// =============================================================
// adapters/lit/scaffold.mjs — component scaffold + drift (WHYNOT-WP-0002 · T07)
//
// Pure functions over ir/ + the Lit source tree (src/elements/*.js). Per
// adapters/ADAPTER_CONTRACT.md:
//   • IR component with no <wn-*> counterpart → a write-once STUB
//     (adapters/lit/stubs/<Name>.js), never into the hand-authored tree.
//   • IR component with a counterpart → a DRIFT REPORT
//     (adapters/lit/drift/<Name>.md + a machine roll-up); never an overwrite.
//
// Behaviour is never generated — stubs carry a TODO; drift is for human triage.
// =============================================================
import { readFileSync, readdirSync, existsSync } from "node:fs";
import { join } from "node:path";

const ELEMENT_FILES = ["atoms.js", "form.js", "layout.js", "chrome.js"];

// ---------- Parse the Lit source tree → tag → element descriptor ----------
// Extract the balanced { … } block that starts at/after `from`.
function balancedBlock(src, from) {
  let i = src.indexOf("{", from), depth = 0;
  const begin = i;
  for (; i < src.length; i++) {
    if (src[i] === "{") depth++;
    else if (src[i] === "}" && --depth === 0) return src.slice(begin, i + 1);
  }
  return src.slice(begin);
}

// Parse a `static properties = { … }` block body into { name: {attribute,type,reflect} }.
function parseProps(block) {
  const props = {};
  // Each entry: `name: { … },` — scan key then its balanced object.
  const re = /([A-Za-z_$][\w$]*)\s*:\s*\{/g;
  let m;
  while ((m = re.exec(block))) {
    const name = m[1];
    const decl = balancedBlock(block, m.index + m[0].length - 1);
    const attrM = /attribute\s*:\s*(false|"([^"]+)"|'([^']+)')/.exec(decl);
    const typeM = /type\s*:\s*([A-Za-z]+)/.exec(decl);
    const reflect = /reflect\s*:\s*true/.test(decl);
    let attribute;
    if (attrM) attribute = attrM[1] === "false" ? false : (attrM[2] || attrM[3]);
    else attribute = name.toLowerCase(); // Lit default: lowercased property name
    props[name] = { attribute, type: typeM ? typeM[1] : "String", reflect };
    re.lastIndex = m.index + m[0].length; // resume after the key (decl re-scanned harmlessly)
  }
  return props;
}

// Find a class's own `static properties` (walks `extends` within the same file set).
function classProps(name, classes) {
  const cls = classes[name];
  if (!cls) return {};
  const own = cls.propsBlock ? parseProps(cls.propsBlock) : {};
  const inherited = cls.extends && classes[cls.extends] ? classProps(cls.extends, classes) : {};
  return { ...inherited, ...own };
}

function classSlots(name, classes) {
  const cls = classes[name];
  if (!cls) return new Set();
  const inherited = cls.extends && classes[cls.extends] ? classSlots(cls.extends, classes) : new Set();
  return new Set([...inherited, ...(cls.slots || [])]);
}

export function parseLitElements(repo) {
  const classes = {}; // className → { propsBlock, extends, file }
  const defines = []; // { tag, className, file }
  for (const file of ELEMENT_FILES) {
    const path = join(repo, "src", "elements", file);
    if (!existsSync(path)) continue;
    const src = readFileSync(path, "utf8");
    const classRe = /class\s+([A-Za-z_$][\w$]*)\s+extends\s+([A-Za-z_$][\w$]*)/g;
    let m;
    while ((m = classRe.exec(src))) {
      const [className, base] = [m[1], m[2]];
      const propsAt = src.indexOf("static properties", m.index);
      // bound the search to before the next class declaration
      classRe.lastIndex = m.index + m[0].length;
      const nextClass = src.indexOf("class ", m.index + m[0].length);
      const propsBlock = propsAt !== -1 && (nextClass === -1 || propsAt < nextClass)
        ? balancedBlock(src, propsAt) : null;
      // Named slots the element renders (e.g. <slot name="actions">) — a prop can
      // be honoured by a same-named slot rather than a reactive property.
      const region = src.slice(m.index, nextClass === -1 ? undefined : nextClass);
      const slots = [...region.matchAll(/<slot\s+name="([\w-]+)"/g)].map((x) => x[1]);
      classes[className] = { propsBlock, extends: base, file, slots };
    }
    const defRe = /customElements\.define\(\s*["']([\w-]+)["']\s*,\s*([A-Za-z_$][\w$]*)\s*\)/g;
    while ((m = defRe.exec(src))) defines.push({ tag: m[1], className: m[2], file });
  }
  const byTag = {};
  for (const d of defines) byTag[d.tag] = { ...d, props: classProps(d.className, classes), slots: classSlots(d.className, classes) };
  return byTag;
}

// ---------- Drift: IR contract vs Lit element ----------
// Actionable drift gates `make adapt-lit` (exit 3). The rest is informational:
//   • non-portable — React style/callbacks that inherently have no attribute form;
//     the Lit element is correct to omit them. Surfaced (never dropped), never gated.
//   • prop-extra   — the Lit element is richer than the minimal React designbook;
//     a divergence worth noting, but not a defect to block on.
const ACTIONABLE = new Set(["prop-missing", "attribute-mismatch", "variant-axis-missing", "tag-mismatch"]);

export function litAttrOf(decl) {
  return decl.attribute === false ? null : decl.attribute;
}

// Human-curated accepted divergences — the auditable output of drift triage for
// divergences that are intentional (e.g. a React monolithic prop modelled
// per-child in a composable Lit element). Keyed `<Component>:<kind>:<prop>` → rationale.
// Read from adapters/lit/drift.accepted.json. An accepted issue is still listed in
// the report (marked "accepted: <why>") but downgraded to info, so it does not gate.
export function loadAccepted(repo) {
  const path = join(repo, "adapters", "lit", "drift.accepted.json");
  if (!existsSync(path)) return {};
  try {
    const out = {};
    for (const e of (JSON.parse(readFileSync(path, "utf8")).accepted || []))
      out[`${e.component}:${e.kind}:${e.prop ?? ""}`] = e.rationale || "accepted";
    return out;
  } catch { return {}; }
}

function classify(issues, component, accepted = {}) {
  for (const i of issues) {
    const key = `${component}:${i.kind}:${i.prop ?? ""}`;
    if (accepted[key]) { i.severity = "info"; i.accepted = accepted[key]; }
    else i.severity = ACTIONABLE.has(i.kind) ? "drift" : "info";
  }
  return issues.some((i) => i.severity === "drift") ? "drift" : "ok";
}

// Find a likely renamed counterpart when no exact tag match (e.g. wn-pipeline-strip → wn-pipeline).
function likelyCounterpart(tag, byTag) {
  if (byTag[tag]) return null;
  const head = tag.replace(/^wn-/, "").split("-")[0]; // "pipeline"
  const hit = Object.keys(byTag).find((t) => t.replace(/^wn-/, "").split("-")[0] === head);
  return hit || null;
}

export function componentDrift(contract, byTag, accepted = {}) {
  const tag = contract.tag;
  const el = byTag[tag];

  if (!el) {
    const alt = likelyCounterpart(tag, byTag);
    if (alt) {
      const issues = [{ kind: "tag-mismatch", expected: tag, actual: alt,
        detail: `IR contract tag '${tag}' has no element; '${alt}' looks like the hand-authored counterpart (rename — resolve in Claude Design or realign the element).` }];
      return { name: contract.name, status: classify(issues, contract.name, accepted), tag, issues };
    }
    return { name: contract.name, status: "new", tag, issues: [
      { kind: "no-counterpart", detail: `no <${tag}> in src/elements/ — stub generated.` },
    ] };
  }

  const issues = [];
  const litProps = el.props;
  const litSlots = el.slots || new Set();
  for (const p of contract.props || []) {
    if (p.portable === false) {
      issues.push({ kind: "non-portable", prop: p.name,
        detail: `type=${p.type}; not attribute-mappable — handle explicitly, never drop.` });
      continue;
    }
    if (p.attribute === false) continue; // property-only by contract
    const lit = litProps[p.name];
    if (!lit) {
      // A content prop can be honoured by a same-named named slot (e.g. PageHeader
      // `actions` → <slot name="actions">) — that is satisfaction, not drift.
      if (litSlots.has(p.name) || litSlots.has(p.attribute)) {
        issues.push({ kind: "prop-via-slot", prop: p.name,
          detail: `IR prop honoured by <slot name="${p.name}"> on <${tag}> (slotted content, not an attribute).` });
        continue;
      }
      issues.push({ kind: "prop-missing", prop: p.name,
        detail: `in IR (attribute '${p.attribute}'), absent on <${tag}>` });
      continue;
    }
    const litAttr = litAttrOf(lit);
    if (litAttr !== p.attribute) {
      issues.push({ kind: "attribute-mismatch", prop: p.name, expected: p.attribute, actual: litAttr === null ? "(property-only)" : litAttr });
    }
  }
  // Variant axes must have a backing property.
  for (const v of contract.variants || []) {
    if (!litProps[v.axis]) issues.push({ kind: "variant-axis-missing", prop: v.axis,
      detail: `IR variant axis '${v.axis}' (${v.values.join("/")}) has no Lit property.` });
  }
  // Extra Lit properties not described by the IR contract.
  const irNames = new Set((contract.props || []).map((p) => p.name));
  for (const name of Object.keys(litProps)) {
    if (!irNames.has(name)) issues.push({ kind: "prop-extra", prop: name,
      detail: `on <${tag}> (attribute '${litAttrOf(litProps[name]) ?? "(property-only)"}'), not in IR contract.` });
  }

  return { name: contract.name, status: classify(issues, contract.name, accepted), tag, issues };
}

// ---------- Stub generation (write-once) ----------
export function renderStub(contract) {
  const tag = contract.tag;
  const cls = "Wn" + contract.name;
  const props = (contract.props || []).filter((p) => p.portable !== false && p.attribute !== false);
  const litType = (t) => (t === "boolean" ? "Boolean" : t === "number" ? "Number" : "String");
  const propLines = props.map((p) => {
    const attr = p.attribute !== p.name.toLowerCase() ? `, attribute: "${p.attribute}"` : "";
    return `    ${p.name}: { type: ${litType(p.type)}${attr} },`;
  }).join("\n");
  const nonPortable = (contract.props || []).filter((p) => p.portable === false);
  const npNote = nonPortable.length
    ? `\n  // Non-portable props (handle explicitly, do not drop): ${nonPortable.map((p) => p.name).join(", ")}.`
    : "";
  const slotMarkup = (contract.slots || []).some((s) => s.name === "default")
    ? "<slot></slot>" : "";
  return `// @generated STUB by adapters/lit (WHYNOT-WP-0002 T07) — from ir/components/${contract.name}.json.
// Write-once scaffold: skeleton + typed reactive properties + a behaviour TODO.
// Move into src/elements/ and implement; the adapter never overwrites this once edited.
import { LitElement, html } from "lit";

export class ${cls} extends LitElement {
  createRenderRoot() { return this; } // light DOM, matches the existing wn-* elements${npNote}
  static properties = {
${propLines || "    // (no attribute-mappable props in the contract)"}
  };
  render() {
    // TODO(${contract.name}): implement per ir/exemplars/${contract.name}.html and the design language.
    return html\`<div class="${tag}" part="root">${slotMarkup}</div>\`;
  }
}
// customElements.define("${tag}", ${cls});  // ← uncomment when integrating
`;
}