pansy/web/src/lib/units.ts

// Unit conversion + display for garden dimensions. The API and DB are metric
// only (centimeters); imperial is purely a display/entry concern here. A minimal
// helper set for #8 — #9's geometry lib consolidates/extends it.

export type UnitPref = 'metric' | 'imperial'

const CM_PER_INCH = 2.54
const CM_PER_METER = 100
const INCHES_PER_FOOT = 12

// Mirrors the server's garden dimension bounds (service/gardens.go): [1cm, 100m].
export const MIN_DIMENSION_CM = 1
export const MAX_DIMENSION_CM = 10_000

// Below this, a garden-scale grid is fine enough to be worth questioning — it
// usually means someone reached for plant spacing, which belongs to the bed, not
// the garden. Soft: the form hints, it doesn't refuse.
export const MIN_GARDEN_GRID_CM = 10

/** Whether a centimeter dimension is within the server's accepted range. */
export function isValidDimensionCm(cm: number): boolean {
  return Number.isFinite(cm) && cm >= MIN_DIMENSION_CM && cm <= MAX_DIMENSION_CM
}

/** Round away IEEE-754 dust without rounding away precision: 12 × 2.54 is
 *  30.479999999999997 in binary floating point, and the 1e-6 cm (10 nm) grain
 *  here is far below anything a garden cares about. Every cm column is REAL, so
 *  entry stays exact — this only stops 30.48 being stored as 30.479999999999997. */
function roundCm(cm: number): number {
  return Math.round(cm * 1e6) / 1e6
}

/** Feet (+ optional inches) → centimeters, exactly (1 ft → 30.48). */
export function cmFromFtIn(feet: number, inches = 0): number {
  return roundCm((feet * INCHES_PER_FOOT + inches) * CM_PER_INCH)
}

/** Meters → centimeters, exactly. */
export function cmFromMeters(meters: number): number {
  return roundCm(meters * CM_PER_METER)
}

/** A value typed in the given unit (meters, or feet) → centimeters. */
export function cmFromDisplay(value: number, unit: UnitPref): number {
  return unit === 'imperial' ? cmFromFtIn(value) : cmFromMeters(value)
}

/** Centimeters → a number in the given unit, for prefilling an input field.
 *  Rounded so cm-quantization doesn't show through (e.g. 244cm shows as 8 ft,
 *  not 8.01): meters to the cm (2 dp), feet to 0.1 ft. */
export function displayFromCm(cm: number, unit: UnitPref): number {
  if (unit === 'imperial') {
    const feet = cm / CM_PER_INCH / INCHES_PER_FOOT
    return Math.round(feet * 10) / 10
  }
  return Math.round((cm / CM_PER_METER) * 100) / 100
}

/** Centimeters → a human string in the given unit (e.g. "1.22 m" or "4′ 0″"). */
export function formatCm(cm: number, unit: UnitPref): string {
  if (unit === 'imperial') {
    const totalInches = cm / CM_PER_INCH
    let feet = Math.floor(totalInches / INCHES_PER_FOOT)
    let inches = Math.round(totalInches - feet * INCHES_PER_FOOT)
    if (inches === INCHES_PER_FOOT) {
      feet += 1
      inches = 0
    }
    return `${feet}′ ${inches}″`
  }
  const meters = Math.round((cm / CM_PER_METER) * 100) / 100
  return `${meters} m`
}

/** Centimeters width × height → a human string in the given unit. */
export function formatDimensions(widthCm: number, heightCm: number, unit: UnitPref): string {
  return `${formatCm(widthCm, unit)} × ${formatCm(heightCm, unit)}`
}

/** The input-field label for a single dimension in the given unit. */
export function dimensionUnitLabel(unit: UnitPref): string {
  return unit === 'imperial' ? 'ft' : 'm'
}

// --- Plant spacing (small scale) -------------------------------------------
// Plant spacing is a handful of centimeters, so meters/feet read poorly here;
// metric shows cm and imperial shows whole inches.

/** Centimeters → a spacing string in the given unit (e.g. "15 cm" or "6″"). */
export function formatSpacing(cm: number, unit: UnitPref): string {
  if (unit === 'imperial') return `${Math.round(cm / CM_PER_INCH)}″`
  return `${Math.round(cm)} cm`
}

/** A spacing value typed in the given unit (cm, or inches) → centimeters,
 *  exactly (12 in → 30.48). */
export function cmFromSpacing(value: number, unit: UnitPref): number {
  return roundCm(unit === 'imperial' ? value * CM_PER_INCH : value)
}

/** Centimeters → a spacing number in the given unit, for prefilling an input.
 *  Inches to 0.1 so cm-quantization doesn't show through. */
export function spacingFromCm(cm: number, unit: UnitPref): number {
  return unit === 'imperial' ? Math.round((cm / CM_PER_INCH) * 10) / 10 : Math.round(cm)
}

/** The spacing input-field unit label. */
export function spacingUnitLabel(unit: UnitPref): string {
  return unit === 'imperial' ? 'in' : 'cm'
}