import type { Combinator, ParseContext, ParseResult } from '../types.ts'
import { rollbackCstCapture, saveCstMark } from '../cst/capture-buffer.ts'
import { matchesEmpty, startsFirstSet } from './first-set.ts'
import { deriveExpected } from './expect.ts'

/**
 * Transactional ordered-choice arm. On failure it restores Parseman's
 * structural capture/trivia/error sinks and reports failure at its entry point;
 * user-owned `ctx.state` is intentionally not cloned or mutated by Parseman.
 */
export function attempt<T>(parser: Combinator<T>): Combinator<T> {
  // First-set fail-fast (mirrors emitAttempt's codegen guard): a non-nullable inner
  // whose first set can't start here can only fail, so reject BEFORE taking the six
  // transaction rollback marks, re-anchoring at `pos` and reporting the same static
  // `expected` the inner start-fail would. Skipped under a completions probe /
  // tolerant recovery, where the swallowed failure still feeds the probe.
  const guardable = parser._meta.firstSet.kind !== 'any' && !matchesEmpty(parser)
  let failExpected: string[] | undefined
  return {
    _tag: 'attempt', _meta: parser._meta, _def: { tag: 'attempt', parser },
    parse(input: string, pos: number, ctx: ParseContext): ParseResult<T> {
      if (guardable && ctx._probe === undefined && !ctx._tolerant && !startsFirstSet(parser, input, pos)) {
        if (failExpected === undefined) {
          const e = deriveExpected(parser)
          failExpected = e.length > 0 ? e : [parser._tag]
        }
        return { ok: false, expected: failExpected, span: { start: pos, end: pos } }
      }
      const mark = saveCstMark(ctx)
      const log = ctx._triviaLog?.length
      const rootLog = ctx._rootTriviaLog?.length
      const result = parser.parse(input, pos, ctx)
      if (result.ok) return result
      rollbackCstCapture(ctx, mark)
      if (log !== undefined && ctx._triviaLog && ctx._triviaLog.length !== log) ctx._triviaLog.length = log
      if (rootLog !== undefined && ctx._rootTriviaLog && ctx._rootTriviaLog.length !== rootLog) ctx._rootTriviaLog.length = rootLog
      if (result.committed) return result
      return { ok: false, expected: result.expected, span: { start: pos, end: pos } }
    },
  }
}