use serde::Deserialize;

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum TestPlanStatus {
    Approved,
    WaitingForApproval,
    Unknown(String),
}

#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub struct StoryMetadata {
    pub name: Option<String>,
    pub test_plan: Option<TestPlanStatus>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum StoryMetaError {
    MissingFrontMatter,
    InvalidFrontMatter(String),
}

impl std::fmt::Display for StoryMetaError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            StoryMetaError::MissingFrontMatter => write!(f, "Missing front matter"),
            StoryMetaError::InvalidFrontMatter(msg) => write!(f, "Invalid front matter: {msg}"),
        }
    }
}

#[derive(Debug, Deserialize)]
struct FrontMatter {
    name: Option<String>,
    test_plan: Option<String>,
}

pub fn parse_front_matter(contents: &str) -> Result<StoryMetadata, StoryMetaError> {
    let mut lines = contents.lines();

    let first = lines.next().unwrap_or_default().trim();
    if first != "---" {
        return Err(StoryMetaError::MissingFrontMatter);
    }

    let mut front_lines = Vec::new();
    for line in &mut lines {
        let trimmed = line.trim();
        if trimmed == "---" {
            let raw = front_lines.join("\n");
            let front: FrontMatter = serde_yaml::from_str(&raw)
                .map_err(|e| StoryMetaError::InvalidFrontMatter(e.to_string()))?;
            return Ok(build_metadata(front));
        }
        front_lines.push(line);
    }

    Err(StoryMetaError::InvalidFrontMatter(
        "Missing closing front matter delimiter".to_string(),
    ))
}

fn build_metadata(front: FrontMatter) -> StoryMetadata {
    let test_plan = front.test_plan.as_deref().map(parse_test_plan_status);

    StoryMetadata {
        name: front.name,
        test_plan,
    }
}

pub fn parse_unchecked_todos(contents: &str) -> Vec<String> {
    contents
        .lines()
        .filter_map(|line| {
            let trimmed = line.trim();
            trimmed
                .strip_prefix("- [ ] ")
                .map(|text| text.to_string())
        })
        .collect()
}

fn parse_test_plan_status(value: &str) -> TestPlanStatus {
    match value {
        "approved" => TestPlanStatus::Approved,
        "waiting_for_approval" => TestPlanStatus::WaitingForApproval,
        other => TestPlanStatus::Unknown(other.to_string()),
    }
}

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

    #[test]
    fn parses_front_matter_metadata() {
        let input = r#"---
name: Establish the TDD Workflow and Gates
test_plan: approved
workflow: tdd
---
# Story 26
"#;

        let meta = parse_front_matter(input).expect("front matter");
        assert_eq!(
            meta,
            StoryMetadata {
                name: Some("Establish the TDD Workflow and Gates".to_string()),
                test_plan: Some(TestPlanStatus::Approved),
            }
        );
    }

    #[test]
    fn rejects_missing_front_matter() {
        let input = "# Story 26\n";
        assert_eq!(
            parse_front_matter(input),
            Err(StoryMetaError::MissingFrontMatter)
        );
    }

    #[test]
    fn rejects_unclosed_front_matter() {
        let input = "---\nname: Test\n";
        assert!(matches!(
            parse_front_matter(input),
            Err(StoryMetaError::InvalidFrontMatter(_))
        ));
    }

    #[test]
    fn parse_unchecked_todos_mixed() {
        let input = "## AC\n- [ ] First thing\n- [x] Done thing\n- [ ] Second thing\n";
        assert_eq!(
            parse_unchecked_todos(input),
            vec!["First thing", "Second thing"]
        );
    }

    #[test]
    fn parse_unchecked_todos_all_checked() {
        let input = "- [x] Done\n- [x] Also done\n";
        assert!(parse_unchecked_todos(input).is_empty());
    }

    #[test]
    fn parse_unchecked_todos_no_checkboxes() {
        let input = "# Story\nSome text\n- A bullet\n";
        assert!(parse_unchecked_todos(input).is_empty());
    }

    #[test]
    fn parse_unchecked_todos_leading_whitespace() {
        let input = "  - [ ] Indented item\n";
        assert_eq!(parse_unchecked_todos(input), vec!["Indented item"]);
    }
}