function getCurrentWord(s, cursor) {
  return s.substring(s.lastIndexOf(' ', cursor - 1) + 1, cursor);
}

function mySplice(s, idx, del, n) {
  return s.substring(0, idx) + n + s.substring(idx + del);
}

function suggestionPosition(el) {
  // el.parentNode is ul#tags-suggestion, which include a template. That's why
  // a -1 is needed here.
  const idx = [...el.parentNode.children].indexOf(el);
  return idx <= 0 ? null : idx - 1;
}

function currentSuggestionElement(idx) {
  if (idx === null)
    return null;
  return document.querySelector("#tags-suggestions").children[idx + 1];
}

document.addEventListener('alpine:init', () => {
  Alpine.data('tagsSuggestions', () => ({
    suggestions: [],
    currentSuggestion: null,
    inputCursor: 0,
    query: '',

    reset() {
      this.suggestions = [];
      this.currentSuggestion = null;
      this.inputCursor = 0;
      this.query = '';
    },

    async fetchSuggestions(evt) {
      this.inputCursor = evt.target.selectionStart;
      this.query = getCurrentWord(evt.target.value, this.inputCursor);
      if (!this.query) {
        this.reset();
        return;
      }

      const params = new URLSearchParams({q: this.query});
      const response = await fetch(`${endpoints.search}?${params}`);

      if (!response.ok) {
        this.reset();
        return;
      }

      this.suggestions = await response.json();
    },

    completeSuggestion(evt) {
      if (this.currentSuggestion === null)
        return;

      const value = this.$refs.tags.value;
      const pos = this.inputCursor - this.query.length;
      const tag = this.suggestions[this.currentSuggestion].display;

      this.$refs.tags.value = mySplice(value, pos, this.query.length,
        tag + ' ');
      this.reset();
      this.$refs.tags.focus();

      // Don't switch focus if we're completing after a Tab press.
      if (evt.type === "keydown" && evt.keyCode === 9)
        evt.preventDefault();
    },

    selectCurrentSuggestion(evt) {
      this.currentSuggestion = suggestionPosition(evt.currentTarget);
      this.completeSuggestion(evt);
    },

    setCurrentSuggestion(evt, amount = 0) {
      currentSuggestionElement(this.currentSuggestion)
        ?.classList.remove("suggestion-hover");

      if (evt === 'mouseenter')
        this.currentSuggestion = suggestionPosition(evt.currentTarget);
      else {
        const len = this.suggestions.length;
        let cur = this.currentSuggestion;

        if (cur === null)
          cur = amount > 0 ? -1 : amount < 0 ? len : 0;
        this.currentSuggestion = (cur + amount + len) % len;
      }

      currentSuggestionElement(this.currentSuggestion)
        ?.classList.add("suggestion-hover");
    }
  }));
});