export type PlainleafTask = {
  ref: string;
  page: string;
  name: string;
  state: string;
  done: boolean;
  scheduled?: string;
  deadline?: string;
  completed?: string;
  repeat?: PlainleafRepeatRule;
  reminder?: string;
  tags?: string[];
  links?: string[];
  parent?: string;
  pageLastModified?: string;
};

export type PlainleafRepeatRule =
  "daily" | "weekdays" | "weekly" | "monthly" | "yearly";

export type PlainleafTaskPatch = {
  name?: string;
  state?: string;
  scheduled?: string | null;
  deadline?: string | null;
  completed?: string | null;
  repeat?: PlainleafRepeatRule | null;
  reminder?: string | null;
  project?: string | null;
  tags?: string[];
};

export type PlainleafNewTask = {
  name: string;
  scheduled?: string | null;
  deadline?: string | null;
  repeat?: PlainleafRepeatRule | null;
  reminder?: string | null;
  project?: string | null;
  tags?: string[];
};

export type PlainleafDeletedTaskBlock = {
  page: string;
  position: number;
  text: string;
};

export type PlainleafTaskList =
  "inbox" | "today" | "planned" | "anytime" | "projects" | "logbook";

export const plainleafTaskInbox = "任务/收件箱";

export const repeatRuleLabels: Record<PlainleafRepeatRule, string> = {
  daily: "每天",
  weekdays: "每个工作日",
  weekly: "每周",
  monthly: "每月",
  yearly: "每年",
};

export function localDateKey(date = new Date()): string {
  const year = date.getFullYear();
  const month = String(date.getMonth() + 1).padStart(2, "0");
  const day = String(date.getDate()).padStart(2, "0");
  return `${year}-${month}-${day}`;
}

export function taskDate(value?: string): string | undefined {
  const match = value?.match(/^\d{4}-\d{2}-\d{2}/);
  if (!match) return undefined;
  const [year, month, day] = match[0].split("-").map(Number);
  const parsed = new Date(year, month - 1, day, 12);
  return parsed.getFullYear() === year &&
    parsed.getMonth() === month - 1 &&
    parsed.getDate() === day
    ? match[0]
    : undefined;
}

function dateFromKey(value: string): Date {
  return new Date(`${value}T12:00:00`);
}

export function addLocalDays(value: string, days: number): string {
  const date = dateFromKey(value);
  date.setDate(date.getDate() + days);
  return localDateKey(date);
}

const chineseWeekdays: Record<string, number> = {
  日: 0,
  天: 0,
  一: 1,
  二: 2,
  三: 3,
  四: 4,
  五: 5,
  六: 6,
};

/** Parses the small, predictable set of Chinese dates used by quick capture. */
export function parseNaturalTaskDate(
  input: string,
  base = new Date(),
): string | undefined {
  const value = input.trim().replace(/\s+/g, "");
  if (!value) return undefined;
  const baseKey = localDateKey(base);
  if (value === "今天") return baseKey;
  if (value === "明天") return addLocalDays(baseKey, 1);
  if (value === "后天") return addLocalDays(baseKey, 2);
  const stable = taskDate(value);
  if (stable && !Number.isNaN(dateFromKey(stable).getTime())) return stable;

  const monthDay = /^(?:(\d{4})年)?(\d{1,2})月(\d{1,2})日?$/.exec(value);
  if (monthDay) {
    const year = Number(monthDay[1] ?? base.getFullYear());
    const month = Number(monthDay[2]);
    const day = Number(monthDay[3]);
    const parsed = new Date(year, month - 1, day, 12);
    if (
      parsed.getFullYear() === year &&
      parsed.getMonth() === month - 1 &&
      parsed.getDate() === day
    ) {
      if (!monthDay[1] && localDateKey(parsed) < baseKey) {
        parsed.setFullYear(year + 1);
      }
      return localDateKey(parsed);
    }
  }

  const weekday = /^(下周|本周|周|星期)([一二三四五六日天])$/.exec(value);
  if (weekday) {
    const target = chineseWeekdays[weekday[2]];
    const current = base.getDay();
    let delta: number;
    if (weekday[1] === "下周") {
      const daysToNextMonday = (8 - current) % 7 || 7;
      delta = daysToNextMonday + (target === 0 ? 6 : target - 1);
    } else if (weekday[1] === "本周") {
      const currentFromMonday = current === 0 ? 6 : current - 1;
      const targetFromMonday = target === 0 ? 6 : target - 1;
      delta = targetFromMonday - currentFromMonday;
    } else {
      delta = (target - current + 7) % 7;
      if (delta === 0 && weekday[1] !== "本周") delta = 7;
    }
    return addLocalDays(baseKey, delta);
  }
  return undefined;
}

export function nextRepeatDate(
  rule: PlainleafRepeatRule,
  from: string,
): string {
  const date = dateFromKey(from);
  if (rule === "daily") return addLocalDays(from, 1);
  if (rule === "weekdays") {
    do date.setDate(date.getDate() + 1);
    while (date.getDay() === 0 || date.getDay() === 6);
    return localDateKey(date);
  }
  if (rule === "weekly") return addLocalDays(from, 7);
  if (rule === "monthly") {
    const targetDay = date.getDate();
    date.setDate(1);
    date.setMonth(date.getMonth() + 1);
    const lastDay = new Date(
      date.getFullYear(),
      date.getMonth() + 1,
      0,
    ).getDate();
    date.setDate(Math.min(targetDay, lastDay));
    return localDateKey(date);
  }
  const month = date.getMonth();
  const day = date.getDate();
  date.setFullYear(date.getFullYear() + 1, month, 1);
  const lastDay = new Date(date.getFullYear(), month + 1, 0).getDate();
  date.setDate(Math.min(day, lastDay));
  return localDateKey(date);
}

export function nextRepeatedTask(
  task: PlainleafTask,
  today = localDateKey(),
): PlainleafNewTask | undefined {
  if (!task.repeat) return undefined;
  const scheduledDate = taskDate(task.scheduled);
  const deadlineDate = taskDate(task.deadline);
  const sourceDate = scheduledDate ?? deadlineDate ?? today;
  const nextDate = nextRepeatDate(task.repeat, sourceDate);
  const scheduled = scheduledDate || !deadlineDate ? nextDate : undefined;
  const deadlineDelta =
    deadlineDate && scheduledDate
      ? Math.round(
          (dateFromKey(deadlineDate).getTime() -
            dateFromKey(scheduledDate).getTime()) /
            86_400_000,
        )
      : undefined;
  return {
    name: task.name.replace(/\s*\[\[[^\]]+\]\]/g, "").trim() || task.name,
    scheduled,
    deadline:
      deadlineDelta === undefined
        ? deadlineDate
          ? nextRepeatDate(task.repeat, deadlineDate)
          : undefined
        : addLocalDays(scheduled!, deadlineDelta),
    repeat: task.repeat,
    reminder: task.reminder
      ? `${scheduled ?? nextDate}T${task.reminder.split("T")[1] ?? "09:00"}`
      : undefined,
    project: task.links?.[0],
    tags: task.tags,
  };
}

export function isOverdueTask(
  task: PlainleafTask,
  today = localDateKey(),
): boolean {
  const deadline = taskDate(task.deadline);
  return !task.done && !!deadline && deadline < today;
}

export function taskBelongsToToday(
  task: PlainleafTask,
  today = localDateKey(),
): boolean {
  if (task.done) return false;
  const scheduled = taskDate(task.scheduled);
  const deadline = taskDate(task.deadline);
  return scheduled === today || (!!deadline && deadline <= today);
}

export function tasksForInbox(tasks: PlainleafTask[]): PlainleafTask[] {
  return tasks.filter(
    (task) =>
      !task.done && task.page.replace(/\.md$/i, "") === plainleafTaskInbox,
  );
}

export function tasksForAnytime(tasks: PlainleafTask[]): PlainleafTask[] {
  return tasks.filter(
    (task) =>
      !task.done &&
      !taskDate(task.scheduled) &&
      !taskDate(task.deadline) &&
      task.page.replace(/\.md$/i, "") !== plainleafTaskInbox,
  );
}

function futureTaskDate(
  task: PlainleafTask,
  today: string,
): string | undefined {
  const scheduled = taskDate(task.scheduled);
  const deadline = taskDate(task.deadline);
  if (scheduled && scheduled > today) return scheduled;
  if (deadline && deadline > today) return deadline;
  return undefined;
}

export function groupScheduledTasks(
  tasks: PlainleafTask[],
  today = localDateKey(),
): Array<{ date: string; tasks: PlainleafTask[] }> {
  const groups = new Map<string, PlainleafTask[]>();
  for (const task of tasks) {
    if (task.done) continue;
    const date = futureTaskDate(task, today);
    if (!date) continue;
    const group = groups.get(date) ?? [];
    group.push(task);
    groups.set(date, group);
  }
  return [...groups.entries()]
    .sort(([a], [b]) => a.localeCompare(b))
    .map(([date, groupedTasks]) => ({ date, tasks: groupedTasks }));
}

export function projectForTask(task: PlainleafTask): string | undefined {
  const explicit = task.links?.find((link) => link.trim());
  if (explicit) return explicit.trim();
  const page = task.page.replace(/\.md$/i, "");
  return page === plainleafTaskInbox ? undefined : page;
}

export function groupTasksByProject(
  tasks: PlainleafTask[],
): Array<{ project: string; tasks: PlainleafTask[] }> {
  const groups = new Map<string, PlainleafTask[]>();
  for (const task of tasks) {
    if (task.done) continue;
    const project = projectForTask(task);
    if (!project) continue;
    const group = groups.get(project) ?? [];
    group.push(task);
    groups.set(project, group);
  }
  return [...groups.entries()]
    .sort(([a], [b]) => a.localeCompare(b, "zh-CN"))
    .map(([project, groupedTasks]) => ({ project, tasks: groupedTasks }));
}

export function projectSummaries(tasks: PlainleafTask[]): Array<{
  project: string;
  open: number;
  completed: number;
  total: number;
}> {
  const summaries = new Map<
    string,
    { project: string; open: number; completed: number; total: number }
  >();
  for (const task of tasks) {
    const project = projectForTask(task);
    if (!project) continue;
    const summary = summaries.get(project) ?? {
      project,
      open: 0,
      completed: 0,
      total: 0,
    };
    summary.total += 1;
    if (task.done) summary.completed += 1;
    else summary.open += 1;
    summaries.set(project, summary);
  }
  return [...summaries.values()].sort((a, b) =>
    a.project.localeCompare(b.project, "zh-CN"),
  );
}

export function taskMatchesFilters(
  task: PlainleafTask,
  filters: { query?: string; tag?: string; project?: string },
): boolean {
  const query = filters.query?.trim().toLocaleLowerCase("zh-CN");
  if (
    query &&
    ![task.name, task.page, ...(task.tags ?? []), ...(task.links ?? [])]
      .join(" ")
      .toLocaleLowerCase("zh-CN")
      .includes(query)
  ) {
    return false;
  }
  if (filters.tag && !task.tags?.includes(filters.tag)) return false;
  if (filters.project && projectForTask(task) !== filters.project) return false;
  return true;
}

export function taskDepth(task: PlainleafTask, tasks: PlainleafTask[]): number {
  const byRef = new Map(tasks.map((candidate) => [candidate.ref, candidate]));
  let depth = 0;
  let parent = task.parent;
  const visited = new Set<string>();
  while (parent && depth < 4 && !visited.has(parent)) {
    visited.add(parent);
    depth += 1;
    parent = byRef.get(parent)?.parent;
  }
  return depth;
}

export function subtaskProgress(
  task: PlainleafTask,
  tasks: PlainleafTask[],
): { completed: number; total: number } | undefined {
  const children = new Map<string, PlainleafTask[]>();
  for (const candidate of tasks) {
    if (!candidate.parent) continue;
    const siblings = children.get(candidate.parent) ?? [];
    siblings.push(candidate);
    children.set(candidate.parent, siblings);
  }
  const descendants: PlainleafTask[] = [];
  const pending = [...(children.get(task.ref) ?? [])];
  const visited = new Set<string>([task.ref]);
  while (pending.length) {
    const candidate = pending.shift()!;
    if (visited.has(candidate.ref)) continue;
    visited.add(candidate.ref);
    descendants.push(candidate);
    pending.push(...(children.get(candidate.ref) ?? []));
  }
  if (!descendants.length) return undefined;
  return {
    completed: descendants.filter((candidate) => candidate.done).length,
    total: descendants.length,
  };
}

export function calendarMonth(
  year: number,
  month: number,
): Array<{ date: string; inMonth: boolean }> {
  const first = new Date(year, month, 1, 12);
  const start = new Date(first);
  start.setDate(first.getDate() - first.getDay());
  return Array.from({ length: 42 }, (_, index) => {
    const date = new Date(start);
    date.setDate(start.getDate() + index);
    return { date: localDateKey(date), inMonth: date.getMonth() === month };
  });
}

export function tasksForCalendarDate(
  tasks: PlainleafTask[],
  date: string,
): PlainleafTask[] {
  return tasks.filter(
    (task) =>
      !task.done &&
      (taskDate(task.scheduled) === date || taskDate(task.deadline) === date),
  );
}

export function dueReminderTasks(
  tasks: PlainleafTask[],
  now = new Date(),
  notified = new Set<string>(),
): PlainleafTask[] {
  const timestamp = now.getTime();
  return tasks.filter((task) => {
    if (
      task.done ||
      !task.reminder ||
      notified.has(`${task.ref}:${task.reminder}`)
    ) {
      return false;
    }
    const reminder = new Date(task.reminder).getTime();
    return !Number.isNaN(reminder) && reminder <= timestamp;
  });
}

export function staleProjects(
  tasks: PlainleafTask[],
  today = localDateKey(),
  afterDays = 14,
): Set<string> {
  const cutoff = addLocalDays(today, -afterDays);
  const stale = new Set<string>();
  for (const group of groupTasksByProject(tasks)) {
    const latest = group.tasks
      .map((task) => taskDate(task.pageLastModified))
      .filter(Boolean)
      .sort()
      .at(-1);
    if (latest && latest < cutoff) stale.add(group.project);
  }
  return stale;
}

export type TaskHealthIssue = {
  ref: string;
  type:
    | "invalid-date"
    | "deadline-before-scheduled"
    | "missing-parent"
    | "duplicate-ref";
  message: string;
};

export function taskHealthIssues(tasks: PlainleafTask[]): TaskHealthIssue[] {
  const issues: TaskHealthIssue[] = [];
  const refs = new Map<string, number>();
  for (const task of tasks) refs.set(task.ref, (refs.get(task.ref) ?? 0) + 1);
  const knownRefs = new Set(refs.keys());
  for (const task of tasks) {
    for (const [field, value] of [
      ["计划日期", task.scheduled],
      ["截止日期", task.deadline],
    ] as const) {
      if (value && !taskDate(value)) {
        issues.push({
          ref: task.ref,
          type: "invalid-date",
          message: `${field}格式无效`,
        });
      }
    }
    const scheduled = taskDate(task.scheduled);
    const deadline = taskDate(task.deadline);
    if (scheduled && deadline && deadline < scheduled) {
      issues.push({
        ref: task.ref,
        type: "deadline-before-scheduled",
        message: "截止日期早于计划日期",
      });
    }
    if (task.parent && !knownRefs.has(task.parent)) {
      issues.push({
        ref: task.ref,
        type: "missing-parent",
        message: "找不到父任务",
      });
    }
    if ((refs.get(task.ref) ?? 0) > 1) {
      issues.push({
        ref: task.ref,
        type: "duplicate-ref",
        message: "任务引用重复",
      });
    }
  }
  return issues;
}

export function logbookTasks(tasks: PlainleafTask[]): PlainleafTask[] {
  return tasks
    .filter((task) => task.done)
    .sort((a, b) =>
      (taskDate(b.completed) ?? b.pageLastModified ?? "").localeCompare(
        taskDate(a.completed) ?? a.pageLastModified ?? "",
      ),
    );
}

export function groupLogbookTasks(
  tasks: PlainleafTask[],
  period: "week" | "month",
): Array<{ period: string; tasks: PlainleafTask[] }> {
  const groups = new Map<string, PlainleafTask[]>();
  for (const task of logbookTasks(tasks)) {
    const key = taskDate(task.completed) ?? taskDate(task.pageLastModified);
    if (!key) continue;
    const date = dateFromKey(key);
    let label: string;
    if (period === "month") {
      label = `${date.getFullYear()}年${date.getMonth() + 1}月`;
    } else {
      const monday = new Date(date);
      const day = monday.getDay() || 7;
      monday.setDate(monday.getDate() - day + 1);
      label = `${localDateKey(monday)} 这一周`;
    }
    const group = groups.get(label) ?? [];
    group.push(task);
    groups.set(label, group);
  }
  return [...groups.entries()].map(([label, groupedTasks]) => ({
    period: label,
    tasks: groupedTasks,
  }));
}

export function sortTodayTasks(
  tasks: PlainleafTask[],
  today = localDateKey(),
): PlainleafTask[] {
  return tasks
    .filter((task) => taskBelongsToToday(task, today))
    .sort((a, b) => {
      const rank = (task: PlainleafTask) => {
        if (isOverdueTask(task, today)) return 0;
        if (taskDate(task.deadline) === today) return 1;
        return 2;
      };
      return rank(a) - rank(b) || a.name.localeCompare(b.name, "zh-CN");
    });
}