vership 0.5.0

use std::collections::BTreeMap;

use chrono::Local;
use regex::Regex;

use crate::git::Commit;

#[derive(Debug, Clone)]
pub struct ConventionalCommit {
    pub commit_type: String,
    pub scope: Option<String>,
    pub description: String,
    pub breaking: bool,
}

/// Parse a conventional commit message. Returns None for non-conventional or merge commits.
pub fn parse_conventional_commit(message: &str) -> Option<ConventionalCommit> {
    if message.starts_with("Merge ") {
        return None;
    }

    let re = Regex::new(r"^(\w+)(?:\(([^)]+)\))?(!)?: (.+)$").expect("valid regex");
    let caps = re.captures(message)?;

    Some(ConventionalCommit {
        commit_type: caps[1].to_string(),
        scope: caps.get(2).map(|m| m.as_str().to_string()),
        breaking: caps.get(3).is_some(),
        description: caps[4].to_string(),
    })
}

/// Map commit type to changelog section name. Returns None for excluded types.
fn type_to_section(commit_type: &str) -> Option<&'static str> {
    match commit_type {
        "feat" => Some("Added"),
        "fix" => Some("Fixed"),
        "perf" => Some("Performance"),
        "change" => Some("Changed"),
        _ => None,
    }
}

/// Generate a changelog section for a release.
///
/// - `commits`: list of commits since the previous tag
/// - `version`: new version string (without `v` prefix)
/// - `previous_tag`: previous tag string (with `v` prefix), or None for first release
/// - `remote_url`: base URL for commit/compare links (e.g. "https://github.com/rvben/vership")
pub fn generate_changelog(
    commits: &[Commit],
    version: &str,
    previous_tag: Option<&str>,
    remote_url: Option<&str>,
) -> String {
    let mut breaking: Vec<String> = Vec::new();
    let mut sections: BTreeMap<&str, Vec<String>> = BTreeMap::new();

    for commit in commits {
        let Some(cc) = parse_conventional_commit(&commit.message) else {
            continue;
        };

        let entry = format_entry(&cc, commit, remote_url);

        if cc.breaking {
            breaking.push(entry.clone());
        }

        if let Some(section) = type_to_section(&cc.commit_type) {
            sections.entry(section).or_default().push(entry);
        }
    }

    let date = Local::now().format("%Y-%m-%d");
    let mut output = String::new();

    // Version header with optional compare link
    match (remote_url, previous_tag) {
        (Some(url), Some(prev)) => {
            // Normalize the previous tag to always have a `v` prefix
            let prev_tag = if prev.starts_with('v') {
                prev.to_string()
            } else {
                format!("v{prev}")
            };
            output.push_str(&format!(
                "## [{version}]({url}/compare/{prev_tag}...v{version}) - {date}\n",
            ));
        }
        _ => {
            output.push_str(&format!("## [{version}] - {date}\n"));
        }
    }

    // Section order: Breaking Changes first, then Added, Changed, Fixed, Performance
    let section_order = [
        "Breaking Changes",
        "Added",
        "Changed",
        "Fixed",
        "Performance",
    ];

    if !breaking.is_empty() {
        output.push_str("\n### Breaking Changes\n\n");
        for entry in &breaking {
            output.push_str(&format!("- {entry}\n"));
        }
    }

    for section_name in &section_order {
        if *section_name == "Breaking Changes" {
            continue; // Already handled above
        }
        if let Some(entries) = sections.get(section_name) {
            output.push_str(&format!("\n### {section_name}\n\n"));
            for entry in entries {
                output.push_str(&format!("- {entry}\n"));
            }
        }
    }

    output
}

fn format_entry(cc: &ConventionalCommit, commit: &Commit, remote_url: Option<&str>) -> String {
    let scope_prefix = cc
        .scope
        .as_ref()
        .map(|s| format!("**{s}**: "))
        .unwrap_or_default();

    let hash_suffix = match remote_url {
        Some(url) => {
            let short_hash = &commit.hash[..7.min(commit.hash.len())];
            format!(" ([{short_hash}]({url}/commit/{}))", commit.hash)
        }
        None => String::new(),
    };

    format!("{scope_prefix}{}{hash_suffix}", cc.description)
}

/// Generate changelog with unconventional commit handling mode.
///
/// - "exclude" (default): silently skip non-conventional commits
/// - "include": add them under an "Other" section
/// - "strict": return an error if any non-conventional commit is found
pub fn generate_changelog_with_mode(
    commits: &[Commit],
    version: &str,
    previous_tag: Option<&str>,
    remote_url: Option<&str>,
    unconventional_mode: &str,
) -> std::result::Result<String, String> {
    if unconventional_mode == "strict" {
        for commit in commits {
            if commit.message.starts_with("Merge ") {
                continue;
            }
            if parse_conventional_commit(&commit.message).is_none() {
                return Err(format!(
                    "non-conventional commit found (strict mode): {} {}",
                    &commit.hash[..7.min(commit.hash.len())],
                    commit.message
                ));
            }
        }
    }

    let mut output = generate_changelog(commits, version, previous_tag, remote_url);

    if unconventional_mode == "include" {
        let unconventional: Vec<&Commit> = commits
            .iter()
            .filter(|c| !c.message.starts_with("Merge "))
            .filter(|c| parse_conventional_commit(&c.message).is_none())
            .collect();

        if !unconventional.is_empty() {
            output.push_str("\n### Other\n\n");
            for commit in unconventional {
                let short_hash = &commit.hash[..7.min(commit.hash.len())];
                match remote_url {
                    Some(url) => output.push_str(&format!(
                        "- {} ([{short_hash}]({url}/commit/{}))\n",
                        commit.message, commit.hash
                    )),
                    None => output.push_str(&format!("- {}\n", commit.message)),
                }
            }
        }
    }

    Ok(output)
}

/// Prepend a new changelog section to an existing CHANGELOG.md content.
/// Creates the standard file structure when no existing content is provided.
pub fn prepend_to_changelog(existing: Option<&str>, new_section: &str) -> String {
    let header = "# Changelog\n\nAll notable changes to this project will be documented in this file.\n\nThe format is based on [Keep a Changelog](https://keepachangelog.com/).\n";

    match existing {
        Some(content) => {
            // Find the first ## heading and insert before it
            if let Some(pos) = content.find("\n## ") {
                let (before, after) = content.split_at(pos + 1);
                format!("{before}\n{new_section}\n{after}")
            } else {
                // No existing versions, append after header
                format!("{content}\n{new_section}")
            }
        }
        None => {
            format!("{header}\n{new_section}")
        }
    }
}

/// Check if a CHANGELOG.md already has an entry for the given version.
pub fn version_exists_in_changelog(content: &str, version: &str) -> bool {
    content.contains(&format!("## [{version}]"))
}