use ruff_text_size::TextLen;
use strum::IntoEnumIterator;

use ruff_diagnostics::{Diagnostic, Edit, Fix, FixAvailability, Violation};
use ruff_macros::{derive_message_formats, ViolationMetadata};
use ruff_source_file::{UniversalNewlineIterator, UniversalNewlines};
use ruff_text_size::Ranged;

use crate::checkers::ast::Checker;
use crate::docstrings::sections::SectionKind;
use crate::docstrings::Docstring;

use crate::rules::pydocstyle::helpers::logical_line;

/// ## What it does
/// Checks for docstrings in which the first line does not end in a period.
///
/// ## Why is this bad?
/// [PEP 257] recommends that the first line of a docstring is written in the
/// form of a command, ending in a period.
///
/// This rule may not apply to all projects; its applicability is a matter of
/// convention. By default, this rule is enabled when using the `numpy` and
/// `pep257` conventions, and disabled when using the `google` convention.
///
/// ## Example
/// ```python
/// def average(values: list[float]) -> float:
///     """Return the mean of the given values"""
/// ```
///
/// Use instead:
/// ```python
/// def average(values: list[float]) -> float:
///     """Return the mean of the given values."""
/// ```
///
/// ## Options
/// - `lint.pydocstyle.convention`
///
/// ## References
/// - [PEP 257 – Docstring Conventions](https://peps.python.org/pep-0257/)
/// - [NumPy Style Guide](https://numpydoc.readthedocs.io/en/latest/format.html)
/// - [Google Python Style Guide - Docstrings](https://google.github.io/styleguide/pyguide.html#38-comments-and-docstrings)
///
/// [PEP 257]: https://peps.python.org/pep-0257/
#[derive(ViolationMetadata)]
pub(crate) struct MissingTrailingPeriod;

impl Violation for MissingTrailingPeriod {
    /// `None` in the case a fix is never available or otherwise Some
    /// [`FixAvailability`] describing the available fix.
    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;

    #[derive_message_formats]
    fn message(&self) -> String {
        "First line should end with a period".to_string()
    }

    fn fix_title(&self) -> Option<String> {
        Some("Add period".to_string())
    }
}

/// D400
pub(crate) fn ends_with_period(checker: &Checker, docstring: &Docstring) {
    let body = docstring.body();

    if let Some(first_line) = body.trim().universal_newlines().next() {
        let trimmed = first_line.trim();

        // Avoid false-positives: `:param`, etc.
        for prefix in [":param", ":type", ":raises", ":return", ":rtype"] {
            if trimmed.starts_with(prefix) {
                return;
            }
        }

        // Avoid false-positives: `Args:`, etc.
        for section_kind in SectionKind::iter() {
            if let Some(suffix) = trimmed.strip_suffix(section_kind.as_str()) {
                if suffix.is_empty() {
                    return;
                }
                if suffix == ":" {
                    return;
                }
            }
        }
    }

    if let Some(index) = logical_line(body.as_str()) {
        let mut lines = UniversalNewlineIterator::with_offset(&body, body.start());
        let line = lines.nth(index).unwrap();
        let trimmed = line.trim_end();

        if trimmed.ends_with('\\') {
            // Ignore the edge case whether a single quoted string is multiple lines through an
            // escape (https://github.com/astral-sh/ruff/issues/7139). Single quote docstrings are
            // flagged by D300.
            // ```python
            // "\
            // "
            // ```
            return;
        }

        if !trimmed.ends_with('.') {
            let mut diagnostic = Diagnostic::new(MissingTrailingPeriod, docstring.range());
            // Best-effort fix: avoid adding a period after other punctuation marks.
            if !trimmed.ends_with([':', ';', '?', '!']) {
                diagnostic.set_fix(Fix::unsafe_edit(Edit::insertion(
                    ".".to_string(),
                    line.start() + trimmed.text_len(),
                )));
            }
            checker.report_diagnostic(diagnostic);
        };
    }
}
