// Read a KomaMRI `.phantom` (HDF5) file into a Phantom, using h5wasm in the
// browser. Robust to missing contrast fields (fills sensible defaults) so it
// can also load arbitrary KomaMRI phantoms, not just our two built-ins.
import * as h5wasm from 'h5wasm'
import type { Phantom } from './phantomTypes.ts'

let readyPromise: Promise<void> | null = null
let counter = 0

async function ensureReady(): Promise<void> {
  if (!readyPromise) {
    readyPromise = h5wasm.ready.then(() => undefined)
  }
  return readyPromise
}

function toF32(v: unknown, ns: number, fallback: number): Float32Array {
  if (v instanceof Float32Array) return v
  if (v instanceof Float64Array || Array.isArray(v)) return Float32Array.from(v as ArrayLike<number>)
  if (ArrayBuffer.isView(v)) return Float32Array.from(v as unknown as ArrayLike<number>)
  const a = new Float32Array(ns)
  a.fill(fallback)
  return a
}

/** Map a contrast group's (possibly Unicode-named) datasets onto our field names. */
const CONTRAST_ALIASES: Record<string, string[]> = {
  rho: ['ρ', 'rho', 'Rho', 'PD'],
  t1: ['T1'],
  t2: ['T2'],
  t2s: ['T2s', 'T2*'],
  dw: ['Δw', 'Deltaw', 'dw', 'B0'],
}

function readGroupField(group: h5wasm.Group | null, aliases: string[]): unknown {
  if (!group) return null
  const keys = group.keys()
  for (const alias of aliases) {
    if (keys.includes(alias)) {
      const ds = group.get(alias)
      if (ds && 'value' in ds) return (ds as h5wasm.Dataset).value
    }
  }
  return null
}

export async function loadPhantom(buffer: ArrayBuffer, fallbackName = 'phantom'): Promise<Phantom> {
  await ensureReady()
  const FS = h5wasm.FS!
  const filename = `/phantom_${counter++}.h5`
  FS.writeFile(filename, new Uint8Array(buffer))
  let f: h5wasm.File | null = null
  try {
    f = new h5wasm.File(filename, 'r')

    const posGroup = f.get('position') as h5wasm.Group | null
    const x0 = readGroupField(posGroup, ['x'])
    const y0 = readGroupField(posGroup, ['y'])
    const z0 = readGroupField(posGroup, ['z'])
    const ns =
      x0 instanceof Float32Array || x0 instanceof Float64Array || Array.isArray(x0)
        ? (x0 as ArrayLike<number>).length
        : 0
    if (!ns) throw new Error('Phantom has no position/x dataset (not a valid .phantom file?)')

    const x = toF32(x0, ns, 0)
    const y = toF32(y0, ns, 0)
    const z = toF32(z0, ns, 0)

    const con = f.get('contrast') as h5wasm.Group | null
    const rho = toF32(readGroupField(con, CONTRAST_ALIASES.rho), ns, 1)
    const t1 = toF32(readGroupField(con, CONTRAST_ALIASES.t1), ns, 1)
    const t2 = toF32(readGroupField(con, CONTRAST_ALIASES.t2), ns, 0.1)
    const t2s = toF32(readGroupField(con, CONTRAST_ALIASES.t2s), ns, 0.05)
    const dw = toF32(readGroupField(con, CONTRAST_ALIASES.dw), ns, 0)

    const nameAttr = f.attrs['Name']?.value
    const name = typeof nameAttr === 'string' && nameAttr.length ? nameAttr : fallbackName

    return { name, ns, x, y, z, rho, t1, t2, t2s, dw }
  } finally {
    f?.close()
    try {
      FS.unlink(filename)
    } catch {
      // ignore
    }
  }
}