/**
 * Copyright (c) 2017 The xterm.js authors. All rights reserved.
 * @license MIT
 */

import { ITerminal } from '../../Types';
import { IColorSet } from '../Types';
import { ICharAtlasConfig } from '../../shared/atlas/Types';
import { generateConfig, configEquals } from './CharAtlasUtils';
import BaseCharAtlas from './BaseCharAtlas';
import NoneCharAtlas from './NoneCharAtlas';
import StaticCharAtlas from './StaticCharAtlas';

const charAtlasImplementations = {
  'none': NoneCharAtlas,
  'static': StaticCharAtlas,
};

interface ICharAtlasCacheEntry {
  atlas: BaseCharAtlas;
  config: ICharAtlasConfig;
  // N.B. This implementation potentially holds onto copies of the terminal forever, so
  // this may cause memory leaks.
  ownedBy: ITerminal[];
}

const charAtlasCache: ICharAtlasCacheEntry[] = [];

/**
 * Acquires a char atlas, either generating a new one or returning an existing
 * one that is in use by another terminal.
 * @param terminal The terminal.
 * @param colors The colors to use.
 */
export function acquireCharAtlas(
  terminal: ITerminal,
  colors: IColorSet,
  scaledCharWidth: number,
  scaledCharHeight: number,
): BaseCharAtlas {
  const newConfig = generateConfig(scaledCharWidth, scaledCharHeight, terminal, colors);

  // Check to see if the terminal already owns this config
  for (let i = 0; i < charAtlasCache.length; i++) {
    const entry = charAtlasCache[i];
    const ownedByIndex = entry.ownedBy.indexOf(terminal);
    if (ownedByIndex >= 0) {
      if (configEquals(entry.config, newConfig)) {
        return entry.atlas;
      } else {
        // The configs differ, release the terminal from the entry
        if (entry.ownedBy.length === 1) {
          charAtlasCache.splice(i, 1);
        } else {
          entry.ownedBy.splice(ownedByIndex, 1);
        }
        break;
      }
    }
  }

  // Try match a char atlas from the cache
  for (let i = 0; i < charAtlasCache.length; i++) {
    const entry = charAtlasCache[i];
    if (configEquals(entry.config, newConfig)) {
      // Add the terminal to the cache entry and return
      entry.ownedBy.push(terminal);
      return entry.atlas;
    }
  }

  const newEntry: ICharAtlasCacheEntry = {
    atlas: new charAtlasImplementations[terminal.options.experimentalCharAtlas](
      document,
      newConfig,
    ),
    config: newConfig,
    ownedBy: [terminal],
  };
  charAtlasCache.push(newEntry);
  return newEntry.atlas;
}