typocomath/src/core/parseReflectedType.ts

export interface FunctionDef {
  name: string,
  signatures: Array<{
    args: Array<{ name: string, type: string }>
    // FIXME: remove undefined in the end
    returns: string | undefined
  }>
}

export interface DependencyDef extends FunctionDef {
  aliasOf: string | undefined
}

/**
 * Parse a reflected type coming out of TypeScript into a structured object, for example:
 *
 *   '<T>(dep: configDependency & { complex: ((re: number) => Complex<number>) | ((re: number, im: number) => Complex<number>); }) => (a: number) => number | Complex<number>'
 */
export function parseReflectedType(name: string, reflectedType: string) : { fn: FunctionDef, dependencies: Record<string, DependencyDef> } {
  const [factoryArgs, fnArgsBlock, returns] = split(reflectedType, '=>').map(trim)
  const args = parseArgs(fnArgsBlock)

  const factoryArgsInner = findBlockContents(factoryArgs, '(', ')')
  const depArg = split(factoryArgsInner.innerText, ':').map(trim)[1]
  const depArgBlocks = split(depArg, '&').map(trim)

  const deps = depArgBlocks
    .filter(depArgBlock => {
      if (depArgBlock.startsWith('{')) {
        return true
      } else {
        console.error(`ERROR: Cannot parse dependency "${depArgBlock}"`)
      }
    })
    .flatMap(parseDependencies)

  const dependencies: Record<string, DependencyDef> = groupBy(deps, 'name')

  return {
    fn: { name, signatures: [{args, returns}] },
    dependencies
  }

  function parseDependencies(deps: string) {
    const inner = findBlockContents(deps, '{', '}').innerText
    return split(inner, ';')
      .map(trim)
      .filter(notEmpty)
      .map(parseDependency)
  }

  // parse a dependency like "complex: ((re: number) => Complex<number>) | ((re: number, im: number) => Complex<number>)"
  function parseDependency(dep: string) {
    const [name, def] = split(dep, ':').map(trim)

    const { aliasOf, innerSignature } = parseAliasOf(def)

    const signatures = split(innerSignature, '|')
      .map(trim)
      .map(stripParenthesis)
      .map(signature => {
        const [argsBlock, returns] = split(signature, '=>').map(trim)

        if (!returns) {
          console.warn(`ERROR: failed to find return type in '${signature}'`)
        }

        return {
          args: parseArgs(argsBlock),
          returns
        }
      })

    return { name, signatures, aliasOf }
  }

  // parse args like "(re: number, im: number)"
  function parseArgs(argsBlock: string) : Array<{name: string, type: string}> {
    const args = findBlockContents(argsBlock, '(', ')').innerText

    return split(args, ',')
      .map(trim)
      .map(arg => {
        const [name, type] = split(arg, ':').map(trim)
        return { name, type}
      })
  }

  // parse "AliasOf<"divide", (a: Complex<T>, b: RealType<Complex<T>>) => Complex<T>>"
  function parseAliasOf(signature: string) : { innerSignature: string, aliasOf: string | undefined } {
    if (!signature.startsWith('AliasOf')) {
      return {
        innerSignature: signature,
        aliasOf: undefined
      }
    }

    const inner = findBlockContents(signature, '<', '>').innerText.trim()
    const [aliasOfWithQuotes, innerSignature] = split(inner, ',').map(trim)
    return {
      innerSignature,
      aliasOf: aliasOfWithQuotes.substring(1, aliasOfWithQuotes.length - 1) // remove double quotes
    }
  }

  // remove the outer parenthesis, for example "((re: number) => Complex<number>)" returns "(re: number) => Complex<number>"
  function stripParenthesis(text: string) : string {
    return text.startsWith('(') && text.endsWith(')')
      ? text.substring(1, text.length - 1)
      : text
  }
}

function findBlockContents(text: string, blockStart: string, blockEnd: string, startIndex = 0) : { start: number, end: number, innerText: string } | undefined {
  let i = startIndex

  while (!matchSubString(text, blockStart, i) && i < text.length) {
    i++
  }

  if (i >= text.length) {
    return undefined
  }

  i++
  const start = i

  while (!matchSubString(text, blockEnd, i) || matchSubString(text, '=>', i - 1)) {
    i = skipBrackets(text, i)

    i++
  }

  if (i >= text.length) {
    return undefined
  }
  const end = i

  return {
    start,
    end,
    innerText: text.substring(start, end)
  }
}

/**
 * Split a string by a delimiter, but ignore all occurrences of the delimiter
 * that are inside bracket pairs <> () [] {}
 */
export function split(text: string, delimiter: string) : string[] {
  const parts: string[] = []

  let i = 0
  let start = 0
  while (i < text.length) {
    i = skipBrackets(text, i)

    if (matchSubString(text, delimiter, i)) {
      parts.push(text.substring(start, i))
      i += delimiter.length
      start = i
    }

    i++
  }

  parts.push(text.substring(start))

  return parts
}

function skipBrackets(text: string, startIndex: number) : number {
  let level = 0
  let i = startIndex

  do {
    if (isBracketOpen(text, i)) {
      level++
    }

    if (isBracketClose(text, i) && level > 0) {
      level--
    }

    if (level === 0) {
      break
    }

    i++
  } while(i < text.length)

  return i
}

function isBracketOpen(text: string, index: number) {
  const char = text[index]
  return char === '(' || char === '<' || char === '[' || char === '{'
}

function isBracketClose(text: string, index: number) {
  const char = text[index]
  // we need to take care of not matching the ">" of the operator "=>"
  return char === ')' || (char === '>' && text[index - 1] !== '=') || char === ']' || char === '}'
}

function matchSubString(text: string, search: string, index: number) : boolean {
  for (let i = 0; i < search.length; i++) {
    if (text[i + index] !== search[i]) {
      return false
    }
  }

  return true
}

function trim(text: string) : string {
  return text.trim()
}

function notEmpty(text: string) : boolean {
  return text.length > 0
}

function groupBy<T>(items: T[], key: string) : Record<string, T> {
  const obj: Record<string, T> = {}

  items.forEach((item) => {
    obj[item[key]] = item
  })

  return obj
}