// Minimal Valve KeyValues (VDF) text parser.
// Handles nested objects and quoted string values. Sufficient for libraryfolders.vdf.

export type VdfNode = { [key: string]: string | VdfNode }

class Cursor {
  constructor(
    public src: string,
    public pos: number = 0
  ) {}
  peek(): string {
    return this.src[this.pos] ?? ''
  }
  next(): string {
    return this.src[this.pos++] ?? ''
  }
  eof(): boolean {
    return this.pos >= this.src.length
  }
}

function skipWhitespaceAndComments(c: Cursor): void {
  for (;;) {
    while (!c.eof() && /\s/.test(c.peek())) c.next()
    if (c.peek() === '/' && c.src[c.pos + 1] === '/') {
      while (!c.eof() && c.next() !== '\n') {
        /* skip line */
      }
      continue
    }
    return
  }
}

function readToken(c: Cursor): string {
  skipWhitespaceAndComments(c)
  if (c.eof()) return ''
  if (c.peek() === '"') {
    c.next()
    let out = ''
    while (!c.eof()) {
      const ch = c.next()
      if (ch === '\\') {
        const next = c.next()
        if (next === 'n') out += '\n'
        else if (next === 't') out += '\t'
        else out += next
        continue
      }
      if (ch === '"') return out
      out += ch
    }
    return out
  }
  if (c.peek() === '{' || c.peek() === '}') return c.next()
  let out = ''
  while (
    !c.eof() &&
    !/\s/.test(c.peek()) &&
    c.peek() !== '{' &&
    c.peek() !== '}'
  ) {
    out += c.next()
  }
  return out
}

function parseObject(c: Cursor): VdfNode {
  const node: VdfNode = {}
  for (;;) {
    skipWhitespaceAndComments(c)
    if (c.eof()) return node
    if (c.peek() === '}') {
      c.next()
      return node
    }
    const key = readToken(c)
    if (!key) return node
    skipWhitespaceAndComments(c)
    if (c.peek() === '{') {
      c.next()
      node[key] = parseObject(c)
    } else {
      node[key] = readToken(c)
    }
  }
}

export function parseVdf(src: string): VdfNode {
  const c = new Cursor(src)
  const root: VdfNode = {}
  for (;;) {
    skipWhitespaceAndComments(c)
    if (c.eof()) break
    const key = readToken(c)
    if (!key) break
    skipWhitespaceAndComments(c)
    if (c.peek() === '{') {
      c.next()
      root[key] = parseObject(c)
    } else {
      root[key] = readToken(c)
    }
  }
  return root
}

function escapeVdfString(s: string): string {
  return s
    .replace(/\\/g, '\\\\')
    .replace(/"/g, '\\"')
    .replace(/\n/g, '\\n')
    .replace(/\t/g, '\\t')
}

export function stringifyVdf(node: VdfNode, indent: number = 0): string {
  const pad = '\t'.repeat(indent)
  let out = ''
  for (const key of Object.keys(node)) {
    const value = node[key]
    if (typeof value === 'string') {
      out += `${pad}"${escapeVdfString(key)}"\t\t"${escapeVdfString(value)}"\n`
    } else {
      out += `${pad}"${escapeVdfString(key)}"\n${pad}{\n`
      out += stringifyVdf(value, indent + 1)
      out += `${pad}}\n`
    }
  }
  return out
}