import CodeFile from "./CodeFile";

/**
 * THe number of lines to display when printing the context of the error.
 */
const CONTEXT_LINES_BEFORE = 5;

export default class CodeLocation {
  constructor(
    file: CodeFile | null = null,
    char: number = 0,
    line: number = 0,
    col: number = 0
  ) {
    this.file = file;
    this.char = char;
    this.line = line;
    this.col = col;
  }

  /**
   * THe file to which this location points.
   */
  readonly file: CodeFile | null;

  /**
   * The character offset in the file contents.
   */
  readonly char: number = 0;

  /**
   * The line number of this location. Zero-indexed.
   */
  readonly line: number = 0;

  /**
   * The column number of this location. Zero-indexed.
   */
  readonly col: number = 0;

  toString(): string {
    return `file '${this.filename}' line ${
      this.line + 1
    } column ${this.col + 1}'`;
  }

  formatWithContext() {
    if(!this.file) {
      throw new Error("No CodeFile associated with this location");
    }
    let outStr = `${this.filename}:${this.line + 1}:${this.col}:\n`;
    const sourceLines = this.file.code.split("\n");
    const contextStartIndex = Math.max(0, this.line - CONTEXT_LINES_BEFORE);

    const linesToDisplay = sourceLines.slice(contextStartIndex, this.line + 1);
    outStr += linesToDisplay.reduce((prev, line, index) => {
      return (
        prev +
        ` ${(contextStartIndex + index + 1).toString().padStart(3)}| ${line}\n`
      );
    }, "");
    outStr += "";
    for (let i = -5; i < this.col; i++) {
      outStr += " ";
    }
    outStr += "^\n";
    return outStr;
  }

  private get filename(): string {
    return this?.file?.filename || "<unknown>"
  }
}