import type { PasswordPolicy } from "../shared/types";

export interface GeneratorState {
  currentLength: number;
  userHasAdjusted: boolean;
}

export interface PolicyResult {
  length: number;
  sliderMin: number;
  sliderMax: number;
  constraintNote: string;
}

const DEFAULT_LENGTH = 64;
const DEFAULT_SLIDER_MIN = 8;
const DEFAULT_SLIDER_MAX = 256;

export function initGeneratorState(): GeneratorState {
  return { currentLength: DEFAULT_LENGTH, userHasAdjusted: false };
}

export function handleLengthChange(state: GeneratorState, length: number): GeneratorState {
  return { ...state, currentLength: length, userHasAdjusted: true };
}

export function initFromPolicy(
  policy: PasswordPolicy | null,
  state: { currentLength: number; userHasAdjusted: boolean },
): PolicyResult {
  const sliderMin = policy?.minLength ? Math.max(1, policy.minLength) : DEFAULT_SLIDER_MIN;
  const sliderMax = policy?.maxLength ? Math.min(DEFAULT_SLIDER_MAX, policy.maxLength) : DEFAULT_SLIDER_MAX;

  let length = state.currentLength;

  if (policy) {
    if (policy.maxLength !== undefined && policy.minLength !== undefined) {
      // Both bounds: always clamp to valid range, regardless of userHasAdjusted
      length = Math.max(policy.minLength, Math.min(policy.maxLength, state.currentLength));
    } else if (policy.maxLength !== undefined) {
      if (!state.userHasAdjusted) {
        // Fresh open: offer the strongest password the site accepts
        length = policy.maxLength;
      } else if (state.currentLength > policy.maxLength) {
        // User above max: snap down
        length = policy.maxLength;
      }
    } else if (policy.minLength !== undefined && state.currentLength < policy.minLength) {
      // Below min: snap up
      length = policy.minLength;
    }
  }

  let constraintNote = "";
  if (policy) {
    if (policy.maxLength !== undefined && length >= policy.maxLength) {
      constraintNote = `This site allows max ${policy.maxLength} characters`;
    } else if (policy.minLength !== undefined && length <= policy.minLength) {
      constraintNote = `This site requires at least ${policy.minLength} characters`;
    }
  }

  return { length, sliderMin, sliderMax, constraintNote };
}