import fs from "node:fs/promises";
import path from "node:path";
import os from "node:os";
import { randomUUID } from "node:crypto";
import { contentDigest } from "../capability-model/evolution.js";
import { editStructure, type StructuralEdit } from "./structural-edits.js";
import { snapshotRepository, localResourceSnapshots } from "./candidate-check.js";
import { compileWorkspaceRepository, compileCapabilityResourceRepository } from "./assembly.js";
import { createGitCapabilityResolver } from "./git-resolver.js";
import { bindingSchema, generateTypeScriptBindings } from "../bindings/index.js";
import { parseQx } from "./source.js";
import { parseQuixosLockDocument } from "../resource-lock/index.js";
import { withFileLock } from "./file-lock.js";

export type StructuralRequest = {
  kind: "workspace" | "interface" | "package";
  source?: { repository: string; commit: string };
  resourceRoot?: string;
  validation?: "syntax" | "resource-graph";
  files: (
    | { file: string; edits: StructuralEdit[] }
    | { file: string; create: string }
    | { file: string; generated: string }
    | { file: string; expected: string; replace: string }
  )[];
};
type Change = { file: string; before: string | null; after: string; mode: number };
type Journal = { schemaVersion: 1; id: string; root: string; phase: "prepared" | "complete"; changes: Change[] };
const safeFile = (file: string) => {
  if (
    !/^(?:[A-Za-z0-9_-][A-Za-z0-9_.-]*\/)*(?:\.gitignore|\.yarnrc.yml|[A-Za-z0-9_-][A-Za-z0-9_.-]*\.(?:qx|graphql|lock|ts|tsx|css|mjs|json|nix|txtpb|md))$/.test(
      file,
    ) ||
    file.split("/").some((part) => [".git", ".jj", ".quixos", "node_modules"].includes(part))
  )
    throw new Error(`Unsafe scaffold path ${file}`);
};
const read = async (root: string, file: string): Promise<string | null> => {
  safeFile(file);
  const target = path.join(root, file);
  try {
    const metadata = await fs.lstat(target);
    if (!metadata.isFile() || metadata.isSymbolicLink() || !(await fs.realpath(target)).startsWith(`${root}/`))
      throw new Error(`Scaffold target is not a contained regular file: ${file}`);
    return await fs.readFile(target, "utf8");
  } catch (error) {
    if ((error as NodeJS.ErrnoException).code === "ENOENT") return null;
    throw error;
  }
};
const containedParent = async (root: string, file: string) => {
  let current = root;
  for (const part of file.split("/").slice(0, -1)) {
    current = path.join(current, part);
    await fs.mkdir(current).catch((error: NodeJS.ErrnoException) => {
      if (error.code !== "EEXIST") throw error;
    });
    const metadata = await fs.lstat(current);
    if (!metadata.isDirectory() || metadata.isSymbolicLink())
      throw new Error("Scaffold parent must be a real directory");
  }
};
const durableJson = async (file: string, value: unknown) => {
  const temporary = `${file}.${randomUUID()}.tmp`;
  const handle = await fs.open(temporary, "wx", 0o600);
  try {
    await handle.writeFile(`${JSON.stringify(value, null, 2)}\n`);
    await handle.sync();
  } finally {
    await handle.close();
  }
  await fs.rename(temporary, file);
  const directory = await fs.open(path.dirname(file), "r");
  try {
    await directory.sync();
  } finally {
    await directory.close();
  }
};

/** Validate the entire edited resource graph in a private snapshot before writes. */
export const planStructure = async (rootPath: string, request: StructuralRequest, snapshotMap?: string) => {
  if (request.validation && !["syntax", "resource-graph"].includes(request.validation))
    throw new Error("Unknown structural validation mode");
  const root = await fs.realpath(rootPath);
  const temporary = await fs.mkdtemp(path.join(os.tmpdir(), "qx-structure-"));
  try {
    const snapshot = await snapshotRepository(root, path.join(temporary, "source"));
    const observed = await Promise.all(
      snapshot.files.map(async ({ name }) => ({
        file: name,
        digest: contentDigest(await fs.readFile(path.join(snapshot.directory, name), "utf8")),
      })),
    );
    const changes: Change[] = [];
    if (!Array.isArray(request.files) || !request.files.length || request.files.length > 100)
      throw new Error("Structural plan requires 1–100 files");
    for (const input of request.files) {
      safeFile(input.file);
      if (changes.some((entry) => entry.file === input.file)) throw new Error("Repeated structural file target");
      const before = await read(root, input.file);
      let after: string;
      if ("create" in input) {
        if (before !== null || typeof input.create !== "string")
          throw new Error("Scaffold creation cannot replace an existing file");
        after = input.create;
      } else if ("replace" in input) {
        if (before !== input.expected || typeof input.replace !== "string")
          throw new Error(`Stale imperative edit: ${input.file}`);
        after = input.replace;
      } else if ("generated" in input) {
        const generated = (text: string) =>
          text.startsWith("// Generated by qx-scaffold-v1\n") ||
          text.startsWith("# Generated by qx-scaffold-v1\n") ||
          (() => {
            try {
              return JSON.parse(text).generatedBy === "qx-scaffold-v1";
            } catch {
              return false;
            }
          })();
        if (
          typeof input.generated !== "string" ||
          !generated(input.generated) ||
          (before !== null && !generated(before))
        )
          throw new Error("Only scaffold-owned generated files may be regenerated");
        after = input.generated;
      } else {
        if (before === null || !Array.isArray(input.edits))
          throw new Error("Structural edit requires an existing source");
        after = input.edits.reduce(editStructure, before);
      }
      if (Buffer.byteLength(after) > 1024 * 1024) throw new Error("Scaffold file exceeds 1 MiB");
      const mode = before === null ? 0o644 : (await fs.stat(path.join(root, input.file))).mode & 0o777;
      changes.push({ file: input.file, before, after, mode });
      await containedParent(snapshot.directory, input.file);
      await fs.writeFile(path.join(snapshot.directory, input.file), after);
    }
    if (request.validation === "syntax") {
      for (const change of changes) {
        if (change.file.endsWith(".qx") && parseQx(change.after, change.file).diagnostics.length)
          throw new Error(`Invalid QX syntax in ${change.file}`);
        if (change.file.endsWith(".lock") && !parseQuixosLockDocument(change.after, change.file).ok)
          throw new Error(`Invalid lock syntax in ${change.file}`);
      }
    } else {
      const localMap = path.join(temporary, "local-resources.json");
      await fs.writeFile(localMap, JSON.stringify(await localResourceSnapshots(root, snapshotMap)));
      const resolveResource = await createGitCapabilityResolver({
        checkoutRoot: path.join(temporary, "resources"),
        snapshotMap: localMap,
      });
      if (
        request.resourceRoot &&
        !/^[A-Za-z0-9_-][A-Za-z0-9_.-]*(?:\/[A-Za-z0-9_-][A-Za-z0-9_.-]*)*$/.test(request.resourceRoot)
      )
        throw new Error("Resource root must be a contained relative directory");
      const resourceRoot = path.join(snapshot.directory, request.resourceRoot ?? "");
      if (request.kind === "workspace")
        await compileWorkspaceRepository({ rootDirectory: resourceRoot, resolveResource });
      else if (["package", "interface"].includes(request.kind) && request.source) {
        const compiled = await compileCapabilityResourceRepository({
          rootDirectory: resourceRoot,
          kind: request.kind as "package" | "interface",
          source: { resolver: "git", ...request.source },
          resolveResource,
        });
        if (compiled.resource.kind === "package") {
          const configuration = JSON.parse(await fs.readFile(path.join(resourceRoot, "quixos.check.json"), "utf8"));
          const artifacts = [
            {
              file: configuration.bindingOutput as string,
              after: generateTypeScriptBindings(
                bindingSchema(compiled),
                compiled.resource.revision.revisionId,
                configuration.options,
              ),
            },
          ];
          for (const artifact of artifacts) {
            const file = request.resourceRoot ? `${request.resourceRoot}/${artifact.file}` : artifact.file;
            safeFile(file);
            if (Buffer.byteLength(artifact.after) > 1024 * 1024)
              throw new Error("Generated scaffold file exceeds 1 MiB");
            const before = await read(root, file);
            if (
              before !== null &&
              !before.startsWith("// Generated by quixos-codegen-ts.") &&
              (() => {
                try {
                  return JSON.parse(before).generatedBy !== "qx-scaffold-v1";
                } catch {
                  return true;
                }
              })()
            )
              throw new Error(`Refusing to overwrite hand-authored generated artifact ${file}`);
            const previous = changes.find((entry) => entry.file === file);
            if (previous) previous.after = artifact.after;
            else changes.push({ file, before, after: artifact.after, mode: 0o644 });
          }
        }
      } else throw new Error("Resource plans require kind and exact authored source identity");
    }
    if (changes.length > 100) throw new Error("Structural plan including generated artifacts exceeds 100 files");
    // Validation may fetch dependencies; reject edits made while it was running.
    for (const entry of changes)
      if ((await read(root, entry.file)) !== entry.before)
        throw new Error(`Source changed while planning: ${entry.file}`);
    for (const entry of observed)
      if (contentDigest(await fs.readFile(path.join(root, entry.file), "utf8")) !== entry.digest)
        throw new Error(`Validation input changed while planning: ${entry.file}`);
    return {
      root,
      changes,
      observed,
      digest: contentDigest(changes),
      validation: request.validation ?? ("resource-graph" as const),
    };
  } finally {
    await fs.rm(temporary, { recursive: true, force: true });
  }
};

/** Replay only exact before/after states. A crash never loses the original text. */
const replayStructure = async (rootPath: string, id: string) => {
  const root = await fs.realpath(rootPath);
  if (!/^[a-f0-9-]{36}$/.test(id)) throw new Error("Invalid scaffold journal ID");
  const journalPath = path.join(root, ".quixos", "scaffolds", `${id}.json`);
  const journal = JSON.parse(await fs.readFile(journalPath, "utf8")) as Journal;
  if (journal.schemaVersion !== 1 || journal.root !== root || journal.id !== id)
    throw new Error("Scaffold journal identity mismatch");
  for (const entry of journal.changes) {
    const current = await read(root, entry.file);
    if (current !== entry.before && current !== entry.after)
      throw new Error(
        `Scaffold conflicts with newer edits: ${entry.file}; original text is retained in ${journalPath}`,
      );
  }
  if (journal.phase === "complete") return { id, journalPath, phase: journal.phase };
  for (const entry of journal.changes) {
    if ((await read(root, entry.file)) === entry.after) continue;
    await containedParent(root, entry.file);
    const target = path.join(root, entry.file);
    const temporary = `${target}.qx-${randomUUID()}.tmp`;
    const handle = await fs.open(temporary, "wx", entry.mode);
    try {
      await handle.writeFile(entry.after);
      await handle.sync();
    } finally {
      await handle.close();
    }
    if (entry.before === null) {
      // link is atomic and fails if another author created the destination.
      await fs.link(temporary, target);
      await fs.unlink(temporary);
    } else {
      if ((await read(root, entry.file)) !== entry.before)
        throw new Error(`Source changed during scaffold: ${entry.file}`);
      await fs.rename(temporary, target);
    }
    const directory = await fs.open(path.dirname(target), "r");
    try {
      await directory.sync();
    } finally {
      await directory.close();
    }
  }
  journal.phase = "complete";
  await durableJson(journalPath, journal);
  return { id, journalPath, phase: journal.phase };
};

const withStructureLock = async <T>(root: string, work: () => Promise<T>) => {
  await containedParent(root, ".quixos/scaffolds/placeholder.json");
  const lock = path.join(root, ".quixos", "scaffolds", "writer.lock");
  return withFileLock(lock, work);
};
export const resumeStructure = async (rootPath: string, id: string) => {
  const root = await fs.realpath(rootPath);
  return withStructureLock(root, () => replayStructure(root, id));
};
export const applyStructure = async (plan: Awaited<ReturnType<typeof planStructure>>, id: string = randomUUID()) =>
  withStructureLock(plan.root, async () => {
    if (!/^[a-f0-9-]{36}$/.test(id)) throw new Error("Invalid scaffold journal ID");
    const directory = path.join(plan.root, ".quixos", "scaffolds");
    try {
      const existing = JSON.parse(await fs.readFile(path.join(directory, `${id}.json`), "utf8")) as Journal;
      if (existing.root !== plan.root || contentDigest(existing.changes) !== plan.digest)
        throw new Error("Scaffold journal identity conflict");
      for (const entry of plan.observed)
        if (
          !plan.changes.some((change) => change.file === entry.file) &&
          contentDigest(await fs.readFile(path.join(plan.root, entry.file), "utf8")) !== entry.digest
        )
          throw new Error(`Stale scaffold validation input: ${entry.file}`);
      return replayStructure(plan.root, id);
    } catch (error) {
      if ((error as NodeJS.ErrnoException).code !== "ENOENT") throw error;
    }
    // An unfinished journal must be recovered before another structural mutation.
    for (const file of await fs.readdir(directory))
      if (file.endsWith(".json")) {
        const prior = JSON.parse(await fs.readFile(path.join(directory, file), "utf8")) as Journal;
        if (prior.phase !== "complete") throw new Error(`Unfinished scaffold ${prior.id}; resume it first`);
      }
    for (const entry of plan.changes)
      if ((await read(plan.root, entry.file)) !== entry.before) throw new Error(`Stale scaffold plan: ${entry.file}`);
    for (const entry of plan.observed)
      if (contentDigest(await fs.readFile(path.join(plan.root, entry.file), "utf8")) !== entry.digest)
        throw new Error(`Stale scaffold validation input: ${entry.file}`);
    await durableJson(path.join(directory, `${id}.json`), {
      schemaVersion: 1,
      id,
      root: plan.root,
      phase: "prepared",
      changes: plan.changes,
    } satisfies Journal);
    return replayStructure(plan.root, id);
  });