package gonexapp

import (
	"encoding/json"
	"fmt"
	"html/template"
	"io/fs"
	"maps"
	"strings"
)

// Phrases is one ExApp's merged Phrase set.
// English is the complete set. A module set is merged with Merge;
// a repeated id uses the set added later.
// The page script receives this set. Library chrome is not included.
type Phrases struct {
	en map[string]string
	de map[string]string
}

// PhrasesFromFS reads i18n/en.json and i18n/de.json.
// Each file is one JSON object of id → text.
func PhrasesFromFS(fsys fs.FS) (Phrases, error) {
	en, err := fs.ReadFile(fsys, "i18n/en.json")
	if err != nil {
		return Phrases{}, fmt.Errorf("read i18n/en.json: %w", err)
	}
	de, err := fs.ReadFile(fsys, "i18n/de.json")
	if err != nil {
		return Phrases{}, fmt.Errorf("read i18n/de.json: %w", err)
	}
	return ParsePhrases(en, de)
}

// ParsePhrases reads an English object and a German object.
func ParsePhrases(en, de []byte) (Phrases, error) {
	enMap, err := decodePhraseFile(en)
	if err != nil {
		return Phrases{}, fmt.Errorf("en: %w", err)
	}
	deMap, err := decodePhraseFile(de)
	if err != nil {
		return Phrases{}, fmt.Errorf("de: %w", err)
	}
	return Phrases{en: enMap, de: deMap}, nil
}

func decodePhraseFile(raw []byte) (map[string]string, error) {
	if len(strings.TrimSpace(string(raw))) == 0 {
		return map[string]string{}, nil
	}
	var m map[string]string
	if err := json.Unmarshal(raw, &m); err != nil {
		return nil, err
	}
	if m == nil {
		m = map[string]string{}
	}
	return m, nil
}

// Merge returns the sets combined in order.
// A repeated id uses the text from the set added later.
func Merge(sets ...Phrases) Phrases {
	out := Phrases{en: map[string]string{}, de: map[string]string{}}
	for _, set := range sets {
		maps.Copy(out.en, set.en)
		maps.Copy(out.de, set.de)
	}
	return out
}

func (p Phrases) has(code string) bool {
	switch code {
	case "en":
		return p.en != nil
	case "de":
		return p.de != nil
	default:
		return false
	}
}

func (p Phrases) texts(lang string) map[string]string {
	if lang == "de" {
		return p.de
	}
	return p.en
}

// Sentence is the finished text for lang.
// A missing text for that language uses the English text.
// An id missing from English is the id.
// A hole with no value stays visible as {name}.
// The result is plain text; the caller escapes it when writing HTML.
func (p Phrases) Sentence(lang, id string, holes map[string]string) string {
	lang = matchLanguage(lang, p.has)
	if text, ok := phraseText(p.texts(lang), id); ok {
		return fillHoles(text, holes)
	}
	if lang != "en" {
		if text, ok := phraseText(p.en, id); ok {
			return fillHoles(text, holes)
		}
	}
	return id
}

func phraseText(m map[string]string, id string) (string, bool) {
	text, ok := m[id]
	if !ok || text == "" {
		return "", false
	}
	return text, true
}

// resolved is the map the page script sees: one text per id for lang,
// with English filling gaps. Ids missing from English are omitted.
func (p Phrases) resolved(lang string) map[string]string {
	lang = matchLanguage(lang, p.has)
	out := map[string]string{}
	for id, text := range p.en {
		if text == "" {
			continue
		}
		out[id] = text
	}
	if lang == "en" {
		return out
	}
	for id, text := range p.de {
		if text == "" {
			continue
		}
		if _, ok := phraseText(p.en, id); !ok {
			continue
		}
		out[id] = text
	}
	return out
}

// Script defines exappPhrase for the page, from this set only.
func (p Phrases) Script(lang string) template.HTML {
	raw, err := json.Marshal(p.resolved(lang))
	if err != nil {
		raw = []byte("{}")
	}
	return template.HTML("<script>\n" + phraseRuntimeJS + "\nwindow.exappPhrase = exappPhraseMap(" + string(raw) + ");\n</script>")
}

const phraseRuntimeJS = `function exappFill(text, holes) {
  if (!holes || text.indexOf("{") < 0) return text;
  var out = "";
  for (var i = 0; i < text.length; i++) {
    if (text.charAt(i) !== "{") { out += text.charAt(i); continue; }
    var end = text.indexOf("}", i + 1);
    if (end < 0) { out += text.charAt(i); continue; }
    var name = text.slice(i + 1, end);
    if (Object.prototype.hasOwnProperty.call(holes, name)) {
      out += String(holes[name]);
      i = end;
      continue;
    }
    out += text.charAt(i);
  }
  return out;
}
function exappPhraseMap(map) {
  return function (id, holes) {
    var text = Object.prototype.hasOwnProperty.call(map, id) ? map[id] : String(id);
    return exappFill(text, holes);
  };
}`

// FillScript replaces English source after load and refreshes Fold from the
// visible item name. It does not parse Phrase text as HTML.
// App navigation includes it. A page the ExApp renders itself places Script
// in the head and FillScript at the end of the body.
func FillScript() template.HTML {
	return phraseFillScript
}

// phraseFillScript replaces English source after load and refreshes Fold
// from the visible item name. It does not parse Phrase text as HTML.
const phraseFillScript = template.HTML(`<script>
(function () {
  function holesOf(el) {
    var raw = el.getAttribute("data-phrase-holes");
    if (!raw) return null;
    try { return JSON.parse(raw); } catch (e) { return null; }
  }
  function apply(el, attr, set) {
    var id = el.getAttribute(attr);
    if (!id || typeof exappPhrase !== "function") return;
    set(exappPhrase(id, holesOf(el)));
  }
  document.querySelectorAll("[data-phrase],[data-phrase-placeholder],[data-phrase-title],[data-phrase-aria-label]").forEach(function (el) {
    apply(el, "data-phrase", function (t) { el.textContent = t; });
    apply(el, "data-phrase-placeholder", function (t) { el.placeholder = t; });
    apply(el, "data-phrase-title", function (t) { el.title = t; });
    apply(el, "data-phrase-aria-label", function (t) { el.setAttribute("aria-label", t); });
  });
  document.querySelectorAll("button.fold").forEach(function (btn) {
    var pattern = btn.getAttribute("data-fold");
    var entry = btn.closest(".app-navigation-entry");
    var name = entry ? entry.querySelector(".app-navigation-entry__name") : null;
    if (!pattern || !name || typeof exappFill !== "function") return;
    btn.setAttribute("aria-label", exappFill(pattern, { label: name.textContent }));
  });
})();
</script>`)