use std::fmt;
use std::str::FromStr;

use pep440_rs::Version;
use tracing::{debug, info};
use uv_client::BaseClientBuilder;

use uv_cache::Cache;

use crate::discovery::{
    find_best_python_installation, find_python_installation, EnvironmentPreference, PythonRequest,
};
use crate::downloads::{DownloadResult, ManagedPythonDownload, PythonDownloadRequest, Reporter};
use crate::implementation::LenientImplementationName;
use crate::managed::{ManagedPythonInstallation, ManagedPythonInstallations};
use crate::platform::{Arch, Libc, Os};
use crate::{Error, Interpreter, PythonFetch, PythonPreference, PythonSource, PythonVersion};

/// A Python interpreter and accompanying tools.
#[derive(Clone, Debug)]
pub struct PythonInstallation {
    // Public in the crate for test assertions
    pub(crate) source: PythonSource,
    pub(crate) interpreter: Interpreter,
}

impl PythonInstallation {
    /// Create a new [`PythonInstallation`] from a source, interpreter tuple.
    pub(crate) fn from_tuple(tuple: (PythonSource, Interpreter)) -> Self {
        let (source, interpreter) = tuple;
        Self {
            source,
            interpreter,
        }
    }

    /// Find an installed [`PythonInstallation`].
    ///
    /// This is the standard interface for discovering a Python installation for creating
    /// an environment. If interested in finding an existing environment, see
    /// [`PythonEnvironment::find`] instead.
    ///
    /// Note we still require an [`EnvironmentPreference`] as this can either bypass virtual environments
    /// or prefer them. In most cases, this should be [`EnvironmentPreference::OnlySystem`]
    /// but if you want to allow an interpreter from a virtual environment if it satisfies the request,
    /// then use [`EnvironmentPreference::Any`].
    ///
    /// See [`find_installation`] for implementation details.
    pub fn find(
        request: &PythonRequest,
        environments: EnvironmentPreference,
        preference: PythonPreference,
        cache: &Cache,
    ) -> Result<Self, Error> {
        let installation = find_python_installation(request, environments, preference, cache)??;
        Ok(installation)
    }

    /// Find an installed [`PythonInstallation`] that satisfies a requested version, if the request cannot
    /// be satisfied, fallback to the best available Python installation.
    pub fn find_best(
        request: &PythonRequest,
        environments: EnvironmentPreference,
        preference: PythonPreference,
        cache: &Cache,
    ) -> Result<Self, Error> {
        Ok(find_best_python_installation(
            request,
            environments,
            preference,
            cache,
        )??)
    }

    /// Find or fetch a [`PythonInstallation`].
    ///
    /// Unlike [`PythonInstallation::find`], if the required Python is not installed it will be installed automatically.
    pub async fn find_or_fetch<'a>(
        request: Option<PythonRequest>,
        environments: EnvironmentPreference,
        preference: PythonPreference,
        python_fetch: PythonFetch,
        client_builder: &BaseClientBuilder<'a>,
        cache: &Cache,
        reporter: Option<&dyn Reporter>,
    ) -> Result<Self, Error> {
        let request = request.unwrap_or_default();

        // Perform a fetch aggressively if managed Python is preferred
        if matches!(preference, PythonPreference::Managed) && python_fetch.is_automatic() {
            if let Some(request) = PythonDownloadRequest::try_from_request(&request) {
                return Self::fetch(request.fill(), client_builder, cache, reporter).await;
            }
        }

        // Search for the installation
        match Self::find(&request, environments, preference, cache) {
            Ok(venv) => Ok(venv),
            // If missing and allowed, perform a fetch
            err @ Err(Error::MissingPython(_))
                if preference.allows_managed()
                    && python_fetch.is_automatic()
                    && client_builder.connectivity.is_online() =>
            {
                if let Some(request) = PythonDownloadRequest::try_from_request(&request) {
                    debug!("Requested Python not found, checking for available download...");
                    Self::fetch(request.fill(), client_builder, cache, reporter).await
                } else {
                    err
                }
            }
            Err(err) => Err(err),
        }
    }

    /// Download and install the requested installation.
    pub async fn fetch<'a>(
        request: PythonDownloadRequest,
        client_builder: &BaseClientBuilder<'a>,
        cache: &Cache,
        reporter: Option<&dyn Reporter>,
    ) -> Result<Self, Error> {
        let installations = ManagedPythonInstallations::from_settings()?.init()?;
        let installations_dir = installations.root();
        let _lock = installations.acquire_lock()?;

        let download = ManagedPythonDownload::from_request(&request)?;
        let client = client_builder.build();

        info!("Fetching requested Python...");
        let result = download.fetch(&client, installations_dir, reporter).await?;

        let path = match result {
            DownloadResult::AlreadyAvailable(path) => path,
            DownloadResult::Fetched(path) => path,
        };

        let installed = ManagedPythonInstallation::new(path)?;
        installed.ensure_externally_managed()?;

        Ok(Self {
            source: PythonSource::Managed,
            interpreter: Interpreter::query(installed.executable(), cache)?,
        })
    }

    /// Create a [`PythonInstallation`] from an existing [`Interpreter`].
    pub fn from_interpreter(interpreter: Interpreter) -> Self {
        Self {
            source: PythonSource::ProvidedPath,
            interpreter,
        }
    }

    /// Return the [`PythonSource`] of the Python installation, indicating where it was found.
    pub fn source(&self) -> &PythonSource {
        &self.source
    }

    pub fn key(&self) -> PythonInstallationKey {
        PythonInstallationKey::new(
            LenientImplementationName::from(self.interpreter.implementation_name()),
            self.interpreter.python_major(),
            self.interpreter.python_minor(),
            self.interpreter.python_patch(),
            self.os(),
            self.arch(),
            self.libc(),
        )
    }

    /// Return the Python [`Version`] of the Python installation as reported by its interpreter.
    pub fn python_version(&self) -> &Version {
        self.interpreter.python_version()
    }

    /// Return the [`LenientImplementationName`] of the Python installation as reported by its interpreter.
    pub fn implementation(&self) -> LenientImplementationName {
        LenientImplementationName::from(self.interpreter.implementation_name())
    }

    /// Return the [`Arch`] of the Python installation as reported by its interpreter.
    pub fn arch(&self) -> Arch {
        Arch::from(&self.interpreter.platform().arch())
    }

    /// Return the [`Libc`] of the Python installation as reported by its interpreter.
    pub fn libc(&self) -> Libc {
        Libc::from(self.interpreter.platform().os())
    }

    /// Return the [`Os`] of the Python installation as reported by its interpreter.
    pub fn os(&self) -> Os {
        Os::from(self.interpreter.platform().os())
    }

    /// Return the [`Interpreter`] for the Python installation.
    pub fn interpreter(&self) -> &Interpreter {
        &self.interpreter
    }

    pub fn into_interpreter(self) -> Interpreter {
        self.interpreter
    }
}

#[derive(Error, Debug)]
pub enum PythonInstallationKeyError {
    #[error("Failed to parse Python installation key `{0}`: {1}")]
    ParseError(String, String),
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct PythonInstallationKey {
    pub(crate) implementation: LenientImplementationName,
    pub(crate) major: u8,
    pub(crate) minor: u8,
    pub(crate) patch: u8,
    pub(crate) os: Os,
    pub(crate) arch: Arch,
    pub(crate) libc: Libc,
}

impl PythonInstallationKey {
    pub fn new(
        implementation: LenientImplementationName,
        major: u8,
        minor: u8,
        patch: u8,
        os: Os,
        arch: Arch,
        libc: Libc,
    ) -> Self {
        Self {
            implementation,
            major,
            minor,
            patch,
            os,
            arch,
            libc,
        }
    }

    pub fn implementation(&self) -> &LenientImplementationName {
        &self.implementation
    }

    pub fn version(&self) -> PythonVersion {
        PythonVersion::from_str(&format!("{}.{}.{}", self.major, self.minor, self.patch))
            .expect("Python installation keys must have valid Python versions")
    }

    pub fn arch(&self) -> &Arch {
        &self.arch
    }

    pub fn os(&self) -> &Os {
        &self.os
    }

    pub fn libc(&self) -> &Libc {
        &self.libc
    }
}

impl fmt::Display for PythonInstallationKey {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "{}-{}.{}.{}-{}-{}-{}",
            self.implementation, self.major, self.minor, self.patch, self.os, self.arch, self.libc
        )
    }
}

impl FromStr for PythonInstallationKey {
    type Err = PythonInstallationKeyError;

    fn from_str(key: &str) -> Result<Self, Self::Err> {
        let parts = key.split('-').collect::<Vec<_>>();
        let [implementation, version, os, arch, libc] = parts.as_slice() else {
            return Err(PythonInstallationKeyError::ParseError(
                key.to_string(),
                "not enough `-`-separated values".to_string(),
            ));
        };

        let implementation = LenientImplementationName::from(*implementation);

        let os = Os::from_str(os).map_err(|err| {
            PythonInstallationKeyError::ParseError(key.to_string(), format!("invalid OS: {err}"))
        })?;

        let arch = Arch::from_str(arch).map_err(|err| {
            PythonInstallationKeyError::ParseError(
                key.to_string(),
                format!("invalid architecture: {err}"),
            )
        })?;

        let libc = Libc::from_str(libc).map_err(|err| {
            PythonInstallationKeyError::ParseError(key.to_string(), format!("invalid libc: {err}"))
        })?;

        let [major, minor, patch] = version
            .splitn(3, '.')
            .map(str::parse::<u8>)
            .collect::<Result<Vec<_>, _>>()
            .map_err(|err| {
                PythonInstallationKeyError::ParseError(
                    key.to_string(),
                    format!("invalid Python version: {err}"),
                )
            })?[..]
        else {
            return Err(PythonInstallationKeyError::ParseError(
                key.to_string(),
                "invalid Python version: expected `<major>.<minor>.<patch>`".to_string(),
            ));
        };

        Ok(Self::new(
            implementation,
            major,
            minor,
            patch,
            os,
            arch,
            libc,
        ))
    }
}

impl PartialOrd for PythonInstallationKey {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        Some(self.cmp(other))
    }
}
impl Ord for PythonInstallationKey {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.to_string().cmp(&other.to_string())
    }
}