/**
 * MTEXT / TEXT 的文字内容解析。
 *
 * MTEXT 的正文里混着 AutoCAD 的格式码（\P 换行、\H 字高、\S 堆叠、{} 分组……），
 * 直接画出来会满屏乱码，所以这里把它拆成「行 → 文字段(run)」的结构，
 * 每个 run 带自己的字高倍数、宽度因子、倾斜、粗斜体、颜色和下划线。
 */

/** %%d 之类的控制码（TEXT 与 MTEXT 通用） */
function replaceSpecial(s) {
  return s
    .replace(/%%[dD]/g, '°')   // 度
    .replace(/%%[cC]/g, '∅')   // 直径 ⌀
    .replace(/%%[pP]/g, '±')   // 正负
    .replace(/%%%/g, '%')
}

/** \U+00B0 形式的 Unicode 转义 */
function replaceUnicode(s) {
  return s.replace(/\\U\+([0-9A-Fa-f]{4})/g, (_, h) => String.fromCharCode(parseInt(h, 16)))
}

const BASE_STYLE = {
  hFactor: 1,        // 相对于实体 textHeight 的倍数
  wFactor: 1,
  oblique: 0,
  bold: false,
  italic: false,
  font: null,
  color: null,       // ACI 索引或 0xRRGGBB（带 trueColor 标记）
  underline: false,
  overline: false,
  strike: false,
  rise: 0,           // 相对基线的抬升（堆叠分数用），单位为字高倍数
}

/**
 * 解析 MTEXT 正文。
 * @returns {{lines: Array<Array<Run>>, columnBreaks: number[]}}
 */
export function parseMText(raw) {
  const lines = [[]]
  if (!raw) return { lines }
  const text = replaceUnicode(raw)
  const stack = []
  let st = { ...BASE_STYLE }
  let buf = ''

  const flush = () => {
    if (!buf) return
    lines[lines.length - 1].push({ ...st, text: replaceSpecial(buf) })
    buf = ''
  }
  const newLine = () => { flush(); lines.push([]) }

  // 读到分号为止的参数
  let i = 0
  const readArg = () => {
    let out = ''
    while (i < text.length && text[i] !== ';') { out += text[i]; i++ }
    i++ // 吃掉 ;
    return out
  }

  while (i < text.length) {
    const ch = text[i]
    if (ch === '\\') {
      const c = text[i + 1]
      i += 2
      switch (c) {
        case 'P': newLine(); break
        case 'X': newLine(); break
        case '~': buf += ' '; break
        case '\\': buf += '\\'; break
        case '{': buf += '{'; break
        case '}': buf += '}'; break
        case 'L': flush(); st = { ...st, underline: true }; break
        case 'l': flush(); st = { ...st, underline: false }; break
        case 'O': flush(); st = { ...st, overline: true }; break
        case 'o': flush(); st = { ...st, overline: false }; break
        case 'K': flush(); st = { ...st, strike: true }; break
        case 'k': flush(); st = { ...st, strike: false }; break
        case 'H': {
          flush()
          const a = readArg()
          const rel = /x$/i.test(a)
          const v = parseFloat(a)
          if (isFinite(v)) st = { ...st, hFactor: rel ? st.hFactor * v : v }
          break
        }
        case 'W': { flush(); const v = parseFloat(readArg()); if (isFinite(v) && v > 0) st = { ...st, wFactor: v }; break }
        case 'Q': { flush(); const v = parseFloat(readArg()); if (isFinite(v)) st = { ...st, oblique: (v * Math.PI) / 180 }; break }
        case 'T': { readArg(); break }        // 字间距，忽略
        case 'A': { readArg(); break }        // 对齐，交由整体对齐处理
        case 'p': { readArg(); break }        // 段落属性，忽略
        case 'C': { flush(); const v = parseInt(readArg(), 10); if (isFinite(v)) st = { ...st, color: { aci: v } }; break }
        case 'c': { flush(); const v = parseInt(readArg(), 10); if (isFinite(v)) st = { ...st, color: { rgb: bgrToRgb(v) } }; break }
        case 'F':
        case 'f': {
          flush()
          const a = readArg()
          const parts = a.split('|')
          const next = { ...st, font: parts[0] || null }
          for (const p of parts.slice(1)) {
            if (/^b1$/i.test(p)) next.bold = true
            else if (/^b0$/i.test(p)) next.bold = false
            else if (/^i1$/i.test(p)) next.italic = true
            else if (/^i0$/i.test(p)) next.italic = false
          }
          st = next
          break
        }
        case 'S': {
          // 堆叠分数： 上^下;  上/下;  上#下;
          flush()
          let a = ''
          while (i < text.length && text[i] !== ';') { a += text[i]; i++ }
          i++
          const m = a.match(/^(.*?)([\^\/#])(.*)$/)
          if (m) {
            const upper = replaceSpecial(m[1]), lower = replaceSpecial(m[3])
            const small = { ...st, hFactor: st.hFactor * 0.65 }
            const arr = lines[lines.length - 1]
            if (upper) arr.push({ ...small, text: upper, rise: 0.55 })
            if (m[2] !== '^' && upper && lower) arr.push({ ...small, text: '/', rise: 0 })
            if (lower) arr.push({ ...small, text: lower, rise: -0.25 })
          } else if (a) {
            buf += replaceSpecial(a)
          }
          break
        }
        default:
          // 未知转义，原样保留字符
          if (c != null) buf += c
      }
    } else if (ch === '{') {
      flush(); stack.push({ ...st }); i++
    } else if (ch === '}') {
      flush(); if (stack.length) st = stack.pop(); i++
    } else if (ch === '\n') {
      newLine(); i++
    } else if (ch === '\r') {
      i++
    } else {
      buf += ch; i++
    }
  }
  flush()
  return { lines }
}

/** DXF 的 true color 在 MTEXT 里是 BGR 顺序 */
function bgrToRgb(v) {
  const b = (v >> 16) & 0xff, g = (v >> 8) & 0xff, r = v & 0xff
  return (r << 16) | (g << 8) | b
}

/** 单行 TEXT / ATTRIB 的内容处理 */
export function parseSimpleText(raw) {
  if (!raw) return ''
  return replaceSpecial(replaceUnicode(String(raw)))
    .replace(/%%[uUoO]/g, '')   // 下划线/上划线开关，画不出来就去掉标记
}