package ucl

import (
	"context"
	"errors"
	"fmt"
	"strings"
)

type evaluator struct {
	inst *Inst
}

func (e evaluator) evalBlock(ctx context.Context, ec *evalCtx, n *astBlock) (lastRes Object, err error) {
	// TODO: push scope?

	for _, s := range n.Statements {
		lastRes, err = e.evalStatement(ctx, ec, s)
		if err != nil {
			return nil, err
		}
	}
	return lastRes, nil
}

func (e evaluator) evalScript(ctx context.Context, ec *evalCtx, n *astScript) (lastRes Object, err error) {
	return e.evalStatement(ctx, ec, n.Statements)
}

func (e evaluator) evalStatement(ctx context.Context, ec *evalCtx, n *astStatements) (Object, error) {
	if n == nil {
		return nil, nil
	}

	res, err := e.evalPipeline(ctx, ec, n.First)
	if err != nil {
		return nil, err
	}
	if len(n.Rest) == 0 {
		return res, nil
	}

	for _, rest := range n.Rest {
		out, err := e.evalPipeline(ctx, ec, rest)
		if err != nil {
			return nil, err
		}
		res = out
	}
	return res, nil
}

func (e evaluator) evalPipeline(ctx context.Context, ec *evalCtx, n *astPipeline) (Object, error) {
	res, err := e.evalCmd(ctx, ec, nil, n.First)
	if err != nil {
		return nil, err
	}
	if len(n.Rest) == 0 {
		return res, nil
	}

	// Command is a pipeline, so build it out
	for _, rest := range n.Rest {
		out, err := e.evalCmd(ctx, ec, res, rest)
		if err != nil {
			return nil, err
		}
		res = out
	}
	return res, nil
}

func (e evaluator) evalCmd(ctx context.Context, ec *evalCtx, currentPipe Object, ast *astCmd) (Object, error) {
	switch {
	case (ast.Name.Arg.Ident != nil) && len(ast.Name.DotSuffix) == 0:
		name := ast.Name.Arg.Ident.String()

		// Regular command
		if cmd := ec.lookupInvokable(name); cmd != nil {
			return e.evalInvokable(ctx, ec, currentPipe, ast, cmd)
		} else if macro := ec.lookupMacro(name); macro != nil {
			return e.evalMacro(ctx, ec, currentPipe != nil, currentPipe, ast, macro)
		} else if missingHandler := e.inst.missingBuiltinHandler; missingHandler != nil {
			return e.evalInvokable(ctx, ec, currentPipe, ast, e.inst.missingHandlerInvokable(name))
		} else {
			return nil, errors.New("unknown command: " + name)
		}
	case len(ast.Args) > 0:
		nameElem, err := e.evalDot(ctx, ec, ast.Name)
		if err != nil {
			return nil, err
		}

		inv, ok := nameElem.(invokable)
		if !ok {
			return nil, errors.New("command is not invokable")
		}

		return e.evalInvokable(ctx, ec, currentPipe, ast, inv)
	}

	nameElem, err := e.evalDot(ctx, ec, ast.Name)
	if err != nil {
		return nil, err
	}
	return nameElem, nil
}

func (e evaluator) evalInvokable(ctx context.Context, ec *evalCtx, currentPipe Object, ast *astCmd, cmd invokable) (Object, error) {
	var (
		pargs   listObject
		kwargs  map[string]*listObject
		argsPtr *listObject
	)

	argsPtr = &pargs
	if currentPipe != nil {
		argsPtr.Append(currentPipe)
	}
	for _, arg := range ast.Args {
		if ident := arg.Arg.Ident; len(arg.DotSuffix) == 0 && ident != nil && ident.String()[0] == '-' {
			// Arg switch
			if kwargs == nil {
				kwargs = make(map[string]*listObject)
			}

			argsPtr = &listObject{}
			kwargs[ident.String()[1:]] = argsPtr
		} else {
			ae, err := e.evalDot(ctx, ec, arg)
			if err != nil {
				return nil, err
			}
			argsPtr.Append(ae)
		}
	}

	invArgs := invocationArgs{eval: e, ec: ec, inst: e.inst, args: pargs, kwargs: kwargs}
	return cmd.invoke(ctx, invArgs)
}

func (e evaluator) evalMacro(ctx context.Context, ec *evalCtx, hasPipe bool, pipeArg Object, ast *astCmd, cmd macroable) (Object, error) {
	return cmd.invokeMacro(ctx, macroArgs{
		eval:    e,
		ec:      ec,
		hasPipe: hasPipe,
		pipeArg: pipeArg,
		ast:     ast,
	})
}

func (e evaluator) evalDot(ctx context.Context, ec *evalCtx, n astDot) (Object, error) {
	res, err := e.evalArg(ctx, ec, n.Arg)
	if err != nil {
		return nil, err
	} else if len(n.DotSuffix) == 0 {
		return res, nil
	}

	for _, dot := range n.DotSuffix {
		var idx Object
		if dot.KeyIdent != nil {
			idx = StringObject(dot.KeyIdent.String())
		} else {
			idx, err = e.evalPipeline(ctx, ec, dot.Pipeline)
			if err != nil {
				return nil, err
			}
		}

		res, err = indexLookup(ctx, res, idx)
		if err != nil {
			return nil, err
		}
	}
	return res, nil
}

func (e evaluator) evalArg(ctx context.Context, ec *evalCtx, n astCmdArg) (Object, error) {
	switch {
	case n.Literal != nil:
		return e.evalLiteral(ctx, ec, n.Literal)
	case n.Ident != nil:
		return StringObject(n.Ident.String()), nil
	case n.Var != nil:
		if v, ok := ec.getVar(*n.Var); ok {
			return v, nil
		}
		return nil, nil
	case n.MaybeSub != nil:
		sub := n.MaybeSub.Sub
		if sub == nil {
			return nil, nil
		}
		return e.evalSub(ctx, ec, sub)
	case n.ListOrHash != nil:
		return e.evalListOrHash(ctx, ec, n.ListOrHash)
	case n.Block != nil:
		return blockObject{block: n.Block, closedEC: ec}, nil
	}
	return nil, errors.New("unhandled arg type")
}

func (e evaluator) evalListOrHash(ctx context.Context, ec *evalCtx, loh *astListOrHash) (Object, error) {
	if loh.EmptyList {
		return listObject{}, nil
	} else if loh.EmptyHash {
		return hashObject{}, nil
	}

	if firstIsHash := loh.Elements[0].Right != nil; firstIsHash {
		h := hashObject{}
		for _, el := range loh.Elements {
			if el.Right == nil {
				return nil, errors.New("miss-match of lists and hash")
			}

			n, err := e.evalDot(ctx, ec, el.Left)
			if err != nil {
				return nil, err
			}

			v, err := e.evalDot(ctx, ec, *el.Right)
			if err != nil {
				return nil, err
			}

			h[n.String()] = v
		}
		return h, nil
	}

	l := listObject{}
	for _, el := range loh.Elements {
		if el.Right != nil {
			return nil, errors.New("miss-match of lists and hash")
		}
		v, err := e.evalDot(ctx, ec, el.Left)
		if err != nil {
			return nil, err
		}
		l = append(l, v)
	}
	return l, nil
}

func (e evaluator) evalLiteral(ctx context.Context, ec *evalCtx, n *astLiteral) (Object, error) {
	switch {
	case n.StrInter != nil:
		sval, err := e.interpolateDoubleQuotedString(ctx, ec, n.StrInter)
		if err != nil {
			return nil, err
		}
		return sval, nil
	case n.SingleStrInter != nil:
		sval, err := e.interpolateSingleQuotedString(ctx, ec, n.SingleStrInter)
		if err != nil {
			return nil, err
		}
		return sval, nil
	case n.Int != nil:
		return IntObject(*n.Int), nil
	}
	return nil, errors.New("unhandled literal type")
}

func (e evaluator) interpolateSingleQuotedString(ctx context.Context, ec *evalCtx, s *astSingleString) (Object, error) {
	var sb strings.Builder
	for _, n := range s.Spans {
		switch {
		case n.Chars != nil:
			sb.WriteString(*n.Chars)
		}
	}
	return StringObject(sb.String()), nil
}

func (e evaluator) interpolateDoubleQuotedString(ctx context.Context, ec *evalCtx, s *astDoubleString) (Object, error) {
	var sb strings.Builder
	for _, n := range s.Spans {
		switch {
		case n.Chars != nil:
			sb.WriteString(*n.Chars)
		case n.Escaped != nil:
			switch (*n.Escaped)[1:] {
			case "\\":
				sb.WriteByte('\\')
			case "n":
				sb.WriteByte('\n')
			case "t":
				sb.WriteByte('\t')
			case "$":
				sb.WriteByte('$')
			default:
				return nil, errors.New("unrecognised escaped pattern: \\" + *n.Escaped)
			}
		case n.IdentRef != nil:
			identVal := (*n.IdentRef)[1:]
			if v, ok := ec.getVar(identVal); ok && v != nil {
				sb.WriteString(v.String())
			}
		case n.LongIdentRef != nil:
			v, err := e.interpolateLongIdent(ctx, ec, n.LongIdentRef)
			if err != nil {
				return nil, err
			}
			sb.WriteString(v)
		case n.SubExpr != nil:
			res, err := e.evalPipeline(ctx, ec, n.SubExpr)
			if err != nil {
				return nil, err
			}
			if res != nil {
				sb.WriteString(res.String())
			}
		}
	}
	return StringObject(sb.String()), nil
}

func (e evaluator) interpolateLongIdent(ctx context.Context, ec *evalCtx, n *astLongIdent) (_ string, err error) {
	res, ok := ec.getVar(n.VarName)
	if !ok {
		return "", nil
	}

	for _, dot := range n.DotSuffix {
		if res == nil {
			return "", errorWithPos{fmt.Errorf("attempt to get field from nil value '%v'", n.VarName), n.Pos}
		}

		var idx Object
		if dot.KeyName != nil {
			idx = StringObject(*dot.KeyName)
		} else {
			idx, err = e.evalPipeline(ctx, ec, dot.Pipeline)
			if err != nil {
				return "", err
			}
		}

		res, err = indexLookup(ctx, res, idx)
		if err != nil {
			return "", err
		}
	}
	if res == nil {
		return "", nil
	}
	return res.String(), nil
}

func (e evaluator) evalSub(ctx context.Context, ec *evalCtx, n *astPipeline) (Object, error) {
	pipelineRes, err := e.evalPipeline(ctx, ec, n)
	if err != nil {
		return nil, err
	}
	return pipelineRes, nil
}