import { readdirSync, readFileSync } from "node:fs";
import { parseSync, transformSync, type types as t } from "@babel/core";
import reactCompiler from "babel-plugin-react-compiler";

// Runs the real React Compiler — the options reactPlugin.ts gives it — over the shipped source and
// reports every function it SKIPS, keyed `file → function → category`. The compiler skips without a
// word (`panicThreshold` is "none" and the build has no logger), so this is the only place a skip is
// visible at all. Used by compilerCoverage.contract.test.ts.

const SRC = new URL("../", import.meta.url);

/** Every file the production build compiles: src, minus tests and test kits. */
export function shippedSources(): string[] {
  return (readdirSync(SRC, { recursive: true }) as string[])
    .map((p) => p.split("\\").join("/"))
    .filter(
      (p) => /\.(ts|tsx)$/.test(p) && !/\.(test|testkit)\.tsx?$/.test(p) && !p.endsWith(".d.ts"),
    )
    .sort();
}

type Node = t.Node & { [k: string]: unknown };
const isFn = (n: Node) =>
  n.type === "FunctionDeclaration" ||
  n.type === "FunctionExpression" ||
  n.type === "ArrowFunctionExpression";

/** The name a reader would look a function up by: its own, the variable it is assigned to (through
 *  a `memo(…)` / `forwardRef(…)` wrapper), or `default` for an anonymous default export. */
function functionNames(ast: t.File): Map<string, string> {
  const names = new Map<string, string>();
  const walk = (node: Node, parents: Node[]) => {
    if (isFn(node) && node.loc) {
      let name = (node as t.FunctionDeclaration).id?.name ?? null;
      for (let i = parents.length - 1; !name && i >= 0; i--) {
        const p = parents[i]!;
        if (p.type === "VariableDeclarator" && p.id.type === "Identifier") name = p.id.name;
        else if (p.type === "ExportDefaultDeclaration") name = "default";
        else if (p.type !== "CallExpression" && p.type !== "TSAsExpression") break;
      }
      names.set(
        `${node.loc.start.line}:${node.loc.start.column}`,
        name ?? `<line ${node.loc.start.line}>`,
      );
    }
    for (const key of Object.keys(node)) {
      if (key === "loc" || key === "leadingComments" || key === "trailingComments") continue;
      const v = node[key];
      if (Array.isArray(v)) {
        for (const c of v)
          if (c && typeof c === "object" && "type" in c) walk(c as Node, [...parents, node]);
      } else if (v && typeof v === "object" && "type" in v) walk(v as Node, [...parents, node]);
    }
  };
  walk(ast as unknown as Node, []);
  return names;
}

type Detail = {
  category?: string;
  reason?: string;
  options?: { category?: string; reason?: string };
};

export interface CompileReport {
  /** file → function → the compiler's category for the skip (Refs, Todo, Immutability, …). */
  skipped: Record<string, Record<string, string>>;
  /** file → the functions it did compile. */
  compiled: Record<string, string[]>;
}

export function compileReport(files: string[]): CompileReport {
  const skipped: CompileReport["skipped"] = {};
  const compiled: CompileReport["compiled"] = {};
  for (const file of files) {
    const source = readFileSync(new URL(file, SRC), "utf8");
    const opts = { filename: file, babelrc: false, configFile: false } as const;
    const ast = parseSync(source, { ...opts, parserOpts: { plugins: ["jsx", "typescript"] } });
    if (!ast) throw new Error(`could not parse ${file}`);
    const names = functionNames(ast);
    const nameAt = (loc: t.SourceLocation | null) =>
      loc
        ? (names.get(`${loc.start.line}:${loc.start.column}`) ?? `<line ${loc.start.line}>`)
        : "<unknown>";
    transformSync(source, {
      ...opts,
      parserOpts: { plugins: ["jsx", "typescript"] },
      plugins: [
        [
          reactCompiler,
          {
            target: "19",
            logger: {
              logEvent: (
                _f: string | null,
                e: {
                  kind: string;
                  fnLoc?: t.SourceLocation | null;
                  detail?: Detail;
                  reason?: string;
                },
              ) => {
                if (e.kind === "CompileSuccess") {
                  (compiled[file] ??= []).push(nameAt(e.fnLoc ?? null));
                  return;
                }
                let category: string;
                if (e.kind === "CompileError")
                  category = e.detail?.options?.category ?? e.detail?.category ?? "Unknown";
                else if (e.kind === "CompileSkip") category = `Skip: ${e.reason}`;
                else if (e.kind === "PipelineError") category = "PipelineError";
                else return;
                const fns = (skipped[file] ??= {});
                // The first reason is the one that stopped it; later ones are the same function.
                fns[nameAt(e.fnLoc ?? null)] ??= category;
              },
            },
          },
        ],
      ],
    });
  }
  return { skipped, compiled };
}