// Public URL grammar: space-delimited tokens and indexed scalar fields, never JSON.
export type QueryRecord = Record<string, string | number | boolean | null | undefined>
const schemas: Record<string, string[]> = {
    conditions: ['field', 'operator', 'value', 'end', 'blank', 'input', 'values'],
    condition_values: ['condition', 'value', 'value_type'],
    drill: ['field', 'grain', 'value', 'value_type'],
    tag_refs: ['name', 'tag_id', 'external_tag_id', 'negative', 'missing'],
    column_order: ['value', 'value_type'],
    measures: ['key', 'axis', 'value', 'value_type'] }


export const queryList = (value: string | null): string[] =>
    value == null || value === '' ? [] : value.split (' ')


export const queryRecords = (params: URLSearchParams, key: string): QueryRecord[] => {
  const indexed = new Map<number, QueryRecord> ()
  for (const [name, value] of params)
  {
    if (!name.startsWith (`${key}.`)) continue
    const parts = name.slice (key.length + 1).split ('.')
    if (parts.length !== 2 || !/^\d{1,2}$/.test (parts[0])
        || !schemas[key]?.includes (parts[1])) continue
    const index = Number (parts[0])
    const record = indexed.get (index) ?? { }
    const field = parts[1]
    record[field] = ['blank', 'negative', 'missing', 'values'].includes (field)
        ? value === '1' : (['tag_id', 'external_tag_id', 'axis', 'condition'].includes (field)
            ? Number (value) : value)
    indexed.set (index, record)
  }
  return [...indexed].sort ((a, b) => a[0] - b[0]).map (([, record]) => {
    if (record.value_type === 'null') record.value = null
    if (record.value_type === 'number') record.value = Number (record.value)
    if (record.value_type === 'boolean') record.value = record.value === 'true'
    delete record.value_type
    return record
  })
}


export const setQueryRecords = (
    params: URLSearchParams,
    key: string,
    records: QueryRecord[],
): void => {
  for (const name of [...params.keys ()])
    if (name === key || name.startsWith (`${key}.`)) params.delete (name)
  params.set (key, '')
  records.forEach ((record, index) => {
    for (const [field, value] of Object.entries (record))
    {
      if (value == null && field !== 'value') continue
      if (!schemas[key]?.includes (field)) continue
      const name = `${key}.${index}.${field}`
      if (field === 'value'
	  && ['drill', 'measures', 'column_order', 'condition_values'].includes (key))
        params.set (`${key}.${index}.value_type`, value == null ? 'null' : typeof value)
      if (value == null) continue
      params.set (name, typeof value === 'boolean'
          ? (['blank', 'negative', 'missing', 'values'].includes (field)
	      ? (value ? '1' : '0') : String (value))
          : String (value))
    }
  })
}


export const readCountState = <T,> (
    params: URLSearchParams,
    key: string,
    fallback: T,
): T => {
  if (!params.has (key)) return fallback
  if (key === 'rows' || key === 'cols')
    return queryList (params.get (key)).map (token => {
      const [field, grain] = token.split (':')
      return grain == null ? { field } : { field, grain }
    }) as T
  const records = queryRecords (params, key)
  if (key === 'conditions')
  {
    const values = queryRecords (params, 'condition_values')
    return records.map ((record, index) => record.values === true
	? { ...record, values: values.filter (entry => entry.condition === index)
	    .map (entry => entry.value) } : record) as T
  }
  return records as T
}


export const encodeCountState = (key: string, records: Record<string, unknown>[]): string => {
  if (key === 'rows' || key === 'cols')
    return records.map (record => record.grain == null
        ? String (record.field) : `${record.field}:${record.grain}`).join (' ')
  const params = new URLSearchParams ()
  const values: QueryRecord[] = []
  const flat = records.map ((record, condition) => {
    if (key !== 'conditions' || !Array.isArray (record.values)) return record as QueryRecord
    const { values: selected, ...fields } = record
    for (const value of selected as unknown[])
      values.push ({ condition, value: value as string | number | boolean })
    return { ...fields, values: true } as QueryRecord
  })
  setQueryRecords (params, key, flat)
  if (key === 'conditions' && flat.some (record => record.values === true))
    setQueryRecords (params, 'condition_values', values)
  return params.toString ()
}


export const setCountState = (params: URLSearchParams, key: string, value: string): void => {
  if (schemas[key] != null)
  {
    const fields = new URLSearchParams (value)
    setQueryRecords (params, key, queryRecords (fields, key))
    if (key === 'conditions')
    {
      for (const name of [...params.keys ()])
        if (name === 'condition_values' || name.startsWith ('condition_values.'))
	  params.delete (name)
      if (fields.has ('condition_values'))
        setQueryRecords (params, 'condition_values', queryRecords (fields, 'condition_values'))
    }
  }
  else params.set (key, value)
}


export const queryRecordParams = (
    params: URLSearchParams,
    key: string,
): Record<string, string> => Object.fromEntries ([...params].filter (([name]) =>
    name === key || name.startsWith (`${key}.`)))