/**
 * CSV utilities — RFC 4180 compliant, no external dependencies.
 */

/** Escape a field value for CSV (wrap in quotes if needed) */
function escapeField(value: string): string {
  if (
    value.includes(",") ||
    value.includes('"') ||
    value.includes("\n") ||
    value.includes("\r")
  ) {
    return `"${value.replace(/"/g, '""')}"`
  }
  return value
}

/** Convert an array of objects to a CSV string */
export function objectsToCsv(
  headers: string[],
  rows: Record<string, string>[]
): string {
  const lines: string[] = []

  // Header row
  lines.push(headers.map(escapeField).join(","))

  // Data rows
  for (const row of rows) {
    const fields = headers.map((h) => escapeField(row[h] ?? ""))
    lines.push(fields.join(","))
  }

  return lines.join("\n")
}

/**
 * Parse a CSV string into an array of objects keyed by header names.
 * Uses a state-machine parser to correctly handle quoted fields.
 */
export function csvToObjects(csvText: string): Record<string, string>[] {
  const rows = parseCsvRows(csvText)
  if (rows.length < 1) return []

  const headers = rows[0]
  const result: Record<string, string>[] = []

  for (let i = 1; i < rows.length; i++) {
    const row = rows[i]
    // Skip empty rows
    if (row.length === 1 && row[0] === "") continue

    const obj: Record<string, string> = {}
    for (let j = 0; j < headers.length; j++) {
      obj[headers[j]] = row[j] ?? ""
    }
    result.push(obj)
  }

  return result
}

/** State-machine CSV parser that handles quoted fields correctly */
function parseCsvRows(text: string): string[][] {
  const rows: string[][] = []
  let currentRow: string[] = []
  let currentField = ""
  let inQuotes = false

  for (let i = 0; i < text.length; i++) {
    const char = text[i]
    const nextChar = text[i + 1]

    if (inQuotes) {
      if (char === '"') {
        if (nextChar === '"') {
          // Escaped quote
          currentField += '"'
          i++ // skip next quote
        } else {
          // End of quoted field
          inQuotes = false
        }
      } else {
        currentField += char
      }
    } else {
      if (char === '"' && currentField === "") {
        // Start of quoted field
        inQuotes = true
      } else if (char === ",") {
        currentRow.push(currentField)
        currentField = ""
      } else if (char === "\n") {
        currentRow.push(currentField)
        currentField = ""
        rows.push(currentRow)
        currentRow = []
      } else if (char === "\r") {
        // Skip carriage return (handle \r\n)
        if (nextChar === "\n") {
          i++ // skip \n
        }
        currentRow.push(currentField)
        currentField = ""
        rows.push(currentRow)
        currentRow = []
      } else {
        currentField += char
      }
    }
  }

  // Handle last field/row
  if (currentField !== "" || currentRow.length > 0) {
    currentRow.push(currentField)
    rows.push(currentRow)
  }

  return rows
}