inline-schema/src/csv-loader/module-gen.ts

import * as path from "path";
import { parseCsv } from "./loader.js";
import { hasNestedReferences } from "./reference-resolver.js";
import type { Schema } from "../types.js";
import type { CsvLoaderOptions, PropertyConfig } from "./types.js";

/**
 * Generate runtime reference resolution code for a schema.
 * Returns a JS expression string that resolves references using lookup maps.
 */
function generateSchemaResolutionCode(
  schema: Schema,
  valueExpr: string,
  lookupVar: (tableName: string) => string,
  pkField: string,
  reverseLookupVar?: (tableName: string, foreignKey: string) => string,
): string {
  switch (schema.type) {
    case "reference": {
      const lookup = lookupVar(schema.tableName);
      if (schema.isOptional) {
        if (schema.isArray) {
          return `(${valueExpr} === null || ${valueExpr} === undefined ? ${valueExpr} : (Array.isArray(${valueExpr}) ? ${valueExpr}.map(id => ${lookup}.get(String(id))) : ${lookup}.get(String(${valueExpr}))))`;
        }
        return `(${valueExpr} === null || ${valueExpr} === undefined ? ${valueExpr} : ${lookup}.get(String(${valueExpr})))`;
      }
      if (schema.isArray) {
        return `(Array.isArray(${valueExpr}) ? ${valueExpr}.map(id => ${lookup}.get(String(id))) : ${valueExpr})`;
      }
      return `${lookup}.get(String(${valueExpr}))`;
    }
    case "reverseReference": {
      if (!reverseLookupVar) return valueExpr;
      const reverseLookup = reverseLookupVar(
        schema.tableName,
        schema.foreignKey,
      );
      if (schema.isOptional) {
        return `(${reverseLookup}.get(String(row.${pkField})) || null)`;
      }
      return `(${reverseLookup}.get(String(row.${pkField})) || [])`;
    }
    case "tuple": {
      const elementResolvers = schema.elements.map((el, i) => {
        if (hasNestedReferences(el.schema)) {
          return generateSchemaResolutionCode(
            el.schema,
            `${valueExpr}[${i}]`,
            lookupVar,
            pkField,
            reverseLookupVar,
          );
        }
        return `${valueExpr}[${i}]`;
      });
      return `[${elementResolvers.join(", ")}]`;
    }
    case "array": {
      if (hasNestedReferences(schema.element)) {
        const itemResolve = generateSchemaResolutionCode(
          schema.element,
          "item",
          lookupVar,
          pkField,
          reverseLookupVar,
        );
        return `(${valueExpr}).map(item => ${itemResolve})`;
      }
      return valueExpr;
    }
    case "union": {
      const refMembers = schema.members.filter((m) => hasNestedReferences(m));
      const nonRefMembers = schema.members.filter(
        (m) => !hasNestedReferences(m),
      );
      const resolveParts: string[] = [];
      for (const member of refMembers) {
        const resolveCode = generateSchemaResolutionCode(
          member,
          valueExpr,
          lookupVar,
          pkField,
          reverseLookupVar,
        );
        resolveParts.push(resolveCode);
      }
      if (nonRefMembers.length > 0) {
        resolveParts.push(valueExpr);
      }
      if (resolveParts.length === 0) return valueExpr;
      if (resolveParts.length === 1) return resolveParts[0];
      return `(${resolveParts.join(" ?? ")})`;
    }
    default:
      return valueExpr;
  }
}

/**
 * Generate JavaScript module code from CSV content.
 * Emits an accessor function for tables with references (lazy resolution),
 * or static JSON for tables without references.
 */
export function csvToModule(
  content: string,
  options: CsvLoaderOptions & { resourceName?: string } = {},
): { js: string; dts?: string } {
  const result = parseCsv(content, { ...options, resolveReferences: false });

  const hasRefs =
    result.referenceFields.length > 0 || result.reverseReferences.length > 0;
  const defaultPrimaryKey = options.defaultPrimaryKey ?? "id";

  const imports: string[] = [];
  const lookupInits: string[] = [];
  const lookupVarMap = new Map<string, string>();

  // Reverse lookup maps: grouped by (tableName, foreignKey)
  const reverseLookupInits: string[] = [];
  const reverseLookupVarMap = new Map<string, string>();

  const currentTableName = options.currentFilePath
    ? path.basename(
        options.currentFilePath,
        path.extname(options.currentFilePath),
      )
    : undefined;

  // Build forward lookup maps for referenced tables
  const uniqueTables = new Set(result.referenceFields.map((f) => f.tableName));
  // Also include tables from reverse references
  for (const decl of result.reverseReferences) {
    uniqueTables.add(decl.tableName);
  }

  uniqueTables.forEach((tableName) => {
    const lookupVar = `_${tableName}Lookup`;
    lookupVarMap.set(tableName, lookupVar);

    if (tableName === currentTableName) {
      lookupInits.push(
        `const ${lookupVar} = new Map(_raw.map(p => [String(p.${defaultPrimaryKey}), p]));`,
      );
    } else {
      const varName = `_${tableName}`;
      imports.push(`import ${varName} from './${tableName}.csv';`);
      lookupInits.push(
        `const ${lookupVar} = new Map(${varName}().map(p => [String(p.${defaultPrimaryKey}), p]));`,
      );
    }
  });

  // Build reverse lookup maps for reverse references
  for (const decl of result.reverseReferences) {
    const key = `${decl.tableName}:${decl.foreignKey}`;
    if (reverseLookupVarMap.has(key)) continue;

    const revLookupVar = `_${decl.tableName}By_${decl.foreignKey}`;
    reverseLookupVarMap.set(key, revLookupVar);

    if (decl.tableName === currentTableName) {
      reverseLookupInits.push(
        `const ${revLookupVar} = new Map();`,
        `for (const r of _raw) {`,
        `  const kv = r.${decl.foreignKey};`,
        `  const k = String(typeof kv === "object" && "${defaultPrimaryKey}" in kv ? kv.${defaultPrimaryKey} : kv);`,
        `  if (!${revLookupVar}.has(k)) ${revLookupVar}.set(k, []);`,
        `  ${revLookupVar}.get(k).push(r);`,
        `}`,
      );
    } else {
      const varName = `_${decl.tableName}`;
      reverseLookupInits.push(
        `const ${revLookupVar} = new Map();`,
        `for (const r of ${varName}()) {`,
        `  const kv = r.${decl.foreignKey};`,
        `  const k = String(typeof kv === "object" && "${defaultPrimaryKey}" in kv ? kv.${defaultPrimaryKey} : kv);`,
        `  if (!${revLookupVar}.has(k)) ${revLookupVar}.set(k, []);`,
        `  ${revLookupVar}.get(k).push(r);`,
        `}`,
      );
    }
  }

  const lookupVar = (tableName: string) => lookupVarMap.get(tableName)!;
  const reverseLookupVar = (tableName: string, foreignKey: string) =>
    reverseLookupVarMap.get(`${tableName}:${foreignKey}`)!;

  const rowResolvers: string[] = [];
  for (const config of result.propertyConfigs) {
    if (config.isReverseReference) {
      // Reverse reference resolution
      const decl = result.reverseReferences.find(
        (d) => d.fieldName === config.name,
      );
      if (decl) {
        const revLookup = reverseLookupVar(decl.tableName, decl.foreignKey);
        if (decl.isOptional) {
          rowResolvers.push(
            `    ${config.name}: (${revLookup}.get(String(row.${defaultPrimaryKey})) || null),`,
          );
        } else {
          rowResolvers.push(
            `    ${config.name}: (${revLookup}.get(String(row.${defaultPrimaryKey})) || []),`,
          );
        }
      }
    } else if (hasNestedReferences(config.schema)) {
      const resolveCode = generateSchemaResolutionCode(
        config.schema,
        `row.${config.name}`,
        lookupVar,
        defaultPrimaryKey,
        reverseLookupVar,
      );
      rowResolvers.push(`    ${config.name}: ${resolveCode},`);
    }
  }

  const rawJson = JSON.stringify(result.data, null, 2);

  const js = [
    ...imports,
    "",
    `const _raw = ${rawJson};`,
    "",
    "let _resolved = null;",
    "",
    "export default function getData() {",
    "  if (_resolved) return _resolved;",
    "  _resolved = _raw;",
    ...lookupInits.map((l) => `  ${l}`),
    ...reverseLookupInits.map((l) => `  ${l}`),
    ...(rowResolvers.length > 0
      ? [
          "  _resolved = _raw.map(row => (",
          ...rowResolvers.map((r) => `    row${r.slice(1)}`),
          "    row));",
        ]
      : []),
    "  return _resolved;",
    "}",
  ].join("\n");

  return {
    js,
    dts: result.typeDefinition,
  };
}