#![doc(test(attr(deny(warnings))))]
#![forbid(unsafe_code)]
#![warn(missing_docs)]
#![allow(
    unknown_lints,
    clippy::unknown_clippy_lints,
    clippy::needless_doctest_main
)]

//! A [`spirit`] fragments and helpers to configure and control logging.
//!
//! The [`Fragment`]s here allow to configure relatively complex logging (multiple loggers,
//! different formats, different destinations), both from command line and the configuration. It
//! allows runtime reloading of them.
//!
//! Internally it is based on the [`fern`] crate and just adds the configuration and runtime
//! reloading (through [`log-reroute`]).
//!
//! It assumes the application doesn't set the global logger itself. It also sets the panic hook
//! through the [`log_panics`] crate. The `with-backtrace` cargo feature is propagated through.
//!
//! # Features
//!
//! * `background`: Includes the ability to log asynchronously ‒ the writing to log files happens
//!   in a background thread and allows the rest of the application to not block on IO.
//! * `cfg-help`: Support for configuration options help at runtime. On by default.
//! * `with-backtrace`: The [`log_panics`] logs with backtraces. On by default.
//! * `syslog`: Adds the support for logging into syslog.
//!
//! # Startup
//!
//! When using the automatic management with a pipeline, this is how a startup happens:
//!
//! * As soon as the pipeline is registered, a logging on the `WARN` level is sent to `stderr`.
//! * After command line arguments are parsed the `stderr` logging is updated to reflect that (or
//!   left on the `WARN` level if nothing is set by the user).
//! * After configuration is loaded from the files, full logging is configured according to that.
//!
//! # Integration with other loggers
//!
//! If you need something specific (for example [`sentry`](https://crates.io/crates/sentry)), you
//! can plug in additional loggers through the pipeline ‒ the [`Dispatch`] allows adding arbitrary
//! loggers. The [`Pipeline::map`][spirit::fragment::pipeline::Pipeline::map] is a good place to do
//! it.
//!
//! # Performance warning
//!
//! This allows the user to create arbitrary number of loggers. Furthermore, the logging is
//! synchronous  by default and not buffered. When writing a lot of logs or sending them over the
//! network, this could become a bottleneck.
//!
//! # Background logging
//!
//! The `background` feature flag adds the ability to do the actual logging in a background thread.
//! This allows not blocking the actual application by IO or other expensive operations.
//!
//! On the other hand, if the application crashes, some logs may be lost (or, depending on setup,
//! when the logging thread doesn't keep up). Also, you need to flush the logger on shutdown, by
//! using the [`FlushGuard`].
//!
//! It is done through the [`Background`] transformation.
//!
//! # Planned features
//!
//! These pieces are planned some time in future, but haven't happened yet (pull requests are
//! welcome).
//!
//! * Reconnecting to the remote server if a TCP connection is lost.
//! * Log file rotation.
//! * Colors on `stdout`/`stderr`.
//!
//! # Usage without Pipelines
//!
//! It is possible to use without the [`Pipeline`][spirit::Pipeline], manually. However,
//! certain care needs to be taken to initialize everything that needs to be initialized.
//!
//! It is either possible to just get the [`Dispatch`] object and call [`apply`][Dispatch::apply],
//! that however is a single-shot initialization and the logger can't be replaced.
//!
//! The helper functions [`init`] and [`install`] can be used to gain the ability to replace
//! [`Dispatch`] loggers multiple times.
//!
//! # Examples
//!
//! ## Manual single use installation
//!
//! ```rust
//! use spirit::AnyError;
//! use spirit::prelude::*;
//! use spirit_log::Cfg;
//!
//! # fn main() -> Result<(), AnyError> {
//! // Well, you'd get it somewhere from configuration, but…
//! let cfg = Cfg::default();
//! let logger = cfg.create("logger")?;
//! logger.apply()?;
//! # Ok(()) }
//! ```
//!
//! ## Manual multiple-use installation
//!
//! ```rust
//! use spirit::AnyError;
//! use spirit::prelude::*;
//! use spirit_log::Cfg;
//!
//! # fn main() -> Result<(), AnyError> {
//! spirit_log::init();
//! // This part can be done multiple times.
//! let cfg = Cfg::default();
//! let logger = cfg.create("logger")?;
//! spirit_log::install(logger);
//! # Ok(()) }
//! ```
//!
//! ## Automatic usage with a Pipeline, reloading and command line options
//!
//! ```rust
//! use log::info;
//! use serde::Deserialize;
//! use spirit::{Pipeline, Spirit};
//! use spirit::prelude::*;
//! use spirit_log::{Cfg as LogCfg, CfgAndOpts as LogBoth, Opts as LogOpts};
//! use structopt::StructOpt;
//!
//! #[derive(Clone, Debug, StructOpt)]
//! struct Opts {
//!     #[structopt(flatten)]
//!     logging: LogOpts,
//! }
//!
//! impl Opts {
//!     fn logging(&self) -> LogOpts {
//!         self.logging.clone()
//!     }
//! }
//!
//! #[derive(Clone, Debug, Default, Deserialize)]
//! struct Cfg {
//!     #[serde(default, skip_serializing_if = "LogCfg::is_empty")]
//!     logging: LogCfg,
//! }
//!
//! impl Cfg {
//!     fn logging(&self) -> LogCfg {
//!         self.logging.clone()
//!     }
//! }
//!
//! fn main() {
//!     Spirit::<Opts, Cfg>::new()
//!         .with(
//!             Pipeline::new("logging").extract(|opts: &Opts, cfg: &Cfg| LogBoth {
//!                 cfg: cfg.logging(),
//!                 opts: opts.logging(),
//!             }),
//!         )
//!         .run(|_spirit| {
//!             info!("Hello world");
//!             Ok(())
//!         });
//! }
//! ```
//!
//! The configuration could look something like this:
//!
//! ```toml
//! [[logging]]
//! level = "DEBUG"
//! type = "file"
//! filename = "/tmp/example.log"
//! clock = "UTC"
//! ```
//!
//! [`log-reroute`]: https://docs.rs/log-reroute
//! [`log_panics`]: https://docs.rs/log_panics

use std::cmp;
use std::collections::HashMap;
use std::fmt::Arguments;
use std::io::{self, Write};
use std::iter;
use std::net::TcpStream;
use std::path::PathBuf;
use std::sync::atomic::{AtomicBool, Ordering};
use std::thread;

use chrono::format::{DelayedFormat, StrftimeItems};
use chrono::{Local, Utc};
use fern::Dispatch;
use itertools::Itertools;
use log::{debug, trace, LevelFilter, Log, STATIC_MAX_LEVEL};
use serde::de::{Deserializer, Error as DeError};
use serde::ser::Serializer;
use serde::{Deserialize, Serialize};
use spirit::extension::{Extensible, Extension};
use spirit::fragment::driver::Trivial as TrivialDriver;
use spirit::fragment::{Fragment, Installer};
use spirit::AnyError;
#[cfg(feature = "cfg-help")]
use structdoc::StructDoc;
use structopt::StructOpt;

#[cfg(feature = "background")]
pub mod background;

#[cfg(feature = "background")]
pub use background::{Background, FlushGuard, OverflowMode};

const UNKNOWN_THREAD: &str = "<unknown>";

// Workaround for https://github.com/TeXitoi/structopt/issues/333
#[cfg_attr(not(doc), allow(missing_docs))]
#[cfg_attr(
    doc,
    doc = r#"
A fragment for command line options.

By flattening this into the top-level `StructOpt` structure, you get the `-l` and `-L` command
line options. The `-l` (`--log`) sets the global logging level for `stderr`. The `-L` accepts
pairs (eg. `-L spirit=TRACE`) specifying levels for specific logging targets.

If used, the logging will be sent to `stderr`.
"#
)]
#[derive(Clone, Debug, StructOpt)]
pub struct Opts {
    /// Log to stderr with this log level.
    #[structopt(short = "l", long = "log", number_of_values(1))]
    log: Option<LevelFilter>,

    /// Log to stderr with overriden levels for specific modules.
    #[structopt(
        short = "L",
        long = "log-module",
        parse(try_from_str = spirit::utils::key_val),
        number_of_values(1),
    )]
    log_modules: Vec<(String, LevelFilter)>,
}

impl Opts {
    fn logger_cfg(&self) -> Option<Logger> {
        self.log.map(|level| Logger {
            level: LevelFilterSerde(level),
            destination: LogDestination::StdErr,
            per_module: self
                .log_modules
                .iter()
                .map(|(module, lf)| (module.clone(), LevelFilterSerde(*lf)))
                .collect(),
            clock: Clock::Local,
            time_format: cmdline_time_format(),
            format: Format::Short,
        })
    }
}

// TODO: OptsExt & OptsVerbose and turn the other things into Into<Opts>

#[derive(Clone, Debug, Deserialize, Serialize, PartialEq)]
#[cfg_attr(feature = "cfg-help", derive(StructDoc))]
#[serde(tag = "type", rename_all = "kebab-case")] // TODO: Make deny-unknown-fields work
enum LogDestination {
    /// Writes the logs into a file.
    File {
        /// The path to the file to store the log into.
        ///
        /// The file will be appended to or created if it doesn't exist. The directory it resides
        /// in must already exist.
        ///
        /// There is no direct support for log rotation. However, as the log file is reopened on
        /// `SIGHUP`, the usual external logrotate setup should work.
        filename: PathBuf,
        // TODO: Truncate
    },

    /// Sends the logs to local syslog.
    ///
    /// Note that syslog ignores formatting options.
    #[cfg(feature = "syslog")]
    Syslog {
        /// Overrides the host value in the log messages.
        #[serde(skip_serializing_if = "Option::is_none")]
        host: Option<String>,
        // TODO: Remote syslog
    },

    /// Sends the logs over a TCP connection over the network.
    Network {
        /// Hostname or IP address of the remote machine.
        host: String,

        /// Port to connect to on the remote machine.
        port: u16,
    },

    /// Writes logs to standard output.
    #[serde(rename = "stdout")]
    StdOut, // TODO: Colors

    /// Writes the logs to error output.
    #[serde(rename = "stderr")]
    StdErr, // TODO: Colors
}

const LEVEL_FILTERS: &[&str] = &["OFF", "ERROR", "WARN", "INFO", "DEBUG", "TRACE"];

// A newtype to help us with serde, structdoc, default... more convenient inside maps and such.
//
// We could get serde support with a feature flag from log itself, but not the rest :-(.
#[derive(Copy, Clone, Debug)]
struct LevelFilterSerde(LevelFilter);

impl Default for LevelFilterSerde {
    fn default() -> LevelFilterSerde {
        LevelFilterSerde(LevelFilter::Error)
    }
}

impl<'de> Deserialize<'de> for LevelFilterSerde {
    fn deserialize<D: Deserializer<'de>>(d: D) -> Result<LevelFilterSerde, D::Error> {
        let s = String::deserialize(d)?;
        s.parse()
            .map(LevelFilterSerde)
            .map_err(|_| D::Error::unknown_variant(&s, LEVEL_FILTERS))
    }
}

impl Serialize for LevelFilterSerde {
    fn serialize<S: Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
        s.serialize_str(&format!("{:?}", self.0).to_uppercase())
    }
}

#[cfg(feature = "cfg-help")]
impl structdoc::StructDoc for LevelFilterSerde {
    fn document() -> structdoc::Documentation {
        use structdoc::{Documentation, Field, Tagging};

        let filters = LEVEL_FILTERS
            .iter()
            .map(|name| (*name, Field::new(Documentation::leaf_empty(), "")));
        Documentation::enum_(filters, Tagging::External)
    }
}

/// This error can be returned when initialization of logging to syslog fails.
#[derive(Clone, Debug)]
#[cfg(feature = "syslog")]
pub struct SyslogError(String);

#[cfg(feature = "syslog")]
impl std::fmt::Display for SyslogError {
    fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
        self.0.fmt(fmt)
    }
}

#[cfg(feature = "syslog")]
impl std::error::Error for SyslogError {}

#[derive(Clone, Copy, Debug, Deserialize, Serialize)]
#[cfg_attr(feature = "cfg-help", derive(StructDoc))]
#[serde(rename_all = "SCREAMING_SNAKE_CASE")]
enum Clock {
    Local,
    Utc,
}

impl Clock {
    fn now(self, format: &str) -> DelayedFormat<StrftimeItems> {
        match self {
            Clock::Local => Local::now().format(format),
            Clock::Utc => Utc::now().format(format),
        }
    }
}

impl Default for Clock {
    fn default() -> Self {
        Clock::Local
    }
}

fn default_time_format() -> String {
    "%+".to_owned()
}

fn cmdline_time_format() -> String {
    "%F %T%.3f".to_owned()
}

#[derive(Clone, Copy, Debug, Deserialize, Serialize)]
#[cfg_attr(feature = "cfg-help", derive(StructDoc))]
#[serde(rename_all = "kebab-case")]
enum Format {
    /// Only the message, without any other fields.
    MessageOnly,
    /// The time, log level, log target and message in columns.
    Short,
    /// The time, log level, thread name, log target and message in columns.
    Extended,
    /// The time, log level, thread name, file name and line, log target and message in columns.
    Full,
    /// The time, log level, thread name, file name and line, log target and message in columns
    /// separated by tabs.
    ///
    /// This format is simpler to machine-parse (because the columns are separated by a single '\t'
    /// character and only the last one should ever contain it), but less human-readable because
    /// the columns don't have to visually align.
    Machine,
    /// The time, log level, thread name, file name and line, log target and message, formatted as
    /// json with these field names:
    ///
    /// * timestamp
    /// * level
    /// * thread_name
    /// * file
    /// * line
    /// * target
    /// * message
    ///
    /// Each message is on a separate line and the JSONs are not pretty-printed (therefore it is
    /// one JSON per line).
    // TODO: Configurable field names?
    Json,
    /// Similar to `json`, however with field names that correspond to default configuration of
    /// logstash.
    ///
    /// * @timestamp
    /// * @version (always set to 1)
    /// * level
    /// * thread_name
    /// * logger_name (corresponds to log target)
    /// * message
    Logstash,
    // TODO: Custom
}

impl Default for Format {
    fn default() -> Self {
        Format::Short
    }
}

#[cfg(not(feature = "background"))]
fn get_thread_name(thread: &thread::Thread) -> &str {
    thread.name().unwrap_or(UNKNOWN_THREAD)
}

#[cfg(feature = "background")]
use background::get_thread_name;

#[derive(Clone, Debug, Deserialize, Serialize)]
#[cfg_attr(feature = "cfg-help", derive(StructDoc))]
#[serde(rename_all = "kebab-case")] // TODO: Make deny-unknown-fields work
struct Logger {
    #[serde(flatten)]
    destination: LogDestination,

    #[serde(default)]
    clock: Clock,

    /// The format of timestamp.
    ///
    /// This is strftime-like time format string, fully specified here:
    ///
    /// https://docs.rs/chrono/~0.4/chrono/format/strftime/index.html
    ///
    /// The default is %+, which corresponds to ISO 8601 / RFC 3339 date & time format.
    #[serde(default = "default_time_format")]
    time_format: String,

    /// Format of log messages.
    #[serde(default)]
    format: Format,

    /// The level on which to log messages.
    ///
    /// Messages with this level or more severe will be written into this logger.
    #[serde(default)]
    level: LevelFilterSerde,

    /// Overrides of log level per each module.
    ///
    /// The map allows for overriding log levels of each separate module (log target) separately.
    /// This allows silencing a verbose one or getting more info out of misbehaving one.
    #[serde(default, skip_serializing_if = "HashMap::is_empty")]
    per_module: HashMap<String, LevelFilterSerde>,
}

impl Logger {
    fn create(&self) -> Result<Dispatch, AnyError> {
        trace!("Creating logger for {:?}", self);
        let mut logger = Dispatch::new().level(self.level.0);
        logger = self
            .per_module
            .iter()
            .fold(logger, |logger, (module, level)| {
                logger.level_for(module.clone(), level.0)
            });
        let clock = self.clock;
        let time_format = self.time_format.clone();
        let format = self.format;
        // Clippy gets angry when the syslog is disabled
        #[allow(clippy::unknown_clippy_lints, clippy::match_single_binding)]
        match self.destination {
            // We don't want to format syslog
            #[cfg(feature = "syslog")]
            LogDestination::Syslog { .. } => (),
            // We do with the other things
            _ => {
                logger = logger.format(move |out, message, record| {
                    match format {
                        Format::MessageOnly => out.finish(format_args!("{}", message)),
                        Format::Short => out.finish(format_args!(
                            "{} {:5} {:30} {}",
                            clock.now(&time_format),
                            record.level(),
                            record.target(),
                            message,
                        )),
                        Format::Extended => {
                            out.finish(format_args!(
                                "{} {:5} {:30} {:30} {}",
                                clock.now(&time_format),
                                record.level(),
                                get_thread_name(&thread::current()),
                                record.target(),
                                message,
                            ));
                        }
                        Format::Full => {
                            out.finish(format_args!(
                                "{} {:5} {:10} {:>25}:{:<5} {:30} {}",
                                clock.now(&time_format),
                                record.level(),
                                get_thread_name(&thread::current()),
                                record.file().unwrap_or("<unknown>"),
                                record.line().unwrap_or(0),
                                record.target(),
                                message,
                            ));
                        }
                        Format::Machine => {
                            out.finish(format_args!(
                                "{}\t{}\t{}\t{}\t{}\t{}\t{}",
                                clock.now(&time_format),
                                record.level(),
                                get_thread_name(&thread::current()),
                                record.file().unwrap_or("<unknown>"),
                                record.line().unwrap_or(0),
                                record.target(),
                                message,
                            ));
                        }
                        Format::Json => {
                            // We serialize it by putting things into a structure and using serde
                            // for that.
                            //
                            // This is a zero-copy structure.
                            #[derive(Serialize)]
                            struct Msg<'a> {
                                timestamp: Arguments<'a>,
                                level: Arguments<'a>,
                                thread_name: &'a str,
                                file: Option<&'a str>,
                                line: Option<u32>,
                                target: &'a str,
                                message: &'a Arguments<'a>,
                            }
                            // Unfortunately, the Arguments thing produced by format_args! doesn't
                            // like to live in a variable ‒ all attempts to put it into a let
                            // binding failed with various borrow-checker errors.
                            //
                            // However, constructing it as a temporary when calling a function
                            // seems to work fine. So we use this closure to work around the
                            // problem.
                            let log = |msg: &Msg| {
                                // TODO: Maybe use some shortstring or so here to avoid allocation?
                                let msg = serde_json::to_string(msg)
                                    .expect("Failed to serialize JSON log");
                                out.finish(format_args!("{}", msg));
                            };
                            log(&Msg {
                                timestamp: format_args!("{}", clock.now(&time_format)),
                                level: format_args!("{}", record.level()),
                                thread_name: &get_thread_name(&thread::current()),
                                file: record.file(),
                                line: record.line(),
                                target: record.target(),
                                message,
                            });
                        }
                        Format::Logstash => {
                            // We serialize it by putting things into a structure and using serde
                            // for that.
                            //
                            // This is a zero-copy structure.
                            #[derive(Serialize)]
                            struct Msg<'a> {
                                #[serde(rename = "@timestamp")]
                                timestamp: Arguments<'a>,
                                #[serde(rename = "@version")]
                                version: u8,
                                level: Arguments<'a>,
                                thread_name: &'a str,
                                logger_name: &'a str,
                                message: &'a Arguments<'a>,
                            }
                            // Unfortunately, the Arguments thing produced by format_args! doesn't
                            // like to live in a variable ‒ all attempts to put it into a let
                            // binding failed with various borrow-checker errors.
                            //
                            // However, constructing it as a temporary when calling a function
                            // seems to work fine. So we use this closure to work around the
                            // problem.
                            let log = |msg: &Msg| {
                                // TODO: Maybe use some shortstring or so here to avoid allocation?
                                let msg = serde_json::to_string(msg)
                                    .expect("Failed to serialize JSON log");
                                out.finish(format_args!("{}", msg));
                            };
                            log(&Msg {
                                timestamp: format_args!("{}", clock.now(&time_format)),
                                version: 1,
                                level: format_args!("{}", record.level()),
                                thread_name: &get_thread_name(&thread::current()),
                                logger_name: record.target(),
                                message,
                            });
                        }
                    }
                });
            }
        }
        match self.destination {
            LogDestination::File { ref filename } => Ok(logger.chain(fern::log_file(filename)?)),
            #[cfg(feature = "syslog")]
            LogDestination::Syslog { ref host } => {
                let formatter = syslog::Formatter3164 {
                    facility: syslog::Facility::LOG_USER,
                    hostname: host.clone(),
                    // TODO: Does this give us the end-user crate or us?
                    process: env!("CARGO_PKG_NAME").to_owned(),
                    pid: 0,
                };
                let sys_logger =
                    syslog::unix(formatter).map_err(|e| SyslogError(format!("{}", e)))?;
                let sys_logger: Box<dyn Log> = Box::new(syslog::BasicLogger::new(sys_logger));
                // TODO: Other destinations than just unix
                Ok(logger.chain(sys_logger))
            }
            LogDestination::Network { ref host, port } => {
                // TODO: Reconnection support
                let conn = TcpStream::connect((&host as &str, port))?;
                Ok(logger.chain(Box::new(conn) as Box<dyn Write + Send>))
            }
            LogDestination::StdOut => Ok(logger.chain(io::stdout())),
            LogDestination::StdErr => Ok(logger.chain(io::stderr())),
        }
    }
}

impl Default for Logger {
    fn default() -> Self {
        Self {
            destination: LogDestination::StdErr,
            level: LevelFilterSerde(LevelFilter::Warn),
            per_module: HashMap::new(),
            clock: Clock::Local,
            time_format: cmdline_time_format(),
            format: Format::Short,
        }
    }
}

fn create<'a, I>(logging: I) -> Result<Dispatch, AnyError>
where
    I: IntoIterator<Item = &'a Logger>,
{
    debug!("Creating loggers");
    logging
        .into_iter()
        .map(Logger::create)
        .fold_results(Dispatch::new(), Dispatch::chain)
        .map_err(AnyError::from)
}

/// A configuration fragment to set up logging.
///
/// By flattening this into the configuration structure, the program can load options for
/// configuring logging. It adds a new top-level array `logging`. Each item describes one logger,
/// with separate log levels and destination.
///
/// See the [crate examples](index.html#examples) for the use.
///
/// # Logger options
///
/// These are valid for all loggers:
///
/// * `level`: The log level to use. Valid options are `OFF`, `ERROR`, `WARN`, `INFO`, `DEBUG` and
///   `TRACE`.
/// * `per-module`: A map, setting log level overrides for specific modules (logging targets). This
///   one is optional.
/// * `type`: Specifies the type of logger destination. Some of them allow specifying other
///   options.
/// * `clock`: Either `LOCAL` or `UTC`. Defaults to `LOCAL` if not present.
/// * `time_format`: Time
///   [format string](https://docs.rs/chrono/*/chrono/format/strftime/index.html). Defaults to
///   `%+` (which is ISO 8601/RFC 3339). Note that the command line logger (one produced by `-l`)
///   uses a more human-friendly format.
/// * `format`: The format to use. There are few presets (and a custom may come in future).
///   - `message-only`: The line contains only the message itself.
///   - `short`: This is the default. `<timestamp> <level> <target> <message>`. Padded to form
///     columns.
///   - `extended`: <timestamp> <level> <thread-name> <target> <message>`. Padded to form columns.
///   - `full`: `<timestamp> <level> <thread-name> <file>:<line> <target> <message>`. Padded to
///     form columns.
///   - `machine`: Like `full`, but columns are not padded by spaces, they are separated by a
///     single `\t` character, for more convenient processing by tools like `cut`.
///   - `json`: The fields of `full` are encoded into a `json` format, for convenient processing of
///     more modern tools like logstash.
///   - `logstash`: `json` format with fields named and formatted according to
///     [Logback JSON encoder](https://github.com/logstash/logstash-logback-encoder#standard-fields)
///
/// The allowed types are:
/// * `stdout`: The logs are sent to standard output. There are no additional options.
/// * `stderr`: The logs are sent to standard error output. There are no additional options.
/// * `file`: Logs are written to a file. The file is reopened every time a configuration is
///   re-read (therefore every time the application gets `SIGHUP`), which makes it work with
///   logrotate.
///   - `filename`: The path to the file where to put the logs.
/// * `network`: The application connects to a given host and port over TCP and sends logs there.
///   - `host`: The hostname (or IP address) to connect to.
///   - `port`: The port to use.
/// * `syslog`: Sends the logs to syslog. This ignores all the formatting and time options, as
///   syslog handles this itself. This depends on the `to-syslog` feature.
#[derive(Clone, Debug, Default, Deserialize, Serialize)]
#[cfg_attr(feature = "cfg-help", derive(StructDoc))]
#[serde(transparent)]
pub struct Cfg(Vec<Logger>);

struct Configured;

impl Cfg {
    /// This provides an [`Extension`] to initialize logging.
    ///
    /// It calls [`init`] and sets up a basic logger (`WARN` and more serious going to `stderr`).
    ///
    /// This is seldom used directly (but can be), the [`LogInstaller`] makes sure it is called.
    pub fn init_extension<E: Extensible>() -> impl Extension<E> {
        |mut e: E| {
            if e.singleton::<Configured>() {
                init();
                let logger = Logger {
                    destination: LogDestination::StdErr,
                    level: LevelFilterSerde(LevelFilter::Warn),
                    per_module: HashMap::new(),
                    clock: Clock::Local,
                    time_format: cmdline_time_format(),
                    format: Format::Short,
                };
                install(create(iter::once(&logger)).unwrap());
            }
            e
        }
    }

    /// Checks if the logging configuration is empty.
    ///
    /// Can be used for skipping serialization of the config array if empty.
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }
}

static INIT_CALLED: AtomicBool = AtomicBool::new(false);

/// Initialize the global state.
///
/// This installs a global logger that can be replaced at runtime and sets a panic hook to also log
/// panics (see [`log_panics`]).
///
/// This allows calling [`install`] later on.
///
/// It is needed only if the crate is used in the manual way. This is taken care of if used through
/// the [Pipeline][spirit::Pipeline].
pub fn init() {
    log_panics::init();
    let _ = log_reroute::init();
    INIT_CALLED.store(true, Ordering::Relaxed);
}

/// Replace the current logger with the provided one.
///
/// This is a lower-level alternative to [`install`]. This allows putting an arbitrary logger in
/// (with the corresponding log level at which it makes sense to try log the messages).
pub fn install_parts(level: LevelFilter, logger: Box<dyn Log>) {
    assert!(
        INIT_CALLED.load(Ordering::Relaxed),
        "spirit_log::init not called yet"
    );
    let actual_level = cmp::min(level, STATIC_MAX_LEVEL);
    log::set_max_level(actual_level);
    log_reroute::reroute_boxed(logger);
    debug!(
        "Installed loggers with global level filter {:?} (compiled with {:?}, runtime config {:?})",
        actual_level, STATIC_MAX_LEVEL, level,
    );
}

/// Replace the current logger with the provided one.
///
/// This can be called multiple times (unlike [`Dispatch::apply`]) and it always replaces the old
/// logger with a new one.
///
/// The logger will be installed in a synchronous way ‒ a call to logging functions may block.
///
/// # Panics
///
/// If [`init`] haven't been called yet.
pub fn install(logger: Dispatch) {
    let (level, logger) = logger.into_log();
    install_parts(level, logger);
}

impl Fragment for Cfg {
    type Driver = TrivialDriver;
    type Seed = ();
    type Resource = Dispatch;
    type Installer = LogInstaller;
    fn make_seed(&self, _name: &str) -> Result<(), AnyError> {
        Ok(())
    }
    fn make_resource(&self, _: &mut (), _name: &str) -> Result<Dispatch, AnyError> {
        create(&self.0)
    }
}

/// A combination of [`Cfg`] and [`Opts`].
///
/// This is a composed [`Fragment`] ‒ the purpose is the caller can combine configuration both from
/// command line options and configuration inside the same [`Pipeline`][spirit::Pipeline] ‒ see the
/// [crate examples](index.html#examples).
///
/// The [`Fragment`] will then combine the options to create the relevant loggers.
///
/// # Interaction on stderr
///
/// There's a little twist around stderr and the interaction between the `-L` option and loggers
/// set up in configuration. This is to act in a way that makes some sense ‒ in particular, we
/// don't want to log to stderr twice. Therefore:
///
/// * If the user specifies `-l` (or `-L`) on the command line, any stderr logger from
///   configuration is skipped (the `-l` takes precedence).
/// * If there are no loggers in configuration but there's no `-l`, errors are logged to stderr.
///   This is the case before configuration is loaded or if it contains no loggers. We want to
///   report errors *somewhere*.
// TODO: Non-owned version too?
#[derive(Clone, Debug)]
pub struct CfgAndOpts {
    /// The configuration options.
    pub cfg: Cfg,
    /// The command line options.
    pub opts: Opts,
}

impl Fragment for CfgAndOpts {
    type Driver = TrivialDriver;
    type Seed = ();
    type Resource = Dispatch;
    type Installer = LogInstaller;
    const RUN_BEFORE_CONFIG: bool = true;
    fn make_seed(&self, _name: &str) -> Result<(), AnyError> {
        Ok(())
    }
    fn make_resource(&self, _: &mut (), _name: &str) -> Result<Dispatch, AnyError> {
        let mut cmd = self.opts.logger_cfg();
        // No logging at all ‒ log errors to stderr
        if self.cfg.0.is_empty() && cmd.is_none() {
            cmd = Some(Logger::default());
        }
        create(
            self.cfg
                .0
                .iter()
                // A command line overrides any logger to stderr in configuration. But only if it
                // is set at all.
                .filter(|l| l.destination != LogDestination::StdErr || cmd.is_none())
                .chain(cmd.as_ref()),
        )
    }
}

/// An [`Installer`] for the [`Dispatch`].
///
/// This is the installer used by default for installing loggers ‒ this is what you get if you use
/// the [`Pipeline`][spirit::Pipeline] with [`Cfg`].
///
/// Loggers installed this way act in a synchronous way ‒ they block on IO.
///
/// Note that it is possible to install other loggers through this too ‒ even the async ones from
/// [`Background`] transformation.
#[derive(Copy, Clone, Debug, Default, Eq, PartialEq, Ord, PartialOrd, Hash)]
pub struct LogInstaller;

impl<O, C> Installer<Dispatch, O, C> for LogInstaller {
    type UninstallHandle = ();
    fn install(&mut self, logger: Dispatch, _: &str) {
        install(logger);
    }
    fn init<B: Extensible<Ok = B>>(&mut self, builder: B, _name: &str) -> Result<B, AnyError> {
        builder.with(Cfg::init_extension())
    }
}

impl<O, C> Installer<(LevelFilter, Box<dyn Log>), O, C> for LogInstaller {
    type UninstallHandle = ();
    fn install(&mut self, (level, logger): (LevelFilter, Box<dyn Log>), _: &str) {
        install_parts(level, logger);
    }
    fn init<B: Extensible<Ok = B>>(&mut self, builder: B, _name: &str) -> Result<B, AnyError> {
        builder.with(Cfg::init_extension())
    }
}