//! chrs-graph library implementation using Dolt for graph persistence.

use chrono::Utc;
use serde_json::Value;
use std::{path::Path, process::Command};
use thiserror::Error;
use uuid::Uuid;

/// Enumeration of possible errors that can arise while interacting with the `DoltGraph`.
///
/// Each variant wraps an underlying error source, making it easier for callers to
/// understand the failure context and decide on remedial actions.
#[derive(Error, Debug)]
pub enum GraphError {
    /// Propagates I/O errors from the standard library (e.g., filesystem access).
    #[error("IO error: {0}")]
    Io(#[from] std::io::Error),
    /// Represents a failure when executing a Dolt command.
    #[error("Command failed: {0}")]
    CommandFailed(String),
    /// Propagates JSON (de)serialization errors from `serde_json`.
    #[error("Serde JSON error: {0}")]
    SerdeJson(#[from] serde_json::Error),
    /// A generic catch‑all for errors that don't fit the other categories.
    #[error("Other error: {0}")]
    Other(String),
}

/// Wrapper around a Dolt repository that stores graph data.
///
/// The `DoltGraph` type encapsulates a path to a Dolt repo and provides high‑level
/// operations such as initializing the repo, committing changes, creating tables, and
/// inserting nodes expressed as JSON objects.
///
/// # Architectural Rationale
/// Dolt offers a Git‑like version‑controlled SQL database, which aligns well with CHORUS's
/// need for an immutable, query‑able history of graph mutations. By wrapping Dolt commands in
/// this struct we isolate the rest of the codebase from the command‑line interface, making the
/// graph layer portable and easier to test.
pub struct DoltGraph {
    /// Filesystem path to the root of the Dolt repository.
    pub repo_path: std::path::PathBuf,
}

impl DoltGraph {
    /// Initialise (or open) a Dolt repository at the given `path`.
    ///
    /// If the directory does not already contain a `.dolt` sub‑directory, the function runs
    /// `dolt init` to create a new repository. Errors from the underlying command are wrapped in
    /// `GraphError::CommandFailed`.
    pub fn init(path: &Path) -> Result<Self, GraphError> {
        if !path.join(".dolt").exists() {
            let status = Command::new("dolt")
                .arg("init")
                .current_dir(path)
                .status()?;
            if !status.success() {
                return Err(GraphError::CommandFailed(format!(
                    "dolt init failed with status {:?}",
                    status
                )));
            }
        }
        Ok(Self {
            repo_path: path.to_path_buf(),
        })
    }

    /// Execute a Dolt command with the specified arguments.
    ///
    /// This helper centralises command execution and error handling. It runs `dolt` with the
    /// provided argument slice, captures stdout/stderr, and returns `GraphError::CommandFailed`
    /// when the command exits with a non‑zero status.
    fn run_cmd(&self, args: &[&str]) -> Result<(), GraphError> {
        let output = Command::new("dolt")
            .args(args)
            .current_dir(&self.repo_path)
            .output()?;
        if !output.status.success() {
            let stderr = String::from_utf8_lossy(&output.stderr);
            return Err(GraphError::CommandFailed(stderr.to_string()));
        }
        Ok(())
    }

    /// Stage all changes and commit them with the provided `message`.
    ///
    /// The method first runs `dolt add -A` to stage modifications, then `dolt commit -m`.
    /// Any failure in these steps propagates as a `GraphError`.
    pub fn commit(&self, message: &str) -> Result<(), GraphError> {
        self.run_cmd(&["add", "-A"])?;
        self.run_cmd(&["commit", "-m", message])?;
        Ok(())
    }

    /// Create a SQL table within the Dolt repository.
    ///
    /// `schema` should be a comma‑separated column definition list (e.g., `"id INT PRIMARY KEY, name TEXT"`).
    /// If the table already exists, the function treats it as a no‑op and returns `Ok(())`.
    pub fn create_table(&self, table_name: &str, schema: &str) -> Result<(), GraphError> {
        let query = format!("CREATE TABLE {} ({})", table_name, schema);
        if let Err(e) = self.run_cmd(&["sql", "-q", &query]) {
            if e.to_string().contains("already exists") {
                // Table is already present – not an error for our use‑case.
                return Ok(());
            }
            return Err(e);
        }
        self.commit(&format!("Create table {}", table_name))?;
        Ok(())
    }

    /// Insert a node represented by a JSON object into the specified `table`.
    ///
    /// The JSON `data` must be an object where keys correspond to column names. Supported value
    /// types are strings, numbers, booleans, and null. Complex JSON structures are rejected because
    /// they cannot be directly mapped to SQL scalar columns.
    pub fn insert_node(&self, table: &str, data: Value) -> Result<(), GraphError> {
        let obj = data
            .as_object()
            .ok_or_else(|| GraphError::Other("Data must be a JSON object".into()))?;
        let columns: Vec<String> = obj.keys().cloned().collect();
        let mut values: Vec<String> = Vec::new();
        for key in &columns {
            let v = &obj[key];
            let sql_val = match v {
                Value::String(s) => format!("'{}'", s.replace('\'', "''")),
                Value::Number(n) => n.to_string(),
                Value::Bool(b) => {
                    if *b {
                        "TRUE".into()
                    } else {
                        "FALSE".into()
                    }
                }
                Value::Null => "NULL".into(),
                _ => return Err(GraphError::Other("Unsupported JSON value type".into())),
            };
            values.push(sql_val);
        }
        let query = format!(
            "INSERT INTO {} ({}) VALUES ({})",
            table,
            columns.join(", "),
            values.join(", ")
        );
        self.run_cmd(&["sql", "-q", &query])?;
        Ok(())
    }
}

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

    #[test]
    fn test_init_create_table_and_commit() {
        let dir = TempDir::new().unwrap();
        // Initialise a Dolt repository in a temporary directory.
        let graph = DoltGraph::init(dir.path()).expect("init failed");
        // Create a simple `nodes` table.
        graph
            .create_table("nodes", "id INT PRIMARY KEY, name TEXT")
            .expect("create table failed");
    }
}