//! Helper functions for purgatory state event processing.
//!
//! These functions handle the late-binding extraction and matching of git refs
//! from state events. Refs are extracted at git push time rather than event
//! arrival time to enable flexible matching logic.

use super::{RefPair, RefUpdate};
use nostr_sdk::prelude::*;
use std::collections::HashMap;

/// Extract ref pairs from a state event (kind 30618).
///
/// Parses all `refs/heads/*` and `refs/tags/*` tags from the event,
/// creating RefPair instances with the full ref name and target object SHA.
///
/// # Arguments
/// * `event` - The state event to extract refs from
///
/// # Returns
/// Vector of RefPair instances, one for each ref tag found
///
/// # Tag Format
/// State events use custom tags where the tag kind is the ref name:
/// - Tag kind: "refs/heads/main" or "refs/tags/v1.0"
/// - First value: commit SHA or annotated tag SHA
///
/// # Example
/// ```ignore
/// // Event with tags:
/// // ["refs/heads/main", "abc123..."]
/// // ["refs/tags/v1.0", "def456..."]
/// let refs = extract_refs_from_state(&event);
/// // Returns: [
/// //   RefPair { ref_name: "refs/heads/main", object_sha: "abc123..." },
/// //   RefPair { ref_name: "refs/tags/v1.0", object_sha: "def456..." }
/// // ]
/// ```
pub fn extract_refs_from_state(event: &Event) -> Vec<RefPair> {
    event
        .tags
        .iter()
        .filter_map(|tag| {
            // Check if this is a custom tag with a ref name
            if let TagKind::Custom(ref_name) = tag.kind() {
                let ref_str = ref_name.as_ref();

                // Only process refs/heads/* and refs/tags/*
                if ref_str.starts_with("refs/heads/") || ref_str.starts_with("refs/tags/") {
                    // Get the object SHA (first value in tag)
                    let parts = tag.clone().to_vec();
                    if parts.len() >= 2 {
                        return Some(RefPair {
                            ref_name: ref_str.to_string(),
                            object_sha: parts[1].clone(),
                        });
                    }
                }
            }
            None
        })
        .collect()
}

/// Check if a state event can be satisfied by ref updates plus local refs.
///
/// Returns true if applying the ref updates to local state results in exactly
/// the state declared in the event. This means:
/// 1. Filter local_refs to only branches (refs/heads/*) and tags (refs/tags/*)
/// 2. Apply pushed_updates to create a "would-be" state
/// 3. Compare would-be state with event's declared state - must match exactly
///
/// This implements correct authorization: the push must transform local state
/// into the declared state, accounting for additions, deletions, and modifications.
///
/// # Arguments
/// * `event` - The state event to check
/// * `pushed_updates` - Ref updates in the current push operation
/// * `local_refs` - Refs already existing locally (ref_name -> SHA)
///
/// # Returns
/// true if push transforms local state into declared state, false otherwise
///
/// # Example
/// ```ignore
/// // State event declares: refs/heads/main@abc123
/// // Local: refs/heads/main@old123, refs/heads/dev@def456
/// // Push updates: main old123->abc123, dev def456->0000 (delete)
/// // Result: false (event doesn't declare dev deletion)
/// ```
pub fn can_satisfy_state(
    event: &Event,
    pushed_updates: &[RefUpdate],
    local_refs: &HashMap<String, String>,
) -> bool {
    let state_refs = extract_refs_from_state(event);

    // Filter local_refs to only branches and tags
    let mut would_be_state: HashMap<String, String> = local_refs
        .iter()
        .filter(|(ref_name, _)| {
            ref_name.starts_with("refs/heads/") || ref_name.starts_with("refs/tags/")
        })
        .map(|(k, v)| (k.clone(), v.clone()))
        .collect();

    // Apply all pushed updates to create the would-be state
    for update in pushed_updates {
        // Only process branches and tags
        if !update.ref_name.starts_with("refs/heads/") && !update.ref_name.starts_with("refs/tags/")
        {
            continue;
        }

        if update.is_deletion() {
            // Remove from would-be state
            would_be_state.remove(&update.ref_name);
        } else {
            // Create or modify in would-be state
            would_be_state.insert(update.ref_name.clone(), update.new_oid.clone());
        }
    }

    // Convert event's state refs to a HashMap for comparison
    let declared_state: HashMap<String, String> = state_refs
        .into_iter()
        .map(|r| (r.ref_name, r.object_sha))
        .collect();

    // would_be_state must exactly match declared_state
    would_be_state == declared_state
}

/// Get refs from state event that aren't in pushed_refs.
///
/// Returns refs that need to be present but aren't being pushed.
/// These refs should exist in local_refs for the state to be satisfiable.
/// Useful for error messages showing what's missing.
///
/// # Arguments
/// * `event` - The state event to check
/// * `pushed_refs` - Refs being pushed in the current operation
///
/// # Returns
/// Vector of RefPair instances for refs not in pushed_refs
///
/// # Example
/// ```ignore
/// // State event declares: refs/heads/main@abc123, refs/heads/dev@def456
/// // Pushed: refs/heads/main@abc123
/// // Result: [RefPair { ref_name: "refs/heads/dev", object_sha: "def456" }]
/// ```
pub fn get_unpushed_refs(event: &Event, pushed_refs: &[RefPair]) -> Vec<RefPair> {
    let state_refs = extract_refs_from_state(event);

    state_refs
        .into_iter()
        .filter(|state_ref| {
            // Include if NOT in pushed_refs (by name and SHA)
            !pushed_refs.iter().any(|pushed_ref| {
                pushed_ref.ref_name == state_ref.ref_name
                    && pushed_ref.object_sha == state_ref.object_sha
            })
        })
        .collect()
}

#[cfg(test)]
mod tests {
    use super::*;
    use nostr_sdk::{EventBuilder, Keys, Tag};

    fn create_test_state_event(identifier: &str, refs: Vec<(&str, &str)>) -> Event {
        let keys = Keys::generate();
        let mut tags = vec![Tag::custom(TagKind::d(), vec![identifier.to_string()])];

        for (ref_name, sha) in refs {
            tags.push(Tag::custom(
                TagKind::custom(ref_name),
                vec![sha.to_string()],
            ));
        }

        EventBuilder::new(Kind::from(30618), "")
            .tags(tags)
            .sign_with_keys(&keys)
            .unwrap()
    }

    #[test]
    fn test_extract_refs_from_state() {
        let event = create_test_state_event(
            "test-repo",
            vec![
                ("refs/heads/main", "abc123"),
                ("refs/heads/dev", "def456"),
                ("refs/tags/v1.0", "789xyz"),
            ],
        );

        let refs = extract_refs_from_state(&event);

        assert_eq!(refs.len(), 3);
        assert!(refs
            .iter()
            .any(|r| r.ref_name == "refs/heads/main" && r.object_sha == "abc123"));
        assert!(refs
            .iter()
            .any(|r| r.ref_name == "refs/heads/dev" && r.object_sha == "def456"));
        assert!(refs
            .iter()
            .any(|r| r.ref_name == "refs/tags/v1.0" && r.object_sha == "789xyz"));
    }

    #[test]
    fn test_extract_refs_ignores_non_ref_tags() {
        let keys = Keys::generate();
        let tags = vec![
            Tag::custom(TagKind::d(), vec!["test-repo".to_string()]),
            Tag::custom(
                TagKind::custom("refs/heads/main"),
                vec!["abc123".to_string()],
            ),
            Tag::custom(TagKind::custom("some-other-tag"), vec!["value".to_string()]),
        ];

        let event = EventBuilder::new(Kind::from(30618), "")
            .tags(tags)
            .sign_with_keys(&keys)
            .unwrap();

        let refs = extract_refs_from_state(&event);

        // Should only extract the refs/heads/main tag
        assert_eq!(refs.len(), 1);
        assert_eq!(refs[0].ref_name, "refs/heads/main");
    }

    #[test]
    fn test_can_satisfy_state_all_in_pushed() {
        let event = create_test_state_event(
            "test-repo",
            vec![("refs/heads/main", "abc123"), ("refs/heads/dev", "def456")],
        );

        let pushed_updates = vec![
            RefUpdate {
                old_oid: "0000000000000000000000000000000000000000".to_string(),
                new_oid: "abc123".to_string(),
                ref_name: "refs/heads/main".to_string(),
            },
            RefUpdate {
                old_oid: "0000000000000000000000000000000000000000".to_string(),
                new_oid: "def456".to_string(),
                ref_name: "refs/heads/dev".to_string(),
            },
        ];

        let local_refs = HashMap::new();

        assert!(can_satisfy_state(&event, &pushed_updates, &local_refs));
    }

    #[test]
    fn test_can_satisfy_state_split_between_pushed_and_local() {
        let event = create_test_state_event(
            "test-repo",
            vec![("refs/heads/main", "abc123"), ("refs/heads/dev", "def456")],
        );

        let pushed_updates = vec![RefUpdate {
            old_oid: "0000000000000000000000000000000000000000".to_string(),
            new_oid: "abc123".to_string(),
            ref_name: "refs/heads/main".to_string(),
        }];

        let mut local_refs = HashMap::new();
        local_refs.insert("refs/heads/dev".to_string(), "def456".to_string());

        assert!(can_satisfy_state(&event, &pushed_updates, &local_refs));
    }

    #[test]
    fn test_can_satisfy_state_missing_ref() {
        let event = create_test_state_event(
            "test-repo",
            vec![("refs/heads/main", "abc123"), ("refs/heads/dev", "def456")],
        );

        let pushed_updates = vec![RefUpdate {
            old_oid: "0000000000000000000000000000000000000000".to_string(),
            new_oid: "abc123".to_string(),
            ref_name: "refs/heads/main".to_string(),
        }];

        let local_refs = HashMap::new();

        // dev ref is missing
        assert!(!can_satisfy_state(&event, &pushed_updates, &local_refs));
    }

    #[test]
    fn test_can_satisfy_state_modification() {
        let event = create_test_state_event(
            "test-repo",
            vec![("refs/heads/main", "abc123"), ("refs/heads/dev", "def456")],
        );

        let pushed_updates = vec![
            RefUpdate {
                old_oid: "old123".to_string(),
                new_oid: "abc123".to_string(),
                ref_name: "refs/heads/main".to_string(),
            },
            RefUpdate {
                old_oid: "wrong-sha".to_string(),
                new_oid: "def456".to_string(),
                ref_name: "refs/heads/dev".to_string(),
            },
        ];

        let mut local_refs = HashMap::new();
        local_refs.insert("refs/heads/main".to_string(), "old123".to_string());
        local_refs.insert("refs/heads/dev".to_string(), "wrong-sha".to_string());

        // Should succeed because push updates both to match event
        assert!(can_satisfy_state(&event, &pushed_updates, &local_refs));
    }

    #[test]
    fn test_can_satisfy_state_rejects_extra_refs() {
        let event = create_test_state_event("test-repo", vec![("refs/heads/main", "abc123")]);

        let pushed_updates = vec![
            RefUpdate {
                old_oid: "0000000000000000000000000000000000000000".to_string(),
                new_oid: "abc123".to_string(),
                ref_name: "refs/heads/main".to_string(),
            },
            RefUpdate {
                old_oid: "old456".to_string(),
                new_oid: "def456".to_string(),
                ref_name: "refs/heads/dev".to_string(),
            },
        ];

        let mut local_refs = HashMap::new();
        local_refs.insert("refs/heads/dev".to_string(), "old456".to_string());

        // Should fail because event doesn't declare dev
        assert!(!can_satisfy_state(&event, &pushed_updates, &local_refs));
    }

    #[test]
    fn test_can_satisfy_state_filters_non_branch_tag_refs() {
        let event = create_test_state_event("test-repo", vec![("refs/heads/main", "abc123")]);

        let pushed_updates = vec![RefUpdate {
            old_oid: "0000000000000000000000000000000000000000".to_string(),
            new_oid: "abc123".to_string(),
            ref_name: "refs/heads/main".to_string(),
        }];

        let mut local_refs = HashMap::new();
        // Add some non-branch/non-tag refs that should be filtered out
        local_refs.insert("refs/pull/123/head".to_string(), "xyz789".to_string());
        local_refs.insert("refs/some/other/thing".to_string(), "aaa111".to_string());

        // Should succeed - non-branch/tag refs are filtered out
        assert!(can_satisfy_state(&event, &pushed_updates, &local_refs));
    }

    #[test]
    fn test_can_satisfy_state_empty_event() {
        let event = create_test_state_event("test-repo", vec![]);
        let pushed_refs = vec![];
        let local_refs = HashMap::new();

        // Empty state event is satisfied
        assert!(can_satisfy_state(&event, &pushed_refs, &local_refs));
    }

    #[test]
    fn test_get_unpushed_refs() {
        let event = create_test_state_event(
            "test-repo",
            vec![
                ("refs/heads/main", "abc123"),
                ("refs/heads/dev", "def456"),
                ("refs/tags/v1.0", "789xyz"),
            ],
        );

        let pushed_refs = vec![RefPair {
            ref_name: "refs/heads/main".to_string(),
            object_sha: "abc123".to_string(),
        }];

        let unpushed = get_unpushed_refs(&event, &pushed_refs);

        assert_eq!(unpushed.len(), 2);
        assert!(unpushed.iter().any(|r| r.ref_name == "refs/heads/dev"));
        assert!(unpushed.iter().any(|r| r.ref_name == "refs/tags/v1.0"));
    }

    #[test]
    fn test_get_unpushed_refs_all_pushed() {
        let event = create_test_state_event("test-repo", vec![("refs/heads/main", "abc123")]);

        let pushed_refs = vec![RefPair {
            ref_name: "refs/heads/main".to_string(),
            object_sha: "abc123".to_string(),
        }];

        let unpushed = get_unpushed_refs(&event, &pushed_refs);

        assert_eq!(unpushed.len(), 0);
    }

    #[test]
    fn test_get_unpushed_refs_sha_mismatch() {
        let event = create_test_state_event("test-repo", vec![("refs/heads/main", "abc123")]);

        let pushed_refs = vec![RefPair {
            ref_name: "refs/heads/main".to_string(),
            object_sha: "different-sha".to_string(), // Different SHA
        }];

        let unpushed = get_unpushed_refs(&event, &pushed_refs);

        // Should still be unpushed because SHA doesn't match
        assert_eq!(unpushed.len(), 1);
        assert_eq!(unpushed[0].ref_name, "refs/heads/main");
        assert_eq!(unpushed[0].object_sha, "abc123");
    }
}