/**
 * Movie Collection API — the whole backend in one file.
 *
 * - Domain: a **Movie** is one entry in the collection. The collection lives at /api/movies.
 * - Storage: a plain JavaScript array. There is no database, so anything you add
 *   disappears when the server restarts.
 * - Validation: zod v4 schemas are the single source of truth. They validate the
 *   request and produce the per-field error messages the frontend renders.
 * - Runs on Node (`node server.js`), which is all this assignment needs.
 */
import express from 'express'
import { readFile } from 'node:fs/promises'
import { fileURLToPath } from 'node:url'
import { z } from 'zod'

const PORT = process.env.PORT || 3000

// ---------------------------------------------------------------------------
// Schemas
// ---------------------------------------------------------------------------

const ID_MESSAGE = 'ID must be a whole number, like 1.'

/** `:id` path param. Accepts "2", rejects "abc", "0", "-1" and "1.5". */
const movieIdSchema = z.coerce.number({ error: ID_MESSAGE }).int(ID_MESSAGE).min(1, ID_MESSAGE)

/** "2010" (from a form or a query string) and 2010 are the same year. */
const yearSchema = z.preprocess(
  (value) => {
    if (value === null || value === undefined) return undefined
    if (typeof value !== 'string') return value

    const trimmed = value.trim()
    if (trimmed === '') return undefined
    return /^-?[0-9]+(\.[0-9]+)?$/.test(trimmed) ? Number(trimmed) : value
  },
  z
    .number({
      error: (issue) =>
        issue.input === undefined ? 'Year is required.' : 'Year must be a number, like 2010.',
    })
    .int('Year must be a whole year, like 2010.')
    .min(1888, 'Year must be 1888 or later.')
    .max(2100, 'Year must be 2100 or earlier.'),
)

/** The fields a client sends. All three are required. */
const movieFields = {
  title: z
    .string({ error: 'Title is required.' })
    .trim()
    .min(1, 'Title is required.')
    .max(120, 'Keep the title under 120 characters.'),
  genre: z
    .string({ error: 'Genre is required.' })
    .trim()
    .min(1, 'Genre is required.')
    .max(60, 'Keep the genre under 60 characters.'),
  year: yearSchema,
}

/** What a client sends to add a movie. */
const movieDraftSchema = z.object(movieFields)

/** What the API stores and returns: the draft, plus the server-assigned id. */
const movieSchema = z.object({ id: z.number().int().min(1), ...movieFields })

/** Every response that returns more than one movie. */
const movieListSchema = z.array(movieSchema)

/** Every error the API returns: a message, plus per-field messages when relevant. */
const errorSchema = z.object({
  error: z.string(),
  fields: z.record(z.string(), z.string()).optional(),
})

// ---------------------------------------------------------------------------
// Store — in-memory, seeded with the three movies the frontend starts with
// ---------------------------------------------------------------------------

let nextId = 1

/** @type {Array<z.infer<typeof movieSchema>>} */
const movies = []

function seed(title, genre, year) {
  movies.push({ id: nextId++, title, genre, year })
}

seed('Interstellar', 'Science Fiction', 2014)
seed('Avengers: Endgame', 'Action', 2019)
seed('Coco', 'Animation', 2017)

const findMovie = (id) => movies.find((movie) => movie.id === id)

/** The message every "no such movie" response uses. */
const missingMovie = (id) => ({ error: `No movie with ID ${id}.` })

// ---------------------------------------------------------------------------
// Validation helpers
// ---------------------------------------------------------------------------

/**
 * Turns a zod failure into the API's one error shape: a summary message plus a
 * `fields` map the frontend can render next to each input.
 */
function validationError(error) {
  const fields = {}

  for (const issue of error.issues) {
    const key = issue.path[0]
    if (typeof key === 'string' && !(key in fields)) fields[key] = issue.message
  }

  return { error: error.issues[0]?.message ?? 'Invalid request.', fields }
}

/** Validates a body/params object; returns either `{ data }` or `{ error }`. */
function parse(schema, value) {
  const result = schema.safeParse(value)
  return result.success ? { data: result.data } : { error: validationError(result.error) }
}

// ---------------------------------------------------------------------------
// The frontend
// ---------------------------------------------------------------------------

const INDEX_HTML_PATH = fileURLToPath(new URL('./index.html', import.meta.url))

// Read per request, so editing index.html shows up without restarting the server.
async function indexResponse(req, res) {
  const html = await readFile(INDEX_HTML_PATH, 'utf8')
  res.type('html').send(html)
}

// ---------------------------------------------------------------------------
// App
// ---------------------------------------------------------------------------

const app = express()
app.disable('x-powered-by')
app.use(express.json())

// ---- Read -------------------------------------------------------------------

// GET /api/movies -> the whole collection
app.get('/api/movies', (req, res) => {
  res.json(movieListSchema.parse(movies))
})

// GET /api/movies/:id -> one movie
app.get('/api/movies/:id', (req, res) => {
  const params = parse(z.object({ id: movieIdSchema }), req.params)
  if (params.error) return res.status(400).json(params.error)

  const movie = findMovie(params.data.id)
  if (!movie) return res.status(404).json(missingMovie(params.data.id))

  res.json(movieSchema.parse(movie))
})

// ---- Create -----------------------------------------------------------------

// POST /api/movies -> add a movie, with the id assigned by the server
app.post('/api/movies', (req, res) => {
  const body = parse(movieDraftSchema, req.body)
  if (body.error) return res.status(400).json(body.error)

  const movie = { id: nextId++, ...body.data }
  movies.push(movie)

  res.status(201).location(`/api/movies/${movie.id}`).json(movieSchema.parse(movie))
})

// ---- Frontend ---------------------------------------------------------------

app.get('/', indexResponse)
app.get('/index.html', indexResponse)

// ---- Fallbacks --------------------------------------------------------------

app.use('/api', (req, res) => {
  res.status(404).json({ error: `No route for ${req.method} ${req.originalUrl}.` })
})

// Anything the API did not answer is a dead link, not a JSON error.
app.use((req, res) => {
  res.status(404).type('txt').send('Not found')
})

// Malformed JSON and anything unexpected land here.
app.use((error, req, res, next) => {
  if (error?.type === 'entity.parse.failed') {
    return res.status(400).json({ error: 'Request body must be valid JSON.' })
  }

  console.error('Unhandled error:', error)
  res.status(500).json({ error: 'Internal server error.' })
})

app.listen(PORT, () => {
  console.log(`Movie API running at http://localhost:${PORT}`)
  console.log(`${movies.length} movies in the in-memory collection`)
})