import { MM_TO_PX, type PageFormatId } from "@/lib/drive/page-formats"
import { DOCS_RULER_INCH_PX } from "@/lib/drive/docs-ruler-scale"

export type DocsRulerUnit = "cm" | "inch"

/** One centimetre in page coordinate space. */
export const DOCS_RULER_CM_PX = MM_TO_PX * 10

const INCH_FORMAT_IDS = new Set<PageFormatId>(["letter", "legal", "tabloid"])
const CM_FORMAT_IDS = new Set<PageFormatId>(["a4", "a5"])

export function resolveRulerUnit(formatId: PageFormatId): DocsRulerUnit {
  if (INCH_FORMAT_IDS.has(formatId)) return "inch"
  if (CM_FORMAT_IDS.has(formatId)) return "cm"
  return "cm"
}

export type DocsRulerUnitConfig = {
  unit: DocsRulerUnit
  majorStepPx: number
  minorDivisions: number
}

export function getRulerUnitConfig(formatId: PageFormatId): DocsRulerUnitConfig {
  const unit = resolveRulerUnit(formatId)
  if (unit === "inch") {
    return {
      unit,
      majorStepPx: DOCS_RULER_INCH_PX,
      minorDivisions: 8,
    }
  }
  return {
    unit,
    majorStepPx: DOCS_RULER_CM_PX,
    minorDivisions: 10,
  }
}

export function formatRulerMajorLabel(value: number, unit: DocsRulerUnit): string {
  if (value === 0) return "0"
  const abs = Math.abs(value)
  if (unit === "cm") {
    return Number.isInteger(abs) ? String(value) : value.toFixed(1).replace(".", ",")
  }
  return Number.isInteger(abs) ? String(value) : String(Math.round(value * 10) / 10)
}

/** Margin distance from page edge, in the ruler unit for the page format. */
export function formatMarginDistanceLabel(
  marginPx: number,
  formatId: PageFormatId
): string {
  const { unit, majorStepPx } = getRulerUnitConfig(formatId)
  const value = marginPx / majorStepPx
  const formatted = formatRulerMajorLabel(value, unit)
  return unit === "inch" ? `${formatted}"` : `${formatted} cm`
}