/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

//copied from https://github.com/Microsoft/vscode/blob/015c3afe96966df50c15a7d66be2ab0ef1dc5f49/src/vs/editor/common/model/indentationGuesser.ts

import { CharCode } from './charCode';
import { TextBuffer } from './textBuffer';

class SpacesDiffResult {
  public spacesDiff = 0;
  public looksLikeAlignment = false;
}

/**
 * Compute the diff in spaces between two line's indentation.
 */
function spacesDiff(a: string, aLength: number, b: string, bLength: number, result: SpacesDiffResult): void {
  result.spacesDiff = 0;
  result.looksLikeAlignment = false;

  // This can go both ways (e.g.):
  //  - a: "\t"
  //  - b: "\t    "
  //  => This should count 1 tab and 4 spaces

  let i: number;

  for (i = 0; i < aLength && i < bLength; i++) {
    const aCharCode = a.charCodeAt(i);
    const bCharCode = b.charCodeAt(i);

    if (aCharCode !== bCharCode) {
      break;
    }
  }

  let aSpacesCnt = 0,
    aTabsCount = 0;
  for (let j = i; j < aLength; j++) {
    const aCharCode = a.charCodeAt(j);
    if (aCharCode === CharCode.Space) {
      aSpacesCnt++;
    } else {
      aTabsCount++;
    }
  }

  let bSpacesCnt = 0,
    bTabsCount = 0;
  for (let j = i; j < bLength; j++) {
    const bCharCode = b.charCodeAt(j);
    if (bCharCode === CharCode.Space) {
      bSpacesCnt++;
    } else {
      bTabsCount++;
    }
  }

  if (aSpacesCnt > 0 && aTabsCount > 0) {
    return;
  }
  if (bSpacesCnt > 0 && bTabsCount > 0) {
    return;
  }

  const tabsDiff = Math.abs(aTabsCount - bTabsCount);
  const spacesDiff = Math.abs(aSpacesCnt - bSpacesCnt);

  if (tabsDiff === 0) {
    // check if the indentation difference might be caused by alignment reasons
    // sometime folks like to align their code, but this should not be used as a hint
    result.spacesDiff = spacesDiff;

    if (spacesDiff > 0 && 0 <= bSpacesCnt - 1 && bSpacesCnt - 1 < a.length && bSpacesCnt < b.length) {
      if (b.charCodeAt(bSpacesCnt) !== CharCode.Space && a.charCodeAt(bSpacesCnt - 1) === CharCode.Space) {
        if (a.charCodeAt(a.length - 1) === CharCode.Comma) {
          // This looks like an alignment desire: e.g.
          // const a = b + c,
          //       d = b - c;
          result.looksLikeAlignment = true;
        }
      }
    }
    return;
  }
  if (spacesDiff % tabsDiff === 0) {
    result.spacesDiff = spacesDiff / tabsDiff;
  }
}

/**
 * Result for a guessIndentation
 */
export interface IGuessedIndentation {
  /**
   * If indentation is based on spaces (`insertSpaces` = true), then what is the number of spaces that make an indent?
   */
  tabSize: number;
  /**
   * Is indentation based on spaces?
   */
  insertSpaces: boolean;
}

export function guessIndentation(source: TextBuffer, defaultTabSize: number, defaultInsertSpaces: boolean): IGuessedIndentation {
  // Look at most at the first 10k lines
  const linesCount = Math.min(source.getLineCount(), 10000);

  let linesIndentedWithTabsCount = 0; // number of lines that contain at least one tab in indentation
  let linesIndentedWithSpacesCount = 0; // number of lines that contain only spaces in indentation

  let previousLineText = ''; // content of latest line that contained non-whitespace chars
  let previousLineIndentation = 0; // index at which latest line contained the first non-whitespace char

  const ALLOWED_TAB_SIZE_GUESSES = [2, 4, 6, 8, 3, 5, 7]; // prefer even guesses for `tabSize`, limit to [2, 8].
  const MAX_ALLOWED_TAB_SIZE_GUESS = 8; // max(ALLOWED_TAB_SIZE_GUESSES) = 8

  const spacesDiffCount = [0, 0, 0, 0, 0, 0, 0, 0, 0]; // `tabSize` scores
  const tmp = new SpacesDiffResult();

  for (let lineNumber = 1; lineNumber <= linesCount; lineNumber++) {
    const currentLineLength = source.getLineLength(lineNumber);
    const currentLineText = source.getLineContent(lineNumber);

    // if the text buffer is chunk based, so long lines are cons-string, v8 will flattern the string when we check charCode.
    // checking charCode on chunks directly is cheaper.
    const useCurrentLineText = currentLineLength <= 65536;

    let currentLineHasContent = false; // does `currentLineText` contain non-whitespace chars
    let currentLineIndentation = 0; // index at which `currentLineText` contains the first non-whitespace char
    let currentLineSpacesCount = 0; // count of spaces found in `currentLineText` indentation
    let currentLineTabsCount = 0; // count of tabs found in `currentLineText` indentation
    for (let j = 0, lenJ = currentLineLength; j < lenJ; j++) {
      const charCode = useCurrentLineText ? currentLineText.charCodeAt(j) : source.getLineCharCode(lineNumber, j);

      if (charCode === CharCode.Tab) {
        currentLineTabsCount++;
      } else if (charCode === CharCode.Space) {
        currentLineSpacesCount++;
      } else {
        // Hit non whitespace character on this line
        currentLineHasContent = true;
        currentLineIndentation = j;
        break;
      }
    }

    // Ignore empty or only whitespace lines
    if (!currentLineHasContent) {
      continue;
    }

    if (currentLineTabsCount > 0) {
      linesIndentedWithTabsCount++;
    } else if (currentLineSpacesCount > 1) {
      linesIndentedWithSpacesCount++;
    }

    spacesDiff(previousLineText, previousLineIndentation, currentLineText, currentLineIndentation, tmp);

    if (tmp.looksLikeAlignment) {
      // if defaultInsertSpaces === true && the spaces count == tabSize, we may want to count it as valid indentation
      //
      // - item1
      //   - item2
      //
      // otherwise skip this line entirely
      //
      // const a = 1,
      //       b = 2;

      if (!(defaultInsertSpaces && defaultTabSize === tmp.spacesDiff)) {
        continue;
      }
    }

    const currentSpacesDiff = tmp.spacesDiff;
    if (currentSpacesDiff <= MAX_ALLOWED_TAB_SIZE_GUESS) {
      spacesDiffCount[currentSpacesDiff]++;
    }

    previousLineText = currentLineText;
    previousLineIndentation = currentLineIndentation;
  }

  let insertSpaces = defaultInsertSpaces;
  if (linesIndentedWithTabsCount !== linesIndentedWithSpacesCount) {
    insertSpaces = linesIndentedWithTabsCount < linesIndentedWithSpacesCount;
  }

  let tabSize = defaultTabSize;

  // Guess tabSize only if inserting spaces...
  if (insertSpaces) {
    let tabSizeScore = insertSpaces ? 0 : 0.1 * linesCount;

    // console.log("score threshold: " + tabSizeScore);

    ALLOWED_TAB_SIZE_GUESSES.forEach((possibleTabSize) => {
      const possibleTabSizeScore = spacesDiffCount[possibleTabSize];
      if (possibleTabSizeScore > tabSizeScore) {
        tabSizeScore = possibleTabSizeScore;
        tabSize = possibleTabSize;
      }
    });

    // Let a tabSize of 2 win even if it is not the maximum
    // (only in case 4 was guessed)
    if (tabSize === 4 && spacesDiffCount[4] > 0 && spacesDiffCount[2] > 0 && spacesDiffCount[2] >= spacesDiffCount[4] / 2) {
      tabSize = 2;
    }
  }

  // console.log('--------------------------');
  // console.log('linesIndentedWithTabsCount: ' + linesIndentedWithTabsCount + ', linesIndentedWithSpacesCount: ' + linesIndentedWithSpacesCount);
  // console.log('spacesDiffCount: ' + spacesDiffCount);
  // console.log('tabSize: ' + tabSize + ', tabSizeScore: ' + tabSizeScore);

  return {
    insertSpaces: insertSpaces,
    tabSize: tabSize,
  };
}
