import { Logger } from '@nestjs/common';
import type { RuleConfigIssue, RuleConfigParser } from './rule-config.types';

/**
 * Where a value is read from: the object, its field path (for messages) and
 * the list the issues go to. Helpers never throw - an invalid or missing key
 * gives the fallback, and an invalid one that is present is reported.
 */
export interface Scope {
  readonly raw: Readonly<Record<string, unknown>>;
  readonly path: string;
  readonly issues: RuleConfigIssue[];
}

const NO_VALUES: Readonly<Record<string, unknown>> = Object.freeze({});

export function asRecord(value: unknown): Record<string, unknown> | null {
  return typeof value === 'object' && value !== null && !Array.isArray(value)
    ? (value as Record<string, unknown>)
    : null;
}

export function rootScope(json: unknown, issues: RuleConfigIssue[]): Scope {
  return { raw: asRecord(json) ?? NO_VALUES, path: '', issues };
}

export function fieldPath(scope: Scope, key: string): string {
  return scope.path === '' ? key : `${scope.path}.${key}`;
}

export function report(scope: Scope, key: string, message: string): void {
  scope.issues.push({ field: fieldPath(scope, key), message });
}

/**
 * A key counts as given when it is present - an explicit null too, which the
 * readers then report as invalid instead of silently using the default.
 */
export function has(scope: Scope, key: string): boolean {
  if (!Object.hasOwn(scope.raw, key)) {
    return false;
  }
  return scope.raw[key] !== undefined;
}

/** An explicit null: on an optional key it clears the value. */
export function isCleared(scope: Scope, key: string): boolean {
  return Object.hasOwn(scope.raw, key) && scope.raw[key] === null;
}

/** The nested object under `key`; a non-object is reported and read as empty. */
export function childScope(scope: Scope, key: string): Scope {
  const path = fieldPath(scope, key);
  if (!has(scope, key)) {
    return { raw: NO_VALUES, path, issues: scope.issues };
  }
  const nested = asRecord(scope.raw[key]);
  if (nested === null) {
    report(scope, key, 'Bitte die Angaben als Gruppe senden.');
    return { raw: NO_VALUES, path, issues: scope.issues };
  }
  return { raw: nested, path, issues: scope.issues };
}

/** Runs `read`; if it reported anything, `fallback()` replaces its result. */
export function orFallback<T>(
  scope: Scope,
  read: () => T,
  fallback: () => T,
): T {
  const before = scope.issues.length;
  const value = read();
  return scope.issues.length > before ? fallback() : value;
}

const numberFormat = new Intl.NumberFormat('de-DE', {
  maximumFractionDigits: 3,
});

export function formatDe(value: number): string {
  return numberFormat.format(value);
}

export function intIn(
  scope: Scope,
  key: string,
  fallback: number,
  min: number,
  max: number,
): number {
  if (!has(scope, key)) {
    return fallback;
  }
  const value = scope.raw[key];
  if (
    typeof value === 'number' &&
    Number.isInteger(value) &&
    value >= min &&
    value <= max
  ) {
    return value;
  }
  report(
    scope,
    key,
    `Bitte eine ganze Zahl zwischen ${formatDe(min)} und ${formatDe(max)} wählen.`,
  );
  return fallback;
}

/** Like intIn, but an absent key stays undefined. */
export function optionalIntIn(
  scope: Scope,
  key: string,
  min: number,
  max: number,
): number | undefined {
  if (!has(scope, key) || isCleared(scope, key)) {
    return undefined;
  }
  const value = intIn(scope, key, Number.NaN, min, max);
  return Number.isNaN(value) ? undefined : value;
}

export interface NumberOptions {
  /** The lower limit itself is not allowed (min < x). */
  exclusiveMin?: boolean;
}

export function numberIn(
  scope: Scope,
  key: string,
  fallback: number,
  min: number,
  max: number,
  options: NumberOptions = {},
): number {
  if (!has(scope, key)) {
    return fallback;
  }
  const value = scope.raw[key];
  if (
    typeof value === 'number' &&
    Number.isFinite(value) &&
    (options.exclusiveMin ? value > min : value >= min) &&
    value <= max
  ) {
    return value;
  }
  const lower = options.exclusiveMin
    ? `größer als ${formatDe(min)}`
    : `mindestens ${formatDe(min)}`;
  report(
    scope,
    key,
    Number.isFinite(max)
      ? `Bitte eine Zahl ${lower} und höchstens ${formatDe(max)} angeben.`
      : `Bitte eine Zahl ${lower} angeben.`,
  );
  return fallback;
}

/** Like numberIn, but an absent key stays undefined. */
export function optionalNumberIn(
  scope: Scope,
  key: string,
  min: number,
  max: number,
  options: NumberOptions = {},
): number | undefined {
  if (!has(scope, key) || isCleared(scope, key)) {
    return undefined;
  }
  const value = numberIn(scope, key, Number.NaN, min, max, options);
  return Number.isNaN(value) ? undefined : value;
}

export function bool(scope: Scope, key: string, fallback: boolean): boolean {
  if (!has(scope, key)) {
    return fallback;
  }
  const value = scope.raw[key];
  if (typeof value === 'boolean') {
    return value;
  }
  report(scope, key, 'Bitte Ja oder Nein wählen.');
  return fallback;
}

export function stringIn(
  scope: Scope,
  key: string,
  fallback: string,
  minLength: number,
  maxLength: number,
  pattern?: RegExp,
): string {
  if (!has(scope, key)) {
    return fallback;
  }
  const value = scope.raw[key];
  if (
    typeof value === 'string' &&
    value.length >= minLength &&
    value.length <= maxLength &&
    (pattern === undefined || pattern.test(value))
  ) {
    return value;
  }
  report(
    scope,
    key,
    `Bitte einen Text mit ${minLength} bis ${maxLength} Zeichen angeben.`,
  );
  return fallback;
}

const MONTH_DAY = /^(\d{2})-(\d{2})$/;

/** 'MM-DD' that exists in a leap year (02-29 is allowed). */
export function isMonthDay(value: unknown): value is string {
  if (typeof value !== 'string') {
    return false;
  }
  const match = MONTH_DAY.exec(value);
  if (!match) {
    return false;
  }
  const month = Number(match[1]);
  const day = Number(match[2]);
  const date = new Date(Date.UTC(2024, month - 1, day));
  return date.getUTCMonth() === month - 1 && date.getUTCDate() === day;
}

export function monthDay(scope: Scope, key: string, fallback: string): string {
  if (!has(scope, key)) {
    return fallback;
  }
  const value = scope.raw[key];
  if (isMonthDay(value)) {
    return value;
  }
  report(scope, key, 'Bitte ein Datum als MM-TT angeben, zum Beispiel 03-20.');
  return fallback;
}

export function months(
  scope: Scope,
  key: string,
  fallback: readonly number[],
): number[] {
  if (!has(scope, key)) {
    return [...fallback];
  }
  const value = scope.raw[key];
  if (
    Array.isArray(value) &&
    value.every(
      (month): month is number =>
        typeof month === 'number' &&
        Number.isInteger(month) &&
        month >= 1 &&
        month <= 12,
    ) &&
    new Set(value).size === value.length
  ) {
    return [...value];
  }
  report(scope, key, 'Bitte Monate von 1 bis 12 angeben, jeden nur einmal.');
  return [...fallback];
}

export function enumValue<T extends string>(
  scope: Scope,
  key: string,
  fallback: T,
  allowed: readonly T[],
): T {
  if (!has(scope, key)) {
    return fallback;
  }
  const value = scope.raw[key];
  if (
    typeof value === 'string' &&
    (allowed as readonly string[]).includes(value)
  ) {
    return value as T;
  }
  report(scope, key, 'Bitte einen gültigen Wert wählen.');
  return fallback;
}

export function enumList<T extends string>(
  scope: Scope,
  key: string,
  fallback: readonly T[],
  allowed: readonly T[],
): T[] {
  if (!has(scope, key)) {
    return [...fallback];
  }
  const value = scope.raw[key];
  if (
    Array.isArray(value) &&
    value.every(
      (entry): entry is T =>
        typeof entry === 'string' &&
        (allowed as readonly string[]).includes(entry),
    ) &&
    new Set(value).size === value.length
  ) {
    return [...value];
  }
  report(scope, key, 'Bitte nur gültige Werte wählen, jeden nur einmal.');
  return [...fallback];
}

const logger = new Logger('RuleConfig');

/**
 * Builds the parser of one rule from its reader. The reader turns the scope
 * into a complete config and reports every invalid key; `parse` logs those
 * (trigger and field, never the value) and returns the config, `validate`
 * returns them.
 */
export function makeParser<T>(
  trigger: string,
  defaults: T,
  read: (scope: Scope) => T,
): RuleConfigParser<T> {
  return {
    defaults,
    parse(json) {
      const issues: RuleConfigIssue[] = [];
      const value = read(rootScope(json, issues));
      for (const issue of issues) {
        logger.warn(
          `Invalid setting ${trigger}.${issue.field}; using the default`,
        );
      }
      return value;
    },
    validate(json) {
      const issues: RuleConfigIssue[] = [];
      read(rootScope(json, issues));
      return issues;
    },
  };
}