// Ported from nanohtml 1.10.0 lib/server.js (MIT) — https://github.com/choojs/nanohtml
// Server-side tagged template. The browserify/babel transform branches of
// the original are gone for good — this is a pure runtime tag.
//
// v8 shape: the tag builds a parts list — static/escaped string runs
// interleaved with unresolved async holes (promises or async iterables in
// child position). A fully-sync template collapses to one string and
// toString() behaves exactly like v7. Async holes make the result
// streamable: iterate it with `for await` (each chunk is a string) — that
// is what choo's toStream() does. toString() on async content throws.
// Async values are only allowed in child position; attribute values must
// be synchronous.

const BOOL_PROPS = [
  'async', 'autofocus', 'autoplay', 'checked', 'controls', 'default',
  'defaultchecked', 'defer', 'disabled', 'formnovalidate', 'hidden',
  'ismap', 'loop', 'multiple', 'muted', 'novalidate', 'open', 'playsinline',
  'readonly', 'required', 'reversed', 'selected'
]

const boolPropRx = new RegExp('([^-a-z](' + BOOL_PROPS.join('|') + '))=["\']?$', 'i')
const handlerRx = /[^-a-z](on[a-z]+)=$/i
const query = /(?:="|&)[^"]*=$/

// minimal parser state, only to distinguish child position from tag position
const TEXT = 0
const TAG = 1
const DQ = 2
const SQ = 3
const COMMENT = 4

function scan (s, state) {
  for (let j = 0; j < s.length; j++) {
    const c = s[j]
    switch (state) {
      case TEXT:
        if (c === '<') {
          if (s.startsWith('!--', j + 1)) { state = COMMENT; j += 3 } else state = TAG
        }
        break
      case TAG:
        if (c === '>') state = TEXT
        else if (c === '"') state = DQ
        else if (c === "'") state = SQ
        break
      case DQ:
        if (c === '"') state = TAG
        break
      case SQ:
        if (c === "'") state = TAG
        break
      case COMMENT:
        if (c === '-' && s.startsWith('->', j + 1)) { state = TEXT; j += 2 }
        break
    }
  }
  return state
}

function isThenable (value) {
  return value && typeof value.then === 'function'
}

function isAsyncIterable (value) {
  return value && typeof value[Symbol.asyncIterator] === 'function'
}

export class HtmlChunks {
  constructor (parts) {
    this.parts = parts // strings and { async: value } holes
    this.__encoded = true
  }

  get async () {
    return this.parts.some((p) => typeof p !== 'string')
  }

  toString () {
    let out = ''
    for (const part of this.parts) {
      if (typeof part !== 'string') {
        throw new Error(
          '@choojs/html: this template has async content and cannot render synchronously — stream it (choo: use toStream() instead of toString())'
        )
      }
      out += part
    }
    return out
  }

  async * [Symbol.asyncIterator] () {
    for (const part of this.parts) {
      if (typeof part === 'string') {
        yield part
      } else {
        yield * resolveAsync(part.async)
      }
    }
  }
}

// Resolve an async hole to string chunks, applying child-value semantics
// to whatever it produces.
async function * resolveAsync (value) {
  if (isThenable(value)) {
    yield * streamChild(await value)
  } else {
    for await (const item of value) {
      yield * streamChild(item)
    }
  }
}

async function * streamChild (value) {
  if (value === null || value === undefined) return
  // HtmlChunks is itself async-iterable: its chunks are final HTML and
  // must never re-enter escaping, so check it before the generic paths
  if (value instanceof HtmlChunks) {
    yield * value[Symbol.asyncIterator]()
    return
  }
  if (isThenable(value) || isAsyncIterable(value)) {
    yield * resolveAsync(value)
    return
  }
  if (Array.isArray(value)) {
    for (const item of value) yield * streamChild(item)
    return
  }
  const str = handleChild(value)
  if (str !== '') yield str
}

export default function html (pieces, ...values) {
  const parts = []
  let acc = ''
  let boolMatch
  let state = TEXT

  for (let i = 0; i < pieces.length; i++) {
    const piece = pieces[i]
    state = scan(piece, state)
    if (i === pieces.length - 1) {
      acc += piece
      break
    }

    const value = values[i]

    if (state === TEXT) {
      // child position: this is where async content may live
      // (HtmlChunks is itself async-iterable, so check it first)
      acc += piece
      if (value instanceof HtmlChunks) {
        // splice nested parts so inner async holes stream through
        for (const part of value.parts) {
          if (typeof part === 'string') acc += part
          else { parts.push(acc, part); acc = '' }
        }
      } else if (isThenable(value) || isAsyncIterable(value)) {
        parts.push(acc, { async: value })
        acc = ''
      } else {
        acc += handleChild(value)
      }
      continue
    }

    // tag position: attributes are synchronous, always
    if (isThenable(value) || isAsyncIterable(value)) {
      throw new Error('@choojs/html: async values are only allowed in child position, not in attributes')
    }

    // Event handlers are behavior, not markup: `onclick=${fn}` renders
    // nothing at all, matching the browser renderer (which sets the
    // handler as a property). v7 serialized a useless onclick="".
    const handlerMatch = handlerRx.exec(piece)
    if (handlerMatch && typeof value === 'function') {
      acc += piece.slice(0, handlerMatch.index + 1).replace(/\s+$/, ' ')
      continue
    }

    if ((boolMatch = boolPropRx.exec(piece))) {
      acc += piece.slice(0, boolMatch.index)
      if (value) {
        acc += boolMatch[1] + '="' + boolMatch[2] + '"'
      }
      continue
    }

    const handled = handleValue(value)
    if (piece[piece.length - 1] === '=' && !query.test(piece)) {
      acc += piece + '"' + handled + '"'
    } else {
      acc += piece + handled
    }
  }

  parts.push(acc)
  return new HtmlChunks(parts)
}

// child-position (text) value → string
function handleChild (value) {
  if (Array.isArray(value)) return value.map(handleChild).join('')
  if (typeof value === 'function') return ''
  if (value === null || value === undefined) return ''
  if (value.__encoded) return value.toString()
  if (typeof value === 'object' && typeof value.outerHTML === 'string') return value.outerHTML
  return escape(value.toString())
}

// tag-position (attribute) value → string; keeps v7 semantics including
// object spread and arrays
function handleValue (value) {
  // Handle each item in array as potential unescaped value
  if (Array.isArray(value)) return value.map(handleValue).join('')

  if (typeof value === 'function') return ''
  if (value === null || value === undefined) return ''
  if (value.__encoded) return value.toString()

  if (typeof value === 'object') {
    if (typeof value.outerHTML === 'string') return value.outerHTML
    return Object.keys(value).reduce(function (str, key) {
      // handlers in spread objects are behavior too — never serialized
      if (typeof value[key] === 'function') return str

      if (str.length > 0) str += ' '

      if (BOOL_PROPS.indexOf(key) !== -1) {
        if (value[key]) {
          return str + key + '="' + key + '"'
        }
        return str
      }

      const handled = handleValue(value[key])
      return str + key + '="' + handled + '"'
    }, '')
  }

  return escape(value.toString())
}

function escape (str) {
  return str
    .replace(/&/g, '&amp;')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
    .replace(/"/g, '&quot;')
    .replace(/'/g, '&#039;')
}

export { html }