dict.db handle. Safe on a nil DreamDict, so a caller that
// never got one can defer it unconditionally.
func (dd *DreamDict) Close() error {
	if dd == nil {
		return nil
	}
	return dd.d.Close()
}

// Langs returns the language codes dict.db was built with, so startup can log
// what it actually got rather than what it hoped for.
func (dd *DreamDict) Langs() []string { return dictionary.Langs() }

// dreamProvider serves one writer: English lookups from dict.db, glossed into
// native. The struct is a value, created per request by [Set.For] — it holds no
// state beyond the shared handle and the language to translate into.
type dreamProvider struct {
	dict   *DreamDict
	native string // the writer's language, e.g. "pt-PT"
}

// maxEtymology caps the free-form Wiktionary etymology. It is the one field
// with no natural length: some entries are a clause, some are four paragraphs
// tracing a word through three dead languages. The popover wants a line.
const maxEtymology = 220

// Lookup fills a Result from dict.db.
//
// The word is de-inflected with the same [candidates] walk the embedded
// datasets use, because dict.db stores headwords: "running" has no definitions
// row of its own. The first candidate that *has* definitions becomes the
// headword every other field is then read from, so a single popover never
// mixes "running"'s frequency with "run"'s definitions.
//
// The gloss is walked separately. A word can be absent from the definitions
// table and still have a translation (and vice versa), and the hover tooltip
// asks for the gloss alone — so tying it to the definition headword would lose
// glosses for no benefit.
func (p dreamProvider) Lookup(word string) (Result, error) {
	res := Result{Word: word, Definitions: []Meaning{}, Synonyms: []string{}, Difficulty: unknownDifficulty}
	norm := strings.ToLower(strings.TrimSpace(word))
	if norm == "" {
		return res, nil
	}

	head := norm
	for _, c := range candidates(norm) {
		defs, err := p.dict.d.Define(c, langEN)
		if err != nil {
			return Result{}, err
		}
		if len(defs) == 0 {
			continue
		}
		head = c
		for _, d := range defs {
			// DreamDict orders by source priority, so the curated senses
			// (WordNet, WOLF) are already ahead of the Wiktionary tail — taking
			// the first few is taking the best few.
			res.Definitions = append(res.Definitions, Meaning{PartOfSpeech: d.POS, Definition: d.Gloss})
			if len(res.Definitions) >= maxDefinitions {
				break
			}
		}
		break
	}

	gloss, err := p.translate(norm)
	if err != nil {
		return Result{}, err
	}
	res.Gloss = gloss

	syns, err := p.dict.d.Synonyms(head, langEN)
	if err != nil {
		return Result{}, err
	}
	if len(syns) > maxSynonyms {
		syns = syns[:maxSynonyms]
	}
	res.Synonyms = append(res.Synonyms, syns...)

	prons, err := p.dict.d.Pronunciation(head, langEN)
	if err != nil {
		return Result{}, err
	}
	res.Phonetic = pickIPA(prons)

	if res.Frequency, err = p.dict.d.Frequency(head, langEN); err != nil {
		return Result{}, err
	}
	if res.Difficulty, err = p.dict.d.Difficulty(head, langEN); err != nil {
		return Result{}, err
	}
	ety, err := p.dict.d.Etymology(head, langEN)
	if err != nil {
		return Result{}, err
	}
	res.Etymology = trimEtymology(ety)

	return res, nil
}

// Gloss returns the writer's-language translation alone — the hover tooltip's
// fast path, one indexed query per candidate form and nothing else.
func (p dreamProvider) Gloss(word string) (GlossResult, error) {
	norm := strings.ToLower(strings.TrimSpace(word))
	if norm == "" {
		return GlossResult{Word: word}, nil
	}
	gloss, err := p.translate(norm)
	if err != nil {
		return GlossResult{}, err
	}
	return GlossResult{Word: word, Gloss: gloss}, nil
}

// maxGlossSenses caps how many translations are strung together. One is often
// too thin to disambiguate; the whole list is a wall of words in a tooltip.
const maxGlossSenses = 3

// translate walks the candidate forms and returns the first that has an
// equivalent in the writer's language, joined into one line.
//
// It asks for Equivalents rather than Translate on the strength of measuring
// both against the real dict.db: Wiktionary's en→pt-PT translation table
// answers for 17% of the 2,000 commonest English words, and the shared-synset
// path answers for 62%. The plan assumed Translate would do — the database
// says otherwise, and a gloss that is absent five times out of six is not a
// gloss. Equivalents falls back to Translate internally, so nothing is lost.
//
// A language dict.db was built without simply has no rows, so this returns "" —
// which is exactly what an unglossed word returns, and the popover already
// renders that case. Spanish today is precisely this: supported by DreamDict,
// absent from the deployed database until it is rebuilt.
func (p dreamProvider) translate(norm string) (string, error) {
	for _, c := range candidates(norm) {
		trs, err := p.dict.d.Equivalents(c, langEN, p.native)
		if err != nil {
			return "", err
		}
		if len(trs) == 0 {
			continue
		}
		if len(trs) > maxGlossSenses {
			trs = trs[:maxGlossSenses]
		}
		return strings.Join(trs, "; "), nil
	}
	return "", nil
}

// pickIPA chooses what to show beside the read-aloud button. IPA is the only
// form worth showing a learner — CMU's "IH0 F EH1 M ER0 AH0 L" is a machine
// format, and printing it would be noise dressed up as help. If there's no IPA,
// there's no phonetic line.
func pickIPA(prons []dictionary.Pronunciation) string {
	for _, p := range prons {
		if strings.EqualFold(p.Format, "ipa") && strings.TrimSpace(p.Value) != "" {
			return strings.Trim(strings.TrimSpace(p.Value), "/[]")
		}
	}
	return ""
}

// trimEtymology cuts Wiktionary's prose down to a line, preferring to stop at a
// sentence boundary so the result reads as a finished thought rather than a
// truncation.
func trimEtymology(text string) string {
	text = strings.Join(strings.Fields(text), " ")
	if utf8.RuneCountInString(text) <= maxEtymology {
		return text
	}
	// Counted and cut in runes, not bytes. An etymology is the one field that
	// is *mostly* not English — ἐφήμερος, ephemerus, 短暫 — and a byte slice
	// through the middle of one of those characters is invalid UTF-8 in the
	// JSON response.
	cut := string([]rune(text)[:maxEtymology-1])
	// Stop at a sentence when one ends late enough to be worth keeping. An
	// early full stop ("From Latin. …") is not a summary, it's a discarded
	// paragraph, so that case falls through to the word-boundary cut.
	if i := strings.LastIndex(cut, ". "); i > len(cut)/2 {
		return cut[:i+1]
	}
	if i := strings.LastIndex(cut, " "); i > 0 {
		cut = cut[:i]
	}
	return cut + "…"
}