use std::collections::HashMap;
use std::env;
use std::fmt;
use std::fs::File;
use std::io::{self, Write};
use std::process::exit;

use crate::flags::{FlagParseError, Flags, ParseOutcome};
use crate::rustc;
use crate::util::*;

#[derive(Debug)]
pub(crate) enum OptionError {
    FlagError(FlagParseError),
    Generic(String),
}

impl fmt::Display for OptionError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Self::FlagError(e) => write!(f, "error parsing flags: {e}"),
            Self::Generic(s) => write!(f, "{s}"),
        }
    }
}

#[derive(Debug)]
pub(crate) struct Options {
    // Contains the path to the child executable
    pub(crate) executable: String,
    // Contains arguments for the child process fetched from files.
    pub(crate) child_arguments: Vec<String>,
    // Contains environment variables for the child process fetched from files.
    pub(crate) child_environment: HashMap<String, String>,
    // If set, create the specified file after the child process successfully
    // terminated its execution.
    pub(crate) touch_file: Option<String>,
    // If set to (source, dest) copies the source file to dest.
    pub(crate) copy_output: Option<(String, String)>,
    // If set, redirects the child process stdout to this file.
    pub(crate) stdout_file: Option<String>,
    // If set, redirects the child process stderr to this file.
    pub(crate) stderr_file: Option<String>,
    // If set, also logs all unprocessed output from the rustc output to this file.
    // Meant to be used to get json output out of rustc for tooling usage.
    pub(crate) output_file: Option<String>,
    // If set, it configures rustc to emit an rmeta file and then
    // quit.
    pub(crate) rustc_quit_on_rmeta: bool,
    // This controls the output format of rustc messages.
    pub(crate) rustc_output_format: Option<rustc::ErrorFormat>,
}

pub(crate) fn options() -> Result<Options, OptionError> {
    // Process argument list until -- is encountered.
    // Everything after is sent to the child process.
    let mut subst_mapping_raw = None;
    let mut stable_status_file_raw = None;
    let mut volatile_status_file_raw = None;
    let mut env_file_raw = None;
    let mut arg_file_raw = None;
    let mut touch_file = None;
    let mut copy_output_raw = None;
    let mut stdout_file = None;
    let mut stderr_file = None;
    let mut output_file = None;
    let mut rustc_quit_on_rmeta_raw = None;
    let mut rustc_output_format_raw = None;
    let mut flags = Flags::new();
    flags.define_repeated_flag("--subst", "", &mut subst_mapping_raw);
    flags.define_flag("--stable-status-file", "", &mut stable_status_file_raw);
    flags.define_flag("--volatile-status-file", "", &mut volatile_status_file_raw);
    flags.define_repeated_flag(
        "--env-file",
        "File(s) containing environment variables to pass to the child process.",
        &mut env_file_raw,
    );
    flags.define_repeated_flag(
        "--arg-file",
        "File(s) containing command line arguments to pass to the child process.",
        &mut arg_file_raw,
    );
    flags.define_flag(
        "--touch-file",
        "Create this file after the child process runs successfully.",
        &mut touch_file,
    );
    flags.define_repeated_flag("--copy-output", "", &mut copy_output_raw);
    flags.define_flag(
        "--stdout-file",
        "Redirect subprocess stdout in this file.",
        &mut stdout_file,
    );
    flags.define_flag(
        "--stderr-file",
        "Redirect subprocess stderr in this file.",
        &mut stderr_file,
    );
    flags.define_flag(
        "--output-file",
        "Log all unprocessed subprocess stderr in this file.",
        &mut output_file,
    );
    flags.define_flag(
        "--rustc-quit-on-rmeta",
        "If enabled, this wrapper will terminate rustc after rmeta has been emitted.",
        &mut rustc_quit_on_rmeta_raw,
    );
    flags.define_flag(
        "--rustc-output-format",
        "Controls the rustc output format if --rustc-quit-on-rmeta is set.\n\
        'json' will cause the json output to be output, \
        'rendered' will extract the rendered message and print that.\n\
        Default: `rendered`",
        &mut rustc_output_format_raw,
    );

    let mut child_args = match flags
        .parse(env::args().collect())
        .map_err(OptionError::FlagError)?
    {
        ParseOutcome::Help(help) => {
            eprintln!("{help}");
            exit(0);
        }
        ParseOutcome::Parsed(p) => p,
    };
    let current_dir = std::env::current_dir()
        .map_err(|e| OptionError::Generic(format!("failed to get current directory: {e}")))?
        .to_str()
        .ok_or_else(|| OptionError::Generic("current directory not utf-8".to_owned()))?
        .to_owned();
    let subst_mappings = subst_mapping_raw
        .unwrap_or_default()
        .into_iter()
        .map(|arg| {
            let (key, val) = arg.split_once('=').ok_or_else(|| {
                OptionError::Generic(format!("empty key for substitution '{arg}'"))
            })?;
            let v = if val == "${pwd}" {
                current_dir.as_str()
            } else {
                val
            }
            .to_owned();
            Ok((key.to_owned(), v))
        })
        .collect::<Result<Vec<(String, String)>, OptionError>>()?;
    let stable_stamp_mappings =
        stable_status_file_raw.map_or_else(Vec::new, |s| read_stamp_status_to_array(s).unwrap());
    let volatile_stamp_mappings =
        volatile_status_file_raw.map_or_else(Vec::new, |s| read_stamp_status_to_array(s).unwrap());
    let environment_file_block = env_from_files(env_file_raw.unwrap_or_default())?;
    let mut file_arguments = args_from_file(arg_file_raw.unwrap_or_default())?;
    // Process --copy-output
    let copy_output = copy_output_raw
        .map(|co| {
            if co.len() != 2 {
                return Err(OptionError::Generic(format!(
                    "\"--copy-output\" needs exactly 2 parameters, {} provided",
                    co.len()
                )));
            }
            let copy_source = &co[0];
            let copy_dest = &co[1];
            if copy_source == copy_dest {
                return Err(OptionError::Generic(format!(
                    "\"--copy-output\" source ({copy_source}) and dest ({copy_dest}) need to be different.",
                )));
            }
            Ok((copy_source.to_owned(), copy_dest.to_owned()))
        })
        .transpose()?;

    let rustc_quit_on_rmeta = rustc_quit_on_rmeta_raw.map_or(false, |s| s == "true");
    let rustc_output_format = rustc_output_format_raw
        .map(|v| match v.as_str() {
            "json" => Ok(rustc::ErrorFormat::Json),
            "rendered" => Ok(rustc::ErrorFormat::Rendered),
            _ => Err(OptionError::Generic(format!(
                "invalid --rustc-output-format '{v}'",
            ))),
        })
        .transpose()?;

    // Prepare the environment variables, unifying those read from files with the ones
    // of the current process.
    let vars = environment_block(
        environment_file_block,
        &stable_stamp_mappings,
        &volatile_stamp_mappings,
        &subst_mappings,
    );
    // Append all the arguments fetched from files to those provided via command line.
    child_args.append(&mut file_arguments);
    let child_args = prepare_args(child_args, &subst_mappings)?;
    // Split the executable path from the rest of the arguments.
    let (exec_path, args) = child_args.split_first().ok_or_else(|| {
        OptionError::Generic(
            "at least one argument after -- is required (the child process path)".to_owned(),
        )
    })?;

    Ok(Options {
        executable: exec_path.to_owned(),
        child_arguments: args.to_vec(),
        child_environment: vars,
        touch_file,
        copy_output,
        stdout_file,
        stderr_file,
        output_file,
        rustc_quit_on_rmeta,
        rustc_output_format,
    })
}

fn args_from_file(paths: Vec<String>) -> Result<Vec<String>, OptionError> {
    let mut args = vec![];
    for path in paths.iter() {
        let mut lines = read_file_to_array(path).map_err(|err| {
            OptionError::Generic(format!(
                "{} while processing args from file paths: {:?}",
                err, &paths
            ))
        })?;
        args.append(&mut lines);
    }
    Ok(args)
}

fn env_from_files(paths: Vec<String>) -> Result<HashMap<String, String>, OptionError> {
    let mut env_vars = HashMap::new();
    for path in paths.into_iter() {
        let lines = read_file_to_array(&path).map_err(OptionError::Generic)?;
        for line in lines.into_iter() {
            let (k, v) = line
                .split_once('=')
                .ok_or_else(|| OptionError::Generic("environment file invalid".to_owned()))?;
            env_vars.insert(k.to_owned(), v.to_owned());
        }
    }
    Ok(env_vars)
}

fn prepare_arg(mut arg: String, subst_mappings: &[(String, String)]) -> String {
    for (f, replace_with) in subst_mappings {
        let from = format!("${{{f}}}");
        arg = arg.replace(&from, replace_with);
    }
    arg
}

/// Apply substitutions to the given param file. Returns the new filename.
fn prepare_param_file(
    filename: &str,
    subst_mappings: &[(String, String)],
) -> Result<String, OptionError> {
    let expanded_file = format!("{filename}.expanded");
    let format_err = |err: io::Error| {
        OptionError::Generic(format!(
            "{} writing path: {:?}, current directory: {:?}",
            err,
            expanded_file,
            std::env::current_dir()
        ))
    };
    let mut out = io::BufWriter::new(File::create(&expanded_file).map_err(format_err)?);
    fn process_file(
        filename: &str,
        out: &mut io::BufWriter<File>,
        subst_mappings: &[(String, String)],
        format_err: &impl Fn(io::Error) -> OptionError,
    ) -> Result<(), OptionError> {
        for arg in read_file_to_array(filename).map_err(OptionError::Generic)? {
            let arg = prepare_arg(arg, subst_mappings);
            if let Some(arg_file) = arg.strip_prefix('@') {
                process_file(arg_file, out, subst_mappings, format_err)?;
            } else {
                writeln!(out, "{arg}").map_err(format_err)?;
            }
        }
        Ok(())
    }
    process_file(filename, &mut out, subst_mappings, &format_err)?;
    Ok(expanded_file)
}

/// Apply substitutions to the provided arguments, recursing into param files.
fn prepare_args(
    args: Vec<String>,
    subst_mappings: &[(String, String)],
) -> Result<Vec<String>, OptionError> {
    args.into_iter()
        .map(|arg| {
            let arg = prepare_arg(arg, subst_mappings);
            if let Some(param_file) = arg.strip_prefix('@') {
                // Note that substitutions may also apply to the param file path!
                prepare_param_file(param_file, subst_mappings)
                    .map(|filename| format!("@{filename}"))
            } else {
                Ok(arg)
            }
        })
        .collect()
}

fn environment_block(
    environment_file_block: HashMap<String, String>,
    stable_stamp_mappings: &[(String, String)],
    volatile_stamp_mappings: &[(String, String)],
    subst_mappings: &[(String, String)],
) -> HashMap<String, String> {
    // Taking all environment variables from the current process
    // and sending them down to the child process
    let mut environment_variables: HashMap<String, String> = std::env::vars().collect();
    // Have the last values added take precedence over the first.
    // This is simpler than needing to track duplicates and explicitly override
    // them.
    environment_variables.extend(environment_file_block);
    for (f, replace_with) in &[stable_stamp_mappings, volatile_stamp_mappings].concat() {
        for value in environment_variables.values_mut() {
            let from = format!("{{{f}}}");
            let new = value.replace(from.as_str(), replace_with);
            *value = new;
        }
    }
    for (f, replace_with) in subst_mappings {
        for value in environment_variables.values_mut() {
            let from = format!("${{{f}}}");
            let new = value.replace(from.as_str(), replace_with);
            *value = new;
        }
    }
    environment_variables
}