// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License in the LICENSE-APACHE file or at:
//     https://www.apache.org/licenses/LICENSE-2.0

//! Options

use super::Error;
use kas::draw::DrawSharedImpl;
use kas_theme::{Theme, ThemeConfig};
use std::env::var;
use std::num::NonZeroU32;
use std::path::PathBuf;
pub use wgpu::{Backends, PowerPreference};

/// Config mode
///
/// See [`Options::from_env`] documentation.
#[derive(Clone, PartialEq, Eq, Hash)]
pub enum ConfigMode {
    /// Read-only mode
    Read,
    /// Read-write mode
    ///
    /// This mode reads config on start and writes changes on exit.
    ReadWrite,
    /// Use default config and write out
    ///
    /// This mode only writes initial (default) config and does not update.
    WriteDefault,
}

/// Shell options
#[derive(Clone, PartialEq, Eq, Hash)]
pub struct Options {
    /// Config file path. Default: empty. See `KAS_CONFIG` doc.
    pub config_path: PathBuf,
    /// Theme config path. Default: empty.
    pub theme_config_path: PathBuf,
    /// Config mode. Default: Read.
    pub config_mode: ConfigMode,
    /// Maximum frame rate (frames per second)
    pub fps_limit: Option<NonZeroU32>,
    /// Adapter power preference. Default value: low power.
    pub power_preference: PowerPreference,
    /// Adapter backend. Default value: PRIMARY (Vulkan/Metal/DX12).
    pub backends: Backends,
    /// WGPU's API tracing path
    pub wgpu_trace_path: Option<PathBuf>,
}

impl Default for Options {
    fn default() -> Self {
        Options {
            config_path: PathBuf::new(),
            theme_config_path: PathBuf::new(),
            config_mode: ConfigMode::Read,
            fps_limit: NonZeroU32::new(60),
            power_preference: PowerPreference::LowPower,
            backends: Backends::all(),
            wgpu_trace_path: None,
        }
    }
}

impl Options {
    /// Construct a new instance, reading from environment variables
    ///
    /// The following environment variables are read, in case-insensitive mode.
    ///
    /// # Config files
    ///
    /// WARNING: file formats are not stable and may not be compatible across
    /// KAS versions (aside from patch versions)!
    ///
    /// The `KAS_CONFIG` variable, if given, provides a path to the KAS config
    /// file, which is read or written according to `KAS_CONFIG_MODE`.
    /// If `KAS_CONFIG` is not specified, platform-default configuration is used
    /// without reading or writing. This may change to use a platform-specific
    /// default path in future versions.
    ///
    /// The `KAS_THEME_CONFIG` variable, if given, provides a path to the theme
    /// config file, which is read or written according to `KAS_CONFIG_MODE`.
    /// If `KAS_THEME_CONFIG` is not specified, platform-default configuration
    /// is used without reading or writing. This may change to use a
    /// platform-specific default path in future versions.
    ///
    /// The `KAS_CONFIG_MODE` variable determines the read/write mode:
    ///
    /// -   `Read` (default): read-only
    /// -   `ReadWrite`: read on start-up, write on exit
    /// -   `WriteDefault`: generate platform-default configuration and write
    ///     it to the config path(s) specified, overwriting any existing config
    ///
    /// Note: in the future, the default will likely change to a read-write mode,
    /// allowing changes to be written out.
    ///
    /// # Graphics options
    ///
    /// The `KAS_FPS_LIMIT` variable may be used to limit the number of frames
    /// per second. The default is 60. The value `0` disables this limit.
    ///
    /// The `KAS_POWER_PREFERENCE` variable supports:
    ///
    /// -   `Default`
    /// -   `LowPower`
    /// -   `HighPerformance`
    ///
    /// The `KAS_BACKENDS` variable supports:
    ///
    /// -   `Vulkan`
    /// -   `GL`
    /// -   `Metal`
    /// -   `DX11`
    /// -   `DX12`
    /// -   `BROWSER_WEBGPU`: web target through webassembly
    /// -   `PRIMARY`: any of Vulkan, Metal or DX12
    /// -   `SECONDARY`: any of GL or DX11
    /// -   `FALLBACK`: force use of fallback (CPU) rendering
    ///
    /// WGPU has an [API tracing] feature for debugging. To use this, ensure the
    /// `wgpu/trace` feature is enabled and set the output path:
    /// ```sh
    /// export KAS_WGPU_TRACE_PATH="api_trace"
    /// ```
    ///
    /// [API tracing]: https://github.com/gfx-rs/wgpu/wiki/Debugging-wgpu-Applications#tracing-infrastructure
    pub fn from_env() -> Self {
        let mut options = Options::default();

        if let Ok(v) = var("KAS_CONFIG") {
            options.config_path = v.into();
        }

        if let Ok(v) = var("KAS_THEME_CONFIG") {
            options.theme_config_path = v.into();
        }

        if let Ok(mut v) = var("KAS_CONFIG_MODE") {
            v.make_ascii_uppercase();
            options.config_mode = match v.as_str() {
                "READ" => ConfigMode::Read,
                "READWRITE" => ConfigMode::ReadWrite,
                "WRITEDEFAULT" => ConfigMode::WriteDefault,
                other => {
                    log::error!("from_env: bad var KAS_CONFIG_MODE={other}");
                    log::error!("from_env: supported config modes: READ, READWRITE, WRITEDEFAULT");
                    options.config_mode
                }
            };
        }

        if let Ok(v) = var("KAS_FPS_LIMIT") {
            match v.parse::<u32>() {
                Ok(x) => options.fps_limit = NonZeroU32::new(x),
                Err(e) => log::error!("from_env: bad var KAS_FPS_LIMIT={v}: {e}"),
            }
        }

        if let Ok(mut v) = var("KAS_POWER_PREFERENCE") {
            v.make_ascii_uppercase();
            options.power_preference = match v.as_str() {
                "DEFAULT" | "LOWPOWER" => PowerPreference::LowPower,
                "HIGHPERFORMANCE" => PowerPreference::HighPerformance,
                other => {
                    log::error!("from_env: bad var KAS_POWER_PREFERENCE={other}");
                    log::error!(
                        "from_env: supported power modes: DEFAULT, LOWPOWER, HIGHPERFORMANCE"
                    );
                    options.power_preference
                }
            }
        }

        if let Ok(mut v) = var("KAS_BACKENDS") {
            v.make_ascii_uppercase();
            options.backends = match v.as_str() {
                "VULKAN" => Backends::VULKAN,
                "GL" => Backends::GL,
                "METAL" => Backends::METAL,
                "DX11" => Backends::DX11,
                "DX12" => Backends::DX12,
                "BROWSER_WEBGPU" => Backends::BROWSER_WEBGPU,
                "PRIMARY" => Backends::PRIMARY,
                "SECONDARY" => Backends::SECONDARY,
                "FALLBACK" => Backends::empty(),
                other => {
                    log::error!("from_env: bad var KAS_BACKENDS={other}");
                    log::error!("from_env: supported backends: VULKAN, GL, METAL, DX11, DX12, BROWSER_WEBGPU, PRIMARY, SECONDARY, FALLBACK");
                    options.backends
                }
            }
        }

        if let Ok(v) = var("KAS_WGPU_TRACE_PATH") {
            options.wgpu_trace_path = Some(v.into());
        }

        options
    }

    pub(crate) fn adapter_options(&self) -> wgpu::RequestAdapterOptions {
        wgpu::RequestAdapterOptions {
            power_preference: self.power_preference,
            force_fallback_adapter: self.backends.is_empty(),
            compatible_surface: None,
        }
    }

    pub(crate) fn backend(&self) -> Backends {
        if self.backends.is_empty() {
            Backends::all()
        } else {
            self.backends
        }
    }

    /// Load/save theme config on start
    pub fn init_theme_config<DS: DrawSharedImpl, T: Theme<DS>>(
        &self,
        theme: &mut T,
    ) -> Result<(), Error> {
        match self.config_mode {
            ConfigMode::Read | ConfigMode::ReadWrite if self.theme_config_path.is_file() => {
                let config: T::Config =
                    kas::config::Format::guess_and_read_path(&self.theme_config_path)?;
                config.apply_startup();
                // Ignore TkAction: UI isn't built yet
                let _ = theme.apply_config(&config);
            }
            ConfigMode::WriteDefault if !self.theme_config_path.as_os_str().is_empty() => {
                let config = theme.config();
                config.apply_startup();
                kas::config::Format::guess_and_write_path(
                    &self.theme_config_path,
                    config.as_ref(),
                )?;
            }
            _ => theme.config().apply_startup(),
        }
        Ok(())
    }

    /// Load/save KAS config on start
    pub fn read_config(&self) -> Result<kas::event::Config, Error> {
        if !self.config_path.as_os_str().is_empty() {
            match self.config_mode {
                ConfigMode::Read | ConfigMode::ReadWrite => {
                    Ok(kas::config::Format::guess_and_read_path(&self.config_path)?)
                }
                ConfigMode::WriteDefault => {
                    let config: kas::event::Config = Default::default();
                    kas::config::Format::guess_and_write_path(&self.config_path, &config)?;
                    Ok(config)
                }
            }
        } else {
            Ok(Default::default())
        }
    }

    /// Save all config (on exit or after changes)
    pub fn write_config<DS: DrawSharedImpl, T: Theme<DS>>(
        &self,
        config: &kas::event::Config,
        theme: &T,
    ) -> Result<(), Error> {
        if self.config_mode == ConfigMode::ReadWrite {
            if !self.config_path.as_os_str().is_empty() && config.is_dirty() {
                kas::config::Format::guess_and_write_path(&self.config_path, &config)?;
            }
            let theme_config = theme.config();
            if !self.theme_config_path.as_os_str().is_empty() && theme_config.is_dirty() {
                kas::config::Format::guess_and_write_path(
                    &self.theme_config_path,
                    theme_config.as_ref(),
                )?;
            }
        }
        Ok(())
    }
}