import { truncateToWidth, visibleWidth } from "@earendil-works/pi-tui";

import type { RpConfig } from "./types.js";

export interface DiffSummaryStats {
  added: number;
  removed: number;
  hunks: number;
  files: number;
}

export type DiffPresentationMode = "split" | "unified" | "compact" | "summary";

const MIN_COMPACT_DIFF_WIDTH = 8;
const MIN_UNIFIED_DIFF_WIDTH = 18;

function pluralize(count: number, singular: string): string {
  return count === 1 ? singular : `${singular}s`;
}

export function normalizeDiffRenderWidth(width: number): number {
  if (!Number.isFinite(width)) {
    return 0;
  }

  return Math.max(0, Math.floor(width));
}

export function resolveDiffPresentationMode(
  config: Pick<RpConfig, "diffViewMode" | "diffSplitMinWidth">,
  width: number,
  canRenderSplitLayout: boolean
): DiffPresentationMode {
  const safeWidth = normalizeDiffRenderWidth(width);

  if (safeWidth < MIN_COMPACT_DIFF_WIDTH) {
    return "summary";
  }

  if (safeWidth < MIN_UNIFIED_DIFF_WIDTH) {
    return "compact";
  }

  switch (config.diffViewMode) {
    case "split":
      return canRenderSplitLayout ? "split" : "unified";
    case "unified":
      return "unified";
    case "auto":
    default:
      return safeWidth >= (config.diffSplitMinWidth ?? 120) && canRenderSplitLayout
        ? "split"
        : "unified";
  }
}

export function buildDiffSummaryText(stats: DiffSummaryStats, width: number): string {
  const safeWidth = normalizeDiffRenderWidth(width);
  if (safeWidth === 0) {
    return "";
  }

  const summaryCandidates = [
    `↳ diff +${stats.added} -${stats.removed} • ${stats.hunks} ${pluralize(stats.hunks, "hunk")} • ${stats.files} ${pluralize(stats.files, "file")}`,
    `↳ diff +${stats.added} -${stats.removed} • ${stats.hunks}h • ${stats.files}f`,
    `↳ diff +${stats.added} -${stats.removed}`,
    `+${stats.added} -${stats.removed}`,
    "diff",
    "…",
  ];

  for (const candidate of summaryCandidates) {
    if (visibleWidth(candidate) <= safeWidth) {
      return candidate;
    }
  }

  return truncateToWidth(summaryCandidates[summaryCandidates.length - 1] ?? "", safeWidth, "");
}