import { CheckedExpr, CheckedType } from "./checked.ts";
import { ParsedExpr as AnyParsedExpr } from "./parsed.ts";
import { CompileError, Position } from "./token.ts";

type ParsedExpr<
    Type extends AnyParsedExpr["exprType"] = AnyParsedExpr["exprType"],
> =
    & AnyParsedExpr
    & {
        exprType: Type;
    };

export type SymbolValue = {
    id: number;
    subject: string;
    valueType: CheckedType;
};

export class SymbolTable {
    private idCounter = 0;
    private symbols: { [key: string]: SymbolValue } = {};

    public define(subject: string, valueType: CheckedType) {
        if (subject in this.symbols) {
            throw new Error("redefinition not implemented");
        }
        const id = this.idCounter;
        this.idCounter++;
        this.symbols[subject] = { id, subject, valueType };
    }
}

export class Checker {
    private symbolTable = new SymbolTable();
    public errors: CompileError[] = [];

    public check(statements: ParsedExpr[]): CheckedExpr[] {
        return statements as CheckedExpr[];
    }

    private searchTopLevelStatements(statements: ParsedExpr[]) {
        for (const statement of statements) {
            switch (statement.exprType) {
                case "fn":
                    this.searchTopLevelFn(statement);
                    break;
                case "let":
                    break;
                default:
                    this.errors.push({
                        pos: statement.pos,
                        message:
                            `statement '${statement.exprType}' not supported in top level`,
                    });
                    break;
            }
        }
    }

    private searchTopLevelFn(statement: ParsedExpr<"fn">) {
    }

    private checkStatement(expr: ParsedExpr): CheckedExpr {
        switch (expr.exprType) {
            case "if":
                return this.checkIfStatement(expr);
            case "let":
                return this.checkLetStatement(expr);
            case "fn":
                return this.checkFnStatement(expr);
            case "return":
                return this.checkReturnStatement(expr);
            case "loop":
                return this.checkLoopStatement(expr);
            case "while":
                return this.checkWhileStatement(expr);
            case "break":
                return this.checkBreakStatement(expr);
            case "continue":
                return this.checkContinueStatement(expr);
            default:
                return this.checkExpr(expr);
        }
    }

    private checkIfStatement(expr: ParsedExpr<"if">): CheckedExpr {
        const condition = this.checkExpr(expr.condition);
        const truthy = this.checkExpr(expr.truthy);
        const falsy = expr.falsy ? this.checkExpr(expr.falsy) : null;
        return {
            pos: expr.pos,
            exprType: "if",
            condition,
            truthy,
            falsy,
            valueType: { pos: expr.pos, typeType: "unit" },
        };
    }

    private checkLetStatement(expr: ParsedExpr<"let">): CheckedExpr {
        throw new Error("not implemented");
    }

    private checkFnStatement(expr: ParsedExpr<"fn">): CheckedExpr {
        throw new Error("not implemented");
    }

    private checkReturnStatement(expr: ParsedExpr<"return">): CheckedExpr {
        throw new Error("not implemented");
    }

    private checkLoopStatement(expr: ParsedExpr<"loop">): CheckedExpr {
        const body = this.checkExpr(expr.body);
        return {
            pos: expr.pos,
            exprType: "loop",
            body,
            valueType: { pos: expr.pos, typeType: "unit" },
        };
    }

    private checkWhileStatement(expr: ParsedExpr<"while">): CheckedExpr {
        const condition = this.checkExpr(expr.condition);
        const body = this.checkExpr(expr.body);
        return {
            pos: expr.pos,
            exprType: "while",
            condition,
            body,
            valueType: { pos: expr.pos, typeType: "unit" },
        };
    }

    private checkBreakStatement(expr: ParsedExpr<"break">): CheckedExpr {
        return { ...expr, valueType: { pos: expr.pos, typeType: "unit" } };
    }

    private checkContinueStatement(expr: ParsedExpr<"continue">): CheckedExpr {
        return { ...expr, valueType: { pos: expr.pos, typeType: "unit" } };
    }

    private checkExpr(expr: ParsedExpr): CheckedExpr {
        switch (expr.exprType) {
            case "error":
                return this.errorExpr(expr.message, expr.pos);
            case "unit":
                return {
                    pos: expr.pos,
                    exprType: "unit",
                    valueType: { pos: expr.pos, typeType: "unit" },
                };
            case "id":
                return this.checkId(expr);
            case "int":
                return this.checkInt(expr);
            case "if":
                return this.checkIf(expr);
            case "block":
                return this.checkBlock(expr);
            case "call":
                return this.checkCall(expr);
            case "index":
                return this.checkIndex(expr);
            case "increment":
                return this.checkIncrement(expr as ParsedExpr<"increment">);
            case "decrement":
                return this.checkDecrement(expr as ParsedExpr<"decrement">);
            case "unary":
                return this.checkUnary(expr);
            case "binary":
                return this.checkBinary(expr);
            case "assign":
                return this.checkAssign(expr);
            default:
                return this.errorExpr(
                    `expected expression, got '${expr.exprType}' statement`,
                    expr.pos,
                );
        }
    }

    private checkId(_expr: ParsedExpr<"id">): CheckedExpr {
        throw new Error("not implemented");
    }

    private checkInt(expr: ParsedExpr<"int">): CheckedExpr {
        if (expr.value >= 1 << 15) {
            return this.errorExpr("16-bit literal too large", expr.pos);
        }
        return {
            pos: expr.pos,
            exprType: "int",
            value: expr.value,
            valueType: { pos: expr.pos, typeType: "i16" },
        };
    }

    private checkIf(expr: ParsedExpr<"if">): CheckedExpr {
        const condition = this.checkExpr(expr.condition);
        const truthy = this.checkExpr(expr.truthy);
        if (!expr.falsy) {
            this.errors.push({
                pos: expr.pos,
                message: "expected else-block in if expression",
            });
            return {
                pos: expr.pos,
                exprType: "if",
                condition,
                truthy,
                falsy: null,
                valueType: { pos: expr.pos, typeType: "unit" },
            };
        }
        const falsy = this.checkExpr(expr.falsy);
        const valueType = this.compatibleType(
            truthy.valueType,
            falsy.valueType,
        );
        return {
            pos: expr.pos,
            exprType: "if",
            condition,
            truthy,
            falsy,
            valueType,
        };
    }

    private checkBlock(expr: ParsedExpr<"block">): CheckedExpr {
        const body = expr.body.map((statement) =>
            this.checkStatement(statement)
        );
        if (expr.value) {
            const value = this.checkExpr(expr.value);
            return {
                pos: expr.pos,
                exprType: "block",
                body,
                value,
                valueType: value.valueType,
            };
        } else {
            return {
                pos: expr.pos,
                exprType: "block",
                body,
                value: null,
                valueType: { pos: expr.pos, typeType: "unit" },
            };
        }
    }

    private checkCall(expr: ParsedExpr<"call">): CheckedExpr {
        throw new Error("not implemented");
    }

    private checkIndex(expr: ParsedExpr<"index">): CheckedExpr {
        throw new Error("not implemented");
    }

    private checkIncrement(expr: ParsedExpr<"increment">): CheckedExpr {
        throw new Error("not implemented");
    }

    private checkDecrement(expr: ParsedExpr<"decrement">): CheckedExpr {
        throw new Error("not implemented");
    }

    private checkUnary(expr: ParsedExpr<"unary">): CheckedExpr {
        throw new Error("not implemented");
    }

    private checkBinary(expr: ParsedExpr<"binary">): CheckedExpr {
        throw new Error("not implemented");
    }

    private checkAssign(expr: ParsedExpr<"assign">): CheckedExpr {
        throw new Error("not implemented");
    }

    private compatibleType(
        a: CheckedType,
        b: CheckedType,
        reversed = false,
    ): CheckedType {
        if (a.typeType === "error") {
            return a;
        } else if (b.typeType === "error") {
            return b;
        } else if (a.typeType === "unit" && b.typeType === "unit") {
            return a;
        } else if (a.typeType === "u16" && b.typeType === "u16") {
            return a;
        } else if (a.typeType === "u16" && b.typeType === "i16") {
            return a;
        } else if (!reversed) {
            return this.compatibleType(b, a, true);
        } else {
            throw new Error("not implemented");
        }
    }

    private errorExpr(message: string, pos: Position): CheckedExpr {
        this.errors.push({ message, pos });
        return {
            pos,
            exprType: "error",
            valueType: { pos, typeType: "unit" },
            message,
        };
    }
}