import { mkdir, readFile, writeFile } from "node:fs/promises";
import path from "node:path";
import {
  contributionLocalName,
  moduleContributionDeclarationSchema,
  moduleDisplayEntrypointSchema,
  packageRelativePathSchema,
} from "@ekklesia/contracts";
import { build, type Plugin } from "esbuild";

/**
 * The one supported way to turn a module's React/TSX UI sources into the compiled browser artifacts
 * its manifest declares as `entrypoints.ui` and `entrypoints.display`.
 *
 * Module authors do not write bundler configuration. They put their UI at
 * the fixed role-specific source locations below, declare either or both artifacts, and run one
 * build; every option below is owned here so one decision applies to every module.
 */
export const MODULE_UI_SOURCE_ENTRYPOINT = "src/ui/index.tsx";
export const MODULE_DISPLAY_SOURCE_ENTRYPOINT = "src/display/index.tsx";
/** Where a declared browser contribution's source lives: `src/contributions/<local-name>/index.tsx`,
 * where the local name is the part of the contribution id after the module's own id. Derived rather
 * than configured, exactly like the two role entrypoints, so an author points the build nowhere. */
export const MODULE_CONTRIBUTION_SOURCE_DIRECTORY = "src/contributions";

export function moduleContributionSourceEntrypoint(contributionId: string): string {
  return `${MODULE_CONTRIBUTION_SOURCE_DIRECTORY}/${contributionLocalName(contributionId)}/index.tsx`;
}
export const MODULE_MANIFEST_FILENAME = "ekklesia.module.json";

/** Matches `browser.json`'s `target`, so what TypeScript typechecks and what esbuild emits agree. */
export const MODULE_UI_BUILD_TARGET = "es2022";

export type ModuleUiBuildErrorCode =
  | "MODULE_UI_MANIFEST_UNREADABLE"
  | "MODULE_UI_ENTRYPOINT_UNSAFE"
  | "MODULE_UI_ENTRYPOINT_COLLISION"
  | "MODULE_UI_SOURCE_MISSING"
  | "MODULE_UI_STYLESHEET_INVALID"
  | "MODULE_UI_STYLESHEET_UNDECLARED"
  | "MODULE_UI_BUILD_FAILED";

export type ModuleUiArtifactKind = "ui" | "display" | "contribution";

const errorMessages: Readonly<Record<ModuleUiBuildErrorCode, string>> = Object.freeze({
  MODULE_UI_MANIFEST_UNREADABLE: `${MODULE_MANIFEST_FILENAME} could not be read or parsed.`,
  MODULE_UI_ENTRYPOINT_UNSAFE:
    "A module UI entrypoint must be a package-relative path to a compiled .js or .mjs artifact inside the module.",
  MODULE_UI_ENTRYPOINT_COLLISION:
    "A display UI entrypoint must not overwrite another declared artifact.",
  MODULE_UI_SOURCE_MISSING: "A declared module UI source entrypoint was not found.",
  MODULE_UI_STYLESHEET_INVALID:
    "A module stylesheet may not define a global Ekklesia theme variable or keep an unresolved @import.",
  MODULE_UI_STYLESHEET_UNDECLARED:
    "A module UI build produced a stylesheet beside its artifact. Every style must be compiled into the declared artifact.",
  MODULE_UI_BUILD_FAILED: "A module UI bundle could not be produced.",
});

/** Carries a stable code and a fixed message. esbuild's own diagnostics are printed to stderr by
 * the CLI, where a developer wants them; the thrown error itself stays sanitized, matching every
 * other Ekklesia error boundary. */
export class ModuleUiBuildError extends Error {
  readonly code: ModuleUiBuildErrorCode;
  /** Safe role vocabulary that lets a developer identify which declared artifact failed without
   * exposing a filesystem path or raw manifest value. */
  readonly kind?: ModuleUiArtifactKind;

  constructor(code: ModuleUiBuildErrorCode, kind?: ModuleUiArtifactKind) {
    super(errorMessages[code]);
    this.name = "ModuleUiBuildError";
    this.code = code;
    if (kind !== undefined) {
      this.kind = kind;
    }
    this.stack = `${this.name}: ${this.message}`;
  }
}

/**
 * A CSS custom property in Ekklesia's own global theme namespace, being **declared** rather than
 * referenced. `var(--ekklesia-x)` and `var(--ekklesia-x, fallback)` are reads and are fine; only a
 * `--ekklesia-x:` declaration matches, because that is what would invent a global theme variable
 * outside the registry a future theme editor enumerates (ADR 0039).
 */
const GLOBAL_THEME_DECLARATION = /--ekklesia-[a-z0-9-]*\s*:/iu;

/** An `@import` that survived compilation — a remote or otherwise unresolvable one. A local import
 * is inlined by the nested bundle below and leaves nothing behind, so anything still here would make
 * the artifact fetch a stylesheet at run time, which is exactly what "self-contained" excludes. */
const SURVIVING_IMPORT = /@import\s/iu;

/**
 * Compiles each imported stylesheet into the artifact instead of emitting a sidecar.
 *
 * esbuild's default for `import "./styles.css"` from JavaScript is to collect every such stylesheet
 * into an `index.css` output beside the artifact. Nothing declares that file, no host fetches it,
 * and the manifest has no field for it — it would work in a local test and silently do nothing in a
 * real host. ADR 0023 therefore rejected the import outright; ADR 0040 compiles it instead.
 *
 * Each `.css` import becomes a JavaScript module whose default export is that stylesheet's compiled
 * text, produced by a nested esbuild run so local `@import`s are resolved and the result is one
 * self-contained string. The author passes that string to `defineModuleUi({ styles })` and the host
 * installs it into the artifact's isolated root. The declared `.js` artifact therefore remains the
 * only file the platform publishes, exactly as before stylesheets existed.
 *
 * Other stylesheet dialects stay rejected. Adding one is a language and toolchain decision, not a
 * detail of this pass, and would need its own ADR.
 */
const STYLESHEET_PLUGIN_NAME = "ekklesia-compile-stylesheet-imports";

function compileStylesheetImports(): Plugin {
  const decoder = new TextDecoder();
  return {
    name: STYLESHEET_PLUGIN_NAME,
    setup(pluginBuild) {
      // No `u` flag, deliberately: esbuild compiles a plugin filter to a Go RE2 expression, which
      // rejects `(?iu)` outright ("filter is not a valid Go regular expression"). These patterns are
      // pure ASCII, so the flag would change nothing anyway.
      pluginBuild.onResolve({ filter: /\.(s[ac]ss|less|styl|pcss|postcss)$/i }, (args) => ({
        errors: [
          {
            text:
              "Module UI supports plain .css only. Other stylesheet dialects have no compilation " +
              "contract in this platform (ADR 0040).",
            location: { file: args.importer },
          },
        ],
      }));

      pluginBuild.onLoad({ filter: /\.css$/i }, async (args) => {
        const compiled = await build({
          bundle: true,
          entryPoints: [args.path],
          logLevel: "silent",
          minify: false,
          target: MODULE_UI_BUILD_TARGET,
          write: false,
        });
        const stylesheet = compiled.outputFiles
          .map((outputFile) => decoder.decode(outputFile.contents))
          .join("\n");

        if (GLOBAL_THEME_DECLARATION.test(stylesheet)) {
          return {
            errors: [
              {
                text:
                  "A module stylesheet may reference Ekklesia's global theme variables but must " +
                  "never declare one. Derive a private alias under your own prefix instead " +
                  "(ADR 0039).",
                location: { file: args.path },
              },
            ],
          };
        }
        if (SURVIVING_IMPORT.test(stylesheet)) {
          return {
            errors: [
              {
                text:
                  "A module stylesheet left an unresolved @import. A declared artifact must be " +
                  "self-contained, so every import has to resolve to a local file (ADR 0040).",
                location: { file: args.path },
              },
            ],
          };
        }

        return { contents: `export default ${JSON.stringify(stylesheet)};`, loader: "js" };
      });
    },
  };
}

export interface BuildModuleUiOptions {
  /** The module package directory containing `ekklesia.module.json`. */
  readonly moduleDirectory: string;
}

export interface ModuleUiBuildResult {
  /** Built artifacts in stable role order: primary UI, then display, then each declared contribution
   * in manifest order. Empty for backend-only modules, which makes the canonical command usable
   * unchanged by every module package. */
  readonly artifacts: readonly ModuleUiBuildArtifactResult[];
}

export interface ModuleUiBuildArtifactResult {
  readonly kind: ModuleUiArtifactKind;
  /** For a contribution, the declared contribution id — so a multi-contribution build reports which
   * artifact it produced. Absent for the two role entrypoints. */
  readonly contributionId?: string;
  /** Absolute path of the artifact actually written, exactly as the manifest declares. */
  readonly outputFile: string;
  /** Absolute path of the fixed source entrypoint that produced it. */
  readonly sourceFile: string;
}

function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === "object" && value !== null && !Array.isArray(value);
}

type DeclaredModuleUiArtifact = ModuleUiBuildArtifactResult;

/** Reads the inert manifest and returns every declared UI artifact in deterministic role order. */
async function resolveDeclaredArtifacts(
  moduleDirectory: string,
): Promise<readonly DeclaredModuleUiArtifact[]> {
  let manifest: unknown;
  try {
    manifest = JSON.parse(
      await readFile(path.join(moduleDirectory, MODULE_MANIFEST_FILENAME), "utf8"),
    ) as unknown;
  } catch {
    throw new ModuleUiBuildError("MODULE_UI_MANIFEST_UNREADABLE");
  }

  const entrypoints = isRecord(manifest) ? manifest.entrypoints : undefined;
  if (!isRecord(entrypoints)) {
    throw new ModuleUiBuildError("MODULE_UI_MANIFEST_UNREADABLE");
  }

  const display = entrypoints.display;
  const manifestContributions = isRecord(manifest) ? manifest.contributions : undefined;
  const declaredContributions = Array.isArray(manifestContributions) ? manifestContributions : [];
  for (const contribution of declaredContributions) {
    if (!moduleContributionDeclarationSchema.safeParse(contribution).success) {
      throw new ModuleUiBuildError("MODULE_UI_MANIFEST_UNREADABLE", "contribution");
    }
  }
  const declarations: readonly {
    readonly contributionId?: string;
    readonly declared: unknown;
    readonly kind: ModuleUiArtifactKind;
    readonly present: boolean;
    readonly source: string;
  }[] = [
    {
      declared: entrypoints.ui,
      kind: "ui",
      present: entrypoints.ui !== undefined,
      source: MODULE_UI_SOURCE_ENTRYPOINT,
    },
    {
      declared: isRecord(display) ? display.artifact : display,
      kind: "display",
      present: display !== undefined,
      source: MODULE_DISPLAY_SOURCE_ENTRYPOINT,
    },
    ...(declaredContributions as { artifact: string; id: string }[]).map((contribution) => ({
      contributionId: contribution.id,
      declared: contribution.artifact,
      kind: "contribution" as const,
      present: true,
      source: moduleContributionSourceEntrypoint(contribution.id),
    })),
  ];
  const artifacts: DeclaredModuleUiArtifact[] = [];

  for (const declaration of declarations) {
    if (!declaration.present) {
      continue;
    }
    const declared = declaration.declared;
    // The path grammar is Core's, not this tool's: reusing the contracts schema means the build can
    // never write somewhere discovery would later reject, even if that grammar changes.
    if (
      typeof declared !== "string" ||
      !packageRelativePathSchema.safeParse(declared).success ||
      ![".js", ".mjs"].includes(path.extname(declared).toLowerCase())
    ) {
      throw new ModuleUiBuildError("MODULE_UI_ENTRYPOINT_UNSAFE", declaration.kind);
    }
    artifacts.push({
      ...(declaration.contributionId === undefined
        ? {}
        : { contributionId: declaration.contributionId }),
      kind: declaration.kind,
      outputFile: path.resolve(moduleDirectory, declared),
      sourceFile: path.join(moduleDirectory, declaration.source),
    });
  }

  if (display !== undefined && !moduleDisplayEntrypointSchema.safeParse(display).success) {
    throw new ModuleUiBuildError("MODULE_UI_MANIFEST_UNREADABLE", "display");
  }

  // No declared artifact may overwrite another declared file — an entrypoint this build does not
  // produce (`server`, `schema`, ...), or another artifact it does. Checked before esbuild runs, so
  // a collision can never destroy output that was already correct.
  const backendEntrypointPaths = new Set(
    (["server", "schema", "migrations", "jobs"] as const)
      .map((entrypointName) => entrypoints[entrypointName])
      .filter((configured): configured is string => typeof configured === "string")
      .map((configured) => path.resolve(moduleDirectory, configured)),
  );
  const claimedOutputs = new Set<string>();
  for (const artifact of artifacts) {
    if (
      backendEntrypointPaths.has(artifact.outputFile) ||
      claimedOutputs.has(artifact.outputFile)
    ) {
      throw new ModuleUiBuildError("MODULE_UI_ENTRYPOINT_COLLISION", artifact.kind);
    }
    claimedOutputs.add(artifact.outputFile);
  }

  // Complete preflight before esbuild starts: a missing second source must not leave the first role's
  // output looking like a successful package build.
  for (const artifact of artifacts) {
    try {
      await readFile(artifact.sourceFile);
    } catch {
      throw new ModuleUiBuildError("MODULE_UI_SOURCE_MISSING", artifact.kind);
    }
  }

  return artifacts;
}

/**
 * Bundles a module's UI into the artifact its manifest declares.
 *
 * Never runs during discovery, startup, or install: this is an authoring-time and packaging-time
 * step only. Core validates the artifact a module ships; it never produces one (ADR 0021).
 */
export async function buildModuleUi(options: BuildModuleUiOptions): Promise<ModuleUiBuildResult> {
  const moduleDirectory = path.resolve(options.moduleDirectory);
  const artifacts = await resolveDeclaredArtifacts(moduleDirectory);
  const pendingWrites: Array<readonly { path: string; contents: Uint8Array }[]> = [];

  for (const artifact of artifacts) {
    try {
      const result = await build({
        absWorkingDir: moduleDirectory,
        // Every dependency, React included, is bundled. The artifact must run in any host, including
        // one that uses no React at all, so nothing is externalized (ADR 0023).
        bundle: true,
        define: {
          // React reads this at module scope. Without it the bundle would reference `process`, a
          // Node global that does not exist in a browser, and crash on load.
          "process.env.NODE_ENV": '"production"',
        },
        entryPoints: [artifact.sourceFile],
        // ESM only: the artifact is imported by a host with a dynamic `import()`, and the contract
        // requires a real default export.
        format: "esm",
        jsx: "automatic",
        // Unminified deliberately: an operator is expected to review the artifact they install
        // (see docs/development/security.md), and nothing else in this repository minifies.
        minify: false,
        outfile: artifact.outputFile,
        platform: "browser",
        plugins: [compileStylesheetImports()],
        sourcemap: true,
        target: MODULE_UI_BUILD_TARGET,
        // Fail rather than silently shipping a partial bundle.
        logLevel: "silent",
        // Compile every role successfully before writing any role. This makes a two-artifact build
        // atomic with respect to parse/resolve/bundle failures rather than leaving a stale partial set.
        write: false,
      });
      // Belt and braces on the stylesheet contract. The plugin above turns every `.css` import into
      // JavaScript, so esbuild has nothing left to emit a stylesheet from — but a future option or
      // loader change could reintroduce a sidecar, and a sidecar is precisely the failure this
      // design exists to make impossible: a file nothing declares, no host fetches, and every local
      // test silently passes without. Producing one fails the build rather than shipping it.
      const sidecar = result.outputFiles.find(
        (outputFile) => path.extname(outputFile.path).toLowerCase() === ".css",
      );
      if (sidecar) {
        throw new ModuleUiBuildError("MODULE_UI_STYLESHEET_UNDECLARED", artifact.kind);
      }
      pendingWrites.push(
        result.outputFiles.map((outputFile) => ({
          contents: outputFile.contents,
          path: outputFile.path,
        })),
      );
    } catch (error) {
      if (error instanceof ModuleUiBuildError) {
        throw error;
      }
      // esbuild's structured diagnostics are surfaced by the CLI; rethrow a sanitized error so a
      // programmatic caller never receives raw paths or internals.
      if (isRecord(error) && Array.isArray(error.errors)) {
        // A stylesheet the module authored broke one of this platform's own rules, rather than
        // failing to compile. Reported with its own code so a caller can tell "your CSS is not
        // allowed to do that" from "your TSX does not compile".
        const code = error.errors.some(
          (diagnostic) => isRecord(diagnostic) && diagnostic.pluginName === STYLESHEET_PLUGIN_NAME,
        )
          ? "MODULE_UI_STYLESHEET_INVALID"
          : "MODULE_UI_BUILD_FAILED";
        throw Object.assign(new ModuleUiBuildError(code, artifact.kind), {
          diagnostics: error.errors,
        });
      }
      throw new ModuleUiBuildError("MODULE_UI_BUILD_FAILED", artifact.kind);
    }
  }

  for (const [index, outputs] of pendingWrites.entries()) {
    try {
      for (const output of outputs) {
        await mkdir(path.dirname(output.path), { recursive: true });
        await writeFile(output.path, output.contents);
      }
    } catch {
      throw new ModuleUiBuildError("MODULE_UI_BUILD_FAILED", artifacts[index]?.kind);
    }
  }

  return Object.freeze({
    artifacts: Object.freeze(artifacts.map((artifact) => Object.freeze({ ...artifact }))),
  });
}