perl-module 0.13.1

//! Single-line Perl import head parsing.
//!
//! Parse a single source line that starts with `use` or `require` and return
//! the first import token with stable byte offsets.

/// When a module is loaded relative to program execution.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum LoadTiming {
    /// Module is loaded at compile time (e.g. `use`).
    CompileTime,
    /// Module is loaded at runtime (e.g. `require`).
    Runtime,
}

/// Whether the module's `import` method is called after loading.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ImportBehavior {
    /// The module's `import` method is called (as with `use`).
    CallsImport,
    /// No `import` call is made (as with `require`).
    NoImport,
}

/// Semantic description of a `use`/`require` dispatch form.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct DispatchSemantics {
    /// When the module load happens.
    pub load_timing: LoadTiming,
    /// Whether `import` is called on the loaded module.
    pub import_behavior: ImportBehavior,
}

impl DispatchSemantics {
    /// A short human-readable description suitable for hover text.
    #[must_use]
    pub fn hover_description(&self) -> &'static str {
        match (self.load_timing, self.import_behavior) {
            (LoadTiming::CompileTime, ImportBehavior::CallsImport) => {
                "compile-time load; calls import()"
            }
            (LoadTiming::Runtime, ImportBehavior::NoImport) => "runtime load; no import() call",
            (LoadTiming::CompileTime, ImportBehavior::NoImport) => {
                "compile-time load; no import() call"
            }
            (LoadTiming::Runtime, ImportBehavior::CallsImport) => "runtime load; calls import()",
        }
    }
}

/// How a `use` statement spells its import list.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ImportListForm {
    /// `use Module;`
    Default,
    /// `use Module ();`
    Empty,
    /// `use Module (...)`
    Explicit,
}

/// Distinguishes the two syntactic forms of `require`.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RequireForm {
    /// `require Module::Name` — bare module name.
    ModuleName,
    /// `require "path/to/file.pm"` or `require 'path/to/file.pm'` — quoted file path.
    FilePath,
}

/// Classifies the import statement form for a parsed line.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ModuleImportKind {
    /// `use Module::Name;`
    Use,
    /// `require Module::Name;` or `require "file.pm";`
    Require,
    /// `use parent ...`
    UseParent,
    /// `use base ...`
    UseBase,
}

impl ModuleImportKind {
    /// Returns the dispatch semantics for this import kind.
    #[must_use]
    pub fn dispatch_semantics(self) -> DispatchSemantics {
        match self {
            ModuleImportKind::Use | ModuleImportKind::UseParent | ModuleImportKind::UseBase => {
                DispatchSemantics {
                    load_timing: LoadTiming::CompileTime,
                    import_behavior: ImportBehavior::CallsImport,
                }
            }
            ModuleImportKind::Require => DispatchSemantics {
                load_timing: LoadTiming::Runtime,
                import_behavior: ImportBehavior::NoImport,
            },
        }
    }
}

/// Parsed leading import token from a `use`/`require` line.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ModuleImportHead<'a> {
    /// Parsed statement kind.
    pub kind: ModuleImportKind,
    /// First token after `use` or `require` (quotes stripped for file-path forms).
    pub token: &'a str,
    /// Inclusive byte start offset of `token` in the full line.
    pub token_start: usize,
    /// Exclusive byte end offset of `token` in the full line.
    pub token_end: usize,
    /// For `require`, whether the argument was a quoted file path or a bare module name.
    /// Always `None` for `use` forms.
    require_form: Option<RequireForm>,
    /// For `use` statements, how the import list is spelled.
    pub import_list: Option<ImportListForm>,
}

/// Resolve a known export tag to its symbol list for a specific module.
///
/// The `tag` argument can be passed with or without a leading `:`.
/// Returns `None` when the module/tag pair is not in the built-in catalog.
#[must_use]
pub fn resolve_known_export_tag(module: &str, tag: &str) -> Option<&'static [&'static str]> {
    let normalized_tag = tag.strip_prefix(':').unwrap_or(tag);
    match (module, normalized_tag) {
        ("POSIX", "sys_wait_h") => Some(&["WIFEXITED", "WEXITSTATUS", "WIFSIGNALED", "WTERMSIG"]),
        ("POSIX", "fcntl_h") => Some(&["F_GETFL", "F_SETFL", "F_SETFD", "F_GETFD"]),
        ("POSIX", "termios_h") => Some(&["TCSANOW", "TCSADRAIN", "TCSAFLUSH", "B9600"]),
        ("File::Find", "find") => Some(&["find", "finddepth"]),
        ("Fcntl", "seek") => Some(&["SEEK_SET", "SEEK_CUR", "SEEK_END"]),
        ("Fcntl", "lock") => Some(&["LOCK_SH", "LOCK_EX", "LOCK_NB", "LOCK_UN"]),
        ("Encode", "fallback") => Some(&["FB_DEFAULT", "FB_CROAK", "FB_QUIET", "FB_WARN"]),
        _ => None,
    }
}

impl<'a> ModuleImportHead<'a> {
    /// Returns the [`RequireForm`] for `require` statements, or `None` for `use` forms.
    #[must_use]
    pub fn require_form(&self) -> Option<RequireForm> {
        self.require_form
    }
}

/// Parse the leading import token of a single Perl source line.
///
/// Returns [`None`] when the line does not start with `use` or `require`
/// (after leading whitespace) or when no token is present after the keyword.
#[must_use]
pub fn parse_module_import_head(line: &str) -> Option<ModuleImportHead<'_>> {
    if let Some((token, token_start, token_end)) = parse_statement_head(line, "use") {
        let kind = match token {
            "parent" => ModuleImportKind::UseParent,
            "base" => ModuleImportKind::UseBase,
            _ => ModuleImportKind::Use,
        };

        let import_list = match kind {
            ModuleImportKind::Use => Some(classify_use_import_list(&line[token_end..])),
            ModuleImportKind::UseParent | ModuleImportKind::UseBase => None,
            ModuleImportKind::Require => None,
        };

        return Some(ModuleImportHead {
            kind,
            token,
            token_start,
            token_end,
            require_form: None,
            import_list,
        });
    }

    if let Some(result) = parse_require_head(line) {
        return Some(result);
    }

    None
}

/// Parse a `require` statement, handling both bare module names and quoted file paths.
fn parse_require_head(line: &str) -> Option<ModuleImportHead<'_>> {
    let trimmed = line.trim_start();
    let leading = line.len().saturating_sub(trimmed.len());

    let rest = trimmed.strip_prefix("require")?;
    if !rest.chars().next().is_some_and(char::is_whitespace) {
        return None;
    }

    let after_keyword = leading + "require".len();

    let rest_trimmed = rest.trim_start();
    let quote_offset = rest.len() - rest_trimmed.len();

    if let Some(quote_char) = rest_trimmed.chars().next().filter(|ch| *ch == '"' || *ch == '\'') {
        let quoted = &rest_trimmed[quote_char.len_utf8()..];
        let close_idx = quoted.find(quote_char)?;
        let inner = &quoted[..close_idx];

        let token_start = after_keyword + quote_offset + quote_char.len_utf8();
        let token_end = token_start + inner.len();
        return Some(ModuleImportHead {
            kind: ModuleImportKind::Require,
            token: inner,
            token_start,
            token_end,
            require_form: Some(RequireForm::FilePath),
            import_list: None,
        });
    }

    let (token, token_rel_start, token_rel_end) = first_token_with_range(rest)?;
    let token_start = after_keyword + token_rel_start;
    let token_end = after_keyword + token_rel_end;

    Some(ModuleImportHead {
        kind: ModuleImportKind::Require,
        token,
        token_start,
        token_end,
        require_form: Some(RequireForm::ModuleName),
        import_list: None,
    })
}

fn classify_use_import_list(rest: &str) -> ImportListForm {
    let trimmed = rest.trim_start();

    if trimmed.is_empty() || trimmed.starts_with(';') {
        return ImportListForm::Default;
    }

    if let Some(after_open) = trimmed.strip_prefix('(')
        && let Some(close_idx) = after_open.find(')')
        && after_open[..close_idx].trim().is_empty()
    {
        let after_close = after_open[close_idx + 1..].trim_start();
        if after_close.is_empty() || after_close.starts_with(';') || after_close.starts_with('#') {
            return ImportListForm::Empty;
        }
    }

    ImportListForm::Explicit
}

fn parse_statement_head<'a>(line: &'a str, keyword: &str) -> Option<(&'a str, usize, usize)> {
    let trimmed = line.trim_start();
    let leading = line.len().saturating_sub(trimmed.len());

    let rest = trimmed.strip_prefix(keyword)?;
    if !rest.chars().next().is_some_and(char::is_whitespace) {
        return None;
    }

    let (token, token_rel_start, token_rel_end) = first_token_with_range(rest)?;
    let token_start = leading + keyword.len() + token_rel_start;
    let token_end = leading + keyword.len() + token_rel_end;

    Some((token, token_start, token_end))
}

fn first_token_with_range(input: &str) -> Option<(&str, usize, usize)> {
    let mut token_start = None;

    for (idx, ch) in input.char_indices() {
        match token_start {
            None => {
                if is_token_delimiter(ch) {
                    continue;
                }
                token_start = Some(idx);
            }
            Some(start) => {
                if is_token_delimiter(ch) {
                    if start == idx {
                        return None;
                    }
                    return Some((&input[start..idx], start, idx));
                }
            }
        }
    }

    if let Some(start) = token_start {
        if start < input.len() { Some((&input[start..], start, input.len())) } else { None }
    } else {
        None
    }
}

fn is_token_delimiter(ch: char) -> bool {
    ch.is_whitespace() || matches!(ch, ';' | '(' | ')')
}