import std.stdio;
import std.string;
import std.conv;
import std.algorithm : canFind;

import parser;
import chunk;
import dbg;

struct Local {
    Symbol sym;
    int depth;
}

class Compiler {

    Function func;
    Parser* parser;
    Local[] locals;
    int localCount;
    int scopeDepth;
    Form current;
    Form previous;

    Form outer;
    int outerIdx;

    void advance() {
        previous = current;
        /*
        if (outer.type != FormType.EOF && outerIdx < outer) {
            current = parser.parseForm();
        } else {
            
        }
        */
        current = parser.parseForm();
    }

    void compileNil(Form form) {
        form.compile(func);
        advance();
    }

    void compileAtom(Form form) {
        form.compile(func);
        advance();
    }

    void compileAdd(Form[] args) {
        resolve(args[0]);

        // (+ n) always returns n
        if (args.length == 1) {
            return;
        }

        for (int i = 1; i < args.length; i++) {
            resolve(args[i]);
            func.chunk.writeOp(OpCode.OP_ADD, current.line);
        }
    }

    void compileNegate(Form arg) {
        resolve(arg);
        func.chunk.writeOp(OpCode.OP_NEGATE, current.line);
    }

    void compileSubtract(Form[] args) {
        resolve(args[0]);
        for (int i = 1; i < args.length; i++) {
            resolve(args[i]);
            func.chunk.writeOp(OpCode.OP_SUBTRACT, current.line);
        }
    }

    void compileLess(Form[] args) {
        if (args.length != 2) {
            writeln("'<' requires 2 arguments");
            return;
        }
        resolve(args[0]);
        resolve(args[1]);
        func.chunk.writeOp(OpCode.OP_LESS, current.line);
    }

    int parseVariable(Def def) {

        declareVariable(def.name);
        if (scopeDepth > 0) {
            return 0;
        }

        int addr = func.chunk.addConstant(makeStringValue(def.name.name));
        return addr;
    }

    void defineVariable(int addr) {
        if (scopeDepth > 0) {
            return;
        }
        func.chunk.writeOp(OpCode.OP_DEF_GLOBAL, current.line);
        func.chunk.writeOp(to!ubyte(addr), current.line);
    }

    void declareVariable(Symbol sym) {

        if (scopeDepth == 0) {
            return;
        }

        for (int i = localCount - 1; i >= 0; i--) {
            Local local = locals[i];
            if (local.depth != -1 && local.depth < scopeDepth) {
                break;
            }

            if (sym.name == local.sym.name) {
                writefln("ERROR: already a variable named '%s' in this scope", sym.name);
                return;
            }
        }

        Local loc = Local(sym, scopeDepth);
        if (localCount == locals.length) {
            locals ~= loc;
        } else {
            locals[localCount] = loc;
        }
        localCount++;
    }

    void compileDef(Form form) {
        Def def = cast(Def)form;

        // resolve the value
        resolve(def.val);

        // add the variable name to the chunk (if applicable)
        int addr = parseVariable(def);

        // are we setting a local?
        if (scopeDepth > 0) {
            func.chunk.writeOp(OpCode.OP_DEF_LOCAL, current.line);
        }

        // define the variable
        defineVariable(addr);
    }

    int resolveLocal(Symbol sym) { 
        for (int i = localCount - 1; i >= 0; i--) {
            Local local = locals[i];
            if (local.sym.name == sym.name) {
                return i;
            }
        }

        return -1;
    }

    void compileSymbol(Form form) {
        Symbol sym = cast(Symbol)form;

        int arg = resolveLocal(sym);
        if (arg != -1) {
            func.chunk.writeOp(OpCode.OP_GET_LOCAL, sym.line);
        } else {
            arg = func.chunk.addConstant(makeStringValue(sym.name));
            func.chunk.writeOp(OpCode.OP_GET_GLOBAL, sym.line);
        }

        // get the variable
        func.chunk.writeOp(to!ubyte(arg), sym.line);

        //advance();
    }

    int jump(OpCode type) {
        func.chunk.writeOp(to!ubyte(type), current.line);
        func.chunk.writeOp(0xff, current.line);
        func.chunk.writeOp(0xff, current.line);
        return to!int(func.chunk.code.length) - 2;
    }

    void patchJump(int offset) {
        // additional -2 to account for the 2 byte jump itself
        int jmp = to!int(func.chunk.code.length) - offset - 2;

        // TODO check to make sure we didn't jump too far?

        this.func.chunk.code[offset] = (jmp >> 8) & 0xff;
        this.func.chunk.code[offset + 1] = jmp & 0xff;
    }

    void compileIf(Form form) {
        If if_ = cast(If)form;

        resolve(if_.cond);

        int thenJump = jump(OpCode.OP_JUMP_IF_FALSE);
        this.func.chunk.writeOp(OpCode.OP_POP, if_.line);

        resolve(if_.thenForm);

        int elseJump = jump(OpCode.OP_JUMP);

        patchJump(thenJump);
        this.func.chunk.writeOp(OpCode.OP_POP, if_.line);

        if (if_.hasElse) {
            resolve(if_.elseForm);
        }

        patchJump(elseJump);

    }

    void compileAnd(Form form) {
        And and_ = cast(And)form;

        resolve(and_.clauses[0]);
        int[] jumps;
        jumps ~= jump(OpCode.OP_JUMP_IF_FALSE);
        int count = 1;
        while (count < and_.clauses.length) {
            this.func.chunk.writeOp(OpCode.OP_POP, and_.line);
            resolve(and_.clauses[count]);
            jumps ~= jump(OpCode.OP_JUMP_IF_FALSE);
            count++;
        }

        // patch all the jumps
        foreach (int jmp; jumps) {
            patchJump(jmp);
        }
    }

    void compileOr(Form form) {
        Or or_ = cast(Or)form;

        resolve(or_.clauses[0]);
        int[] jumps;
        jumps ~= jump(OpCode.OP_JUMP_IF_TRUE);
        int count = 1;
        while (count < or_.clauses.length) {
            this.func.chunk.writeOp(OpCode.OP_POP, or_.line);
            resolve(or_.clauses[count]);
            jumps ~= jump(OpCode.OP_JUMP_IF_TRUE);
            count++;
        }

        // patch all the jumps
        foreach (int jmp; jumps) {
            patchJump(jmp);
        }
    }

    void compileBlock(Form form) {
        Block block = cast(Block)form;
        beginScope();
        foreach (Form inner; block.blockBody) {
            resolve(inner);
        }
        endScope();
    }

    void beginScope() {
        scopeDepth++;
    }

    void endScope() {

        scopeDepth--;

        while (localCount > 0 &&
                locals[localCount - 1].depth > scopeDepth) {
            func.chunk.writeOp(OpCode.OP_POPB, -1);
            localCount--;
        }
    }

    void compileCons(Form form) {
        Cons cons = cast(Cons)form;
        Form head = cons.head;
        if (head.type != FormType.SYMBOL) {
            writeln("cons must start with a symbol");
            return;
        }

        Symbol sym = cast(Symbol)head;
        switch (sym.name) {
            case "+":
                compileAdd(cons.tail);
                break;
            case "-":
                if (cons.tail.length == 1) {
                    compileNegate(cons.tail[0]);
                } else {
                    compileSubtract(cons.tail);
                }
                break;
            case "<":
                compileLess(cons.tail);
                break;
            default:
                /*
                writefln("unsure how to compile %s", sym.name);
                advance();
                */
                resolve(head);
                break;
        }

    }

    void resolve(Form form) {
        //printForm(form);
        switch(form.type) {
            case FormType.ATOM:
                this.compileAtom(form);
                break;
            case FormType.CONS:
                this.compileCons(form);
                break;
            case FormType.NIL:
                this.compileNil(form);
                break;
            case FormType.DEF:
                this.compileDef(form);
                break;
            case FormType.SYMBOL:
                this.compileSymbol(form);
                break;
            case FormType.BLOCK:
                this.compileBlock(form);
                break;
            case FormType.IF:
                this.compileIf(form);
                break;
            case FormType.AND:
                this.compileAnd(form);
                break;
            case FormType.OR:
                this.compileOr(form);
                break;
            default:
                write("not sure how to resolve: ");
                printForm(form);
                advance();
                break;
        }
    }

    Function compile() {
        advance();
        while(current.type != FormType.EOF) {
            resolve(current);
        }
        
        return finish();
    }

    Function finish() {
        this.func.chunk.writeOp(OpCode.OP_RETURN, current.line);
        disassembleChunk(func.chunk, to!string(func));
        return func;
    }

    this(ObjType type, Parser* parser) {
        this.parser = parser;
        this.func = new Function(type);
        //localCount = 0;

        locals ~= Local(new Symbol("", -1), 0);
        localCount++;
    }
}