//! Determines how version info is generated for pairs of game and loader
//! versions.
//!
//! When a user installs a version of the game, they install two things: the
//! game (of some specific version), and a loader (of some other specific
//! version). Each combination of game and loader version requires a specific
//! configuration, like a specific set of libraries that must be downloaded and
//! run along with the game. However, some versions of the game or loader may
//! change configuration requirements without the other version being affected.
//! For example, pre-26.x game versions with Quilt require the Quilt `hashed`
//! libraries to also be downloaded. However, 26.x and later don't require the
//! `hashed` libraries, and don't even have a download for them. The problem is
//! that Quilt loader 0.30.0 can be used for both pre-26.x and 26.x - but our v0
//! manifest files can't differentiate the two. The result is that you either
//! break compatibility for 0.30.0 game versions pre-26.x, or break 0.30.0
//! on 26.x and later.
//!
//! To fix this, v1 introduces the concept of *version groups*: game versions
//! before 26.x are version group v1, and 26.x and later are v2. Then, we
//! parameterize our version info on both version group and loader version,
//! letting us specify the right configuration based on both game version and
//! loader version.
//!
//! Why not parameterize on game version and loader version directly? Most game
//! versions have the same configuration as their surrounding game versions, so
//! we'd end up with many duplicate configurations: the number of game versions
//! multiplied by the number of loader versions.
//!
//! This file lets you configure what game versions are grouped together.
//!
//! Each version group is templated from a specific game version - e.g. game
//! version 1.21 is used as the template file for 1.20, 1.19, etc.

pub const UNIVERSAL_METADATA_GROUP: &str = "universal";
pub const QUILT_LEGACY_METADATA_GROUP: &str = "v1";
pub const QUILT_MODERN_METADATA_GROUP: &str = "v2";

pub struct MetadataGroup {
    pub id: &'static str,
    /// Minecraft version used to fetch and template this group's loader profiles.
    pub loader_profile_template_game_version: String,
    pub game_versions: Vec<String>,
}

pub fn metadata_groups<'a>(
    mod_loader: &str,
    game_versions: impl IntoIterator<Item = &'a str>,
) -> Vec<MetadataGroup> {
    // Non-Quilt loaders don't need the concept of version groups, so we just
    // make one "universal" group, and template it on 1.21.
    if mod_loader != "quilt" {
        return vec![MetadataGroup {
            id: UNIVERSAL_METADATA_GROUP,
            loader_profile_template_game_version: "1.21".to_string(),
            game_versions: game_versions
                .into_iter()
                .map(|x| x.to_string())
                .collect(),
        }];
    }

    let game_versions = game_versions.into_iter().collect::<Vec<_>>();
    let legacy_game_versions = game_versions
        .iter()
        .copied()
        .filter(|game_version| {
            metadata_group_id_for_game_version(mod_loader, game_version)
                == QUILT_LEGACY_METADATA_GROUP
        })
        .collect::<Vec<_>>();
    let modern_game_versions = game_versions
        .iter()
        .copied()
        .filter(|game_version| {
            metadata_group_id_for_game_version(mod_loader, game_version)
                == QUILT_MODERN_METADATA_GROUP
        })
        .collect::<Vec<_>>();

    let mut groups = Vec::new();

    if !legacy_game_versions.is_empty() {
        groups.push(MetadataGroup {
            id: QUILT_LEGACY_METADATA_GROUP,
            loader_profile_template_game_version: legacy_game_versions
                .iter()
                .find(|x| **x == "1.21")
                .copied()
                .unwrap_or(legacy_game_versions[0])
                .to_string(),
            game_versions: legacy_game_versions
                .iter()
                .map(|x| x.to_string())
                .collect(),
        });
    }

    if !modern_game_versions.is_empty() {
        groups.push(MetadataGroup {
            id: QUILT_MODERN_METADATA_GROUP,
            loader_profile_template_game_version: modern_game_versions[0]
                .to_string(),
            game_versions: modern_game_versions
                .iter()
                .map(|x| x.to_string())
                .collect(),
        });
    }

    groups
}

pub fn metadata_group_for_game_version<'a>(
    groups: &'a [MetadataGroup],
    mod_loader: &str,
    game_version: &str,
) -> Option<&'a MetadataGroup> {
    let group_id = metadata_group_id_for_game_version(mod_loader, game_version);

    groups.iter().find(|group| group.id == group_id)
}

fn metadata_group_id_for_game_version(
    mod_loader: &str,
    game_version: &str,
) -> &'static str {
    if mod_loader == "quilt" && is_modern_quilt_game_version(game_version) {
        QUILT_MODERN_METADATA_GROUP
    } else if mod_loader == "quilt" {
        QUILT_LEGACY_METADATA_GROUP
    } else {
        UNIVERSAL_METADATA_GROUP
    }
}

// Update these Quilt group boundaries if upstream loader profiles gain another
// structural incompatibility between Minecraft versions.
fn is_modern_quilt_game_version(game_version: &str) -> bool {
    let major = game_version
        .split(['.', 'w'])
        .next()
        .and_then(|x| x.parse::<usize>().ok());

    major.is_some_and(|x| x >= 26)
}