// Per-token tag autocomplete for comma-separated tag inputs, shared by the
// upload and manage pages. Suggestions come from /tags.json (regenerated on
// every build), so new tags appear on the next load. Only the token after the
// last comma is completed; earlier tags in the field are left untouched.
//
// Usage: add data-tagcomplete to an <input>, or call TagComplete.attach(input)
// for inputs created dynamically. TagComplete.invalidate() drops the cached
// tag list after an edit that may have introduced new tags.
(function () {
  let tags = null; // cached list of tag names
  let inflight = null;

  const menu = document.createElement("div");
  menu.className = "tagac-menu";
  menu.style.display = "none";
  menu.setAttribute("role", "listbox");
  document.body.appendChild(menu);

  let items = []; // currently shown suggestions
  let sel = -1; // highlighted index

  function loadTags() {
    if (tags) return Promise.resolve(tags);
    if (inflight) return inflight;
    inflight = fetch("/tags.json", { headers: { Accept: "application/json" } })
      .then((r) => (r.ok ? r.json() : []))
      .then((list) => {
        tags = (list || []).map((t) => t.tag);
        return tags;
      })
      .catch(() => {
        tags = [];
        return tags;
      });
    return inflight;
  }

  // The token being typed is the text after the last comma.
  function lastToken(value) {
    return value.slice(value.lastIndexOf(",") + 1).replace(/^\s+/, "");
  }

  function replaceLastToken(value, tag) {
    const i = value.lastIndexOf(",");
    const head = i < 0 ? "" : value.slice(0, i + 1) + " ";
    return head + tag + ", ";
  }

  function presentTags(value) {
    return value
      .split(",")
      .map((s) => s.trim().toLowerCase())
      .filter(Boolean);
  }

  function hide() {
    menu.style.display = "none";
    sel = -1;
    items = [];
  }

  function highlight() {
    [...menu.children].forEach((c, i) => c.classList.toggle("sel", i === sel));
    if (sel >= 0 && menu.children[sel]) {
      menu.children[sel].scrollIntoView({ block: "nearest" });
    }
  }

  function render(input) {
    const token = lastToken(input.value).toLowerCase();
    if (!token) {
      hide();
      return;
    }
    const present = new Set(presentTags(input.value));
    items = (tags || [])
      .filter((t) => t.toLowerCase().includes(token) && !present.has(t.toLowerCase()))
      .slice(0, 8);
    if (items.length === 0) {
      hide();
      return;
    }
    sel = 0;
    menu.innerHTML = "";
    items.forEach((t, idx) => {
      const row = document.createElement("div");
      row.className = "tagac-item" + (idx === 0 ? " sel" : "");
      row.setAttribute("role", "option");
      row.textContent = t;
      // mousedown (not click) so it fires before the input's blur.
      row.addEventListener("mousedown", (e) => {
        e.preventDefault();
        choose(input, idx);
      });
      menu.appendChild(row);
    });
    const r = input.getBoundingClientRect();
    menu.style.left = window.scrollX + r.left + "px";
    menu.style.top = window.scrollY + r.bottom + "px";
    menu.style.width = r.width + "px";
    menu.style.display = "block";
  }

  function choose(input, idx) {
    if (idx < 0 || idx >= items.length) return;
    input.value = replaceLastToken(input.value, items[idx]);
    hide();
    input.focus();
    input.dispatchEvent(new Event("input", { bubbles: true }));
  }

  function attach(input) {
    if (!input || input.dataset.tagacBound) return;
    input.dataset.tagacBound = "1";
    input.setAttribute("autocomplete", "off");
    input.addEventListener("focus", () => loadTags().then(() => render(input)));
    input.addEventListener("input", () => loadTags().then(() => render(input)));
    input.addEventListener("keydown", (e) => {
      if (menu.style.display === "none" || items.length === 0) return;
      if (e.key === "ArrowDown") {
        e.preventDefault();
        sel = (sel + 1) % items.length;
        highlight();
      } else if (e.key === "ArrowUp") {
        e.preventDefault();
        sel = (sel - 1 + items.length) % items.length;
        highlight();
      } else if (e.key === "Enter" || e.key === "Tab") {
        if (sel >= 0) {
          e.preventDefault();
          choose(input, sel);
        }
      } else if (e.key === "Escape") {
        hide();
      }
    });
    // Delay so a mousedown on the menu is processed before hiding.
    input.addEventListener("blur", () => setTimeout(hide, 120));
  }

  window.TagComplete = {
    attach,
    invalidate() {
      tags = null;
      inflight = null;
    },
  };

  document.addEventListener("DOMContentLoaded", () => {
    document.querySelectorAll("input[data-tagcomplete]").forEach(attach);
  });
})();