use std::{
    collections::{BTreeSet, HashMap},
    fs,
    path::{Path, PathBuf},
};

use anyhow::{Context, Result, bail};
use clap::ValueEnum;
use esp_metadata::Chip;
use serde::Deserialize;
use strum::IntoEnumIterator as _;

use crate::windows_safe_path;

/// A single, configured example (or test).
#[derive(Debug, Clone)]
pub struct Metadata {
    example_path: PathBuf,
    chip: Chip,
    configuration_name: String,
    features: Vec<String>,
    tag: Option<String>,
    description: Option<String>,
    env_vars: HashMap<String, String>,
    cargo_config: Vec<String>,
}

impl Metadata {
    /// Absolute path to the example.
    pub fn example_path(&self) -> &Path {
        &self.example_path
    }

    /// Name of the example.
    pub fn binary_name(&self) -> String {
        self.example_path()
            .file_name()
            .unwrap()
            .to_string_lossy()
            .replace(".rs", "")
    }

    /// Name of the example, including the name of the configuration.
    pub fn output_file_name(&self) -> String {
        if self.configuration_name.is_empty() {
            self.binary_name()
        } else {
            format!("{}_{}", self.binary_name(), self.configuration_name)
        }
    }

    /// The name of the configuration.
    pub fn configuration(&self) -> &str {
        &self.configuration_name
    }

    /// Name of the example, including the name of the configuration.
    pub fn name_with_configuration(&self) -> String {
        if self.configuration_name.is_empty() {
            self.binary_name()
        } else {
            format!("{} ({})", self.binary_name(), self.configuration_name)
        }
    }

    /// A list of all features required for building a given example.
    pub fn feature_set(&self) -> &[String] {
        &self.features
    }

    /// A list of all env vars to build a given example.
    pub fn env_vars(&self) -> &HashMap<String, String> {
        &self.env_vars
    }

    /// A list of all cargo `--config` values to use.
    pub fn cargo_config(&self) -> &[String] {
        &self.cargo_config
    }

    /// If the specified chip is in the list of chips, then it is supported.
    pub fn supports_chip(&self, chip: Chip) -> bool {
        self.chip == chip
    }

    /// Optional tag of the example.
    pub fn tag(&self) -> Option<String> {
        self.tag.clone()
    }

    /// Optional description of the example.
    pub fn description(&self) -> Option<String> {
        self.description.clone()
    }

    /// Check if the example matches the given filter.
    pub fn matches(&self, filter: Option<&str>) -> bool {
        let Some(filter) = filter else {
            return false;
        };

        filter == self.binary_name() || filter == self.output_file_name()
    }

    /// Check if the example matches the given name (case insensitive).
    pub fn matches_name(&self, name: &str) -> bool {
        name.to_lowercase() == self.binary_name() || name.to_lowercase() == self.output_file_name()
    }
}

/// A single configuration of an example, as parsed from metadata lines.
#[derive(Debug, Default, Clone)]
pub struct Configuration {
    chips: Vec<Chip>,
    name: String,
    cargo_config: Vec<String>,
    features: Vec<String>,
    esp_config: HashMap<String, String>,
    tag: Option<String>,
}

struct ConfigurationCollector<'a> {
    configurations: &'a mut HashMap<String, Configuration>,
    all_configurations: &'a mut Configuration,
    meta_line: &'a MetaLine,
}

impl ConfigurationCollector<'_> {
    fn apply(&mut self, callback: impl Fn(&mut Configuration)) {
        if self.meta_line.config_names.is_empty() {
            callback(self.all_configurations);
        } else {
            for config_name in &self.meta_line.config_names {
                let meta = self
                    .configurations
                    .entry(config_name.clone())
                    .or_insert_with(|| Configuration {
                        name: config_name.clone(),
                        ..Configuration::default()
                    });
                callback(meta);
            }
        }
    }
}

struct MetaLine {
    key: String,
    config_names: Vec<String>,
    value: String,
}

/// Parse a metadata line from an example file.
///
/// Metadata lines come in the form of:
///
/// - `//% METADATA_KEY: value` or
/// - `//% METADATA_KEY(config_name_1, config_name_2, ...): value`.
fn parse_meta_line(line: &str) -> anyhow::Result<MetaLine> {
    let Some((key, value)) = line.trim_start_matches("//%").split_once(':') else {
        bail!("Metadata line is missing ':': {}", line);
    };

    let (key, config_names) = if let Some((key, config_names)) = key.split_once('(') {
        let config_names = config_names
            .trim_end_matches(')')
            .split(',')
            .map(str::trim)
            .map(ToString::to_string)
            .collect();
        (key.trim(), config_names)
    } else {
        (key, Vec::new())
    };

    let key = key.trim();
    let value = value.trim();

    Ok(MetaLine {
        key: key.to_string(),
        config_names,
        value: value.to_string(),
    })
}

/// Load all examples at the given path, and parse their metadata.
pub fn load(path: &Path) -> Result<Vec<Metadata>> {
    let mut examples = Vec::new();

    for entry in fs::read_dir(path).context("Failed to read {path}")? {
        log::debug!("Loading example from path: {}", path.display());
        let path = windows_safe_path(&entry?.path());
        let text = fs::read_to_string(&path)
            .with_context(|| format!("Could not read {}", path.display()))?;

        let description = parse_description(&text);

        // When the list of configuration names is missing, the metadata is applied to
        // all configurations. Each configuration encountered will create a
        // separate Metadata entry. Different metadata lines referring to the
        // same configuration will be merged.
        //
        // If there are no named configurations, an unnamed default is created.
        let mut all_configuration = Configuration {
            chips: Chip::iter().collect::<Vec<_>>(),
            ..Configuration::default()
        };

        let mut configurations = HashMap::<String, Configuration>::new();

        // Unless specified, an example is assumed to be valid for all chips.
        for (line_no, line) in text
            .lines()
            .enumerate()
            .filter(|(_, line)| line.starts_with("//%"))
        {
            let meta_line = parse_meta_line(line)
                .with_context(|| format!("Failed to parse line {}", line_no + 1))?;

            let mut relevant_metadata = ConfigurationCollector {
                configurations: &mut configurations,
                all_configurations: &mut all_configuration,
                meta_line: &meta_line,
            };

            match meta_line.key.as_str() {
                // A list of chips that can run the example using the current configuration.
                "CHIPS" => {
                    let chips = meta_line
                        .value
                        .split_ascii_whitespace()
                        .map(|s| Chip::from_str(s, false).unwrap())
                        .collect::<Vec<_>>();
                    relevant_metadata.apply(|meta| meta.chips = chips.clone());
                }
                // A list of cargo `--config` configurations.
                "CARGO-CONFIG" => {
                    relevant_metadata
                        .apply(|meta| meta.cargo_config.push(meta_line.value.to_string()));
                }
                // Cargo features to enable for the current configuration.
                "FEATURES" => {
                    let mut values = meta_line
                        .value
                        .split_ascii_whitespace()
                        .map(ToString::to_string)
                        .collect::<Vec<_>>();

                    // Sort the features so they are in a deterministic order:
                    values.sort();

                    relevant_metadata.apply(|meta| meta.features.extend_from_slice(&values));
                }
                // esp-config env vars, one per line
                "ENV" => {
                    let (env_var, value) = meta_line
                        .value
                        .split_once('=')
                        .with_context(|| "CONFIG metadata must be in the form 'CONFIG=VALUE'")?;

                    let env_var = env_var.trim();
                    let value = value.trim();

                    relevant_metadata.apply(|meta| {
                        meta.esp_config
                            .insert(env_var.to_string(), value.to_string());
                    });
                }
                // Tags by which the user can filter examples.
                "TAG" => {
                    relevant_metadata.apply(|meta| meta.tag = Some(meta_line.value.to_string()));
                }
                key => log::warn!("Unrecognized metadata key '{key}', ignoring"),
            }
        }

        // Merge "all" into configurations
        for meta in configurations.values_mut() {
            // Chips is a filter, inherit if empty
            if meta.chips.is_empty() {
                meta.chips = all_configuration.chips.clone();
            }

            // Tag is an ID, inherit if empty
            if meta.tag.is_none() {
                meta.tag = all_configuration.tag.clone();
            }

            // Other values are merged
            meta.features.extend_from_slice(&all_configuration.features);
            meta.esp_config.extend(all_configuration.esp_config.clone());
            meta.cargo_config
                .extend(all_configuration.cargo_config.clone());
        }

        // If no configurations are specified, fall back to the unnamed one. Otherwise
        // ignore it, it has been merged into the others.
        if configurations.is_empty() {
            configurations.insert(String::new(), all_configuration);
        }

        // Generate metadata

        for configuration in configurations.values_mut() {
            // Sort the features so they are in a deterministic order:
            configuration.features.sort();

            for chip in &configuration.chips {
                examples.push(Metadata {
                    // File properties
                    example_path: path.clone(),
                    description: description.clone(),

                    // Configuration
                    chip: *chip,
                    configuration_name: configuration.name.clone(),
                    features: configuration.features.clone(),
                    tag: configuration.tag.clone(),
                    env_vars: configuration.esp_config.clone(),
                    cargo_config: configuration.cargo_config.clone(),
                })
            }
        }
    }

    // Sort by feature set, to prevent rebuilding packages if not necessary.
    examples.sort_by_key(|e| e.feature_set().join(","));

    Ok(examples)
}

#[derive(Debug, Deserialize)]
struct CargoToml {
    features: HashMap<String, Vec<String>>,
}

/// Load all examples by finding all packages in the given path, and parsing their metadata.
pub fn load_cargo_toml(examples_path: &Path) -> Result<Vec<Metadata>> {
    let mut examples = Vec::new();

    let mut packages = crate::find_packages(examples_path)?;
    packages.sort();

    for package_path in packages {
        log::debug!("Loading package from path: {}", package_path.display());
        let cargo_toml_path = package_path.join("Cargo.toml");
        let main_rs_path = package_path.join("src").join("main.rs");

        if !cargo_toml_path.exists() || !main_rs_path.exists() {
            continue;
        }

        let text = fs::read_to_string(&main_rs_path)?;
        let description = parse_description(&text);

        let toml = fs::read_to_string(&cargo_toml_path)?;
        let toml: CargoToml = toml_edit::de::from_str(&toml)?;

        let chips = toml
            .features
            .keys()
            .map(|chip| Chip::from_str(&chip, true).unwrap())
            .collect::<BTreeSet<_>>();

        for chip in chips {
            examples.push(Metadata {
                example_path: package_path.clone(),
                chip,
                configuration_name: String::new(),
                features: vec![],
                tag: None,
                description: description.clone(),
                env_vars: HashMap::new(),
                cargo_config: Vec::new(),
            });
        }
    }

    Ok(examples)
}

fn parse_description(text: &str) -> Option<String> {
    let mut description = None;

    for line in text.lines().filter(|line| line.starts_with("//!")) {
        let line = line.trim_start_matches("//!");
        let mut descr: String = description.unwrap_or_default();
        descr.push_str(line);
        descr.push('\n');
        description = Some(descr);
    }

    log::debug!("Parsed description: {:?}", description);

    description
}