// Package db manages the SQLite connection and schema migrations.
package db

import (
	"database/sql"
	"fmt"
	"os"
	"path/filepath"

	_ "modernc.org/sqlite" // pure-Go SQLite driver, no CGo required
)

// schema creates all tables if they do not already exist.
const schema = `
CREATE TABLE IF NOT EXISTS instructions (
    id                   TEXT PRIMARY KEY,
    content              TEXT NOT NULL,
    status               TEXT NOT NULL DEFAULT 'pending',
    created_at           TEXT NOT NULL,
    updated_at           TEXT NOT NULL,
    consumed_at          TEXT,
    consumed_by_agent_id TEXT,
    position             INTEGER NOT NULL DEFAULT 0
);

CREATE INDEX IF NOT EXISTS idx_instructions_status   ON instructions(status);
CREATE INDEX IF NOT EXISTS idx_instructions_position ON instructions(position);

CREATE TABLE IF NOT EXISTS settings (
    key   TEXT PRIMARY KEY,
    value TEXT NOT NULL
);

CREATE TABLE IF NOT EXISTS agent_activity (
    agent_id         TEXT PRIMARY KEY,
    last_seen_at     TEXT NOT NULL,
    last_fetch_at    TEXT NOT NULL,
    last_result_type TEXT NOT NULL
);
`

// defaultSettings seeds initial values; OR IGNORE means existing rows are unchanged.
const defaultSettings = "" +
	"INSERT OR IGNORE INTO settings (key, value) VALUES ('default_wait_seconds', '10');\n" +
	"DELETE FROM settings WHERE key = 'default_empty_response';\n" +
	"DELETE FROM settings WHERE key = 'agent_stale_after_seconds';\n"

// Open opens (creating if necessary) a SQLite database at dbPath, applies the
// schema, and seeds default settings.
func Open(dbPath string) (*sql.DB, error) {
	dir := filepath.Dir(dbPath)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return nil, fmt.Errorf("create db directory: %w", err)
	}

	db, err := sql.Open("sqlite", dbPath+"?_pragma=journal_mode(WAL)&_pragma=foreign_keys(on)&_pragma=busy_timeout(5000)")
	if err != nil {
		return nil, fmt.Errorf("open database: %w", err)
	}

	// Serialise all writes through a single connection to avoid locking.
	db.SetMaxOpenConns(1)

	if _, err := db.Exec(schema); err != nil {
		_ = db.Close()
		return nil, fmt.Errorf("apply schema: %w", err)
	}

	if _, err := db.Exec(defaultSettings); err != nil {
		_ = db.Close()
		return nil, fmt.Errorf("seed settings: %w", err)
	}

	return db, nil
}