// Parser for oxy conflict markers (spec §9.5). No vscode imports, so it is
// tested with plain Node.
//
//   <<<<<<< oxy conflict 1 of 2, side 1 of 2: change k7m2p9 "Add retry loop"
//   ...
//   ======= oxy conflict 1 of 2, side 2 of 2: change q3x8w1 "Refactor client"
//   ...
//   >>>>>>> oxy conflict 1 of 2 end
//
// A delete/insert conflict's first side reads `deleted by change X` and is
// followed by a `-------` line and the deleted context.

export interface ConflictSide {
  /** 1-based side number. */
  number: number;
  /** `k7m2p9 "Add retry loop"` or `deleted by change k7m2p9`. */
  label: string;
  deleted: boolean;
  /** Line index of the side's header. */
  header: number;
  /** Content lines (exclusive end). */
  start: number;
  end: number;
}

export interface ConflictRegion {
  number: number;
  total: number;
  /** Line index of `<<<<<<<`. */
  start: number;
  /** Line index of `>>>>>>>`. */
  end: number;
  sides: ConflictSide[];
}

const OPEN = /^<<<<<<< oxy conflict (\d+) of (\d+), side (\d+) of (\d+): (.*)$/;
const NEXT = /^======= oxy conflict (\d+) of (\d+), side (\d+) of (\d+): (.*)$/;
const CLOSE = /^>>>>>>> oxy conflict (\d+) of (\d+) end$/;

export function parseConflicts(lines: string[]): ConflictRegion[] {
  const regions: ConflictRegion[] = [];
  let current: ConflictRegion | undefined;
  let side: ConflictSide | undefined;
  for (let i = 0; i < lines.length; i++) {
    const line = lines[i];
    const open = OPEN.exec(line);
    if (open && !current) {
      current = { number: Number(open[1]), total: Number(open[2]), start: i, end: -1, sides: [] };
      side = newSide(Number(open[3]), open[5], i);
      if (side.deleted && lines[i + 1] === "-------") {
        side.start = i + 2;
        i += 1;
      }
      current.sides.push(side);
      continue;
    }
    const next = current ? NEXT.exec(line) : null;
    if (next && current && side) {
      side.end = i;
      side = newSide(Number(next[3]), next[5], i);
      current.sides.push(side);
      continue;
    }
    const close = current ? CLOSE.exec(line) : null;
    if (close && current && side) {
      side.end = i;
      current.end = i;
      regions.push(current);
      current = undefined;
      side = undefined;
    }
  }
  return regions;
}

function newSide(number: number, label: string, header: number): ConflictSide {
  const deleted = label.startsWith("deleted by change ");
  return { number, label: deleted ? label : label.replace(/^change /, ""), deleted, header, start: header + 1, end: header + 1 };
}

/** The lines that replace a region when `keep` (side numbers) are kept, in order. */
export function resolveRegion(lines: string[], region: ConflictRegion, keep: number[]): string[] {
  const out: string[] = [];
  for (const n of keep) {
    const side = region.sides.find((s) => s.number === n);
    if (!side || side.deleted) {
      continue;
    }
    out.push(...lines.slice(side.start, side.end));
  }
  return out;
}

/** A conflict candidate file's real name, or undefined. */
export function candidateBase(path: string): string | undefined {
  const m = /^(.*)\.oxy-conflict-\d+$/.exec(path);
  return m ? m[1] : undefined;
}