// json_scan_guard.hako — JsonScanGuardBox
// Responsibility: escape-aware JSON scanning with step budget (Fail-Fast)

using selfhost.shared.json.core.string_scan as StringScanBox

static box JsonScanGuardBox {
  // Seek the end index (inclusive) of an object starting at `start` (must be '{').
  // Returns: end index or -1 on failure/budget exceeded.
  seek_obj_end(text, start, budget) {
    if text == null { return -1 }
    if start < 0 || start >= text.length() { return -1 }
    if text.substring(start, start+1) != "{" { return -1 }
    local n = text.length()
    local depth = 0
    local i = start
    local steps = 0
    loop (i < n) {
      if steps >= budget { return -1 }
      steps = steps + 1
      local ch = StringScanBox.read_char(text, i)
      if ch == "\\" { i = i + 2  continue }
      if ch == "\"" {
        // jump to end quote (escape-aware)
        local j = StringScanBox.find_quote(text, i+1)
        if j < 0 { return -1 }
        i = j + 1
        continue
      }
      if ch == "{" { depth = depth + 1 }
      if ch == "}" { depth = depth - 1  if depth == 0 { return i } }
      i = i + 1
    }
    return -1
  }

  // Seek the end index (inclusive) of an array starting at `start` (must be '[').
  // Returns: end index or -1 on failure/budget exceeded.
  seek_array_end(text, start, budget) {
    if text == null { return -1 }
    if start < 0 || start >= text.length() { return -1 }
    if text.substring(start, start+1) != "[" { return -1 }
    local n = text.length()
    local depth = 0
    local i = start
    local steps = 0
    loop (i < n) {
      if steps >= budget { return -1 }
      steps = steps + 1
      local ch = StringScanBox.read_char(text, i)
      if ch == "\\" { i = i + 2  continue }
      if ch == "\"" {
        local j = StringScanBox.find_quote(text, i+1)
        if j < 0 { return -1 }
        i = j + 1
        continue
      }
      if ch == "[" { depth = depth + 1 }
      if ch == "]" { depth = depth - 1  if depth == 0 { return i } }
      i = i + 1
    }
    return -1
  }
}
