use std::ffi::OsString;

use crate::{Defaults, MagicSignature, SearchMode};

///

pub mod from_environment {

    /// The error returned by [Defaults::from_environment()](super::Defaults::from_environment()).

    #[derive(Debug, thiserror::Error)]

    #[allow(missing_docs)]

    pub enum Error {

        #[error(transparent)]

        ParseValue(#[from] gix_config_value::Error),

        #[error("Glob and no-glob settings are mutually exclusive")]

        MixedGlobAndNoGlob,

    }

}

impl Defaults {

    /// Initialize this instance using information from the environment as

    /// [per the official documentation](https://git-scm.com/book/en/v2/Git-Internals-Environment-Variables) *(look for `PATHSPECS`)*,

    /// calling `var(variable_name)` for each variable that should be obtained.

    ///

    /// Used environment variables are `GIT_GLOB_PATHSPECS`, `GIT_NOGLOB_PATHSPECS`, `GIT_LITERAL_PATHSPECS` and `GIT_ICASE_PATHSPECS`.

    /// Note that there are lot of failure modes, and instead of offering lenient parsing, the caller may ignore errors and

    /// use other defaults instead.

    ///

    /// ### Deviation

    ///

    /// Instead of failing if `GIT_LITERAL_PATHSPECS` is used with glob globals, we ignore these. Also our implementation allows global

    /// `icase` settings in combination with this setting.

    pub fn from_environment(var: &mut dyn FnMut(&str) -> Option<OsString>) -> Result<Self, from_environment::Error> {

        let mut env_bool = |name: &str| -> Result<Option<bool>, gix_config_value::Error> {

            var(name)

                .map(|val| gix_config_value::Boolean::try_from(val).map(|b| b.0))

                .transpose()

        };

        let literal = env_bool("GIT_LITERAL_PATHSPECS")?.unwrap_or_default();

        let signature = env_bool("GIT_ICASE_PATHSPECS")?

            .and_then(|val| val.then_some(MagicSignature::ICASE))

            .unwrap_or_default();

        if literal {

            return Ok(Defaults {

                signature,

                search_mode: SearchMode::Literal,

                literal,

            });

        }

        let glob = env_bool("GIT_GLOB_PATHSPECS")?;

        let mut search_mode = glob

            .and_then(|glob| glob.then_some(SearchMode::PathAwareGlob))

            .unwrap_or_default();

        search_mode = env_bool("GIT_NOGLOB_PATHSPECS")?

            .map(|no_glob| {

                if glob.unwrap_or_default() && no_glob {

                    Err(from_environment::Error::MixedGlobAndNoGlob)

                } else {

                    Ok(SearchMode::Literal)

                }

            })

            .transpose()?

            .unwrap_or(search_mode);

        Ok(Defaults {

            signature,

            search_mode,

            literal,

        })

    }

}