gossamer

import gleam/option.{type Option}
import gossamer/iterator_result.{type IteratorResult}

@external(javascript, "./iterator.type.ts", "Iterator$")
pub type Iterator(a, return, next)

@external(javascript, "./iterator.ffi.mjs", "new_")
pub fn new(
  next: fn(Option(next)) -> IteratorResult(a, return),
) -> Iterator(a, return, next)

/// Creates an iterator from a Gleam list.
///
@external(javascript, "./iterator.ffi.mjs", "from_list")
pub fn from_list(list: List(a)) -> Iterator(a, Nil, Nil)

/// Collects all values from an iterator into a list. Consumes the iterator.
///
@external(javascript, "./iterator.ffi.mjs", "to_list")
pub fn to_list(iterator: Iterator(a, return, next)) -> List(a)

@external(javascript, "./iterator.ffi.mjs", "with_return")
pub fn with_return(
  iterator: Iterator(a, return, next),
  return: fn(Option(return)) -> IteratorResult(a, return),
) -> Iterator(a, return, next)

@external(javascript, "./iterator.ffi.mjs", "with_throw")
pub fn with_throw(
  iterator: Iterator(a, return, next),
  throw: fn(e) -> IteratorResult(a, return),
) -> Iterator(a, return, next)

@external(javascript, "./iterator.ffi.mjs", "next")
pub fn next(iterator: Iterator(a, return, next)) -> IteratorResult(a, return)

@external(javascript, "./iterator.ffi.mjs", "next_with")
pub fn next_with(
  iterator: Iterator(a, return, next),
  value: next,
) -> IteratorResult(a, return)

@external(javascript, "./iterator.ffi.mjs", "return_")
pub fn return(
  iterator: Iterator(a, return, next),
) -> Result(IteratorResult(a, return), Nil)

@external(javascript, "./iterator.ffi.mjs", "return_with")
pub fn return_with(
  iterator: Iterator(a, return, next),
  value: return,
) -> Result(IteratorResult(a, return), Nil)

@external(javascript, "./iterator.ffi.mjs", "throw_")
pub fn throw(
  iterator: Iterator(a, return, next),
  reason reason: e,
) -> Result(IteratorResult(a, return), Nil)

@external(javascript, "./iterator.ffi.mjs", "for_")
pub fn for(in iterator: Iterator(a, return, next), run fun: fn(a) -> any) -> Nil

/// Returns a new iterator that yields the results of applying the callback to
/// each value from the source iterator.
///
@external(javascript, "./iterator.ffi.mjs", "map")
pub fn map(
  over iterator: Iterator(a, return, next),
  with callback: fn(a) -> b,
) -> Iterator(b, Nil, Nil)

/// Returns a new iterator that yields only the values from the source iterator
/// for which the predicate returns `True`.
///
@external(javascript, "./iterator.ffi.mjs", "filter")
pub fn filter(
  in iterator: Iterator(a, return, next),
  keeping predicate: fn(a) -> Bool,
) -> Iterator(a, Nil, Nil)

/// Returns a new iterator that yields at most `limit` values from the source
/// iterator.
///
@external(javascript, "./iterator.ffi.mjs", "take")
pub fn take(
  from iterator: Iterator(a, return, next),
  up_to limit: Int,
) -> Iterator(a, Nil, Nil)

/// Returns a new iterator that skips the first `count` values from the source
/// iterator, then yields the rest.
///
@external(javascript, "./iterator.ffi.mjs", "drop")
pub fn drop(
  from iterator: Iterator(a, return, next),
  up_to count: Int,
) -> Iterator(a, Nil, Nil)

/// Returns a new iterator that applies the callback to each value from the
/// source iterator and yields all values from the resulting iterators.
///
@external(javascript, "./iterator.ffi.mjs", "flat_map")
pub fn flat_map(
  over iterator: Iterator(a, return, next),
  with callback: fn(a) -> Iterator(b, Nil, Nil),
) -> Iterator(b, Nil, Nil)

/// Consumes the iterator, calling the reducer with each value and an
/// accumulator. Returns the final accumulator value.
///
@external(javascript, "./iterator.ffi.mjs", "reduce")
pub fn reduce(
  over iterator: Iterator(a, return, next),
  from initial: b,
  with callback: fn(b, a) -> b,
) -> b

/// Consumes the iterator and returns `True` if the predicate returns `True`
/// for any value. Short-circuits on the first match.
///
@external(javascript, "./iterator.ffi.mjs", "some")
pub fn some(
  in iterator: Iterator(a, return, next),
  satisfying predicate: fn(a) -> Bool,
) -> Bool

/// Consumes the iterator and returns `True` if the predicate returns `True`
/// for every value. Short-circuits on the first non-match.
///
@external(javascript, "./iterator.ffi.mjs", "every")
pub fn every(
  in iterator: Iterator(a, return, next),
  satisfying predicate: fn(a) -> Bool,
) -> Bool

/// Consumes the iterator and returns the first value for which the predicate
/// returns `True`. Returns an error if no value matches.
///
@external(javascript, "./iterator.ffi.mjs", "find")
pub fn find(
  in iterator: Iterator(a, return, next),
  one_that predicate: fn(a) -> Bool,
) -> Result(a, Nil)