// 光标处展开（方案 §4.5）。
//
// 实现为纯函数：装饰集 = f(语法树, selection)。v1 取行粒度（决策 E6）：
// 光标/选区触及的行，其语法标记整体展开为源码。行粒度对 IME 最安全 ——
// 组字所在行永远是展开态，组合过程中不会被 replace 掉 DOM。
//
// span 级展开（Typora 的「光标进入行内节点才展开」）列入方案 §10.2。

import type { EditorState } from '@codemirror/state'
import type { Spec } from './syntax'

export interface Range {
  from: number
  to: number
}

/** 选区（全部 range，非仅 main）所触及的整行区间集合（升序、互不相交）。 */
export function activeLineRanges(state: EditorState): Range[] {
  const out: Range[] = []
  const seen = new Set<number>()
  for (const r of state.selection.ranges) {
    const start = state.doc.lineAt(r.from)
    const end = state.doc.lineAt(r.to)
    for (let n = start.number; n <= end.number; n++) {
      if (seen.has(n)) continue
      seen.add(n)
      const line = state.doc.line(n)
      out.push({ from: line.from, to: line.to })
    }
  }
  return out
}

/**
 * 选区**端点**所在的整行（CM 只把选区端点所在的块渲染在视口之外，
 * 不会渲染整个选区跨越的每一行）。用于决定「除可见区间外还要装饰哪些行」，
 * 避免 Cmd+A 这种整篇选区触发全文档装饰构建。
 */
export function selectionEndpointLines(state: EditorState): Range[] {
  const out: Range[] = []
  const seen = new Set<number>()
  for (const r of state.selection.ranges) {
    for (const pos of [r.from, r.to]) {
      const line = state.doc.lineAt(pos)
      if (seen.has(line.number)) continue
      seen.add(line.number)
      out.push({ from: line.from, to: line.to })
    }
  }
  return out
}

/** [from, to) 是否与任一展开区间相交。零长区间不与任何行相交。 */
export function intersectsAny(ranges: readonly Range[], from: number, to: number): boolean {
  if (to <= from) return false
  for (const r of ranges) {
    if (from <= r.to && r.from <= to) return true
  }
  return false
}

/** 把区间排序并合并，得到互不相交的升序区间，供二分查询使用。 */
function mergeRanges(ranges: readonly Range[]): Range[] {
  if (ranges.length < 2) return ranges.map((r) => ({ from: r.from, to: r.to }))
  const sorted = ranges
    .map((r) => ({ from: r.from, to: r.to }))
    .sort((a, b) => a.from - b.from || a.to - b.to)
  const out: Range[] = [sorted[0]]
  for (let i = 1; i < sorted.length; i++) {
    const last = out[out.length - 1]
    if (sorted[i].from <= last.to) last.to = Math.max(last.to, sorted[i].to)
    else out.push(sorted[i])
  }
  return out
}

/**
 * 消除 O(装饰数 × 展开区间数)：展开区间先合并再二分。
 * 整篇选区（Cmd+A）在长文档下会产生数千个展开区间，线性扫描会让单帧成本失控。
 */
export function intersectsMerged(sortedMerged: readonly Range[], from: number, to: number): boolean {
  if (to <= from) return false
  let lo = 0
  let hi = sortedMerged.length - 1
  let idx = -1
  while (lo <= hi) {
    const mid = (lo + hi) >> 1
    if (sortedMerged[mid].from <= to) {
      idx = mid
      lo = mid + 1
    } else {
      hi = mid - 1
    }
  }
  return idx >= 0 && sortedMerged[idx].to >= from
}

/**
 * 丢掉落在展开区间内的「标记替代物」，保留样式类装饰。
 * 结果仍是文档顺序（collectSpecs 输出即有序）。
 */
export function applyReveal(specs: readonly Spec[], ranges: readonly Range[]): Spec[] {
  if (ranges.length === 0) return specs.slice()
  const merged = mergeRanges(ranges)
  return specs.filter((s) => !(s.reveal && intersectsMerged(merged, s.from, s.to)))
}