/**
 * Pixel ↔ time conversions for the timetable canvas.
 *
 * The grid is anchored on a CarbonImmutable `gridStart` (typically
 * the sub-event's start_at, possibly extended to the previous hour
 * boundary). All other coordinates are derived from minutes-since-
 * `gridStart` × `pxPerMin`.
 *
 * Pure functions — no DOM access. Input is ISO-8601 strings or epoch ms;
 * the grid origin is captured once per render in the page entry.
 */

export interface TimeGridConfig {

  /** Minute 0 of the canvas, as ISO-8601 (the sub-event start anchor). */
  gridStartIso: string

  /** Total minutes spanned by the canvas (e.g. 13h × 60 = 780). */
  totalMinutes: number

  /** Horizontal pixels per minute (drives stretch/zoom). */
  pxPerMin: number
}

export function isoToMinutes(iso: string, gridStartIso: string): number {
  const start = Date.parse(gridStartIso)
  const at = Date.parse(iso)

  return Math.round((at - start) / 60_000)
}

export function minutesToIso(minutes: number, gridStartIso: string): string {
  const start = Date.parse(gridStartIso)

  return new Date(start + minutes * 60_000).toISOString()
}

export function minutesToPx(minutes: number, pxPerMin: number): number {
  return minutes * pxPerMin
}

export function pxToMinutes(px: number, pxPerMin: number): number {
  if (pxPerMin <= 0)
    return 0

  return px / pxPerMin
}

/**
 * The wall-clock label for a tick at `minute`. RFC v0.2 §D21 defaults
 * to a 24h HH:MM format in nl-NL locale; days-spanning canvases
 * preserve the wrap (00:00 + minutes since previous midnight).
 */
export function formatTickLabel(minute: number, gridStartIso: string): string {
  const iso = minutesToIso(minute, gridStartIso)
  const date = new Date(iso)

  return date.toLocaleTimeString('nl-NL', { hour: '2-digit', minute: '2-digit', hour12: false })
}

/**
 * Generate evenly-spaced tick positions in [0, totalMinutes] at `intervalMin`.
 */
export function generateTicks(totalMinutes: number, intervalMin: number): number[] {
  const ticks: number[] = []
  for (let m = 0; m <= totalMinutes; m += intervalMin)
    ticks.push(m)

  return ticks
}