import { combine, err, ok, Result } from 'neverthrow'
import { SemVerT } from './_types'

const separator = '.'

const create = (
  input: Readonly<{ major: number; minor: number; patch: number }>,
): SemVerT => {
  const { major, minor, patch } = input
  const toString = (): string =>
    [major, minor, patch]
      .map((n: number): string => n.toString())
      .join(separator)

  const equals = (other: SemVerT): boolean =>
    other.major === major && other.minor === minor && other.patch === patch

  return {
    major,
    minor,
    patch,
    equals,
    toString,
  }
}

const fromBuffer = (buf: Buffer): Result<SemVerT, Error> => {
  const expectedByteCount = 3
  if (buf.length !== expectedByteCount) {
    return err(
      new Error(
        `Incorrect length of buffer, expected #${expectedByteCount} bytes, but got: #${buf.length}`,
      ),
    )
  }

  const major = buf.readUInt8(0)
  const minor = buf.readUInt8(1)
  const patch = buf.readUInt8(2)

  return ok(create({ major, minor, patch }))
}

const fromString = (versionString: string): Result<SemVerT, Error> => {
  const components = versionString.split(separator)
  const expectedComponentCount = 3
  if (components.length !== expectedComponentCount) {
    return err(
      new Error(
        `Expected semantic version to contain ${expectedComponentCount} components.`,
      ),
    )
  }
  const numAtIndex = (index: number): Result<number, Error> => {
    let parsedInt = undefined
    try {
      parsedInt = parseInt(components[index], 10)
    } catch (e) {
      return err(new Error('Failed to parse integer'))
    }
    if (!Number.isInteger(parsedInt)) {
      return err(new Error('Found no integer'))
    }
    return ok(parsedInt)
  }

  return combine([numAtIndex(0), numAtIndex(1), numAtIndex(2)]).map(
    resultList => {
      const major = resultList[0]
      const minor = resultList[1]
      const patch = resultList[2]
      return create({
        major,
        minor,
        patch,
      })
    },
  )
}

export const SemVer = {
  fromBuffer,
  fromString,
  create,
}