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use std::time::SystemTime;

use anyhow::{anyhow, Context, Result};
use cargo_metadata::Metadata;
use chrono::{DateTime, NaiveDateTime, Utc};
use git2::Repository;
use semver::Version;

pub struct BuildContext {
    pub git_repository: Repository,
    pub cargo_metadata: Metadata,
    pub git_sha: String,
    pub git_latest_version: Option<Version>,
    pub git_commit_timestamp: Option<DateTime<Utc>>,
    pub cargo_version: Version,
}

impl BuildContext {
    pub fn dev_version(&self) -> Result<Version> {
        let timestamp: DateTime<Utc> = self
            .git_commit_timestamp
            .unwrap_or_else(|| SystemTime::now().into());
        let timestamp_formatted = timestamp.format("%Y%m%d%H%M%S");

        let dev_version = format!(
            "{}-dev.{}+{}",
            self.cargo_version, timestamp_formatted, self.git_sha
        );

        Version::parse(&dev_version).with_context(|| "Failed to generate valid dev version.")
    }
}

pub fn load_build_context() -> Result<BuildContext> {
    let mut cmd = cargo_metadata::MetadataCommand::new();
    cmd.manifest_path("./Cargo.toml");
    let cargo_metadata = cmd
        .exec()
        .context("Could not find the cargo metadata. Tried ./Cargo.toml")?;

    let git_repository = Repository::open("./")
      .context("Could not find a git repository. Please run from the top-level folder of a git repository.")?;

    let git_sha = get_git_sha(&git_repository)?;
    let git_latest_version = get_git_latest_version(&git_repository)?;
    let cargo_version = get_cargo_version(&cargo_metadata)?;
    let git_commit_timestamp = get_git_commit_timestamp(&git_repository).ok();

    let build_context = BuildContext {
        git_repository,
        cargo_metadata,
        git_sha,
        git_latest_version,
        git_commit_timestamp,
        cargo_version,
    };

    Ok(build_context)
}

fn get_git_sha(git_repository: &Repository) -> Result<String> {
    let mut sha = git_repository
        .head()?
        .target()
        .ok_or_else(|| anyhow!("Could not determin git commit SHA!"))?
        .to_string();
    sha.truncate(7);

    Ok(sha)
}

fn get_git_latest_version(git_repository: &Repository) -> Result<Option<Version>> {
    let mut tags: Vec<Version> = git_repository
        .tag_names(Some("v*"))?
        .into_iter()
        .flatten()
        .flat_map(|v| v.strip_prefix('v'))
        .flat_map(semver::Version::parse)
        .collect();
    tags.sort();
    tags.reverse();

    let current_release_version = tags.first().cloned();

    Ok(current_release_version)
}

fn get_git_commit_timestamp(git_repository: &Repository) -> Result<DateTime<Utc>> {
    let head_ref = git_repository.find_reference("HEAD")?;
    let head_direct = head_ref.resolve()?;
    let head_refspec = head_direct.name().expect("invalid name");
    let head_oid = git_repository.refname_to_id(head_refspec)?;
    let commit = git_repository.find_commit(head_oid)?;
    let commit_timestamp = commit.time().seconds();
    let timestamp: DateTime<Utc> =
        DateTime::<Utc>::from_utc(NaiveDateTime::from_timestamp(commit_timestamp, 0), Utc);

    Ok(timestamp)
}

fn get_cargo_version(cargo_metadata: &Metadata) -> Result<Version> {
    // TODO: handle cargo workspaces correctly.
    let root = cargo_metadata.workspace_members.first().unwrap();
    let package = cargo_metadata
        .packages
        .iter()
        .find(|p| p.id == *root)
        .ok_or_else(|| anyhow!("Could not determine cargo package version."))?;
    Ok(package.version.clone())
}