import type { ConfigDiffView, DiffLine } from "../contracts/workspace";

export function computeLineDiff(previous: string, next: string): DiffLine[] {
  const previousLines = previous.split("\n");
  const nextLines = next.split("\n");
  const m = previousLines.length;
  const n = nextLines.length;
  // classic LCS table; config files are small enough for O(m*n)
  const lcs: number[][] = Array.from({ length: m + 1 }, () => new Array<number>(n + 1).fill(0));
  for (let i = m - 1; i >= 0; i -= 1) {
    for (let j = n - 1; j >= 0; j -= 1) {
      lcs[i][j] = previousLines[i] === nextLines[j] ? lcs[i + 1][j + 1] + 1 : Math.max(lcs[i + 1][j], lcs[i][j + 1]);
    }
  }
  const lines: DiffLine[] = [];
  let i = 0;
  let j = 0;
  while (i < m && j < n) {
    if (previousLines[i] === nextLines[j]) {
      lines.push({ kind: "same", text: previousLines[i] });
      i += 1;
      j += 1;
    } else if (lcs[i + 1][j] >= lcs[i][j + 1]) {
      lines.push({ kind: "removed", text: previousLines[i] });
      i += 1;
    } else {
      lines.push({ kind: "added", text: nextLines[j] });
      j += 1;
    }
  }
  while (i < m) {
    lines.push({ kind: "removed", text: previousLines[i] });
    i += 1;
  }
  while (j < n) {
    lines.push({ kind: "added", text: nextLines[j] });
    j += 1;
  }
  return lines;
}

export function buildConfigDiff(serverInstanceId: string, previous: string, next: string): ConfigDiffView {
  const lines = computeLineDiff(previous, next);
  const added = lines.filter((line) => line.kind === "added").length;
  const removed = lines.filter((line) => line.kind === "removed").length;
  return {
    serverInstanceId,
    summary: `+${added} / -${removed} 行变更`,
    lines,
    nextContent: next
  };
}

export function diffHasChanges(diff: ConfigDiffView): boolean {
  return diff.lines.some((line) => line.kind !== "same");
}