import type { FactIndex } from "../facts/index.js";

import { makeFinding } from "./finding.js";
import type { Finding } from "./types.js";
import { cssVariableNames } from "./utils.js";

export const RULE_ID = "tokens/require-dual-fallback";
export const RULE_VERSION = "1";

const CSS_VAR_WITH_OPTIONAL_FALLBACK = /var\(\s*(--[A-Za-z0-9_-]+)(\s*,\s*[^)]*)?\)/g;

/**
 * The dual-fallback convention — `var(--token, $token)` — is only meaningful in
 * a Sass pipeline, where the `$token` half resolves at build time. In plain CSS
 * (`.css`/`.module.css`), inline styles, or CSS-in-JS, a `$token` literal is
 * invalid and would silently break the declaration, so the rule (and its
 * autofix) must never touch those files.
 */
const SASS_FILE = /\.(scss|sass)$/i;

export function ruleTokensRequireDualFallback(ix: FactIndex): Finding[] {
  const policy = ix.policy.ruleConfig(RULE_ID);
  if (!policy?.enabled) return [];

  const knownTokenVars = cssVariableNames(ix.tokens.list());
  const findings: Finding[] = [];

  for (const decl of ix.byKind("style_declaration")) {
    if (!SASS_FILE.test(decl.file)) continue;
    CSS_VAR_WITH_OPTIONAL_FALLBACK.lastIndex = 0;
    let match: RegExpExecArray | null;
    while ((match = CSS_VAR_WITH_OPTIONAL_FALLBACK.exec(decl.value)) !== null) {
      const tokenName = match[1];
      const hasFallback = match[2] !== undefined;
      if (hasFallback) continue;
      if (!knownTokenVars.has(tokenName) && !tokenName.startsWith("--fui-")) continue;

      const rawValue = match[0];
      const scssVar = tokenName.replace(/^--/, "$");
      const replacement = `var(${tokenName}, ${scssVar})`;
      const nextValue = decl.value.replace(rawValue, replacement);

      findings.push(
        makeFinding({
          ruleId: RULE_ID,
          ruleVersion: RULE_VERSION,
          severity: policy.severity ?? "warn",
          message: `var(${tokenName}) is missing an SCSS fallback. Use var(${tokenName}, ${scssVar}).`,
          location: decl.location,
          evidence: ix.evidence([decl.id, policy.id]),
          fingerprintIdentity: {
            file: decl.file,
            selector: decl.selector,
            declarationPath: decl.declarationPath,
            property: decl.property,
            tokenName,
          },
          fix: {
            kind: "replaceStyleValue",
            title: `Add fallback for ${tokenName}`,
            property: decl.property,
            value: nextValue,
            deterministic: true,
          },
          attributes: {
            property: decl.property,
            rawValue: decl.value,
            tokenName,
            suggestedValue: nextValue,
            source: "css",
          },
        }),
      );
    }
  }

  return findings;
}