localGetDiff.ts

import { debug } from "../../debug"
import { spawn } from "child_process"

const d = debug("localGetDiff")
const useCommittedDiffArgs = (base: string, head: string) => [
  "diff",
  "--src-prefix='a/' --dst-prefix='b/'",
  `${base}...${head}`,
]
const useStagingChanges = () => ["diff", "--src-prefix='a/' --dst-prefix='b/'", "--staged"]

export const localGetDiff = (base: string, head: string, staging: boolean = false) =>
  new Promise<string>((done) => {
    const args = staging ? useStagingChanges() : useCommittedDiffArgs(base, head)
    let stdout = ""

    const child = spawn("git", args, { env: process.env })
    d("> git", args.join(" "))

    child.stdout.on("data", (chunk) => {
      stdout += chunk
    })

    child.stderr.on("data", (data) => {
      console.error(`Could not get diff from git between ${base} and ${head}`)
      throw new Error(data.toString())
    })

    child.on("close", function (code) {
      if (code === 0) {
        done(stdout)
      }
    })
  })