import type { ErrorCode } from "./error";

export const LIBRARY_OVERRIDE_FRESHNESS_SCHEMA = 1 as const;
export const LIBRARY_OVERRIDE_COMMIT_OPERATION = "COMMIT_OVERRIDE" as const;

export interface OverrideFreshnessStateIR {
  schemaVersion: typeof LIBRARY_OVERRIDE_FRESHNESS_SCHEMA;
  sourceLibraryId: string;
  sourceGeneration: number;
  sourceRevision: number;
  dependencyClosureSha256: string;
  invalidationToken: string;
  localDataBlockId: string;
  referenceSourceDataBlockId: string;
  hierarchyRootDataBlockId: string;
  owner: "LOCAL_OVERRIDE";
  readOnly: false;
  referenceReadOnly: true;
}

export interface OverrideFreshnessRequestIR {
  schemaVersion: typeof LIBRARY_OVERRIDE_FRESHNESS_SCHEMA;
  operation: typeof LIBRARY_OVERRIDE_COMMIT_OPERATION;
  sourceLibraryId: string;
  sourceGeneration: number;
  sourceRevision: number;
  dependencyClosureSha256: string;
  invalidationToken: string;
  baseRevision: number;
  localDataBlockId: string;
  referenceSourceDataBlockId: string;
  hierarchyRootDataBlockId: string;
  owner: "LOCAL_OVERRIDE";
  readOnly: false;
  referenceReadOnly: true;
}

export interface OverrideFreshnessDecisionIR {
  status: "READY" | "BLOCKED";
  code: ErrorCode | null;
}

export class OverrideFreshnessValidationError extends Error {
  readonly code: ErrorCode;
  readonly path?: string;

  constructor(code: ErrorCode, message: string, path?: string) {
    super(`${code}: ${message}`);
    this.name = "OverrideFreshnessValidationError";
    this.code = code;
    this.path = path;
  }
}

const LIBRARY_ID = /^library:[a-f0-9]{64}$/;
const SHA256 = /^[a-f0-9]{64}$/;
const TOKEN = /^override-token:[a-f0-9]{64}$/;
const DATA_BLOCK_ID = /^[A-Za-z0-9][A-Za-z0-9:._/ -]{0,255}$/;

function record(value: unknown, path: string): Record<string, unknown> {
  if (typeof value !== "object" || value === null || Array.isArray(value)) throw new OverrideFreshnessValidationError("TASK_VALIDATION_FAILED", `${path} must be an object`, path);
  return value as Record<string, unknown>;
}

function exactKeys(value: Record<string, unknown>, expected: readonly string[], path: string): void {
  const actual = Object.keys(value).sort();
  const allowed = [...expected].sort();
  if (actual.length !== allowed.length || actual.some((key, index) => key !== allowed[index])) throw new OverrideFreshnessValidationError("TASK_VALIDATION_FAILED", `${path} contains undeclared fields`, path);
}

function integer(value: unknown, path: string): number {
  if (typeof value !== "number" || !Number.isSafeInteger(value) || value < 0) throw new OverrideFreshnessValidationError("TASK_VALIDATION_FAILED", `${path} must be a safe integer >= 0`, path);
  return value;
}

function id(value: unknown, path: string): string {
  if (typeof value !== "string" || !DATA_BLOCK_ID.test(value)) throw new OverrideFreshnessValidationError("TASK_VALIDATION_FAILED", `${path} is invalid`, path);
  return value;
}

function digest(value: unknown, path: string): string {
  if (typeof value !== "string" || !SHA256.test(value)) throw new OverrideFreshnessValidationError("TASK_VALIDATION_FAILED", `${path} must be a SHA-256 digest`, path);
  return value;
}

function library(value: unknown, path: string): string {
  if (typeof value !== "string" || !LIBRARY_ID.test(value)) throw new OverrideFreshnessValidationError("TASK_VALIDATION_FAILED", `${path} must be a library identity`, path);
  return value;
}

function token(value: unknown, path: string): string {
  if (typeof value !== "string" || !TOKEN.test(value)) throw new OverrideFreshnessValidationError("TASK_VALIDATION_FAILED", `${path} must be an invalidation token`, path);
  return value;
}

function ownership(value: Record<string, unknown>, path: string): void {
  if (value.owner !== "LOCAL_OVERRIDE" || value.readOnly !== false || value.referenceReadOnly !== true) throw new OverrideFreshnessValidationError("LINKED_DATA_MUTATION_BLOCKED", `${path} ownership semantics are invalid`, path);
}

const COMMON_KEYS = ["schemaVersion", "sourceLibraryId", "sourceGeneration", "sourceRevision", "dependencyClosureSha256", "invalidationToken", "localDataBlockId", "referenceSourceDataBlockId", "hierarchyRootDataBlockId", "owner", "readOnly", "referenceReadOnly"] as const;

export function parseOverrideFreshnessState(value: unknown): OverrideFreshnessStateIR {
  const state = record(value, "state");
  exactKeys(state, COMMON_KEYS, "state");
  if (state.schemaVersion !== LIBRARY_OVERRIDE_FRESHNESS_SCHEMA) throw new OverrideFreshnessValidationError("PROTOCOL_MISMATCH", "Unsupported override freshness state schema", "schemaVersion");
  ownership(state, "state");
  const sourceLibraryId = library(state.sourceLibraryId, "sourceLibraryId");
  return {
    schemaVersion: LIBRARY_OVERRIDE_FRESHNESS_SCHEMA,
    sourceLibraryId,
    sourceGeneration: integer(state.sourceGeneration, "sourceGeneration"),
    sourceRevision: integer(state.sourceRevision, "sourceRevision"),
    dependencyClosureSha256: digest(state.dependencyClosureSha256, "dependencyClosureSha256"),
    invalidationToken: token(state.invalidationToken, "invalidationToken"),
    localDataBlockId: id(state.localDataBlockId, "localDataBlockId"),
    referenceSourceDataBlockId: id(state.referenceSourceDataBlockId, "referenceSourceDataBlockId"),
    hierarchyRootDataBlockId: id(state.hierarchyRootDataBlockId, "hierarchyRootDataBlockId"),
    owner: "LOCAL_OVERRIDE",
    readOnly: false,
    referenceReadOnly: true,
  };
}

export function parseOverrideFreshnessRequest(value: unknown): OverrideFreshnessRequestIR {
  const request = record(value, "request");
  exactKeys(request, [...COMMON_KEYS, "operation", "baseRevision"], "request");
  if (request.schemaVersion !== LIBRARY_OVERRIDE_FRESHNESS_SCHEMA) throw new OverrideFreshnessValidationError("PROTOCOL_MISMATCH", "Unsupported override freshness request schema", "schemaVersion");
  if (request.operation !== LIBRARY_OVERRIDE_COMMIT_OPERATION) throw new OverrideFreshnessValidationError("TASK_VALIDATION_FAILED", "override commit operation is invalid", "operation");
  ownership(request, "request");
  return {
    schemaVersion: LIBRARY_OVERRIDE_FRESHNESS_SCHEMA,
    operation: LIBRARY_OVERRIDE_COMMIT_OPERATION,
    sourceLibraryId: library(request.sourceLibraryId, "sourceLibraryId"),
    sourceGeneration: integer(request.sourceGeneration, "sourceGeneration"),
    sourceRevision: integer(request.sourceRevision, "sourceRevision"),
    dependencyClosureSha256: digest(request.dependencyClosureSha256, "dependencyClosureSha256"),
    invalidationToken: token(request.invalidationToken, "invalidationToken"),
    baseRevision: integer(request.baseRevision, "baseRevision"),
    localDataBlockId: id(request.localDataBlockId, "localDataBlockId"),
    referenceSourceDataBlockId: id(request.referenceSourceDataBlockId, "referenceSourceDataBlockId"),
    hierarchyRootDataBlockId: id(request.hierarchyRootDataBlockId, "hierarchyRootDataBlockId"),
    owner: "LOCAL_OVERRIDE",
    readOnly: false,
    referenceReadOnly: true,
  };
}

export function gateOverrideFreshness(stateValue: unknown, requestValue: unknown): OverrideFreshnessDecisionIR {
  let state: OverrideFreshnessStateIR;
  let request: OverrideFreshnessRequestIR;
  try {
    state = parseOverrideFreshnessState(stateValue);
    request = parseOverrideFreshnessRequest(requestValue);
  }
  catch (error) {
    return { status: "BLOCKED", code: error instanceof OverrideFreshnessValidationError ? error.code : "TASK_VALIDATION_FAILED" };
  }
  if (request.baseRevision !== state.sourceRevision || request.sourceLibraryId !== state.sourceLibraryId || request.sourceGeneration !== state.sourceGeneration || request.sourceRevision !== state.sourceRevision || request.dependencyClosureSha256 !== state.dependencyClosureSha256 || request.invalidationToken !== state.invalidationToken) {
    return { status: "BLOCKED", code: "REVISION_CONFLICT" };
  }
  if (request.localDataBlockId !== state.localDataBlockId || request.referenceSourceDataBlockId !== state.referenceSourceDataBlockId || request.hierarchyRootDataBlockId !== state.hierarchyRootDataBlockId) {
    return { status: "BLOCKED", code: "ASSET_SOURCE_HASH_MISMATCH" };
  }
  return { status: "READY", code: null };
}