//! Markdown file–backed `MemoryRepository` implementation.
//!
//! Each memory is stored as a `.md` file with YAML-ish frontmatter.
//! Filenames are derived from the memory's `name` via slugification
//! (see `Memory::slugify`).
//!
//! ## File Format
//! ```text
//! ---
//! name: my-memory
//! description: A useful lesson
//! kind: lesson
//! created_at: 1700000000
//! updated_at: 1700000000
//! lifecycle: active
//! outcome: success
//! scope: global
//! before: old content
//! after: new content
//! provenances: tool1, tool2
//! ---
//! Free-form markdown content body...
//! ```
//!
//! ## Data Flow
//! - `list()`: scan `*.md` files (excluding `MEMORY.md`), return slugs
//! - `load()`: read file → strip `---\n...\n---\n` frontmatter → parse fields
//! - `save()`: build frontmatter → write to temp file → rename atomically
//! - `delete()`: remove file from disk
//!
//! ## Atomicity
//! Writes use temp-file + rename + parent-directory fsync for crash safety.

use std::collections::HashMap;
use std::io::Write;
use std::path::Path;

use crate::domain::error::RepositoryError;
use crate::domain::memory::Memory;
use crate::domain::repository::MemoryRepository;

/// File-based `MemoryRepository` that stores memories as `.md` files with frontmatter.
///
/// Each file has a YAML-ish `---\n...\n---\n` header followed by free-form
/// markdown content. Filenames are derived from `Memory.name` via slugification.
#[derive(Debug, Clone, Default)]
pub struct MarkdownMemoryRepository;

impl MarkdownMemoryRepository {
    /// Create a new repository instance.
    pub fn new() -> Self {
        Self
    }

    /// Build the YAML-ish frontmatter string for a memory.
    ///
    /// Only non-empty optional fields are included in the output.
    fn build_frontmatter(memory: &Memory) -> String {
        let outcome_line = memory
            .outcome
            .as_ref()
            .map(|o| format!("outcome: {o}\n"))
            .unwrap_or_default();
        let scope_line = memory
            .scope
            .as_ref()
            .map(|s| format!("scope: {s}\n"))
            .unwrap_or_default();
        let before_line = memory
            .before_snippet
            .as_ref()
            .map(|s| format!("before: {s}\n"))
            .unwrap_or_default();
        let after_line = memory
            .after_snippet
            .as_ref()
            .map(|s| format!("after: {s}\n"))
            .unwrap_or_default();
        let prov_line = if memory.provenances.is_empty() {
            String::new()
        } else {
            format!("provenances: {}\n", memory.provenances.join(", "))
        };
        format!(
            "name: {name}\ndescription: {desc}\nkind: {kind}\n\
             created_at: {created}\nupdated_at: {updated}\nlifecycle: {lifecycle}\n\
             {outcome}{scope}{before}{after}{prov}",
            name = memory.name,
            desc = memory.description,
            kind = memory.kind,
            created = memory.created_at,
            updated = memory.updated_at,
            lifecycle = memory.lifecycle,
            outcome = outcome_line,
            scope = scope_line,
            before = before_line,
            after = after_line,
            prov = prov_line,
        )
    }

    /// Parse frontmatter lines into a `HashMap<String, String>`.
    ///
    /// Flow: split lines → for each non-empty line, split on first ':' → insert.
    /// Malformed lines (no ':') are silently skipped.
    fn parse_frontmatter(front: &str) -> HashMap<String, String> {
        front
            .lines()
            .filter_map(|l| {
                let mut it = l.splitn(2, ':');
                Some((it.next()?.trim().to_string(), it.next()?.trim().to_string()))
            })
            .collect()
    }

    /// Parse a memory file's full contents (frontmatter + body) into a `Memory`.
    ///
    /// Flow: strip `---\n` prefix → split on `\n---\n` → parse front half with
    /// `parse_frontmatter()` → use back half as content body → build Memory.
    ///
    /// Returns `InvalidData` error if the frontmatter delimiter is missing.
    fn parse(content: &str) -> std::io::Result<Memory> {
        let content = content.strip_prefix("---\n").unwrap_or(content);
        let parts: Vec<&str> = content.splitn(2, "\n---\n").collect();
        if parts.len() < 2 {
            return Err(std::io::Error::new(
                std::io::ErrorKind::InvalidData,
                "missing frontmatter",
            ));
        }
        let front = Self::parse_frontmatter(parts[0]);
        let body = parts.get(1).unwrap_or(&"").trim().to_string();
        Ok(Memory {
            name: front.get("name").cloned().unwrap_or_default(),
            description: front.get("description").cloned().unwrap_or_default(),
            content: body,
            kind: front
                .get("kind")
                .cloned()
                .unwrap_or_else(|| "reference".to_string()),
            created_at: front
                .get("created_at")
                .and_then(|v| v.parse().ok())
                .unwrap_or(0),
            updated_at: front
                .get("updated_at")
                .and_then(|v| v.parse().ok())
                .unwrap_or(0),
            outcome: front.get("outcome").cloned().filter(|s| !s.is_empty()),
            lifecycle: front
                .get("lifecycle")
                .cloned()
                .unwrap_or_else(|| "new".to_string()),
            scope: front.get("scope").cloned().filter(|s| !s.is_empty()),
            before_snippet: front.get("before").cloned().filter(|s| !s.is_empty()),
            after_snippet: front.get("after").cloned().filter(|s| !s.is_empty()),
            provenances: front
                .get("provenances")
                .cloned()
                .map(|s| {
                    s.split(", ")
                        .map(std::string::ToString::to_string)
                        .collect()
                })
                .unwrap_or_default(),
        })
    }
}

impl MemoryRepository for MarkdownMemoryRepository {
    /// List all memory slugs in `memory_dir` by scanning `*.md` files.
    ///
    /// Flow: read directory entries → filter `*.md` → strip extension → exclude MEMORY.md.
    /// Returns empty Vec if the directory doesn't exist.
    fn list(&self, memory_dir: &Path) -> Result<Vec<String>, RepositoryError> {
        let Ok(entries) = std::fs::read_dir(memory_dir) else {
            return Ok(Vec::new());
        };
        let slugs: Vec<String> = entries
            .filter_map(std::result::Result::ok)
            .filter(|e| e.path().extension().is_some_and(|x| x == "md"))
            .filter_map(|e| {
                let name = e.file_name().to_string_lossy().to_string();
                // Skip special summary file
                if name == "MEMORY.md" {
                    return None;
                }
                name.strip_suffix(".md")
                    .map(std::string::ToString::to_string)
            })
            .collect();
        Ok(slugs)
    }

    /// Load a single `Memory` by name from `memory_dir`.
    ///
    /// Flow: resolve file path → read file → parse frontmatter + body → return Memory.
    fn load(&self, memory_dir: &Path, name: &str) -> Result<Memory, RepositoryError> {
        tracing::debug!("loading memory '{name}'");
        let path = Memory::path(memory_dir, name);
        let content = std::fs::read_to_string(&path)?;
        let memory = Self::parse(&content)
            .map_err(|e| RepositoryError::Other(format!("failed to parse memory '{name}': {e}")))?;
        Ok(memory)
    }

    fn save(&self, memory_dir: &Path, memory: &Memory) -> Result<(), RepositoryError> {
        let path = Memory::path(memory_dir, &memory.name);
        let parent = path.parent().unwrap();
        std::fs::create_dir_all(parent)?;

        let frontmatter = Self::build_frontmatter(memory);
        let content = format!("---\n{frontmatter}---\n\n{}", memory.content);

        let tmp = parent.join(format!(".{}.tmp", uuid::Uuid::new_v4()));
        {
            let mut f = std::fs::OpenOptions::new()
                .create(true)
                .truncate(true)
                .write(true)
                .open(&tmp)?;
            f.write_all(content.as_bytes())?;
            f.sync_all()?;
        }
        std::fs::rename(&tmp, &path)?;
        if let Some(p) = path.parent() {
            if let Ok(d) = std::fs::File::open(p) {
                let _ = d.sync_all();
            }
        }
        tracing::debug!("memory saved to '{}'", path.display());
        Ok(())
    }

    fn delete(&self, memory_dir: &Path, name: &str) -> Result<(), RepositoryError> {
        let path = Memory::path(memory_dir, name);
        if path.exists() {
            std::fs::remove_file(&path)?;
            tracing::debug!("memory deleted: '{}'", path.display());
        } else {
            tracing::warn!(
                "memory '{name}' not found at '{}', skipping delete",
                path.display()
            );
        }
        Ok(())
    }
}