use crate::env_file::{ApplyEnvironmentFile, ApplyOptions};
use crate::EnvironmentFile;
use std::fmt::Display;
use std::fs::File;
use std::io::Read;
use std::path::Path;

#[derive(Debug, thiserror::Error)]
#[allow(clippy::enum_variant_names)]
pub enum EnvFsError {
	/// Error opening the file, or reading it into a buffer.
	#[error(transparent)]
	IoError(#[from] std::io::Error),
	/// Error parsing the file from a string into an EnvironmentFile. Denotes syntax errors in the
	/// file.
	#[error(transparent)]
	ParseError(#[from] crate::EnvironmentFileError),
	/// An error thrown specifically when the given environment variable exists, but is cannot be
	/// represented in Rust (e.g. not Unicode). This error does **not** occur when the environment
	/// variable exists as valid Unicode.
	#[error("The target environment variable exists, but is not Unicode")]
	EnvironmentError,
}

/// Reads the file `.env` into memory, but does not apply it to the environment.
pub fn env_file() -> Result<EnvironmentFile, EnvFsError> {
	env_file_from_path(".env")
}

/// Reads the file `.env.<environment>` into memory, but does not apply it to the environment.
///
/// ### Example
///
/// Calling `env_file_suffix("production")` will attempt to read the file `.env.production` in the
/// directory the server was launched from.
pub fn env_file_suffix(environment: impl Display) -> Result<EnvironmentFile, EnvFsError> {
	env_file_from_path(format!(".env.{}", environment))
}

/// Reads the file at the specified path into memory, but does not apply it to the environment.
pub fn env_file_from_path(path: impl AsRef<Path>) -> Result<EnvironmentFile, EnvFsError> {
	let mut file = File::open(path)?;
	let mut buffer = String::new();
	file.read_to_string(&mut buffer)?;
	Ok(buffer.parse()?)
}

/// Look up a `.env` file in the working directory and apply its contents to the current environment.
///
/// ### Errors
///
/// This method returns an error under the following circumstances:
///
/// - The target file does not exist
/// - There was an error when reading the target file
/// - The target was not a correctly formatted `.env` file
///
/// ### Example
///
/// This example will attempt to read the file `.env` in the directory the server was launched from.
/// ```rust
/// use envish::dotenv;
/// let _ = dotenv();
/// ```
pub fn dotenv() -> Result<(), EnvFsError> {
	env_file()?.apply(Default::default());
	Ok(())
}

/// Look up a `.env` file in the working directory and apply its contents to the current environment,
/// with the provided options, allowing for prefixing and overwriting existing values.
///
/// ### Errors
///
/// This method returns an error under the following circumstances:
///
/// - The target file does not exist
/// - There was an error when reading the target file
/// - The target was not a correctly formatted `.env` file
///
/// ### Example
///
/// This example will attempt to read the file `.env`, and will prepend the given prefix to all the
/// contained variables. For example, a variable in the file named "DATABASE_URL" will be added to
/// the environment as "APP_DATABASE_URL".
///
/// ```rust
/// use envish::{dotenv_opts, ApplyOptions};
/// let _ = dotenv_opts(ApplyOptions::with_prefix("APP_"));
/// ```
pub fn dotenv_opts(options: ApplyOptions) -> Result<(), EnvFsError> {
	env_file()?.apply(options);
	Ok(())
}

/// Look up a `.env` file with the provided suffix in the working directory and apply its contents
/// to the current environment.
///
/// ### Errors
///
/// This method returns an error under the following circumstances:
///
/// - The target file does not exist
/// - There was an error when reading the target file
/// - The target was not a correctly formatted `.env` file
///
/// ### Example
///
/// This example will attempt to read the file `.env.development`
///
/// ```rust
/// use envish::dotenv_suffix;
/// let _ = dotenv_suffix("development");
/// ```
pub fn dotenv_suffix(environment: impl Display) -> Result<(), EnvFsError> {
	env_file_suffix(environment)?.apply(Default::default());
	Ok(())
}

/// Look up an environment file at the given path and apply its contents to the current environment.
///
/// ### Errors
///
/// This method returns an error under the following circumstances:
///
/// - The target file does not exist
/// - There was an error when reading the target file
/// - The target was not a correctly formatted `.env` file
///
/// ### Example
///
/// This example will attempt to read the file `my_dotenv_file` at the specified path. The file must
/// be correctly formatted as any other .env file, but does not need to have a specific name.
///
/// ```rust
/// use envish::dotenv_from;
/// let _ = dotenv_from("/some/other/path/to/my_dotenv_file");
/// ```
pub fn dotenv_from(path: impl AsRef<Path>) -> Result<(), EnvFsError> {
	env_file_from_path(path)?.apply(Default::default());
	Ok(())
}