/**
 * A link that opens the generator with somebody's work already in it.
 *
 * WHY THE FRAGMENT
 *
 * Everything rides after the `#`. A fragment is never transmitted: it does not
 * reach Flask, it is not in the IIS log, and the proxy between the two never
 * sees it. A query string would put the encoded content in all three, and the
 * whole point of this feature is to send somebody a code they can print - which
 * means the content is often an asset number, a serial, or a URL somebody would
 * rather not scatter through logs.
 *
 * It is NOT secrecy. The link still sits in a chat message, in browser history
 * and in whatever archives that chat. Anyone holding the link has the content.
 * Secure Send exists for the case where that matters.
 *
 * WHAT TRAVELS
 *
 * What was typed (content, label, copies, the CSV) plus the settings that
 * change how the label looks. Not the picture: a data URL runs to megabytes and
 * would produce a link no chat client will carry.
 */

// Short keys because the whole thing has to survive being pasted into a chat
// box. `c` is the content, `t` the code type, `p` the label preset.
const SHORT = {
  c: 'content',
  l: 'label',
  n: 'copies',
  b: 'back',
  v: 'csv',
  s: 'source',
  t: 'codetype',
  e: 'errorcorrection',
  p: 'preset',
}

// Layout values travel under their own names - there are enough of them that
// abbreviating would cost more in confusion than it saves in characters.
const PASSTHROUGH = [
  'labelwidth', 'labelheight', 'padding', 'quiet', 'gap', 'codesize',
  'barheight', 'labelfont', 'layout', 'align', 'valign',
  'contentx', 'contenty', 'nudgex', 'nudgey', 'dpi',
  'backenabled', 'backsource', 'backcodetype', 'backtext', 'backlayout',
  'backorder',
]

const LONG = Object.fromEntries(Object.entries(SHORT).map(([k, v]) => [v, k]))

/**
 * Build the fragment for a state object. Returns '' when there is nothing to
 * share, so a caller can disable its button rather than emit a bare '#'.
 */
export function buildFragment (state, defaults = {}) {
  const params = new URLSearchParams()

  for (const [key, name] of Object.entries(SHORT)) {
    const value = state[name]
    if (value === undefined || value === null || value === '') continue
    // Copies of 1 is what everybody has; it does not need saying.
    if (name === 'copies' && Number(value) === 1) continue
    params.set(key, String(value))
  }

  // Only the layout values that DIFFER from this browser's current settings.
  // Sending all twenty would make a link four times longer for no gain, and the
  // recipient's own saved settings are a reasonable starting point.
  for (const name of PASSTHROUGH) {
    const value = state[name]
    if (value === undefined || value === null || value === '') continue
    if (defaults[name] !== undefined && String(defaults[name]) === String(value)) continue
    params.set(name, String(value))
  }

  const encoded = params.toString()
  return encoded ? '#' + encoded : ''
}

/**
 * Read a fragment back into a partial state object.
 *
 * Unknown keys are ignored rather than refused: a link made by a newer version
 * must still open here, minus whatever this version does not understand.
 */
export function readFragment (hash) {
  const raw = String(hash || '').replace(/^#/, '')
  if (!raw) return {}

  const params = new URLSearchParams(raw)
  const state = {}

  for (const [key, value] of params.entries()) {
    const name = SHORT[key] || (PASSTHROUGH.includes(key) ? key : null)
    if (!name) continue
    state[name] = value
  }
  return state
}

/**
 * Coerce a fragment value to the type the ref already holds.
 *
 * Everything arrives as a string. Assigning '203' to a numeric input renders,
 * but the moment it is used in arithmetic it concatenates - so a nudge of 0
 * plus '2' becomes '02'. Match the current value's type instead.
 */
export function coerce (value, current) {
  if (typeof current === 'number') {
    const number = Number(value)
    return Number.isFinite(number) ? number : current
  }
  if (typeof current === 'boolean') {
    return value === 'true' || value === '1'
  }
  return value
}