/**
 * Build and send Discord channel webhook messages.
 *
 * Discord embed limits we respect:
 *   - field.value <= 1024 chars
 *   - up to 25 fields
 *   - total embed <= 6000 chars
 * See: https://discord.com/developers/docs/resources/webhook
 */

import type { BatchState, LibraryItem } from "./types.js";
import { figmaFileUrl } from "./figma.js";

const MAX_ITEMS_PER_FIELD = 15;
const FIELD_VALUE_MAX = 1024;

export interface DiscordEmbed {
  title: string;
  url: string;
  description?: string;
  timestamp?: string;
  color?: number;
  fields?: Array<{ name: string; value: string; inline?: boolean }>;
  footer?: { text: string };
}

/**
 * Format a list of library items into a Discord field value. Truncates to
 * MAX_ITEMS_PER_FIELD entries and/or the field-value character limit, adding
 * a "+ X more" tail when necessary.
 */
function formatItemList(items: LibraryItem[]): string {
  if (items.length === 0) return "";

  const shown = items.slice(0, MAX_ITEMS_PER_FIELD);
  const remaining = items.length - shown.length;

  const lines = shown.map((it) => `\u2022 ${it.name}`);
  if (remaining > 0) lines.push(`\u2026 + ${remaining} more`);

  let value = lines.join("\n");
  if (value.length > FIELD_VALUE_MAX) {
    // Hard cap: trim and append an ellipsis.
    value = value.slice(0, FIELD_VALUE_MAX - 1) + "\u2026";
  }
  return value;
}

export function buildEmbed(batch: BatchState): DiscordEmbed {
  const components = Object.values(batch.items.components);
  const styles = Object.values(batch.items.styles);
  const variables = Object.values(batch.items.variables);

  const fields: DiscordEmbed["fields"] = [];
  if (components.length > 0) {
    fields.push({
      name: `Components (${components.length})`,
      value: formatItemList(components),
    });
  }
  if (styles.length > 0) {
    fields.push({
      name: `Styles (${styles.length})`,
      value: formatItemList(styles),
    });
  }
  if (variables.length > 0) {
    fields.push({
      name: `Variables (${variables.length})`,
      value: formatItemList(variables),
    });
  }

  const embed: DiscordEmbed = {
    title: `\u{1F4E6} ${batch.fileName} \u2014 library published`,
    url: figmaFileUrl(batch.fileKey, batch.fileName),
    timestamp: new Date(batch.firstSeenAt).toISOString(),
    color: 0x0acf83, // Figma green-ish
  };

  if (batch.fileDescription && batch.fileDescription.trim().length > 0) {
    embed.description = batch.fileDescription.slice(0, 4096);
  }
  if (fields.length > 0) embed.fields = fields;

  return embed;
}

/**
 * POST an embed to a Discord channel webhook URL. Returns the HTTP response
 * so the caller can decide whether to retry.
 */
export async function sendToDiscord(
  webhookUrl: string,
  embed: DiscordEmbed,
): Promise<Response> {
  return fetch(webhookUrl, {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ embeds: [embed] }),
  });
}