use ruff_diagnostics::{Diagnostic, Violation};
use ruff_macros::{derive_message_formats, violation};
use ruff_python_ast::name::UnqualifiedName;
use ruff_python_ast::{self as ast, Expr};
use ruff_python_semantic::{BindingKind, ScopeKind};
use ruff_text_size::Ranged;

use crate::checkers::ast::Checker;

/// ## What it does
/// Checks for accesses on "private" class members.
///
/// ## Why is this bad?
/// In Python, the convention is such that class members that are prefixed
/// with a single underscore, or prefixed but not suffixed with a double
/// underscore, are considered private and intended for internal use.
///
/// Using such "private" members is considered a misuse of the class, as
/// there are no guarantees that the member will be present in future
/// versions, that it will have the same type, or that it will have the same
/// behavior. Instead, use the class's public interface.
///
/// ## Example
/// ```python
/// class Class:
///     def __init__(self):
///         self._private_member = "..."
///
///
/// var = Class()
/// print(var._private_member)
/// ```
///
/// Use instead:
/// ```python
/// class Class:
///     def __init__(self):
///         self.public_member = "..."
///
///
/// var = Class()
/// print(var.public_member)
/// ```
///
/// ## Options
/// - `lint.flake8-self.ignore-names`
///
/// ## References
/// - [_What is the meaning of single or double underscores before an object name?_](https://stackoverflow.com/questions/1301346/what-is-the-meaning-of-single-and-double-underscore-before-an-object-name)
#[violation]
pub struct PrivateMemberAccess {
    access: String,
}

impl Violation for PrivateMemberAccess {
    #[derive_message_formats]
    fn message(&self) -> String {
        let PrivateMemberAccess { access } = self;
        format!("Private member accessed: `{access}`")
    }
}

/// SLF001
pub(crate) fn private_member_access(checker: &mut Checker, expr: &Expr) {
    let Expr::Attribute(ast::ExprAttribute { value, attr, .. }) = expr else {
        return;
    };

    if checker.semantic().in_annotation() {
        return;
    }

    if (attr.starts_with("__") && !attr.ends_with("__"))
        || (attr.starts_with('_') && !attr.starts_with("__"))
    {
        if checker
            .settings
            .flake8_self
            .ignore_names
            .contains(attr.as_ref())
        {
            return;
        }

        // Ignore accesses on instances within special methods (e.g., `__eq__`).
        if let ScopeKind::Function(ast::StmtFunctionDef { name, .. }) =
            checker.semantic().current_scope().kind
        {
            if matches!(
                name.as_str(),
                "__lt__"
                    | "__le__"
                    | "__eq__"
                    | "__ne__"
                    | "__gt__"
                    | "__ge__"
                    | "__add__"
                    | "__sub__"
                    | "__mul__"
                    | "__matmul__"
                    | "__truediv__"
                    | "__floordiv__"
                    | "__mod__"
                    | "__divmod__"
                    | "__pow__"
                    | "__lshift__"
                    | "__rshift__"
                    | "__and__"
                    | "__xor__"
                    | "__or__"
                    | "__radd__"
                    | "__rsub__"
                    | "__rmul__"
                    | "__rmatmul__"
                    | "__rtruediv__"
                    | "__rfloordiv__"
                    | "__rmod__"
                    | "__rdivmod__"
                    | "__rpow__"
                    | "__rlshift__"
                    | "__rrshift__"
                    | "__rand__"
                    | "__rxor__"
                    | "__ror__"
                    | "__iadd__"
                    | "__isub__"
                    | "__imul__"
                    | "__imatmul__"
                    | "__itruediv__"
                    | "__ifloordiv__"
                    | "__imod__"
                    | "__ipow__"
                    | "__ilshift__"
                    | "__irshift__"
                    | "__iand__"
                    | "__ixor__"
                    | "__ior__"
            ) {
                return;
            }
        }

        // Allow some documented private methods, like `os._exit()`.
        if let Some(qualified_name) = checker.semantic().resolve_qualified_name(expr) {
            if matches!(qualified_name.segments(), ["os", "_exit"]) {
                return;
            }
        }

        if let Expr::Call(ast::ExprCall { func, .. }) = value.as_ref() {
            // Ignore `super()` calls.
            if let Some(name) = UnqualifiedName::from_expr(func) {
                if matches!(name.segments(), ["super"]) {
                    return;
                }
            }
        }

        if let Some(name) = UnqualifiedName::from_expr(value) {
            // Ignore `self` and `cls` accesses.
            if matches!(name.segments(), ["self" | "cls" | "mcs"]) {
                return;
            }
        }

        if let Expr::Name(name) = value.as_ref() {
            // Ignore accesses on class members from _within_ the class.
            if checker
                .semantic()
                .resolve_name(name)
                .and_then(|id| {
                    if let BindingKind::ClassDefinition(scope) = checker.semantic().binding(id).kind
                    {
                        Some(scope)
                    } else {
                        None
                    }
                })
                .is_some_and(|scope| {
                    checker
                        .semantic()
                        .current_scope_ids()
                        .any(|parent| scope == parent)
                })
            {
                return;
            }
        }

        checker.diagnostics.push(Diagnostic::new(
            PrivateMemberAccess {
                access: attr.to_string(),
            },
            expr.range(),
        ));
    }
}
