plato-tile-import 0.1.0

//! plato-tile-import — Import/export knowledge tiles from external formats.
//! Supports Markdown, JSON, CSV, and plaintext. Zero external dependencies.

/// A knowledge tile imported from an external format.
#[derive(Debug, Clone, PartialEq)]
pub struct Tile {
    pub question: String,
    pub answer: String,
    pub tags: Vec<String>,
    pub domain: String,
}

impl Tile {
    pub fn new(question: impl Into<String>, answer: impl Into<String>) -> Self {
        Self {
            question: question.into(),
            answer: answer.into(),
            tags: vec![],
            domain: String::new(),
        }
    }
}

// ── Markdown ──────────────────────────────────────────────────────────────────

/// Import tiles from Markdown.
/// Each `## Header` section becomes a tile:
///   - question = the header text (stripped of ##)
///   - answer = the body text (trimmed)
///   - tags = [BracketedWord] anchors found in body
///   - domain = first word of question, lowercased
/// Sections with empty body are skipped.
pub fn import_markdown(md: &str) -> Vec<Tile> {
    let mut tiles = Vec::new();
    let mut current_q: Option<String> = None;
    let mut current_body = String::new();

    let flush = |current_q: &mut Option<String>, current_body: &mut String, tiles: &mut Vec<Tile>| {
        if let Some(q) = current_q.take() {
            let body = current_body.trim().to_string();
            if !body.is_empty() {
                let tags = extract_bracketed_tags(&body);
                let domain = q.split_whitespace().next().unwrap_or("").to_lowercase();
                tiles.push(Tile {
                    question: q,
                    answer: body,
                    tags,
                    domain,
                });
            }
        }
        current_body.clear();
    };

    for line in md.lines() {
        if let Some(header) = line.strip_prefix("## ") {
            flush(&mut current_q, &mut current_body, &mut tiles);
            current_q = Some(header.trim().to_string());
        } else if current_q.is_some() {
            if !current_body.is_empty() {
                current_body.push('\n');
            }
            current_body.push_str(line);
        }
    }
    flush(&mut current_q, &mut current_body, &mut tiles);
    tiles
}

/// Extract [BracketedWord] tokens from a string.
fn extract_bracketed_tags(s: &str) -> Vec<String> {
    let mut tags = Vec::new();
    let mut chars = s.chars().peekable();
    while let Some(c) = chars.next() {
        if c == '[' {
            let mut tag = String::new();
            let mut closed = false;
            for inner in chars.by_ref() {
                if inner == ']' {
                    closed = true;
                    break;
                }
                tag.push(inner);
            }
            if closed && !tag.is_empty() && tag.split_whitespace().count() == 1 {
                tags.push(tag);
            }
        }
    }
    tags
}

// ── JSON ──────────────────────────────────────────────────────────────────────

/// Import tiles from JSON array.
/// Expected format: [{"question": "...", "answer": "...", "tags": [...], "domain": "..."}]
/// Fields "tags" and "domain" are optional (default to empty).
/// Parse manually (no serde dependency).
pub fn import_json(json: &str) -> Vec<Tile> {
    let mut tiles = Vec::new();
    let trimmed = json.trim();
    if !trimmed.starts_with('[') {
        return tiles;
    }

    // Split objects by scanning depth
    let mut depth = 0i32;
    let mut current = String::new();
    let mut in_string = false;
    let mut escape_next = false;

    for c in trimmed.chars() {
        if escape_next {
            escape_next = false;
            if depth >= 1 {
                current.push(c);
            }
            continue;
        }
        if in_string {
            if c == '\\' {
                escape_next = true;
                if depth >= 1 {
                    current.push(c);
                }
                continue;
            }
            if c == '"' {
                in_string = false;
            }
            if depth >= 1 {
                current.push(c);
            }
            continue;
        }
        match c {
            '"' => {
                in_string = true;
                if depth >= 1 {
                    current.push(c);
                }
            }
            '{' => {
                depth += 1;
                if depth > 1 {
                    current.push(c);
                }
            }
            '}' => {
                depth -= 1;
                if depth == 0 {
                    let obj = current.trim().to_string();
                    current.clear();
                    if let Some(tile) = parse_json_object(&obj) {
                        tiles.push(tile);
                    }
                } else {
                    current.push(c);
                }
            }
            _ => {
                if depth >= 1 {
                    current.push(c);
                }
            }
        }
    }
    tiles
}

/// Parse a single JSON object body (contents between `{` and `}`) into a Tile.
fn parse_json_object(obj: &str) -> Option<Tile> {
    let question = json_string_value(obj, "question")?;
    let answer = json_string_value(obj, "answer")?;
    let domain = json_string_value(obj, "domain").unwrap_or_default();
    let tags = json_string_array(obj, "tags");
    Some(Tile { question, answer, tags, domain })
}

/// Extract the string value for a given key from a flat JSON object body.
/// Finds `"key": "value"` and returns `value`.
fn json_string_value(obj: &str, key: &str) -> Option<String> {
    let needle = format!("\"{}\"", key);
    let start = obj.find(&needle)?;
    let after_key = &obj[start + needle.len()..];
    // skip whitespace and colon
    let after_colon = after_key.trim_start().strip_prefix(':')?.trim_start();
    if !after_colon.starts_with('"') {
        return None;
    }
    let content = &after_colon[1..];
    let mut out = String::new();
    let mut chars = content.chars();
    loop {
        match chars.next()? {
            '\\' => {
                match chars.next()? {
                    'n' => out.push('\n'),
                    't' => out.push('\t'),
                    other => out.push(other),
                }
            }
            '"' => break,
            c => out.push(c),
        }
    }
    Some(out)
}

/// Extract a JSON string array value for a given key.
/// Returns empty Vec if key not found or value is not a string array.
fn json_string_array(obj: &str, key: &str) -> Vec<String> {
    let needle = format!("\"{}\"", key);
    let start = match obj.find(&needle) {
        Some(s) => s,
        None => return vec![],
    };
    let after_key = &obj[start + needle.len()..];
    let after_colon = match after_key.trim_start().strip_prefix(':') {
        Some(s) => s.trim_start(),
        None => return vec![],
    };
    if !after_colon.starts_with('[') {
        return vec![];
    }
    let inner_start = 1;
    // find closing bracket
    let end = match after_colon.find(']') {
        Some(e) => e,
        None => return vec![],
    };
    let array_body = &after_colon[inner_start..end];
    let mut result = Vec::new();
    // scan for quoted strings inside the array
    let mut chars = array_body.chars().peekable();
    while let Some(c) = chars.next() {
        if c == '"' {
            let mut s = String::new();
            let mut closed = false;
            loop {
                match chars.next() {
                    None => break,
                    Some('\\') => {
                        if let Some(e) = chars.next() {
                            s.push(e);
                        }
                    }
                    Some('"') => { closed = true; break; }
                    Some(other) => s.push(other),
                }
            }
            if closed {
                result.push(s);
            }
        }
    }
    result
}

// ── CSV ───────────────────────────────────────────────────────────────────────

/// Import tiles from CSV.
/// Format: question,answer,domain (header row required with those names)
/// Comma-separated, values may be quoted with double quotes.
/// Tags field is optional and skipped.
pub fn import_csv(csv: &str) -> Vec<Tile> {
    let mut tiles = Vec::new();
    let mut lines = csv.lines();

    // Read and parse header
    let header_line = loop {
        match lines.next() {
            None => return tiles,
            Some(l) if !l.trim().is_empty() => break l,
            _ => {}
        }
    };

    let headers: Vec<String> = csv_parse_row(header_line)
        .into_iter()
        .map(|h| h.trim().to_lowercase())
        .collect();

    let question_idx = headers.iter().position(|h| h == "question");
    let answer_idx = headers.iter().position(|h| h == "answer");
    let domain_idx = headers.iter().position(|h| h == "domain");

    let (qi, ai) = match (question_idx, answer_idx) {
        (Some(q), Some(a)) => (q, a),
        _ => return tiles,
    };

    for line in lines {
        let line = line.trim();
        if line.is_empty() {
            continue;
        }
        let fields = csv_parse_row(line);
        let question = match fields.get(qi) {
            Some(v) => v.trim().to_string(),
            None => continue,
        };
        let answer = match fields.get(ai) {
            Some(v) => v.trim().to_string(),
            None => continue,
        };
        if question.is_empty() {
            continue;
        }
        let domain = domain_idx
            .and_then(|di| fields.get(di))
            .map(|d| d.trim().to_string())
            .unwrap_or_default();
        tiles.push(Tile { question, answer, tags: vec![], domain });
    }
    tiles
}

/// Parse a single CSV row, handling double-quote quoting.
fn csv_parse_row(line: &str) -> Vec<String> {
    let mut fields = Vec::new();
    let mut field = String::new();
    let mut in_quotes = false;
    let mut chars = line.chars().peekable();

    while let Some(c) = chars.next() {
        match c {
            '"' if in_quotes => {
                if chars.peek() == Some(&'"') {
                    // escaped quote
                    chars.next();
                    field.push('"');
                } else {
                    in_quotes = false;
                }
            }
            '"' => {
                in_quotes = true;
            }
            ',' if !in_quotes => {
                fields.push(field.clone());
                field.clear();
            }
            other => {
                field.push(other);
            }
        }
    }
    fields.push(field);
    fields
}

// ── Plaintext ─────────────────────────────────────────────────────────────────

/// Import tiles from plain text.
/// Split by double-newline (paragraph boundaries).
/// Within each paragraph: first non-empty line = question, remaining lines joined = answer.
/// Skip paragraphs with no answer.
pub fn import_plaintext(text: &str) -> Vec<Tile> {
    let mut tiles = Vec::new();
    // Split on double newlines
    let paragraphs: Vec<&str> = text.split("\n\n").collect();

    for para in paragraphs {
        let mut non_empty_lines: Vec<&str> = para.lines().filter(|l| !l.trim().is_empty()).collect();
        if non_empty_lines.len() < 2 {
            continue;
        }
        let question = non_empty_lines.remove(0).trim().to_string();
        let answer = non_empty_lines.join(" ").trim().to_string();
        if answer.is_empty() {
            continue;
        }
        tiles.push(Tile::new(question, answer));
    }
    tiles
}

// ── Export ────────────────────────────────────────────────────────────────────

/// Export tiles to Markdown format.
/// Each tile: "## {question}\n{answer}\n\n"
pub fn export_markdown(tiles: &[Tile]) -> String {
    tiles
        .iter()
        .map(|t| format!("## {}\n{}\n\n", t.question, t.answer))
        .collect()
}

// ── Tests ─────────────────────────────────────────────────────────────────────

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

    // --- import_markdown ---

    #[test]
    fn test_markdown_parses_sections() {
        let md = "## What is Rust?\nA systems programming language.\n\n## What is cargo?\nThe Rust package manager.";
        let tiles = import_markdown(md);
        assert_eq!(tiles.len(), 2);
        assert_eq!(tiles[0].question, "What is Rust?");
        assert_eq!(tiles[0].answer, "A systems programming language.");
        assert_eq!(tiles[1].question, "What is cargo?");
        assert_eq!(tiles[1].answer, "The Rust package manager.");
    }

    #[test]
    fn test_markdown_skips_empty_sections() {
        let md = "## Empty Section\n\n## Real Section\nHas content here.";
        let tiles = import_markdown(md);
        assert_eq!(tiles.len(), 1);
        assert_eq!(tiles[0].question, "Real Section");
    }

    #[test]
    fn test_markdown_extracts_bracketed_tags() {
        let md = "## What is [Rust]?\nA language. See [Systems] and [Memory] safety.";
        let tiles = import_markdown(md);
        assert_eq!(tiles.len(), 1);
        assert!(tiles[0].tags.contains(&"Systems".to_string()));
        assert!(tiles[0].tags.contains(&"Memory".to_string()));
        // "Rust]?" should not parse as a tag since it's in the header not the body
    }

    #[test]
    fn test_markdown_domain_from_first_word() {
        let md = "## Ownership in Rust\nCore memory concept.";
        let tiles = import_markdown(md);
        assert_eq!(tiles[0].domain, "ownership");
    }

    #[test]
    fn test_markdown_multiline_answer() {
        let md = "## Question\nLine one.\nLine two.\nLine three.";
        let tiles = import_markdown(md);
        assert_eq!(tiles.len(), 1);
        assert!(tiles[0].answer.contains("Line one."));
        assert!(tiles[0].answer.contains("Line two."));
        assert!(tiles[0].answer.contains("Line three."));
    }

    // --- import_json ---

    #[test]
    fn test_json_parses_basic_array() {
        let json = r#"[{"question":"What is 2+2?","answer":"4","domain":"math"}]"#;
        let tiles = import_json(json);
        assert_eq!(tiles.len(), 1);
        assert_eq!(tiles[0].question, "What is 2+2?");
        assert_eq!(tiles[0].answer, "4");
        assert_eq!(tiles[0].domain, "math");
    }

    #[test]
    fn test_json_handles_missing_optional_fields() {
        let json = r#"[{"question":"Q?","answer":"A."}]"#;
        let tiles = import_json(json);
        assert_eq!(tiles.len(), 1);
        assert_eq!(tiles[0].domain, "");
        assert!(tiles[0].tags.is_empty());
    }

    #[test]
    fn test_json_skips_objects_without_question_or_answer() {
        let json = r#"[{"domain":"math"},{"question":"Q?","answer":"A."}]"#;
        let tiles = import_json(json);
        assert_eq!(tiles.len(), 1);
        assert_eq!(tiles[0].question, "Q?");
    }

    #[test]
    fn test_json_parses_tags_array() {
        let json = r#"[{"question":"Q","answer":"A","tags":["tag1","tag2"]}]"#;
        let tiles = import_json(json);
        assert_eq!(tiles[0].tags, vec!["tag1", "tag2"]);
    }

    // --- import_csv ---

    #[test]
    fn test_csv_parses_header_and_rows() {
        let csv = "question,answer,domain\nWhat is Rust?,A systems language,programming\nWhat is cargo?,Package manager,tooling";
        let tiles = import_csv(csv);
        assert_eq!(tiles.len(), 2);
        assert_eq!(tiles[0].question, "What is Rust?");
        assert_eq!(tiles[0].answer, "A systems language");
        assert_eq!(tiles[0].domain, "programming");
    }

    #[test]
    fn test_csv_quoted_fields() {
        let csv = "question,answer\n\"Question, with comma\",\"Answer, with comma\"";
        let tiles = import_csv(csv);
        assert_eq!(tiles.len(), 1);
        assert_eq!(tiles[0].question, "Question, with comma");
        assert_eq!(tiles[0].answer, "Answer, with comma");
    }

    // --- import_plaintext ---

    #[test]
    fn test_plaintext_splits_on_double_newlines() {
        let text = "Question one\nAnswer one\n\nQuestion two\nAnswer two";
        let tiles = import_plaintext(text);
        assert_eq!(tiles.len(), 2);
    }

    #[test]
    fn test_plaintext_first_line_is_question() {
        let text = "What is the sky?\nBlue.";
        let tiles = import_plaintext(text);
        // Single paragraph: question = "What is the sky?", answer = "Blue."
        // But wait — single \n, not double, so whole thing is one paragraph
        assert_eq!(tiles.len(), 1);
        assert_eq!(tiles[0].question, "What is the sky?");
        assert_eq!(tiles[0].answer, "Blue.");
    }

    #[test]
    fn test_plaintext_skips_paragraphs_with_no_answer() {
        let text = "Lonely header\n\nReal Question\nReal Answer";
        let tiles = import_plaintext(text);
        assert_eq!(tiles.len(), 1);
        assert_eq!(tiles[0].question, "Real Question");
    }

    // --- export_markdown ---

    #[test]
    fn test_export_markdown_format() {
        let tiles = vec![Tile::new("What is pi?", "Approximately 3.14159.")];
        let md = export_markdown(&tiles);
        assert!(md.contains("## What is pi?"));
        assert!(md.contains("Approximately 3.14159."));
    }

    #[test]
    fn test_export_markdown_roundtrip_with_import() {
        let original = vec![
            Tile::new("What is Rust?", "A systems language."),
            Tile::new("What is cargo?", "The package manager."),
        ];
        let md = export_markdown(&original);
        let imported = import_markdown(&md);
        assert_eq!(imported.len(), 2);
        assert_eq!(imported[0].question, original[0].question);
        assert_eq!(imported[0].answer, original[0].answer);
        assert_eq!(imported[1].question, original[1].question);
        assert_eq!(imported[1].answer, original[1].answer);
    }

    #[test]
    fn test_import_export_markdown_consistency() {
        let md = "## Alpha\nFirst answer.\n\n## Beta\nSecond answer.\n\n";
        let tiles = import_markdown(md);
        let re_exported = export_markdown(&tiles);
        let re_imported = import_markdown(&re_exported);
        assert_eq!(tiles.len(), re_imported.len());
        for (a, b) in tiles.iter().zip(re_imported.iter()) {
            assert_eq!(a.question, b.question);
            assert_eq!(a.answer, b.answer);
        }
    }
}