import type { RuntimeConfigArtifact } from "./release-artifacts.ts";

/**
 * §6.4. Which environment an artifact is allowed to be deployed to.
 *
 * Release coherence answers "do these artifacts describe each other?". It does
 * not answer "is this the artifact production should receive?", and the two are
 * not the same question: a build whose runtime document says `APP_ENV: local`,
 * `AUTH_MODE: demo` and `API_BASE_URL: http://localhost:8080/` is perfectly
 * coherent with itself. Without an admission step such a build is a valid
 * release candidate, and the only thing standing between it and production is
 * that nobody happened to promote it.
 *
 * Admission is therefore a separate, declared decision: a caller states the
 * target it intends, and this module says whether the artifact may go there.
 * Every rule below is a refusal, so an unrecognised target or an unreadable
 * field fails closed rather than passing by omission.
 */

export const DEPLOYMENT_TARGETS = Object.freeze([
  "local",
  "development",
  "staging",
  "production",
] as const);

export type DeploymentTarget = (typeof DEPLOYMENT_TARGETS)[number];

/**
 * Targets that serve real users over the public internet. They carry the full
 * rule set; `local` and `development` only have to be honest about what they
 * are.
 */
const PUBLIC_TARGETS: ReadonlySet<DeploymentTarget> = new Set([
  "staging",
  "production",
]);

/** Placeholder identifiers a developer build emits when nothing supplied one. */
const PLACEHOLDER_IDENTIFIERS: ReadonlySet<string> = new Set([
  "local-build",
  "local-release",
  "local",
  "dev",
  "unknown",
]);

export type AdmissionViolation = Readonly<{ field: string; reason: string }>;

export type AdmissionInput = RuntimeConfigArtifact &
  Readonly<{ BUILD_ID?: string; RELEASE_ID?: string }>;

export function isDeploymentTarget(value: unknown): value is DeploymentTarget {
  return (
    typeof value === "string" &&
    (DEPLOYMENT_TARGETS as readonly string[]).includes(value)
  );
}

/**
 * Every reason this artifact may not be deployed to `target`. An empty list is
 * the only admission.
 */
export function findAdmissionViolations(
  target: DeploymentTarget,
  config: AdmissionInput,
): readonly AdmissionViolation[] {
  const violations: AdmissionViolation[] = [];
  if (config.APP_ENV !== target) {
    violations.push({
      field: "APP_ENV",
      reason: `artifact declares ${config.APP_ENV} but is being admitted to ${target}`,
    });
  }
  if (!PUBLIC_TARGETS.has(target)) return Object.freeze(violations);

  if (config.AUTH_MODE !== "external") {
    violations.push({
      field: "AUTH_MODE",
      reason: `${target} requires an external identity provider, not ${config.AUTH_MODE}`,
    });
  }
  violations.push(...publicEndpointViolations("API_BASE_URL", config.API_BASE_URL));
  if (config.TELEMETRY_ENABLED && !config.TELEMETRY_ENDPOINT) {
    violations.push({
      field: "TELEMETRY_ENDPOINT",
      reason: "telemetry is enabled without an endpoint",
    });
  }
  if (config.TELEMETRY_ENDPOINT) {
    violations.push(
      ...publicEndpointViolations("TELEMETRY_ENDPOINT", config.TELEMETRY_ENDPOINT),
    );
  }
  for (const field of ["BUILD_ID", "RELEASE_ID"] as const) {
    const value = config[field];
    if (typeof value !== "string" || value.length === 0) {
      violations.push({ field, reason: `${target} requires a build identity` });
      continue;
    }
    if (PLACEHOLDER_IDENTIFIERS.has(value.toLowerCase())) {
      violations.push({
        field,
        reason: `${value} is a developer placeholder, not a released identity`,
      });
    }
  }
  return Object.freeze(violations);
}

function publicEndpointViolations(
  field: string,
  value: string,
): readonly AdmissionViolation[] {
  let url: URL;
  try {
    url = new URL(value);
  } catch {
    return [{ field, reason: "is not an absolute URL" }];
  }
  const violations: AdmissionViolation[] = [];
  if (url.protocol !== "https:") {
    violations.push({ field, reason: `${url.protocol} is not permitted; use https` });
  }
  if (isNonPublicHost(url.hostname)) {
    violations.push({
      field,
      reason: `${url.hostname} is not reachable from a user's browser`,
    });
  }
  return violations;
}

/**
 * Hosts that only resolve inside the machine or network that built the
 * artifact. A deployment pointing at one of these is a developer configuration
 * that escaped, not a production endpoint.
 */
function isNonPublicHost(hostname: string): boolean {
  const host = hostname.toLowerCase().replace(/^\[|\]$/gu, "");
  if (
    host === "localhost" ||
    host.endsWith(".localhost") ||
    host === "::1" ||
    host === "0.0.0.0" ||
    host === "::"
  ) {
    return true;
  }
  const octets = /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/u.exec(host);
  if (!octets) return false;
  const [first, second] = [Number(octets[1]), Number(octets[2])];
  return (
    first === 127 ||
    first === 10 ||
    (first === 192 && second === 168) ||
    (first === 172 && second >= 16 && second <= 31) ||
    (first === 169 && second === 254)
  );
}