use argon2::{
    Argon2, PasswordHash, PasswordVerifier,
    password_hash::{PasswordHasher, SaltString, rand_core::OsRng},
};
use rand_core::RngCore;
use sha2::{Digest, Sha256};

use crate::{
    app::AppState,
    db::{NewRepository, NewUser},
    error::{AppError, AppResult},
    git,
    models::{
        AccessMode, AccessTokenResponse, Branch, CollaboratorResponse, CompareCommit,
        CompareFile, CompareRequest, CompareResponse, CreateAccessTokenRequest,
        CreateAccessTokenResponse, CreatePullRequestRequest, CreateRepositoryRequest,
        CreateUserRequest, ForkRepositoryRequest, LoginRequest, LoginResponse,
        MergePullRequestRequest, PullRequest, PullRequestDetailResponse, PullRequestResponse,
        PullRequestStatus, RepositoryPermission, RepositoryWithOwner, UpsertCollaboratorRequest,
        User,
    },
    repox,
};

const TOKEN_TTL_DAYS: i64 = 365;
const MAX_PER_PAGE: i64 = 100;

pub fn create_user(state: &AppState, req: CreateUserRequest) -> AppResult<User> {
    validate_user_name(&req.username)?;
    validate_email(&req.email)?;
    if req.password.len() < 8 {
        return Err(AppError::Validation(
            "password must be at least 8 characters".to_string(),
        ));
    }

    let salt = SaltString::generate(&mut OsRng);
    let password_hash = Argon2::default()
        .hash_password(req.password.as_bytes(), &salt)
        .map_err(|err| AppError::Validation(format!("password hashing failed: {err}")))?
        .to_string();

    state.db.create_user(NewUser {
        username: &req.username,
        full_name: &req.full_name,
        email: &req.email,
        password_hash: &password_hash,
        is_active: req.is_active,
        is_admin: req.is_admin,
    })
}

pub fn get_user(state: &AppState, username: &str) -> AppResult<User> {
    state
        .db
        .get_user_by_username(username)?
        .ok_or_else(|| AppError::NotFound(format!("user not found: {username}")))
}

pub fn should_allow_bootstrap_admin(state: &AppState) -> AppResult<bool> {
    Ok(state.db.user_count()? == 0)
}

pub fn login(state: &AppState, req: LoginRequest) -> AppResult<LoginResponse> {
    let user = authenticate_password(state, &req.login, &req.password)?;
    let token = issue_login_access_token(state, user.id)?;

    Ok(LoginResponse {
        token: token.token,
        user,
    })
}

fn issue_login_access_token(state: &AppState, user_id: i64) -> AppResult<CreateAccessTokenResponse> {
    let token = random_token();
    let token_hash = hash_token(&token);
    let record = state.db.replace_access_token(user_id, "login", &token_hash)?;

    Ok(CreateAccessTokenResponse {
        id: record.id,
        name: record.name,
        token,
        created_unix: record.created_unix,
        updated_unix: record.updated_unix,
    })
}

pub fn issue_access_token(
    state: &AppState,
    user_id: i64,
    req: CreateAccessTokenRequest,
) -> AppResult<CreateAccessTokenResponse> {
    if req.name.trim().is_empty() {
        return Err(AppError::Validation(
            "token name cannot be empty".to_string(),
        ));
    }

    let token = random_token();
    let token_hash = hash_token(&token);
    let record = state
        .db
        .create_access_token(user_id, req.name.trim(), &token_hash)?;

    Ok(CreateAccessTokenResponse {
        id: record.id,
        name: record.name,
        token,
        created_unix: record.created_unix,
        updated_unix: record.updated_unix,
    })
}

pub fn list_access_tokens(
    state: &AppState,
    user_id: i64,
    page: i64,
    per_page: i64,
) -> AppResult<Vec<AccessTokenResponse>> {
    let (limit, offset) = pagination(page, per_page);
    let tokens = state.db.list_access_tokens_by_user(user_id, limit, offset)?;
    Ok(tokens
        .into_iter()
        .map(|token| AccessTokenResponse {
            id: token.id,
            name: token.name,
            created_unix: token.created_unix,
            updated_unix: token.updated_unix,
        })
        .collect())
}

pub fn delete_access_token(state: &AppState, user_id: i64, token_id: i64) -> AppResult<()> {
    if state.db.delete_access_token_by_id(user_id, token_id)? {
        return Ok(());
    }
    Err(AppError::NotFound(format!(
        "access token not found: {token_id}"
    )))
}

pub fn authenticate_token(state: &AppState, bearer_token: &str) -> AppResult<User> {
    let token_hash = hash_token(bearer_token);
    let token = state
        .db
        .get_access_token_by_hash(&token_hash)?
        .ok_or_else(|| AppError::Unauthorized("invalid access token".to_string()))?;

    if is_token_expired(&token) {
        return Err(AppError::Unauthorized("access token expired".to_string()));
    }

    if let Err(err) = state.db.touch_access_token(token.id) {
        eprintln!("warning: touch_access_token({}) failed: {err}", token.id);
    }
    let user = state
        .db
        .get_user_by_id(token.user_id)?
        .ok_or_else(|| AppError::Unauthorized("token owner not found".to_string()))?;

    if !user.is_active {
        return Err(AppError::Unauthorized("inactive user".to_string()));
    }

    Ok(user)
}

pub fn authenticate_http_basic(state: &AppState, login: &str, secret: &str) -> AppResult<User> {
    match login_with_password(state, login, secret) {
        Ok(user) => Ok(user),
        Err(AppError::Unauthorized(_)) => {
            authenticate_token(state, secret).or_else(|_| authenticate_token(state, login))
        }
        Err(err) => Err(err),
    }
}

pub fn create_repository(
    state: &AppState,
    owner: &User,
    req: CreateRepositoryRequest,
) -> AppResult<RepositoryWithOwner> {
    validate_repo_name(&req.name)?;

    let repo_path = repox::repository_path(&state.config.repository.root, &owner.name, &req.name);
    if repo_path.exists() {
        return Err(AppError::Conflict(format!(
            "repository directory already exists: {}",
            repo_path.display()
        )));
    }

    let repo = state.db.create_repository(NewRepository {
        owner_id: owner.id,
        owner_name: &owner.name,
        name: &req.name,
        description: &req.description,
        default_branch: &state.config.repository.default_branch,
        is_private: req.is_private,
        is_bare: !req.auto_init,
        is_fork: false,
        fork_id: 0,
    })?;

    if let Err(err) = git::init_bare_repo_with_binary(
        &state.config.repository.git_binary,
        &repo_path,
        &state.config.repository.default_branch,
    ) {
        let _ = std::fs::remove_dir_all(&repo_path);
        let _ = state.db.delete_repository_by_id(repo.id);
        return Err(err);
    }

    if req.auto_init {
        let readme = format!("# {}\n", req.name);
        if let Err(err) = git::create_initial_commit_with_binary(
            &state.config.repository.git_binary,
            &repo_path,
            &state.config.repository.default_branch,
            &readme,
            &owner.name,
            &owner.email,
        ) {
            let _ = std::fs::remove_dir_all(&repo_path);
            let _ = state.db.delete_repository_by_id(repo.id);
            return Err(err);
        }
    }

    Ok(RepositoryWithOwner {
        repo,
        owner: owner.clone(),
    })
}

pub fn fork_repository(
    state: &AppState,
    acting_user: &User,
    base_owner_name: &str,
    base_repo_name: &str,
    req: ForkRepositoryRequest,
) -> AppResult<RepositoryWithOwner> {
    let base_repo = get_repository(state, base_owner_name, base_repo_name)?;
    ensure_repo_access(state, Some(acting_user), &base_repo, AccessMode::Read)?;
    if acting_user.id == base_repo.owner.id {
        return Err(AppError::Validation(
            "cannot fork to the same owner".to_string(),
        ));
    }
    if state.db.has_forked_by(base_repo.repo.id, acting_user.id)? {
        return Err(AppError::Conflict(
            "repository already forked by this user".to_string(),
        ));
    }
    validate_repo_name(&req.name)?;

    let repo = state.db.create_repository(NewRepository {
        owner_id: acting_user.id,
        owner_name: &acting_user.name,
        name: &req.name,
        description: &req.description,
        default_branch: &base_repo.repo.default_branch,
        is_private: base_repo.repo.is_private,
        is_bare: true,
        is_fork: true,
        fork_id: base_repo.repo.id,
    })?;

    let source_repo_path = repox::repository_path(
        &state.config.repository.root,
        &base_repo.owner.name,
        &base_repo.repo.name,
    );
    let target_repo_path =
        repox::repository_path(&state.config.repository.root, &acting_user.name, &req.name);
    if let Err(err) = git::clone_bare_repo_with_binary(
        &state.config.repository.git_binary,
        &source_repo_path,
        &target_repo_path,
    ) {
        let _ = std::fs::remove_dir_all(&target_repo_path);
        let _ = state.db.delete_repository_by_id(repo.id);
        return Err(err);
    }

    Ok(RepositoryWithOwner {
        repo,
        owner: acting_user.clone(),
    })
}

pub fn upsert_collaborator(
    state: &AppState,
    acting_user: &User,
    owner_name: &str,
    repo_name: &str,
    req: UpsertCollaboratorRequest,
) -> AppResult<CollaboratorResponse> {
    let repo = get_repository(state, owner_name, repo_name)?;
    ensure_repo_owner(acting_user, &repo)?;

    let collaborator = get_user(state, &req.username)?;
    if collaborator.id == repo.owner.id {
        return Err(AppError::Validation(
            "repository owner cannot be added as collaborator".to_string(),
        ));
    }

    let mode = AccessMode::parse_permission(&req.permission).ok_or_else(|| {
        AppError::Validation("permission must be one of: read, write, admin".to_string())
    })?;
    state
        .db
        .upsert_collaboration(repo.repo.id, collaborator.id, mode)?;

    Ok(CollaboratorResponse {
        user: collaborator,
        mode,
    })
}

pub fn remove_collaborator(
    state: &AppState,
    acting_user: &User,
    owner_name: &str,
    repo_name: &str,
    collaborator_name: &str,
) -> AppResult<()> {
    let repo = get_repository(state, owner_name, repo_name)?;
    ensure_repo_owner(acting_user, &repo)?;
    let collaborator = get_user(state, collaborator_name)?;
    state.db.delete_collaboration(repo.repo.id, collaborator.id)
}

pub fn list_collaborators(
    state: &AppState,
    requesting_user: Option<&User>,
    owner_name: &str,
    repo_name: &str,
    page: i64,
    per_page: i64,
) -> AppResult<Vec<CollaboratorResponse>> {
    let repo = get_repository(state, owner_name, repo_name)?;
    ensure_repo_readable(state, requesting_user, &repo)?;
    let (limit, offset) = pagination(page, per_page);
    state.db.list_collaborators(repo.repo.id, limit, offset)
}

pub fn get_collaborator(
    state: &AppState,
    requesting_user: Option<&User>,
    owner_name: &str,
    repo_name: &str,
    collaborator_name: &str,
) -> AppResult<CollaboratorResponse> {
    let repo = get_repository(state, owner_name, repo_name)?;
    ensure_repo_readable(state, requesting_user, &repo)?;
    let collaborator = get_user(state, collaborator_name)?;
    state
        .db
        .get_collaborator(repo.repo.id, collaborator.id)?
        .ok_or_else(|| AppError::NotFound(format!("collaborator not found: {collaborator_name}")))
}

pub fn list_repositories_by_owner(
    state: &AppState,
    requesting_user: Option<&User>,
    owner_name: &str,
    query: &str,
    page: i64,
    per_page: i64,
) -> AppResult<Vec<RepositoryWithOwner>> {
    let owner = get_user(state, owner_name)?;
    let (limit, offset) = pagination(page, per_page);
    let repos = state.db.list_repositories_with_owners_by_owner(owner.id, limit, offset)?;
    filter_visible_repositories(state, requesting_user, repos, query)
}

pub fn list_visible_repositories(
    state: &AppState,
    requesting_user: Option<&User>,
    query: &str,
    page: i64,
    per_page: i64,
) -> AppResult<Vec<RepositoryWithOwner>> {
    let (limit, offset) = pagination(page, per_page);
    let repos = state.db.list_repositories_with_owners(limit, offset)?;
    filter_visible_repositories(state, requesting_user, repos, query)
}

pub fn repository_permission(
    state: &AppState,
    requesting_user: Option<&User>,
    repo: &RepositoryWithOwner,
) -> AppResult<RepositoryPermission> {
    let mode = effective_access_mode(state, requesting_user, repo)?;
    Ok(RepositoryPermission {
        mode,
        can_read: (mode as i64) >= (AccessMode::Read as i64),
        can_write: (mode as i64) >= (AccessMode::Write as i64),
        can_admin: (mode as i64) >= (AccessMode::Admin as i64),
        is_owner: mode == AccessMode::Owner,
    })
}

pub fn list_branches(
    state: &AppState,
    requesting_user: Option<&User>,
    owner_name: &str,
    repo_name: &str,
) -> AppResult<Vec<Branch>> {
    let repo = get_repository(state, owner_name, repo_name)?;
    ensure_repo_access(state, requesting_user, &repo, AccessMode::Read)?;

    let repo_path = repox::repository_path(&state.config.repository.root, owner_name, repo_name);
    let branches = git::list_branches_with_binary(&state.config.repository.git_binary, &repo_path)?;
    Ok(branches.into_iter().map(|name| Branch { name }).collect())
}

pub fn create_pull_request(
    state: &AppState,
    acting_user: &User,
    base_owner_name: &str,
    base_repo_name: &str,
    req: CreatePullRequestRequest,
) -> AppResult<PullRequestResponse> {
    if req.title.trim().is_empty() {
        return Err(AppError::Validation(
            "pull request title cannot be empty".to_string(),
        ));
    }

    let base_repo = get_repository(state, base_owner_name, base_repo_name)?;
    ensure_repo_access(state, Some(acting_user), &base_repo, AccessMode::Read)?;

    let base_repo_path = repox::repository_path(
        &state.config.repository.root,
        &base_repo.owner.name,
        &base_repo.repo.name,
    );
    if !git::branch_exists_with_binary(
        &state.config.repository.git_binary,
        &base_repo_path,
        &req.base_branch,
    )? {
        return Err(AppError::NotFound(format!(
            "base branch not found: {}",
            req.base_branch
        )));
    }

    let head_repo = get_repository(state, &req.head_owner, &req.head_repo)?;
    let same_repo = head_repo.repo.id == base_repo.repo.id;
    if same_repo && req.head_branch == req.base_branch {
        return Err(AppError::Validation(
            "head and base branch cannot be the same".to_string(),
        ));
    }
    if !same_repo && (!head_repo.repo.is_fork || head_repo.repo.fork_id != base_repo.repo.id) {
        return Err(AppError::NotFound(
            "head repository is not a fork of base repository".to_string(),
        ));
    }

    ensure_repo_access(state, Some(acting_user), &head_repo, AccessMode::Write)?;

    let head_repo_path = repox::repository_path(
        &state.config.repository.root,
        &head_repo.owner.name,
        &head_repo.repo.name,
    );
    if !git::branch_exists_with_binary(
        &state.config.repository.git_binary,
        &head_repo_path,
        &req.head_branch,
    )? {
        return Err(AppError::NotFound(format!(
            "head branch not found: {}",
            req.head_branch
        )));
    }

    if state
        .db
        .get_unmerged_pull_request(
            head_repo.repo.id,
            base_repo.repo.id,
            &req.head_branch,
            &req.base_branch,
        )?
        .is_some()
    {
        return Err(AppError::Conflict(
            "an open pull request already exists for this head/base branch pair".to_string(),
        ));
    }

    let merge_base = git::merge_base_with_binary(
        &state.config.repository.git_binary,
        &base_repo_path,
        &req.base_branch,
        &head_repo_path,
        &req.head_branch,
    )?;
    if merge_base.is_empty() {
        return Err(AppError::Validation(
            "no merge base between branches".to_string(),
        ));
    }
    let status = if git::test_merge_with_binary(
        &state.config.repository.git_binary,
        &base_repo_path,
        &req.base_branch,
        &head_repo_path,
        &req.head_branch,
    )? {
        PullRequestStatus::Mergeable
    } else {
        PullRequestStatus::Conflict
    };

    let pull_request = state.db.create_pull_request(crate::db::NewPullRequest {
        title: req.title.trim(),
        body: req.body.trim(),
        status,
        head_repo_id: head_repo.repo.id,
        base_repo_id: base_repo.repo.id,
        head_user_name: head_repo.owner.name.as_str(),
        head_branch: req.head_branch.as_str(),
        base_branch: req.base_branch.as_str(),
        merge_base: merge_base.as_str(),
        poster_id: acting_user.id,
    })?;

    Ok(PullRequestResponse {
        pull_request,
        head_repo,
        base_repo,
    })
}

pub fn merge_pull_request(
    state: &AppState,
    acting_user: &User,
    base_owner_name: &str,
    base_repo_name: &str,
    index: i64,
    req: MergePullRequestRequest,
) -> AppResult<PullRequestResponse> {
    let base_repo = get_repository(state, base_owner_name, base_repo_name)?;
    ensure_repo_access(state, Some(acting_user), &base_repo, AccessMode::Write)?;

    let pull = state
        .db
        .get_pull_request_by_base_repo_and_index(base_repo.repo.id, index)?
        .ok_or_else(|| AppError::NotFound(format!("pull request not found: {index}")))?;
    if pull.has_merged || pull.is_closed {
        return Err(AppError::Conflict(
            "pull request is already closed".to_string(),
        ));
    }
    if pull.status != PullRequestStatus::Mergeable {
        return Err(AppError::Conflict(
            "pull request cannot be merged automatically".to_string(),
        ));
    }

    let head_repo = get_repository_by_id(state, pull.head_repo_id)?;
    let base_repo_path = repox::repository_path(
        &state.config.repository.root,
        &base_repo.owner.name,
        &base_repo.repo.name,
    );
    let head_repo_path = repox::repository_path(
        &state.config.repository.root,
        &head_repo.owner.name,
        &head_repo.repo.name,
    );
    let message = if req.message.trim().is_empty() {
        format!(
            "Merge branch '{}' of {}/{} into {}",
            pull.head_branch, head_repo.owner.name, head_repo.repo.name, pull.base_branch
        )
    } else {
        req.message.trim().to_string()
    };

    let merged_commit_id = git::merge_pull_request_with_binary(
        &state.config.repository.git_binary,
        &base_repo_path,
        &pull.base_branch,
        &head_repo_path,
        &pull.head_branch,
        &acting_user.name,
        &acting_user.email,
        &message,
    )?;
    let pull_request = state
        .db
        .mark_pull_request_merged(pull.id, &merged_commit_id)?;
    build_pull_request_response(state, pull_request, Some(head_repo), Some(base_repo))
}

pub fn close_pull_request(
    state: &AppState,
    acting_user: &User,
    base_owner_name: &str,
    base_repo_name: &str,
    index: i64,
) -> AppResult<PullRequestResponse> {
    let base_repo = get_repository(state, base_owner_name, base_repo_name)?;
    let pull = state
        .db
        .get_pull_request_by_base_repo_and_index(base_repo.repo.id, index)?
        .ok_or_else(|| AppError::NotFound(format!("pull request not found: {index}")))?;
    ensure_pull_request_admin(state, acting_user, &base_repo, &pull)?;
    if pull.has_merged {
        return Err(AppError::Conflict(
            "merged pull request cannot be closed".to_string(),
        ));
    }
    if pull.is_closed {
        return Err(AppError::Conflict(
            "pull request is already closed".to_string(),
        ));
    }

    let pull_request = state
        .db
        .update_pull_request_open_state(pull.id, true, pull.status)?;
    build_pull_request_response(state, pull_request, None, Some(base_repo))
}

pub fn reopen_pull_request(
    state: &AppState,
    acting_user: &User,
    base_owner_name: &str,
    base_repo_name: &str,
    index: i64,
) -> AppResult<PullRequestResponse> {
    let base_repo = get_repository(state, base_owner_name, base_repo_name)?;
    let pull = state
        .db
        .get_pull_request_by_base_repo_and_index(base_repo.repo.id, index)?
        .ok_or_else(|| AppError::NotFound(format!("pull request not found: {index}")))?;
    ensure_pull_request_admin(state, acting_user, &base_repo, &pull)?;
    if pull.has_merged {
        return Err(AppError::Conflict(
            "merged pull request cannot be reopened".to_string(),
        ));
    }
    if !pull.is_closed {
        return Err(AppError::Conflict(
            "pull request is already open".to_string(),
        ));
    }

    if let Some(existing) = state.db.get_unmerged_pull_request(
        pull.head_repo_id,
        pull.base_repo_id,
        &pull.head_branch,
        &pull.base_branch,
    )? {
        if existing.id != pull.id {
            return Err(AppError::Conflict(
                "an open pull request already exists for this head/base branch pair".to_string(),
            ));
        }
    }

    let head_repo = get_repository_by_id(state, pull.head_repo_id)?;
    let base_repo_path = repox::repository_path(
        &state.config.repository.root,
        &base_repo.owner.name,
        &base_repo.repo.name,
    );
    let head_repo_path = repox::repository_path(
        &state.config.repository.root,
        &head_repo.owner.name,
        &head_repo.repo.name,
    );
    if !git::branch_exists_with_binary(
        &state.config.repository.git_binary,
        &base_repo_path,
        &pull.base_branch,
    )? {
        return Err(AppError::NotFound(format!(
            "base branch not found: {}",
            pull.base_branch
        )));
    }
    if !git::branch_exists_with_binary(
        &state.config.repository.git_binary,
        &head_repo_path,
        &pull.head_branch,
    )? {
        return Err(AppError::NotFound(format!(
            "head branch not found: {}",
            pull.head_branch
        )));
    }
    let merge_base = git::merge_base_with_binary(
        &state.config.repository.git_binary,
        &base_repo_path,
        &pull.base_branch,
        &head_repo_path,
        &pull.head_branch,
    )?;
    if merge_base.is_empty() {
        return Err(AppError::Validation(
            "no merge base between branches".to_string(),
        ));
    }
    let status = if git::test_merge_with_binary(
        &state.config.repository.git_binary,
        &base_repo_path,
        &pull.base_branch,
        &head_repo_path,
        &pull.head_branch,
    )? {
        PullRequestStatus::Mergeable
    } else {
        PullRequestStatus::Conflict
    };

    let pull_request = state
        .db
        .update_pull_request_open_state(pull.id, false, status)?;
    build_pull_request_response(state, pull_request, Some(head_repo), Some(base_repo))
}

pub fn list_pull_requests(
    state: &AppState,
    requesting_user: Option<&User>,
    owner_name: &str,
    repo_name: &str,
    page: i64,
    per_page: i64,
) -> AppResult<Vec<PullRequestResponse>> {
    let base_repo = get_repository(state, owner_name, repo_name)?;
    ensure_repo_access(state, requesting_user, &base_repo, AccessMode::Read)?;

    let (limit, offset) = pagination(page, per_page);
    let pulls = state
        .db
        .list_pull_requests_by_base_repo(base_repo.repo.id, limit, offset)?;
    let mut result = Vec::with_capacity(pulls.len());
    for pull in pulls {
        result.push(build_pull_request_response(
            state,
            pull,
            None,
            Some(base_repo.clone()),
        )?);
    }
    Ok(result)
}

pub fn get_pull_request_detail(
    state: &AppState,
    requesting_user: Option<&User>,
    owner_name: &str,
    repo_name: &str,
    index: i64,
) -> AppResult<PullRequestDetailResponse> {
    let base_repo = get_repository(state, owner_name, repo_name)?;
    ensure_repo_readable(state, requesting_user, &base_repo)?;
    let pull_request = state
        .db
        .get_pull_request_by_base_repo_and_index(base_repo.repo.id, index)?
        .ok_or_else(|| AppError::NotFound(format!("pull request not found: {index}")))?;
    let head_repo = get_repository_by_id(state, pull_request.head_repo_id)?;
    let compare = build_compare_for_pull_request(state, &base_repo, &head_repo, &pull_request)?;
    Ok(PullRequestDetailResponse {
        pull_request,
        head_repo,
        base_repo,
        compare,
    })
}

pub fn compare_repositories(
    state: &AppState,
    acting_user: &User,
    owner_name: &str,
    repo_name: &str,
    req: CompareRequest,
) -> AppResult<CompareResponse> {
    let base_repo = get_repository(state, owner_name, repo_name)?;
    ensure_repo_access(state, Some(acting_user), &base_repo, AccessMode::Read)?;

    let head_repo = get_repository(state, &req.head_owner, &req.head_repo)?;
    let same_repo = head_repo.repo.id == base_repo.repo.id;
    if !same_repo && (!head_repo.repo.is_fork || head_repo.repo.fork_id != base_repo.repo.id) {
        return Err(AppError::NotFound(
            "head repository is not a fork of base repository".to_string(),
        ));
    }
    ensure_repo_access(state, Some(acting_user), &head_repo, AccessMode::Read)?;

    build_compare_for_refs(
        state,
        &base_repo,
        &head_repo,
        req.base.trim(),
        req.head_branch.trim(),
    )
}

pub fn get_repository(
    state: &AppState,
    owner_name: &str,
    repo_name: &str,
) -> AppResult<RepositoryWithOwner> {
    let owner = get_user(state, owner_name)?;
    let repo = state
        .db
        .get_repository_by_name(owner.id, repo_name)?
        .ok_or_else(|| {
            AppError::NotFound(format!("repository not found: {owner_name}/{repo_name}"))
        })?;
    Ok(RepositoryWithOwner { repo, owner })
}

pub fn get_repository_by_id(state: &AppState, repo_id: i64) -> AppResult<RepositoryWithOwner> {
    let repo = state
        .db
        .get_repository_by_id(repo_id)?
        .ok_or_else(|| AppError::NotFound(format!("repository not found: {repo_id}")))?;
    let owner = state.db.get_user_by_id(repo.owner_id)?.ok_or_else(|| {
        AppError::NotFound(format!("repository owner not found: {}", repo.owner_id))
    })?;
    Ok(RepositoryWithOwner { repo, owner })
}

pub fn get_repository_for_read(
    state: &AppState,
    requesting_user: Option<&User>,
    owner_name: &str,
    repo_name: &str,
) -> AppResult<RepositoryWithOwner> {
    let repo = get_repository(state, owner_name, repo_name)?;
    ensure_repo_readable(state, requesting_user, &repo)?;
    Ok(repo)
}

fn build_pull_request_response(
    state: &AppState,
    pull_request: PullRequest,
    head_repo: Option<RepositoryWithOwner>,
    base_repo: Option<RepositoryWithOwner>,
) -> AppResult<PullRequestResponse> {
    let head_repo = match head_repo {
        Some(repo) => repo,
        None => get_repository_by_id(state, pull_request.head_repo_id)?,
    };
    let base_repo = match base_repo {
        Some(repo) => repo,
        None => get_repository_by_id(state, pull_request.base_repo_id)?,
    };
    Ok(PullRequestResponse {
        pull_request,
        head_repo,
        base_repo,
    })
}

fn build_compare_for_pull_request(
    state: &AppState,
    base_repo: &RepositoryWithOwner,
    head_repo: &RepositoryWithOwner,
    pull_request: &PullRequest,
) -> AppResult<CompareResponse> {
    if pull_request.has_merged && !pull_request.merged_commit_id.is_empty() {
        let base_repo_path = repox::repository_path(
            &state.config.repository.root,
            &base_repo.owner.name,
            &base_repo.repo.name,
        );
        let result = git::compare_rev_range_with_binary(
            &state.config.repository.git_binary,
            &base_repo_path,
            &pull_request.merge_base,
            &pull_request.merged_commit_id,
        )?;
        Ok(map_compare_result(
            pull_request.base_branch.as_str(),
            pull_request.head_branch.as_str(),
            if result.files.is_empty() && result.commits.is_empty() {
                PullRequestStatus::Mergeable
            } else {
                pull_request.status
            },
            result,
        ))
    } else {
        build_compare_for_refs(
            state,
            base_repo,
            head_repo,
            &pull_request.base_branch,
            &pull_request.head_branch,
        )
    }
}

fn build_compare_for_refs(
    state: &AppState,
    base_repo: &RepositoryWithOwner,
    head_repo: &RepositoryWithOwner,
    base_branch: &str,
    head_branch: &str,
) -> AppResult<CompareResponse> {
    let base_repo_path = repox::repository_path(
        &state.config.repository.root,
        &base_repo.owner.name,
        &base_repo.repo.name,
    );
    if !git::branch_exists_with_binary(
        &state.config.repository.git_binary,
        &base_repo_path,
        base_branch,
    )? {
        return Err(AppError::NotFound(format!(
            "base branch not found: {base_branch}"
        )));
    }

    let head_repo_path = repox::repository_path(
        &state.config.repository.root,
        &head_repo.owner.name,
        &head_repo.repo.name,
    );
    if !git::branch_exists_with_binary(
        &state.config.repository.git_binary,
        &head_repo_path,
        head_branch,
    )? {
        return Err(AppError::NotFound(format!(
            "head branch not found: {head_branch}"
        )));
    }

    let result = git::compare_refs_with_binary(
        &state.config.repository.git_binary,
        &base_repo_path,
        base_branch,
        &head_repo_path,
        head_branch,
    )?;
    let status = if result.merge_base == result.head_commit_id {
        PullRequestStatus::Mergeable
    } else if git::test_merge_with_binary(
        &state.config.repository.git_binary,
        &base_repo_path,
        base_branch,
        &head_repo_path,
        head_branch,
    )? {
        PullRequestStatus::Mergeable
    } else {
        PullRequestStatus::Conflict
    };
    Ok(map_compare_result(base_branch, head_branch, status, result))
}

fn map_compare_result(
    base_branch: &str,
    head_branch: &str,
    status: PullRequestStatus,
    result: git::CompareResult,
) -> CompareResponse {
    let is_nothing_to_compare = result.merge_base == result.head_commit_id;
    CompareResponse {
        base_branch: base_branch.to_string(),
        head_branch: head_branch.to_string(),
        merge_base: result.merge_base,
        head_commit_id: result.head_commit_id,
        status,
        commits: result
            .commits
            .into_iter()
            .map(|commit| CompareCommit {
                id: commit.id,
                summary: commit.summary,
                author_name: commit.author_name,
                author_email: commit.author_email,
            })
            .collect(),
        files: result
            .files
            .into_iter()
            .map(|file| CompareFile {
                path: file.path,
                additions: file.additions,
                deletions: file.deletions,
            })
            .collect(),
        is_nothing_to_compare,
    }
}

fn ensure_repo_readable(
    state: &AppState,
    requesting_user: Option<&User>,
    repo: &RepositoryWithOwner,
) -> AppResult<()> {
    ensure_repo_access(state, requesting_user, repo, AccessMode::Read)
}

fn ensure_repo_access(
    state: &AppState,
    requesting_user: Option<&User>,
    repo: &RepositoryWithOwner,
    desired: AccessMode,
) -> AppResult<()> {
    let mode = effective_access_mode(state, requesting_user, repo)?;
    if (mode as i64) >= (desired as i64) {
        return Ok(());
    }
    if repo.repo.is_private {
        return Err(AppError::NotFound(format!(
            "repository not found: {}/{}",
            repo.owner.name, repo.repo.name
        )));
    }
    Err(AppError::Forbidden("repository access denied".to_string()))
}

fn ensure_pull_request_admin(
    state: &AppState,
    acting_user: &User,
    base_repo: &RepositoryWithOwner,
    pull: &PullRequest,
) -> AppResult<()> {
    let is_writer = state.db.authorize(
        acting_user.id,
        base_repo.repo.id,
        AccessMode::Write,
        base_repo.owner.id,
        base_repo.repo.is_private,
    )?;
    if is_writer || acting_user.id == pull.poster_id {
        return Ok(());
    }

    Err(AppError::Forbidden(
        "pull request status change denied".to_string(),
    ))
}

pub fn login_with_password(state: &AppState, login: &str, password: &str) -> AppResult<User> {
    authenticate_password(state, login, password)
}

fn authenticate_password(state: &AppState, login: &str, password: &str) -> AppResult<User> {
    let user = if login.contains('@') {
        state
            .db
            .get_user_by_email(login)?
            .ok_or_else(|| AppError::Unauthorized("invalid credentials".to_string()))?
    } else {
        state
            .db
            .get_user_by_username(login)?
            .ok_or_else(|| AppError::Unauthorized("invalid credentials".to_string()))?
    };

    if !user.is_active {
        return Err(AppError::Unauthorized("inactive user".to_string()));
    }

    let parsed_hash = PasswordHash::new(&user.password_hash)
        .map_err(|_| AppError::Unauthorized("invalid credentials".to_string()))?;
    Argon2::default()
        .verify_password(password.as_bytes(), &parsed_hash)
        .map_err(|_| AppError::Unauthorized("invalid credentials".to_string()))?;

    Ok(user)
}

fn is_token_expired(token: &crate::models::AccessToken) -> bool {
    crate::db::now_unix() - token.created_unix > TOKEN_TTL_DAYS * 86400
}

fn pagination(page: i64, per_page: i64) -> (i64, i64) {
    let page = page.max(1);
    let per_page = per_page.clamp(1, MAX_PER_PAGE);
    let limit = per_page;
    let offset = (page - 1) * per_page;
    (limit, offset)
}

fn validate_user_name(name: &str) -> AppResult<()> {
    validate_name(name, &[".git", ".wiki"], "username")
}

fn validate_repo_name(name: &str) -> AppResult<()> {
    validate_name(name, &[".git", ".wiki"], "repository name")
}

fn validate_name(name: &str, forbidden_suffixes: &[&str], field: &str) -> AppResult<()> {
    if name.is_empty() {
        return Err(AppError::Validation(format!("{field} cannot be empty")));
    }
    if matches!(name, "." | "..") {
        return Err(AppError::Validation(format!("{field} is reserved")));
    }
    if forbidden_suffixes
        .iter()
        .any(|suffix| name.ends_with(suffix))
    {
        return Err(AppError::Validation(format!("{field} has reserved suffix")));
    }
    if !name
        .chars()
        .all(|ch| ch.is_ascii_alphanumeric() || matches!(ch, '-' | '_' | '.'))
    {
        return Err(AppError::Validation(format!(
            "{field} must contain only ASCII letters, digits, '-', '_' or '.'"
        )));
    }
    Ok(())
}

fn validate_email(email: &str) -> AppResult<()> {
    if email.contains('@') && !email.starts_with('@') && !email.ends_with('@') {
        return Ok(());
    }
    Err(AppError::Validation("email is invalid".to_string()))
}

fn ensure_repo_owner(acting_user: &User, repo: &RepositoryWithOwner) -> AppResult<()> {
    if acting_user.id != repo.owner.id {
        return Err(AppError::Forbidden(
            "only repository owner can manage collaborators".to_string(),
        ));
    }
    Ok(())
}

fn filter_visible_repositories(
    state: &AppState,
    requesting_user: Option<&User>,
    repos: Vec<RepositoryWithOwner>,
    query: &str,
) -> AppResult<Vec<RepositoryWithOwner>> {
    let query = query.trim().to_ascii_lowercase();
    let mut visible = Vec::new();
    for repo in repos {
        let mode = effective_access_mode(state, requesting_user, &repo)?;
        if mode == AccessMode::None {
            continue;
        }
        if !query.is_empty() && !repository_matches_query(&repo, &query) {
            continue;
        }
        visible.push(repo);
    }
    Ok(visible)
}

fn repository_matches_query(repo: &RepositoryWithOwner, query: &str) -> bool {
    repo.repo.lower_name.contains(query)
        || repo.owner.lower_name.contains(query)
        || repo
            .repo
            .description
            .to_ascii_lowercase()
            .contains(query)
        || format!("{}/{}", repo.owner.lower_name, repo.repo.lower_name).contains(query)
}

fn effective_access_mode(
    state: &AppState,
    requesting_user: Option<&User>,
    repo: &RepositoryWithOwner,
) -> AppResult<AccessMode> {
    let user_id = requesting_user.map(|user| user.id).unwrap_or(0);
    state
        .db
        .access_mode(user_id, repo.repo.id, repo.owner.id, repo.repo.is_private)
}

fn random_token() -> String {
    let mut bytes = [0_u8; 32];
    OsRng.fill_bytes(&mut bytes);
    hex::encode(bytes)
}

fn hash_token(token: &str) -> String {
    hex::encode(Sha256::digest(token.as_bytes()))
}