live_vue

import type { Operation } from "./jsonPatch.js"

export const decodeCompactPatch = (payload: string | null): Operation[] => {
  if (!payload) return []

  const operations: Operation[] = []
  let offset = 0

  while (offset < payload.length) {
    const code = payload[offset++]

    if (code === "n") {
      offset = skipDigits(payload, offset)
      continue
    }

    const op = opFromCode(code)
    const pathLength = readLength(payload, offset)
    offset = pathLength.offset

    const path = payload.slice(offset, offset + pathLength.value)
    offset += pathLength.value

    if (op === "remove") {
      operations.push({ op, path })
      continue
    }

    const tag = payload[offset++]

    if (tag === "z") {
      operations.push({ op, path, value: null } as Operation)
      continue
    }

    if (tag === "b") {
      operations.push({ op, path, value: payload[offset++] === "1" } as Operation)
      continue
    }

    const valueLength = readLength(payload, offset)
    offset = valueLength.offset

    const rawValue = payload.slice(offset, offset + valueLength.value)
    offset += valueLength.value

    if (tag === "n") {
      operations.push({ op, path, value: Number(rawValue) } as Operation)
    } else if (tag === "s") {
      operations.push({ op, path, value: rawValue } as Operation)
    } else if (tag === "J") {
      operations.push({ op, path, value: decodeCompactJson(rawValue) } as Operation)
    } else {
      throw new Error(`Unknown LiveVue patch value tag: ${tag}`)
    }
  }

  return operations
}

const opFromCode = (code: string): Operation["op"] => {
  switch (code) {
    case "a":
      return "add"
    case "d":
      return "remove"
    case "r":
      return "replace"
    case "u":
      return "upsert"
    case "l":
      return "limit"
    default:
      throw new Error(`Unknown LiveVue patch operation code: ${code}`)
  }
}

const readLength = (payload: string, offset: number): { value: number; offset: number } => {
  let value = 0
  let hasDigits = false

  while (offset < payload.length) {
    const code = payload.charCodeAt(offset)
    if (code < 48 || code > 57) break
    value = value * 10 + code - 48
    offset++
    hasDigits = true
  }

  if (!hasDigits || payload[offset] !== ":") throw new Error("Invalid LiveVue patch length prefix")
  return { value, offset: offset + 1 }
}

const skipDigits = (payload: string, offset: number): number => {
  while (offset < payload.length) {
    const code = payload.charCodeAt(offset)
    if (code < 48 || code > 57) break
    offset++
  }

  return offset
}

export const decodeCompactJson = (value: string): any => {
  return JSON.parse(
    value.replace(/~~|~\^|\^/g, match => {
      if (match === "~~") return "~"
      if (match === "~^") return "^"
      return '"'
    })
  )
}