//
use crate as git;
use git_next_config as config;

use tracing::{error, info, warn};

pub type Result<T> = core::result::Result<T, Error>;

#[derive(Debug)]
pub struct Positions {
    pub main: git::Commit,
    pub next: git::Commit,
    pub dev: git::Commit,
    pub dev_commit_history: Vec<git::Commit>,
}

#[allow(clippy::cognitive_complexity)] // TODO: (#83) reduce complexity
pub fn validate_positions(
    repository: &git::OpenRepository,
    repo_details: &git::RepoDetails,
    repo_config: config::RepoConfig,
) -> Result<Positions> {
    let main_branch = repo_config.branches().main();
    let next_branch = repo_config.branches().next();
    let dev_branch = repo_config.branches().dev();
    // Collect Commit Histories for `main`, `next` and `dev` branches
    repository.fetch()?;
    let commit_histories =
        get_commit_histories(repository, &repo_config).map_err(Error::CommitLog)?;
    // branch tips
    let main = commit_histories
        .main
        .first()
        .cloned()
        .ok_or_else(|| Error::BranchHasNoCommits(main_branch.clone()))?;
    let next = commit_histories
        .next
        .first()
        .cloned()
        .ok_or_else(|| Error::BranchHasNoCommits(next_branch.clone()))?;
    let dev = commit_histories
        .dev
        .first()
        .cloned()
        .ok_or_else(|| Error::BranchHasNoCommits(dev_branch.clone()))?;
    // Validations:
    // Dev must be on main branch, else the USER must rebase it
    if is_not_based_on(&commit_histories.dev, &main) {
        warn!("Dev '{dev_branch}' not based on main '{main_branch}' - user must rebase",);
        return Err(Error::DevBranchNotBasedOn {
            dev: dev_branch,
            other: main_branch,
        });
    }
    // verify that next is on main or at most one commit on top of main, else reset it back to main
    if is_not_based_on(&commit_histories.next[0..=1], &main) {
        info!("Main not on same commit as next, or it's parent - resetting next to main",);
        return reset_next_to_main(repository, repo_details, &main, &next, &next_branch);
    }
    // verify that next is an ancestor of dev, else reset it back to main
    if is_not_based_on(&commit_histories.dev, &next) {
        info!("Next is not an ancestor of dev - resetting next to main");
        return reset_next_to_main(repository, repo_details, &main, &next, &next_branch);
    }

    Ok(git::validation::positions::Positions {
        main,
        next,
        dev,
        dev_commit_history: commit_histories.dev,
    })
}

fn reset_next_to_main(
    repository: &crate::OpenRepository,
    repo_details: &crate::RepoDetails,
    main: &crate::Commit,
    next: &crate::Commit,
    next_branch: &config::BranchName,
) -> Result<Positions> {
    git::push::reset(
        repository,
        repo_details,
        next_branch,
        &main.clone().into(),
        &git::push::Force::From(next.clone().into()),
    )
    .map_err(|err| {
        warn!(?err, "Failed to reset next to main");
        Error::FailedToResetBranch {
            branch: next_branch.clone(),
            commit: next.clone(),
        }
    })?;
    Err(Error::NextBranchResetRequired(next_branch.clone()))
}

fn is_not_based_on(commits: &[crate::commit::Commit], needle: &crate::Commit) -> bool {
    commits.iter().filter(|commit| *commit == needle).count() == 0
}

fn get_commit_histories(
    repository: &git::repository::OpenRepository,
    repo_config: &config::RepoConfig,
) -> git::commit::log::Result<git::commit::Histories> {
    let main = (repository.commit_log(&repo_config.branches().main(), &[]))?;
    let main_head = [main[0].clone()];
    let next = repository.commit_log(&repo_config.branches().next(), &main_head)?;
    let dev = repository.commit_log(&repo_config.branches().dev(), &main_head)?;
    let histories = git::commit::Histories { main, next, dev };
    Ok(histories)
}

#[derive(Debug, thiserror::Error)]
pub enum Error {
    #[error("fetch: {0}")]
    Fetch(#[from] git::fetch::Error),

    #[error("commit log: {0}")]
    CommitLog(#[from] git::commit::log::Error),

    #[error("failed to reset branch '{branch}' to {commit}")]
    FailedToResetBranch {
        branch: config::BranchName,
        commit: git::Commit,
    },

    #[error("next branch '{0}' needs to be reset")]
    NextBranchResetRequired(config::BranchName),

    #[error("branch '{0}' has no commits")]
    BranchHasNoCommits(config::BranchName),

    #[error("dev branch '{dev}' not based on branch '{other}' ")]
    DevBranchNotBasedOn {
        dev: config::BranchName,
        other: config::BranchName,
    },
}