import { describe, it, expect, beforeEach, afterEach } from "bun:test"
import { readFileSync, writeFileSync, existsSync, rmSync, mkdirSync } from "fs"
import { join } from "path"
import { tmpdir } from "os"
import { writeFileAtomically } from "./write-file-atomically"

const testDir = join(tmpdir(), "write-file-atomically-test-" + Date.now())

beforeEach(() => {
  mkdirSync(testDir, { recursive: true })
})

afterEach(() => {
  rmSync(testDir, { recursive: true, force: true })
})

describe("writeFileAtomically", () => {
  it("writes content to a new file", () => {
    // given
    const filePath = join(testDir, "new-file.txt")
    const content = "hello world"

    // when
    writeFileAtomically(filePath, content)

    // then
    expect(existsSync(filePath)).toBe(true)
    expect(readFileSync(filePath, "utf-8")).toBe(content)
  })

  it("#given target file exists #when writeFileAtomically called #then overwrites successfully", () => {
    // given
    const filePath = join(testDir, "existing-file.txt")
    const originalContent = "original content"
    const newContent = "new content"
    writeFileSync(filePath, originalContent, "utf-8")

    // when
    writeFileAtomically(filePath, newContent)

    // then
    expect(existsSync(filePath)).toBe(true)
    expect(readFileSync(filePath, "utf-8")).toBe(newContent)
    expect(existsSync(`${filePath}.tmp`)).toBe(false)
  })

  it("#given parent directory does not exist #when writeFileAtomically called #then throws", () => {
    // given
    const filePath = join(testDir, "nonexistent", "deep", "file.txt")

    // when/then
    expect(() => writeFileAtomically(filePath, "content")).toThrow()
  })

  it("#given fsync fails with EPERM (synced folder) #when writeFileAtomically called #then write succeeds", () => {
    // given
    const filePath = join(testDir, "synced-folder.txt")
    const content = "content from a synced folder where fsync is rejected"

    // when
    writeFileAtomically(filePath, content, {
      fsyncSync: () => {
        const error = new Error("EPERM: operation not permitted, fsync") as NodeJS.ErrnoException
        error.code = "EPERM"
        throw error
      },
    })

    // then
    expect(existsSync(filePath)).toBe(true)
    expect(readFileSync(filePath, "utf-8")).toBe(content)
  })

  it("#given fsync fails with EIO (real I/O error) #when writeFileAtomically called #then propagates the error", () => {
    // given
    const filePath = join(testDir, "io-error.txt")

    // when/then
    expect(() =>
      writeFileAtomically(filePath, "content", {
        fsyncSync: () => {
          const error = new Error("EIO: input/output error") as NodeJS.ErrnoException
          error.code = "EIO"
          throw error
        },
      }),
    ).toThrow("EIO")
  })
})