import { lineToString } from './pkt-line'

export const ZERO_SHA = '0000000000000000000000000000000000000000'

export interface Advertisement {
  /** Ref name -> object SHA (unpeeled). For annotated tags this is the tag object. */
  refs: Map<string, string>
  /** For annotated tags, the `<tag>^{}` peeled line: ref name -> commit SHA. */
  peeled: Map<string, string>
  capabilities: Set<string>
}

/**
 * Parse a git ref advertisement (protocol v0) from a list of pkt-line
 * payloads (flush-pkts already stripped by the reader).
 *
 * Handles three shapes that occur in practice:
 *   - smart-HTTP prelude: a leading `# service=git-upload-pack` line, which
 *     the ssh transport omits;
 *   - a populated repo: `<sha> <refname>\0<caps>` on the first ref line,
 *     `<sha> <refname>` thereafter, with `<sha> <refname>^{}` peeled lines
 *     for annotated tags;
 *   - an empty repo: a single `<zero-sha> capabilities^{}\0<caps>` line that
 *     carries capabilities but advertises no usable ref.
 */
export function parseAdvertisement(lines: Buffer[]): Advertisement {
  const refs = new Map<string, string>()
  const peeled = new Map<string, string>()
  const capabilities = new Set<string>()

  let first = true
  for (const raw of lines) {
    const line = lineToString(raw)
    if (line.startsWith('# service=')) continue

    let sha: string
    let rest: string
    if (first) {
      const nul = line.indexOf('\0')
      const head = nul === -1 ? line : line.slice(0, nul)
      const caps = nul === -1 ? '' : line.slice(nul + 1)
      for (const cap of caps.split(' ')) {
        if (cap) capabilities.add(cap)
      }
      first = false
      const sp = head.indexOf(' ')
      sha = head.slice(0, sp)
      rest = head.slice(sp + 1)
      // Empty-repo sentinel: zero SHA + the literal "capabilities^{}" name.
      if (sha === ZERO_SHA && rest === 'capabilities^{}') continue
    }
    else {
      const sp = line.indexOf(' ')
      sha = line.slice(0, sp)
      rest = line.slice(sp + 1)
    }

    if (rest.endsWith('^{}')) {
      peeled.set(rest.slice(0, -3), sha)
    }
    else {
      refs.set(rest, sha)
    }
  }

  return { refs, peeled, capabilities }
}