import { $ } from "bun"
import * as git from "../git.ts"
import { requireSession } from "./helpers.ts"

export async function action(branch: string) {
  const { session } = await requireSession(branch)

  // Check for uncommitted changes (staged + unstaged)
  const status = await $`git -C ${session.worktree} status --porcelain`.nothrow().quiet()
  if (status.exitCode !== 0) {
    console.error("✖ git status failed")
    process.exit(1)
  }

  let args: string[]
  if (status.text().trim().length > 0) {
    // Show uncommitted changes (both staged and unstaged)
    const hasHead = await $`git -C ${session.worktree} rev-parse --verify HEAD`.nothrow().quiet()
    args = hasHead.exitCode === 0 ? ["diff", "HEAD"] : ["diff"]
  } else {
    // No uncommitted changes — show full branch diff vs main
    const main = await git.mainBranch(session.worktree)
    args = ["diff", `${main}...${branch}`]
  }

  // Run git diff with inherited stdio so external diff tools (e.g. difftastic)
  // see a real TTY and git can use its own pager
  const proc = Bun.spawn(["git", "-C", session.worktree, ...args], {
    stdin: "inherit",
    stdout: "inherit",
    stderr: "inherit",
  })
  const exitCode = await proc.exited
  if (exitCode !== 0) {
    process.exit(exitCode)
  }
}