import { App, moment } from "obsidian";
import { formatSpan, parseMoment } from "./moment-utils";
import { normalizeConfig, parseConfig, parseYamlConfig } from "./config";
import type { DateCalcConfig, DateCalcResult, DateCalcSettings } from "./types";

/** Read a string or Date value out of frontmatter, ignoring any other shape. */
function frontmatterField(
  fm: Record<string, unknown> | undefined,
  key: string
): string | Date | undefined {
  const value = fm?.[key];
  return typeof value === "string" || value instanceof Date ? value : undefined;
}

/** Dispatch to the calculator for `type`, catching and surfacing any error inline. */
export function calculateDateResult(
  type: string,
  cfg: DateCalcConfig,
  app: App,
  sourcePath: string,
  verbose: boolean
): DateCalcResult {
  const useVerbose = cfg.verbose !== undefined ? cfg.verbose : verbose;

  try {
    switch (type) {
      case "birthday":
        return calculateBirthday(cfg, app, sourcePath, useVerbose);
      case "countdown":
        return calculateCountdown(cfg, useVerbose);
      case "diff":
        return calculateDiff(cfg, useVerbose);
      case "since":
        return calculateSince(cfg, useVerbose);
      default:
        return { text: "date-calc: Unknown type. Supported: birthday, countdown, diff, since" };
    }
  } catch (e: unknown) {
    const message = e instanceof Error ? e.message : String(e);
    return { text: `date-calc error: ${message}` };
  }
}

function calculateBirthday(
  cfg: DateCalcConfig,
  app: App,
  sourcePath: string,
  verbose: boolean
): DateCalcResult {
  const fm = app.metadataCache.getCache(sourcePath)?.frontmatter;

  const bstr =
    cfg.birthday ?? cfg.birthdate ?? cfg.date ??
    frontmatterField(fm, "birthday") ?? frontmatterField(fm, "birthdate");
  const bd = parseMoment(bstr)?.startOf("day");
  if (!bd) return { text: `date-calc: Missing or invalid "birthday" date.` };

  const today = moment().startOf("day");
  const age = today.diff(bd, "years");

  const next = bd.clone().year(today.year());
  if (next.isBefore(today, "day")) next.add(1, "year");
  const daysUntil = next.diff(today, "days");

  let msg: string;
  if (daysUntil === 0) {
    msg = verbose ? "Wish them Happy Birthday!" : "Happy bday!";
  } else if (daysUntil === 1) {
    msg = verbose ? "Their birthday is tomorrow!" : "Bday's tomorrow!";
  } else if (daysUntil > 31) {
    const monthsUntil = next.diff(today, "months");
    msg = verbose ? `Next birthday in ${monthsUntil} months.` : `Next bday in ${monthsUntil}mo`;
  } else {
    msg = verbose ? `Next birthday in ${daysUntil} days.` : `Next bday in ${daysUntil}d`;
  }

  const ageStr = verbose ? `${age} years old` : `${age}y`;
  // Custom label > frontmatter-name personalization > plain "Age:" default.
  const name = frontmatterField(fm, "name");
  const label = cfg.label ?? (typeof name === "string" ? `${name}'s age:` : "Age:");
  return { text: `${label} ${ageStr}. ${msg}`, tooltip: bd.format("MMMM Do, YYYY") };
}

function calculateCountdown(cfg: DateCalcConfig, verbose: boolean): DateCalcResult {
  const to = parseMoment(cfg.to ?? cfg.date ?? cfg.until);
  if (!to) return { text: `date-calc: Missing or invalid "to" date.` };

  const from = parseMoment(cfg.from) ?? moment();
  const label = cfg.label ? `${cfg.label}: ` : "";
  const span = formatSpan(from, to, verbose);

  const text = !span.isNegative
    ? `${label}${verbose ? "Countdown: " : ""}${span.text}`
    : `${label}${verbose ? "Event passed " : ""}${span.text}${verbose ? " ago" : ""}`;

  return { text };
}

function calculateDiff(cfg: DateCalcConfig, verbose: boolean): DateCalcResult {
  const from = parseMoment(cfg.from ?? cfg.start);
  const to = parseMoment(cfg.to ?? cfg.end);
  if (!from || !to) return { text: `date-calc: Provide valid "from" and "to" dates.` };

  const span = formatSpan(from, to, verbose);

  const text = verbose
    ? `Difference: ${span.text}${span.isNegative ? " (to is before from)" : ""}`
    : `Diff: ${span.text}${span.isNegative ? " (reverse)" : ""}`;

  return { text };
}

function calculateSince(cfg: DateCalcConfig, verbose: boolean): DateCalcResult {
  const since = parseMoment(cfg.since ?? cfg.from ?? cfg.date);
  if (!since) return { text: `date-calc: Missing or invalid "since" date.` };

  const now = moment();
  const span = formatSpan(since, now, verbose);

  const text = !span.isNegative
    ? `Since: ${span.text}${verbose ? " ago" : ""}`
    : `In: ${span.text}`;

  return { text };
}

/** Parse and evaluate a `date-calc: ...` inline code span's raw text. */
export function processInlineCode(
  raw: string,
  app: App,
  sourcePath: string,
  settings: DateCalcSettings
): DateCalcResult {
  if (!/^date-calc\s*:/.test(raw)) return { text: "" };

  const paramsRaw = raw.replace(/^date-calc\s*:/, "").trim();
  const cfg = parseConfig(paramsRaw);
  const norm = normalizeConfig(paramsRaw, cfg);

  if (!norm.type) return { text: "" };

  return calculateDateResult(norm.type, norm.cfg, app, sourcePath, settings.verbose);
}

/** Parse and evaluate a fenced ```date-calc``` block's YAML body. */
export function processFencedBlock(
  source: string,
  app: App,
  sourcePath: string,
  settings: DateCalcSettings
): DateCalcResult {
  const cfg = parseYamlConfig(source);
  const norm = normalizeConfig("", cfg);
  if (!norm.type) {
    return { text: 'date-calc: Missing "type" (birthday/countdown/diff/since).' };
  }

  return calculateDateResult(norm.type, norm.cfg, app, sourcePath, settings.verbose);
}