import { parseICSDate } from "@/lib/agenda/agenda-date"
import type { AgendaApiEvent } from "@/lib/agenda/agenda-types"

function unfoldIcsLines(raw: string): string[] {
  const physical = raw.replace(/\r\n/g, "\n").replace(/\r/g, "\n").split("\n")
  const lines: string[] = []
  for (const line of physical) {
    if ((line.startsWith(" ") || line.startsWith("\t")) && lines.length > 0) {
      lines[lines.length - 1] += line.slice(1)
    } else {
      lines.push(line)
    }
  }
  return lines
}

function parseIcsProperty(line: string): { name: string; value: string } | null {
  const idx = line.indexOf(":")
  if (idx <= 0) return null
  const rawName = line.slice(0, idx)
  const value = line.slice(idx + 1).trim()
  const name = rawName.split(";")[0]?.toUpperCase() ?? ""
  if (!name) return null
  return { name, value }
}

function isAllDayProperty(rawName: string, value: string): boolean {
  if (/VALUE=DATE/i.test(rawName)) return true
  return /^\d{8}$/.test(value)
}

function extractVEventBlocks(lines: string[]): string[][] {
  const blocks: string[][] = []
  let current: string[] | null = null
  for (const line of lines) {
    const upper = line.trim().toUpperCase()
    if (upper === "BEGIN:VEVENT") {
      current = []
      continue
    }
    if (upper === "END:VEVENT") {
      if (current) blocks.push(current)
      current = null
      continue
    }
    if (current) current.push(line)
  }
  return blocks
}

function parseVEventBlock(lines: string[], index: number): AgendaApiEvent | null {
  let uid = ""
  let summary = ""
  let description = ""
  let location = ""
  let start = ""
  let end = ""
  let allDay = false

  for (const line of lines) {
    const idx = line.indexOf(":")
    if (idx <= 0) continue
    const rawName = line.slice(0, idx)
    const value = line.slice(idx + 1).trim()
    const prop = parseIcsProperty(line)
    if (!prop) continue

    switch (prop.name) {
      case "UID":
        uid = value
        break
      case "SUMMARY":
        summary = value
        break
      case "DESCRIPTION":
        description = value.replace(/\\n/g, "\n").replace(/\\,/g, ",")
        break
      case "LOCATION":
        location = value.replace(/\\,/g, ",")
        break
      case "DTSTART":
        start = value
        allDay = isAllDayProperty(rawName, value)
        break
      case "DTEND":
        end = value
        break
      default:
        break
    }
  }

  if (!start) return null
  if (!uid) uid = `ext-${index}-${start}`

  return {
    uid,
    summary: summary || "(Sans titre)",
    description,
    location,
    start,
    end: end || start,
    all_day: allDay,
    path: uid,
  }
}

/** Parse un flux ICS en événements API agenda. */
export function parseIcsFeed(raw: string): AgendaApiEvent[] {
  const lines = unfoldIcsLines(raw)
  const blocks = extractVEventBlocks(lines)
  const events: AgendaApiEvent[] = []

  blocks.forEach((block, index) => {
    const event = parseVEventBlock(block, index)
    if (!event) return
    if (!parseICSDate(event.start)) return
    events.push(event)
  })

  return events
}