/** @module src/checkGr */
import km100s from './km100.js'
function invalidGridRef(gr) {
throw `The value '${gr}' is not recognised as a valid grid reference.`
}
/**
* Given a grid reference (British National Grid, Irish Grid or UTM zone 30N shorthand),
* check that ths is a valid GR. If it is, return an object which includes the
* GR precision in metres, the prefix and the two-letter projection code.
* If an invalid grid reference is supplied throws an error.
* @param {string} gr - the grid reference.
* @returns {object} Object of the form {precision: n, prefix: 'prefix', projection: 'code'}.
*/
export function checkGr (gr) {
const r100km = RegExp('^[a-zA-Z]{1,2}$')
const rHectad = RegExp('^[a-zA-Z]{1,2}[0-9]{2}$')
const rQuandrant = RegExp('^[a-zA-Z]{1,2}[0-9]{2}[SsNn][WwEe]$')
const rTetrad = RegExp('^[a-zA-Z]{1,2}[0-9]{2}[a-np-zA-NP-Z]$')
const rMonad = RegExp('^[a-zA-Z]{1,2}[0-9]{4}$')
const r6fig = RegExp('^[a-zA-Z]{1,2}[0-9]{6}$')
const r8fig = RegExp('^[a-zA-Z]{1,2}[0-9]{8}$')
const r10fig = RegExp('^[a-zA-Z]{1,2}[0-9]{10}$')
const match = gr.match(/^[A-Za-z]+/)
if (!match) invalidGridRef(gr)
const prefix = match[0].toUpperCase()
const km100 = km100s[prefix]
if (!km100) invalidGridRef(gr)
const ret = {precision: null, prefix: prefix, projection: km100.proj}
if (r100km.test(gr)) {
// The GR is a 100 km square reference
ret.precision = 100000
} else if (rHectad.test(gr)) {
// The GR is a hectad
ret.precision = 10000
} else if (rQuandrant.test(gr)) {
// The GR is a quandrant
ret.precision = 5000
} else if (rTetrad.test(gr)) {
// The GR is a tetrad
ret.precision = 2000
} else if (rMonad.test(gr)) {
// The GR is a monad
ret.precision = 1000
} else if (r6fig.test(gr)) {
// The GR is a 6 figure GR
ret.precision = 100
} else if (r8fig.test(gr)) {
// The GR is a 8 figure GR
ret.precision = 10
} else if (r10fig.test(gr)) {
// The GR is a 10 figure GR
ret.precision = 1
} else {
invalidGridRef(gr)
}
return ret
}