//! Debian control-file handling: a minimal deb822 paragraph parser/writer
//! plus a `debian/control` model.
//!
//! Implements the subset of RFC822-ish parsing needed for `debian/control`,
//! `debian/files`, `.dsc`, `.changes` and `.buildinfo` files: paragraphs
//! separated by blank lines, `Field: value` entries with continuation lines
//! starting by a single space or tab, and `#` comments.

use std::path::Path;

/// A single deb822 paragraph: an ordered list of `(field, value)` pairs.
///
/// The parser is lenient: duplicate field names are kept as separate entries
/// (accessors see the first one; `set` collapses them back to a single one).
///
/// Values are stored with continuation-line breaks as `\n` and without the
/// leading whitespace of continuation lines. Serialization re-adds a single
/// leading space in front of every continuation line, matching dpkg output;
/// blank lines inside a value are encoded as ` .` (and decoded back) so they
/// survive a write/parse round-trip.
#[derive(Debug, Clone, Default, PartialEq)]
pub struct Paragraph {
    fields: Vec<(String, String)>,
}

impl Paragraph {
    /// Create an empty paragraph.
    pub fn new() -> Self {
        Self::default()
    }

    /// Look up a field value (case-insensitive field name).
    ///
    /// Returns the first match. The parser is lenient and keeps duplicate
    /// field names as-is; use [`Paragraph::iter`] to reach the other
    /// occurrences. [`Paragraph::set`] collapses them.
    pub fn get(&self, field: &str) -> Option<&str> {
        self.fields
            .iter()
            .find(|(k, _)| k.eq_ignore_ascii_case(field))
            .map(|(_, v)| v.as_str())
    }

    /// Set a field value, replacing all case-insensitive duplicates: after
    /// the call at most one entry with this field name remains — the updated
    /// one, kept at its original position. Appends the field at the end if
    /// no entry existed yet.
    pub fn set(&mut self, field: &str, value: &str) {
        let mut updated = false;
        self.fields.retain_mut(|(k, v)| {
            if k.eq_ignore_ascii_case(field) {
                if updated {
                    return false;
                }
                *v = value.to_string();
                updated = true;
            }
            true
        });
        if !updated {
            self.fields.push((field.to_string(), value.to_string()));
        }
    }

    /// Remove a field (case-insensitive). Returns true if it was present.
    pub fn remove(&mut self, field: &str) -> bool {
        let before = self.fields.len();
        self.fields.retain(|(k, _)| !k.eq_ignore_ascii_case(field));
        self.fields.len() != before
    }

    /// Iterate over the `(field, value)` pairs in order.
    pub fn iter(&self) -> impl Iterator<Item = (&str, &str)> {
        self.fields.iter().map(|(k, v)| (k.as_str(), v.as_str()))
    }

    /// Return true if the paragraph holds no field.
    pub fn is_empty(&self) -> bool {
        self.fields.is_empty()
    }
}

/// Parse a deb822 document into a list of paragraphs.
///
/// Comment lines (starting with `#`) are ignored. Blank lines separate
/// paragraphs. Continuation lines must start with a space or a tab; exactly
/// one leading space (or tab) is stripped from the stored value, and a
/// continuation whose content is a lone `.` decodes to an empty line
/// (dpkg's encoding for blank lines inside field values).
pub fn parse_paragraphs(input: &str) -> Vec<Paragraph> {
    let mut paragraphs = Vec::new();
    let mut current = Paragraph::new();
    let mut last_field: Option<String> = None;

    for raw_line in input.lines() {
        let line = raw_line.strip_suffix('\r').unwrap_or(raw_line);

        // Comments and blank lines
        if line.starts_with('#') {
            continue;
        }
        if line.trim().is_empty() {
            if !current.is_empty() {
                paragraphs.push(std::mem::take(&mut current));
                last_field = None;
            }
            continue;
        }

        // Continuation line
        if line.starts_with(' ') || line.starts_with('\t') {
            // Exactly one leading space or tab is stripped.
            let content = line
                .strip_prefix(' ')
                .or_else(|| line.strip_prefix('\t'))
                .unwrap_or(line);
            // dpkg encodes a blank line inside a value as a lone `.` after
            // the leading whitespace; mirror that on read.
            let content = if content == "." { "" } else { content };
            if let Some(field) = &last_field
                && let Some((_, v)) = current
                    .fields
                    .iter_mut()
                    .rev()
                    .find(|(k, _)| k.eq_ignore_ascii_case(field))
            {
                v.push('\n');
                v.push_str(content);
                continue;
            }
            // Continuation without a preceding field line: skip it (malformed)
            continue;
        }

        // Field line: `Name: value`
        if let Some(colon) = line.find(':') {
            let name = line[..colon].trim();
            let value = line[colon + 1..].trim_start();
            if name.is_empty() {
                continue;
            }
            current.fields.push((name.to_string(), value.to_string()));
            last_field = Some(name.to_string());
        }
        // Anything else is malformed: ignore the line
    }

    if !current.is_empty() {
        paragraphs.push(current);
    }

    paragraphs
}

/// Serialize a paragraph to its deb822 textual representation (with a
/// trailing newline).
///
/// A value starting with `\n` is rendered as a field with no inline first
/// line (`Field:` followed by ` line` continuations), matching dpkg output
/// for pre-wrapped values such as `Changes`, `Files` or `Environment`.
pub fn write_paragraph(p: &Paragraph) -> String {
    let mut out = String::new();
    for (name, value) in p.iter() {
        out.push_str(name);
        out.push(':');
        let mut lines = value.split('\n').peekable();
        // An empty first segment means: no value on the field header line;
        // discard it so it is not rendered as an empty continuation line.
        if lines.peek().is_some_and(|first| !first.is_empty()) {
            out.push(' ');
            out.push_str(lines.next().unwrap());
        } else {
            lines.next();
        }
        for line in lines {
            out.push('\n');
            if line.is_empty() {
                // dpkg encodes a blank line inside a value as ` .`; writing a
                // bare continuation line would be mistaken for a paragraph
                // separator on re-parse and silently drop the rest.
                out.push_str(" .");
            } else {
                out.push(' ');
                out.push_str(line);
            }
        }
        out.push('\n');
    }
    out
}

/// Return the signed body of a clearsigned message, as a slice of `text`.
///
/// If `text` starts with the OpenPGP clearsigned-marker line, the armor
/// header block (the `Hash: ...` line and any `Comment:` lines, up to and
/// including the blank line that closes the header) is skipped, and the
/// result is cut at the `-----BEGIN PGP SIGNATURE-----` marker so the
/// signature trailer is dropped as well. This keeps the armor metadata from
/// being parsed as deb822 fields (`Hash:` would otherwise land in the first
/// stanza and `Comment:` in the last one).
///
/// Input that is not clearsigned is returned unchanged, so callers can apply
/// this unconditionally before parsing.
pub fn strip_clearsigned_armour(text: &str) -> &str {
    const BEGIN_SIGNED: &str = "-----BEGIN PGP SIGNED MESSAGE-----";
    const BEGIN_SIGNATURE: &str = "-----BEGIN PGP SIGNATURE-----";

    if !text.starts_with(BEGIN_SIGNED) {
        return text;
    }

    // Walk past the armor headers to the blank line that precedes the body.
    let mut body = text;
    loop {
        match body.split_once('\n') {
            Some((line, remainder)) => {
                body = remainder;
                // An empty line ends the armor header block (`\r` covers a
                // CRLF-terminated blank line).
                if line.is_empty() || line == "\r" {
                    break;
                }
            }
            // Malformed armor: no body at all.
            None => return "",
        }
    }

    // Cut off the signature block, if present.
    match body.find(BEGIN_SIGNATURE) {
        Some(i) => &body[..i],
        None => body,
    }
}

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

    #[test]
    fn parse_simple_control() {
        let input = "Source: hello\nSection: devel\n\nPackage: hello\nDepends: libc6\n";
        let paras = parse_paragraphs(input);
        assert_eq!(paras.len(), 2);
        assert_eq!(paras[0].get("Source"), Some("hello"));
        assert_eq!(paras[0].get("section"), Some("devel"));
        assert_eq!(paras[1].get("Package"), Some("hello"));
        assert_eq!(paras[1].get("Depends"), Some("libc6"));
    }

    #[test]
    fn parse_multiline_and_comments() {
        let input = "# a comment\nDescription: short\n long description\n" //
            .to_string()
            + " spanning lines\n\nPackage: x\n";
        let paras = parse_paragraphs(&input);
        assert_eq!(paras.len(), 2);
        assert_eq!(
            paras[0].get("Description"),
            Some("short\nlong description\nspanning lines")
        );
    }

    #[test]
    fn roundtrip_multiline() {
        let value = "short\nlong description\nspanning lines";
        let mut p = Paragraph::new();
        p.set("Description", value);
        let text = write_paragraph(&p);
        assert_eq!(
            text,
            "Description: short\n long description\n spanning lines\n"
        );
        let reparsed = parse_paragraphs(&text);
        assert_eq!(reparsed[0].get("Description"), Some(value));
    }

    #[test]
    fn blank_lines_survive_roundtrip() {
        let mut p = Paragraph::new();
        p.set("Description", "a\n\nb");
        let text = write_paragraph(&p);
        // dpkg encoding: a blank line inside a value is written as ` .`.
        assert_eq!(text, "Description: a\n .\n b\n");
        // parse -> write -> parse must not lose data.
        let reparsed = parse_paragraphs(&text);
        assert_eq!(reparsed[0].get("Description"), Some("a\n\nb"));
        assert_eq!(
            parse_paragraphs(&write_paragraph(&reparsed[0]))[0].get("Description"),
            Some("a\n\nb")
        );
    }

    #[test]
    fn parse_lone_dot_continuation_is_blank_line() {
        let paras = parse_paragraphs("Description:\n a\n .\n b\n");
        assert_eq!(paras[0].get("Description"), Some("\na\n\nb"));
    }

    #[test]
    fn tab_continuation_strips_exactly_one_tab() {
        let paras = parse_paragraphs("Description: a\n\tb\n\t\tdeep\n");
        assert_eq!(paras[0].get("Description"), Some("a\nb\n\tdeep"));
    }

    #[test]
    fn strip_armour_extracts_signed_dsc_body() {
        let signed = "\
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

Format: 3.0 (native)
Source: hello
Binary: hello
Architecture: any
Version: 1.0-1
Checksums-Sha256:
 abc 100 hello_1.0.tar.gz

-----BEGIN PGP SIGNATURE-----

iQEcBAABCgAGBQJabcdAAoJEL abc
-----END PGP SIGNATURE-----
";
        let body = strip_clearsigned_armour(signed);
        assert!(body.starts_with("Format:"));
        assert!(!body.contains("SIGNATURE"));
        let paras = parse_paragraphs(body);
        assert_eq!(paras.len(), 1);
        // The armor `Hash:` header must not land in the stanza...
        assert!(paras[0].get("Hash").is_none());
        assert_eq!(paras[0].get("Source"), Some("hello"));
        // ...and the signature trailer must not contribute a `Comment:` field.
        assert!(paras[0].get("Comment").is_none());
        assert_eq!(
            paras[0].get("Checksums-Sha256"),
            Some("\nabc 100 hello_1.0.tar.gz")
        );
    }

    #[test]
    fn strip_armour_passes_unsigned_text_through() {
        let plain = "Source: hello\nVersion: 1.0\n";
        assert_eq!(strip_clearsigned_armour(plain), plain);
    }

    #[test]
    fn set_replaces_case_insensitive() {
        let mut p = Paragraph::new();
        p.set("Source", "a");
        p.set("source", "b");
        assert_eq!(p.get("SOURCE"), Some("b"));
        assert_eq!(p.iter().count(), 1);
    }

    #[test]
    fn lenient_parse_keeps_duplicate_fields() {
        let paras = parse_paragraphs("Package: hello\nDepends: a\ndepends: b\n");
        let p = &paras[0];
        // deb822 forbids duplicate fields but the parser is lenient and keeps
        // both entries; `get` returns the first.
        let depends: Vec<_> = p
            .iter()
            .filter(|(k, _)| k.eq_ignore_ascii_case("Depends"))
            .collect();
        assert_eq!(depends, [("Depends", "a"), ("depends", "b")]);
        assert_eq!(p.get("Depends"), Some("a"));
    }

    #[test]
    fn set_removes_case_insensitive_duplicates() {
        let mut paras = parse_paragraphs("Package: hello\nDepends: a\ndepends: b\n");
        let mut p = paras.remove(0);
        p.set("Depends", "c");
        // Exactly one depends-family entry remains, with the new value.
        let depends: Vec<_> = p
            .iter()
            .filter(|(k, _)| k.eq_ignore_ascii_case("Depends"))
            .collect();
        assert_eq!(depends, [("Depends", "c")]);
        assert_eq!(p.get("depends"), Some("c"));
        // ...kept at its original position, and a write round-trip no longer
        // leaks the stale duplicate.
        assert_eq!(write_paragraph(&p), "Package: hello\nDepends: c\n");
    }

    #[test]
    fn remove_field() {
        let mut p = Paragraph::new();
        p.set("A", "1");
        assert!(p.remove("a"));
        assert!(!p.remove("a"));
        assert!(p.is_empty());
    }
}

/// Parsed `debian/control`: the source stanza plus all binary stanzas.
#[derive(Debug, Clone)]
pub struct ControlInfo {
    /// First paragraph (source package stanza).
    pub source: Paragraph,
    /// Remaining paragraphs (binary package stanzas).
    pub binaries: Vec<Paragraph>,
}

impl ControlInfo {
    /// Parse a `debian/control` file.
    pub fn parse(path: &Path) -> Result<ControlInfo, Box<dyn std::error::Error>> {
        let content = std::fs::read_to_string(path)
            .map_err(|e| format!("failed to read control file '{}': {}", path.display(), e))?;
        content
            .parse::<ControlInfo>()
            .map_err(|e| format!("invalid control file '{}': {}", path.display(), e).into())
    }

    /// Parse control content from a string.
    ///
    /// Prefer [`std::str::FromStr`] (`"...".parse::<ControlInfo>()`).
    pub fn parse_content(content: &str) -> Result<ControlInfo, String> {
        let paragraphs = parse_paragraphs(content);
        let mut iter = paragraphs.into_iter();
        let source = iter
            .next()
            .ok_or_else(|| "control file has no paragraphs".to_string())?;
        if source.get("Source").is_none() {
            return Err("first control paragraph has no 'Source' field".to_string());
        }
        let binaries: Vec<Paragraph> = iter.collect();
        for bin in &binaries {
            if bin.get("Package").is_none() {
                return Err("binary control paragraph has no 'Package' field".to_string());
            }
        }
        Ok(ControlInfo { source, binaries })
    }

    /// The source package name.
    pub fn source_name(&self) -> &str {
        self.source.get("Source").expect("checked at parse")
    }

    /// Section from the source stanza, or `'-'`.
    pub fn section(&self) -> &str {
        self.source.get("Section").unwrap_or("-")
    }

    /// Priority from the source stanza, or `'-'`.
    pub fn priority(&self) -> &str {
        self.source.get("Priority").unwrap_or("-")
    }
}

impl std::str::FromStr for ControlInfo {
    type Err = String;

    fn from_str(content: &str) -> Result<Self, Self::Err> {
        ControlInfo::parse_content(content)
    }
}

#[cfg(test)]
mod control_info_tests {
    use super::*;
    use std::str::FromStr;

    #[test]
    fn control_parsing() {
        let ci = ControlInfo::from_str(
            "Source: hello\nSection: utils\nPriority: optional\nMaintainer: A B <a@b.c>\nBuild-Depends: debhelper\n\nPackage: hello\nArchitecture: any\nDescription: test\n long\n",
        )
        .unwrap();
        assert_eq!(ci.source_name(), "hello");
        assert_eq!(ci.section(), "utils");
        assert_eq!(ci.priority(), "optional");
        assert_eq!(ci.binaries.len(), 1);
        assert_eq!(ci.binaries[0].get("Package"), Some("hello"));
    }

    #[test]
    fn control_defaults() {
        let ci = ControlInfo::from_str("Source: x\n\nPackage: x\nDescription: d\n").unwrap();
        assert_eq!(ci.section(), "-");
        assert_eq!(ci.priority(), "-");
    }
}