// A source map for the page's script as web/build.mts makes it, files joined one after another
// (#390): each line of the joined script maps to its line in the file it came from. Given to swc
// as the input map, the built script then maps to web/src/*.ts file by file, which is what the
// coverage report needs. Only a coverage build uses it.

export interface SourceMap {
  version: 3;
  sources: string[];
  sourcesContent: string[];
  names: string[];
  mappings: string;
}

const B64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

/// One number in a source map's base64 VLQ: sign in the lowest bit, five bits a digit.
export function vlq(n: number): string {
  let v = n < 0 ? (-n << 1) | 1 : n << 1;
  let out = '';
  do {
    let digit = v & 31;
    v >>>= 5;
    if (v) digit |= 32;
    out += B64[digit];
  } while (v);
  return out;
}

/// The map of `files` joined with '\n' between them, as build.mts joins them.
export function concatMap(files: { name: string; text: string }[]): SourceMap {
  const lines: string[] = [];
  // Each segment's fields are relative to the one before: source, line in it, column.
  let lastSource = 0, lastLine = 0;
  files.forEach((f, source) => {
    const count = f.text.split('\n').length;
    for (let line = 0; line < count; line++) {
      lines.push(vlq(0) + vlq(source - lastSource) + vlq(line - lastLine) + vlq(0));
      lastSource = source;
      lastLine = line;
    }
  });
  return {
    version: 3,
    sources: files.map((f) => f.name),
    sourcesContent: files.map((f) => f.text),
    names: [],
    mappings: lines.join(';'),
  };
}