import { compress } from '../compress.js';
import type { GraphqlRequestData } from '../interfaces.js';
import type { GqlFragment } from './fragment.js';
import { isGqlVariable, isGqlFragment, isGqlTemplate, GQL_TEMPLATE, GQL_VARIABLE, GQL_FRAGMENT } from './symbols.js';
import { GqlTemplate, type GqlTemplateContent, type GqlTemplateValue } from './template.js';
import type { GqlVariable } from './variable.js';

const CHARS = [...'abcdefghijklmnopqrstuvwxyz'];

/** 创建变量名 */
function createVariableName(index: number): string {
    if (index < CHARS.length) return `_` + CHARS[index]!;
    return `${createVariableName(Math.trunc(index / CHARS.length) - 1)}${CHARS[index % CHARS.length]!}`;
}

/** 构造模板 */
export function template(operation: string, query: TemplateStringsArray, args: GqlTemplateValue[]): GraphqlRequestData {
    if (args.length === 0) {
        return { query: `${operation}{${compress(query.raw[0]!).trim()}}` };
    }

    const fragments = new Map<GqlFragment, string>();
    const variables = new Map<GqlVariable, string>();
    let queryBody = '';

    const appendPart = (part: GqlTemplateContent): void => {
        if (isGqlVariable(part)) {
            let name = variables.get(part);
            if (!name) {
                name = createVariableName(variables.size);
                variables.set(part, name);
            }
            queryBody += `$${name}`;
        } else if (isGqlFragment(part)) {
            let name = fragments.get(part);
            if (!name) {
                name = createVariableName(fragments.size);
                fragments.set(part, name);
            }
            queryBody += name;
        } else if (isGqlTemplate(part)) {
            const args = part[GQL_TEMPLATE];
            const { parts } = part;
            for (let i = 0; i < args.length; ++i) {
                queryBody += parts[i]!;
                appendPart(args[i]!);
            }
            queryBody += parts.at(-1);
        } else if (Array.isArray(part)) {
            for (const item of part) {
                appendPart(item);
            }
        } else {
            queryBody += part;
        }
    };

    appendPart(GqlTemplate(query, args));

    let queryVariables = '';
    const map: NonNullable<GraphqlRequestData['variables']> = {};
    for (const [{ value, [GQL_VARIABLE]: type }, name] of variables) {
        map[name] = value ?? null;
        if (queryVariables) queryVariables += ',';
        queryVariables += `$${name}:${type}`;
    }
    if (queryVariables) queryVariables = `(${queryVariables})`;
    let queryFragments = '';
    for (const [{ fragment, [GQL_FRAGMENT]: type }, name] of fragments) {
        queryFragments += `fragment ${name} on ${type}{${fragment}}`;
    }
    return {
        query: `${queryFragments}${operation}${queryVariables}{${queryBody.trim()}}`,
        variables: queryVariables ? map : undefined,
    };
}