<?php

declare(strict_types=1);

require_once __DIR__ . '/database.php';

header('Content-Type: application/json; charset=utf-8');
header('Cache-Control: no-store');

try {
    $pdo = getDatabase();

    switch ($_SERVER['REQUEST_METHOD']) {
        case 'GET':
            getTasks($pdo);
            break;

        case 'POST':
            createTask($pdo);
            break;

        case 'PUT':
        case 'PATCH':
            updateTask($pdo);
            break;

        case 'DELETE':
            deleteTask($pdo);
            break;

        default:
            jsonResponse(
                ['error' => 'Method not allowed.'],
                405
            );
    }
} catch (InvalidArgumentException $exception) {
    jsonResponse(
        ['error' => $exception->getMessage()],
        422
    );
} catch (Throwable $exception) {
    error_log($exception->__toString());

    jsonResponse(
        ['error' => 'An internal server error occurred.'],
        500
    );
}

function getTasks(PDO $pdo): never
{
    $id = filter_input(
        INPUT_GET,
        'id',
        FILTER_VALIDATE_INT
    );

    if ($id !== null && $id !== false) {
        $task = findTask($pdo, $id);

        if ($task === null) {
            jsonResponse(
                ['error' => 'Task not found.'],
                404
            );
        }

        jsonResponse(['task' => $task]);
    }

    $statement = $pdo->query(
        <<<'SQL'
        SELECT *
        FROM kanban_tasks
        ORDER BY column_id ASC, position ASC, id ASC
        SQL
    );

    $tasks = array_map(
        'formatTask',
        $statement->fetchAll()
    );

    jsonResponse(['tasks' => $tasks]);
}

function createTask(PDO $pdo): never
{
    $input = getJsonInput();

    $columnId = requireInteger(
        $input,
        'columnId',
        1,
        6
    );

    $content = trim((string) ($input['content'] ?? ''));

    if ($content === '') {
        throw new InvalidArgumentException(
            'Task name is required.'
        );
    }

    $pdo->beginTransaction();

    try {
        $positionStatement = $pdo->prepare(
            <<<'SQL'
            SELECT COALESCE(MAX(position), -1) + 1
            FROM kanban_tasks
            WHERE column_id = :column_id
            SQL
        );

        $positionStatement->execute([
            'column_id' => $columnId,
        ]);

        $position = (int) $positionStatement->fetchColumn();

        $statement = $pdo->prepare(
            <<<'SQL'
            INSERT INTO kanban_tasks (
                column_id,
                position,
                assign_to,
                content,
                description,
                tags,
                color,
                due_at,
                start_date,
                priority,
                complexity,
                estimate_hours,
                time_spent_hours
            ) VALUES (
                :column_id,
                :position,
                :assign_to,
                :content,
                :description,
                :tags,
                :color,
                :due_at,
                :start_date,
                :priority,
                :complexity,
                :estimate_hours,
                :time_spent_hours
            )
            SQL
        );

        $statement->execute([
            'column_id' => $columnId,
            'position' => $position,
            'assign_to' => cleanString(
                $input['assign'] ?? 'me',
                'me'
            ),
            'content' => $content,
            'description' => nullableString(
                $input['description'] ?? null
            ),
            'tags' => nullableString(
                $input['tags'] ?? null
            ),
            'color' => cleanString(
                $input['color'] ?? 'yellow',
                'yellow'
            ),
            'due_at' => nullableString(
                $input['due'] ?? null
            ),
            'start_date' => nullableString(
                $input['start'] ?? null
            ),
            'priority' => boundedInteger(
                $input['priority'] ?? 0,
                0,
                10
            ),
            'complexity' => boundedInteger(
                $input['complexity'] ?? 0,
                0,
                10
            ),
            'estimate_hours' => nullableNumber(
                $input['estimate'] ?? null
            ),
            'time_spent_hours' => nullableNumber(
                $input['timeSpent'] ?? null
            ),
        ]);

        $taskId = (int) $pdo->lastInsertId();

        $pdo->commit();

        jsonResponse(
            ['task' => findTask($pdo, $taskId)],
            201
        );
    } catch (Throwable $exception) {
        if ($pdo->inTransaction()) {
            $pdo->rollBack();
        }

        throw $exception;
    }
}

function updateTask(PDO $pdo): never
{
    $input = getJsonInput();

    $taskId = requireInteger(
        $input,
        'id',
        1
    );

    $pdo->beginTransaction();

    try {
        $currentTask = findRawTask($pdo, $taskId);

        if ($currentTask === null) {
            $pdo->rollBack();

            jsonResponse(
                ['error' => 'Task not found.'],
                404
            );
        }

        $currentColumn = (int) $currentTask['column_id'];
        $currentPosition = (int) $currentTask['position'];

        $targetColumn = array_key_exists('columnId', $input)
            ? boundedInteger($input['columnId'], 1, 6)
            : $currentColumn;

        $targetPosition = array_key_exists('position', $input)
            ? max(0, (int) $input['position'])
            : $currentPosition;

        if (
            $targetColumn !== $currentColumn ||
            $targetPosition !== $currentPosition
        ) {
            moveTask(
                $pdo,
                $taskId,
                $currentColumn,
                $currentPosition,
                $targetColumn,
                $targetPosition
            );
        }

        $fields = [];
        $parameters = [
            'id' => $taskId,
        ];

        addField(
            $fields,
            $parameters,
            $input,
            'content',
            'content',
            static function (mixed $value): string {
                $content = trim((string) $value);

                if ($content === '') {
                    throw new InvalidArgumentException(
                        'Task name is required.'
                    );
                }

                return $content;
            }
        );

        addField(
            $fields,
            $parameters,
            $input,
            'assign',
            'assign_to',
            static fn(mixed $value): string =>
                cleanString($value, 'me')
        );

        addField(
            $fields,
            $parameters,
            $input,
            'description',
            'description',
            'nullableString'
        );

        addField(
            $fields,
            $parameters,
            $input,
            'tags',
            'tags',
            'nullableString'
        );

        addField(
            $fields,
            $parameters,
            $input,
            'color',
            'color',
            static fn(mixed $value): string =>
                cleanString($value, 'yellow')
        );

        addField(
            $fields,
            $parameters,
            $input,
            'due',
            'due_at',
            'nullableString'
        );

        addField(
            $fields,
            $parameters,
            $input,
            'start',
            'start_date',
            'nullableString'
        );

        addField(
            $fields,
            $parameters,
            $input,
            'priority',
            'priority',
            static fn(mixed $value): int =>
                boundedInteger($value, 0, 10)
        );

        addField(
            $fields,
            $parameters,
            $input,
            'complexity',
            'complexity',
            static fn(mixed $value): int =>
                boundedInteger($value, 0, 10)
        );

        addField(
            $fields,
            $parameters,
            $input,
            'estimate',
            'estimate_hours',
            'nullableNumber'
        );

        addField(
            $fields,
            $parameters,
            $input,
            'timeSpent',
            'time_spent_hours',
            'nullableNumber'
        );

        if ($fields !== []) {
            $fields[] = 'updated_at = CURRENT_TIMESTAMP';

            $sql = sprintf(
                'UPDATE kanban_tasks
                 SET %s
                 WHERE id = :id',
                implode(', ', $fields)
            );

            $statement = $pdo->prepare($sql);
            $statement->execute($parameters);
        }

        $pdo->commit();

        jsonResponse([
            'task' => findTask($pdo, $taskId),
        ]);
    } catch (Throwable $exception) {
        if ($pdo->inTransaction()) {
            $pdo->rollBack();
        }

        throw $exception;
    }
}

function moveTask(
    PDO $pdo,
    int $taskId,
    int $currentColumn,
    int $currentPosition,
    int $targetColumn,
    int $targetPosition
): void {
    /*
     * First remove the task from its current ordering.
     */
    $closeGap = $pdo->prepare(
        <<<'SQL'
        UPDATE kanban_tasks
        SET position = position - 1
        WHERE column_id = :column_id
          AND position > :position
          AND id != :id
        SQL
    );

    $closeGap->execute([
        'column_id' => $currentColumn,
        'position' => $currentPosition,
        'id' => $taskId,
    ]);

    /*
     * When moving downward in the same column, removing the
     * task causes the requested position to decrease by one.
     */
    if (
        $targetColumn === $currentColumn &&
        $targetPosition > $currentPosition
    ) {
        $targetPosition--;
    }

    $countStatement = $pdo->prepare(
        <<<'SQL'
        SELECT COUNT(*)
        FROM kanban_tasks
        WHERE column_id = :column_id
          AND id != :id
        SQL
    );

    $countStatement->execute([
        'column_id' => $targetColumn,
        'id' => $taskId,
    ]);

    $numberOfTasks = (int) $countStatement->fetchColumn();

    $targetPosition = min(
        max(0, $targetPosition),
        $numberOfTasks
    );

    /*
     * Create room in the destination column.
     */
    $openGap = $pdo->prepare(
        <<<'SQL'
        UPDATE kanban_tasks
        SET position = position + 1
        WHERE column_id = :column_id
          AND position >= :position
          AND id != :id
        SQL
    );

    $openGap->execute([
        'column_id' => $targetColumn,
        'position' => $targetPosition,
        'id' => $taskId,
    ]);

    $moveStatement = $pdo->prepare(
        <<<'SQL'
        UPDATE kanban_tasks
        SET column_id = :column_id,
            position = :position,
            updated_at = CURRENT_TIMESTAMP
        WHERE id = :id
        SQL
    );

    $moveStatement->execute([
        'column_id' => $targetColumn,
        'position' => $targetPosition,
        'id' => $taskId,
    ]);
}

function deleteTask(PDO $pdo): never
{
    $input = getJsonInput();

    $taskId = isset($input['id'])
        ? (int) $input['id']
        : 0;

    if ($taskId < 1) {
        throw new InvalidArgumentException(
            'A valid task ID is required.'
        );
    }

    $pdo->beginTransaction();

    try {
        $task = findRawTask($pdo, $taskId);

        if ($task === null) {
            $pdo->rollBack();

            jsonResponse(
                ['error' => 'Task not found.'],
                404
            );
        }

        $statement = $pdo->prepare(
            'DELETE FROM kanban_tasks WHERE id = :id'
        );

        $statement->execute([
            'id' => $taskId,
        ]);

        $reorderStatement = $pdo->prepare(
            <<<'SQL'
            UPDATE kanban_tasks
            SET position = position - 1
            WHERE column_id = :column_id
              AND position > :position
            SQL
        );

        $reorderStatement->execute([
            'column_id' => (int) $task['column_id'],
            'position' => (int) $task['position'],
        ]);

        $pdo->commit();

        jsonResponse([
            'success' => true,
            'id' => $taskId,
        ]);
    } catch (Throwable $exception) {
        if ($pdo->inTransaction()) {
            $pdo->rollBack();
        }

        throw $exception;
    }
}

function findTask(PDO $pdo, int $id): ?array
{
    $task = findRawTask($pdo, $id);

    return $task === null
        ? null
        : formatTask($task);
}

function findRawTask(PDO $pdo, int $id): ?array
{
    $statement = $pdo->prepare(
        'SELECT *
         FROM kanban_tasks
         WHERE id = :id'
    );

    $statement->execute([
        'id' => $id,
    ]);

    $task = $statement->fetch();

    return $task === false ? null : $task;
}

function formatTask(array $task): array
{
    return [
        'id' => (int) $task['id'],
        'columnId' => (int) $task['column_id'],
        'status' => (int) $task['column_id'],
        'position' => (int) $task['position'],
        'assign' => $task['assign_to'],
        'content' => $task['content'],
        'description' => $task['description'] ?? '',
        'tags' => $task['tags'] ?? '',
        'color' => $task['color'],
        'due' => $task['due_at'] ?? '',
        'start' => $task['start_date'] ?? '',
        'priority' => (int) $task['priority'],
        'complexity' => (int) $task['complexity'],
        'estimate' => $task['estimate_hours'] === null
            ? null
            : (float) $task['estimate_hours'],
        'timeSpent' => $task['time_spent_hours'] === null
            ? null
            : (float) $task['time_spent_hours'],
    ];
}

function addField(
    array &$fields,
    array &$parameters,
    array $input,
    string $inputName,
    string $columnName,
    callable $filter
): void {
    if (!array_key_exists($inputName, $input)) {
        return;
    }

    $parameterName = 'field_' . $inputName;

    $fields[] = sprintf(
        '%s = :%s',
        $columnName,
        $parameterName
    );

    $parameters[$parameterName] = $filter(
        $input[$inputName]
    );
}

function getJsonInput(): array
{
    $body = file_get_contents('php://input');

    if ($body === false || trim($body) === '') {
        return [];
    }

    try {
        $input = json_decode(
            $body,
            true,
            512,
            JSON_THROW_ON_ERROR
        );
    } catch (JsonException) {
        throw new InvalidArgumentException(
            'Invalid JSON request body.'
        );
    }

    if (!is_array($input)) {
        throw new InvalidArgumentException(
            'The JSON body must be an object.'
        );
    }

    return $input;
}

function requireInteger(
    array $input,
    string $name,
    int $minimum,
    ?int $maximum = null
): int {
    if (!array_key_exists($name, $input)) {
        throw new InvalidArgumentException(
            sprintf('%s is required.', $name)
        );
    }

    return boundedInteger(
        $input[$name],
        $minimum,
        $maximum
    );
}

function boundedInteger(
    mixed $value,
    int $minimum,
    ?int $maximum = null
): int {
    if (
        filter_var(
            $value,
            FILTER_VALIDATE_INT
        ) === false
    ) {
        throw new InvalidArgumentException(
            'An integer value was expected.'
        );
    }

    $number = (int) $value;

    if ($number < $minimum) {
        throw new InvalidArgumentException(
            'The integer value is too small.'
        );
    }

    if ($maximum !== null && $number > $maximum) {
        throw new InvalidArgumentException(
            'The integer value is too large.'
        );
    }

    return $number;
}

function nullableString(mixed $value): ?string
{
    if ($value === null) {
        return null;
    }

    $value = trim((string) $value);

    return $value === '' ? null : $value;
}

function cleanString(
    mixed $value,
    string $default
): string {
    $value = trim((string) $value);

    return $value === '' ? $default : $value;
}

function nullableNumber(mixed $value): ?float
{
    if ($value === null || $value === '') {
        return null;
    }

    if (!is_numeric($value)) {
        throw new InvalidArgumentException(
            'A numeric value was expected.'
        );
    }

    $number = (float) $value;

    if ($number < 0) {
        throw new InvalidArgumentException(
            'The number cannot be negative.'
        );
    }

    return $number;
}

function jsonResponse(
    array $data,
    int $status = 200
): never {
    http_response_code($status);

    echo json_encode(
        $data,
        JSON_THROW_ON_ERROR |
        JSON_UNESCAPED_SLASHES |
        JSON_UNESCAPED_UNICODE
    );

    exit;
}