use std::borrow::Cow;
use std::env;
use std::error::Report;
use std::sync::Arc;

pub use rustc_error_messages::{FluentArgs, LazyFallbackBundle};
use tracing::{debug, trace};

use crate::error::{TranslateError, TranslateErrorKind};
use crate::snippet::Style;
use crate::{DiagArg, DiagMessage, FluentBundle};

/// Convert diagnostic arguments (a rustc internal type that exists to implement
/// `Encodable`/`Decodable`) into `FluentArgs` which is necessary to perform translation.
///
/// Typically performed once for each diagnostic at the start of `emit_diagnostic` and then
/// passed around as a reference thereafter.
pub fn to_fluent_args<'iter>(iter: impl Iterator<Item = DiagArg<'iter>>) -> FluentArgs<'static> {
    let mut args = if let Some(size) = iter.size_hint().1 {
        FluentArgs::with_capacity(size)
    } else {
        FluentArgs::new()
    };

    for (k, v) in iter {
        args.set(k.clone(), v.clone());
    }

    args
}

#[derive(Clone)]
pub struct Translator {
    /// Localized diagnostics for the locale requested by the user. If no language was requested by
    /// the user then this will be `None` and `fallback_fluent_bundle` should be used.
    pub fluent_bundle: Option<Arc<FluentBundle>>,
    /// Return `FluentBundle` with localized diagnostics for the default locale of the compiler.
    /// Used when the user has not requested a specific language or when a localized diagnostic is
    /// unavailable for the requested locale.
    pub fallback_fluent_bundle: LazyFallbackBundle,
}

impl Translator {
    pub fn with_fallback_bundle(
        resources: Vec<&'static str>,
        with_directionality_markers: bool,
    ) -> Translator {
        Translator {
            fluent_bundle: None,
            fallback_fluent_bundle: crate::fallback_fluent_bundle(
                resources,
                with_directionality_markers,
            ),
        }
    }

    /// Convert `DiagMessage`s to a string, performing translation if necessary.
    pub fn translate_messages(
        &self,
        messages: &[(DiagMessage, Style)],
        args: &FluentArgs<'_>,
    ) -> Cow<'_, str> {
        Cow::Owned(
            messages
                .iter()
                .map(|(m, _)| self.translate_message(m, args).map_err(Report::new).unwrap())
                .collect::<String>(),
        )
    }

    /// Convert a `DiagMessage` to a string, performing translation if necessary.
    pub fn translate_message<'a>(
        &'a self,
        message: &'a DiagMessage,
        args: &'a FluentArgs<'_>,
    ) -> Result<Cow<'a, str>, TranslateError<'a>> {
        trace!(?message, ?args);
        let (identifier, attr) = match message {
            DiagMessage::Str(msg) | DiagMessage::Translated(msg) => {
                return Ok(Cow::Borrowed(msg));
            }
            DiagMessage::FluentIdentifier(identifier, attr) => (identifier, attr),
        };
        let translate_with_bundle =
            |bundle: &'a FluentBundle| -> Result<Cow<'_, str>, TranslateError<'_>> {
                let message = bundle
                    .get_message(identifier)
                    .ok_or(TranslateError::message(identifier, args))?;
                let value = match attr {
                    Some(attr) => message
                        .get_attribute(attr)
                        .ok_or(TranslateError::attribute(identifier, args, attr))?
                        .value(),
                    None => message.value().ok_or(TranslateError::value(identifier, args))?,
                };
                debug!(?message, ?value);

                let mut errs = vec![];
                let translated = bundle.format_pattern(value, Some(args), &mut errs);
                debug!(?translated, ?errs);
                if errs.is_empty() {
                    Ok(translated)
                } else {
                    Err(TranslateError::fluent(identifier, args, errs))
                }
            };

        try {
            match self.fluent_bundle.as_ref().map(|b| translate_with_bundle(b)) {
                // The primary bundle was present and translation succeeded
                Some(Ok(t)) => t,

                // If `translate_with_bundle` returns `Err` with the primary bundle, this is likely
                // just that the primary bundle doesn't contain the message being translated, so
                // proceed to the fallback bundle.
                Some(Err(
                    primary @ TranslateError::One {
                        kind: TranslateErrorKind::MessageMissing, ..
                    },
                )) => translate_with_bundle(&self.fallback_fluent_bundle)
                    .map_err(|fallback| primary.and(fallback))?,

                // Always yeet out for errors on debug (unless
                // `RUSTC_TRANSLATION_NO_DEBUG_ASSERT` is set in the environment - this allows
                // local runs of the test suites, of builds with debug assertions, to test the
                // behaviour in a normal build).
                Some(Err(primary))
                    if cfg!(debug_assertions)
                        && env::var("RUSTC_TRANSLATION_NO_DEBUG_ASSERT").is_err() =>
                {
                    do yeet primary
                }

                // ..otherwise, for end users, an error about this wouldn't be useful or actionable, so
                // just hide it and try with the fallback bundle.
                Some(Err(primary)) => translate_with_bundle(&self.fallback_fluent_bundle)
                    .map_err(|fallback| primary.and(fallback))?,

                // The primary bundle is missing, proceed to the fallback bundle
                None => translate_with_bundle(&self.fallback_fluent_bundle)
                    .map_err(|fallback| TranslateError::primary(identifier, args).and(fallback))?,
            }
        }
    }
}