// What the import form reads out of a file in the browser: a small CSV reader (RFC 4180: quoted fields,
// doubled quotes, LF or CRLF) and the rows as the service takes them. No component here, so a test reads
// it directly; the service still validates every row and reports the ones it refuses.

import { IMPORT_CHUNK_ROWS, type ImportRow } from "../contract/index.js"

const REQUIRED = ["code", "name", "base_unit"] as const

/** The records of a CSV text, each a list of fields. Blank lines are records of one empty field. */
export function csvRows(text: string): string[][] {
  const records: string[][] = []
  let record: string[] = []
  let field = ""
  let quoted = false
  for (let at = 0; at < text.length; at += 1) {
    const char = text[at]
    if (quoted) {
      if (char !== '"') field += char
      else if (text[at + 1] === '"') {
        field += '"'
        at += 1
      } else quoted = false
    } else if (char === '"') quoted = true
    else if (char === ",") {
      record.push(field)
      field = ""
    } else if (char === "\n" || char === "\r") {
      if (char === "\r" && text[at + 1] === "\n") at += 1
      record.push(field)
      records.push(record)
      record = []
      field = ""
    } else field += char
  }
  if (field !== "" || record.length > 0) {
    record.push(field)
    records.push(record)
  }
  return records
}

export type ParsedProducts = { kind: "rows"; rows: ImportRow[] } | { kind: "unreadable"; missing: string[] }

/** The product rows of a CSV file, by header name, or the required columns its header lacks. */
export function parseProductCsv(text: string): ParsedProducts {
  const records = csvRows(text.replace(/^/, ""))
  const header = (records[0] ?? []).map((name) => name.trim().toLowerCase())
  const missing = REQUIRED.filter((name) => !header.includes(name))
  if (missing.length > 0) return { kind: "unreadable", missing }
  const column = (record: readonly string[], name: string): string => {
    const at = header.indexOf(name)
    return at < 0 ? "" : (record[at] ?? "").trim()
  }
  const rows: ImportRow[] = []
  records.slice(1).forEach((record, at) => {
    if (record.every((value) => value.trim() === "")) return
    const description = column(record, "description")
    const revision = column(record, "revision")
    rows.push({
      // The line a person sees in the file: the header is line 1.
      sourceRow: at + 2,
      ...(revision === "" ? {} : { revision }),
      product: {
        code: column(record, "code"),
        name: column(record, "name"),
        baseUnit: column(record, "base_unit"),
        ...(description === "" ? {} : { description }),
      },
    })
  })
  return { kind: "rows", rows }
}

/** Rows in chunks of the size one request may carry. */
export function chunksOf<T>(rows: readonly T[]): T[][] {
  const chunks: T[][] = []
  for (let at = 0; at < rows.length; at += IMPORT_CHUNK_ROWS) chunks.push(rows.slice(at, at + IMPORT_CHUNK_ROWS))
  return chunks
}