//! `diff <pr> [repo]` — print the unified diff for a PR.
//!
//! By default any per-file section whose target path matches a
//! known autogenerated lockfile (`flake.lock`, `Cargo.lock`,
//! `package-lock.json`, …) is collapsed to a single
//! `[<path>: contents changed (+N -M, --full for content)]`
//! line so a `flake.lock` rev bump doesn't drown the human-
//! authored changes in 5 000 lines of lock churn (#222). The
//! per-file git headers (`diff --git`, `index`, `---`, `+++`,
//! and any rename / mode metadata) are suppressed alongside the
//! hunks since the placeholder already carries the file path and
//! the +/- magnitude — the headers add four lines of noise per
//! lockfile without any information the reader can act on.
//! Pass `--full` to dump the unfiltered diff.

use anyhow::Result;
use clap::Args as ClapArgs;

use crate::client::Client;

#[derive(ClapArgs)]
pub struct Args {
    /// PR number.
    number: u64,
    /// Print the unfiltered diff including autogenerated-file
    /// hunks (`flake.lock`, `Cargo.lock`, etc.). Default is to
    /// collapse those hunks to a placeholder so the human-authored
    /// changes aren't drowned in lock churn.
    #[arg(long)]
    full: bool,
}

pub fn run(client: &Client, args: Args) -> Result<()> {
    let repo = client.repo();
    let diff = client.get_text(
        &format!("/repos/{repo}/pulls/{}.diff", args.number),
        "text/plain",
    )?;
    let out = if args.full {
        diff
    } else {
        collapse_autogenerated(&diff)
    };
    print!("{out}");
    Ok(())
}

/// Walk a unified diff line-by-line. When a `diff --git` line
/// names a known autogenerated file (`is_autogenerated`), suppress
/// every line of that per-file section (the git headers AND the
/// hunks) and emit a single `[file.lock: contents changed (+N -M,
/// --full for content)]` line in their place. Non-autogenerated
/// files pass through unchanged.
fn collapse_autogenerated(diff: &str) -> String {
    let mut out = String::with_capacity(diff.len());
    let mut state: Option<CollapseState> = None;

    for line in diff.lines() {
        if let Some(rest) = line.strip_prefix("diff --git ") {
            // New file section — flush prior collapse counter.
            if let Some(s) = state.take() {
                out.push_str(&s.placeholder());
            }
            let path = parse_diff_git_path(rest);
            if let Some(p) = path.as_deref()
                && is_autogenerated(p)
            {
                // Suppress the entire per-file block (headers and
                // hunks alike). The placeholder we emit on flush
                // carries the path, so the git headers are pure
                // noise.
                state = Some(CollapseState::new(p.to_owned()));
                continue;
            }
            out.push_str(line);
            out.push('\n');
            continue;
        }
        if let Some(s) = state.as_mut() {
            // Inside an autogenerated section. Tally `+`/`-` body
            // lines for the placeholder; drop everything else
            // (headers, `@@` markers, context lines).
            if s.in_body || line.starts_with("@@") {
                s.in_body = true;
                if !line.starts_with("@@") {
                    match line.as_bytes().first() {
                        Some(b'+') => s.added += 1,
                        Some(b'-') => s.removed += 1,
                        _ => {}
                    }
                }
            }
            continue;
        }
        out.push_str(line);
        out.push('\n');
    }
    if let Some(s) = state.take() {
        out.push_str(&s.placeholder());
    }
    out
}

/// Per-file accumulator for the collapsed placeholder. Tracks
/// the file's display name plus `+`/`-` line counts (excluding
/// the `@@` hunk header), so the placeholder shows operator-
/// meaningful magnitude instead of "N lines omitted" (which
/// mixed context + added + removed indistinguishably).
struct CollapseState {
    path: String,
    in_body: bool,
    added: u32,
    removed: u32,
}

impl CollapseState {
    fn new(path: String) -> Self {
        Self {
            path,
            in_body: false,
            added: 0,
            removed: 0,
        }
    }

    fn placeholder(&self) -> String {
        format!(
            "[{}: contents changed (+{} -{}, --full for content)]\n",
            self.path, self.added, self.removed
        )
    }
}

/// `rest` is everything after `diff --git `, e.g. `a/foo b/foo`
/// or `"a/path with space" "b/path with space"`. Return the
/// post-rename (`b/`-side) path so renames report the new path.
///
/// Git uses C-style quoting (`\"`, `\\`, octal escapes) for paths
/// with spaces or unusual bytes — we don't unescape because we
/// only need the bytewise file name for the lockfile allowlist
/// match. We do parse the quoted-vs-unquoted form correctly so a
/// whitespace-containing path doesn't break `split_whitespace`.
fn parse_diff_git_path(rest: &str) -> Option<String> {
    if let Some(after_open) = rest.strip_prefix('"') {
        // Quoted form: `"a/<path>" "b/<path>"`. Find the closing
        // quote of the a-side (skipping `\"` escapes so a path
        // containing `"` doesn't terminate early).
        let mut iter = after_open.char_indices();
        let mut a_close = None;
        while let Some((i, c)) = iter.next() {
            if c == '\\' {
                // Skip the next char — it's part of the escape.
                iter.next();
                continue;
            }
            if c == '"' {
                a_close = Some(i);
                break;
            }
        }
        let a_close = a_close?;
        // After the a-side closing quote, we expect `" "b/...`.
        // `after_open` skipped the leading `"`, so the b-side
        // starts in `after_open[a_close + 1..]` — strip leading
        // space + opening quote + `b/`, then strip trailing `"`.
        let after_a = after_open.get(a_close + 1..)?;
        let after_a = after_a.strip_prefix(' ')?;
        let b_inside = after_a.strip_prefix('"')?;
        // Find b-side's closing quote with the same escape rule.
        let mut iter = b_inside.char_indices();
        let mut b_close = None;
        while let Some((i, c)) = iter.next() {
            if c == '\\' {
                iter.next();
                continue;
            }
            if c == '"' {
                b_close = Some(i);
                break;
            }
        }
        let b_close = b_close?;
        let b_path = b_inside.get(..b_close)?;
        Some(b_path.strip_prefix("b/").unwrap_or(b_path).to_owned())
    } else {
        // Unquoted: paths have no whitespace, so `split_whitespace`
        // gives exactly two tokens.
        let token = rest.split_whitespace().nth(1)?;
        Some(token.strip_prefix("b/").unwrap_or(token).to_owned())
    }
}

/// File-name match against a small whitelist of well-known
/// machine-generated lockfiles. We deliberately don't pattern-match
/// extensions like `*.lock` because some real human-authored files
/// use that suffix (e.g. `keep.lock` config markers); explicit
/// listing avoids surprising the user.
fn is_autogenerated(path: &str) -> bool {
    let name = path.rsplit('/').next().unwrap_or(path);
    matches!(
        name,
        "flake.lock"
            | "Cargo.lock"
            | "package-lock.json"
            | "pnpm-lock.yaml"
            | "yarn.lock"
            | "Gemfile.lock"
            | "poetry.lock"
            | "Pipfile.lock"
            | "composer.lock"
            | "go.sum"
    )
}

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

    #[test]
    fn detects_known_lockfiles() {
        assert!(is_autogenerated("flake.lock"));
        assert!(is_autogenerated("a/flake.lock"));
        assert!(is_autogenerated("hive-c0re/Cargo.lock"));
        assert!(is_autogenerated(
            "frontend/packages/dashboard/package-lock.json"
        ));
        assert!(!is_autogenerated("src/main.rs"));
        assert!(!is_autogenerated("Cargo.toml"));
        // Suffix-only files we deliberately don't match — keep
        // `is_autogenerated` allowlist-driven, not pattern-driven.
        assert!(!is_autogenerated("config/keep.lock"));
    }

    #[test]
    fn collapse_replaces_lockfile_hunks_with_placeholder() {
        let diff = "\
diff --git a/Cargo.lock b/Cargo.lock
index 1111..2222 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,3 +1,3 @@
 [[package]]
-name = \"old\"
+name = \"new\"
diff --git a/src/main.rs b/src/main.rs
index 3333..4444 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,2 +1,2 @@
-fn main() {}
+fn main() { println!(\"hi\"); }
";
        let out = collapse_autogenerated(diff);
        // Per-file git headers for the lockfile are suppressed —
        // the placeholder already carries the path, so the four
        // header lines are pure noise (4 lines per lockfile, stacks
        // fast on a multi-lockfile PR).
        assert!(!out.contains("diff --git a/Cargo.lock"));
        assert!(!out.contains("--- a/Cargo.lock"));
        assert!(!out.contains("+++ b/Cargo.lock"));
        assert!(!out.contains("[[package]]"));
        // Stat-style placeholder: 1 added (`+name = "new"`), 1
        // removed (`-name = "old"`); context line and `@@` header
        // don't count.
        assert!(
            out.contains("[Cargo.lock: contents changed (+1 -1, --full for content)]"),
            "expected one-line placeholder, got: {out}"
        );
        // Non-lockfile file passes through untouched.
        assert!(out.contains("diff --git a/src/main.rs"));
        assert!(out.contains("fn main() {}"));
        assert!(out.contains("println!(\"hi\")"));
    }

    #[test]
    fn collapse_passes_normal_diff_through() {
        let diff = "\
diff --git a/src/lib.rs b/src/lib.rs
index aaaa..bbbb 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,1 +1,1 @@
-fn old() {}
+fn new() {}
";
        let out = collapse_autogenerated(diff);
        assert_eq!(out, diff);
    }

    #[test]
    fn collapse_handles_trailing_lockfile() {
        // Lockfile is the LAST file in the diff — exercises the
        // post-loop flush path.
        let diff = "\
diff --git a/README.md b/README.md
index aaaa..bbbb 100644
--- a/README.md
+++ b/README.md
@@ -1,1 +1,1 @@
-old
+new
diff --git a/flake.lock b/flake.lock
index 1111..2222 100644
--- a/flake.lock
+++ b/flake.lock
@@ -1,2 +1,2 @@
 lock-line-one
-lock-line-two
+lock-line-two-bumped
";
        let out = collapse_autogenerated(diff);
        // README.md (non-lockfile) passes through with its full
        // header + hunks intact.
        assert!(out.contains("diff --git a/README.md"));
        assert!(out.contains("-old"));
        assert!(out.contains("+new"));
        // Lockfile is fully suppressed — no headers, no content.
        assert!(!out.contains("diff --git a/flake.lock"));
        assert!(!out.contains("lock-line-one"));
        assert!(
            out.contains("[flake.lock: contents changed (+1 -1, --full for content)]"),
            "expected one-line placeholder, got: {out}"
        );
    }

    #[test]
    fn collapse_counts_distinguish_added_and_removed() {
        // Big asymmetric churn — flake.lock rev bump with several
        // adds and one removal in the worker fields. Verifies
        // we don't conflate `+`/`-` totals.
        let diff = "\
diff --git a/flake.lock b/flake.lock
index 1111..2222 100644
--- a/flake.lock
+++ b/flake.lock
@@ -1,5 +1,8 @@
 {
-  \"old\": 1
+  \"new\": 1,
+  \"another\": 2,
+  \"and\": 3,
+  \"more\": 4
 }
";
        let out = collapse_autogenerated(diff);
        assert!(
            out.contains("[flake.lock: contents changed (+4 -1, --full for content)]"),
            "expected +4 -1, got: {out}"
        );
    }

    #[test]
    fn parse_diff_git_path_picks_b_side() {
        assert_eq!(parse_diff_git_path("a/foo b/foo"), Some("foo".to_owned()));
        assert_eq!(
            parse_diff_git_path("a/old.txt b/new.txt"),
            Some("new.txt".to_owned())
        );
        assert_eq!(
            parse_diff_git_path("a/dir/Cargo.lock b/dir/Cargo.lock"),
            Some("dir/Cargo.lock".to_owned())
        );
    }

    #[test]
    fn parse_diff_git_path_handles_quoted_paths_with_spaces() {
        // Git quotes paths with spaces / unusual chars per
        // `core.quotePath`. The b-side path must survive intact.
        assert_eq!(
            parse_diff_git_path("\"a/foo bar\" \"b/foo bar\""),
            Some("foo bar".to_owned())
        );
        // Rename with quoted sides.
        assert_eq!(
            parse_diff_git_path("\"a/old name\" \"b/new name\""),
            Some("new name".to_owned())
        );
        // Lockfile inside a directory whose name has a space.
        assert_eq!(
            parse_diff_git_path("\"a/dir with space/Cargo.lock\" \"b/dir with space/Cargo.lock\""),
            Some("dir with space/Cargo.lock".to_owned())
        );
    }

    #[test]
    fn parse_diff_git_path_handles_escaped_quote_inside_path() {
        // Git escapes embedded `"` as `\"`. The closing-quote
        // search must skip these so it doesn't terminate early.
        // Path is literally `a/has"quote` / `b/has"quote`.
        let rest = r#""a/has\"quote" "b/has\"quote""#;
        assert_eq!(
            parse_diff_git_path(rest),
            // Bytewise: backslash + quote stay in the result
            // because we don't unescape (allowlist match is by
            // file name, never contains escapes).
            Some(r#"has\"quote"#.to_owned())
        );
    }

    #[test]
    fn collapse_recognises_lockfile_in_quoted_path() {
        // Path "a/odd dir/Cargo.lock" forces git to use the
        // quoted form. We must still detect it as a lockfile.
        let diff = "\
diff --git \"a/odd dir/Cargo.lock\" \"b/odd dir/Cargo.lock\"
index 1111..2222 100644
--- \"a/odd dir/Cargo.lock\"
+++ \"b/odd dir/Cargo.lock\"
@@ -1,1 +1,1 @@
-old
+new
";
        let out = collapse_autogenerated(diff);
        // Entire per-file block suppressed (lockfile detected).
        assert!(!out.contains("diff --git"), "headers leaked: {out}");
        assert!(!out.contains("old\n"), "lock content leaked: {out}");
        assert!(!out.contains("+new"), "lock content leaked: {out}");
        // Placeholder uses the parsed b-side path (without quotes).
        assert!(
            out.contains("[odd dir/Cargo.lock: contents changed (+1 -1, --full for content)]"),
            "expected one-line placeholder for quoted-path lockfile, got: {out}"
        );
    }
}