//! `/api/v1/admin/admins/*` — admin user CRUD. Guarded by
//! `require_admin`; every authenticated admin can call all of these.
//! Role/permission walls land later (see blueprint §11.4 — no
//! privilege levels in this cut).
//!
//! "Last active admin" protection lives at the service layer (not just
//! the DB) so it can produce a clean 422 with a human-readable message
//! rather than a SQL constraint violation. Deactivating a user also
//! wipes their sessions; deleting cascades through the FK.

use std::sync::Arc;

use axum::extract::{Path, State};
use axum::http::StatusCode;
use axum::response::{IntoResponse, Json, Response};
use axum::routing::get;
use axum::Router;
use chrono::{DateTime, Utc};
use picloud_shared::AdminUserId;
use serde::{Deserialize, Serialize};
use serde_json::json;

use crate::admin_session_repo::AdminSessionRepository;
use crate::admin_user_repo::{AdminUserRepository, AdminUserRepositoryError, AdminUserRow};
use crate::auth::hash_password;

/// Validation knobs are tuned by NIST 800-63B-ish guidance: username is
/// a strict ASCII subset so the lookup column stays predictable, and
/// password has a minimum length but no complexity rules (complexity
/// rules push users to predictable patterns).
const USERNAME_MIN: usize = 2;
const USERNAME_MAX: usize = 32;
const PASSWORD_MIN: usize = 8;

#[derive(Clone)]
pub struct AdminsState {
    pub users: Arc<dyn AdminUserRepository>,
    pub sessions: Arc<dyn AdminSessionRepository>,
}

pub fn admins_router(state: AdminsState) -> Router {
    Router::new()
        .route("/admins", get(list_admins).post(create_admin))
        .route(
            "/admins/{id}",
            get(get_admin).patch(patch_admin).delete(delete_admin),
        )
        .with_state(state)
}

// ----------------------------------------------------------------------------
// DTOs
// ----------------------------------------------------------------------------

#[derive(Debug, Serialize)]
pub struct AdminDto {
    pub id: AdminUserId,
    pub username: String,
    pub is_active: bool,
    pub created_at: DateTime<Utc>,
    pub last_login_at: Option<DateTime<Utc>>,
}

impl From<AdminUserRow> for AdminDto {
    fn from(r: AdminUserRow) -> Self {
        Self {
            id: r.id,
            username: r.username,
            is_active: r.is_active,
            created_at: r.created_at,
            last_login_at: r.last_login_at,
        }
    }
}

#[derive(Debug, Deserialize)]
pub struct CreateAdminRequest {
    pub username: String,
    pub password: String,
}

#[derive(Debug, Deserialize, Default)]
pub struct PatchAdminRequest {
    pub username: Option<String>,
    pub password: Option<String>,
    pub is_active: Option<bool>,
}

// ----------------------------------------------------------------------------
// Handlers
// ----------------------------------------------------------------------------

async fn list_admins(
    State(state): State<AdminsState>,
) -> Result<Json<Vec<AdminDto>>, AdminApiError> {
    let rows = state.users.list().await?;
    Ok(Json(rows.into_iter().map(Into::into).collect()))
}

async fn get_admin(
    State(state): State<AdminsState>,
    Path(id): Path<AdminUserId>,
) -> Result<Json<AdminDto>, AdminApiError> {
    state
        .users
        .get(id)
        .await?
        .map(AdminDto::from)
        .map(Json)
        .ok_or(AdminApiError::NotFound(id))
}

async fn create_admin(
    State(state): State<AdminsState>,
    Json(input): Json<CreateAdminRequest>,
) -> Result<(StatusCode, Json<AdminDto>), AdminApiError> {
    let username = input.username.trim();
    validate_username(username)?;
    validate_password(&input.password)?;
    let hash = hash_password(&input.password).map_err(|e| AdminApiError::Hash(e.to_string()))?;
    let row = state.users.create(username, &hash).await?;
    Ok((StatusCode::CREATED, Json(row.into())))
}

async fn patch_admin(
    State(state): State<AdminsState>,
    Path(id): Path<AdminUserId>,
    Json(input): Json<PatchAdminRequest>,
) -> Result<Json<AdminDto>, AdminApiError> {
    // Verify the target exists upfront — keeps the error path uniform
    // for "rename a missing user" etc.
    let _ = state
        .users
        .get(id)
        .await?
        .ok_or(AdminApiError::NotFound(id))?;

    let mut latest: Option<AdminUserRow> = None;

    if let Some(raw_username) = input.username.as_deref() {
        let new_username = raw_username.trim();
        validate_username(new_username)?;
        latest = Some(state.users.update_username(id, new_username).await?);
    }

    if let Some(new_password) = input.password.as_deref() {
        validate_password(new_password)?;
        let hash = hash_password(new_password).map_err(|e| AdminApiError::Hash(e.to_string()))?;
        latest = Some(state.users.update_password_hash(id, &hash).await?);
        // Best practice: rotating your own password should still keep
        // your session alive, so we don't wipe sessions here. (If we
        // wanted "log everyone else out on password change", that'd be
        // a `delete_for_user` + re-issue current session. Out of scope
        // for the initial cut.)
    }

    if let Some(new_active) = input.is_active {
        // Last-active-admin guard: only when transitioning to inactive.
        if !new_active {
            let remaining = state.users.count_active_excluding(id).await?;
            if remaining == 0 {
                return Err(AdminApiError::LastActiveAdmin);
            }
        }
        latest = Some(state.users.set_active(id, new_active).await?);
        // Deactivation invalidates all of the user's sessions. Cheap
        // and safer than waiting for sliding-window expiry.
        if !new_active {
            if let Err(err) = state.sessions.delete_for_user(id).await {
                tracing::error!(?err, "failed to delete sessions for deactivated admin");
            }
        }
    }

    let row = match latest {
        Some(r) => r,
        None => state
            .users
            .get(id)
            .await?
            .ok_or(AdminApiError::NotFound(id))?,
    };
    Ok(Json(row.into()))
}

async fn delete_admin(
    State(state): State<AdminsState>,
    Path(id): Path<AdminUserId>,
) -> Result<StatusCode, AdminApiError> {
    let target = state
        .users
        .get(id)
        .await?
        .ok_or(AdminApiError::NotFound(id))?;
    if target.is_active {
        let remaining = state.users.count_active_excluding(id).await?;
        if remaining == 0 {
            return Err(AdminApiError::LastActiveAdmin);
        }
    }
    state.users.delete(id).await?;
    // Sessions cascade via FK; no explicit delete needed.
    Ok(StatusCode::NO_CONTENT)
}

// ----------------------------------------------------------------------------
// Validation
// ----------------------------------------------------------------------------

fn validate_username(s: &str) -> Result<(), AdminApiError> {
    if s.len() < USERNAME_MIN || s.len() > USERNAME_MAX {
        return Err(AdminApiError::InvalidUsername(format!(
            "username must be {USERNAME_MIN}-{USERNAME_MAX} characters"
        )));
    }
    if !s
        .bytes()
        .all(|b| b.is_ascii_lowercase() || b.is_ascii_digit() || matches!(b, b'.' | b'_' | b'-'))
    {
        return Err(AdminApiError::InvalidUsername(
            "username may contain only lowercase letters, digits, dot, underscore, and hyphen"
                .to_string(),
        ));
    }
    Ok(())
}

fn validate_password(s: &str) -> Result<(), AdminApiError> {
    if s.chars().count() < PASSWORD_MIN {
        return Err(AdminApiError::InvalidPassword(format!(
            "password must be at least {PASSWORD_MIN} characters"
        )));
    }
    Ok(())
}

// ----------------------------------------------------------------------------
// Errors
// ----------------------------------------------------------------------------

#[derive(Debug, thiserror::Error)]
pub enum AdminApiError {
    #[error("admin user not found: {0}")]
    NotFound(AdminUserId),

    #[error("{0}")]
    InvalidUsername(String),

    #[error("{0}")]
    InvalidPassword(String),

    #[error("cannot leave the system with zero active admins")]
    LastActiveAdmin,

    #[error("failed to hash password: {0}")]
    Hash(String),

    #[error("repository error: {0}")]
    Repo(#[from] AdminUserRepositoryError),
}

impl IntoResponse for AdminApiError {
    fn into_response(self) -> Response {
        let (status, message) = match &self {
            Self::NotFound(_) => (StatusCode::NOT_FOUND, self.to_string()),
            Self::Repo(AdminUserRepositoryError::DuplicateUsername(_)) => {
                (StatusCode::CONFLICT, self.to_string())
            }
            Self::InvalidUsername(_) | Self::InvalidPassword(_) | Self::LastActiveAdmin => {
                (StatusCode::UNPROCESSABLE_ENTITY, self.to_string())
            }
            Self::Repo(AdminUserRepositoryError::NotFound(_)) => {
                (StatusCode::NOT_FOUND, self.to_string())
            }
            Self::Repo(AdminUserRepositoryError::Db(e)) => {
                tracing::error!(error = %e, "admin_users db error");
                (
                    StatusCode::INTERNAL_SERVER_ERROR,
                    "internal error".to_string(),
                )
            }
            Self::Hash(_) => {
                tracing::error!(error = %self, "password hashing failed");
                (
                    StatusCode::INTERNAL_SERVER_ERROR,
                    "internal error".to_string(),
                )
            }
        };
        (status, Json(json!({ "error": message }))).into_response()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn username_validation_accepts_valid() {
        for u in ["ab", "alice", "user.name", "a_b-c", "00bot00"] {
            assert!(validate_username(u).is_ok(), "should accept {u}");
        }
    }

    #[test]
    fn username_validation_rejects_invalid() {
        for u in ["", "a", "Alice", "user name", "user@domain", "user!"] {
            assert!(validate_username(u).is_err(), "should reject {u:?}");
        }
        let too_long = "x".repeat(33);
        assert!(validate_username(&too_long).is_err());
    }

    #[test]
    fn password_validation_enforces_min_length() {
        assert!(validate_password("1234567").is_err());
        assert!(validate_password("12345678").is_ok());
        assert!(validate_password("a-very-long-password-with-spaces and stuff").is_ok());
    }
}