import {
    BinaryType,
    ParsedExpr,
    ParsedParameter,
    ParsedType,
} from "./parsed.ts";
import {
    CompileError,
    Position,
    Token,
    TokenIter,
    TokenType,
} from "./token.ts";

export class Parser {
    private current: Token;
    public errors: CompileError[] = [];

    public constructor(private lexer: TokenIter) {
        this.current = lexer.next();
    }

    public parse(): ParsedExpr[] {
        while (this.currentIs("semicolon")) this.step();
        const statements: ParsedExpr[] = [];
        while (!this.done()) {
            while (this.currentIs("semicolon")) this.step();
        }
        return statements;
    }

    private checkAndSkipStatementLinebreak() {
        if (!this.currentIs("semicolon")) {
            this.errors.push({
                pos: this.position(),
                message:
                    `expected ';' after statement, got '${this.current.tokenType}'`,
            });
        } else {
            this.step();
        }
    }

    public parseStatement(): ParsedExpr {
        if (this.currentIs("fn")) {
            return this.parseFn();
        } else if (this.currentIs("if")) {
            return this.parseIf();
        } else if (this.currentIs("loop")) {
            return this.parseLoop();
        } else if (this.currentIs("while")) {
            return this.parseWhile();
        } else if (this.currentIs("return")) {
            const statement = this.parseReturn();
            this.checkAndSkipStatementLinebreak();
            return statement;
        } else if (this.currentIs("break")) {
            const statement = this.parseBreak();
            this.checkAndSkipStatementLinebreak();
            return statement;
        } else if (this.currentIs("continue")) {
            const statement = this.parseContinue();
            this.checkAndSkipStatementLinebreak();
            return statement;
        } else if (this.currentIs("let")) {
            const statement = this.parseLet();
            this.checkAndSkipStatementLinebreak();
            return statement;
        } else {
            const statement = this.parseAssign();
            this.checkAndSkipStatementLinebreak();
            return statement;
        }
    }

    private parseFn(): ParsedExpr {
        const pos = this.position();
        this.step();
        if (this.done() || this.current.tokenType != "id") {
            return this.errorExpr(
                `expected 'Id' after 'fn' as function name, got '${this.current.tokenType}'`,
            );
        }
        const subject = this.current.value;
        this.step();
        if (!this.currentIs("lparen")) {
            return this.errorExpr(
                `expected '(' before function-parameters, got '${this.current.tokenType}'`,
            );
        }
        this.step();
        const params: ParsedParameter[] = [];
        params.push(this.parseParam());
        while (this.currentIs("comma")) {
            this.step();
            if (this.done() || this.currentIs("rparen")) break;
            params.push(this.parseParam());
        }
        if (!this.currentIs("rparen")) {
            return this.errorExpr(
                `expected ')' after function-parameters, got '${this.current.tokenType}'`,
            );
        }
        this.step();
        let returnType: ParsedType | null = null;
        if (this.currentIs("minusgt")) {
            this.step();
            returnType = this.parseType();
        }
        if (!this.currentIs("lbrace")) {
            return this.errorExpr(
                `expected '{' after 'loop', got '${this.current.tokenType}'`,
            );
        }
        const body = this.parseBlock();
        return {
            pos,
            exprType: "fn",
            subject,
            params,
            returnType,
            body,
        };
    }

    private parseLoop(): ParsedExpr {
        const pos = this.position();
        this.step();
        if (!this.currentIs("lbrace")) {
            return this.errorExpr(
                `expected '{' after 'loop', got '${this.current.tokenType}'`,
            );
        }
        const body = this.parseBlock();
        return {
            pos,
            exprType: "loop",
            body,
        };
    }

    private parseWhile(): ParsedExpr {
        const pos = this.position();
        this.step();
        const condition = this.parseExpr();
        if (!this.currentIs("lbrace")) {
            return this.errorExpr(
                `expected '{' after while-condition, got '${this.current.tokenType}'`,
            );
        }
        const body = this.parseBlock();
        return {
            pos,
            exprType: "while",
            condition,
            body,
        };
    }

    private parseReturn(): ParsedExpr {
        const pos = this.position();
        this.step();
        let value: ParsedExpr | null = null;
        if (!this.done() && this.current.tokenType != "semicolon") {
            value = this.parseExpr();
        }
        return { pos, exprType: "return", value };
    }

    private parseBreak(): ParsedExpr {
        const pos = this.position();
        this.step();
        return { pos, exprType: "break" };
    }

    private parseContinue(): ParsedExpr {
        const pos = this.position();
        this.step();
        return { pos, exprType: "continue" };
    }

    private parseLet(): ParsedExpr {
        const pos = this.position();
        this.step();
        const param = this.parseParam();
        if (!this.currentIs("equal")) {
            return this.errorExpr(
                `expected '=' after let-parameter, got '${this.current.tokenType}'`,
            );
        }
        this.step();
        const value = this.parseExpr();
        return {
            pos,
            exprType: "let",
            param,
            value,
        };
    }

    private parseParam(): ParsedParameter {
        const pos = this.position();
        const mutable = this.currentIs("mut");
        if (mutable) this.step();
        if (this.done() || this.current.tokenType != "id") {
            return this.errorParam(
                `expected 'id' in parameter, got '${this.current.tokenType}'`,
            );
        }
        const subject = this.current.value;
        this.step();
        let valueType: ParsedType | null = null;
        if (this.currentIs("colon")) {
            this.step();
            valueType = this.parseType();
        }
        return {
            pos,
            paramType: "value",
            subject,
            valueType,
            mutable,
        };
    }

    private parseAssign(): ParsedExpr {
        const pos = this.position();
        const subject = this.parseExpr();
        if (this.currentIs("equal")) {
            this.step();
            const value = this.parseExpr();
            return {
                pos,
                exprType: "assign",
                assignType: "equal",
                subject,
                value,
            };
        } else if (this.currentIs("plusequal")) {
            this.step();
            const value = this.parseExpr();
            return {
                pos,
                exprType: "assign",
                assignType: "add",
                subject,
                value,
            };
        } else if (this.currentIs("minusequal")) {
            this.step();
            const value = this.parseExpr();
            return {
                pos,
                exprType: "assign",
                assignType: "subtract",
                subject,
                value,
            };
        } else if (this.currentIs("ampersandequal")) {
            this.step();
            const value = this.parseExpr();
            return {
                pos,
                exprType: "assign",
                assignType: "and",
                subject,
                value,
            };
        } else if (this.currentIs("pipeequal")) {
            this.step();
            const value = this.parseExpr();
            return {
                pos,
                exprType: "assign",
                assignType: "or",
                subject,
                value,
            };
        } else if (this.currentIs("hatequal")) {
            this.step();
            const value = this.parseExpr();
            return {
                pos,
                exprType: "assign",
                assignType: "xor",
                subject,
                value,
            };
        } else {
            return subject;
        }
    }

    public parseExpr(): ParsedExpr {
        return this.parseLogOr();
    }

    private binaryExpr(
        binaryType: BinaryType,
        left: ParsedExpr,
        right: ParsedExpr,
        pos: Position,
    ): ParsedExpr {
        return {
            pos,
            exprType: "binary",
            binaryType,
            left,
            right,
        };
    }

    private parseLogOr(): ParsedExpr {
        const pos = this.position();
        let left = this.parseLogAnd();
        while (!this.done()) {
            if (this.currentIs("or")) {
                this.step();
                const right = this.parseLogAnd();
                left = this.binaryExpr("log_or", left, right, pos);
            } else {
                break;
            }
        }
        return left;
    }

    private parseLogAnd(): ParsedExpr {
        const pos = this.position();
        let left = this.parseBitOr();
        while (!this.done()) {
            if (this.currentIs("and")) {
                this.step();
                const right = this.parseBitOr();
                left = this.binaryExpr("log_and", left, right, pos);
            } else {
                break;
            }
        }
        return left;
    }

    private parseBitOr(): ParsedExpr {
        const pos = this.position();
        let left = this.parseBitXor();
        while (!this.done()) {
            if (this.currentIs("pipe")) {
                this.step();
                const right = this.parseBitXor();
                left = this.binaryExpr("bit_or", left, right, pos);
            } else {
                break;
            }
        }
        return left;
    }

    private parseBitXor(): ParsedExpr {
        const pos = this.position();
        let left = this.parseBitAnd();
        while (!this.done()) {
            if (this.currentIs("hat")) {
                this.step();
                const right = this.parseBitAnd();
                left = this.binaryExpr("bit_xor", left, right, pos);
            } else {
                break;
            }
        }
        return left;
    }

    private parseBitAnd(): ParsedExpr {
        const pos = this.position();
        let left = this.parseEquality();
        while (!this.done()) {
            if (this.currentIs("ampersand")) {
                this.step();
                const right = this.parseEquality();
                left = this.binaryExpr("bit_and", left, right, pos);
            } else {
                break;
            }
        }
        return left;
    }

    private parseEquality(): ParsedExpr {
        const pos = this.position();
        let left = this.parseComparison();
        while (!this.done()) {
            if (this.currentIs("equalequal")) {
                this.step();
                const right = this.parseComparison();
                left = this.binaryExpr("equal", left, right, pos);
            } else if (this.currentIs("exclamationequal")) {
                this.step();
                const right = this.parseComparison();
                left = this.binaryExpr("inequal", left, right, pos);
            } else {
                break;
            }
        }
        return left;
    }

    private parseComparison(): ParsedExpr {
        const pos = this.position();
        const left = this.parseAddSubtract();
        if (this.currentIs("lt")) {
            this.step();
            const right = this.parseAddSubtract();
            return this.binaryExpr("lt", left, right, pos);
        } else if (this.currentIs("gt")) {
            this.step();
            const right = this.parseAddSubtract();
            return this.binaryExpr("gt", left, right, pos);
        } else if (this.currentIs("ltequal")) {
            this.step();
            const right = this.parseAddSubtract();
            return this.binaryExpr("ltequal", left, right, pos);
        } else if (this.currentIs("gtequal")) {
            this.step();
            const right = this.parseAddSubtract();
            return this.binaryExpr("gtequal", left, right, pos);
        } else {
            return left;
        }
    }

    private parseAddSubtract(): ParsedExpr {
        const pos = this.position();
        let left = this.parseUnary();
        while (!this.done()) {
            if (this.currentIs("plus")) {
                this.step();
                const right = this.parseUnary();
                left = this.binaryExpr("add", left, right, pos);
            } else if (this.currentIs("minus")) {
                this.step();
                const right = this.parseUnary();
                left = this.binaryExpr("subtract", left, right, pos);
            } else {
                break;
            }
        }
        return left;
    }

    private parseUnary(): ParsedExpr {
        if (this.currentIs("minus")) {
            const pos = this.position();
            this.step();
            return {
                pos,
                exprType: "unary",
                unaryType: "negate",
                subject: this.parseUnary(),
            };
        } else if (this.currentIs("not")) {
            const pos = this.position();
            this.step();
            return {
                pos,
                exprType: "unary",
                unaryType: "log_not",
                subject: this.parseUnary(),
            };
        } else if (this.currentIs("tilde")) {
            const pos = this.position();
            this.step();
            return {
                pos,
                exprType: "unary",
                unaryType: "bit_not",
                subject: this.parseUnary(),
            };
        } else if (this.currentIs("ampersand")) {
            const pos = this.position();
            this.step();
            return {
                pos,
                exprType: "unary",
                unaryType: "addressof",
                subject: this.parseUnary(),
            };
        } else if (this.currentIs("asterisk")) {
            const pos = this.position();
            this.step();
            return {
                pos,
                exprType: "unary",
                unaryType: "dereference",
                subject: this.parseUnary(),
            };
        } else {
            return this.parseCallIndex();
        }
    }

    private parseCallIndex(): ParsedExpr {
        const pos = this.position();
        let subject = this.parseOperand();
        while (!this.done()) {
            if (this.currentIs("lparen")) {
                this.step();
                const args: ParsedExpr[] = [];
                if (!this.done() && this.current.tokenType != "rparen") {
                    args.push(this.parseExpr());
                    while (this.currentIs("comma")) {
                        this.step();
                        if (this.done() || this.currentIs("rparen")) {
                            break;
                        }
                        args.push(this.parseExpr());
                    }
                }
                if (!this.currentIs("rparen")) {
                    return this.errorExpr(
                        `expected ')', got '${this.current.tokenType}'`,
                    );
                }
                this.step();
                subject = {
                    pos,
                    exprType: "call",
                    subject,
                    args,
                };
            } else if (this.currentIs("lbracket")) {
                this.step();
                const value = this.parseExpr();
                if (!this.currentIs("rbracket")) {
                    return this.errorExpr(
                        `expected ']', got '${this.current.tokenType}'`,
                    );
                }
                this.step();
                subject = {
                    pos,
                    exprType: "index",
                    subject,
                    value,
                };
            } else {
                break;
            }
        }
        return subject;
    }

    private parseOperand(): ParsedExpr {
        if (this.current.tokenType == "id") {
            const pos = this.position();
            const value = this.current.value;
            this.step();
            return {
                pos,
                exprType: "id",
                value,
            };
        } else if (this.current.tokenType == "int") {
            const pos = this.position();
            const value = this.current.value;
            this.step();
            return {
                pos,
                exprType: "int",
                value,
            };
        } else if (this.currentIs("lparen")) {
            const pos = this.position();
            this.step();
            if (this.currentIs("rparen")) {
                this.step();
                return { pos, exprType: "unit" };
            }
            const subject = this.parseExpr();
            if (!this.currentIs("rparen")) {
                return this.errorExpr(
                    `expected ')', got '${this.current.tokenType}'`,
                );
            }
            this.step();
            subject.pos = pos;
            return subject;
        } else if (this.currentIs("if")) {
            return this.parseIf();
        } else if (this.currentIs("lbrace")) {
            return this.parseBlock();
        } else {
            return this.errorExpr(
                `expected operand, got '${this.current.tokenType}'`,
            );
        }
    }

    private parseIf(): ParsedExpr {
        const pos = this.position();
        this.step();
        const condition = this.parseExpr();
        if (!this.currentIs("lbrace")) {
            return this.errorExpr(
                `expected '{' after if-condition, got '${this.current.tokenType}'`,
            );
        }
        const truthy = this.parseBlock();
        let falsy: ParsedExpr | null = null;
        if (this.currentIs("else")) {
            this.step();
            if (!this.currentIs("lbrace")) {
                return this.errorExpr(
                    `expected '{' after 'else', got '${this.current.tokenType}'`,
                );
            }
            falsy = this.parseBlock();
        }
        return {
            pos,
            exprType: "if",
            condition,
            truthy,
            falsy,
        };
    }

    private parseBlock(): ParsedExpr {
        const pos = this.position();
        this.step();
        while (this.currentIs("semicolon")) this.step();
        const body: ParsedExpr[] = [];
        let value: ParsedExpr | null = null;
        while (!this.done() && this.current.tokenType != "rbrace") {
            const exprOrStatement = this.parseStatement();
            if (this.currentIs("semicolon")) {
                body.push(exprOrStatement);
                while (this.currentIs("semicolon")) this.step();
            } else {
                value = exprOrStatement;
                break;
            }
        }
        if (!this.currentIs("rbrace")) {
            return this.errorExpr(
                `expected '}' after block, got '${this.current.tokenType}'`,
            );
        }
        this.step();
        return {
            pos,
            exprType: "block",
            body,
            value,
        };
    }

    private parseType(): ParsedType {
        return this.parsePointerType();
    }

    private parsePointerType(): ParsedType {
        if (this.currentIs("asterisk")) {
            const pos = this.position();
            this.step();
            let mutable = false;
            if (this.currentIs("mut")) {
                mutable = true;
                this.step();
            }
            const subject = this.parseTypeOperand();
            return {
                pos,
                typeType: "pointer",
                subject,
                mutable,
            };
        } else {
            return this.parseTypeOperand();
        }
    }

    private parseTypeOperand(): ParsedType {
        if (this.current.tokenType == "id") {
            const pos = this.position();
            const value = this.current.value;
            this.step();
            return {
                pos,
                typeType: "id",
                value,
            };
        } else if (this.currentIs("lparen")) {
            const pos = this.position();
            this.step();
            if (this.currentIs("rparen")) {
                this.step();
                return { pos, typeType: "unit" };
            }
            const subject = this.parseType();
            if (!this.currentIs("rparen")) {
                return this.errorType(
                    `expected ')', got '${this.current.tokenType}'`,
                );
            }
            this.step();
            subject.pos = pos;
            return subject;
        } else {
            return this.errorType(
                `expected type, got '${this.current.tokenType}'`,
            );
        }
    }

    private errorExpr(
        message: string,
        pos: Position = this.position(),
    ): ParsedExpr {
        this.errors.push({ pos, message });
        return {
            pos,
            exprType: "error",
            message,
        };
    }

    private errorParam(
        message: string,
        pos: Position = this.position(),
    ): ParsedParameter {
        this.errors.push({ pos, message });
        return {
            pos,
            paramType: "error",
            message,
        };
    }

    private errorType(
        message: string,
        pos: Position = this.position(),
    ): ParsedType {
        this.errors.push({ pos, message });
        return {
            pos,
            typeType: "error",
            message,
        };
    }

    private position() {
        return this.current.pos;
    }

    private step() {
        this.current = this.lexer.next();
    }

    private currentIs(tokenType: TokenType): boolean {
        return this.current.tokenType == tokenType;
    }

    private done(): boolean {
        return this.current.tokenType == "eof";
    }
}