// 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)
}

/** 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
}

// --- Dimension entry -------------------------------------------------------
// Imperial dimensions are typed the way people say them — 2' 7", not 2.6 — while
// a bare number still means feet so nothing anyone typed before this existed
// breaks. Metric entry is decimal meters, unchanged.

// Feet, then optionally inches. The inch mark is optional once feet are explicit,
// because "2' 7" is a natural thing to type and unambiguous.
const FT_IN_RE = /^(\d*\.?\d+)\s*(?:'|ft|feet|foot)(?:\s*(\d*\.?\d+)\s*(?:"|in|inch|inches)?)?$/
// Inches alone, where the mark is required — a bare number means feet.
const IN_ONLY_RE = /^(\d*\.?\d+)\s*(?:"|in|inch|inches)$/
// A bare decimal, which means feet (imperial) or meters (metric).
const BARE_RE = /^(\d*\.?\d+)$/
const METERS_RE = /^(\d*\.?\d+)\s*m?$/

/** Normalize the characters people actually paste: typographic quotes and the
 *  various unicode dashes, so text copied from anywhere parses like text typed
 *  here. Lowercased so "FT"/"In" work too. */
function normalizeEntry(s: string): string {
  return s
    .trim()
    .replace(/[′’‵]/g, "'")
    .replace(/[″”‶]/g, '"')
    .replace(/[−–—]/g, '-')
    .toLowerCase()
}

/** Split a leading sign off a normalized entry. The sign belongs to the WHOLE
 *  value, not just its first term: -2' 6" is −(2ft + 6in) = −30in, not −2ft + 6in. */
function splitSign(s: string): { sign: number; rest: string } {
  if (s.startsWith('-')) return { sign: -1, rest: s.slice(1).trim() }
  if (s.startsWith('+')) return { sign: 1, rest: s.slice(1).trim() }
  return { sign: 1, rest: s }
}

/**
 * Parse a typed dimension into centimeters, or null if it isn't a dimension.
 *
 * Imperial accepts `2' 7"`, `2′ 7″`, `2ft 7in`, `2' 7`, `31"`, `2'`, and a bare
 * `2.5` still meaning 2½ feet. Metric accepts decimal meters with an optional
 * `m`. Null means "don't commit anything" — never a silent zero, which would
 * turn a typo into a destructive edit.
 */
export function parseDimension(input: string, unit: UnitPref): number | null {
  const { sign, rest } = splitSign(normalizeEntry(input))
  if (rest === '') return null

  if (unit !== 'imperial') {
    const m = rest.match(METERS_RE)
    return m ? sign * cmFromMeters(parseFloat(m[1])) : null
  }

  const bare = rest.match(BARE_RE)
  if (bare) return sign * cmFromFtIn(parseFloat(bare[1]))

  const ftIn = rest.match(FT_IN_RE)
  if (ftIn) return sign * cmFromFtIn(parseFloat(ftIn[1]), ftIn[2] ? parseFloat(ftIn[2]) : 0)

  const inOnly = rest.match(IN_ONLY_RE)
  if (inOnly) return sign * cmFromFtIn(0, parseFloat(inOnly[1]))

  return null
}

/**
 * Centimeters → the string a dimension input shows, and the exact string
 * parseDimension round-trips. Imperial reads `2′ 7″`; inches carry one decimal
 * (`7′ 10.5″`) because 0.1″ is ~0.25 cm, so what's displayed stays honest about
 * what's stored rather than rounding a dragged position to the nearest inch.
 */
export function formatDimensionInput(cm: number, unit: UnitPref): string {
  if (unit !== 'imperial') return String(displayFromCm(cm, unit))
  const { feet, inches } = feetAndInches(cm, 1)
  // Only sign a value that actually rounded to something: a hair below zero is
  // 0′ 0″, and "-0′ 0″" would be both wrong and un-round-trippable.
  const sign = cm < 0 && (feet || inches) ? '-' : ''
  return `${sign}${feet}′ ${inches}″`
}

/**
 * The inputMode a dimension field should ask for. Imperial entry needs ' and ",
 * which no numeric keypad offers, so those fields get the full keyboard; metric
 * is pure decimals and keeps the keypad. A bare number still means feet, so the
 * keypad path stays usable either way.
 */
export function dimensionInputMode(unit: UnitPref): 'text' | 'decimal' {
  return unit === 'imperial' ? 'text' : 'decimal'
}

/**
 * Decompose centimeters into feet and inches, rounding inches to `decimals` and
 * carrying 12″ up to the next foot. Magnitude only — the sign is the caller's to
 * apply, and only once it knows the rounded result isn't zero.
 */
function feetAndInches(cm: number, decimals: number): { feet: number; inches: number } {
  const scale = 10 ** decimals
  const totalInches = Math.abs(cm) / CM_PER_INCH
  let feet = Math.floor(totalInches / INCHES_PER_FOOT)
  let inches = Math.round((totalInches - feet * INCHES_PER_FOOT) * scale) / scale
  if (inches >= INCHES_PER_FOOT) {
    feet += 1
    inches = 0
  }
  return { feet, inches }
}

/** 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 { feet, inches } = feetAndInches(cm, 0)
    return `${cm < 0 && (feet || inches) ? '-' : ''}${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'
}