/*
 * Copyright 2024 Adobe. All rights reserved.
 * This file is licensed to you under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License. You may obtain a copy
 * of the License at http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under
 * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
 * OF ANY KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */
import {RenderProps, RuntimeStyleFunction} from './types';

// taken from: https://stackoverflow.com/questions/51603250/typescript-3-parameter-list-intersection-type/51604379#51604379
type ArgTypes<T> = T extends (props: infer V) => any ? NullToObject<V> : never;
type NullToObject<T> = T extends (null | undefined) ? {} : T;
type BoxedTupleTypes<T extends any[]> = { [P in keyof T]: [ArgTypes<T[P]>] }[Exclude<keyof T, keyof any[]>];
type BoxedReturnTypes<T extends any[]> = { [P in keyof T]: [InferReturn<T[P]>] }[Exclude<keyof T, keyof any[]>];
type UnboxIntersection<T> = T extends { 0: infer U } ? U : never;
type Arg<X, R> = RuntimeStyleFunction<X, R> | null | undefined;
type NoInfer<T> = [T, void][T extends any ? 0 : 1];
type InferReturn<T> = T extends (props: any) => infer R ? NullToObject<R> : never;
type UnionToIntersection<U> = (U extends any ? (k: U) => void : never) extends ((k: infer I) => void) ? I : never;
type InferReturnType<T extends any[]> = UnboxIntersection<UnionToIntersection<BoxedReturnTypes<T>>>;

// Two overloads:
// 1. If a render props type is expected based on the return type, forward that type to all arguments.
// 2. Otherwise, infer the return type based on the arguments.
export function merge<R extends RenderProps<string> = never, X = {}>(...args: Arg<NoInfer<X>, NoInfer<R>>[]): RuntimeStyleFunction<X, R>;
export function merge<T extends Arg<any, any>[]>(...args: T): RuntimeStyleFunction<InferReturnType<T>, UnboxIntersection<UnionToIntersection<BoxedTupleTypes<T>>>>;
export function merge(...args: any[]): RuntimeStyleFunction<any, any> {
  return (props) => {
    return mergeStyles(...args.map(f => typeof f === 'function' ? f(props) : null));
  };
}

export function mergeStyles(...styles: (string | null | undefined)[]): string {
  let map = new Map();
  for (let style of styles) {
    if (style) {
      for (let [k, v] of parse(style)) {
        map.set(k, v);
      }
    }
  }
  
  let res = '';
  for (let value of map.values()) {
    res += value;
  }
  return res;
}

function parse(s: string) {
  let properties = new Map<string, string>();
  let i = 0;
  while (i < s.length) {
    while (i < s.length && s[i] === ' ') {
      i++;
    }

    let start = i;
    readValue(); // property index

    // read conditions (up to the last segment)
    let condition = i;
    while (i < s.length && s[i] !== ' ') {
      readValue();
    }

    let property = s.slice(start, condition);
    properties.set(property, (properties.get(property) || '') + ' ' + s.slice(start, i));
  }

  function readValue() {
    if (s[i] === '-') {
      // the beginning and end of arbitrary values are marked with -
      while (i < s.length && s[i] !== ' ') {
        i++;
        if (s[i] === '-') {
          i++;
          break;
        }
      }
    } else {
      while (i < s.length) {
        if (s[i] === '_') {
          i++;
        } else {
          i++;
          break;
        }
      }
    }
  }

  return properties;
}