import type { Command, Option } from "commander"

/** Generate fish completions dynamically from the Commander program tree. */
export function action(program: Command) {
  const lines: string[] = [
    "# Fish completions for sandlot (auto-generated)",
    "# Install: sandlot completions > ~/.config/fish/completions/sandlot.fish",
    "",
    "complete -c sandlot -f",
    "",
    "function __sandlot_sessions",
    `    command sandlot list --json 2>/dev/null | string match -r '"branch":\\s*"[^"]+"' | string replace -r '.*"branch":\\s*"([^"]+)".*' '$1'`,
    "end",
    "",
  ]

  const branchCommands: string[] = []

  for (const cmd of program.commands) {
    const name = cmd.name()
    const desc = cmd.description()
    const subs = cmd.commands as Command[]

    if (subs.length > 0) {
      // Parent command (e.g. "vm") — register it plus its subcommands
      lines.push(`complete -c sandlot -n __fish_use_subcommand -a ${name} -d ${esc(desc)}`)
      const subNames = subs.filter(s => !(s as any)._hidden).map(s => s.name())
      const guard = `"__fish_seen_subcommand_from ${name}; and not __fish_seen_subcommand_from ${subNames.join(" ")}"`
      for (const sub of subs) {
        if ((sub as any)._hidden) continue
        lines.push(`complete -c sandlot -n ${guard} -a ${sub.name()} -d ${esc(sub.description())}`)
      }
      // Options on subcommands
      for (const sub of subs) {
        if ((sub as any)._hidden) continue
        emitOptions(lines, `${name} ${sub.name()}`, sub.options)
      }
    } else {
      // Leaf command
      lines.push(`complete -c sandlot -n __fish_use_subcommand -a ${name} -d ${esc(desc)}`)
      emitOptions(lines, name, cmd.options)

      // Track commands that accept a <branch> / [branch] argument
      const hasBranch = cmd.registeredArguments.some(a => a.name() === "branch")
      if (hasBranch) branchCommands.push(name)
    }
  }

  // Session completions for all branch-taking commands
  if (branchCommands.length > 0) {
    lines.push("")
    lines.push(`complete -c sandlot -n "__fish_seen_subcommand_from ${branchCommands.join(" ")}" -xa "(__sandlot_sessions)"`)
  }

  lines.push("")
  process.stdout.write(lines.join("\n") + "\n")
}

function esc(s: string): string {
  return `"${s.replace(/"/g, '\\"')}"`
}

function emitOptions(lines: string[], cmdName: string, options: readonly Option[]) {
  for (const opt of options) {
    const parts = [`complete -c sandlot -n "__fish_seen_subcommand_from ${cmdName}"`]
    if (opt.short) parts.push(`-s ${opt.short.replace("-", "")}`)
    if (opt.long) parts.push(`-l ${opt.long.replace("--", "")}`)
    parts.push(`-d ${esc(opt.description)}`)
    if (opt.required) parts.push("-r")
    lines.push(parts.join(" "))
  }
}