import { describe, expect, it } from 'vitest'
import { wordBand } from './wordband'

describe('wordBand', () => {
  it('says nothing when the dictionary knows nothing', () => {
    // The embedded datasets carry no scores at all, and this is the common
    // case for a zh-pair writer. An unknown word must produce no chip rather
    // than a default one — "standard" would be an invention.
    expect(wordBand(0, -1)).toBeNull()
  })

  it('bands the words a writer actually looks up', () => {
    // Real scores from the deployed dict.db. These are the sanity checks that
    // would catch a threshold drifting away from the data.
    expect(wordBand(1000, 0.304)).toBe('simple') // cat
    expect(wordBand(1000, 0.326)).toBe('simple') // house, write
    expect(wordBand(1000, 0.37)).toBe('simple') // beautiful
    expect(wordBand(600, 0.462)).toBe('standard') // ephemeral
    expect(wordBand(400, 0.53)).toBe('standard') // serendipity
    expect(wordBand(50, 0.8)).toBe('advanced') // antidisestablishmentarianism
  })

  it('prefers difficulty over frequency when both are known', () => {
    // Difficulty is the finer signal — 206 distinct values against frequency's
    // handful of buckets — so a hard word with a high frequency reads as hard.
    expect(wordBand(1000, 0.9)).toBe('advanced')
    expect(wordBand(2, 0.2)).toBe('simple')
  })

  it('falls back to frequency for a word with no difficulty score', () => {
    expect(wordBand(1000, -1)).toBe('simple')
    expect(wordBand(500, -1)).toBe('standard')
    expect(wordBand(10, -1)).toBe('advanced')
  })

  it('treats a difficulty of exactly zero as a score, not as missing', () => {
    // 0.0 is the easiest word there is. The API sends -1 for unknown precisely
    // so this case survives; a falsy check here would throw it away.
    expect(wordBand(0, 0)).toBe('simple')
  })
})