import { lstat, readFile } from "node:fs/promises";
import path from "node:path";
import { parseQuixosLockDocument, type QuixosLockDiagnostic, type QuixosLockParseResult } from "./parser.js";
import type { LockedResource, QuixosLockDocument, QuixosRepositoryLock } from "./types.js";

export type QuixosLockSourceReader = (relativePath: string) => Promise<string>;

const diagnostic = (code: string, message: string, fileName: string, path?: string): QuixosLockDiagnostic => ({
  phase: "resolution",
  code,
  message,
  fileName,
  line: 1,
  column: 0,
  path,
});

export const resolveQuixosLock = async (
  rootSource: string,
  readSource: QuixosLockSourceReader,
  rootFileName = "quixos.lock",
): Promise<QuixosLockParseResult> => {
  const root = parseQuixosLockDocument(rootSource, rootFileName);
  if (!root.ok) return root;
  if (root.document.kind !== "root") {
    return {
      ok: false,
      diagnostics: [
        diagnostic("expected-root-lock", "The entrypoint must be a root Quixos lock, not a fragment", rootFileName),
      ],
    };
  }

  const diagnostics: QuixosLockDiagnostic[] = [];
  const resources: LockedResource[] = [];
  const sourceFiles = [rootFileName];
  const visited = new Set<string>();
  const active: string[] = [];

  const addResources = (document: QuixosLockDocument, fileName: string) => {
    for (const resource of document.resources) {
      const duplicate = resources.find((entry) => entry.kind === resource.kind && entry.binding === resource.binding);
      if (duplicate) {
        diagnostics.push(
          diagnostic(
            "duplicate-resource-binding",
            `Duplicate ${resource.kind} binding ${resource.binding} across imported lock files`,
            fileName,
            `${resource.kind}.${resource.binding}`,
          ),
        );
      } else {
        resources.push(resource);
      }
    }
  };

  const visit = async (importPath: string) => {
    if (active.includes(importPath)) {
      diagnostics.push(
        diagnostic("import-cycle", `Lock import cycle: ${[...active, importPath].join(" -> ")}`, importPath),
      );
      return;
    }
    if (visited.has(importPath)) return;
    active.push(importPath);
    let source: string;
    try {
      source = await readSource(importPath);
    } catch (cause) {
      diagnostics.push(
        diagnostic(
          "import-read-failed",
          `Could not read lock import ${importPath}: ${cause instanceof Error ? cause.message : String(cause)}`,
          importPath,
        ),
      );
      active.pop();
      return;
    }
    const parsed = parseQuixosLockDocument(source, importPath);
    if (!parsed.ok) {
      diagnostics.push(...parsed.diagnostics);
      active.pop();
      return;
    }
    if (parsed.document.kind !== "fragment") {
      diagnostics.push(
        diagnostic(
          "imported-root-lock",
          `Imported file ${importPath} must begin with "quixos-lock fragment"`,
          importPath,
        ),
      );
      active.pop();
      return;
    }
    visited.add(importPath);
    sourceFiles.push(importPath);
    addResources(parsed.document, importPath);
    for (const nested of parsed.document.imports) await visit(nested);
    active.pop();
  };

  addResources(root.document, rootFileName);
  for (const importPath of root.document.imports) await visit(importPath);
  if (diagnostics.length) return { ok: false, diagnostics };
  const lock: QuixosRepositoryLock = {
    formatVersion: 1,
    quixos: root.document.quixos,
    resources,
    sourceFiles,
  };
  return { ok: true, lock, diagnostics: [] };
};

export const loadQuixosLock = async (fileName: string): Promise<QuixosLockParseResult> => {
  const absoluteRoot = path.resolve(fileName);
  const repositoryRoot = path.dirname(absoluteRoot);
  const rootName = path.basename(absoluteRoot);
  const rootSource = await readFile(absoluteRoot, "utf8");
  return await resolveQuixosLock(
    rootSource,
    async (relativePath) => {
      let absoluteImport = repositoryRoot;
      const segments = relativePath.split("/");
      for (const [index, segment] of segments.entries()) {
        absoluteImport = path.join(absoluteImport, segment);
        const metadata = await lstat(absoluteImport);
        if (metadata.isSymbolicLink()) {
          throw new Error("imports must not traverse symbolic links");
        }
        const final = index === segments.length - 1;
        if ((!final && !metadata.isDirectory()) || (final && !metadata.isFile())) {
          throw new Error("imports must be ordinary files beneath ordinary directories");
        }
      }
      return await readFile(absoluteImport, "utf8");
    },
    rootName,
  );
};