/* =============================================================================
 * ui_template_sheet_formula.ts
 * 표 식 읽기 · 풀기 — 옛 `B08_Quantity_Formula.ts`(git 8472fc9f) 파서를 되살려 표 참조를 더함.
 *
 * 식 말: 사칙 · 괄호 · 비교(= <> < <= > >=) · 함수 SUM · INT · ROUND · ROUNDUP · ROUNDDOWN ·
 *   MIN · MAX · IF · 참조 `[열id]`(같은 줄) · `[열id@줄id]`(한 칸) · `[$이름]`(문서 변수).
 * `SUM([열id])` = 그 열의 본문 줄 전부. 빈 칸은 0(엑셀과 같음).
 * ⚠ `eval` 을 쓰지 않음 — 식은 사용자 글이라 직접 짠 파서로만 읽음.
 * 우선순위는 엑셀과 같음 — 부호 > `* /` > `+ -` > 비교. 같은 단은 왼쪽부터.
 * ========================================================================== */

import {
  add,
  cmp,
  div,
  type Frac,
  frac,
  FormulaError,
  type IntMode,
  mul,
  parseDecimal,
  roundAt,
  sub,
  toInteger,
  ZERO,
} from "./ui_template_sheet_frac";

type Token =
  | { kind: "num"; text: string }
  | { kind: "str"; text: string }
  | { kind: "id"; text: string }
  | { kind: "ref"; text: string }
  | { kind: "op"; text: string };

export type Node =
  | { type: "num"; value: Frac }
  | { type: "str"; value: string }
  | { type: "ref"; col: string; row: string | null }
  | { type: "var"; name: string }
  | { type: "unary"; op: string; arg: Node }
  | { type: "binary"; op: string; left: Node; right: Node }
  | { type: "call"; name: string; args: Node[] };

export type Value = Frac | string | boolean;

/** 풀 때 참조를 대 주는 쪽 — 표 풀이(`_recalc`)가 채움. */
export interface Scope {
  cell(col: string, row: string | null): Value;
  column(col: string): Frac[];
  variable(name: string): Value;
}

const OPERATORS = ["<=", ">=", "<>", "+", "-", "*", "/", "(", ")", ",", "=", "<", ">"];
const COMPARISONS = new Set(["=", "<>", "<", "<=", ">", ">="]);
const ROUNDERS: Record<string, IntMode> = { ROUND: "round", ROUNDUP: "away", ROUNDDOWN: "trunc" };

function tokenize(source: string): Token[] {
  const tokens: Token[] = [];
  let i = 0;
  while (i < source.length) {
    const ch = source[i];
    if (/\s/.test(ch)) {
      i += 1;
      continue;
    }
    const number = /^(\d+(\.\d*)?|\.\d+)([eE][+-]?\d+)?/.exec(source.slice(i));
    if (number) {
      tokens.push({ kind: "num", text: number[0] });
      i += number[0].length;
      continue;
    }
    if (ch === "[") {
      const end = source.indexOf("]", i + 1);
      if (end < 0) throw new FormulaError("「[」가 닫히지 않음");
      tokens.push({ kind: "ref", text: source.slice(i + 1, end).trim() });
      i = end + 1;
      continue;
    }
    if (ch === "'" || ch === '"') {
      const end = source.indexOf(ch, i + 1);
      if (end < 0) throw new FormulaError("따옴표가 닫히지 않음");
      tokens.push({ kind: "str", text: source.slice(i + 1, end) });
      i = end + 1;
      continue;
    }
    const identifier = /^[\p{L}_][\p{L}\p{N}_]*/u.exec(source.slice(i));
    if (identifier) {
      tokens.push({ kind: "id", text: identifier[0].toUpperCase() });
      i += identifier[0].length;
      continue;
    }
    const op = OPERATORS.find((candidate) => source.startsWith(candidate, i));
    if (!op) throw new FormulaError(`읽을 수 없는 글자: ${ch}`);
    tokens.push({ kind: "op", text: op });
    i += op.length;
  }
  return tokens;
}

function refNode(text: string): Node {
  if (!text) throw new FormulaError("빈 참조 []");
  if (text.startsWith("$")) return { type: "var", name: text.slice(1).trim() };
  const at = text.indexOf("@");
  if (at < 0) return { type: "ref", col: text, row: null };
  return { type: "ref", col: text.slice(0, at).trim(), row: text.slice(at + 1).trim() };
}

/** 앞에 `=` 가 붙어 있어도 됨(엑셀 버릇). */
export function parseFormula(source: string): Node {
  const tokens = tokenize(source.trim().replace(/^=/, ""));
  let at = 0;
  const peek = (): Token | undefined => tokens[at];
  const isOp = (text: string): boolean => peek()?.kind === "op" && peek()?.text === text;
  const expect = (text: string): void => {
    if (!isOp(text)) throw new FormulaError(`「${text}」가 있어야 함`);
    at += 1;
  };

  const comparison = (): Node => {
    let left = additive();
    while (peek()?.kind === "op" && COMPARISONS.has(peek()!.text)) {
      const op = tokens[at++].text;
      left = { type: "binary", op, left, right: additive() };
    }
    return left;
  };
  const additive = (): Node => {
    let left = term();
    while (isOp("+") || isOp("-")) {
      const op = tokens[at++].text;
      left = { type: "binary", op, left, right: term() };
    }
    return left;
  };
  const term = (): Node => {
    let left = unary();
    while (isOp("*") || isOp("/")) {
      const op = tokens[at++].text;
      left = { type: "binary", op, left, right: unary() };
    }
    return left;
  };
  const unary = (): Node => {
    if (isOp("-") || isOp("+")) {
      const op = tokens[at++].text;
      return { type: "unary", op, arg: unary() };
    }
    return primary();
  };
  const primary = (): Node => {
    const token = peek();
    if (!token) throw new FormulaError("식이 중간에 끝남");
    at += 1;
    if (token.kind === "num") return { type: "num", value: parseDecimal(token.text) };
    if (token.kind === "str") return { type: "str", value: token.text };
    if (token.kind === "ref") return refNode(token.text);
    if (token.kind === "id") {
      if (!isOp("(")) throw new FormulaError(`모르는 이름: ${token.text} — 칸은 [열id] 로`);
      at += 1;
      const args: Node[] = [];
      if (!isOp(")")) {
        args.push(comparison());
        while (isOp(",")) {
          at += 1;
          args.push(comparison());
        }
      }
      expect(")");
      return { type: "call", name: token.text, args };
    }
    if (token.text === "(") {
      const inner = comparison();
      expect(")");
      return inner;
    }
    throw new FormulaError(`여기에 올 수 없음: ${token.text}`);
  };

  if (!tokens.length) throw new FormulaError("빈 식");
  const tree = comparison();
  if (at < tokens.length) throw new FormulaError(`식 끝에 남은 글: ${tokens[at].text}`);
  return tree;
}

/** 식이 가리키는 참조 — 순환 · 없는 열 검사용. */
export function* refsOf(node: Node): Generator<Node & { type: "ref" | "var" }> {
  if (node.type === "ref" || node.type === "var") yield node;
  else if (node.type === "unary") yield* refsOf(node.arg);
  else if (node.type === "binary") {
    yield* refsOf(node.left);
    yield* refsOf(node.right);
  } else if (node.type === "call") for (const arg of node.args) yield* refsOf(arg);
}

const isFrac = (v: Value): v is Frac => typeof v === "object";

export function asFrac(value: Value): Frac {
  if (isFrac(value)) return value;
  if (typeof value === "boolean") return frac(value ? 1n : 0n);
  throw new FormulaError(`수 자리에 글이 옴: ${value}`);
}

function truthy(value: Value): boolean {
  if (typeof value === "boolean") return value;
  if (isFrac(value)) return value.n !== 0n;
  throw new FormulaError(`조건 자리에 글이 옴: ${value}`);
}

function compareValues(a: Value, b: Value): number {
  if (typeof a === "string" || typeof b === "string") {
    if (typeof a !== "string" || typeof b !== "string") {
      throw new FormulaError("글과 수를 견줄 수 없음");
    }
    return a === b ? 0 : a < b ? -1 : 1;
  }
  return cmp(asFrac(a), asFrac(b));
}

function digitsOf(node: Node | undefined, scope: Scope): number {
  if (!node) return 0;
  const value = asFrac(evaluate(node, scope));
  if (value.d !== 1n) throw new FormulaError("자리 수는 정수");
  return Number(value.n);
}

export function evaluate(node: Node, scope: Scope): Value {
  switch (node.type) {
    case "num":
    case "str":
      return node.value;
    case "ref":
      return scope.cell(node.col, node.row);
    case "var":
      return scope.variable(node.name);
    case "unary": {
      const value = asFrac(evaluate(node.arg, scope));
      return node.op === "-" ? sub(ZERO, value) : value;
    }
    case "binary": {
      const left = evaluate(node.left, scope);
      const right = evaluate(node.right, scope);
      if (COMPARISONS.has(node.op)) {
        const order = compareValues(left, right);
        return {
          "=": order === 0,
          "<>": order !== 0,
          "<": order < 0,
          "<=": order <= 0,
          ">": order > 0,
          ">=": order >= 0,
        }[node.op]!;
      }
      const a = asFrac(left);
      const b = asFrac(right);
      if (node.op === "+") return add(a, b);
      if (node.op === "-") return sub(a, b);
      if (node.op === "*") return mul(a, b);
      return div(a, b);
    }
    case "call": {
      const { name, args } = node;
      if (name === "IF") {
        if (args.length !== 3) throw new FormulaError("IF 는 인자가 셋(조건, 참, 거짓)");
        // 고른 갈래만 풂 — 안 고른 갈래의 오류가 칸을 막지 않게
        return evaluate(truthy(evaluate(args[0], scope)) ? args[1] : args[2], scope);
      }
      if (name === "SUM") {
        let total = ZERO;
        for (const arg of args) {
          const values =
            arg.type === "ref" && arg.row === null
              ? scope.column(arg.col)
              : [asFrac(evaluate(arg, scope))];
          for (const value of values) total = add(total, value);
        }
        return total;
      }
      if (name === "INT") {
        if (args.length !== 1) throw new FormulaError("INT 는 인자가 하나");
        return frac(toInteger(asFrac(evaluate(args[0], scope)), "floor"));
      }
      if (name in ROUNDERS) {
        if (args.length < 1 || args.length > 2) throw new FormulaError(`${name} 는 (값, 자리)`);
        return roundAt(asFrac(evaluate(args[0], scope)), digitsOf(args[1], scope), ROUNDERS[name]);
      }
      if (name === "MIN" || name === "MAX") {
        const values = args.map((arg) => asFrac(evaluate(arg, scope)));
        if (!values.length) throw new FormulaError(`${name} 에 인자가 없음`);
        return values.reduce((best, v) => (cmp(v, best) < 0 === (name === "MIN") ? v : best));
      }
      throw new FormulaError(`모르는 함수: ${name}`);
    }
  }
}