import evaluate from '@/astride/evaluate.js';
import Scope from '@/astride/scope.js';
import traverse from '@/astride/traverse.js';

const YIELD_NONE = 0;
const YIELD_PROMISE = 1;
const YIELD_LOOP_UPDATE = 2;
const YIELD_RETURN = 3;

export default class Sandbox {

  ast;
  $$execution;
  scopes;

  constructor(ast, context = {}) {
    this.ast = ast;
    this.$$context = context;
    this.compile();
  }

  clone() {
    return new this.constructor(
      this.ast,
      {
        ...this.$$context,
      }
    );
  }

  compile() {
    let scope = new Scope();
    scope.context = this.$$context;
    this.scopes = new Map([[this.ast, scope]]);
    traverse(
      this.ast,
      (node, verb) => {
        if (
          'BlockStatement' === node.type
          || 'ForStatement' === node.type
        ) {
          switch (verb) {
            case 'enter': {
              scope = new Scope(scope);
              break;
            }
            case 'exit': {
              scope = scope.parent;
              break;
            }
          }
        }
        if ('enter' === verb) {
          this.scopes.set(node, scope);
        }
      },
    );
  }

  get context() {
    return this.$$context;
  }

  destructureArray(id, init) {
    const scope = this.scopes.get(id);
    const {elements} = id;
    for (let i = 0; i < elements.length; ++i) {
      const element = elements[i];
      if (null === element) {
        continue;
      }
      if ('Identifier' === element.type) {
        scope.allocate(element.name, init[i]);
      }
      /* v8 ignore next 3 */
      else {
        throw new Error(`destructureArray(): Can't array destructure type ${element.type}`);
      }
    }
    return init;
  }

  destructureObject(id, init) {
    const scope = this.scopes.get(id);
    const {properties} = id;
    for (let i = 0; i < properties.length; ++i) {
      const property = properties[i];
      if ('ObjectPattern' === property.value.type) {
        this.destructureObject(property.value, init[property.key.name]);
      }
      else {
        scope.allocate(
          property.value.name,
          init[property.key.name],
        );
      }
    }
    return init;
  }

  evaluate(node) {
    return evaluate(
      node,
      {scope: this.scopes.get(node)},
    );
  }

  evaluateToResult(node) {
    const {async, value} = this.evaluate(node);
    return {
      value,
      yield: async ? YIELD_PROMISE : YIELD_NONE,
    };
  }

  executeSync(node, depth) {
    let result;
    const isReplaying = depth < this.$$execution.stack.length;
    const isReplayingThisLevel = depth === this.$$execution.stack.length - 1;
    if (!isReplaying) {
      this.$$execution.stack.push(node);
    }
    // Substitute executing the node for its deferred result.
    else if (isReplayingThisLevel) {
      if (this.$$execution.stack[depth] === node) {
        result = this.$$execution.deferred.get(node);
        this.$$execution.deferred.delete(node);
        this.$$execution.stack.pop();
        return result;
      }
    }
    switch (node.type) {
      case 'ArrayExpression':
      case 'AssignmentExpression':
      case 'BinaryExpression':
      case 'CallExpression':
      case 'ChainExpression':
      case 'ObjectExpression':
      case 'Identifier':
      case 'LogicalExpression':
      case 'MemberExpression':
      case 'UnaryExpression':
      case 'UpdateExpression': {
        result = this.evaluateToResult(node);
        if (result.yield) {
          return result;
        }
        break;
      }
      case 'AwaitExpression': {
        const coerce = !this.$$execution.deferred.has(node.argument);
        result = this.executeSync(node.argument, depth + 1);
        if (coerce) {
          result = {
            value: result.value,
            yield: YIELD_PROMISE,
          };
        }
        if (result.yield) {
          return result;
        }
        /* v8 ignore next 2 */
        break;
      }
      case 'BlockStatement': {
        result = {
          value: undefined,
          yield: YIELD_NONE,
        };
        let skipping = isReplaying;
        for (const child of node.body) {
          if (skipping && child === this.$$execution.stack[depth + 1]) {
            skipping = false;
          }
          /* v8 ignore next 3 */
          if (skipping) {
            continue;
          }
          result = this.executeSync(child, depth + 1);
          if (result.yield) {
            return result;
          }
        }
        break;
      }
      case 'ConditionalExpression': {
        const shouldVisitChild = (child) => (
          isReplaying
            ? (!this.$$execution.stack[depth + 1] || this.$$execution.stack[depth + 1] === child)
            : true
        );
        if (shouldVisitChild(node.test)) {
          const test = this.executeSync(node.test, depth + 1);
          if (test.yield) {
            return test;
          }
          this.$$execution.deferred.set(node.test, test);
        }
        const test = this.$$execution.deferred.get(node.test);
        if (test.value) {
          result = this.executeSync(node.consequent, depth + 1);
        }
        else {
          result = this.executeSync(node.alternate, depth + 1);
        }
        if (result.yield) {
          return result;
        }
        break;
      }
      case 'DoWhileStatement': {
        const shouldVisitChild = (child) => (
          isReplaying
            ? (!this.$$execution.stack[depth + 1] || this.$$execution.stack[depth + 1] === child)
            : true
        );
        if (this.$$execution.stack[depth + 1] === node) {
          this.$$execution.stack.pop();
        }
        result = this.$$execution.deferred.get(node.body);
        if (shouldVisitChild(node.body)) {
          const body = this.executeSync(node.body, depth + 1);
          if (body.yield) {
            return body;
          }
          this.$$execution.deferred.set(node.body, body);
        }
        if (shouldVisitChild(node.test)) {
          const test = this.executeSync(node.test, depth + 1);
          if (test.yield) {
            return test;
          }
          if (!test.value) {
            this.$$execution.deferred.delete(node.body);
            break;
          }
        }
        // Yield
        this.$$execution.stack.push(node);
        return {
          value: undefined,
          yield: YIELD_LOOP_UPDATE,
        };
      }
      case 'ExpressionStatement': {
        result = this.executeSync(node.expression, depth + 1);
        if (result.yield) {
          return result;
        }
        break;
      }
      case 'ForStatement': {
        const shouldVisitChild = (child) => (
          isReplaying
            ? (!this.$$execution.stack[depth + 1] || this.$$execution.stack[depth + 1] === child)
            : true
        );
        if (shouldVisitChild(node.init)) {
          const init = this.executeSync(node.init, depth + 1);
          if (init.yield) {
            return init;
          }
        }
        if (this.$$execution.stack[depth + 1] === node) {
          this.$$execution.stack.pop();
        }
        result = this.$$execution.deferred.get(node.body) || {
          value: undefined,
          yield: YIELD_NONE,
        };
        if (shouldVisitChild(node.test)) {
          const test = this.executeSync(node.test, depth + 1);
          if (test.yield) {
            return test;
          }
          if (!test.value) {
            this.$$execution.deferred.delete(node.body);
            break;
          }
        }
        if (shouldVisitChild(node.body)) {
          const body = this.executeSync(node.body, depth + 1);
          if (body.yield) {
            return body;
          }
          this.$$execution.deferred.set(node.body, body);
        }
        if (shouldVisitChild(node.update)) {
          const update = this.executeSync(node.update, depth + 1);
          if (update.yield) {
            return update;
          }
          this.$$execution.deferred.set(node.update, update);
        }
        // Yield
        this.$$execution.stack.push(node);
        const update = this.$$execution.deferred.get(node.update);
        this.$$execution.deferred.delete(node.update);
        return {
          value: update.value,
          yield: YIELD_LOOP_UPDATE,
        };
      }
      case 'IfStatement': {
        const shouldVisitChild = (child) => (
          isReplaying
            ? (!this.$$execution.stack[depth + 1] || this.$$execution.stack[depth + 1] === child)
            : true
        );
        result = {
          value: undefined,
          yield: YIELD_NONE,
        };
        if (shouldVisitChild(node.test)) {
          const test = this.executeSync(node.test, depth + 1);
          if (test.yield) {
            return test;
          }
          this.$$execution.deferred.set(node.test, test);
        }
        const test = this.$$execution.deferred.get(node.test);
        if (test.value) {
          result = this.executeSync(node.consequent, depth + 1);
        }
        else if (node.alternate) {
          result = this.executeSync(node.alternate, depth + 1);
        }
        if (result.yield) {
          return result;
        }
        this.$$execution.deferred.delete(node.test);
        break;
      }
      case 'Literal': {
        result = {value: node.value, yield: YIELD_NONE};
        break;
      }
      case 'Program': {
        result = {value: undefined, yield: YIELD_NONE};
        let skipping = isReplaying;
        for (const child of node.body) {
          if (skipping && child === this.$$execution.stack[depth + 1]) {
            skipping = false;
          }
          if (skipping) {
            continue;
          }
          result = this.executeSync(child, depth + 1);
          if (result.yield) {
            return result;
          }
        }
        result = {value: result.value, yield: YIELD_RETURN};
        break;
      }
      case 'ReturnStatement': {
        if (!node.argument) {
          return {
            value: undefined,
            yield: YIELD_RETURN,
          };
        }
        const argument = this.executeSync(node.argument, depth + 1);
        if (argument.yield) {
          return argument;
        }
        result = {
          value: argument.value,
          yield: YIELD_RETURN,
        };
        break;
      }
      case 'VariableDeclaration': {
        let skipping = isReplaying;
        for (const child of node.declarations) {
          if (skipping && child === this.$$execution.stack[depth + 1]) {
            skipping = false;
          }
          /* v8 ignore next 3 */
          if (skipping) {
            continue;
          }
          const result = this.executeSync(child, depth + 1);
          if (result.yield) {
            return result;
          }
        }
        result = {value: undefined, yield: YIELD_NONE};
        break;
      }
      case 'VariableDeclarator': {
        const {id} = node;
        const scope = this.scopes.get(node);
        if (null === node.init) {
          scope.allocate(id.name, undefined);
          result = {value: undefined, yield: YIELD_NONE};
        }
        else {
          const init = this.executeSync(node.init, depth + 1);
          if ('Identifier' === id.type) {
            if (init.yield) {
              return {
                value: Promise.resolve(init.value)
                  .then((value) => scope.allocate(id.name, value)),
                yield: init.yield,
              };
            }
            else {
              result = {
                value: scope.allocate(id.name, init.value),
                yield: YIELD_NONE,
              };
            }
          }
          else if ('ArrayPattern' === id.type) {
            if (init.yield) {
              return {
                value: Promise.resolve(init.value)
                  .then((value) => this.destructureArray(id, value)),
                yield: init.yield,
              };
            }
            else {
              result = {
                value: this.destructureArray(id, init.value),
                yield: YIELD_NONE,
              };
            }
          }
          else if ('ObjectPattern' === id.type) {
            if (init.yield) {
              return {
                value: Promise.resolve(init.value)
                  .then((value) => this.destructureObject(id, value)),
                yield: init.yield,
              };
            }
            else {
              result = {
                value: this.destructureObject(id, init.value),
                yield: YIELD_NONE,
              };
            }
          }
        }
        break;
      }
      case 'WhileStatement': {
        const shouldVisitChild = (child) => (
          isReplaying
            ? (!this.$$execution.stack[depth + 1] || this.$$execution.stack[depth + 1] === child)
            : true
        );
        if (this.$$execution.stack[depth + 1] === node) {
          this.$$execution.stack.pop();
        }
        result = this.$$execution.deferred.get(node.body) || {
          value: undefined,
          yield: YIELD_NONE,
        };
        if (shouldVisitChild(node.test)) {
          const test = this.executeSync(node.test, depth + 1);
          if (test.yield) {
            return test;
          }
          if (!test.value) {
            this.$$execution.deferred.delete(node.body);
            break;
          }
        }
        if (shouldVisitChild(node.body)) {
          const body = this.executeSync(node.body, depth + 1);
          if (body.yield) {
            return body;
          }
          this.$$execution.deferred.set(node.body, body);
        }
        // Yield
        this.$$execution.stack.push(node);
        return {
          value: undefined,
          yield: YIELD_LOOP_UPDATE,
        };
      }
      /* v8 ignore next 7 */
      default:
        console.log(
          node.type,
          Object.keys(node)
            .filter((key) => !['start', 'end'].includes(key)),
        );
        throw new Error('not implemented');
    }
    this.$$execution.stack.pop();
    return result;
  }

  reset() {
    this.$$execution = undefined;
    for (const scope of this.scopes.values()) {
      scope.context = {};
    }
    this.scopes.get(this.ast).context = this.$$context;
  }

  run(ops = 1000) {
    let result;
    for (let i = 0; i < ops; ++i) {
      result = this.step();
      if (result.done || result.async) {
        break;
      }
    }
    return result;
  }

  step() {
    if (!this.$$execution) {
      this.$$execution = {
        deferred: new Map(),
        stack: [],
      };
    }
    let result = this.executeSync(this.ast, 0);
    const stepResult = {async: false, done: false, value: undefined};
    switch (result.yield) {
      case YIELD_PROMISE: {
        stepResult.async = true;
        stepResult.value = Promise.resolve(result.value)
          .then((value) => {
            const top = this.$$execution.stack[this.$$execution.stack.length - 1];
            this.$$execution.deferred.set(top, {
              value,
              yield: YIELD_NONE,
            });
          });
        break;
      }
      case YIELD_LOOP_UPDATE: {
        stepResult.value = result.value;
        break;
      }
      case YIELD_RETURN: {
        stepResult.done = true;
        stepResult.value = result.value;
      }
    }
    if (stepResult.done) {
      this.reset();
    }
    return stepResult;
  }

}