//
//  SQLiteStatement.swift
//
//  Copyright 2026 Brendan Szymanski <hello@bscubed.dev>
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
//
//  SPDX-License-Identifier: GPL-3.0-or-later
//

import CSQLite
import Foundation
import LuminateCore

/// `SQLITE_TRANSIENT`. The C macro is a cast of `-1` and does not survive into Swift, so the bit
/// pattern is reconstructed here; it tells SQLite to copy the bound bytes.
private let sqliteTransient = unsafeBitCast(-1, to: sqlite3_destructor_type.self)

/// A prepared SQLite statement with typed binding and column helpers.
final class SQLiteStatement {
    private let database: SQLiteDatabase
    private let handle: OpaquePointer

    /// Prepares `sql` against `database`.
    ///
    /// - Parameters:
    ///   - database: The open database that owns the statement.
    ///   - sql: The SQL statement to prepare.
    /// - Throws: ``PreferenceStoreError/sqlite(message:)`` when preparation fails.
    init(database: SQLiteDatabase, sql: String) throws {
        self.database = database
        var statement: OpaquePointer?
        let result = sqlite3_prepare_v2(database.handle, sql, -1, &statement, nil)
        guard result == SQLITE_OK, let statement else {
            throw PreferenceStoreError.sqlite(message: database.errorMessage)
        }
        handle = statement
    }

    deinit {
        sqlite3_finalize(handle)
    }

    /// Binds a scalar preference value at a 1-based parameter index.
    ///
    /// - Parameters:
    ///   - index: The SQLite parameter index.
    ///   - value: The scalar value to bind.
    /// - Throws: ``PreferenceStoreError/sqlite(message:)`` when binding fails.
    func bind(_ index: Int32, _ value: StoredPreference) throws {
        let result: Int32
        switch value {
        case .integer(let value):
            result = sqlite3_bind_int64(handle, index, value)
        case .real(let value):
            result = sqlite3_bind_double(handle, index, value)
        case .text(let value):
            result = bindText(index, value)
        case .blob(let value):
            if value.isEmpty {
                result = sqlite3_bind_zeroblob(handle, index, 0)
            } else {
                result = value.withUnsafeBytes { bytes in
                    sqlite3_bind_blob(handle, index, bytes.baseAddress, Int32(value.count), sqliteTransient)
                }
            }
        }
        try check(result)
    }

    /// Binds a string at a 1-based parameter index.
    ///
    /// - Parameters:
    ///   - index: The SQLite parameter index.
    ///   - text: The string to bind.
    /// - Throws: ``PreferenceStoreError/sqlite(message:)`` when binding fails.
    func bind(_ index: Int32, text: String) throws {
        try check(bindText(index, text))
    }

    /// Steps the statement once.
    ///
    /// - Returns: `true` when a row is available, or `false` when the statement is complete.
    /// - Throws: ``PreferenceStoreError/sqlite(message:)`` for any other SQLite result.
    func step() throws -> Bool {
        switch sqlite3_step(handle) {
        case SQLITE_ROW:
            return true
        case SQLITE_DONE:
            return false
        default:
            throw PreferenceStoreError.sqlite(message: database.errorMessage)
        }
    }

    /// Reads an integer result column.
    /// - Parameter index: The zero-based result column index.
    /// - Returns: The SQLite integer value.
    func integer(at index: Int32) -> Int32 {
        sqlite3_column_int(handle, index)
    }

    /// Reads a nullable string column.
    ///
    /// - Parameter index: The zero-based result column index.
    /// - Returns: The column text, or `nil` for SQL NULL.
    func text(at index: Int32) -> String? {
        guard let pointer = sqlite3_column_text(handle, index) else { return nil }
        let count = Int(sqlite3_column_bytes(handle, index))
        return String(decoding: UnsafeBufferPointer(start: pointer, count: count), as: UTF8.self)
    }

    /// Reads the SQLite storage-class value from a result column.
    ///
    /// - Parameter index: The zero-based result column index.
    /// - Returns: The scalar value, or `nil` for SQL NULL or an unsupported storage class.
    func preference(at index: Int32) -> StoredPreference? {
        switch sqlite3_column_type(handle, index) {
        case SQLITE_INTEGER:
            return .integer(sqlite3_column_int64(handle, index))
        case SQLITE_FLOAT:
            return .real(sqlite3_column_double(handle, index))
        case SQLITE_TEXT:
            guard let value = text(at: index) else { return nil }
            return .text(value)
        case SQLITE_BLOB:
            let length = Int(sqlite3_column_bytes(handle, index))
            guard let pointer = sqlite3_column_blob(handle, index), length > 0 else {
                return .blob(Data())
            }
            return .blob(Data(bytes: pointer, count: length))
        default:
            return nil
        }
    }

    private func bindText(_ index: Int32, _ value: String) -> Int32 {
        value.utf8CString.withUnsafeBufferPointer { buffer in
            sqlite3_bind_text(handle, index, buffer.baseAddress, Int32(buffer.count - 1), sqliteTransient)
        }
    }

    private func check(_ result: Int32) throws {
        guard result == SQLITE_OK else {
            throw PreferenceStoreError.sqlite(message: database.errorMessage)
        }
    }
}