//! Everything the preview panel shows about one commit.

use crate::git::git;
use serde::Serialize;
use std::path::Path;

#[derive(Serialize, Debug, PartialEq)]
pub struct ChangedFile {
    /// One letter: A added, M modified, D deleted, R renamed, C copied, T type changed.
    pub status: String,
    pub path: String,
    /// The path before a rename or copy.
    pub old_path: Option<String>,
    /// Line counts; `None` for binary files.
    pub added: Option<u32>,
    pub deleted: Option<u32>,
}

#[derive(Serialize, Debug)]
pub struct CommitDetails {
    hash: String,
    author: String,
    author_email: String,
    author_time: i64,
    committer: String,
    committer_email: String,
    commit_time: i64,
    parents: Vec<String>,
    /// The full message, subject line included.
    message: String,
    files: Vec<ChangedFile>,
}

/// Parses `git diff-tree -z --name-status` and `-z --numstat` output for the same diff.
pub fn parse_files(name_status: &str, numstat: &str) -> Vec<ChangedFile> {
    let mut counts = Vec::new();
    let mut num = numstat.split('\0').filter(|s| !s.is_empty());
    while let Some(head) = num.next() {
        let mut f = head.splitn(3, '\t');
        let added = f.next().and_then(|n| n.parse().ok());
        let deleted = f.next().and_then(|n| n.parse().ok());
        // A rename has an empty path here, followed by the old and new paths.
        if f.next().unwrap_or("").is_empty() {
            num.next();
            num.next();
        }
        counts.push((added, deleted));
    }

    let mut files = Vec::new();
    let mut ns = name_status.split('\0').filter(|s| !s.is_empty());
    while let Some(code) = ns.next() {
        let status = code[..1].to_string();
        let first = ns.next().unwrap_or_default().to_string();
        let (path, old_path) = if status == "R" || status == "C" {
            (ns.next().unwrap_or_default().to_string(), Some(first))
        } else {
            (first, None)
        };
        let (added, deleted) = counts.get(files.len()).copied().unwrap_or((None, None));
        files.push(ChangedFile { status, path, old_path, added, deleted });
    }
    files
}

pub fn load(dir: &Path, hash: &str) -> Result<CommitDetails, String> {
    // The hash comes from the window; refuse anything git could read as an option.
    if hash.is_empty() || !hash.chars().all(|c| c.is_ascii_hexdigit()) {
        return Err(format!("not a commit hash: {hash}"));
    }
    let info = git(
        dir,
        &["show", "-s", "--format=%H%x1f%an%x1f%ae%x1f%at%x1f%cn%x1f%ce%x1f%ct%x1f%P%x1f%B", hash, "--"],
    )?;
    let f: Vec<&str> = info.splitn(9, '\x1f').collect();
    if f.len() < 9 {
        return Err(format!("unexpected git show output for {hash}"));
    }
    let parents: Vec<String> = f[7].split_whitespace().map(String::from).collect();

    // A merge is compared with its first parent; other commits with their only parent,
    // or with nothing when they are the first commit.
    let mut args = vec!["diff-tree", "-r", "-M", "-z"];
    if let Some(first) = parents.first().filter(|_| parents.len() > 1) {
        args.push(first);
    } else {
        args.extend(["--root", "--no-commit-id"]);
    }
    args.push(hash);
    let with = |flag: &'static str| {
        let mut a = args.clone();
        a.insert(1, flag);
        git(dir, &a)
    };
    let files = parse_files(&with("--name-status")?, &with("--numstat")?);

    Ok(CommitDetails {
        hash: f[0].to_string(),
        author: f[1].to_string(),
        author_email: f[2].to_string(),
        author_time: f[3].parse().unwrap_or(0),
        committer: f[4].to_string(),
        committer_email: f[5].to_string(),
        commit_time: f[6].parse().unwrap_or(0),
        parents,
        message: f[8].trim_end().to_string(),
        files,
    })
}

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

    fn file(status: &str, path: &str, old: Option<&str>, a: Option<u32>, d: Option<u32>) -> ChangedFile {
        ChangedFile {
            status: status.into(),
            path: path.into(),
            old_path: old.map(String::from),
            added: a,
            deleted: d,
        }
    }

    #[test]
    fn parses_plain_changes() {
        let ns = "M\0src/a.ts\0A\0src/b.ts\0D\0old.txt\0";
        let num = "3\t1\tsrc/a.ts\09\t0\tsrc/b.ts\00\t40\told.txt\0";
        assert_eq!(
            parse_files(ns, num),
            vec![
                file("M", "src/a.ts", None, Some(3), Some(1)),
                file("A", "src/b.ts", None, Some(9), Some(0)),
                file("D", "old.txt", None, Some(0), Some(40)),
            ]
        );
    }

    #[test]
    fn parses_renames_and_binary_files() {
        let ns = "R087\0lib/old.rs\0lib/new.rs\0M\0logo.png\0";
        let num = "2\t2\t\0lib/old.rs\0lib/new.rs\0-\t-\tlogo.png\0";
        assert_eq!(
            parse_files(ns, num),
            vec![
                file("R", "lib/new.rs", Some("lib/old.rs"), Some(2), Some(2)),
                file("M", "logo.png", None, None, None),
            ]
        );
    }

    #[test]
    fn parses_an_empty_diff() {
        assert_eq!(parse_files("", ""), vec![]);
    }
}