use std::sync::LazyLock;

use regex::Regex;

use ruff_diagnostics::{Diagnostic, Violation};
use ruff_macros::{derive_message_formats, ViolationMetadata};
use ruff_python_ast::str::raw_contents;
use ruff_python_ast::{self as ast, Expr, Operator};
use ruff_text_size::Ranged;

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

static SQL_REGEX: LazyLock<Regex> = LazyLock::new(|| {
    Regex::new(
        r"(?isx)
        \b
        (select\s+.*\s+from\s
        |delete\s+from\s
        |(insert|replace)\s+.*\s+values\s
        |update\s+.*\s+set\s
        )
    ",
    )
    .unwrap()
});

/// ## What it does
/// Checks for strings that resemble SQL statements involved in some form
/// string building operation.
///
/// ## Why is this bad?
/// SQL injection is a common attack vector for web applications. Directly
/// interpolating user input into SQL statements should always be avoided.
/// Instead, favor parameterized queries, in which the SQL statement is
/// provided separately from its parameters, as supported by `psycopg3`
/// and other database drivers and ORMs.
///
/// ## Example
/// ```python
/// query = "DELETE FROM foo WHERE id = '%s'" % identifier
/// ```
///
/// ## References
/// - [B608: Test for SQL injection](https://bandit.readthedocs.io/en/latest/plugins/b608_hardcoded_sql_expressions.html)
/// - [psycopg3: Server-side binding](https://www.psycopg.org/psycopg3/docs/basic/from_pg2.html#server-side-binding)
#[derive(ViolationMetadata)]
pub(crate) struct HardcodedSQLExpression;

impl Violation for HardcodedSQLExpression {
    #[derive_message_formats]
    fn message(&self) -> String {
        "Possible SQL injection vector through string-based query construction".to_string()
    }
}

/// S608
pub(crate) fn hardcoded_sql_expression(checker: &Checker, expr: &Expr) {
    let content = match expr {
        // "select * from table where val = " + "str" + ...
        Expr::BinOp(ast::ExprBinOp {
            op: Operator::Add, ..
        }) => {
            // Only evaluate the full BinOp, not the nested components.
            if checker
                .semantic()
                .current_expression_parent()
                .is_some_and(ruff_python_ast::Expr::is_bin_op_expr)
            {
                return;
            }
            if is_explicit_concatenation(expr) != Some(true) {
                return;
            }
            checker.generator().expr(expr)
        }
        // "select * from table where val = %s" % ...
        Expr::BinOp(ast::ExprBinOp {
            left,
            op: Operator::Mod,
            ..
        }) => {
            let Some(string) = left.as_string_literal_expr() else {
                return;
            };
            string.value.to_str().escape_default().to_string()
        }
        Expr::Call(ast::ExprCall { func, .. }) => {
            let Expr::Attribute(ast::ExprAttribute { attr, value, .. }) = func.as_ref() else {
                return;
            };
            // "select * from table where val = {}".format(...)
            if attr != "format" {
                return;
            }
            let Some(string) = value.as_string_literal_expr() else {
                return;
            };
            string.value.to_str().escape_default().to_string()
        }

        // f"select * from table where val = {val}"
        Expr::FString(f_string) => concatenated_f_string(f_string, checker.locator()),
        _ => return,
    };

    if SQL_REGEX.is_match(&content) {
        checker.report_diagnostic(Diagnostic::new(HardcodedSQLExpression, expr.range()));
    }
}

/// Concatenates the contents of an f-string, without the prefix and quotes,
/// and escapes any special characters.
///
/// ## Example
///
/// ```python
/// "foo" f"bar {x}" "baz"
/// ```
///
/// becomes `foobar {x}baz`.
fn concatenated_f_string(expr: &ast::ExprFString, locator: &Locator) -> String {
    expr.value
        .iter()
        .filter_map(|part| raw_contents(locator.slice(part)))
        .collect()
}

/// Returns `Some(true)` if an expression appears to be an explicit string concatenation,
/// `Some(false)` if it's _not_ an explicit concatenation, and `None` if it's ambiguous.
fn is_explicit_concatenation(expr: &Expr) -> Option<bool> {
    match expr {
        Expr::BinOp(ast::ExprBinOp { left, right, .. }) => {
            let left = is_explicit_concatenation(left);
            let right = is_explicit_concatenation(right);
            match (left, right) {
                // If either side is definitively _not_ a string, neither is the expression.
                (Some(false), _) | (_, Some(false)) => Some(false),
                // If either side is definitively a string, the expression is a string.
                (Some(true), _) | (_, Some(true)) => Some(true),
                _ => None,
            }
        }
        // Ambiguous (e.g., `x + y`).
        Expr::Call(_) => None,
        Expr::Subscript(_) => None,
        Expr::Attribute(_) => None,
        Expr::Name(_) => None,

        // Non-strings.
        Expr::Lambda(_) => Some(false),
        Expr::List(_) => Some(false),
        Expr::Tuple(_) => Some(false),
        Expr::Dict(_) => Some(false),
        Expr::Set(_) => Some(false),
        Expr::Generator(_) => Some(false),
        Expr::Yield(_) => Some(false),
        Expr::YieldFrom(_) => Some(false),
        Expr::Await(_) => Some(false),
        Expr::Starred(_) => Some(false),
        Expr::Slice(_) => Some(false),
        Expr::BooleanLiteral(_) => Some(false),
        Expr::EllipsisLiteral(_) => Some(false),
        Expr::NumberLiteral(_) => Some(false),
        Expr::ListComp(_) => Some(false),
        Expr::SetComp(_) => Some(false),
        Expr::DictComp(_) => Some(false),
        Expr::Compare(_) => Some(false),
        Expr::FString(_) => Some(true),
        Expr::StringLiteral(_) => Some(true),
        Expr::BytesLiteral(_) => Some(false),
        Expr::NoneLiteral(_) => Some(false),
        Expr::IpyEscapeCommand(_) => Some(false),

        // Conditionally strings.
        Expr::Named(ast::ExprNamed { value, .. }) => is_explicit_concatenation(value),
        Expr::If(ast::ExprIf { body, orelse, .. }) => {
            let body = is_explicit_concatenation(body);
            let orelse = is_explicit_concatenation(orelse);
            match (body, orelse) {
                // If either side is definitively a string, the expression could be a string.
                (Some(true), _) | (_, Some(true)) => Some(true),
                // If both sides are definitively _not_ a string, neither is the expression.
                (Some(false), Some(false)) => Some(false),
                _ => None,
            }
        }
        Expr::BoolOp(ast::ExprBoolOp { values, .. }) => {
            let values = values
                .iter()
                .map(is_explicit_concatenation)
                .collect::<Vec<_>>();
            if values.iter().any(|v| *v == Some(true)) {
                Some(true)
            } else if values.iter().all(|v| *v == Some(false)) {
                Some(false)
            } else {
                None
            }
        }
        Expr::UnaryOp(ast::ExprUnaryOp { operand, .. }) => is_explicit_concatenation(operand),
    }
}
